KSP 2 before KSP 2: 16807 (on Reddit) made a working interstellar non-FTL von Neumann probe in KSP [2021 update: generation ship]

Pipcard · June 6, 2018

2021 update: generation ship

This person continues to top their previous missions listed in the album. First visiting Jool and the planets from the Outer Planets Mod (which inspired me to revive my KASDA thread), then conducting a Daedalus-style interstellar flyby ("Star Boom 1") with a fusion-powered spacecraft assembled using Extraplanetary Launchpads and KSP Interstellar Extended and fueled using a Jool SSTO with nuclear turbojets - that's right, it enters Jool's atmosphere to scoop Deuterium and Helium-3 (although it would take days of real life time, so save file editing was used), then returns to orbit. And now, they've made an interstellar probe that slows down at the target star, using a small miner to build bigger miners, which are then used to build exploration probes and copies of the interstellar spacecraft itself. I've never seen anyone do anything like this before, and it deserves more attention. Here's just a preview:

The mission is called "Star Boom 2," and consists of 2 acceleration stages and 2 deceleration stages that let it reach Nova Kirbani (from Kerbal Star Systems) in just a few Kerbin decades.

Deuterium and Helium-3 mined from the atmosphere of Urlum (from the Outer Planets Mod) with a larger version of the aforementioned nuclear SSTO

Arriving at a small moon (captured asteroid) in another star system

https://i.imgur.com/NIDqDwf.mp4

An "interplanetary explorer" manufactured within the system, designed to carry landers to other planets.

Edited April 19, 2021 by Pipcard

linuxgurugamer · June 6, 2018

WOW!

Xurkitree · June 6, 2018

A Von Neumann? I'm flabbergasted by this guy's ingenuity and ... my computer wont load the imgur album without freezing entirely. Crap.

But still . Deep respect. I even got a bit jealous of this guy, but it passed.

Pipcard · June 6, 2018

1 hour ago, Xurkitree said:

A Von Neumann? I'm flabbergasted by this guy's ingenuity and ... my computer wont load the imgur album without freezing entirely. Crap.

But still . Deep respect. I even got a bit jealous of this guy, but it passed.

Okay, I will list their every image/clip and caption under these spoilers. (I think your computer's freezing because of all the .mp4s trying to load, so they are only listed as links [plus, I can't even embed them anyway])

First half:

Spoiler

https://i.imgur.com/xXUFw7y.mp4

It is the distant future, 250 years after the founding of the space program. Kerbalkind assumes type 1 status on the Kardashev scale. This album is a part of a series I'm making. It seeks to colonize the stars using only well known physics and nonexotic matter (no antimatter, warp drives, EMdrives, etc.). Previous albums, below:

Jool: http://imgur.com/a/tiHZ0 | https://www.reddit.com/r/KerbalSpaceProgram/comments/5khzqw/the_voyage_of_the_enterprise_a_jool_5_mission/

Sarnus: http://imgur.com/a/lMkod | https://www.reddit.com/r/KerbalSpaceProgram/comments/5sk3xa/the_second_voyage_of_the_enterprise_a_sarnus_5/

Urlum: http://imgur.com/a/8Z8Cd | https://www.reddit.com/r/KerbalSpaceProgram/comments/5y0l0s/the_third_voyage_of_the_enterprise_a_10_year/

Neidon: http://imgur.com/a/pLJn5 | https://www.reddit.com/r/KerbalSpaceProgram/comments/630i7f/the_fourth_voyage_of_the_enterprise_stranded_at/

Plock: http://imgur.com/a/2wnpX | https://www.reddit.com/r/KerbalSpaceProgram/comments/6jhrkp/the_final_voyage_of_the_enterprise_the_mission_to/

Interstellar Flyby: https://imgur.com/a/jGMB4 | https://www.reddit.com/r/KerbalSpaceProgram/comments/76ertm/the_voyage_of_star_boom_1_an_interstellar_flyby/ Craft and save files for all episodes can be found here: https://drive.google.com/drive/folders/0B2omh3rCD1VMVWVlZzVvZGc0bTA?usp=sharing

The mission here has the same Δv requirements as a real world analogue. Throughout the album, we'll occasionally draw parallels to a real life real life starship proposal first drafted by nanotechnologist Robert Freitas, which you can read here: http://www.rfreitas.com/Astro/ReproJBISJuly1980.htm

I'm running KSP 1 . 2 with the following mods:

Extraplanetary Launchpads (backported from latest version)

KerbalJointReinforcement

KSP Interstellar Extended

Civilian Populations

Firespitter

Outer Planets Mod

Kerbal Star Systems

https://i.imgur.com/5K66c69.mp4

6 years ago, the Kerbals of Laythe conducted the first ever interstellar flyby. The flyby probe was sent to the nearest star system, "Nova Kirbani." Nova Kirbani is an Alpha Centauri analogue from the "Kerbal Star Systems" mod by StarCrusher96. It hosts three stars and many habitable planets. Its distance was manually tweaked to replicate the Δv requirements of a real mission to Alpha Centauri.

The flyby was the culmination of a mission that began almost 70 years earlier. That mission's name: "Star Boom 1."

Kerbalkind has not stood still in the intervening 70 years. Though nuclear pulse engines were originally designed for the interstellar mission, they have since found use around Kerbol.

https://i.imgur.com/wD8iIGJ.mp4

Nuclear pulse engines kickstart a revolution in interplanetary trade.

100 years ago, a one way trip to Urlum took 3 years, with 40 Tons of payload and a crew of 8. More than 90% of the ship was fuel, and the ship would need to refuel for the return journey.

Nowadays, a trip to Urlum can be done in under a month, and that's with 300 tons of payload and a crew of 74. Only half of the ship is fuel, and most of that is spare.

The interplanetary ships (example shown here) are modified versions of Star Boom 1's upper stage. They feature smaller fuel tanks, bigger engines, and oversized RCS thrusters mounted on a foreward facing "docking bus". Some craft also feature adjustable radiators for use in the inner system.

Wet mass: 1000 T

Payload: 300T

Thrust: 2000kN

Fuel range: 1.5%c (with recommended payload)

https://i.imgur.com/BnvuUqh.mp4

Nuclear pulse engines have sweeping effects on society. For one thing, they present regulatory challenges. At 0.2% the speed of light, a run-of-the-mill 1000T freighter (shown here, in real time) has a kinetic energy equivalent to the largest nuclear bomb ever detonated.

The governments of Kerbin and Laythe each implement their own interplanetary licensing system for the sale of relativistic vehicles. There are also strict speed limits. The speed limit within Kerbin controlled space is 0.1% the speed of light. Even at this speed, you can still do some heavy damage. A single vehicle striking the atmosphere could produce a field of charged particles strong enough to damage unprotected satellites for years. The effect would be very similar to a high altitude nuclear weapons test.

With a large enough fleet, it's theoretically possible for a single bad actor to inflict a thermonuclear holocaust on a planet. In practice, only the largest governments and corporations are able to possess fleets of this size.

https://i.imgur.com/0LM4Ndd.mp4

Nuclear Pulse engines also have sweeping effects on the economy. These engines rely on Deuterium and Helium3, which plays a vital role in the interplanetary economy much like crude oil does in the real life global economy. All interplanetary trade relies on the fuel. Entire industries emerge to mine and ship it. Entire economies rise and fall by its price.

The fuel is an extremely precious substance. The Kerbals of Laythe must mine the fuel from Jool using SSTOs of titanic proportion. As atmospheric launch vehicles, the SSTOs can't rely on Nuclear pulse engines. They have to rely on conventional nuclear turbojets with nonrelativistic Isps.

https://i.imgur.com/D7zC4Iw.mp4

The SSTOs run on fission, which requires a nuclear fuel of its own kind: Uranium Tetraflouride. The substance is produced from two source minerals: Uranite and Flourite.

Since Uranium is a heavy element, it is much more abundant among inner planets. Minimus is the chief exporter of UF4. It has the only known region in the system that's rich in both source minerals.

Every year, hundreds of tons of UF4 are brought to orbit on disposable chemical rockets such as this one.

Wet mass: 330 T

Payload: 270T

Thrust: 250kN

Fuel range: 300m/s

The mining industry also requires manpower, and most of that comes from Kerbin. Kerbinese passenger liners like the one shown here can comfortably accomodate 60 kerbals at a time. However colonial populations are reaching self sustaining numbers, and passenger transport isn't as lucrative as it once was. It was never as lucrative as H2/He3 mining, to begin with. Kerbin spends more in H2/He3 than it earns in passenger transport. A dramatic trade imbalance results - Kerbin owes a lot of money to the Laythans.

Kerbin must change its business model or suffer economic ruin. The policy makers of Kerbin set out to enter the H2/He3 market. That's petty ambitious - H2/He3 mining is a well established industry. That, plus there's not enough H2/He3 on all of Kerbin to power a single spaceship.

There are some things that work in Kerbin's favor, though. Laythan corporations may hold a monopoly on the H2/He3 industry, but their prospects are dwindling. Jool's gravity makes mining difficult, and it appears mining operations have maxed out. Joolean SSTOs can only lift 1000 tons of payload at a time. The engineers of Laythe try to scale SSTO payload by an order of magnitude, but the resulting craft is... large.

It's so large it pushes the boundaries of KSP-IE's vanilla tweakscale config. Reactors and fuel tanks only scale up to 40m in diameter, and this places limits on payload size. Its flight characteristics are also way different from the old miners, and that means it needs lots of testing. The new miner languishes in development hell.

[Note the damaged runway. It was crushed under the weight of the craft.]

While Laythe stagnates, Kerbin does its best to correct the trade imbalance. The ice giants are still unclaimed territory, and their comparatively weak gravity makes them much easier to mine. It's not easy to reach the ice giants, but Nuclear Pulse engines are making it easier. Perhaps now it makes economic sense to mine them?

With little fanfare, Kerbin establishes a small mining base over Tal. Tal is the sub-satellite of Wal, which itself is a satellite of Urlum. The Kerbinese see Tal as a location of strategic importance. Wal's gravity well makes it easy to intercept, and Tal's small size makes it easy to mine.

https://i.imgur.com/fqHZrCB.mp4

Urlum's weak gravity makes it much easier to scale up operations. A mining ship just slightly bigger than the Joolean SSTO can easily carry an order of magnitude more payload.

Wet mass: 40kT

Payload: 25kT

Thrust: 166MN

Fuel range: 2.5 km/s

https://i.imgur.com/krGI1N9.mp4

In just several years, Kerbin floods the market with cheap H2/He3. Costs for H2/He3 plummet, and Kerbin seizes a substantial market share. By the time Laythe catches wind, Kerbin already has a firm hold on the Urlumese system.

https://i.imgur.com/kg9lpXW.mp4

Despite their economic rivalry, Kerbin and Laythe get along fine politically. Its been almost a century since Laythe succeeded from Kerbin's interplanetary empire, and tensions have long since eased. In fact, the next interstellar mission will be a joint venture between the two worlds. Laythe manufactures hardware while Kerbin designs spacecraft and supplies fuel.

In the shipyards above Pol, the ship for this mission is assembled...

Behold: "Star Boom 2".

Wet mass: 130 kT

Payload: 50T

Thrust: 100 MN

Fuel range: 20%c

https://i.imgur.com/JtU1E7c.mp4

Star Boom 2 measures 1/3 km in length. Its length and mass are comparable to that of a real life Nimitz-class aircraft carrier. Thrust is twice that of the Saturn V, and payload is comparable to that of the Falcon Heavy.

Star Boom 2 carries on the design legacy of Star Boom 1, but with several key differences.

Payload is only a third that of Star Boom 1. That's 50 tons. Star Boom 2 won't need as much payload because it will decelerate at its destination, and thereby make heavy use of ISRU. Payload is mostly comprised of communication equipment.

Decelerating also means the upper stage engines need to power back on after several decades of disuse. That requires a reliable power source. Star Boom 1 used fission reactors, but its fuel was nearly gone by the time it reached its destination. So the upper stages of Star Boom 2 use a combination of fission and fusion. A 500MW fission reactor can sustain minimal power for several decades, after which it has just enough juice to kickstart a larger fusion reaction. The fusion reaction can then reliably power the lasers that initiate the explosive fusion reaction that propels the ship.

Last but not least, deceleration means double the Δv requirements. Two stages have been added since Star Boom 1, which serve to accelerate the craft. Their engines are also powered by fusion reactors, the largest being 50GW (enough to power all of Great Britain). The radiators on the lowermost stage are disproportionately large due to a simple scaling law: thrust scales with volume, but thermal dissipation scales with surface area.

It's also worth noting this is the first craft I ever designed using a computer algorithm. I used a gradient descent algorithm to determine the size of tanks, engines, reactors, and radiators. This is the same sort of algorithm that's often used to train neural networks. The algorithm easily halved the fuel mass of the craft while keeping mission time under 60 years.

You can download the python script I used here:

https://drive.google.com/file/d/1RkEIHvyQVmDp1ebTIVmwDNG9sWLQOnSn/view?usp=sharing

https://i.imgur.com/0vENoy8.mp4

It is launch day.

Star Boom 2 undocks from the shipyard. A small dedicated tug (bottom left) pushes the ship out. At first, the tug only uses RCS thrusters, lest it irradiate the dock workers with its nuclear pulse engines. When a sufficient distance is reached, the tug ignites its nuclear pulse engines, and the ship is off.

Destination: Urlum.

https://i.imgur.com/TSH06EV.mp4

The tug parks the starship in low orbit around Urlum. A mining SSTO comes up from the atmosphere to fuel it.

The SSTO is not designed for precision docking, and neither is Star Boom 2, so the tug module is used to transfer fuel from one craft to the other.

The fuelling process is completely autonomous. There's not a kerbal around for several million kilometers. The only oversight comes from the ship's artificial intelligence construct. It is a neural imitation network that has been trained to imitate the behavior of retired astronaut, Bob Kerman.

I call him "Bob".

I'm a Dennis Taylor fan.

https://i.imgur.com/DMoDeOm.mp4

It takes five SSTO flights to fully fuel the star ship. That's 3 kerbin years worth of atmospheric flight. The nuclear ramjet aboard the Urlum miner can keep it aloft for decades, so fuel isn't a problem, but it would take a human player 3 real world months to fuel the miner at x4 physics warp.

As I mention in the previous album, I fuel up using save hacks. However, I do make sure the miner is able to reorbit with max payload. I do try to ensure all craft are at least capable of conducting their missions.

Once the starship is fully fueled, the tug module is set loose. The tug module docking interface is jettisoned. Bob reports his progress, then ignites the Stage 1 engine.

https://i.imgur.com/Op4NtUr.mp4

year 1: 4.2% lightspeed

Stage 1 Separates.

Stage 2 Engines ignite.

https://i.imgur.com/apsslzp.mp4

year 2: 8% lightspeed

Stage 2 Engine shutdown.

The ship enters cruise mode. The blastshield separates from the starship. To reduce the risk of secondary debris strike, the blastshield will drift out several kilometers beyond the ship. The blastshield is equipped with its own RTG powersource and RCS, which allows it to maintain distance from the craft after debris strike.

https://i.imgur.com/uFOA9tL.mp4

Once the blastshield reaches an appropriate distance, the craft rotates. The second stage serves as a auxillary blastshield while in cruise.

year 5: communications weaken.

Beyond this point, all communication is done through a single massive relay constructed on Pol. The size of the dish made it necessary to build it on the surface. Nevertheless, Pol's mountains of perpetual light allow a single dish to provide round-the-clock coverage.

This is a major improvement since the last mission. The last mission used a single large dish at KSC that only provided sporadic coverage.

https://i.imgur.com/fCBCnjd.mp4

Year 57: 50 years into cruise, 316 years into the space program. 2 years remain until intercept.

Stage 2 separates.

The Stage 3 engine ignites.

https://i.imgur.com/bxhyNJg.mp4

Year 58: the ship has slowed to 5%c.

Stage 2 separates.

Stage 1 engine ignites.

Things are starting to deviate from the plan. The stage 4 fusion reactor runs out of deuterium halfway through deceleration. Fortunately, I've also misjudged the rate of uranium depletion, so there's still plenty of fuel left in the auxiliary fission reactor. There's also a healthy propellant supply - the uppermost stage is equipped with a second set of propellant tanks for exploring its destination. This could be used in an emergency as an extra fuel source, but it's hardly even worked through the first set of larger tanks.

Bob will simply adapt. The fission reactor will not be jettisoned as originally intended. Neither will the first set of propellant tanks. The ship will have to carry more mass, but that's OK thanks to the surplus fuel. The auxiliary fission reactor doesn't provide a lot of power, but it does provide just enough to fire the ship's engines at low thrust.

These are all things I'll have to keep in mind as I design for the manned mission.

Second half (arrival at Nova Kirbani):

Spoiler

https://i.imgur.com/NIDqDwf.mp4

year 59: the ship has slowed to several dozen km/s. Star Boom 2 has successfully decelerated into the Nova Kirbani system.

The ship intercepts Kernim, a red dwarf star and Proxima Centauri analogue. In the earlier flyby mission, a small metal rich body was discovered here orbiting a Duna-like planet. Orbital velocity there is only several meters per second, which makes it perfect for industrial operations.

https://i.imgur.com/3kMVbDm.mp4

Bob gets to work and deploys his mining craft, the "Star Germ".

The design of Star Germ was heavily constrained by mission parameters. Star Boom 2 has to travel light, and so must Star Germ. Star Germ mines for metal ore, but lacks the equipment needed for refining, which only Star Boom 2 can provide. Chemical rockets are used for Star Germ's propulsion, since at this scale nuclear engines are needlessly heavy. Solar panels are also used for Star Germ's electrical generation, since reactors are heavy, and beamed power is not possible at this point in the mission.

Star Germ must also operate with a high degree of reliability after decades of transport. Chemical propellant is not easily stored for decades at a time, so Star Boom 2 carries a small tank of chemically inert ore. The ore is refined into fuel as the ship arrives at its destination.

Wet mass: 11T

Payload: 5T

Thrust: 16kN

Fuel range: 300 m/s

https://i.imgur.com/XNWIDsA.mp4

Star Boom 2 is a Von Neumann probe: it is able to build objects of arbitrary complexity, up to and including itself. As soon as it can, Star Boom 2 uses the metal from Star Germ to produce a second generation of miner, called "Star Germ 2" :

Wet mass: 95T

Payload: 80T

Thrust: 80kN

Fuel range: 80 m/s

https://i.imgur.com/upAP6tv.mp4

Star Germ 2 itself mines the ore that's needed to create a third generation miner, called "Star Germ 3":

Wet mass: 720T

Payload: 700T

Thrust: 80kN

Fuel range: 20 m/s

Bob designs the Star Germs specifically for this asteroid. Both are driven strictly by monoprop, since higher isp engines are unnecessary and use of multiple propellants would only complicate design.

https://i.imgur.com/IUcAAIU.mp4

Time passes as the Von Neumann probe builds up infrastructure.

I think a lot about what this production facility might look like.

Picture a set of 6 axis CNC machines. They produce objects from a number of materials with the help of a shared automatic tool changer system. With the right tool, they could extrude thermoplastic, lay ceramic paste, weave fabric, mill titanium, weld inconel, pick-and-place circuit components, and many other things. The machines also manufacture other tools as need arises. With the right tooling and ingredients, they could print you a coffee mug, bake the ceramic, pour the coffee, and add some creamer to taste. A miniaturized "lights-out" fabrication plant produces integrated circuits from a collection of onboard system-on-a-chip photomask sets, ranging from a simple drone core to a neural network ASIC for the ship's own artificial intelligence. Other photomask sets could be manufactured as need arises. An ISRU plant synthesizes chemical rocket fuel, and an automated refinery processes metal from ore. Finally, several large "candadarm"-like machines move end-over-end along the truss system of the uppermost stage. With automated tool changing, they too can perform a variety of tasks, ranging from swapping out broken parts, stocking source material, assembling large components, and welding large monolithic parts like rocket engines and fusion reactors.

The automation aboard the Star Boom is nothing new. Each individual component has existed since the start of the space program. But tying it together was still a major undertaking. Never before has such a system been attempted. To mitigate risk of failure, all components for the mission are designed from the ground up to simplify manufacture by the ship's automation. Even for such an advanced civilization, it is a multi-national, multi-corporate endeavor. Key players from industries across Kerbin and Laythe come together to provide funding and manpower to the mission, if at least so they can develop hardware that completely replaces their workforce.

Any civilization that is capable of building such a thing is clearly post-scarcity, and it is hard to predict how Kerbin society will adapt following the mission.

It is now 72 years into the mission, 329 years into the space program. The mission is ready to move to its next phase: exploration.

Bob does not risk the Star Boom 2 on exploration - it has the only nuclear reactor in the trinary star system, and if that reactor fails, he won't be able to travel to other stars. Bob lacks the infrastructure needed to manufacture nuclear fuel, and even if that weren't the case, the ship automation lacks the ability to bring new reactors online.

So Bob manufactures a solar powered "Interplanetary Explorer".

Wet mass: 260T

Payload: 50T

Thrust: 300kN

Fuel range: 110 km/s

The Interplanetary Explorer is powered by a large supercapacitor. The supercapacitor is slowly charged by two giant solar panels. It holds just enough juice to fire a nuclear pulse engine for short periods of time. With enough patience, it can transfer between the planets of Kernim. (NOTE: I would have made it beam-powered, but I've identified a bug with using beamed power in the Kernim system that prevents me from doing so.)

The ship is equipped with approximately 50 tons of pre-manufactured rocket parts. The Interplanetary Explorer has some modest automation aboard it which allows it to assemble landing craft from component parts, *in situ*. It only makes sense that a civilization capable of producing Von Neumann probes would also make use of automated manufacturing elsewhere. And besides, doing it this way reduces turnaround time.

https://i.imgur.com/cykfChb.mp4

The Interplanetary Explorer sets out to survey the planets of the Kernim system:

First is Dunem, the duna-like planet mentioned earlier.

Landing here is trivial. A standard landing craft is used, which carries a small rover.

Wet mass: 2.7T

Payload: 2T

Thrust: 64kN

Fuel range: 1400 m/s

https://i.imgur.com/l3qHTye.mp4

Narath, a tidally locked planet in the habitable zone. It is an "eyeball planet", with a darkside covered in ice, and liquid oceans on the dayside.

Narath has a heavy atmosphere. Pressure transitions rapidly with altitude, so the landing craft needs to decelerate quickly before it loses altitude. A ballute proves essential.

The probe itself is inspired by the television adaptation of Wayne Douglas Barlowe's "Expedition". It is a balloon probe, able to examine local wildlife in complete silence for extended periods of time. The balloon probe is powered by fuel cells when in flight, since solar panels are obscured by the envelope. An ISRU plant aboard the craft allows it to operate indefinitely. This is definitely one of my favorite designs from the mission.

https://i.imgur.com/mdtR1IG.mp4

Iain, a massive super-kerbin close to its parent star. Were it any bigger, it would be a gas giant.

The landing craft is a standard probe used for gas giants. Landing is complicated by the nature of Iain's atmosphere. The gravity is strong, and the atmosphere is rich in heavy molecules, so the air tends to pack close to the surface. The atmosphere goes from 100 bars to 0 in only 30km, and the probe needs to shed a lot of speed due to the size of the planet.

https://i.imgur.com/hW5WL2b.mp4

Erel, an airless super-kerbin. Its atmosphere was blasted away by the ionizing radiation of its star.

Erel is by far the hardest place to land. The landing craft features a crash booster with an oversized engine. The lander is comparable to a Kerbin-class launch vehicle, minus the aerodynamic payload fairing.

Wet mass: 24T

Payload: 2T

Thrust: 650kN

Fuel range: 4000 m/s

You might wonder: "why do probes still use chemical propulsion this far into the future?" Well, aside from practical gameplay reasons, chemical rocket engines are relatively easy to manufacture, their propellants are easy to mine, and their high TWR is ideal for landing on airless bodies. If all you're manufacturing are disposable probes, I figure they do make sense, especially this far out from civilization and its well-established infrastructure.

While this goes on, Bob is free to work on house keeping. A beamed power relay is established in low orbit around Kernim, an orbital factory is established along the same orbit as Star Boom 2, and on the north pole of the asteroid, a large communication dish is constructed that provides round-the-clock coverage across the trinary system.

https://i.imgur.com/Iunzjis.mp4

Bob is finished here. The upper stage of Star Boom 2 is elongated to include a tank of spare rocket parts. Bob spends the next 5 years travelling to the second star in the trinary system, Kelin.

Kelin is an orange main sequence star, an analogue to Alpha Centauri B.

https://i.imgur.com/FEtMs2v.mp4

Star Germ was frankly a pain to use, so Bob won't use Star Germ like last time. He's got a better idea. Bob builds a sizeable lander with some modest automated manufacturing capability. It lands on the surface of "Phain", a small ice moon of the planet "Elno".

Wet mass: 20T

Payload: 10T

Thrust: 60kN

Max speed: 1km/s

The probe has a small reserve of pre-assembled rocket parts. It's just enough to manufacture some mining equipment. Once it has some basic mining equipment, it scales up operations by building new modules. It builds a larger mining facility, a launchpad, a solar power plant, and a ballast tank for support when carrying rockets on its pad.

https://i.imgur.com/F1FYHqV.mp4

When the time is right, the Von Neumann base constructs a disposable tanker drone, and carts a shipment of metal back to Star Boom 2.

Wet mass: 1050T

Payload: 900T

Thrust: 2000kN

Max speed: 400 m/s

Building on the surface vastly simplified my operations, for several reasons:

* I no longer had to waste several design iterations making a mining craft that would later be scrapped

* I no longer had to bother returning mining craft to the surface.

* I no longer had to consider mass balance issues.

* I no longer had to design everything ahead of time before I launched my craft.

Doing it this way also meant I could build more modularly: a single addon to my base has just one purpose, whereas a single mining craft needs several perfectly functioning subsystems, like communications and RCS. I highly recommend building on the surface, where possible. It's interesting to note this is how Robert Frietas first envisioned his Von Neumann Probe.

In no time at all, Bob manufactures the planetary explorer. The probes are dispatched...

https://i.imgur.com/Gdv2Llr.mp4

Elno, a ringed Hoth-like planet. Gravity is comparable to Tylo, yet there is an anoxic atmosphere 1/10 that of Kerbin's.

A combination of parachutes and engines are needed to land the probe.

https://i.imgur.com/2BIvGaz.mp4

Alar, a moon of Blalo made temporarily habitable from a recent impact event. The moon is wrapped in scalding hot lakes of liquid water and a rarified anoxic atmosphere.

Alar's gravity is 1/6 Kerbin's, and its atmosphere is 1/20. Terminal velocity is sqrt(20/6) = 1.8 times that of Kerbin. An airplane needs 1.8 times the wing area in order to take off, all things being equal.

An electric UAV is chosen to probe the moon. Lox/fuel is used to generate electricity when in flight. Lox/fuel also powers a pair of RCS thrusters that perform orbital maneuvers and low gravity VTOL. Its definitely another one of my favorite designs. Handles beautifully on lots of planets.

Wet mass: 8T

Payload: 1T

Thrust: 40kN

Max speed: 300 m/s

Hardly any fuel is spent while probing the moon. Drag is reduced in the rarified atmosphere, and an electric propeller can easily approach orbital velocity. However, slowing the craft to landing speed takes a bit longer. Flaps come in handy.

https://i.imgur.com/HGeP8kb.mp4

Blalo, a mysterious twin-Kerbin. The previous mission had to forgo study of the planet when a probe there accidentally impacted the surface at relativistic speed. Fortunately, a survey finds only localized damage, comparable to that done by a nuclear weapons test.

https://i.imgur.com/IG63C5o.mp4

Alva, a habitable desert planet, much like Tatooine. Preliminary probes curiously reveal an oxic atmosphere, so Bob sends a modified Alar probe that uses jet engines instead of electric propellers.

https://i.imgur.com/7dTTgrq.mp4

Esle, another airless super-Kerbin like Elno, but this one features oceans of molten rock. Sometimes I think this mod hates me.

To add to the difficulty, the planetary explorer's resources are nearly depleted. It doesn't have the resources needed to build a copy of the Elno probe. So the planetary explorer sacrifices itself to serve as a "crash booster". It burns just enough delta v to land a modified probe with reduced payload.

https://i.imgur.com/ZaQjPZ7.mp4

Next, Bob travels to Kirb, a yellow main sequence star similar to Kerbol. Kirb is much closer, so transit time takes only a year.

Bob sets up shop in the outer system, around the gas giant "Keles". Keles hosts only a single moon, Orph, which entered the system in an ancient orbital migration event and kicked out all the native moons of the system.

https://i.imgur.com/imowgWa.mp4

The process begins again: the Von Neuman base is deployed, and in several years it sends back enough metal to construct a planetary explorer. The planetary explorer heads on...

https://i.imgur.com/yKMcI4x.mp4

"Vesp", moon of the gas giant "Mirn". Despite its rarified atmosphere, the terminal velocity is roughly equivalent to that of Kerbin due to weak gravity. Hence, the aerial probe is very similar to a plane built for Kerbin.

https://i.imgur.com/89QRLgn.mp4

Taythe, another moon of Mirn, this one heavily inspired by the moon of Pandora, from Avatar. A standard balloon probe is sent here.

https://i.imgur.com/25Dgkp5.mp4

Sulph, a moon of Mirn featuring a sulphuric atmopshere. I'm not sure whether its a bug or a feature, but the upper atmosphere is so thick that terminal velocity is no more than a few m/s. I wind up designing a probe specifically for this planet. It features an extremely aerodynamic nose cone and an electric propeller to push its way down into the atmosphere. But despite my best efforts, I run out of electricity long before reaching the surface.

https://i.imgur.com/M9KpAem.mp4

Ilve, a habitable super-Kerbin. Gravity is 2.2 times that of Kerbin, and it influences all aspects of the planet.

The atmosphere transitions 2.2 times as sharply as Kerbin. The likelihood of mountains is probably reduced by a similar factor. This behavior is governed by the what's known as the Boltzmann distribution.

Life, where present, is stocky. The majority of the surface is covered by rolling grasslands. Tree trunks are sqrt(2.2) = 1.5 times the width of their Kerbin equivalents, given well known allometric relationships. The same could be said for the legs of animals - they would either be 1.5 times as thick, or 1.5 times as numerous, all other things being equal. However, there are no animals, because Ilve lacks the oxygen atmosphere that's necessary for motility. It's not clear why Ilve lacks oxygen given it there is photosynthetic life, but it is possible that the more massive atmosphere takes longer to become oxidized.

The balloon probe for Ilve is modified with an electric propeller that works in the anoxic atmosphere. Entry into the atmosphere is rough, but the landing craft requires no modification.

https://i.imgur.com/QGfykKl.mp4

Cal, the fiery moon of Ilve. Tidal heating causes vast oceans of molten rock to form on the surface.

It's virtually certain such a world would have an atmosphere, but it's difficult for me to predict the constituents. We do know the molecules of the atmosphere would have to be massive enough not to escape the weak gravity at the temperatures present. We can again use the Boltzmann distribution to make guesses. Gravity is 1/5 that of Kerbin, and given a surface temperature 3 times that of Kerbin (in Kelvin), we might guess an atmospheric molecular mass 3*5 = 15 times that of Kerbin. So instead of something like nitrogen (14g/mol), think of something heavier (14*15 = 210g/mol).

We also know the compounds must be gaseous, chemically inert, and relatively abundant given constraints. Mercury vapor is probably present (200g/mol, boiling point 630K), but there may be other, more common compounds of lighter elements. I really don't know. Suggestions are welcome.

https://i.imgur.com/vZZxWmI.mp4

It is the 150th year of the mission, 410 years into the space program.

Having seen all the planets of the star system, Star Boom 2 fulfills its role as a Von Neumann probe. Two child rockets are manufactured:

The first rocket carries a Von Neumann base similar to the ones used over Kirb and Kelin. This rocket will head out to a new star system, continuing the cycle of exploration and propagation.

The second rocket carries a modest crew quarters and cryogenic chambers. This rocket will stay put, and serve as the return vehicle for a future manned mission.

https://i.imgur.com/BGiVrSS.mp4

The Kerbals have to wonder. As hard as it was constructing a Von Neumann probe, it only took 400 years following the discovery of space flight. That might sound like a long time, but 400 years is inconsequential compared to the age of the galaxy. Surely some other intelligent species must have constructed their own Von Neumann probe by now. But if that's the case, where are they? Shouldn't they have visited Kerbin?

What does this mean for the Kerbals? Should they be afraid? Do species die off shortly after becoming technological? Do they escape into virtual worlds? Do they never leave their parent stars? Are Kerbals the only species to have done so?

And what do we make of Bob and his Von Neumann machines? In every technical sense, they are alive: they reproduce, they consume energy and material, they respond to their environment, and they collectively grow and change. But they are a new kind of life, one that can live for centuries, reproduce like rabbits, and assume any body shape needed by their environment. Such an organism easily outcompetes any other known form of life.

So do Kerbals stand a chance against them? Does the future even need them?

Will the machines continue to serve their masters? Will they rebel? Will they compete for resources? Will they even bother with interaction?

And if all goes well, how will Kerbal society adapt to the post-scarcity conditions offered by self reproducing machines?

Perhaps these questions are best left to another mission: a manned mission to the stars. Only time will tell. Stay tuned!

Edited June 6, 2018 by Pipcard

Xurkitree · June 7, 2018

Mad props to this guy!

Luc1fer · June 7, 2018

On 6/6/2018 at 3:33 AM, Pipcard said:

Reddit post

Full imgur album

This person continues to top their previous missions listed in the album. First visiting Jool and the planets from the Outer Planets Mod (which inspired me to revive my KASDA thread), then conducting a Daedalus-style interstellar flyby ("Star Boom 1") with a fusion-powered spacecraft assembled using Extraplanetary Launchpads and KSP Interstellar Extended and fueled using a Jool SSTO with nuclear turbojets - that's right, it enters Jool's atmosphere to scoop Deuterium and Helium-3 (although it would take days of real life time, so save file editing was used), then returns to orbit. And now, they've made an interstellar probe that slows down at the target star, using a small miner to build bigger miners, which are then used to build exploration probes and copies of the interstellar spacecraft itself. I've never seen anyone do anything like this before, and it deserves more attention. Here's just a preview:

The mission is called "Star Boom 2," and consists of 2 acceleration stages and 2 deceleration stages that let it reach Nova Kirbani (from Kerbal Star Systems) in just a few Kerbin decades.

Deuterium and Helium-3 mined from the atmosphere of Urlum (from the Outer Planets Mod) with a larger version of the aforementioned nuclear SSTO

Arriving at a small moon (captured asteroid) in another star system

https://i.imgur.com/NIDqDwf.mp4

An "interplanetary explorer" manufactured within the system, designed to carry landers to other planets.

Meanwhile I can’t manage to reach planets further duna... i have a huge problem with fuel efficiency.

:confused:

But how is he gonna construct ships in the space? Can you do that in vanilla? If not then what mod is he using to construct?

Pipcard · June 7, 2018

5 minutes ago, Luc1fer said:

Meanwhile I can’t manage to reach planets further duna... i have a huge problem with fuel efficiency.

But how is he gonna construct ships in the space? Can you do that in vanilla? If not then what mod is he using to construct?

The in-space construction mod is called Extraplanetary Launchpads, and the nuclear fusion engine is from KSP Interstellar Extended. They also used Tweakscale to change the size of parts.

Edited June 7, 2018 by Pipcard

Luc1fer · June 7, 2018

1 minute ago, Pipcard said:

The in-space construction mod is called Extraplanetary Launchpads, and the nuclear fusion engine is from KSP Interstellar Extended.

Thx m8

June 7, 2018

Hi guys,

I'm the one responsible for this mission. Great to see this is getting a wider audience on the KSP forums! I'm open to questions in case anyone wants to do something similar. There's lots of things I had to work around to get to this state, and there's lots of things I'd do different if I had to do it again.

11 hours ago, Pipcard said:

The in-space construction mod is called Extraplanetary Launchpads, and the nuclear fusion engine is from KSP Interstellar Extended. They also used Tweakscale to change the size of parts.

I think it's important to note I used a slightly modified version of Extraplanetary Launchpads - I had to make a new part to enable autonomous construction. You can see that part's config file in my pull request here.

I originally intended to use the Civilian Population Mod to achieve autonomous construction. An earlier version of CPM offered a "construction drone" part that could be used alongside Extraplanetary Launchpads to construct spacecraft without having Kerbals on board, but the functionality was never ported to newer versions of KSP. Fortunately, there was a recent change to EL that allowed the creation of just such a part. There were only two problems: 1.) the part would still have to be created, and 2.) the functionality in EL would have to be backported to the version of KSP I was using for my 250 year old save file (v1.2).

So I backported the most recent version of EL and recreated CPM's construction drone using the mesh from earlier versions. This was for my own personal use so I still haven't bothered asking anyone for permission. For part settings I copied most of the values from the EL workshop, with the exception of productivity, which I lowered by a factor of 5 to balance for the fact the part didn't need Kerbals on board in order to work.

In other words, this playthrough's very existance relied on me modding the game. So I can never really claim it's a "legit" playthrough. There are plenty of other hacks I had to pull anyways (documented here) but it's probably the best a player can do at this point while conducting a mission of this kind.

Edited June 7, 2018 by 16807
fixing quote

Pipcard · June 7, 2018

4 hours ago, 16807 said:

Hi guys,

I'm the one responsible for this mission. Great to see this is getting a wider audience on the KSP forums! I'm open to questions in case anyone wants to do something similar. There's lots of things I had to work around to get to this state, and there's lots of things I'd do different if I had to do it again.

I think it's important to note I used a slightly modified version of Extraplanetary Launchpads - I had to make a new part to enable autonomous construction. You can see that part's config file in my pull request here.

I originally intended to use the Civilian Population Mod to achieve autonomous construction. An earlier version of CPM offered a "construction drone" part that could be used alongside Extraplanetary Launchpads to construct spacecraft without having Kerbals on board, but the functionality was never ported to newer versions of KSP. Fortunately, there was a recent change to EL that allowed the creation of just such a part. There were only two problems: 1.) the part would still have to be created, and 2.) the functionality in EL would have to be backported to the version of KSP I was using for my 250 year old save file (v1.2).

So I backported the most recent version of EL and recreated CPM's construction drone using the mesh from earlier versions. This was for my own personal use so I still haven't bothered asking anyone for permission. For part settings I copied most of the values from the EL workshop, with the exception of productivity, which I lowered by a factor of 5 to balance for the fact the part didn't need Kerbals on board in order to work.

In other words, this playthrough's very existance relied on me modding the game. So I can never really claim it's a "legit" playthrough. There are plenty of other hacks I had to pull anyways (documented here) but it's probably the best a player can do at this point while conducting a mission of this kind.

Welcome to the forum! One of the other things I liked about the report was how technological progress and the "interplanetary economy" were depicted - "100 years ago, a one way trip to Urlum took 3 years, with 40 Tons of payload and a crew of 8. More than 90% of the ship was fuel, and the ship would need to refuel for the return journey. Nowadays, a trip to Urlum can be done in under a month, and that's with 300 tons of payload and a crew of 74. Only half of the ship is fuel, and most of that is spare."

Edited June 7, 2018 by Pipcard

June 7, 2018

Oops, I fixed that quote you mentioned. Guess I'm still getting the hang of things.

37 minutes ago, Pipcard said:

how technological progress and the "interplanetary economy" were depicted

Yeah, I tend to get carried away with those XD. I'm a hard sci-fi nut and I think it bleeds into gameplay. The game tends to force you to clarify things you don't see otherwise. The thing about mining Urlum is actually an idea put forward by project Icarus and it just so happened to conveniently solve the problem I was running into while trying to increase fuel production: https://www.centauri-dreams.org/2011/06/01/starship-fuel-from-the-outer-system/

Nivee~ · June 8, 2018

Oh.My.God...... The HECK was that??? :blink: Unbelievable...

6 hours ago, 16807 said:

https://www.centauri-dreams.org/2011/06/01/starship-fuel-from-the-outer-system/

I think I discovered a rabbit hole...... Jumping right in!

Edited June 8, 2018 by Nivee~

Pipcard · June 8, 2018

According to the in-game Transfer Window Planner mod, if a "month" is defined as 30 Kerbin days (180 hours), it would take 700,000-800,000 m/s to get to Urlum in that time.

June 8, 2018

8 hours ago, Pipcard said:

According to the in-game Transfer Window Planner mod, if a "month" is defined as 30 Kerbin days (180 hours), it would take 700,000-800,000 m/s to get to Urlum in that time

That sounds about right. That's ~1/10 the Isp of the Daedalus engine, or ~1/5 the dv listed for the craft, so the freighters could make a few trips like that before returning to Jool for fuel. In practice, there was no need for me to travel that fast, so I often traveled slower, maybe like 3 months. That way I wouldn't have to watch my fuel as much.

Edited June 8, 2018 by 16807

Archgeek · July 27, 2018

It took me a while to drill through that whole series, but holy schnikes that was cool. I like how the ships' capabilities got high enough that delta-v just turned into %c. It leads, though, to the amusing thought that absurdly capable craft could see delta-v values in multiples of c.

ExtremeSquared · July 27, 2018

34 minutes ago, Archgeek said:

It took me a while to drill through that whole series, but holy schnikes that was cool. I like how the ships' capabilities got high enough that delta-v just turned into %c. It leads, though, to the amusing thought that absurdly capable craft could see delta-v values in multiples of c.

I wonder how relativistic speeds would play havok with the inner working of a rocket turbine...

This being on reddit is amusing as well. It's like finding a peer-reviewed neuroscience article on buzzfeed.

Pipcard · February 20, 2020

Now imagine being able to do most (if not all) of this in stock in KSP 2.

Edited February 20, 2020 by Pipcard

Pipcard · April 18, 2021

They finally finished Star Boom 3, the first interstellar colonization mission

(imgur gallery)

I will again repost it here under the spoilers if you can't load the imgur gallery.

The Star Boom 2 mission of robotic von Neumann probes continues to explore other star systems (Nova Kirbani to Kurvin system):

Spoiler

It is the distant future, 700 years after the founding of the space program.

This album is the finale to a series I'm making. It seeks to colonize the stars using only well known physics and nonexotic matter (no antimatter, warp drives, EMdrives, etc.). Previous albums, below:

Mun: https://imgur.com/a/u5Rg7 | https://www.reddit.com/r/KerbalSpaceProgram/comments/6npxkn/the_voyage_of_the_dinky_hops_the_dawn_of_a_new/

Duna: https://imgur.com/a/cZkWR | https://www.reddit.com/r/KerbalSpaceProgram/comments/6ekppe/duna_7_kerbals_1_rocket/

Jool: http://imgur.com/a/tiHZ0 | https://www.reddit.com/r/KerbalSpaceProgram/comments/5khzqw/the_voyage_of_the_enterprise_a_jool_5_mission/

Sarnus: http://imgur.com/a/lMkod | https://www.reddit.com/r/KerbalSpaceProgram/comments/5sk3xa/the_second_voyage_of_the_enterprise_a_sarnus_5/

Urlum: http://imgur.com/a/8Z8Cd | https://www.reddit.com/r/KerbalSpaceProgram/comments/5y0l0s/the_third_voyage_of_the_enterprise_a_10_year/

Neidon: http://imgur.com/a/pLJn5 | https://www.reddit.com/r/KerbalSpaceProgram/comments/630i7f/the_fourth_voyage_of_the_enterprise_stranded_at/

Plock: http://imgur.com/a/2wnpX | https://www.reddit.com/r/KerbalSpaceProgram/comments/6jhrkp/the_final_voyage_of_the_enterprise_the_mission_to/

Interstellar Flyby: https://imgur.com/a/jGMB4 |
https://www.reddit.com/r/KerbalSpaceProgram/comments/76ertm/the_voyage_of_star_boom_1_an_interstellar_flyby/

Von Neumann Probe: https://imgur.com/a/EHUwh | https://www.reddit.com/r/KerbalSpaceProgram/comments/8osi7v/the_voyage_of_star_boom_2_a_von_neumann_probe/

Save files for all episodes can be found here: https://drive.google.com/drive/folders/0B2omh3rCD1VMVWVlZzVvZGc0bTA?usp=sharing

Craft files for this episode can be found here: https://drive.google.com/file/d/1BPGUTriYqD8Wz0HV5jfnSfz04c2FpZ-D/view?usp=sharing

The mission here has the same Δv requirements as a real world analogue. Mission times in Kerbin years are comparable to a real life mission in Earth years. Throughout the album, we'll occasionally draw upon several published sources, including "The High Frontier" by Gerard O'Neill, and at least one study on population sizes.

I'm running KSP 1 . 5 with the following mods:
Extraplanetary Launchpads
KSP Interstellar Extended
Tweakscale (packaged with KSPIE)
Better Time Warp (packaged with KSPIE)
Civilian Populations
Procedural Parts
DeepFreeze
Outer Planets Mod
Kerbal Star Systems (now part of "Galaxies Unbound")
HangarExtender
KerbalJointReinforcement

https://i.imgur.com/KqExQnQ.mp4

Far off in the star system of "Nova Kirbani", on a small moon around a gas giant, self replicating "Von Neumann" machines prepare for their next mission to the stars.

Here, the Von Neumann machines have established a modest manufacturing facility, producing launch vehicles with up to 15 kiloton payloads.

Wet Mass: 24.5kT
Payload: 15kT
Thrust: 32MN
Fuel Range: ~1.4km/s

This particular launch vehicle carries metal ore and an assortment of automated construction machinery into high orbit around the moon. The machinery uses the metal ore to manufacture a beamed power station, capable of providing up to 6 gigawatts of concentrated solar power to the surface through a soft x-ray laser beam.

https://i.imgur.com/pvjm20N.mp4

With the power station in place, new launch vehicles are built to harness the beamed energy using highly efficient plasma thrusters with exhaust velocities of around 10km/s.

Wet Mass: 26.7kT
Payload: 15kT
Thrust: 36MN (stage 1)
Fuel Range: ~3km/s

https://i.imgur.com/kb462YK.mp4

The new launch vehicle stops to refuel around the gas giant. Automation aboard the craft constructs new engines and tanks, trading thrust for a higher exhaust velocity.

Wet Mass: 23kT
Payload: 15kT
Thrust: variable
Fuel Range: ~7km/s

When modifications are complete, it heads off to a low stellar orbit, where it is uses the remaining metal to construct beamed power facilities of even higher wattage.

https://i.imgur.com/3t7Bnos.mp4

The facility around the moon sends one last launch vehicle to low orbit around the gas giant. There, it manufactures an orbital gas mining facility, able to extract a rare mixture of Deuterium and Helium-3 from the atmosphere that can be used to power the nuclear pulse engines of star ships.

https://i.imgur.com/JpQDSIJ.mp4

There is 1 kiloton of raw material left over from building the mining facility. With it, the automation aboard the gas mining facility builds a starship, fueled with 20 kilotons of H2/He3 from the mining facility.

Wet Mass: 20kT
Payload: 12T
Thrust: 19MN (stage 1)
Fuel Range: ~15%c

https://i.imgur.com/etF93W8.mp4

Within its first year, the starship accelerates to 5% the speed of light. First stage tanks separate.

https://i.imgur.com/Wcr3Q0q.mp4

2 years, 10%c. Stage separation.

https://i.imgur.com/M3dvLTO.mp4

3 years, 15%c. Second stage tanks separate. The starship now enters cruise mode.

The starship spends the next 30 years traveling 3.5 light years to the next star over - Kurvin. Kurvin is an analogue to the real life Luhman 16, the star system closest to Alpha Centauri. As a mirror to real life, Kurvin is the star system closest to Nova Kirbani.

https://i.imgur.com/gzubMea.mp4

3 years prior to its arrival, the starship deploys a magnetic "aerobrake".

In essence, the aerobrake is a powerful magnetic field generator which interacts with interstellar gas for miles around the craft. This has the effect of increasing the surface area of the craft to the point where drag forces become significant, a nominal 1 m/s.

In real life, the magnetic aerobrake was originally conceived by Robert Bussard in the 1960s as a magnetic scoop that could capture interstellar gas to be used for propellant mass in an "interstellar ramjet". Studies since then have shown the magnetic scoop would always generate more drag than the thrust from the propellant mass, though this by itself is not all that bad, since the scoop can still serve as a way to slow the craft without propellant. The aerobrake in this mission cuts fuel requirements by a full order of magnitude.

Interstellar drag force follows the same law that we see in aerodynamics: drag force is proportionate to the cross sectional area and the square of velocity. Drag force rapidly decreases as the craft decelerates.

https://i.imgur.com/tPdNJ5Z.mp4

At around 5% the speed of light, the drag force experienced by this particular vehicle becomes insignificant, so the craft must decelerate the remaining 5%c using a small amount of propellant mass. A bigger aerobrake could be used, but the mass of its reactor would outweigh any fuel savings it could offer.

A python script was used in calculating the appropriate size of aerobrakes and reactors for this mission, which you can see here: https://drive.google.com/file/d/1lt6I36R_YZDGpc6L0G6zyuvmQrmwcLwE/view?usp=sharing

https://i.imgur.com/77ptyqd.mp4

The craft has arrived at its destination: a binary system of two brown dwarves

https://i.imgur.com/V3WRdZo.mp4

The brown dwarves here were never able to ignite their full supply of hydrogen. Only isotopes like deuterium could fuse inside them. Had they ignited their full supply, they would have pushed out surrounding interplanetary dust with their stellar wind, but the planets instead formed close to their parents.

Despite their close proximity, the planets are cold, bathed in only faint red and infrared light. No heat shielding is needed to travel so close to the dwarves, but the fuel needed for even basic orbital maneuvers is considerable.

Liquid fuel is too unstable to be stored across the multi-decade mission, so to prevent complicating the mission, the craft uses its few remaining fusion pellets to intercept the only atmospheric body in the star system, where it will use the atmosphere to land a probe on its surface.

https://i.imgur.com/OIwlEj2.mp4

Its systems failing, the interstellar space probe now serves only as a crash booster for its most precious cargo: an 10 ton self replicator.

The self replicator lands safely on this alien planet. Not long from now, yet another star system will by conquered by the Von Neumann probes.

Two centuries pass in this manner. It is now 900 years since the founding of the space program. 6.5 light years away, the Kerbals look on at their creations with a mix of pride, fascination, and perhaps fear. Surface construction facilities, orbital gas mining, aerobrakes... All these were the inventions of the artificial intelligences aboard the Von Neumann probes. They have become exceedingly efficient at their purpose: to construct the infrastructure that would enable future crewed missions to the stars. They have built beamed power facilities, communication relays, and orbital habitats wherever they go. The kerbals are relieved to see the Von Neumann machines have since then carried out their mission faithfully. And yet, so many centuries later, where are the Kerbals?

Planning and designing the first crewed interstellar colonization mission:

Spoiler

600 years ago, the governments of Kerbin and Laythe made their first mission to the stars, and drafted the first serious plans for interstellar colonization. In that time, technology has advanced, political institutions have come and gone, languages and cultures themselves have evolved beyond recognition. Interstellar travel is now as old as the printing press. Space travel is as old as windmills. And despite all this, there has never been a crewed mission to the stars.

Early optimistic plans at the start of the interstellar age thought that crewed missions could be conducted by repurposing the designs for "Star Boom 2", the ur-probe from which all modern-day Von Neumann probes descend.

The early plans for Star Boom 3 called for a round trip to the stars with a small crew in cryogenic hibernation. With all the tricks in the book, you could shorten a realistic mission to maybe 40 years. Advances in aerobraking might shorten the mission further to 25 years.

However as the crewed mission started requiring commitment, holes in the logic began to show. Even if you could find a crew of level headed astronauts that were nevertheless willing to consume their full adult lives on a mission, what representative government would sponsor them to do so?

Perhaps you could get around it by changing the political dynamics of the future, or by changing underlying crew constraints. You could assume for instance that the mission is conducted by a dictatorship, where individual preferences don't matter and the state doesn't care what anyone thinks. Alternatively, you could assume that people live long enough in the future that a 25 year mission is nothing to them. The first possibility is disheartening and the second is not guaranteed.

And to what end would such a mission serve? A handful of crew return from a star, but that does little towards the ultimate goal of making life interstellar.

The Kerbals are at the limits to what can be safely assumed for the near future given current understanding of physics and biology. We're fairly confident that nuclear pulse engines and aerobrakes can be done, but everything past that requires speculation.

The Kerbals are so tantalizingly close, and yet so far away.

There is really only one possibility left - a generational star ship. But generational star ships have political, ethical, and social concerns of their own. How could one create such a thing and ethically compel people to devote their lives to such a project, and how could one construct such a thing to withstand not only the decay of parts, but the decay of the very social institutions that built them?

In the end, the call to action comes not from large governments and contractors. It doesn't even come from small SpaceX-style startups. No, it in fact comes from...

the real estate industry?

A generational starship needn't be hard to build. Any existing design for an O'Neill cylinder could be reused for the living quarters. O'Neill cylinders, 1/2 km in diameter like the one shown here, have by this point existed for centuries. Property is bought and sold aboard them as with any housing project. Millions of civilians spend their entire lives aboard these habitats, comfortably.

Ordinary steel provides all the tensile strength needed to build pressurized spinning habitats that are kilometers in length, and the design is so simple that even primitive 3d printing could trivialize their construction.

https://i.imgur.com/7hQZxKg.mp4

Metal hauling rigs on Hale (shown here) produce the metal for the O'Neill cylinders. In a single launch, they ship megatons of raw material off to Sarnus, where on-board atmospheric scoops collect just enough propellant to head off anywhere in the Kerbolar system on high efficiency electric engines.

Wet Mass: 12MT
Payload: 10MT
Thrust: ~1GN
Fuel Range: ~1.6km/s

https://i.imgur.com/AM4gkOu.mp4

The manufacturing infrastructure was initially used to create beamed power stations in low Kerbolar orbit that now form a nascent Dyson swarm, but since then it has been repurposed to create O'Neill cylinders, and it can certainly be repurposed again.

And the Dyson swarm itself can be repurposed for the mission, providing terawatts of power to the first stage engines as far out as the Oort cloud.

Almost all the infrastructure for building a generational starship is already in place!

And the Kerbals need not live in want aboard these starships. Each habitat carries with it thousands of acres, enough to provide ample farmland for every Kerbal using the same agricultural practices that are used on Kerbin. There is enough space aboard every habitat to live at whatever population density one feels comfortable, from a bustling metropolis to a pastoral village.

If one of these cylinders could be equipped with a nuclear pulse engine, a journey to the stars could be made trivial!

Property could be bought and sold aboard the starship just as with any space habitat. After a decent amount of time to make the Kerbals feel at home, the engines fire and they head out for the stars. From then on, Kerbals could spend their lives aboard a starship just as they would any other cylinder, only now with the affirmation that just by living their lives they contribute to something extraordinary.

No mod exists currently to represent the habitats on this scale (enterprising modders, take note!). I currently use procedural tanks to represent the mass of the cylinder. However, the artist depiction shown here illustrates what life might be like aboard the habitats, and I'll be as true-to-life as I can when designing one.

The first question we ought to ask is "how big should it be?" Since radius determines the mass of the walls and blast shield, not to mention the cross section exposed to potentially damaging interstellar debris, we want to minimize radius. However, it cannot be too small, since you need to build big enough to generate gravity comfortably. You cannot have a generational ship without gravity of some kind (in real life, it would be essential for healthy pregnancy), and considering the outright hazard involved with a temporary loss of gravity on this scale (imagine your farm's top soil floating off), you would likely need to provide it without interruption.

So we need the smallest radius we can get away with while still providing comfortable gravity. But what radius is that?

In his 1977 book, "The High Frontier" Gerard O'Neill discusses the possibility of creating long term human settlements aboard giant rotating habitats, now called "O'Neill" cylinders. In it, he discusses this very issue. Based on studies from the 1960s, he determines a 2 rpm rotation rate is the minimum that could be allowed for long term habitation, but even the most sensitive individuals require no acclimation to a 1 rpm rotation rate. Since we are obliged to accommodate generations of people to come, we will have to pick the more conservative estimate.

At 1 rpm, you'd need a cylinder 1km in radius to generate 1 g of gravity. However, since we already assume that sustainable colonies exist on Duna, we might also assume we could get by with as little as 1/3 g of gravity, which requires only 1/3km radius at this rpm. Please note this assumption is not a strict requirement for this mission. We could build a 1g setup without adding significant mass, and the steel should still be able to handle the tensile stresses generated. We'd just have to build a bigger ship.

As for length: we want to minimize the length of the cylinder as much as possible, since length adds mass. The length of the cylinder would be affected by the size of the population.

Some research suggests a minimum population of ~500 to maintain genetic diversity, but this is a general estimate that's only meant as a safe bet for most species. A more recent study (published in the book shown above) was geared for this specific scenario. It suggests a population of 160 would be sufficient for a 200 year transit period. You could reduce the population needed if you took genetic stores along with you, and you would probably take genetic stores along anyways in case of emergencies (the mass to do so is inconsequential, so there's no sense not to). These stores could maybe last 50 years without degradation. However requiring the use genetic stores to minimize population gets into uncomfortable territory where we're telling people what to do, so we won't go there.

You can lower the land area needed across ships if there are more than 3 ships. Multiple ships would have to be created anyways for testing, and creating ships in larger batches would only stand to drive down production costs and increase chance of success through redundancy.

It's important to note here a principle that we haven't previously stated: we are no longer dealing with crew members, here. There can be no crew members aboard the ship, since you could never expect to meaningfully pay someone for a life time of labor several light years away where no one is present to sell you things. There is only a population, people who have in effect bought property aboard the ship. Of course, the passengers have every reason as property owners to keep their property in good condition, especially when they need it to keep them alive, but it's not certain whether the institutional knowledge needed to conduct one-time mission procedures could survive long enough to last the full length of the mission. While we can allow the passengers to make decisions concerning the mission if they want to, it would be unreasonable to expect them to perform any sort of specialized mission procedure manually unless they were confident in doing so.

Since we are only dealing with civilian populations, we have to design for it. Hundreds of people would live out a significant portion of their lives under your engineering decisions. The closest modern parallel would be designing a passenger liner, or a housing complex. Normal operations must allow for comfort, and emergency operations must allow for ample civility. You can't wind up with a situation like the Titanic where you only have life boats for a fraction of the passengers. You can't wind up with a situation like Pruitt-Igoe where your tenants fear going out into public spaces. You can't wind up with a situation where a population rebels due to strict mission parameters. Your minimums must center around accommodations that are generous by any standard. And as with any modern manned aerospace engineering, triple redundancy for safety critical components is mandatory.

So we start with the following requirements:
* remaining ship(s) must be able to accommodate population of 2 ships
* minimum population after 200 years must be 160 people after 2 ships lost
* maximum transit time must be 200 years

We find the situation reduces to the following relations:

(n-2) * p ≥ 160

(n-2) * P = n * p

where n is the number of ships, p is the population per ship, and P is the maximum population each ship needs to allow for in terms of land area.

Using 4 ships would more than halve the total land area needed across ships, and would require 80 people per ship with the ability to accommodate up to 160 in an emergency. In the worst scenario allotted for, where the population of two ships are lost, the surviving population could then continue for 200 years without suffering genetic decline.

Using 5 ships would cut land area down by a third, but would require 50 people per ship. You could design the mission to allow regular transport between ships, but 50 people may be a little low for the number of people you could regularly interact with.

So total fleet population is 320, with 4 ships each of 80, each able to accommodate for 160. If any two ships fail for any reason, the population aboard those ships can evacuate to the remaining ships and still be able to live modestly for the rest of the transit period. In the worst scenario allotted for, where the population of two ships are lost, the surviving population can continue for 200 years without suffering genetic decline.

So we now know how wide the ship ought to be based on human factors, and we know how many people we need to support based on genetic factors. Now we just need to know how much land we need to support each of them, and that will determine the length of the craft.

There's some research that suggests using current agricultural techniques for a U.S. standard of living would need 15,000 m^2 per person. This would imply 2km^2 per ship.

During emergency operation, the ship will accommodate up to 160 people with enough space to allow for third world country living standards. From the same source, this is about 2500 m2 per person. That means we'll need 1km^2 per ship.

We will go by the higher estimate, or 2km^2 per ship. This might require a cylinder 1.2km in length, but several megatons of dry mass.

The plan for the generational ship is shown above. It is only a modest sized O'Neill cylinder, 2/3km in diameter.

While initially promising, issues with the generational ship become apparent as the plans progress. As always, the major problem isn't building the ship, but fueling it.

The mission time we drafted earlier was limited to 200 years due to genetic constraints. To reach the nearest star system in this time requires a top speed of ~2%c. The ship is too large and too slow for an aerobrake to work, so half of your propellant would be needed to decelerate. So the delta-V budget is 4%c. This is roughly the exhaust velocity of the engines, so that means the mass ratio is ~1:3, and the ship weighs ~7 megatons. So let's say... 20 megatons of fuel. *sigh*

Trying to build an SSTO that fuels the ship in reasonable time pushes against the limits of the default tweakscale. Let's define "reasonable" as anything that takes less than 10 flights to fuel the starship. An SSTO would need to carry 1/10 of our fuel requirements, or 2MT. You might recall in the last mission I tried building an SSTO to launch 10kT from Jool. This by itself was nearly impossible. You could move operations to Urlum and scale up your payload by an order of magnitude, but even then, you still come up shy by an order of magnitude.

Another way to think about it: A maxed out 40m fission reactor in KSPIE produces 600MN of thrust at standard atmosphere. This is enough to push this payload with a thrust-to-weight ratio of 0.03. Even subsonic aircraft have thrust to weight ratios on the order of 0.2, and we would need to build an aircraft capable of hypersonic flight.

I thought instead I should go the orbital refinery route, but the resulting craft (shown here) is also... large.
It's so large that it exploded as soon as I tried finalizing construction in orbit, and since then I've somehow gotten it stuck up past where Hangar Extender won't let me reach it. Yep, I am very definitely reaching the limits to this game.

I'm not saying it's impossible to create either of these craft (e.g. simply increase the number of reactors by 10), but the act of trying to do so is becoming painful, and I have to wonder if this really is the first thing that we would try in order to get people to the stars. There might be an easier approach.

In his book, "The High Frontier", Gerard O'Neill provides some suggestions on the land area that's needed to sustain human settlement. It turns out the amount of farmland that's actually needed to support a human is much less than what's allotted by traditional agriculture. Since crops are small during their first few months of growth, you can grow an older generation of crops above them while the new generation is just getting started.

Picture a process similar to what this man is doing: https://www.youtube.com/watch?v=adW3GCQGHug&t=330s.

While it may not be practical for industrial agriculture, it may be useful to a colony that needs to save on space. This technique can massively increase yield per unit of farmland. A single acre of farmland could provide enough food to feed 25 people on a varied diet.

At 25 people per acre, you could support our target population of 160 people with just 6.4 acres. During regular operation, when not in an emergency, the same land belongs to only half this number. This provides everyone with about 1/3 acre of land, and they have all 6.4 acres to wander if they're comfortable sharing. Picture a set of luxury condominiums surrounded by dense automated communal gardens.

With this amount of living space you'd only need a cylinder that's 13m in length. At this point, the bulk of the mass is wasted on the walls, so we reconfigure the walls to serve as the floor. The O'Neill cylinder is now just a habitat dome in a centrifuge (shown above, with the space plane hanger shown for scale).

This needn't be the only configuration, mind you. For instance, instead of using a centrifuge, you could instead just kick the ship in and out of a spin every burn. As long as the engines have enough thrust to cause noticeable gravity, you can expect to have some amount of gravity aboard. This would vastly simplify ship design, since you now only have a single axis along which tension or compression could occur, but it severely complicates course correction and ship keeping. It's pretty wild to imagine a 1 kilometer star ship kicking itself into a 1 rpm spin, but ultimately I went with a more conservative design that I feel would be far more likely to see in reality.

Switching to the smaller habitat saved me lots of mass. The combined habitat space now weighs only 4kT. The upper stage dry mass is 6kT, just small enough to allow for the largest available aerobrake and its surrounding hardware. The dry mass of the entire assembly is just 40kT. I can now build and fuel the entire starship without having to design any extra infrastructure, and still wind up with a top speed of 10%c. Mission time is just 40 years!

It was also much more enjoyable designing the habitat dome than it was for the O'Neill cylinder. The O'Neill cylinder has to be represented with a bland grey fuel tank from the Procedural Parts mod (enterprising modders, take note!). The habitat dome on the other hand comes from the Civilian Populations mod. If I put two habitat domes at the largest Tweakscale setting on opposite ends of the centrifuge then I get just enough space to support 160 people. The result looks a lot nicer and I get a lot of nice screenshots of what people see when they're in the habitat. It also feels much like playing Sim City in Kerbal Space Program.

Even though our craft needs only to last only 40 years, we still have to consider whether it can last that long with passengers aboard. We might take some precedence from oil tankers, here: they're mobile, they spend their entire service life floating in their operational environment, and most of the time, the repairs they need are small, affecting an area that's not on the same order of magnitude as the ship itself. The real life oil tanker, "MS Berge Stahl" has a deadweight tonnage that's comparable to the mass of our generational starship, around 300 kilotons. It was built in 1986 and still sees operation to this day, 34 years later. So there is some precedence for structures of this scale to last for the duration we need. And arguably the problem becomes even easier in space, where we no longer have to worry about operating in a highly corrosive salt water environment.

But the major difference here is that oil tankers can fuel up when they get back to harbor. We still have to consider consumables like fuel or air. The issues with fuel storage have already been addressed by others (see the technical report for Project Daedalus, referenced in the first interstellar mission write up), but this is the first interstellar mission where we have to concern ourselves with air.

It's almost certain that air will leak in transit, but we have to define what amount is acceptable. We are interested in the size of a leak needed to drain a volume of space within 40 years to some unacceptable threshold. We will assume the volume begins at room temperature with 1 atm of pressure, and our threshold of interest is 15% (bringing us to about the air pressure of Denver). The pressure we end up with is close enough to our starting pressure that we will assume the air loss is linear. Since the leak will be most severe when the volume is fully pressurized, and since we are modeling for the worst case, we extrapolate from the loss rate at the start of the leak. (R code shown above, no apologies for lack of clarity)
We find that if no resupply is ever sent to the ship, it would only take a hole 7.5mm in diameter to bring the atmosphere to intolerable levels by the end of the mission. We'll note that leakage is linear to the area of the leak in the model, so if two holes add up to the area of that 7.5mm hole, it will still lose air at the same rate.

You would expect that shortening mission time would permit for larger holes, but if the likelihood of the hole scales with diameter then the effect is lackluster. A mission of 10 years could still be foiled by a 15mm hole.

I think the best solution might be to imitate submarines, which pump water out to allow long duration stays beneath the water. However, rather than pumping water out, we will pump the air back in. If the cylinder is double walled, the air between the walls can be evacuated. If there is a leak in one wall, it will take a while before the space between walls equilibrates. This can be modeled by the same equations shown earlier. Pressure in the space between can be monitored to check for leaks, and a pump can push air back into the cylinder when a leak is detected. If there is a leak in both walls, then as long as the pumps reduce pressure in the space between, the loss of air will be minimized. We could add any number of redundant walls as needed.

I depict this double wall visually within the domes of the ship (shown above).

Preparation, assembly, and the societal structure of a generation ship:

Spoiler

Time passes. A set of prototypes for the upper stage are created, which remain in the Kerbolar system. Property is bought and sold aboard the prototypes just as with any other space habitat. However these habitats are different. Their engines allow for interplanetary travel, with enough delta-V to last many years without refueling. Every once and a while, a prototype ship fires its engines, and it travels to another destination in the Kerbolar system, perhaps in a repeating cycle. The residents get a pleasant change in scenery every once in a while, and a handsome premium is charged for the estates. The premium is fed right back into developing the 1st stage rocket that will accelerate the interstellar variant.

It turns out the business proposal looks a lot like that of the real life Freedom ship project (https://en.wikipedia.org/wiki/Freedom_Ship), which still has yet to see execution.

As this goes on, a hauling vessel in low Sarnusian orbit uses its self reproducing machinery to manufacture the orbital gas mining vessel that will provide fuel for the starship.

The process mirrors what we saw earlier from the Von Neumann probe: the gas miner takes a small amount of metal from the hauling vessel, and uses its own self reproducing machinery to eventually build several starships out of the spare metal.

A single starship requires 300 kilotons of fuel. It takes 3 years for the orbital gas miner to supply this fuel.

Now that I've downscaled the size of the starship, the fuel requirements for the mission are actually comparable to that required by the previous one, Star Boom 2. In fact, it would be totally possible to reuse the Urlum SSTO from that mission, instead of this gas miner. The Urlum SSTO could stay aloft indefinitely on nuclear powered turbojets, but since it required 3 months of real life time to fly the thing at max physics warp, the only way it could be used in the game was with fuel hacks. Fuel hacks are annoying to perform, and since later versions of KSPIE allow tweakscaling scoops to much larger sizes, it made perfect sense during this mission to switch over to orbital gas miners. Nevertheless, the rate of collection is much faster on the Urlum SSTO, and given the real life scarcity of the fuel is an order of magnitude greater than what is represented within the game, I'm inclined to think the Urlum SSTO is actually more likely to be built in real life, requiring much smaller vessels that fly much more often.

Once fuel is procured, the orbital miner pulls into a higher orbit where drag is reduced and begins constructing a new fleet of ships. These ships will be equipped with the lower stage and aerobrake, and if everything checks out, they will function as the generational star ships.

Even with the Hangar Extender mod installed, the ships are far larger than what the VAB can handle, so they must be assembled in pieces. Each individual piece is about as large as can be managed in the VAB with the Hangar Extender mod. There are 5 pieces in total:

* Lower stage
* Hub
* Habitat booms (x2)
* Aerobrake assembly

Behold! Star Boom 3:

Wet Mass: 315kT
Payload: 4kT
Thrust: ~255MN
Fuel Range: ~10%c

https://i.imgur.com/Np1DO8E.mp4

The first ship in the fleet is ready to unmoor. Its nuclear pulse engines ignite and the ship slowly drifts from the gas miner.

First, the ship enters a high orbit so it can safely run a long duration burn to its next destination...

https://i.imgur.com/pqi8S0D.mp4

But wait, something is wrong.

Automation aboard the craft attempts to burn for the next destination, but it appears there's a software malfunction. It fails to consider the position of Sarnus as performs its burn. It's heading directly for the gas giant!

[Real life reason: relativistic engines make it really easy to simply align SAS to target and burn, I simply focused too much on the Navball and forgot Sarnus was there. The scene was so cool that I decided to keep the save, despite the setback]

https://i.imgur.com/ROJcXLK.mp4

The ship enters the atmosphere at a steep angle. The footage captured from automated cameras is stunningly apocalyptic. The energy involved as the 1km, 300 kiloton ship nose dives into the atmosphere is staggering.

Fortunately, the craft at this point was automated, and no one was aboard the craft during the incident. However, it is still a terrible setback for the project. All told, the incident costs 6 years of construction time, 30 kilotons of metal, 300 kilotons of precious fuel, and an unquantified loss in reputation.

Nevertheless, the Kerbals persist. In time, the cause of the problem is found and steps are taken to prevent it from occurring again. New ships are manufactured.

The starships spend a decade in the Kerbolar system to test for star-worthiness, cycling through the planets much like the prototypes. Property on the star ships is bought and sold just as with any other property. Most property is bought by those who already own property aboard the prototypes, since by now the residents there would be well adjusted to the living arrangements and can upgrade to a much more prestigious residence.

Governance is established while the ships go through proofing.

A home owners association is setup on each habitat. By-laws as part of that association place penalties on households exceeding a certain number of occupants, direct repair work within the habitat, and designate officials such as sheriff, communications officer, etc. A board of directors oversees changes to policies. Limits on the size of a household are designed to make sure the population remains stable. Most of the people here have shared years together living aboard prototype ships and they tend to be like-minded concerning the project, so even at the outset they form a fairly tight knit community. Certain things like the size of families might simply come down to a gentleman's agreement.

Small government has its share of problems, such as nepotism, incompetence, bike-shedding, short-term thinking, or deadlock. If left unchecked, these problems could prove catastrophic aboard a generational starship. To combat them, the responsibilities of the home owner's association are limited to the ship's habitats. A ship council is elected by the general population to oversee matters outside of habitation, concerning the maintenance of the ship and execution of its mission procedures. Members of the council are required to hold some degree of higher learning that pertains to their specialization, and much like the U.S. supreme court, they serve lifetime appointments to prevent politics from getting in the way of passenger safety. Virtually all responsibilities of the council could be subsumed by the ship A.I. should it need to, but having the council aboard allows the residents to exercise some sense of control over their lives. If the ship council is unable to come to a unanimous decision then the decision automatically defers to the ship A.I. The ship A.I. selects competing solutions from a number of subsystems, much like how Google runs their current search algorithm. Subsystems include an expert system designed by mission planners at the start of the mission, an A.I. that implements high level council directives to the best extent possible, and an A.G.I. that provides creative solutions in the event of unforeseen situations. Council members have the ability to view all competing solutions and pick from them as well, and if they their decision is unanimous, they override the master A.I.

Council business rarely intersects with those of the residents, but to promote transparency, a member of the ship council serves as outreach. The role is largely a formality, though. Remember, we're only talking about 80 people here. It's the responsibility of the outreach, for instance, to write the council's monthly newsletter.

It is now the 910th year of the space age. The estate ships have been in operation for well over a decade. 5 years ago, the ship councils announced plans to begin acceleration maneuvers. Those plans were to go into effect this year, and it doesn't seem like those plans are changing.

The last port of call is Kerbin, which provides specialty resources that the ship can't procure anywhere else.

Since passenger transport around Kerbin is contracted out using the Civilian Populations mod, this also provides me an out-of-universe mechanic to populate the starships without having to conduct too many routine boarding missions. However, in real life I think any civilization capable of interstellar travel would by this point be able to take up passengers from anywhere in the system.

Some passengers take the opportunity to visit the planet of Kerbin. Most of the residents grew up on other planets or cylinders, so they have no strong ties to Kerbin, but a few take the opportunity to visit planet-side and see all the landmarks. Some visit the surface just for bragging rights, much like visiting the shores on both sides of a continent. Others take advantage of the opportunity to stock up on some luxury goods that will appreciate in value, like fine wine, wooden furniture, or the seeds of exotic plants.

https://i.imgur.com/ql1tKfN.mp4

A small base on Minimus supplies ore for the ship's chemical fuel stores. Liquid fuel doesn't store well in a multi-decade mission, so the ship instead carries ore to be processed as need arises.

The launch vehicle is a standard disposable chemical rocket.

Wet Mass: 590T
Payload: 240T
Thrust: 2MN
Fuel Range: ~2.1km/s

https://i.imgur.com/KkupCYK.mp4

Meanwhile, Kerbin supplies a compound known as Glykerol, a resource provided by the DeepFreeze mod. The ship carries lifeboats in the event of emergency, which rely on cryogenic chambers to keep the passengers alive for several decades. Glykerol is needed for these cryogenic chambers to function, which only Kerbin has the manufacturing capability for.

The launch vehicle is a standard beamed power SSTO: simple, efficient, reliable, reusable. Just needs a beamed power network with ample power and coverage.

Wet Mass: 52T
Payload: 6.5kT
Thrust: 600kN
Fuel Range: 9km/s

https://i.imgur.com/9fXVnOi.mp4

Docking with the vessel is an awesome experience. At over 1 km in length, the ship looms in the background as you approach, a city floating in the void.

https://i.imgur.com/VjfVorN.mp4

You only start to appreciate the scale as you get up close.

https://i.imgur.com/fzXkf51.mp4

It takes several minutes to run along the full length of the ship, after which you reach the docks. On the way there, you see the engines, radiators, habitats, lifeboats... each one looks small at a distance, but as you approach you discover they are quite sizable in their own right.

https://i.imgur.com/eD3kzKN.mp4

The docks were an interesting thing to design. Since the ship in concept must always rotate to generate artificial gravity, it can never stop for you to dock with it. The front half of the vehicle is taken up by the aerobrake though, so you can't provide a central docking bay a la Space Odyssey.

Fortunately, the ship only rotates at 1 rpm. The hub at the docking bay is only 20m in diameter (~63m in circumference) so it's only spinning a little over 1m/s, slow enough for a nimble ship to approach it. Bigger ships could likely dock as well but would require reducing gravity in the centrifuge. The solution I came up with is to use a rotating platform. Every once a minute, the craft that's docking has an opportunity to advance into the path of the oncoming platform, where it waits for the platform to sweep it up. A lip runs along the platform, preventing the craft from sliding off if it idles there for too long. Once the craft is on the platform, it can then dock at its leisure. Larger craft do the same thing, only they step directly into the path of an oncoming docking port, which is positioned along the side of a tower. The tower is only ~20m off from the axis, so it only travels at about ~1 m/s.

Side note: I discovered a bug in the game while trying to dock with the ship. For some reason docking does not work on a ship of this size. I suspect this is a floating point precision issue having to do with the size of the ship. In any case, I carry on by fueling up with a save hack.

Pic unrelated, I just thought it was neat how big the ship's RCS nozzles were.

The fleet of four ships launches from the Kerbol system to Nova Kirbani:

Spoiler

In high orbit above Kerbin, the fleet assembles. Four starships were built in total. Each starship houses 80 residents during normal use, and allows for up to 160 residents in an emergency. Total fleet population is 320. Up to two starships can fail while still allowing passengers to flee to the remaining ships, and even if the residents of a single ship are lost, the fleet population can continue with enough genetic diversity to last for 200 years, during which future emigrations are planned. Genetic stores aboard the starships can further extend population lifespan but must be used in the first 50 years of the mission to be viable.

The ships are well over a kilometer long, and RCS propellant must be conserved for the upcoming mission, so flying them in close formation is no small matter. At any point I was only able to get two of them within the 2km render distance.

https://i.imgur.com/2YHBf1w.mp4

At last, the day arrives: it is launch day.

The trip begins just like any other routine transfer burn, with a nominal 1m/s acceleration (shown here is a timelapse over several days). However this time, the burn keeps going. Minutes turn to hours, hours turn to days, yet the acceleration does not stop.

In real life, the ship's habitat booms might have joints built in them to allow the habitats to swing into the G-force. This would prevent any risky situations where contents in the habitats slide around in the lateral acceleration. Since I'm only using KSP 1.5, I don't have the option to represent joints with the Breaking Ground DLC, but I will assume they're there for narrative purposes.

https://i.imgur.com/LU9tt1h.mp4

Several months into the voyage, the starships are now far enough from the sun to deploy their main radiators.

https://i.imgur.com/fqxfUJq.mp4

1 year into the mission: tank separation. The kerbals look on as the massive tanks float by, each one as large as their habitats.

https://i.imgur.com/fqxfUJq.mp4

2 years into the mission: the ships enter cruise mode. The starship turns retrograde, the first stage separates, and the radiators align to serve as blast shields for the habitats.

Previous interstellar missions did not use radiators as blast shields, opting instead for dedicated blast shields at the fore of the ship. However this couldn't be done for this craft, since the fore of the ship was already occupied by the aerobrake.

Nevertheless, it would be essential to provide shielding to the habitats since an impact there could result in loss of life. But the habitats are a large and constantly rotating protrusion. The blast shield would need to be a radius equal to theirs, and this would be a considerable amount of mass.

However the blast shield need not be thick enough to block everything it comes into contact with. Whatever strikes the blast shield will likely be obliterated from relativistic impact, so your only concern then becomes secondary debris strike. If you move the blast shield several kilometers out in front of the ship, the dispersion renders secondary debris strike negligible.

So blast shields can be wafer thin, just like radiators, and it just so happens the radiators were already about the same size needed to protect the habitats. Why not use radiators then?

You can further save on shielding mass if the blast shield rotates in lockstep with the habitats, but this requires the blast shield to have good balance. Since I'm re-purposing the radiators as the blast shield, this means the first stage also needs good balance. The radiators should offer protection perpendicular to one of the principle axes of the first stage, and the axis of protection should run along the center of mass. I usually align radiators to run parallel to the thrust axis, but the center of mass changes along the thrust axis of the first stage depending on things like RCS propellant, violating the second condition.

I could solve the problem using a ballast tank to store unused RCS propellant, but this would require constantly adjusting ballast throughout flight. To avoid over engineering the problem, I simply rotated the radiators by 90 degrees. The radiators are still the biggest thing on the first stage so the principle axis it rotates along shouldn't change. The radiators in this configuration would likely be in poor alignment with the sun most of the time, but this is okay since the vast majority of operation is spent in interstellar space where heat from the sun is negligible. The ship engines merely run on reduced power when in the inner system, then when the ship reaches the outer system the main radiators deploy, allowing long duration burns at higher thrust.

To avoid the risk of secondary debris strike, the first stage has its own guidance and RCS systems that allow it to travel several kilometers ahead of the vehicle and keep aligned. The same systems will be used to keep lock step with the habitats, providing continuous protection from relativistic impact with interstellar dust.

https://i.imgur.com/x04GYA2.mp4

And now, we wait. 40 years pass as the fleet is in transit. I periodically pause to switch between ships to keep populations at the right size.

Two generations are born while the ship is in transit. Four generations exist on board the ships, in total. Each has their own perspectives of the mission based upon their upbringing and the circumstances that brought them here.

The oldest generation are responsible for funding the mission through their purchase of real estate aboard the ship. The generation that purchases the real estate would be fabulously wealthy: eccentric noveau riche with little taste for luxury. They are fanatics who believe in the ideals of the mission so strongly that they are willing to spend their money and lives on it. As such, we will call them "the financiers". It is their goal to live long enough to see their arrival at the new star systems.

It's likely that anyone who's had enough time to gather such a fortune would already be past the typical age to have children. I'm sure in the spirit of the free market the property would be available for purchase to anyone willing to pay for it, regardless whether they have children, but it would be antithetical to the project if all but a few families die off before reaching the destination, and the residents know it. Buying an estate here only makes sense when someone is around to inherit it. Someone among their next of kin should be willing enough to travel with them and inherit the estate. Obviously, this goes a little easier when the person doing so is making the choice for themselves. It makes the most sense for this younger generation to be in their twenties or thirties, old enough to make decisions for themselves but young enough to have children that will never miss Kerbin, maybe a few entrepreneurially minded sorts that take after their parents and have it in mind to inherit the family business of sorts. We'll call this generation "the protégés".

For those too young to decide for themselves whether to take the trip, either those born after embarkment or those who were too young to decide, they will have a much different narrative to tell. Let's call them the "shipborn". Some of their story mirrors those of the U.S. immigrants of the 1800s, children sent overseas with their parents with little prospect of return and little say in the matter, and children born after the emigration who have no memory of the old country. So there is some precedence that the people of this generation could adapt and still live well adjusted lives. For the bulk of their adult lives, life would be much like that in an isolated rural community. All this generation ever knows is a small town of 80 people, and a few scarcely visited settlements on other ships in the fleet. The petabytes of Kerbin records aboard the ship are all available to them though, and one day they'll get to see things like mountains and oceans, just not right now.

Among the shipborn, some are comfortable enough to stay where they are and foster a sense of community. The vast majority might be satisfied enough just to move to a new ship where they can get away from their relatives and establish their own identity. Lifeboats are available if a large enough fraction of them want to return to Kerbol, and even if only a few want to leave, it is within the capabilities of Kerbol to send out sleeper ships for a return. However, precision issues at these distances prohibit the game from simulating docking while in interstellar space, so we forgo demonstrating the capability.

The generation that comes after the shipborn have few ties to the old star system. This generation better identifies as residents of the new star system, and so we will call them "the Kirbani". To this generation, taking a ship back to Kerbin would make as much sense as an average American uprooting to live in Europe with some distant cousins from his great grand dad's line. The records of Kerbol are fun to pour over, but more for their retro charm than for any sense of nostalgia or longing.

Deceleration and arrival at Nova Kirbani:

Spoiler

https://i.imgur.com/Me7jnje.mp4

The ship council settles on a date for deceleration years in advance. Weeks ahead, the council outreach gives advice on what to expect in a newsletter. Most of the people who still remember the acceleration from the start of the mission are in their 60s now, so this will be new to the rest of the passengers. Even the old timers haven't seen the aerobrakes in action, though.

The event proceeds much like the viewing of an eclipse. People gather. Some watch from their roofs or the rims of the dome. A familiar voice calls out mission milestones over the loudspeaker. It's the council outreach speaking. Next callout is for unfurling, now at T-10. The crowd fills the rest of the countdown. 5, 4, 3, 2, 1...

And the aerobrake unfurls, filling a large fraction of their field of view.

Next callout is activation. An aurora slowly emerges, starting from the center of the aerobrake. Ions strike the magnetic field at relativistic speed. Oohs and aahs.

The power to the aerobrakes is turned on slowly, over many days, so that the habitats don't experience any sudden shifts in gravity. The auroras eventually grow to encompass half of the viewing field, but the centrifuges slowly spiral noseward so gravity continues running tangent to the floor of the habitat. People notice their view from the dome is changing to face the engines.

https://i.imgur.com/7FR8VsD.mp4

After a while, deceleration slows. The aurora dies down, and the centrifuges return to their usual position. The craft has reached the end to what its aerobrakes can meaningfully accomplish, and the engines must now shed the remaining velocity. The aerobrake is jettisoned (a countdown party of its own), carrying with it a heavy power plant and its radiators. The remaining upper stage has a much smaller fusion reactor, and should an emergency call for it, a laser from the aerobrake assembly can beam power to a receiver aboard the remaining upper stage.

https://i.imgur.com/un9JF2V.mp4

Four ships must perform their deceleration maneuvers at roughly the same time. I break the maneuver into stages so I can switch between vessels and make sure that none overshoot their destinations.

The "Toolik" is the first to deploy her aerobrakes. She spent a concerning amount of fuel in her course corrections, but its ship council has plenty of time to recognize the issue. They compensate by deploying her aerobrake extra early. The Toolik cuts loose from its aerobrake assembly while traveling at only 2.5%c.

The Toolik decelerates into the Proxima Kerbani system with little incident. There, they set orbit around the planet of "Narath", a habitable "eyeball" world where tidal locking causes one side to always face the sun.

Many residents have spent their entire lives without seeing anything but stars outside their ship. To the star-weary travelers, the planets are like titanic visitors in the sky, portending to something momentous.

https://i.imgur.com/L1LWzkZ.mp4

The "Amana" arrives next. She is the oldest ship in the fleet, first of the "Amana" class starships - the most overbuilt, but also least refined. She completes her journey safely, but not without incident. She runs out of liquid helium shortly before entering her target star system. This liquid helium was used as propellant for her reaction control systems. The ship council nevertheless steers the ship into a stable orbit, using the gimbaled thrust of its engines to orient the ship at a glacial pace. This causes her to eventually exhaust the propellant in her main tanks, but fortunately by this point she is already safely in orbit around the star. A negligible amount of propellant is transferred from her life boats shortly before completing her journey.

She flies by the moon of "Alar" before settling in orbit around "Blalo", a habitable planet orbiting The analogue of Alpha Centauri B.

The "Wikieup" fares best among the ships in the fleet. She arrives at her target star system with a healthy supply of propellant and RCS fuel. Plans are drafted for her to set orbit around "Ilve", a habitable super-Kerbin with an anoxic atmosphere.

That just leaves the "Ahmeek", though. Things don't go so well for her.

Problems emerge as the craft tries to decelerate. The onboard fusion reactor is not able to supply the nominal 2 terawatts to the aerobrake. The reason behind this design flaw is never fully understood, but I think a change was made specific to this ship.

As a result of the design flaw, the aerobrakes can only run at half power. Normally, this would not be a serious issue. The situation could be resolved simply by deploying the aerobrakes extra early. However, by the time the design flaw is discovered, it is already too late to deploy them early. No procedure was put into place to test the aerobrakes before its deceleration, since the effects of a design change like this were never considered.

The ship still has options though. The aerobrake slows the craft at a rate that's proportionate to the square of its velocity, so it becomes much less effective at low velocity. However the engines can decelerate at any speed up to a certain limit, and each ship comes equipped with a a little extra fuel for such occasions. So the ship council need only offset the time spent on the aerobrakes for time spent on the engines. The council decide they will run the aerobrake for as long as needed until the ship can kill its remaining speed with the current remaining fuel reserves.

This string of events plays out over the course of several years, which is just enough time for the ship council to enter a dangerous state of complacency. Handling unforeseen circumstances such as this is a regular part of council membership at this stage in the mission. The ship has seen continuous habitation for over 40 years, during which many components have reached the end of their service lives and have needed replacement, while other components have experienced unforeseen wear due to regular interaction with the residents. Inexperience also starts to play a role at this point in the mission. Many of the original council members from the start of the mission have since retired or passed on, leaving a second generation of less experienced council members to take their place. The news about the aerobrakes comes off as no cause for concern. The ship council carries on making decisions. The ship A.I. is largely out of the situation, and the residents are either ill-informed or ill-attentive.

Banking on the surplus fuel for deceleration turns out to be the last mistake the council makes. The fuel reserves are either overestimated, or the ship council fails to account for losses due to course correction, but in either case, the miscalculation soon becomes apparent. The ship will run out of fuel before it fully decelerates.

What was once thought to be a recoverable error now turns out to be much more serious. The residents cannot simply transfer to another ship, since those ships are also in the process of decelerating. Having them match speed with the Ahmeek would place their own residents in danger, since they would themselves likely run out of fuel. The only remaining course of action is to abandon ship.

There are 66 souls aboard the Ahmeek at this point. There are lifeboats available that seat up to 80. The Ahmeek is fortunate that its home owner's association was able to limit the size of its population in recent years. Many of the first generation Ahmeek residents have passed on from old age in recent years, and birth rates have temporarily slowed thanks to a political climate that has favored stiff taxes placed on large households and a vocal PR campaign.

The council outreach makes the difficult but dutiful announcement to the residents. By year's end, the residents will have to leave their homes and belongings, and board the lifeboats.

Despite the circumstances, the situation aboard the Ahmeek is fairly civil. There are lifeboats for all, plenty of time to prepare, and a clear call to action. Nevertheless, a tense political battle emerges between the board of directors and ship council. The former tries to wrest control of the ship from the latter, seeing the council as inept. The latter fights the attempt, seeing it as irresponsible. The fight amounts to little. While the council is locked in battle with the board, the ship A.I. carries on its duties, managing the ship. Regardless of who wins, everyone agrees the ship must be abandoned.

After a year of deceleration, the engines exhaust their propellant. The craft now travels at 1%c.

https://i.imgur.com/S8fYkU4.mp4

As with all "Amana"-class starships, the "Ahmeek" comes equipped with two lifeboats. Each lifeboat carries up to 40 passengers. The lifeboats are, in effect, miniature versions of the Ahmeek. If pressed, they could make the entire journey back to Kerbin on their own, the only downside being the decades of time spent in hibernation. These lifeboats however need not make the journey back. They're already inside their target star system, traveling at a leisurely 1%c. They need only spend a small amount of fuel to decelerate.

https://i.imgur.com/ozvwvNV.mp4

Each lifeboat comes equipped with its own aerobrakes, its own nuclear pulse engine, and its own propellant supply. Power to the aerobrake and engine is supplied by a 10GW thermovoltaic receiver, which receives beamed power either from beamed power stations around the target star or from the other ships in fleet. As of right now, the lifeboats are close enough to the target star system that they can rely solely on the beamed power stations.

Each lifeboat uses the same H2/He3 propellant that's used by the Ahmeek. A single lifeboat has a delta-V of 10%c. The propellant on board the life boats is no where near enough to decelerate the entire Ahmeek, but it is way more than enough to decelerate the lifeboats safely into the target star system.

The Ahmeek is abandoned. In 54 years, it will pass out of the star system. Its environmental control systems were left fully operational, the evacuating residents paying little attention to the matter. The ship A.I. is now left alone, and with no one aboard to override its decisions, it takes up control over the habitats in addition to all the usual ship maintenance. In a way, it retires and takes up gardening.

For a time, the plants and insects aboard the ship carry out their lives as usual, now undisturbed by the residents. The residents planned for the ship to be habitable for many decades upon reaching its target star, so there is still plenty of surplus air and water for all of them. Just as long as there is power.

The ship no longer has enough fuel to power its reactors. Virtually all of its fuel was spent during deceleration. It was expected the ship could rely on a modest supply of beamed power for its remaining mission, but that beamed power is soon also cut. The lifeboats need it much more.

There is still charge left in its supercapacitors. There is in fact a lot of charge in the supercapacitors, since they were overbuilt as an added safety feature. However, in time, this too will fail. The ship A.I. will have to increasingly cut power to nonessentials, until at last only two essentials remain. The first essential is the ship's environmental control systems, allowing primitive plant and insect life to continue in the habitats. The second essential is the ship's own consciousness, its A.I.

It sacrifices the latter.

The ship still functions off a redundant drone core. It draw much less power than the A.I., but its functions are now limited to only the most formulaic tasks. This is not enough to keep up with the unforeseen maintenance of the habitats.

The habitats soon grow feral. They are starting to present multiple points of failure. Ivy covers the inner domes, trying to gain purchase over trusses and gaskets, perhaps breaking through to colonize the space between walls. Plants produce an unforeseen surplus of oxygen, causing structures to corrode at a faster rate, and presenting the risk of fire. Insects chew through wires. It is now a race to see if the life within the habitat snuffs itself out before the power goes out.

Beyond this point the number of possibilities escapes our grasp, but we learn from studying entropy that the number of equiprobable possibilities that lead to an outcome dictates the outcome's probability. In this case, there are many possibilities, all presumed equiprobable, but virtually all lead to the same outcome:

The temperature inside the ship settles to the same temperature as cosmic background, 3 degrees above absolute zero.

https://i.imgur.com/028pUXP.mp4

While unfortunate, the loss of a vehicle need not result in the loss of its passengers. One of the remaining ships, the Wikieup, redirects to Taythe in response to the disaster. This is done both to ease the burden on the lifeboats as well as to ensure the colonization of a higher priority destination.

In a year's time, the lifeboats intercept the Wikieup. No casualties are reported.

https://i.imgur.com/Y3l8XCY.mp4

Lifeboats are built for high reliability: essential components are made redundant, and nonessential components are removed to reduce the risks of complexity. Docking ports exist on the lifeboat, but none are capable of docking with the specialized interface at the hub of the starship. Furthermore, both the starship and the lifeboats lack all but nuclear pulse engines for propulsion, so they can only match speed with each other if they are at a safe distance, lest they irradiate the residents. Finally, the majority of the residents would be young, inexperienced, or infirm.

For all these reasons, shuttle craft would have to be sent out from the Wikieup to intercept the lifeboat while miles distant. However, the docking bug I noted at the start of the mission precludes redocking shuttles with the starship, so my in-game solution is simply to EVA each resident individually. It's tedious work, but it makes for a much more cinematic experience.

The crisis is resolved, now. All residents of the four ships have safely inserted into the target star system. The Kerbals look forward, pragmatic. The home owner associations lift measures to restrict populations. Over the next few decades, the populations within the star system will nearly double. In the workshops of the starships (shown here), crew members build implements of colonization.

https://i.imgur.com/LADWeLB.mp4

Those implements: Von Neumann Probes. Each starship sends out its own probe to the surface of its respective planet.

https://i.imgur.com/mTr8EBU.mp4

The Von Neumann probes each build bases to prepare for the coming of the Kerbals. The Blalo base shown here includes housing for up to 60 civilians, a satellite dish designed for hook up with the local interstellar relay, and a launchpad prepped with a primitive chemical rocket, allowing the first party of explorers to return to the Starship. The base can be expanded indefinitely, as need arises.

https://i.imgur.com/bpekm3r.mp4

The migration to the surface will start gradually, building up over many years, and will be carried out at the leisure of the residents. Some residents, namely the older generation, may choose never to leave the starship, whereas younger generations may want to explore the planets at first opportunity. Transport will gradually become regular, to the point where residents can travel to and from the surface as they please, but for now, they settle with sending a small party of three to explore the surface.

A space capsule is tailor made for the planet. It is constructed in the automated workshops aboard the starship, then fueled with propellant made fresh from stocks of ore.

The space capsule is a primitive design that's almost as old as space flight itself. However, it is perfect for frontier life amongst the stars: simple, reliable, easy to build, and serviceable in the absence of infrastructure. It features oversized landing gear and engines to account for the slightly higher gravity of the planet.

Wet Mass: 10T
Payload: 3 passengers
Thrust: 200kN (1 atm)
Fuel Range: ~1.5km/s

https://i.imgur.com/QYyfTnw.mp4

Members of the third generation were recruited to conduct the expedition. There was little formality to the selection, just what the council could decide on. With little fanfare, a young couple from Amana become the first two astronauts to ever set foot on a habitable extrasolar planet. They venture outside their capsule to look out upon the strange sky.

We would love to say more on what happens to the Kerbals: the civilizations that flourish on these worlds, and their conquest of the stars beyond, but our story ends here. Beyond this point, we soon run against the limits to what the game can represent.

Migrations to other star systems will likely be expedited now that precedence is set, but it will still take many generations for the interest to be generated to do so. Nova Kirbani will provide ample opportunities for exploration for a very long time.

When the time finally does come to explore other star systems, the transit time will likely match that of this mission. We do not presume the Kerbals ever discover technology to allow convenient travel between stars, but it matters little. Barring the discovery of unforeseen technology, the Kerbals are now spread so far across so many different stars and planets that their survival is now more favorable than ever before. Progress will be slow, but inevitable.

Though there is no sign that the Von Neumann probes will ever go away, there is no reason to believe that coexistence with them is not possible for hundreds of millennia to come. The planets on which the Kerbals reside are too large for the machines to practically mine. The machines are much more successful colonizing the stars breadth-first, disregarding terrestrial planets to focus on the moons and gas giants from which they derive fuel and metal. At the current rates of travel within our game, it will take at least a hundred thousand years before they are even capable of traversing the full length of the galaxy, saying nothing of when they will reach saturation. The galaxy is vast, and can provide for us all.

It is likely the Kerbals will never catch up to the accomplishments of the machines, but again, it matters little. The continued prosperity of biological life is all the Kerbals could ever want. There is the comfort of simple living, and the challenge of a boundless frontier. On many habitable worlds, the Kerbals can live as they always have. Some populations may advance. Some may retreat to agrarian life, or to hunter-gathering. Some may undergo countless cycles of decay and renewal before returning to the stars all over again. Some will evolve and diverge into forms beyond our wildest imagination. And together, they will be as numerous as the stars.

It is the distant future, one millennium after the founding of the space program.

The Kerbals have reached the stars.

The End

Edited April 18, 2021 by Pipcard

theJesuit · April 19, 2021

Fantastic... and is inspiring me to do something similar with the Simplex mods. I love the self replicating concept and the long term vision.

Peace.

KSP 2 before KSP 2: 16807 (on Reddit) made a working interstellar non-FTL von Neumann probe in KSP [2021 update: generation ship]

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