SaturnianBlue

Chapter 4: Fusion Propulsion Now we come to fusion propulsion—a truly powerful form of travel. Magneto Inertial Fusion \ I have a feeling the ships get longer every chapter... How It Works Rings of Lithium are injected into the chamber, then crushed with powerful electromagnets around fusion fuel, which ignites and shoots out of a magnetic nozzle at high speed. These pulses occur every few seconds. Why Use It? Compared to many of the designs that will be covered in this chapter, this propulsion system does not need massive amounts of radiators, thanks to the fact that the exhaust carries the waste heat away. Why Not? For a fusion drive, this design has a rather low exhaust velocity, therefore having an Isp of 4452 seconds. Additionally, it provides fairly little thrust for its weight. In Testing This vessel comes in at around 1000 tons fully loaded with a 300 tons of cargo and about 450 tons of Lithium propellant. The version of the magneto inertial fusion drive is upscaled to around 100 tons, and produces only about 950 kilonewtons of thrust. The vessel had to burn for about 3 hours for a burn of around 12 km/s. It took 209 days to reach Jool, and after another long thrusting, I managed to reach orbit with a rather thin fuel margin. I decided to wait 9 days before attempting to orbit Vall, which I succeeded, but only barely—not only did I nearly collide with Vall, I used up all the fuel to enter orbit. What Should It Be For? The Magneto Inertial Fusion engine would provide an alternative to the open cycle gas core engine, as the engine involves less radiation, are simpler, and probably harder to maintain. Additionally, they would be more likely to be used to travel between lithium-rich planetary systems, due to the fuel used. However, I do not believe they would be particularly dominant, as they don’t perform as well as other engines. When? The Magneto Inertial Fusion engine can be built rather easily with current technology, though that design is low thrust. That said, higher thrust levels can be achieved with relatively little steps for technology. Out of the fusion designs covered, this is the most feasible, having the least problems that need to be solved—with the engines available in-game, this would likely be the first. Use In a Story While I haven’t found much on how these can cause a convenient engine failure for a story, I think that the Lithium rings could misfire and be smashed by the magnets without the fusion fuel, and possibly damage the engine with the debris. A demand for more lithium might arise from the creation of such an engine, encouraging new mining operations, Tokamak Fusion Rocket How It Works A Tokamak uses magnetic fields to confine a plasma in a torus, and the basis for many fusion reactor designs. This rocket uses that for propulsion by heating up hydrogen as well as the fusion products and directing it out of the spacecraft with a magnetic nozzle. However, it is more efficient to simply use the fusion products, though this comes with less thrust. The Stellerator is a rather similar type of reactor, and performs similarly. Why Use It? With the plasma nozzle part, the Tokamak rocket achieves an impressive specific impulse of 7513 seconds—on par with the MPD using something like Helium. However, with the magnetic nozzle part, a far higher specific impulse of around one million seconds can be achieved, though with less thrust without the “afterburner” that the additional reaction mass provides. Why Not? The engine has rather low thrust; despite a 90 ton reactor, my test ship would only manage around 800 kilonewtons of thrust. This is still far more than the electric propulsion ships, and the ship can still burn on short time scales. Though of course not modelled in-game, the engine would be rather radioactive, especially with Deuterium-Tritium fusion, where many lethal neutrons are released. In Testing I based this new ship partially off of the Discovery II, a NASA concept of the Discovery from 2001: A Space Odyssey that would actually work, using a Tokamak just like this one! With the plasma nozzle, the ship accelerated at only 0.86 m/s even with a giant reactor, so I installed the Better Time Warp mod to make the Kerbin departure burn happen quickly. For the 17,000 m/s burn that took several hours to complete, this was very helpful. After 160 days, the thousand ton ship arrived at Jool, and began the process of slowing down. I didn’t reach Vall as I approached, but I was able to do so on the next orbit, and the Tokamak did provide enough thrust to make the course corrections bearable. After a quick Tylo flyby, the ship arrived at Vall with a large 900 M/s burn with over 2,000 m/s left in the tanks. With a magnetic nozzle design not unlike the Discovery II, the thrust was about half of the plasma nozzle, but the magnetic nozzle allows time warp during acceleration, so it was rather bearable. After leaving Kerbin, I burned with the lower thrust modes with Isp around 500,000, and just before crossing Dres, I flip and start burning the other way. This proved to be quite early with the higher thrust, yet I still arrived at Jool just 95 days in the mission and entered Vall immediately. Provided I took a riskier route, I think the Tokamak can reach Jool in 70 days. "I'm sorry Dave, but I'm afraid I can't do that" When? The achievability of this design depends on whether nuclear fusion is feasible, among other things like making magnetic nozzles work. Though I tend to dislike putting a date on these, I think the general consensus is that a fusion rocket like this is “late 21st century-era” technology. Though the reactor can power electric drives during transit, the engine itself can replace them, since it can burn at low thrust for an extended period of time. What Should It Be For? These ships would replace most of the vessels that use one engine for high thrust, and another for higher exhaust velocity, since the Tokamak can do both at the same time. Provided more advanced engines are not introduced, they will likely dominate interplanetary travel. I don’t think they’d be very effective on in-system transit, considering the low delta-V requirements, which mostly negates their advantage, and they would be poorly built for landing or takeoff. Use In a Story With a fusion rocket, the time scales of travel are lessened a lot, so there’s probably a lot less “downtime” for the story as the kerbals do not need to spend many Muns traveling to the outer planets. With powerful magnetic fields inside the rocket, having several on a single ship would be a very dangerous idea, and the direction of very hot propellant could be disrupted, causing an explosion. VISTA (Vehicle of Interplanetary Space Transport Application) How It Works This powerful fusion engine works by shooting out pellets of deuterium and tritium surrounded by propellant, which are then zapped by an array of powerful lasers, compressing the pellet till nuclear fusion is initiated. The propellant is then directed by magnetic coils and accelerated to high speed. Why Use It? The VISTA provides thrust comparable to the above engines (not much), but in return has much higher specific impulse at the top thrust, 15678, while being much lighter. The thrust can be lowered to reach 27144, though this does reduce thrust. For reference, the actual concept design only puts out about 240 kilonewtons while being considerably heavier. Why Not? The VISTA fusion rocket happens to use Deuterium-Tritium fusion, which puts out a lot of waste neutron radiation and will kill nearby kerbals. In fact, the VISTA concept was cone shaped to reduce the radiation exposure. The bit depicted by the KSP part is actually far bigger in real life, at over 100 meters wide! Roughly something like this—a flying saucer of sorts. In Testing The VISTA cannot thrust during on-rails time warp, so again the Better Time Warp mod steps in. Without it, I probably wouldn’t have bothered, since the departure burn of 57 km/s took 4 days! With that, the ship skipped across the solar system and only 59 days later it arrived in Jool’s SOI, where I immediately began burning to slow down for a slightly shorter burn, thanks to the lowered mass. After 3 days of semi-continuous burning, the ship is captured by Jool. After a small correction burn and an orbit later, I arrive at Vall with a short burn in a mere 72 days with enough delta-V to make it back to Kerbin, though much slower. When? As @MatterBeam made aware of, pulsed fusion designs like these would be easier to develop, since the fusion only has to be sustained for very brief periods at a time, not continuously. Of course, the VISTA is very powerful compared to the Tokamak, so for balancing purposes, one might want to keep the thrust of these quite low in the beginning when they are initially invented. Use In a Story For an example, a warship is attempting to get away, so the thrust is increased by adding more propellant; this only prevents the fusion pellets from igniting, and they fail. Another scenario: the ship is in the middle of a big turn, and the lasers cannot adjust to this when the fuel pellets are shot through, causing them to miss, or fly off. "It's goin' as far as it can go, Captain!" What Should It Be For? It’s in the name of the vehicle—interplanetary space transport! Since it’s so expensive, I think it would be mainly put on routes to the outer planets (of various mods), where shorter travel time can always be used, and the colonization of said areas would be completed much quicker. However, their efficiency wouldn’t be good enough for interstellar applications. As the VISTA becomes more and more frequent, they should become cheaper and cheaper, and they may even see use in warships in its higher thrust mode, though a space admiral must pay close attention to not irradiate one of his own ships. However, their use as the primary high-speed ship may eventually be replaced by the following engines... TORCHSHIPS These are the Really, Really, Really powerful engines—able to accelerate at a considerable fraction of one G, while being extremely efficient. Some of these engines can point right at the target, flip, then slow down, practically traveling in a straight line in a brachistochrone trajectory. Project Daedalus Fusion Engine How It Works The Daedalus fusion engine is the one of the most efficient engines available in KSP-Interstellar Extended. A form of nuclear pulse propulsion, the engine uses tiny pellets of deuterium and helium-3 that are bombarded with electron beams and effectively explode like small nuclear bombs. The plasma that results from this is directed by a magnetic nozzle. Why Use It? Finally, a ship is capable of constant thrust throughout the journey! Not only does this allow the ship to achieve incredible speeds, the ship can provide gravity purely by the force of its engine, with no need for huge centrifuges. The Daedalus fusion engine has a specific impulse of one million, while providing hundreds of kilonewtons of thrust! The engine acts as a powerful transmitter, so those very far away can communicate. Why Not? The problem with the Daedalus fusion engine is its fuel—helium-3 and deuterium makes for a fusion reaction with less neutron radiation, but helium-3 is extremely rare. Even Moho or the Mun, which would likely have helium-3 might not have enough; mining at Jool or some other gas giant may be required, and leaving the atmospheres of gas giants is very difficult, and the methods of cheaper methods like launch loops may be initially too expensive. Additionally, the high specific impulse of the Daedalus might be just too high for interplanetary use—the engine just doesn’t have the time to use all its fuel at times! In Testing I chose to increase the cargo from 300 tons to 475, and the whole thing weighed just 658 tons wet, because only 41 tons of fuel pellets were needed for a delta-V of 631 km/s! The acceleration at departure was a fairly low 0.95 m/s. It still proved to be more than enough to leave Kerbin, and would be still provide some useful amount of gravity. As I expected, the ship was more than enough to conduct a constant thrust brachistochrone trajectory, attaining a speed of 250 km/s before flipping around and slowing down for an arrival at the Joolian system 30 days after departing from Kerbin! Now that I think about it, I probably should've just burned straight at Vall if I wanted to get there! The ship has so much delta-V it wouldn't make a difference! When? This is a highly advanced fusion drive, which probably won’t come along till after the VISTA. Even if it can be built, the use of helium-3 may discourage its development, and even then it doesn’t guarantee that they would be very common, unlike the VISTA. What Should It Be For? As helium-3 is rather rare without mining the gas giants or scraping massive quantities of it from fusion reactors, they would best be used sparingly, like on a starship, which was the purpose of the Project Daedalus concept by the British Interplanetary Society, that would allow a ship to fly past Barnard’s star in only 50 years. Later, I got the ship up to 0.06 C—I could go even faster, but for some reason the ship wouldn't want to! Even my replica is a little small compared to the real thing! The high Isp should allow a ship to reach several percent of light speed, making sure any star systems are in reach for colonization. Almost a thousand passengers onboard! Provided this kerbal future has access to plentiful helium-3, then now the doors to ultra-fast transport are opened. Needing to catch a business trip on Duna from Kerbin in a week? Fear no longer, the Space Concorde’s got you covered! Well, if it doesn’t become unprofitable... Use In a Story The methods of failure are probably quite similar to the VISTA—involving lasers and fuel pellets. For a potential scenario—perhaps the lasers are hijacked just before a starship begins slowing down to orbit a star with no help for light years! The Kerbstein Drive How It Works The fusion drive based off the ones seen in the book series and TV show The Expanse. Having read the first three books, they mention fuel pellets—implying a form of inertial confinement fusion like those covered above. The version of the drive in KSP-Interstellar seems to be based off the MCRN Tachi/Rocinanate’s stats. A quick little replica of the Tachi Rocinante! It can get up to 2 Gees, though the thrust tails off very quickly. Why Use It? The Kerbstein drive has half the efficiency of the Daedalus fusion engine, but also uses lithium hydride, which is almost certainly more abundant than helium-3, which makes it potentially cheaper and thus better suited for interplanetary travel. It is also somewhat lighter and smaller than the Daedalus, with higher thrust as well. Why Not? However, it takes significantly more power to run, and cannot be scaled below 5 meters in diameter. Additionally, it has a tendency to overheat when pushed at its highest thrust. In Testing The function that allows acceleration during timewarp only seems to allow a certain amount. Therefore, I upped the amount of the amount of cargo to 787 tons to make full use of the engine’s thrust. In the end, it still wasn’t enough, and I had to limit thrust. The ability to accelerate quickly puts this engine in the advantage over the Daedalus, and now the engine can actually make full use of a larger fuel reserve of 316 tons. It should come as no surprise that this engine shot to Jool in 14 days. With such short travel times, it soon becomes a waste to wait for gravity assists to get around Jool! What Should It Be For? If the Kerbstein drive really is as apparently cheap as the Epstein drive seems to be in The Expanse, with every large ship using it, then this would open up interplanetary travel to most people! Even if it is expensive, they would finally give a solution for a high thrust, high efficiency drive, making warships equipped with these drives both powerful in combat and very quick to respond. When? I’m not sure if the Daedalus or Kerbstein would be created first, but the proton-Lithium fusion of a Kerbstein drive would be harder to achieve, so that may make it come later. In any case, this is a very powerful engine that would take a long time to arise. The Orion Drive “old Boom-Boom” How It Works Considering the radiation blasted out by the open-cycle gas core and many of the fusion drives, perhaps it’s no surprise that this powerful engine is also quite dangerous… Because it’s propelled by nuclear bombs… The spacecraft is mounted on a thick pusher plate and small shaped nuclear bombs are shot through the center of the plate and detonated to push the ship forward. An occupied ship would be equipped with shock absorbers to suppress the jolt of the ship. Though fission or fusion bombs can be used, I figured that it would fit here with many other… Extreme designs, so to speak. Two updated mods provide Orion drives— the TD edition and the USI one. Why Use It? Was it really worth it? The Orion drive provides massive amounts of thrust, and can easily accelerate at over one G, even reaching levels that are dangerous to any crew on board taking off from planets with lots of gravity… Sure, they are nuclear bombs, but small ones, so the damage will be fairly limited. Why Not? The Orion drive isn’t as efficient as many of the other designs, though it’s rather hard to find solid numbers. Additionally, the ride would be rather uncomfortable, even with shock absorbers, with nuclear bombs releasing their energy in a very brief amount of time. What Should It Be For? Uchuu Senkan Orion! Seriously, an actual design had an Orion drive powered ship strapped with naval guns, nuclear missiles, point defense guns, and Casaba Howitzers that would direct the energy of a nuke into a tiny angle! These would likely be the first torchships, and would probably be the powerhouse of the first starships as well. Thanks to the high acceleration, they would be good launchers, but poor atmospheric landers, since the vehicle would fly into it’s own nuclear fireball… The acceleration would be welcomed on a naval capital ship that needs to accelerate quickly to dodge enemies. When? The Orion drive can be built with current technology, though the incentive to build such an engine is rather low at the moment. However, as space becomes more developed, a high payload capacity vessel may be welcome. In Testing For the tests, I used the TD edition Orion drive with the 15 kiloton nukes! The ship carried a payload of 475 tons, and it accelerated at 85 Gs! The game lagged a lot, and without an accurate delta-V reading, I had to guess how much I had. Thanks to the killer (literally…) acceleration, I reached upwards of 150 km/s in just an hour! Even though this isn’t as high as the other engines, because the burn was so short, it spent less time at low speed. The vessel arrived at Jool in 22 days, and I almost got into orbit, but was short by about 20 km/s. However, arrival at Jool in 25 days is perfectly possible, and travel to Eve at its closest might be as short as 5! Use In a Story Since the Orion drive can be built with today (and yesterday’s) technology, it opens a storytelling opportunity where the Orion drive was actually built and used to colonize space. The pulse units can detonate too close and vaporize much of the pusher plate, or veer off to the side and create an asymmetrical force that flips the ship. If a malicious faction gets their hands on an Orion drive-propelled vessel, whether it crashes, is hijacked, or something else, they have plenty of opportunity to cause great destruction if they can repurpose the pulse units… Summary Fusion engines do not come around until later, but when they do, such designs are extremely powerful, and excel at providing both high thrust and high efficiency. Thanks for Reading! Next: "Other" propulsion methods and the Colonizing Dres chapter!

War spacecraft would probably be pretty pointy to deflect enemy shells and increase the effective armor thickness. I don't know if it would work for particularly high velocity weapons, but maybe for conventional guns strapped on drones they would definitely work.I'd imagine most of the armament would be forward-mounted to increase protection and firepower at once. Missiles would also be pointed shaped so that oncoming fire would get deflected.

Very nice! As for the slow performance of your computer, it might have to do with the part count of the submarine or maybe the graphics mods you're using—I encountered this issue a lot when I made my naval ships, since they came it at around 800-1100 parts.

Today I finished the Magneto Inertial Fusion and VISTA engines!

Remember the Cant! I drew the Canterbury from The Expanse with pencil and pen/marker. The pencil went pretty well as usual, but I think the pens took away some of the detail that the drawing had. That said, I haven't used the pens in a while.

My Tokamak rocket design arriving at Jool and its many Muns after just 160 days of travel.

Version: KSP OSX 1.3 (Uncertain if 32bit or 64 bit) Mod List: Like some other reports, KSP is about at the end of the loading, when it crashes. A few mods seem to cause this, and a few examples seem to include BDArmory (but not Baha Turret), SM Armory (with SM Industries), and Modular Kolonization System (MKS). The above are the mods that DO seem to work, though adding any of the ones I just listed makes the game crash. I assume it isn't related to memory, because if I remove a big folder like the BoulderCo from Andromeda: Daydream and add BDA, it still crashes. Link to the Player.log

@Kosmonaut I suppose it's only fair that it's the first ship in the Atomic Rockets page for realistic designs!

The habitats don't need to be shielded that much, but even those ships require shadow shields to protect themselves.

Discovery One near Jupiter from 2001: A Space Odyssey. Io was surprisingly good, considering I'm not very used to drawing planets and moons. My attempt at drawing a realistic space battle. Admittedly the two ships are way closer than they'd usually be in combat, but it's nice to draw an actual target. The stream of bullets are from the conventional machine gun, while the guns in the rear are high-velocity railguns. The orange for the top bit of the ship is supposed to symbolize laser damage, since you can't actually see a laser in space. Also, the ship has radiators!

Here's the chapter on nuclear propulsion! As with last time, you can also check it out of the chapter III post, though I'll leave the old version there. Chapter 3: Nuclear Propulsion This next chapter will focus on the methods of propulsion that involve nuclear fission. Solid Core Nuclear Thermal Rockets How It Works The concept behind the NTR is rather simple—a nuclear reactor heats a propellant to high temperatures and ejects it through a nozzle, where it expands and creates thrust. This design is relatively simple and was tested in the 1950’s to the 70’s. The LV-N part in the stock game is based off this type of engine. Why Use It? In stark contrast to the electric engines covered earlier, the solid core NTRs provide considerable thrust, providing hundreds of kilonewtons of thrust. The nuclear reactors that power the engine are also capable of powering the ship as well. NTRs can be configured to use different propellants, so their choice of fuel could be adapted for the destination or route. This includes the ability to inject oxygen with hydrogen to create an “afterburner” mode that increases the thrust at the cost of efficiency. Why Not? Especially when compared to the electric engines, the nuclear thermal rocket is rather inefficient, though this is considerably better than chemical thrusters. Running the nuclear reactor core at higher temperatures generally makes for better efficiency, but this means that the core can melt, and subjects the engine to major stresses. Additionally, any crew on-board will have to deal with the radiation from the engines, though this can be solved by an adequate shielding. When? As mentioned in the beginning, the solid core NTRs have existed for a long time, and are well tested. For a story set in Kerbanity’s first steps of colonizing the Kerbol system, these engines would be an important part of the story. However, they would eventually be phased out in favor of the next rockets in this chapter, and thus the NTRs would probably be a rare sight by the time space colonization really picks up. In Testing In KSP-Interstellar, there are several options for solid core nuclear rockets, so in this section I’ve decided to do major full-scale tests for one engine, and compare the others to it. That engine would be the Solid Core Nuclear Engine part. Like the rest of the craft, the target is Jool. Due to this ship’s lower delta-V, I considered waiting for the transfer window, but decided against it, since the circumstances of the launch would be different, and I wanted to have them be the same for a fairer comparison. This also meant that the low delta-V NTR was forced to pretty much do a Hohmann transfer orbit to reach Jool, which took a year and 40 days. However, it was able to successfully enter Vall’s orbit with fuel to spare, which clearly shows the benefit of high amounts of thrust. ALL THESE WORLDS ARE YOURS - EXCEPT VALL.ATTEMPT NO LANDINGS THERE. Additionally, the ship was equipped with two escape pods that can carry four each. These use the CANDLE Travelling Wave Reactor engine. While the reactor is a detailed concept, I simply don’t know enough about it’s use as an engine to really write much about it. That said, in-game it is a handy engine for small craft like the escape pod, which could travel from Vall to Pol with fuel to return. What Should It Be For? In general, situations where chemical rockets aren’t efficient enough, and electric propulsion creates too little thrust. They would be particularly useful in planetary systems like Jool, where the delta-V demands are high, but require quick burns to transfer between moons and orbits. The solid core nuclear thermal rocket would be very useful for departure burns from Kerbin, whether as a space tug, or as the central propulsion source. The on-board reactor could also be utilized to power an electric drive like an MPD during the cruise section of the flight to cut flight time, which is particularly useful since the efficiency of the NTR is fairly low. When it approaches the destination, the spaceship can slow down using the NTR and prevent many incidents where an MPD-only ship shoots off into deep space because it couldn’t slow fast enough. An early form of a space warship would probably use these rockets—the high acceleration would be required to dodge incoming missiles. However, the engine’s take a while to throttle up, which would make them somewhat ineffective. Variants First, there is the pebble bed reactor design, where the pebble bed reactor is its own part, and a nozzle can be attached to use it as a rocket, which provides decent thrust and slightly higher Isp. Takes a while to throttle up, but when it does, it produces a LOT of thrust Another NTR is the Project Timberwind particle bed engine, based on the real life design funded by the Strategic Defense Initiative (yes, “Star Wars”). This engine provides far more thrust than the basic Solid Core design, with an exceptional thrust to weight ratio. Placing just one of these engines yielded far better acceleration. Lastly, the molten salt reactor can also be used in the same way as the pebble bed, though it’s Isp is slightly lower. However, the reactor has long uranium reserves and can create tritium fusion fuel. Use In a Story Colonists may choose to land at a hotspot for radioactive materials to fuel their NTRs, and set up refineries to get propellant too. The engines would probably need to be repaired after each mission, since they face both cryogenic temperatures of the fuel and extremely hot cores. While the failure modes aren’t necessarily explosive, they can eventually render an engine totally useless. Open Cycle Gas Core Nuclear Thermal Rocket (OCGCNTR) How It Works The open cycle gas core nuclear rocket is a rather kerbal concept—instead of having the core melting be a problem, it becomes an advantage because higher temperatures can be reached. Gaseous uranium is injected into the chamber, and then liquid hydrogen, which is directly heated by the uranium and shot out of the chamber. Why Use It? The OCGC engine has an excellent efficiency of 5000 seconds, which is 5 times better than the solid core NTR, though the thrust of the gas core engine is lower. The reactor can also be used for power generation. Why Not? The trouble with this engine is that it leaves a trail of radioactive exhaust, as some of the uranium is lost in the exhaust. This makes them very dangerous to use next to a space station, for example. In Testing Since the temperatures involved with the gas core rocket are so high, the plasma nozzle has to be used to make full use of it. Ignore the fact that it's pointed towards Jool while preparing to slow down... I sent it towards Jool, like the other ships. Despite having a relatively high thrust, it took some 2 or so hours in-game for the burn from Kerbin, and then I overestimated the delta-V it would take to go into Jool’s orbit. As such, I didn’t manage to get into Jool orbit in the 206 day trajectory, but I do think that if I opted for a slower 250 day trajectory I would’ve succeeded. When? Due to the difficulties in keeping the uranium fuel in the reactor, this would be an advanced form of fission rocket that would likely come after the closed cycle variant of the gas core, which I cover after this. What Should It Be For? When built, it would be one of the most powerful engines available, so provided there is a method to push the spacecraft away from populated areas, this would be a great propulsion source for large interplanetary vessels. Such ships should be flexible enough for use between all the planets, provided that they all have a source of hydrogen. Use In a Story If the uranium gas is shifted and strikes the walls of the reaction chamber, the walls are sure to melt. If the rocket is subject to much acceleration, the engine is subject to buoyancy, and the uranium fuel will “sink”, and increase the rate at which it is lost. If the radioactive exhaust wasn’t bad enough, this would certainly prevent the engine’s use on the planet, where it would be subject to acceleration. Perhaps if a major accident involving an OCGCNTR occurs near a space station, it could be very destructive and if the event was malicious, it could be a major point in the plot. Closed Cycle Gas Core Nuclear Thermal Rocket (CCGCNTR) How It Works Nicknamed the “nuclear lightbulb”, this spacecraft engine separates its uranium plasma fuel with a quartz wall. The reactor is operated at 25,000 kelvin, so hot that much of the light is in the UV range, and passes through the quartz wall to heat the reaction mass. Why Use It? At launch, this weighs literally more than the space shuttle, can go to the Mun, deliver it's 500,000 kg payload, load up on new payload, come back and land... Unlike it’s open cycle relative, the nuclear lightbulb has no uranium escaping into the exhaust. This means that it can be used as a launcher stage for a rocket, and the high Isp and decent thrust of the rocket easily makes huge reusable launchers possible. Why Not? However, placing the gaseous fuel in a solid chamber means reintroducing physical walls, which the open cycle engines were made to work around. This means the closed cycle engine has an Isp of up to 3000, not 5000, which is still high, but not as much so. What Should It Be For? As I showed off in the electric propulsion episode, they would make great space tugs, with their thrust, decent efficiency, and their safety. They would also be excellent lifter stages, provided a few boosters are attached. Propelled by a single extremely powerful closed cycle gas core engine, it's got 4 railguns, lasers, and plenty of space to store missiles. Like the solid core engines, they would be good boost stages for transferring to the planets, before the reactors are used to power electric engines in-transit, and using the gas core to slow down at the destination. Compared to the NTR, these would be more effective warship engines, even though the thrust is slightly lower, because less fuel is needed, and consequently less place to armor. In Testing Using the same ship as earlier, I test the CCGC rocket with a very large engine—the engine has less thrust than the solid core, and has to burn longer due to the higher delta-V needs. It takes a burn that lasts over 30 minutes to accelerate 8 km/s. After 326 days, it reaches Jool. I try to directly enter Vall’s orbit, but the long burn results in the ship missing the first attempt, but the ship is safely in Jool’s orbit. After just 9 days, the freighter comes back for another burn, which succeeds. I even send down the escape shuttle to Vall’s surface—if a tank is ejected, the shuttle becomes light enough to land, though it did so quite hard, knocking off an antenna. I attempted landing there, I succeeded, I guess the world's mine! Though the nuclear lightbulb’s efficiency is comparable to the ATILLA, it’s thrust is far higher. When? While this is purely an opinion, I think that due to their complexity closed cycle gas core rockets will take a substantial time to be introduced, with thousands of kerbals are already living in space. Suddenly, NTRs are far less useful, since a far more efficient engine that can be flown in the atmosphere is introduced. The problems of containing the fuel in an open cycle engine will likely mean that closed cycle engines are introduced first. Use In a Story The introduction of such a rocket could affect a story, because the capability of rockets is suddenly increased, and if there’s a rivalry, there could be a race to see who gets the engine first. As for a realistic method of failure that should explain a sudden engine failure, the uranium can become hotter or colder, and this would shift the wavelength of light emitted and cause the quartz to melt easily. In general, many of the ways the gas core would fail involve the quartz walls, which are subject to all sorts of conditions, and could shatter if they take much damage. Dusty Plasma Fission Fragment Rocket Engine (FFRE) How It Works All the other designs have used a separate propellant as reaction mass, but this design is different; it directly uses the fission products for thrust. Why Use It? The fission fragment rocket is an extremely efficient engine, with a specific impulse of ONE MILLION! This is a whole order higher than the most efficient thruster covered so far, the Wakefield. Why Not? However, the tradeoff for this excellent thrust is thrust. While the Isp and thrust can be changed, but even at the highest thrust my test engine managed only 14.7 kilonewtons. Additionally, the engine is shooting out fission fragments—though in very low quantity, it would still be dangerous. Shields may be required to protect any crew or payload on board. In Testing I know, the magnetic nozzle fits rather awkwardly on the tug. The engine in KSP is a bit inaccurate—it uses liquid hydrogen propellant, even though fission fragments are really the propellant. With the FFRE’s high Isp, I removed most of the tanks I had in the other setups—the engine would never be able to consume the fuel in time. Additionally, I choose to use the same space tug that I used in the electric propulsion episodes to get the initial kick out of orbit, which was more than usual thanks to the lower mass from the lower amount of fuel. When slowing down, I figured that if the arrival time increases, I need to wait, and if it's decreasing too quickly, I need to throttle up. I think it worked quite well. After only 140 days, the ship arrived at the Jool system, and because I planned the insertion burn carefully, I managed to achieve orbit! However, I didn’t get into Vall orbit—with some careful burns and flybys you should be able to reach it, but this is nonetheless difficult and it would certainly help to have a higher thrust system to accompany the FFRE. What Should It Be For? Two gas core engines on the side should be enough to get out of orbit, the only issue is the (presumed) maintenance. The FFRE would work well as a “cruise engine” that would burn during the cruise stage of a spacecraft to add some speed. The FFRE’s high efficiency would be more useful when used to reach distant targets in the Kerbol system. In fact, one application conceived for the FFRE was to reach the point where the sun could be used as a gravitational lens, and to reach the Oort cloud. When? I haven’t found many details about how advanced fission fragment engines are, but from what I can find, such engines seem to be fairly feasible in the "near" future. Summary With a few exceptions, nuclear propulsions are not as efficient as electric engines, but they provide enough thrust to easily leave planetary systems and orbital insertion burns. They will be key for opening up the entire Kerbol system for colonization.

Since the closed cycle gas core nuclear thermal rocket produces plenty of thrust , is very efficient, and works in atmosphere, I figured that this would be perfect for a rocket; this is the result. The payload I picked out was 500,000 kilograms of liquid ammonia, and that in itself required a fairing from the TD Orion drive mod to actually fit in. Next, I arranged the nuclear lightbulbs in a cluster of 7. However, even this wasn't enough to reach a TWR of 1, so I attached 16 of the Aluminum-Oxygen engines of the stock size. As it turns out, this rocket has enough delta-V to get into orbit, deliver a payload into the Mun's orbit, come back, and probably land vertically for reuse (if it survives reentry). Since the mass of the side boosters was pretty low, I think I could make this an single-stage-to-mun-orbit.

Here's a screenshot of the closed cycle gas core engine I tested earlier, now I just have to test the fission fragment rocket!

I got to test the basic solid core NTR today, I'll probably test the variants of this design, but I won't go too in-depth into them. After that I'm doing the gas core rockets the the Fission Fragment reactor. This ship actually has escape pods!

I actually did this a while ago, but this is worth sharing—I sent a ship at Jool traveling 1% of the speed of light. First, I sent the ship far out, then had it slow down and head back towards the Kerbol system. After a few careful burns, I was on my way to Jool, and this gif is pretty much real-time.

I've finished the electric propulsion chapter! While I added it at Chapter 2 (you can still read the old one), you can read it here:

I tested the performance of the Plasma Wakefield Accelerator engine for the Imaging a Kerbal Future series. After that, a few little screenshots and I can post the chapter! Or so I thought, because when I restarted the game, this very peculiar bug happened... It's some strange mirage/shadow of the ship I'm flying when I send it to space. I fixed it by reinstalling some of the graphics mods, but it's strange indeed...

Sneak peek on the electric propulsion chapter, which'll replace the Medium-size ship propulsion (though I'll keep the old chapter in a spoiler). Is anyone sure of what the Plasma Wakefield engine in KSP-Interstellar is supposed to be? Looking at the Atomic Rockets Engine List, I see a Wakefield E-Beam design, but i'm uncertain whether that's it.

Propulsion it is then! For now I've decided to split the sections into Electric, Fission, Fusion, and Other. I'm also planning on adding a bit to how this could be useful for a story, but I'd be open to suggestions for more sections. Edit: I've also patched up Chapter I to have a bit more info.

I've got two ideas for what to do next, and I'm asking you, the reader, to vote on which I should do first; the Colonizing Dres episode, or would you like to see a revamp of the propulsion chapter and have them be reorganized better (into categories like nuclear, electric, fusion...), since I felt some sections were redundant. In this I would also add more details on which eras such engines would be used in, and also add some engines I left out. If you've got more ideas for what could be improved, feel free to tell me!

I'm pretty sure its the "Hot Springs Geothermal Plant" part.

In this chapter we finally get to the Duna system—perhaps the favorite for colonization, for reason too. While Duna has disadvantages that will be covered later on, it’s surface temperature is roughly equal to that at the poles of Kerbin, which is quite manageable. Why Settle? On Duna, the materials for supporting industries and basic operations are readily available to Dunan colonists, such as metals and minerals, allowing for resources to be quickly mined, in contrast to Eve, where temperatures are high. This gives Dunan colonists potential to be completely self-sufficient from Kerbin, provided plenty of time. If Kerbin ever comes in short supply of certain rare materials that the Mun may not have access to, Duna is the logical choice for getting it. According to two orbital surveys in two saves, Duna has a fairly similar level of resources compared to a survey of Kerbin, which means a few things. First, colonies can utilize geothermal energy (from WBI), though the results are consistently low (2.7% and 3.2%), compared to Kerbin’s ~20%. Second, Duna has a decent supply of water, probably trapped in the poles. For supporting a colony, this is incredibly important. Breathable air is also an important requirement, and Duna’s thin atmosphere can provide at least some of it, with a small percentage of oxygen and nitrogen. However, the carbon dioxide that makes up almost all of the atmosphere can be split with the aid of a lot of energy, resulting in plenty of oxygen for the colonists. In addition to those benefits, the water can be split into oxygen and hydrogen, and using the Sabatier process the Co2 from the atmosphere can be used to create methane, an especially useful propellant. Therefore, rockets will be able to refuel at Duna before returning to their main destination, which significantly reduces fuel needs. Ike, the relatively large moon of Duna, can provide more resources with little fuel. It is, in a sense, to Duna as the Mun is to Kerbin. Such an analogy is quite appropriate considering that Duna would likely be the first interplanetary power to successfully break from Kerbin. Like Duna, it generally has the same resources as Duna, sans water. The surface of Ike is a mere 4 and ½ hours and 800 M/s of delta-V from Duna orbit, which is already easy to reach with rockets alone, and would be even easier with mass drivers, for example. The easy access to resources could make Ike a valuable propellant depot, making interplanetary travel very cheap, and much like with the Mun, orbital space colonies could be built around Duna by utilizing such easily available resources. Unlike Eve, where resource gathering may be quite difficult early on due to the fairly harsh conditions, and unlike Moho, which would likely be overlooked in early colonization efforts while being quite hard to reach, the environment on the surface is not especially harsh. The somewhat less severe conditions make the expansion of colonies becomes quite easy— it’s cheaper to gather resources and also set up more complex operations, such as resource processing and manufacturing. No, the pole unfortunately does not extend all the way down in-game Despite Ike being in the way of constructing a space elevator or tether, it is not a major problem, as the two planetary bodies are tidally locked, meaning that aside from the area of Ike’s SOI (which changes a little in the sky due to Ike’s elliptical orbit), they can be built anywhere. With the low gravity of Duna, the construction of a space elevator would be very easy, though a space tether would still help reduce transport costs while easier to build, whether it simply be to orbit or beyond, which can be done if the structure extends far beyond Dunastationary orbit. Such options will encourage settlement of the Duna system, as transportation costs become very low. However, this will be a late-term project that would not initially encourage early investment, especially those wanting a quick profit (which is almost everyone). Issues While potentially more hospitable than other various locations in the Kerbol system, the Duna system faces its fair share of issues. First, transfer windows between Duna and Kerbin are the lowest in the entire stock game, which requires trade between the two to have at least a whole Kerbin year break, which essentially prevents Duna from delivering on-demand, while a planet like Moho has multiple opportunities in just a SINGLE Kerbin year. The low gravity of Duna is helpful for vessels with low thrust, and makes building large structures like geodesic domes (which are already strong) stronger and easier to build. While the low gravity is still better than no gravity, kerbals may still suffer health effects from the low gravity, and may require the construction of rotating habitats (which might be disorienting and in the end they may just be used in the development stage of a kerbal) or major genetic/cybernetic breakthroughs that allow normal development of the Kerbal body. The Duna system's distance to Kerbol means that solar panels are significantly less effective than on Kerbin. While solar power is a fairly harmless form of energy that could still receive decent amounts of power, such a disadvantage may encourage Duna to improve fission/fusion reactors to compensate for this shortcoming. Aside from construction, nuclear reactors should be fine on Duna, which has access to uranium and thorium. Lacking a strong magnetosphere, the Duna system is bombarded with radiation, and the atmosphere of Duna will not be too effective, especially at the higher altitudes. While this can be mostly solved fairly easily with adequate habitat protection, Dunan colonists will have to go out, whether it be to repair broken equipment or for scientific interests, and their spacesuits will not be able to protect the astronauts very well, potentially forcing a ration on EVAs, requiring better, lighter shielding, or better medical treatment. Depressurization is a serious threat to Dunan colonists, as the atmosphere has just 1/15th the atmospheric pressure as Kerbin. The habitats would therefore be rounded to prevent certain weak points in the structure. Ike is much like the Mun, where even lower gravity does little to prevent health effects, and the regolith there might also be similarly dangerous, with a lack of an atmosphere. The little protection Duna has from depressurization is completely gone. Colony Designs A small colony home to perhaps 1000 residents, this is likely a remote settlement or an early stage one Finally, the section on what Duna colonies may look like. There would likely be two main designs for the habitat. The first option would be a covered colony. Much like the Kerbin orbital colonies and the Mun, these habitats would be covered with a layer of soil to protect residents from the dangerous effects of radiation. Expansion could be as easy as inflating a habitat, connecting it to life support, and covering it with Dunan soil. Due to the ineffectiveness of solar power, nuclear or fusion reactors will be used to power the colonies instead. This also means that the habitat can be located in the polar regions with access to water ice without the concern of Kerbol near the horizon harming sunlight received. These colonies may be able to support themselves by invention and intellectual capital, with the environment ever pushing kerbals to innovate. To supply air and food to the colonists, plants (or whatever Kerbals grow...) will be in greenhouses that are located underground, with artificial lighting. This is simpler than kerbollight-exposed greenhouses, which will need radiation shielding while letting light through, and then one must put up with the low amount of light due to Duna’s distance from Kerbol. The amount of light received can be boosted by mirrors, but this would still make it complicated. Perhaps a kerbal analogue to algae might be grown, utilizing the light well and providing a fair share of nutrients. Easily the hardest drawing I've done for this series—a full-on dome city with easily hundreds of thousands of Kerbals residing. The choice between covering the dome and having it be transparent can be explained by two ways—first is that transparent radiation shielding wasn't initially available, or that eventually no one cared about an outside view... The second concept would be to construct geodesic domes, much like what I discussed on Evian colonies. For their structure and mass, geodesic domes create a lot of volume. Once the infrastructure for constructing the panels is established, their construction can quickly advance—if the technology exists for them to shield the colonists. By the time such technology is developed, plants will likely have far more efficient photosynthesis to take advantage of what little light is available. Additionally, they provide views of the outside and Kerbolight to reduce a feeling of claustrophobia. The turbojets are reusable—provided their insanely high TWRs screw the landing up The colonies will likely focus their efforts on mining resources and processing them into manufactured products. To transport such resources, rockets will be used in the early stages. In this stage I would imagine closed cycle gas core rockets being used, as they perform well in both space and in the atmosphere. Such rockets could be launched sideways with nuclear turbojets attached to the side, which provide much of the thrust required to reach orbit. Eventually, mass drivers will be used to accelerate payloads—with very low atmospheric pressure, the drag losses would be minor, though some shielding may be required. For a particularly advanced Duna colony, a space tether as mentioned earlier would be quite effective; simply fly up to the tether, and have it release the ship higher up for a free boost to Kerbin or another destination. A Duna space elevator would deliver those benefits without having to accelerate quite quickly, but it would be more difficult and expensive to construct. Put in a bit of liquid fuel, and it becomes a space shuttle too! *Radiation safety not guaranteed Transportation between colonies could be provided via nuclear turbojet aircraft, though this option would be mostly reserved for passenger flights. For most transport, trains could swiftly travel between large colonies, delivering massive amounts of kerbals and freight without the need for sophisticated vacuum tunnels. In areas that are particularly isolated, trucks would travel in convoys, ready to support each other if one of them breaks down. The design of Ikeian colonies would probably be similar to that of the Mun—habitats located either underground (which gives the convenient effect of needing less to illustrate) or in regolith shielded habitats. Ike would probably focus on mining and industry, with the resources of the moon available to be sent off interplanetary or to major orbital colonies. The Progression of the Duna System The first permanent settlements in the Duna system may surprisingly be located on Ike—you could conceivably set up a fuel depot there, and with the low delta-V requirements it would be easy to reach, unlike Duna which requires a fair bit more effort. However, Duna would be more effective at actually creating propellant, thanks to its capability to more easily obtain volatiles, which tend to be rocket fuels. Though the very first kerballed operation on Duna would be mainly scientific, these colonies could also act as a refuel and repair location for ships headed farther into the Kerbol system. Eventually, a well-established Ike colony could act as the starting base for more colonization efforts. As mentioned earlier, a good place for such colonies will be in the polar regions, where ice is plentiful. As transport of ice and other resources overland improves, colonies can slowly work their way towards the equator, where more orbits are available, and it is easier to reach orbit. As Duna grows to that size, it will become increasingly easier for businesses to invest in a colony of that sort—earlier, it would probably serve them just as well to invest in the development of the Mun, which would probably see a far quicker return on investment. However, Ike will remain the more economical option for ISRU operations. It’s population will be comparatively lower, but it would nonetheless be vital to the Duna system. With the population of Duna growing, domed colonies are built, providing more space to the colonists than the covered colonies would, along with railway links to the various colonies scattered across the planet. Space tethers, mass drivers and space elevators are constructed to massively decrease the price of shipping. Eventually, Duna may completely break away from the Kerbin system, as it becomes largely self-sufficient aside from a few products. Red Duna or Blue Duna? At this point, an important question must be answered—should Duna be terraformed? Should the planet be preserved as is, or should it be turned into an environment that is habitable for kerbals to live in, without the need for space suits or complex structures? End of Chapter XII Thanks for Watching Next Time: The Expansion/Revamping of the Propulsion Chapters and Colonizing Dres (and asteroids?)

Sorry for the lack of updates—I'm almost finished with the Duna chapter. Here's another sneak peek for the chapter. The only things needed to be done are: a colony drawing (only exists on paper now, and it'll probably the hardest/most detailed I'll probably do) and a terraformed Duna...

Yikes, I had most of mine done already - just the math one - of course, it's probably the hardest one of them... Thanks! I'll probably still have to draw some of the colonies, since the parts available to me don't really allow me to built at those scales.

Because the next chapter is quite long and I have quite a lot of things to do (school's ending), I haven't been able to finish the chapter. However, I have a screenshot of what's to come in the next chapter!