Imagining a Kerbal Future: What Would the Future of Kerbals Look Like? (Chapter XLIII: Epilogue)

[SaturnianBlue]

Nearly finished writing the next chapter, where I have chosen to merge the Duna and Ike chapters—I decided that Ike on itself would be too dull a chapter, especially considering its rather Munlike nature.

[SaturnianBlue]

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!

[Kosmonaut]

1 hour ago, SaturnianBlue said:

(school's ending)

I have six exams and one province-wide standardized test... i sympathize

My exam tomorrow is writing a short essay and the only experience i have had with writing exams this year is one exam that was 7000 words long and I had two weeks to do but this one is 400-600 words long and I have 1.5 hours. It's a whole new ball game and a whole new writing style and it's quite stressful. It's funny- I'm more stressed about the exam for my first language (english) than I am for the exam for my second language (Quebecois French)

I also find it really cool that you actually did the stuff in KSP

[SaturnianBlue]

1 hour ago, Kosmonaut said:

I have six exams and one province-wide standardized test... i sympathize

My exam tomorrow is writing a short essay and the only experience i have had with writing exams this year is one exam that was 7000 words long and I had two weeks to do but this one is 400-600 words long and I have 1.5 hours. It's a whole new ball game and a whole new writing style and it's quite stressful. It's funny- I'm more stressed about the exam for my first language (english) than I am for the exam for my second language (Quebecois French)

I also find it really cool that you actually did the stuff in KSP

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.

[SaturnianBlue]

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...

[Kosmonaut]

Oh boy

[SaturnianBlue]

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?)

Edited August 1, 2017 by SaturnianBlue

[NotAgain]

12 hours ago, SaturnianBlue said:

First, colonies can utilize geothermal energy (from WBI)

Does anyone know what part I actually need to exploit/harvest geothermal energy? I can't for the life of me find it.

[SaturnianBlue]

51 minutes ago, NotAgain said:

Does anyone know what part I actually need to exploit/harvest geothermal energy? I can't for the life of me find it.

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

[SaturnianBlue]

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!

[insert_name]

Propulsion sounds interesting, though i know the dres fandom will say otherwise

[Kosmonaut]

Propulsion

I'm in the Doctor Who and Lucifer fandoms so I won't freak if you delay dres

[Skylon]

Propulsion

But I don't mind too much.

[NotAgain]

I'm also voting propulsion.

[SaturnianBlue]

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.

Edited June 23, 2017 by SaturnianBlue

[SaturnianBlue]

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.

Edited June 26, 2017 by SaturnianBlue

[SaturnianBlue]

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:

Spoiler

Chapter 2: Electric Propulsion

The next few chapters will help answer the question: which thrusters should be used, and when? To find out, we first take a look at electric engines.

Electromagnetic Thrusters

Test Subject: Magnetoplasmadynamic Thruster

How It Works

The test ship, equipped with a (fake) centrifuge!

The Magnetoplasmadynamic (MPD) thruster (MPDT) is a form of electrical propulsion that utilizes electromagnetic fields to accelerate a propellant to very high speeds, relying on the Lorentz force. Among the various methods of electromagnetic propulsion, this one produces exceptional thrust, though that arguably means less than it sounds…

Why Use It?

It is a very efficient engine, with a specific impulse of 11213 secs using hydrogen as a propellant—almost 3x more efficient than the Ion thruster provided by the stock game. In both KSP-Interstellar and real-life, many different propellants can be used by MPD thrusters, including Lithium (in-game, it’s efficiency is about ½ of Hydrogen, but twice the thrust, and in real life is regarded as the best propellant), and Methane.

Why Not?

    It has a single great drawback to it—thrust. Even when supplied by a few GIGAwatts of power, it provides only a few dozen kilonewtons of thrust! This is probably even worse in real-life, where there are various stresses with such high-power thrusters, and according to the designer of the hard Sci-fi Children of a Dead Earth, you’d need literally many tons of radiators. While KSP already somewhat cheats by having an insanely powerful ion engine, you might want to keep your thrust quite low if you want to replicate the even lower thrust of a real MPD…  

When?

Now! Magnetoplasmadynamic thrusters are a working design that has been tested for decades, though their thrust has been limited without large nuclear reactors. Therefore, a KSP story set with technology on the lower end of the range this series covers (tech ~100 years in the future) would see this thruster used the most, before they are largely phased out by more powerful engines that have even higher efficiencies such as the D-T Vista or the magnetic/plasma nozzle rockets. However, they can always be used for small scouts, as they can be tweakscaled to tiny sizes and use beamed power for electricity.

What Should I Use it For?

    Mainly for long-range civilian vessels during the relatively early era of colonization, especially those who want rapid transit. Their low thrust makes the rocket completely ineffective for intra-planetary system movements, and possibly even for moving between Kerbin and Duna at opposition, even. However, they would be very helpful for reaching Dres, Jool and beyond, as there would be ample time to speed up and slow down.

As mentioned earlier, scouts too!

    If there is one thing they will never, ever, ever be used for, it’ll be warships; in no purpose-built way could a vessel that literally accelerates at hundredths of a G could evade oncoming vessels.

    When it comes to size, the engine would be better used on relatively small vessels, especially considering the stresses involved in huge MPDTs.

In Testing

Although fuels like Lithium generate more thrust with the MPDT, it would be more ideal to use Hydrogen since the thrust is already quite low, and the ship gets better efficiency at the cost of a huge tank, but for civilian purposes there shouldn’t be too much of a problem with that. The test vehicle is carrying 421 metric tons of water.

Therefore, the craft I tested the MPDT with is powered by liquid hydrogen. However, I realized that the MPDT’s thrust was simply too low to leave Kerbin orbit in one burn, so I decided that a space tug would be ideal. Considering the tech “era”, the two engines are best used for this space tug are the NTR or the closed cycled gas core engines. For this example I used the Closed Cycle Gas Core, which is more efficient than the NTR, and doesn’t produce the radioactive threat it’s open cycle counterpart does.

Starting from Kerbostationary orbit, which I assume to be a start point for spacecraft, the methane-fuel space tug allows the ship to leave Kerbin orbit, where it then separates with plenty of fuel left for it to return to the start point.

The Magnetoplasmadynamic thruster then puts out a few feeble kilonewtons of thrust., burning for weeks after it leaves Kerbin to head for Jool. It then flips itself to begin slowing down. Everything looks good, with a Jool arrival a mere 250 days in the mission.

However, I misjudged how early I’d have to start burning, and I had to burn for several days after periapsis to get in an orbit—one that lasted a 100 days… If I’m very careful I can eventually enter orbit of one of the Muns, but the low thrust is quite a limiting factor intra-planetary, and could be complemented by a secondary propulsion system.

Use in a Story

    As a result of the low thrust of the engines, pilots in such a setting might risk failure of the engines for a bit of higher thrust to reach their destination in less time, and over time, without any repairs, wear and tear could easily result in an engine failure, stranding ships in space… Such a failure could present an interesting scenario where the crew may have to come up with clever solutions to save the ship, or to amplify the threats that already face them.

Test Subject: VASIMR (Variable Specific Impulse Magnetoplasma Rocket)

While I did most of the testing with the inline version, there's a radial version too

How It Works

    The Variable Specific Impulse Magnetoplasma Rocket is another electromagnetic thruster that accelerates a plasma for thrust.

Why Use It?

A unique advantage of this thruster is that for increased thrust, it can lower its Isp and vice-versa, the Isp of which ranges from 2956 to 29560, at least for liquid Hydrogen.

Why Not?

    The thrust of the VASIMR is even lower than the MPDT, and while the thrust can be raised, it would also lower the Isp. As with the MPDT, the amount of radiators needed may be of concern.

In Testing

    In many concepts, the VASIMR uses it’s high-thrust mode to leave the orbiting planet, but this takes up valuable time that could be utilized transiting between the target planet. I use the same ship as the MPDT.

    The mission profile of the VASIMR is more or less the same—the ship gets to Jool, but ends up in an elliptical orbit, and planning flybys to adjust your course is quite tedious and difficult with such low thrust.

When and What Should it be For?

VASIMR Freighter: Duna Colonization Version
    The VASIMR is currently being tested, so like the MPDT they would be used mainly in the early period of colonization. Due to the fact that it can “switch gears” the same ship could be used for a wide variety of interplanetary destinations, unlike the MPD which is largely limited. The engine doesn’t use electrodes, which tend to wear out, so from a worldbuilding perspective, it would ideal for mission that may have to burn for years to reach, such as the planets in the Outer Planets Mod.

For civilian interplanetary vessels, this is a rather ideal engine, but maneuvers in-system will be difficult, especially in the Joolian system, and a higher acceleration rocket may be necessary. That could encourage a space tug industry to grow, offering to push about such ships for a fee, and would have saved both of the engine tests.

Like the MPDT, these would best be used aboard ships on the small end.

Use In A Story

"Whatever, just let the computer decide. Let's get out the snacks!"

    The crew of a VASIMR ship on with a low amount of fuel coming up on a critical burn could be forced to debate at what level they should run the rockets at—razor-thin margin but taking less time, or burn with a sizable delta-V margin in the tank, but the low thrust putting the ship at risk of missing their target…

Test Subject: Electrostatic Ion Thrusters

Blue for Xenon, Purple for Argon

How They Work

Electrostatic thrusters use the Coulomb force to accelerate ions. These thrusters can use many different propellants, but most current ones use Xenon. The Hall effect and gridded ion thrusters (both found in Near Future Propulsion) fall into this category.

Why Use It?

Electrostatic thrusters are capable of very high efficiencies in the several thousands, with the dual-stage 4-grid thruster achieving 21,400 secs.

Why Not?

Like the thrusters covered earlier, their thrust in-game is low, and in real-life ion thrusters will likely not achieve anywhere near the kilonewton range without becoming extremely heavy. In fact, ion drives cannot have high thrusts.

In Testing

Using NFP’s overpowered 4-grid thrusters with KSP-I’s rather overpowered reactors resulted in a very powerful relay sat, with 210,000 m/s of delta-V. However, the time warp function doesn’t support NFP thrusters, which makes it overly time consuming to watch the ship thrust despite the high acceleration.

What Should It Be For?

Electrostatic thrusters will  work well with small probes such as relays, especially with beamed power. However, I doubt that they would see much use in larger ships.

Use In a Story

Certain Electrostatic thrusters use electrodes, which degrade over time, leading to a sudden failure if not replaced. The thruster has a neutralizer to balance the charge, or else the charge builds to a point where the exhaust would refuse to leave the engine...

Electrothermal Thrusters

How They Work

The small ones are the arc jet and resistojet RCS, and the bigger side ones are the ATILLA and the central one is the Wakefield Accelerator

The design of electrothermal thrusters is quite simple—the propellent is electrically heated and shot through a nozzle. Examples of these thrusters as provided by KSP-I Extended would be the arcjet and resistojet RCS, the ATILLA thruster, and the Plasma Wakefield Accelerator Engine. Since the arcjet and resistojets RCS is not a primary propulsion system, i’ll only cover the latter two in detail.

Test Subject: ATILLA (Adjustable Throttle Inductively Afterburning Arcjet)

An arcjet, this thruster heats a propellent with an electric arc, but this design in particular uses magnetic induction to increase thrust.

Why Use It?

In-game, this arcjet thruster provides more thrust than the thrusters already covered, but I’m uncertain if this is actually true in reality.

Why Not?

The Isp of the ATILLA thruster is quite low, at a mere 2854 secs for liquid hydrogen, the most efficient. This is more or less equivalent to some fission rockets i’ll go into detail in the next chapter, though it is also capable of being scaled down.

In Testing

Equipped with the same ship as the MPDT and VASIMR, the ATILLA  showed higher thrust levels of about 150 Kn but significantly lower Isp, resulting in a delta-V of 10km/s as opposed to 30 or more. I decided to target it for Eve, which happened to be in the right point for a transfer window. The ejection burn was done in one go with the ATILLA, but this would be unlikely to happen in real life.

At least it's failure wasn't because I messed up newton-seconds and pound-seconds!

Thanks to the high thrust it got there in only 39 days, but since I was a bit careless the ship burned up in the atmosphere…

What Should It Be For?

If you’re willing to break a little from reality, you can use these highly scalable engines to power small ships at insane accelerations using beamed power, and missiles would especially benefit from that, since they would have more delta-V than conventional chemical thrusts.

If not, I don’t see too many uses, but maybe you could find some.

Use In a Story

Arcjet designs use electrodes, which wear out even quicker than usual due to the use of electrical arcs involved. If this happens during an important burn, it could easily jeopardize the mission, whatever it may be…

Test Subject: Plasma Wakefield Accelerator

How It Works

A Plasma Wakefield Accelerator uses a powerful laser or electrons to ionize the propellant, which ride an electrostatic wake. I haven’t been able to find much on this engine aside from a regolith propelled one that produced a 4.6 kilonewtons with 60 MW of power.

Why Use It

When utilizing liquid hydrogen fuel, this rocket can achieve 10,000 Isp at maximum thrust, and 100,000 at the lowest thrust levels. Going by Isp and thrust, this is the best thruster I’ve covered so far, though I’m not particularly sure how they perform IRL.

Why Not

Like most electrical engines, the Wakefield Accelerator engines provide little thrust. Additionally, the base power supply required for the engine’s operation is very high, requiring large reactors.

In Testing

Again, I utilized the space tug to push this ship out of Kerbin orbit. The Wakefield rocket accelerates far more, though that’s just because of the large reactor I’m using, and I found out that you’ll want to either switch fusion modes or bring lots of a certain fusion fuel to keep the ship running, and prevent the cryostats from boiling all the hydrogen into space.

Though it’s acceleration is higher, I once again misjudged the deceleration burn, and I flew by Jool. The ship has plenty of delta-V, so you should be able to get back to Jool, albeit with far more time spent than the <100 days you spent in the first place.

What Should It Be For?

This 110 meter long version weighs 3,000 mT!

These engines would be geared for relatively low acceleration civilian ships on interplanetary routes. Also, the large power requirement means that these ships would be better used on larger ships on which it makes proportional sense to have the huge reactors that power these engines.

When?

    While Plasma Wakefield Accelerators do exist, they aren’t used as a form of propulsion, and since I’ve seen fairly little on these engines, I think it’s safe to say that they are more advanced design compared to all the earlier engines covered earlier.

Summary

In the grand scope of things, electric propulsion is a fairly low tech but high efficiency option for spacecraft propulsion. However, their low thrust significantly complicates ship burns, which would lead to most of them being replaced by advanced engines that have high thrust and efficiency in the long term, so stories that depict kerbalkind’s first major colonization efforts will likely see this propulsion type the most.

 

[Kosmonaut]

whooooooooooooooooo yeah

[SaturnianBlue]

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!

[Kosmonaut]

That's beautiful...

[SaturnianBlue]

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

[SaturnianBlue]

 

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.

 

Edited July 4, 2017 by SaturnianBlue

[Kosmonaut]

If the ship using radioactive engines is built right, no shielding is necessary due to the way radiation travels. Here are some diagrams fromt he old constellation program, and their MTV design using NTRs. This is a diagram of the habitat modules and their placement

 

[SaturnianBlue]

23 minutes ago, Kosmonaut said:

If the ship using radioactive engines is built right, no shielding is necessary due to the way radiation travels. Here are some diagrams fromt he old constellation program, and their MTV design using NTRs. This is a diagram of the habitat modules and their placement

 

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

Edited July 4, 2017 by SaturnianBlue

[Kosmonaut]

It's interesting. You always see the Discovery MTV, but you almost never see it's sister ship the A.C. Clark. I find the Clark much cooler than the Discovery.