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

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           This report/analysis seeks to answer the question: What would the future of the Kerbals look like? Specifically in the time frame of say, 100-300 years, a future firmly ingrained in realism and hard Sci-Fi.. I’ve had the idea of creating a story set in that approximate era, but being an extraordinarily extravagant idea, this series is dedicated to finding out the specifics. I also hope that this series will help future writers help flesh out their futuristic universes as well. :)  

Things to Note:

-There’s a fair amount of mods used in this series—but i’ll try to keep it at minimum

-Nothing too implausible will be used (no warp drives, but certainly nuclear fusion)

-If you’ve got an idea for a chapter, let me know!

-Want to contribute directly to the project? Come to the ToughSciFi discord, where this series has a channel for itself.

-It helps to read the comments, since some bring up some good points

-When writing these chapters, I do tend to assume that kerbals have a similar physiology to humans... But greener and smaller?

-The goal of this series? Consider all the essentials for world building a futuristic Kerbol System

-For engines I try to mix info from the game and real life, but the pros and cons, as well as the uses sections generally reflect the in-game depiction of the engine

-Since I have both near Near Future Electric and KSP-I installed, a modifier lowers the output of KSP-I stuff* 

*I later chose to just work with the power output in KSP-Interstellar, so I amended most of the chapters to reflect this

Table of Contents


Chapter I—Atmospheric Propulsion

Chapter II—Electric Propulsion

Chapter III—Nuclear Propulsion

Chapter IV—Fusion Propulsion

Chapter V—Mixing Propulsion Systems

Chapter VI—Beamed Power


Chapter VII—Colonizing Moho

Chapter VIII—Colonizing Eve

a. Colonizing Gilly

Chapter IX—Colonizing Kerbin Orbit

Chapter X—Colonizing the Mun

Chapter XI—Colonizing Minmus

Chapter XII—Colonizing the Duna System

Chapter XIII—Other Propulsion Systems

Chapter XIV—Colonizing Dres

Chapter XV—Colonizing Jool

Chapter XVI—Colonizing Laythe

Chapter XVII—Colonizing Vall

Chapter XVIII—Colonizing Tylo

Chapter XIX—Colonizing Bop and Pol

Chapter XX—Colonizing Eeloo


Chapter XXI: Non-Rocket Spacelaunch—Part One

Chapter XXII: Non-Rocket Spacelaunch—Part Two

Chapter XXIII: The Ship Design Process I

Chapter XXIV: The Ship Design Process II

Chapter XXV: Depicting the Future In KSP



Chapter XXVI: Who and Why Would Kerbals Colonize Space?

Chapter XXVII: Moho in a Colonized Kerbol System

Chapter XXVIII: Moho in a Colonized Kerbol System, Part Two

Chapter XXIX: Eve in a Colonized Kerbol System

Chapter XXX: Eve in a Colonized Kerbol System, Part Two

Chapter XXXI: The Kerbin System in a Colonized Kerbol System, Part One

Chapter XXXII: The Kerbin System in a Colonized Kerbol System, Part Two

Chapter XXXIII: The Kerbin System in a Colonized Kerbol System, Part Three

Chapter XXXIV: The Duna System in a Colonized Kerbol System, Part One

Chapter XXXV: The Duna System in a Colonized Kerbol System, Part Two

Chapter XXXVI: Dres in a Colonized Kerbol System

Chapter XXXVII: The Joolian System in a Colonized Kerbol System, Part One

Chapter XXXVIII: The Joolian System in a Colonized Kerbol System, Part Two

Chapter XXXIX: Eeloo in a Colonized Kerbol System



Chapter XL: Overview of In-Game Space Warfare

Chapter XLI: Approaches to Depicting Space Warfare

Chapter XLII: Space Warfare, In-Game

Chapter XLIII: Combined Approach Space Warfare & Epilogue

Craft Files:

The Uncatchable Swift

Mod List (Incomplete):



KSP Interstellar Extended—Extensive supply of futuristic propulsion

Near Future Propulsion—Provides several detailed engines

"Project Orion" Nuclear Pulse Engine—An interesting, plausible engine type

Netherdyne Mass Drivers

General Part Mod:


HLAirships—Eve Colonies

Near Future Technology


Procedural Parts


Module Kolonization System


Civilian population


At times Sci-Fi Visual Enhancements, SVE, Spectra, and Andromeda: Daydream

Power Generation:

Near Future Electrical (old chapters only)


DMagic Science


BDArmory (Modified)






Ubio Welding Mod




Physics Range Extender

Hanger Extender




Further Info (I mainly cover topics when applied specifically to KSP, these cover a broader range of topics)

Without further ado, let's get started!

Chapter I: Atmospheric Propulsion

"It’s a bird! It’s a plane! No, it’s a nuclear-powered hypersonic ramjet airliner!"-Linus Kerman


A hypersonic, heavily-modified concept version of the Stearwing A300 that utilizes nuclear ramjets

    Perhaps we should start with something that is readily available to kerbals—flight. With jet fueled engines it is possible to reach speeds of over Mach 5. While that is excellent, major problems arise from its use—large portions of the plane are reserved for fuel, not passenger space, and a large amount of funds are used on fuel. Preferably there should be a way to reach those speeds without fuel...


A conventional 16-passenger hypersonic aircraft, almost half of its takeoff mass was dedicated to fuel.

The main focus of this chapter is thus about finding new ways of (supersonic) aviation.

    The way in question (with the mods available) is the powerful nuclear jet, generally produced in two varieties; turbojet and ramjet. On Kerbin they achieve speeds similar to that of the liquid fuel jet planes, with higher thrust. They perform exceptionally well on all atmospheric bodies, with tests on Duna achieving orbital velocity. Without the need to load fuel, planes could be lighter and take less time to be able to fly. 


A basic fighter design that can reach hypersonic speeds and reach space on Eve. Such designs could easily outmaneuver jet fuel enemies, but you probably don't want a nuclear jet flying over your own territory...


Duna, where nuclear ramjets achieved an apoapsis of ~5000 km


    Sadly, this is where we must look at the disadvantages. There’s one obvious one—the radiation hazards. Shielding (though we must take in the "future tech" factor) would be very heavy, and of course nobody would want to sit next to a nuclear reactor (10% flight ticket discount for sitting next to it?).That said, they could still be used on special SSTO launches in certain areas. Second, they would be expensive (likely initially and maybe for maintenance), which would make their flights high-priced but also keeps them from being used for missiles (Well, except for the fact that the TORY ramjet part is based off a supersonic nuclear bomb delivery method called Project Pluto...).


A 64-Passenger concept aircraft that would use nuclear jets, with a conventional rocket thruster to reach orbit, at which point it can safely return with a powered landing.

Provided enough shielding is given, they could be practically everywhere in locations with poor infrastructures and no alternatives, a fate likely for the planet Eve.


How Would I Use This In a Story?

As a method of getting around on planets, and the best part is that you can actually make the plane in game, so you don't have to resort to pure prose or drawings. As for part of the story, I'm not exactly sure what they might be used in, but perhaps a radioactive crash involving such a plane could have be a plot point...

End of Chapter One: Atmospheric Propulsion

Next Time: Spacecraft Propulsion (Electric)

Thanks for reading!



Edited by SaturnianBlue
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11 hours ago, MaxL_1023 said:

I think the Kerbals would have fusion by this point - either laser-detonated pellet-driven pulsejets or some sort of steady-state confinement reactor. 

You're probably right, but the nuclear turbojet was the best option I found with the minimal mods I gave myself. I'll probably discuss fusion in a later chapter. :) 

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Well, to quote another forum-goer (don't remember whom it is off the top of my head): color me intrigued. Not a lot of mission reports I've seen here touch on the foundations of having a futuristic setting. The typical format seems to be modlist; backstory; mission-report. Kudos to you, good sir. :)

As for the chapter after the next chapter - how about fusion propulsion (i.e. the D-T Vista from KSPI-E)? I know you said fusion reactors would be touched upon in another chapter, but I feel that fusion drives are different (ish).

Keep 'em coming!

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43 minutes ago, TotallyNotHuman_ said:

Well, to quote another forum-goer (don't remember whom it is off the top of my head): color me intrigued. Not a lot of mission reports I've seen here touch on the foundations of having a futuristic setting. The typical format seems to be modlist; backstory; mission-report. Kudos to you, good sir. :)

As for the chapter after the next chapter - how about fusion propulsion (i.e. the D-T Vista from KSPI-E)? I know you said fusion reactors would be touched upon in another chapter, but I feel that fusion drives are different (ish).

Keep 'em coming!

For the next chapter I sort of plan of touching up on Magnetoplasmadynamic, Nuclear Lightbulb, and VASIMIR, but the D-T Vista is worth covering, since it's quite possible that Kerbals could have it/are inventing it. I might also do Daedalus, though it slightly overlaps with the D-T Vista.

Edited by SaturnianBlue
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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…  


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.IDBS2ox.png

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.


    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.


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.

The old version of this chapter, here.

Chapter 2: Propulsion for Medium-Size Spaceships

“To Jool in 326 days!”

In this series, I will refer to ships of a fully-loaded mass of 75,000 kg to 250,000 kg as “medium-sized”. A ship of this size could be many things, including a passenger vessel, a warship, and cargo ships, but for this section, a cargo tanker with 100,000 kg of liquid fuel will be the base for the following tests.

Test Subject: VASIMIR (Variable Specific Impulse Magnetoplasma Rocket), the KSP Interstellar Version


A Quick Overview 

VASIMIR operates by ionizing and heating a propellent and then accelerating the propellant with a magnetic field. In the example of VASIMIR I use for this series, I chose Liquid Methane, being fairly dense and giving a higher specific impulse (let’s hope kerbals don’t care about the smell).


In Testing

Taking advantage of a Jool launch window, a burn was executed in one go (from kerbostationary orbit, since a space elevator probably would exist), taking the spacecraft out of orbit. You should definitely use mods that let you accelerate during time warp, as some of these burns took longer than the time it takes a fast ship to get from Kerbin to the Mun.


In a mere 402 days the tanker reached Jool. I could have entered orbit, but I underestimated just how low the thrust was, but I know for a fact that there would still be more fuel.



The efficiency of the VASIMIR ranges from “pretty good” to “really good”, that is, around a few thousand to around ten thousand. It was also the smallest of the designs I tested.


Even at the highest thrust setting, the engine produces very little thrust, with thrusting burns lasting for hours. Of course, the thrust of the engines in-game are still exponentially better than the real life counterparts… It's like the difference in the speed of the slowest sloth and a snail. One is definitely faster, but they're still slow.


The exceptionally high ISP of the engine could allow tankers to reach far targets (like Urlum in OPM) in fairly little time with a somewhat longer tank.

Test Subject: Magnetoplasmadynamic (KSP Interstellar, Near Future Propulsion)


A Quick Overview
In a nutshell, MPD thruster is a form of electrically powered thruster that uses the force on a charged particle of generate thrust and is one the highest thrust electromagnetic engine types.

In Testing

 The Magnetoplasmadynamic thruster from KSP Interstellar performed quite well, getting the tanker to Jool in about 330 days, but it was about ~800 m/s short of a successful orbital insertion.


The Near Future Propulsion engine is less efficient but has a far higher thrust, which is why it has 4 lithium tanks as opposed to two for the KSP-Interstellar version. I chose to take it on a slower route with an arrival 357 days after launch. However I can’t seem to get the time warp mod to work for the engine, so I gave up part way through. Despite this, I’m fairly confident that the spacecraft would have entered orbit around Jool, then Tylo.



The engines are highly efficient, providing very high amounts of Delta-V, combined with decent thrust that lets the ship leave Kerbin from kerbostationary orbit in one single burn.


Sadly, the thrust is still low, though like the VASIMIR it has a far higher thrust than its real life counterpart, and a high amount of power is required. The engines also have a generally lower ISP than the VASIMIRs.



The MPD would serve a midway point between the VASIMIR and the next engine design, and would probably be the most favored engine type.

Test Subject: Closed Cycle Gas Core Engine(KSP Interstellar)

A Quick Overview

A rocket engine powered by the coolant of a gaseous fission reactor (that is, a reactor with gaseous nuclear fuel), with the closed part coming from how the fuel is contained in a solid structure.


In Testing

This craft utilized one of the largest fuel tanks, even while using denser liquid methane fuel, and still had less Delta-V than the other designs. However, the thrust output was enormous. It should be able to reach Jool in under an year without any issue, though.


The main advantage is excellent acceleration, meaning important insertion burns are easier to carry out. The spacecraft does not require heavy additional reactors, as it is included with the engine.


The efficiency of the “Nuclear Lightbulb” is far better than a chemical rocket, but also quite poor compared to the other engines covered in this chapter.



The low efficiency restrict these engines mainly to routes between Kerbin, Duna, and Eve. The high thrust would make them the prime propulsion method for warships, as they may require quick bursts of thrust in combat.

Test Subject: Open Cycle Gas Core Engine (KSP Interstellar)


A Quick Overview

Similar to the Closed-Cycle, but now nuclear fuel is being shot into the reaction chamber, rapidly heating up the liquid hydrogen, which leads to a higher efficiency, but fuel is lost in the exhaust, making it quite radioactive.

In Testing

You will need an enormous tank to make this ship viable, due to the incredibly low density of Liquid Hydrogen. If such a tank is obtained, then the spacecraft will be packed with Delta-V.


High efficiency paired with decent thrust, and comes with a reactor that creates large amounts of power.


An enormous tank with a fairly poor ratio of tank mass to propellent. Not to mention a radioactive exhaust, which would probably result in it being using with something else to push the ship away before ignition.



It would take a similar role to Magnetoplasmadynamic thrusters, but it would likely be rarer due to the giant docks that would be required for the ships, and the radioactive exhaust.


Thanks for Reading!

End of Chapter II!

Next Time: Heavy/Super-Heavy Mass Spacecraft Propulsion Nuclear Propulsion!

Edited by SaturnianBlue
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14 minutes ago, KAL 9000 said:

Antimatter warheads

That's too much - do you really want to trust anybody related to Jeb with ANTIMATTER? Honestly I would limit them to poodles - MAYBE skippers if they are on their best behavior. 

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A tip for you: when using such designs, liquid hydrogen is the propellant, and liquid deuterium and tritium is the fuel. If you keep adding hydrogen tanks and the delta V decreases, then you don't have enough deuterium/tritium. Add some cryostats with those resources. OTOH, if you have only a little fuel, decrease the amount of deuterium/tritium in the engine until you start losing delta V. Then bump your fuel up a notch, and you'll have enough fuel without wasting any.

Hope this helps, and good luck! :)

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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.


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.



    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.




    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. 


    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.


    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.


    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.


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.


The old version of the chapter


Chapter 3: Heavy/Super-Heavy Vessel Propulsion Systems

“Riding the Waves of Nuclear Fire”-The Kerbin Navy

    The series labels ships amassing 250,000-1,000,000kg as “heavy ships”, with anything over that being called “super-heavy ships”. The example of a heavy ship in this chapter is another tanker, but this time carrying 340,000 kg of Xenon (no doubt a very expensive product).

While I will not cover the earlier propulsion systems for redundancy, it is important to note that the Closed Cycle Gas Core engine still works very well at this scale, carrying a 1,100 metric ton vessel to Duna in 120 days.


Personally I do not think that the VASIMIR performs best at this scale, but the Magnetoplasmadynamic thruster does, with a design that carries 108 mT of Hydrogen and weighing in total 678 mT—resulting in a total of 19,000 M/s of acceleration when all tanks are full. It reached Jool in 238 days, but be warned—the thruster guzzles electricity.


Test Subject: VISTA Fusion Engine/Daedalus


A Quick Overview

The VISTA fusion engine operates by ejecting fuel pellets before smashing them with high-energy laser beams to the pressure and temperature where nuclear fusion is initiated, creating a hot plasma and a small explosion. Daedalus works much the same way, using pellets of deuterium and helium-3.

In Testing



The spacecraft accelerated quite quickly and then successfully reach Jool in 230 days. This is a picture of the Tylo flyby, occurring at 12,700 m/s.


The spacecraft then slowed, successfully entering Tylo orbit with large amounts of fuel to spare.


I even tested a gigantic 17,000 metric ton ship with 2,200 metric tons of fuel with the VISTA engine, which gave it an impressive 35,000 m/s of Delta-V at the highest setting.



With a comparatively lower thrust, I needed to tweakscale the engine to a giant size to accelerate a 21,360 metric ton ship at good speed. While I didn’t do a full test, I believe the ship could easily reach Jool in under 150 days, being even more efficient than even the VISTA engine.


The spacecraft did not have to initiate it's orbit insertion maneuver a day early, thanks to the thrust

The VISTA/Daedalus engines are incredibly efficient and feature good thrust, especially in the case of the VISTA (more than the real concept, but not by an extreme amount like with the MPD).



In this screenshot the VISTA-powered ship is maneuvering to intercept Tylo.

Due to fuels they consume, both ships would be rather expensive and the designs requires large fuel tanks. Additionally, an immense neutron flux is created, essentially requiring space tugs to push the spaceship away from any station to avoid killing anyone within a considerable radius.


It would be likely used on the largest of cargo ships, which will require high thrust and efficiency to travel immense distances in short time. Both would also be used on warships that would benefit from the same reasons, though potential fleets would have to be widely spaced out, unless the armor proves to protect the ships quite well. Daedalus could conceivably used for an interstellar starship, just like the real design, which could achieve 12% of the speed of light if built.

Project Orion/Medusa Nuclear Pulse Engine “Old Boom-Boom”


Unleash the power!

A Quick Overview

In the designs we’ve examined, it appears that the better performing the design is, the more dangerous the design is. This is certainly no exception. The Orion/Medusa quite literally detonates nuclear bombs behind the ship, the blast pushing a thick pusher plate, thrusting the ship forward.


In Testing

The Orion drive produces levels of thrust that are far more than enough to get the “heavy” mass ship off the ground. The incredible thrust and efficiency allow a burn of 25 km/s to be conducted in less than an hour, letting the ship arrive at Jool in an astounding 80 days, where the ship slows easily into orbit (no day long burns unlike with other propulsion systems). The ship easily reaches Tylo with fuel to spare.

I didn’t bother with testing the Medusa, as the Orion had already proved its worth as a powerful ship.


Yes, the ship is being sent retrograde to reach Dres. It actually did so in 180 days with around 45% of its fuel left.


Combining efficiency and pure thrust, Hohmann transfers windows can be practically ignored. Even a single Orion drive should propel a 100,000 mT vessel with considerable force. Lastly, an Orion drive should be able to carry the heaviest of payloads into space from the surface.


Unfortunately, said rocket would destroy the surrounding area for quite apparent reasons. In space this would necessitate another form of propulsion to push the ships away from a space station. That propulsion would also be needed for small course adjustments, as each nuke pushes the ship far too much for a tiny change. The nukes would be expensive to produce, and environmentalists would be more than furious.



Only the largest of ships should require such powerful propulsion. Large warships requiring fast acceleration in combat may be a major user. In my opinion I don’t think tankers/freighters would need to travel so quickly. Fast travel would be important for passenger ships, but with better communication and well stocked ships, this would not be so important. As with Daedalus, large interstellar ships could use the Orion/Medusa drives to accelerate the ship to very high speeds.


While the MPD and Gas Core Reactor rockets are quite powerful, both VISTA/Daedalus and Orion/Medusa are far more so, and though expensive, these propulsion systems are very effective at delivering massive payloads to far away places in very little time.

End of Chapter III

Thanks for Reading!

Next Chapter: Small/Tiny Mass Spacecraft Propulsion Fusion Propulsion!


Edited by SaturnianBlue
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Well this is really cool.

However, I noticed something on chapter II. 

I noticed that the Closed Cycle Gas Core Engine was cited as being from KSP Interstellar, and so was the open-cycle fusion engine. However, although I may be wrong, the Gas Core is from Atomic Age and the fusion rocket is from Deep Space Exploration Vessels. I could be wrong, but maybe you got your mods jumbled?

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6 minutes ago, Kosmonaut said:

Well this is really cool.

However, I noticed something on chapter II. 

I noticed that the Closed Cycle Gas Core Engine was cited as being from KSP Interstellar, and so was the open-cycle fusion engine. However, although I may be wrong, the Gas Core is from Atomic Age and the fusion rocket is from Deep Space Exploration Vessels. I could be wrong, but maybe you got your mods jumbled?


I believe the parts come from those packs, but they are bundled with KSP Interstellar, which might cause confusion.

Edited by SaturnianBlue
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15 hours ago, SaturnianBlue said:

I believe the parts come from those packs, but they are bundled with KSP Interstellar, which might cause confusion.

Ahh. Ok. Thanks.


Also, I'm really enjoying this thread

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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.


    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"


    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.


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.

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...


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!

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!


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!


This ship carries 2500 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.


    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 (deprecated)  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.


    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…


    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 Systems (Ch. 13), then Mixing Propulsion Systems


The Old Version of the Chapter


CHAPTER 4: Propulsion for Small/Tiny Spacecraft

In the last of the main propulsion chapters, we’ll be covering small (10,000-75,000 kg), to tiny (below 10,000 kg) sized vessels. It’s a bit hard to guess what would be in this size range (though this is up to writers to decide), as tankers of this size would likely be uneconomical, which is why I will leave out the “uses” section for this chapter. Most likely is that this regime of spacecraft will be used mainly between moons and their host planet or in the inner Kerbol system.

I have chosen a 24-passenger ferry as the test subject.

While I have left out the uses section for individual engines, I've got a few ideas for this size of ship, such as: Short distance transports, drones, missiles, science vessels, communication platforms, personal craft, and tankers of low-weight materials.

Low Acceleration Thrusters

The reason for the split is that the cost will almost certainly outweigh profits for these engines, unless a cheap way of making the fuel is found. In general, these options have low thrust but high-efficiency (and use high cost fuels). Of course, the thrust is still far higher than the real-life counterpart.


VASIMIR (KSP-Interstellar Extended Version)

In Testing

While I concluded that it was a good option for mid-size ships, the large reactors needed to power the system could not be used on smaller ships, and this resulted in dismal amounts of thrust with the small reactors. It could get to Duna in good time, but the slow rate of acceleration meant that to slow into orbit around Duna, one would have to start slowing before entering the SOI!

Therefore, the VASIMIR would be best suited for the gas giants, though larger ships would ultimately do the job better in most cases.

Pulsed Inductive Thruster (Near Future Propulsion)


A Quick Overview

A form of ion thruster that uses perpendicular electric and magnetic fields to accelerate a plasma to very high velocities.

In Testing

The ship got to Duna in 80 days, and had fairly low amounts of acceleration (over 1M/s^2). However, I ran out of fuel to get into orbit, though a few hundred more m/s of Delta-V would have done the trick. Because KSP expects an insertion burn to take no time, it’s not great at calculating the actual delta-V for slow ships like this one.


I also tested the PIT on a tiny 4,500 kg probe, and it was able to achieve orbit around Ike in 97 days.


It is an efficient engine that can use a fairly low mass reactor for its electricity.



The design requires a fairly expensive reactor to power it, and the acceleration is quite poor, and the choice of fuel as argon (though real designs could use a variety of fuels) results in an incredibly expensive cost per trip, not to mention the use of a fission reactor (though beamed power is always a possibility).


 Close, but no snacks. (Around 250 M/s short of orbit)

Magnetoplasmadynamic Thruster (KSP-I Extended, NFP)


In Testing

The MPD remains a fairly viable option in this size range, though like the PIT it must burn before entry into Duna’s gravity well to achieve orbit. I used Lithium fuel, which is rather cheap in the game. Unfortunately, expensive fission/fusion reactors are required to power the engines independently.

The MPDs from Near Future Propulsion provide somewhat better thrust, at the cost of far less Isp.



All of the above engines have high-efficiency, but have poor thrust and use enormous amounts of electricity, not to mention using mostly costly fuels. These rocket engines would be better used near planets with larger gravity wells to utilize the Oberth effect.


Higher Acceleration Engines

Thermal Launch Nozzle


A Quick Overview

An option I had overlooked in previous chapters, it gets its power from the reactor, the type of which determines the efficiency and thrust.

In Testing

The TLN was able to accelerate at around ½ a G while having 11,000 m/s of delta-v, which is rather low, but the ship weighed just over 50,000 kg. In fact, this rocket could actually be used with the larger ships as well. The maximum possible efficiency appears to be around ~2300 secs, with thousands of kilonewtons of thrust possible with just the 1.25 meter variant.


The TLN has lower efficiency compared to the above engines, though still high. Secondly, the fuel has a potential to be quite expensive (I used Methane), as do the reactors.

Closed Cycle Gas Core

Tested rather extensively, this rocket system remains very potent. However, the TLN has an edge at this scale, as it is smaller and still has competitive stats.

In Testing


The ship accelerated at well over 1G (at the end, it reached 2.5 G), and pulled into Duna orbit 89 days after launch (though it is stuck in highly elliptical orbit).



These engine concepts would be split into two sections. I believe that the ships of the latter type, using more common resources and generally costing less. That said, a potential option I’ve left behind remains—the chemical rocket. As it is far cheaper than any of these options, it could potentially still remain for cheap, small craft...

If you would like to see another propulsion system, let me know!

End of Chapter IV

Thanks for Reading!

I have two ideas for next chapter: Beamed Power or Mixing Propulsion Systems. Let me know what you think should be first!




Edited by SaturnianBlue
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8 hours ago, Kosmonaut said:

Even better... 

The fallout from that spacecraft would be incredible

Although the fallout would still be less than that of an Open Cycle Gas Core, where radioactive materials are definitely in the exhaust. Of course, if a serious accident ever took place, there would probably be a fair amount of fallout...

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2 hours ago, SaturnianBlue said:

Although the fallout would still be less than that of an Open Cycle Gas Core, where radioactive materials are definitely in the exhaust. Of course, if a serious accident ever took place, there would probably be a fair amount of fallout...

Don't forget the hydrogen bombs being detonated behind the spacecraft

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