Submitted by rosTopicEchoChamber t3_zxuwtv in space

I've read that in the 1960s all the way to 1990s ish, the US built and tested nuclear powered spacecraft engines, in particular the nuclear thermal rocket. They even had the idea to propel a spacecraft using nuclear explosions.

For reference, project Timberwind* built an engine with specific impulse of 1000 seconds and thrust of 441.3 kN from a 1500 kg engine. Also for reference, the Spacex Raptor engine** has a specific impulse of 363 seconds and thrust of 1810 kN from a 1600 kg engine. I've also read a bit from project rho*** which discusses several (realistic ish) sci fi engine concepts. So I'd like ask, suppose we did keep working on nuclear spacecraft propulsion and applied all the technological advancements from 1990 to today. What kind of engines would we see today? (speculatively of course) How would they perform in terms of their mass, thrust and specific impulse?







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HeebieMcJeeberson t1_j22k5c1 wrote

Maybe 20 years ago I read about a theoretical engine called a Nuclear Lightbulb. It contains basically a large quartz bulb with a cloud of gaseous uranium hexafluoride inside, compressed by air jets blowing in to make it dense enough to fission and not let it touch the bulb. The glowing ball of fissioning plasma emits intense UV, which the quartz is 100% transparent to.

Around the outside of the quartz bulb flows a stream of hydrogen gas doped with some other material (I forget what) which highly absorbs the UV, heating the hydrogen, which expands and goes out through a rocket nozzle to produce thrust.

Power - The specific impulse of this engine would be on the order of 30,000 seconds - something like 60 or 80x that of the space shuttle main engine. The guy who wrote the article gave a design weighing 3000 tons (the weight of a Saturn V), but in the nuclear rocket 1/3 of that would be cargo. A thousand tons of cargo per launch.

Safety - The plasma cloud in the bulb is self-containing, because if it gets too hot it expands, making it no longer dense enough to be critical, so it stops fissioning. The whole thing is in a chamber lined with boron or something (whatever they use in nuclear reactors to absorb neutrons). So there's no emission of radiation or radioactive material, just very hot gas. Even if the entire rocket blew up in the atmosphere it would release 2% of the radioactive material of a typical 1950s atom bomb test.

With so much cargo capacity this rocket could take a fully equipped base to Mars in one shot, along with dozens of inhabitants and provisions, in about three months. It could have a double hull containing a foot-thick layer of water, which would shield the passengers from 95% of the radiation that would hit the ship during the trip. The outer few inches would freeze in space, providing passive self-healing in case of micrometeorites, because punctures would instantly leak water and freeze.

The author mentioned another cool feature. When a rocket is launched it always has a parabolic trajectory and then does an engine burn to circularize the orbit. This circularization burn is aimed toward space, so if it were timed right it could be used to eject a small amount of nuclear waste aimed at the sun. The rocket's exhaust velocity would be sufficient to send material out of orbit on a slow trip ending at the sun. What a great way to gradually get rid of nuclear waste.

I can no longer find the original articles I read, but here's one from 2020


dern_the_hermit t1_j22zlmo wrote

> What a great way to gradually get rid of nuclear waste.

Well, for its own waste, sure, since it's already out of Earth's gravity well. For current terrestrial stuff I say we just blast it with lasers until it's whittled down to less-harmful elements. Bonus: We can do this with other toxic substances too.


HeebieMcJeeberson t1_j23042o wrote

Wow that sounds like the magic bullet the nuclear industry has been waiting for. I never even heard of "Chirped Pulse Amplification" before.


dern_the_hermit t1_j230adl wrote

It's crazy energy-intensive, so only makes sense with a very robust and non-emitting energy grid. So waste is gonna be sitting in those concrete casks for many decades yet.

Still, I favor this option over burying it.


zdakat t1_j232pk1 wrote

Guess the waste pack atomizer in Rimworld is based on a real thing then


Pirat6662001 t1_j253bhd wrote

Fusion, basically all of our future techs depend on fusion becoming an actual reality


dern_the_hermit t1_j254b45 wrote

Renewables, actually, and solar in particular. A large amount of solar installation will create an interesting paradigm: If designed around being sufficient during the annual minimum (ie- winter), seasonal variation will net a huge excess of generation in the summer. Tap some of that excess to break down harmful substances.


Blakut t1_j2387ey wrote

nuclear waste is made into something more than it is by climate activists, in reality all the dangerous waste ever produced would fit on cube the size of a football field.


HeebieMcJeeberson t1_j2395rr wrote

Yeah the thing is that it's not a cube the size of a football field, it's in thousands of containers in numerous storage locations all over, and in every place the containers have to be checked and periodically replaced or repaired. I know some people overplay the danger but it's not a trivial problem to underplay either.


ShaggysGTI t1_j23rvhj wrote


HeebieMcJeeberson t1_j264fc6 wrote

This is the story of a 1987 incident in Brazil, in which a small canister of Cesium^137 that had been left in an abandoned cancer treatment facility was found by randos who sold it to a junk dealer, who noticed it glowing blue at night and opened it. A handful of cesium chloride crystals and dust ended up being distributed to people around the community, who used it to bling their bodies and possessions. When people immediately got sick the news reached national authorities, who eventually tested over 100,000 people for exposure. Almost 250 people were highly contaminated, 4 died and 20 developed serious injuries, losing fingers and other body parts. A city block of buildings was demolished and the debris was sealed up along with cars, clothing, family possessions, etc. It was the worst radiological disaster in Brazil's history.

It's a good story about the dangers of badly managing radioactive materials, and what can happen when concentrated nuclides used in thousands of hospitals around the world are opened and handled by people who don't know what they're doing. I'm guessing somebody thought this was relevant to my statement that a total rocket failure would release 2% of the contaminants from a single typical 1950s atom bomb test (more than 2000 of which were performed worldwide).


boh_nor12 t1_j24r3ki wrote

But definitely in the size of a few foot all fields. At least for the North American WIPP site (been there in person a few times).


HeebieMcJeeberson t1_j25whne wrote

Nuclear waste depositories in America

When WIPP says "disposal" they mean "storage".


boh_nor12 t1_j26hwfd wrote

You know, that's an interesting thought.... Disposal vs storage. What classifies as "disposal?" Physically altering something? I'm going to think on this a little.

Edit: and apologies for not commenting on your link. You are correct, those are sites of commercial byproduct. From my understanding, the WIPP is only utilized for federal nuclear waste. At the moment, the US does not have a permanent geological storage/disposal facility for commercial waste. Each of those on that map are most facilities that used to have a reactor nearby.


Withstrangeaeons_ t1_j26j6n3 wrote

Yes. And I think this is kind of good - after all, why bury that much potential energy when you can just use it.


The_Illist_Physicist t1_j23drw8 wrote

It's a fairly common laser amplification technique, the lab I work in uses Chirped Pulse Amplification for a lot of our pulsed lasers.

In order to get an ultrashort pulse of light (short in the time domain) it must be made of a large spectrum of frequencies/colors (long in the spectral domain). This is essentially the Fourier transform relationship, similar to the uncertainty principle.

The problem with high energy, ultrashort pulses is that they like to burn optics. You'll toast a lens if you send a beam with enough power through it. So what you do is separate the pulse into its many colors, amplify them individually, and then recombine. It's simple yet brilliant at the same time.


Withstrangeaeons_ t1_j26i3cf wrote

We already have the magic bullet, and we've had it since the US government made nukes. Search up "nuclear waste reprocessing", but also the costs associated with it. Then Google the price to mine one kg of uranium or thorium, and you'll see why reprocessing hasn't been done yet. Sure would be a shame if the unwashed masses decided to just bury all that potential energy, though (in case it becomes more expensive to mine radioactive material), out of fear of anything having to do with radiation.


HeebieMcJeeberson t1_j27phgg wrote

If you want to go down the government rabbit hole think about thorium reactors, which would be safer and cheaper than uranium/plutonium and with much less waste. We could have had these long ago, but thorium reactors can't produce weapons-grade plutonium, which is why the research money didn't go that route.


Withstrangeaeons_ t1_j2duwzp wrote

Exactly. My take on those people's thinking:

"Say, boss, I noticed that this thing called thorium is also radioactive."

"Can it be turned into nukes?"

"Uhhhh.... It's harder, but yo-"

"Scrap it! Uranium is better for our purposes, then. Forget about thorium."


doctorcrimson t1_j2386a6 wrote

Uh, hang on, how does it stay cool? Nuclear reactors require constant cooling to prevent meltdowns, you can't just use the same materials and expect this sort of craft to not begin shooting high energy beams through the hull midflight.


Dmgfh t1_j23olzp wrote

The hydrogen being pumped around it probably doubles as coolant


doctorcrimson t1_j2465oo wrote

That checks out if there's enough space between the wall and the bulb where it is being heated to the point of becoming rocket propellant, I think this would actually work pretty well for larger rockets and cargo rockets as was stated.


Mayor__Defacto t1_j24y9ux wrote

The hydrogen being ejected is coolant and propellant at the same time.


Weazy-N420 t1_j23gw2x wrote

The water for radiation shielding & hole plugging is absolutely insane level genius I think. It is quite heavy though which could be why it’s not even considered. You’d think even a 12” layer of H2O would provide some protection.


Blakut t1_j23892g wrote

how would one prevent neutrons from totally wrecking yout shit?


HeebieMcJeeberson t1_j238pkg wrote

The casing around the thing is a neutron-absorbant boron material, the same as used in conventional reactors. Eventually the boron becomes radioactive and has to be changed, and this is the waste the author talked about ejecting toward the sun.


Makhnos_Tachanka t1_j24trec wrote

Oh that's nothing. A dusty plasma fission fragment rocket can deliver an ISP of 1-2 million seconds, using technology with already high TRLs.


HeebieMcJeeberson t1_j25z74f wrote

Thanks, this is yet another design I hadn't heard of. Here's a PDF describing it in detail. The "dusty plasma" engine does have the drawback of being unable to land due to spewing highly radioactive rocket exhaust. So for missions that involve landing it would have to carry a conventional lander with it, or an unmanned one could be sent more slowly to rendezvous near the destination.


Benway23 t1_j24wd85 wrote

Jesus fuckin chrst. That is amazing.


serialteg t1_j26h73p wrote

Is ejecting waste into the Sun a plausible solution in general?


HeebieMcJeeberson t1_j27op8z wrote

Well yeah, it would permanently remove the waste from the Earth and reduce it to indisdinguishable subatomic particles and plasma inside the sun. Adding it a little at a time to a stream of rocket exhaust with the velocity to easily reach the sun is highly plausible.

Could this damage or affect the sun somehow? No, every week the sun spits out about 1 to 20 coronal mass ejections of roughly a billion tons each. All the nuclear waste in the world amounts to about 250,000 tons, and the rocket would send maybe 100 pounds at a time toward the sun. Very tiny farts compared to a continuous series of very large hurricanes.


serialteg t1_j2c4sb3 wrote

I've theorized about that for a long time.


ArceusTheLegendary50 t1_j2fome5 wrote

>What a great way to gradually get rid of nuclear waste.

Kurzgesagt made a video on this and explains precisely why this is a terrible idea. The basic gist of it is that "what goes around comes around" is very literally the problem: aiming at the sun isn't actually very easy and there's still a good chance it'll go back to Earth.


HeebieMcJeeberson t1_j2ftpvm wrote

The Kurzgesagt video is well produced but surprisingly misleading. The drawbacks it brings up are all based on launching all of our nuclear waste into space, using present-day rockets with today's reliability levels, dedicated entirely to this one purpose, and each carrying the largest possible payload of waste. Most puzzlingly, it dismisses hitting the sun as difficult - as if it's any harder than hitting the moon, Mars, an asteroid, or any other space object we've been hitting consistently for decades. "What goes around comes around" is literally a terrible oversimplification that ignores reality.

The impracticalities the video discusses simply aren't relevant to adding a modest amount of waste to rocket exhaust as I described. But yes I agree that the strawman concept of launching nuclear waste into space on the scale described in the video would be a terrible idea.


hdufort t1_j22mrun wrote

The most badass (and probably feasible) design, in my opinion, is Zubrin's nuclear salt water rocket.,or%2020%20percent%20enriched%20uranium.


TK-741 t1_j22y2ja wrote

Imagine. 60 years of travel to Alpha Centauri. That seems so close — almost on the cusp of being feasible for us to get unmanned probes out there, even. If only we had invested in this type of tech, we could even be halfway there by now. I could have theoretically seen another star and it’s planets from satellite photos from within its solar system, in my lifetime.

It pains me to see what humanity has instead dedicated itself to. We are wasted potential, squandering all the greatness and opportunity for exploration. We could build something incredible and yet we can’t even agree on whether we should.


ShaggysGTI t1_j23s2yb wrote

I doubt we’ll ever become Star children… we’re too busy squabbling over this rock.


Diggitydave76 t1_j24jyed wrote

By the time we figure out it's in our best interests, it will be too late.


pgriz1 t1_j23zy5p wrote

Harnessing powerful technology before we learn to play nice with each other is just giving us more powerful weapons. I very much want humanity to explore the solar system and then the solar neighbourhood, but we also have to figure out how to control our baser impulses in order for that investment of time, money and effort to be positive, rather than another expansion/colonization effort based on the destruction of whatever is there already.


CoivaraPA t1_j24w5lj wrote

We will never play nice with another, its not in our nature. And competition between each other is key to human advancement


pgriz1 t1_j25oekv wrote

Then for humans to advance further, we'll need to learn to compete without destroying.


omegasix321 t1_j26pv2i wrote

Or bypass human nature altogether. After all, since when has what was natural stopped us before?


pgriz1 t1_j27dq6f wrote

If AI development results in a self-learning system that achieves self-awareness, we may find ourselves as potentially endangered species. Using human history as a dataset, it may decide that human management of affairs is lacking, and may choose to limit human influence to things that don't cause harm. And if we don't agree... Taking over the controls of water, power, transportation, and potentially even the military systems, may persuade us to play nice. But at that point, the sentience running the planet won't be human.


omegasix321 t1_j28mpaj wrote

None of that sounds like a bad thing. If the AI is smart enough to manage resources better than us, with the end goal of improving human quality of life in mind, I see no problem. Who cares what's running everything so long as things get done and the people are prospering?

Even more so if it can do it in a way that denies resources from its detractors while providing infrastructure to those that allow it to work for them. Visibly improving society as it does so. Effectively shutting down our more violent, power-hungry, and suicidally independent natures without firing a single bullet.


pgriz1 t1_j28sq3t wrote

>Who cares what's running everything so long as things get done and the people are prospering?

That's the big "if" - would such an AI put human interests high on its priority list, or will it decide that we're (ie, humanity) more trouble than it's worth and need to kept limited (or even, severely reduced). Would it decide that our concepts of rights, freedoms, opportunities are now quaint anachronisms, and coerce us to a zoo-like existence? And all that speculation is not taking into account that it may feel that humanity has not proven itself capable of self-regulation, and may decide to impose "corrective" measures to restore balance.

There are also possibilities that the human contributors to the AI development deliberately fed it "curated" examples of human behaviour which then skews the AI response to favour certain groups over others.


SubterrelProspector t1_j275yrs wrote

I saw one that said 40 years. 40-60 years though damn we could already have something going into that system.


Derringer62 t1_j232ncv wrote

It's pretty much the only true torch drive — one with both high thrust-to-weight AND high specific impulse — feasible at our current technology level. Who needs a launch window when you have enough Δv to kick in the door and enough thrust to circularize from a hyperbolic flyby? Just... the exhaust is all kinds of awful, so forget about using it in atmosphere, and even in space there might be some traffic control issues.


rosTopicEchoChamber OP t1_j23vew9 wrote

>(and probably feasible)

I personally disagree, a nuclear salt water rocket is literally a continuous explosion and nothing close has been physically built. I think most feasible rockets would be more advanced variations of nuclear thermal rocket.

Ideally a pulsed nuclear thermal rocket, which can significantly amplify the specific impulse of a nuclear thermal rocket by a factor of 2x to 7x (Isp of 2000 s to 7000 s). I think this engine is the most promising next technological development for nuclear spacecraft propulsion because it is an advancement of the already developed and tested nuclear thermal rocket.

However, in the far far future, then yes, perhaps the engineering challenges with a nuclear salt water rocket can be addressed we would have torch drives like in The Expanse.


Radioactiveglowup t1_j23cc7e wrote

The chaddest of Nuclear Thermal Rocket possible. A real fission torchdrive.


quadlord t1_j22iz6b wrote

Unfortunately, had that work progressed we would have engines with no mission to use them.

NERVA produced motors that were all but flight ready, but they had no missions to fly on. Timberwind similarly was far along but there was no use for a nuclear thermal engine, and public opinion of nuclear power was/is extremely negative. So away they went.


Perfect-Organism t1_j238h7v wrote

Nuclear thermal propulsion is controversial among designers because despite the improved thrust from the engine, the additional mass required by the engine and the rest of the payload for shielding and other things may result in a system that isn’t much better performing over a typical chemical engine.

An NTP engine uses stored liquid hydrogen, which must be very cold. The engine itself produces a lot of radiation, which heats and boils off the hydrogen before it can be used. So you have to isolate the systems with shielding. Then, depending on your mission, you need to worry about orientation to the sun and how to shield that well at the same time. It becomes a challenging thermal problem to extend the life of the LH2 long enough to the point where individual copper wires for sensors can conduct too much heat.

That all being said, NTP is seeing a comeback and systems that could be bound for Mars are under active development right now.


Reddit-runner t1_j29w8w0 wrote

Very good points.

I really don't see a way how thermal nuclear will be more ecconomally than methane rockets in the inner solar system.

Density, thermal properties, development and retail cost, maintenance, thrust, common propulsion system with landers / launch vehicles...

All this heavily favours methane propulsion systems.


TexasTokyo t1_j23s7c3 wrote

Meh, I'm still a fan of Orion. Nothing fancy and you can build it as big as you want...actually bigger is better.


dittybopper_05H t1_j23zbfz wrote

Plus, you can use the pusher plate as a shield. Once you're done thrusting, flip the craft around and fly plate-first, so any bits of dust you meet aren't going to destroy the craft.


CoivaraPA t1_j24wb6i wrote

Same, same. The biggest issue is the pusher plate, we know how to make nukes. Nothing fancy, you could build it with 70s tech


stewartm0205 t1_j22ya9c wrote

Solid core nuclear rocket could have taken us to Mars forty years ago. We built and tested them. We are going to need nuclear power to conquer the solar system.


Reddit-runner t1_j29wl7p wrote

NTR also died because of their cost, difficulty to repair them during the mission (or even after) and the volume of the propellant.


stewartm0205 t1_j2au6yp wrote

Repair? No one repairs rocket engine especially back then. And volume of propellant shouldn’t be a big deal since ISP would be two to three times H2 + O2 if you needed a high enough delta V.


Reddit-runner t1_j2ax7a8 wrote

>No one repairs rocket engine especially back then

Right. Not even after a static fire test.

But one idea was to use NTR tech in a reusable space tug. Reusability is very difficult to achieve if you can't even maintain your engine.

With that limitation NTR was confined to single use missions. Like pushing something to Mars and then getting deposited in a solar orbit.

But for such a use case NTR doesn't offer much advantage over LH2/LOX. The tanks need to be enormous, they need heavy insulation against boil-off, the NTR engines need heavy shielding, thrust is low, etc.


stewartm0205 t1_j2bs81v wrote

In space, a NTR wouldn’t need much shielding. In space, a tank wouldn’t need much insulation.


Reddit-runner t1_j2ctl6v wrote


You need heavy shielding to not irradiate the payload

And the insulation is necessary because the tanks are in constant exposure to the sun.


stewartm0205 t1_j2fin05 wrote

The reactor is at the other end of the rocket far away from the payload in the high radiation environment of space. At worse, a small block of material should be enough of a shield. The radiation will dissipate at square the distance from the reactor. Then it had to penetrate the liquid hydrogen in the tank. As for the tank, a shiny thin Mylar sheet would be enough to reflect the rays of the sun. The Vacuum of space makes for a perfect insulator.


Reddit-runner t1_j2fxmzm wrote

> The Vacuum of space makes for a perfect insulator.

Yeah, that's the problem. Do the math


downtune79 t1_j22f7w7 wrote

I'm looking forward to the responses. I personally have no idea but I would love to learn more.


ERROR_396 t1_j237t3j wrote

Just look at NASAs post-Apollo plan from the 60s


dittybopper_05H t1_j23wxd7 wrote

If we had put the money into developing Nuclear Pulse Propulsion, and insisted that propulsive uses of nuclear explosions in space would be permissible, we could have had unmanned probes fly through the closest star systems already.

Apparently the upper theoretical limit for NPP is around 10% the speed of light.

Alpha Centauri is about 4.37 light years away, so travel time would be 43.7 years. If launched at the same time as the Voyager spacecraft (ie., in 1977), a probe like that would have made the fly-by of the system in 2020. We know how to make spacecraft that last that long, as both Voyagers are still kicking and would be more capable if not hobbled by decaying RTG's as a power source. NPP allows you to have a huge number of RTG's for the "cruise" portion, and also a nuclear reactor that can be activated during the exploration phase to provide plenty of power to enable relatively high data rates back to Earth.


Triabolical_ t1_j2674pp wrote

I have a video on NASA's current NTP program and a series on a bunch of different nuclear designs. And a video on using NTP designs to build a space tug.

This area is a bit of a hobby of mine.

The problem with NTR designs is that the old projects such as NERVA weren't really designed to build real engines. They did a lot of testing and came up with something that kindof worked but still had issues.

There have been numerous designs since then and a lot of assertions about how great NTR will be because "will you look at that Isp?".

There are two big obstacles.

The first is weight. The combustion chambers in chemical rockets are mostly empty space so those engines are light, while NTR engines have heavy nuclear cores. They also require shielding to keep from irradiating the payload, and their Isp benefit comes because they use liquid hydrogen, which requires larger tanks than chemical rockets (LOX is around 15 times more dense than LH2).

The second issues is durability. Chemical engines run at temperatures up to around 3300 kelvin, but NTR are typically designed at 2700K and a lot of the NERVA versions ran closer to 2200K. The problem is that it's really hard to design a reactor that runs with a very high thermal load and holds together, but you need that high temp or you don't get the Isp that you are hoping for. The nerva designs tended to spit their insides out during full power runs; this was somewhat fixed with plating the inside of the propellant channels, but they never achieved significant full-power runs with one engine.

You will find lots of assertions that new materials and new designs will fix these issues. NASA's NTR program gives us a chance of actually answering those questions, but they've set the bar fairly low in my opinion, which improves the chances of success - actually building and maybe testing a flight reactor - which is the right goal at this point of time.


Reddit-runner t1_j29xkui wrote

Propellant volume, mass, complexity and difficulty of maintenance put NTR engines at such a disadvantageous position that it will be difficult to find missions that justifies their usage over methane engines.


Triabolical_ t1_j2a1rrp wrote

That is generally my belief - they are mostly in the "wouldn't it be great" category.

I do support the NASA program because there's an open question as to practicality of NTR engines and I think settling those kinds of questions aligns well with NASA's charter.


Zarkathan t1_j22x2ml wrote

Entry and exit to/from earth would still need to be non-nuclear. Nuclear becomes ideal with deep space travel where you can accelerate slowly but constantly - an issue we would run into is the inability to communicate with the ship once reaching a certain distance. Space is largely empty but there is still interference and tech deteriorates over time. Communication gets solved once we figure out how to use quantum entanglement to communicate.

Two forms of nuclear propulsion I've heard of are literally releasing bombs on the back end and capturing that "wave" and, more realistically, directing radioactive emission off the back as thrust (extremely slow but consistent acceleration).


rosTopicEchoChamber OP t1_j23w5rg wrote

I think eventually closed cycle nuclear propulsion would be used to exit from earth. A more advanced variation of nuclear thermal rocket with higher specific impulse and still having enough thrust would be more efficient, requiring less propellant than chemical rockets. Since its closed cycle the exhaust won't be radioactive waste.

The issue isn't with nuclear propulsion per say, but what happens if the launch sequence fail (wether its by chemical engine failure or otherwise) with a nuclear reactor (active or not).


rendakun t1_j27iju5 wrote

> Communication gets solved once we figure out how to use quantum entanglement to communicate

You cannot send meaningful information through quantum entanglement. The fact that the particles interact FTL might as well be a technicality. It's fascinating for sure though


Zarkathan t1_j27kiqx wrote

Why not? Don't entangled particles maintain opposite spin?


drmyk t1_j24jtp9 wrote

Since about 1 percent of our high end rocket missions end catastrophically, odds are we'd have a couple of very radioactive launch areas by now.


Willbilly1221 t1_j22r851 wrote

For a power supply for the ship is one thing, and somewhat a bit sketchy at that (a hypothetical of the challenger event spreading radiation across the upper atmosphere of our globe, and what those ramifications would be comes to mind). But atomic propulsion is an entire can of worms unto itself. In space i can propel my body in a space suit with a can of compressed air like computer duster. Granted not very far or for very long. The size of the reactor, combined with the size of the thruster, combined with the size of the fuel load, and ignoring the safety ramifications, makes it all one giant, overcomplicated machine long before we have considered payload, plus passengers. Not to say some smart cookie hasn’t or couldn’t come up with such a system, but if i was the pilot of an imaginary spaceship such as this, id rather prefer you send me up there with a mega sized can of computer duster.


dittybopper_05H t1_j23z2ww wrote

>a bit sketchy at that (a hypothetical of the challenger event spreading radiation across the upper atmosphere of our globe, and what those ramifications would be comes to mind).

Except that things like RTG's for space use are designed to be strong enough that a Challenger-type event wouldn't result in the release of any radioactive materials. The RTG's themselves and the General Purpose Heat Sources (GPHS) inside them are designed to withstand re-entry from low Earth orbit without any release of radioactive material.

There is no reason why a spacecraft propelled by a nuclear thermal rocket in space couldn't be designed in a similar fashion, such that the heating elements are protected until they are deployed in the engine, which wouldn't happen until the spacecraft is actually in orbit.

Or maybe just send the engine up by itself, fully assembled but inactive and in a protective case designed to permit a safe reentry, and mate it with the rest of the spacecraft once in orbit.


Takseen t1_j2437tb wrote

Makes sense. Most of our bigger spaceships will be built or at least assembled in orbit anyway.


dittybopper_05H t1_j243mri wrote

We've already been doing it for decades. Mir, the ISS, and Tiangong weren't sent up in one piece, but were assembled in orbit from component pieces.

We know how to do this already.


triffid_hunter t1_j22j7e4 wrote

Add NSWR and FFR to your reading list - that fission fragment rocket has some impressive paper specs, eg Isp of up to 100,000


earthman34 t1_j22m948 wrote

The nuclear engine concept was abandoned because the weight of the engine was massive, and because of the social and political implications of what would happen if there was a launch accident or a crash.


PiPaLiPkA t1_j23ljuj wrote

That's not really true. Nuclear thermal rocket development stopped when military funding dried up. Project NERVA was originally project ROVER which was developing NTR for the upper stage of an ICBM. In 1958 it was transferred to NASA after the launch of Sputnik as it seemed more applicable, but as rockets got larger the efficiency gained from the NTR was less relevant for ICBMs and the advent of LH2 didn't help. Obviously there was still strategic value of exploring space, but then the space race ended so there was even less need to develop it, subsequently it was cancled in 1973.


AresV92 t1_j22z5c7 wrote

I think we would see mining of asteroids by now and the use of that mined material to refuel in space and build space habitats. Nuclear engines are most useful for maneuvering in space, not during launch, since space is already full of radiation so releasing more doesn't really matter. Their downside is the added need for shielding mass on manned missions. Maybe we will see a resurgence in interest towards nuclear propulsion once we get a permanent base on the moon and/or Mars or we are moving asteroids around because then the increased efficiency really starts to matter.


Warrior096 t1_j231yvd wrote

The main issue is reaching escape velocity because nce you get there space travel is relitivley easy. I'll post more when I wake up.


Raspberry-Famous t1_j247cb3 wrote

Yeah but that means that modest mass savings on the upper stage translates into a massive savings on the lower stages.


Reddit-runner t1_j2azsdc wrote

Which doesn't make much sense if you start making your payload increasingly expensive just to get the launch mass down.

Better design a heavy lift reusable system with an "oversized" payload capacity but relatively low launch price.

If you have to shave off mass off your payload your inevitable will add billions of costs. But if you can double the mass of your payload while keeping the requirements the same your development costs gets down fourfold.

Using nuclear engines just to make the payload a few hundred kilograms lighter would the the pinnacle of ineffectiveness. Sure, kg by kg your mission might be more "efficient" but your budget has grown exponentially.

We really have to let go of the idea that we nedd to count kilograms in our mission planning. Better just add the masses of everything you need in the end and then just launch enough propellant to get you where you want to go.

By doing this we could massively increase the science per dollar we get out of every mission.


[deleted] t1_j23ebad wrote



Techutante t1_j23efc4 wrote

Somehow google was able to find this for me after I spouted out a random garble of " that book about the nuclear bombs and spaceships and alien invasions..."

AI has come for the job of the bookstore owner who people used to ask dumb questions to.


Limegem3 t1_j23vgpw wrote

i think they called it project Prometheus but the change of presidency made them cut funding


shuckster t1_j24qt6p wrote

I don’t see how we’re going to avoid developing nuclear engines.

Chemical engines are the only game in town for hoisting stuff into orbit, but once you’re there, using the same stuff for human rated interplanetary travel just seems completely wasteful.

I see us building nuclear infra with chem rockets, then finally shipping up the actual engines.


Content_Ad3604 t1_j24r4f1 wrote

Certainly great ideas indeed. The real reason we dont is because having nukes in space and being launched makes other countries paranoid but then also they can in turn do the same which makes us paranoid so... no nukes in space.


gaunt79 t1_j250c7g wrote

NTP hasn't really gone anywhere yet, but work on that line of research hasn't really stopped, either.

DARPA is due to announce its Phase 2/3 (ground validation and flight demonstration) contract award for the DRACO project anytime now. Time will tell how far that actually gets.

NASA is continuing to make slow progress on its own NTP project, though that's still entirely a drawing board exercise.


Bulky-Major6427 t1_j25bjbs wrote

I don't think it would ever happen on earth. But maybe from the moon to the rest of the solar system.


Feisty-Juan t1_j25g6ln wrote

Only reason the U.S. military gives up any weapon tech is if they’ve found something better. Look up Moscovium


stormhawk427 t1_j2615z6 wrote

We’d have a base on the moon and on Mars by now. F**king idiots in Congress.


JamesTKierkegaard t1_j26hj2r wrote

One of the biggest challenges isn't the technology, but getting it into space. Even though there have only been a handful of launch failures, by percentage it is the most dangerous form of travel (besides shark surfing, of course). Putting enough fissile material on a rocket and launching it into space has a pretty high chance of dispersion. Granted, the actual danger of that dispersion, particularly done from an isolated location, is lower than most people would expect, but public fears concerning nuclear energy, and especially critical mass nuclear, creates a political barrier that will likely never be overcome.

If we were ever to get nuclear-powered spaceships, the material will have to be mined and refined off-planet, and there are a lot of steps before we get close to that.


Withstrangeaeons_ t1_j26iz08 wrote

I'm just gonna throw this out there for the people who don't know - reprocessing is a thing.

I've been seeing a bit of discussion about nuclear waste in a few threads, and it kind of infuriates me how ignorant some are, even though I was once just as ignorant.

Google "costs of reprocessing one kilogram of depleted nuclear fuel", "cost to mine one kg of uranium", and "cost to mine one kg of thorium". Then you'll see why it hasn't been widely implemented.

Also google: "uranium in granite", "dose of radiation from a plane flight", and "radioactive material released from coal power per year".


no_name_left_to_give t1_j26rk7y wrote

The NERVA project was the closest we got. NASA was ready to build a prototype and send it up for testing and it actually had support in Congress (unlike every other non-Shuttle thing), but Nixon killed it out of spite because Congress killed the American Concorde project. Some people in Congress even tried to tie it to the Shuttle (imagine the possibilities of Shuttle launch nuclear thermal kick stage) but Nixon being the petty b*tch he was told NASA to not use the money Congress allocated for it.


stewartm0205 t1_j2brri2 wrote

A tug would have been a dumb idea. Thrust would have been sufficient for a rocket leaving orbit. A factor of 2 or 3 in ISP makes a big difference if you are going interplanetary.


Successful-Swim-3708 t1_j233c45 wrote

I am hoping for a tech race between nuclear engines and warp engines now that they finally achieved fusion.


Dismal-Philosopher-4 t1_j244pq8 wrote

I don't think history would've changed much. Nuclear energy and reactions have never stopped being researched. If anything amazing and useful to space travel had come along it would've certainly been implemented.

The fact is also that we can reach pretty much anything in the Solar system with normal propulsion anyway + non-human crafts and probes can be smaller and smaller.


CoivaraPA t1_j24wph1 wrote

Chem engines can't deliver quick travel beyond the Earth-Moon system. Six months to Mars is a joke


Nemo_Shadows t1_j24ejtu wrote

Uncontrolled Explosions especially nuclear are NOT a good Idea, it requires a controlled and responsive engine with a vessel who's structural integrity wont be compromised when directional changes are required especially under collision conditions, and there is also those little pieces of sand moving at speeds that turn them into BOMBS with the explosive capacity of a small nuclear weapon under certain conditions of impact.

E=MC^2 is the same as F=MS^2 when you get right down to it so a shielding of some type that redirects the impact instead of colliding with it.

Yesterday's Science Fiction becomes todays Science Facts if you work on it and not surprising there just might be a way.

N. Shadows


Itsyamatey t1_j24glv2 wrote

3 out of 4 species wouldn’t like this idea at all, and we would be in trouble with the galactic federation.


hawkwings t1_j235bq9 wrote

If you used most types of nuclear propulsion at low altitude, you would pollute the atmosphere. It would make sense to wait until you are past the moon before firing up your nuclear engines.


amitym t1_j237t7s wrote

I doubt the nuclear thermal concept would have advanced much beyond where they took it in the 1960s. Iirc they had pretty much nailed it. Maybe later designs improved reactor characteristics.

Anyway one of the main issues is scale. Just a single NERVA engine is in like the same mass neighborhood as the entire space shuttle orbiter. And NERVA is only good for orbital maneuvers. So to be economical, you need something ISS sized to move around, and we just haven't had anything like that. That's billions of dollars.


dittybopper_05H t1_j243gto wrote

You've got a major misconception there.

XE Prime, the last NERVA engine developed, weighed 40,000 lbs. Launch mass of a shuttle orbiter was 240,000 lbs, and it could loft 53,000 lbs to LEO. Dimensionally, you could have easily fit XE Prime in the cargo bay of a shuttle orbital vehicle.

So no, it's not "like in the same mass neighborhood". You're off by a whole order of magnitude.

Plus, we stopped development of NERVA in 1973. It is now almost 2023, fifty years later.

Today, we have advanced materials and manufacturing techniques like additive manufacturing that weren't available in the early 1970's. That means that we could make an NTR much lighter and more efficient than we could back then.


amitym t1_j245ihm wrote

I'm all for it if it's true. But from everything I've seen, 40 years of R&D after the original NERVA project netted all of a 5% increase in Iₛₚ. Sure you can make one that's ⅓ of mass, but that doesn't help much if you will still end up needing 3 of them. You know?


dittybopper_05H t1_j2531cx wrote

That's just it: There really hasn't been any actual R&D after NERVA shut down. There has been (to my knowledge, anyway) *ZERO* hardware built since the late 1960's.

Everything since then has just been paper studies.


amitym t1_j25cff8 wrote

I mean paper studies still count as "R" if not "D..."

But leaving that aside. Let's get back to the original point. There is no application for nuclear thermal propulsion right now. Everyone is all about surface-to-surface reusable transatmospheric launchers and low-earth orbit delivery. If we were ready to build something in the 50T range to act as a permanent shuttle between Earth orbit and Lunar orbit, I don't see why we wouldn't happily use NERVA as we had already developed and tested it. It seems already there. In terms of being ready for that application.


dittybopper_05H t1_j25ohpo wrote

Even the paper studies (such as they are) haven't been well-funded.

There actually are several different possible applications for NTR. Getting to Mars and back in half the time it takes by chemical rocket is a good one. Getting there and back quickly makes the problem a whole lot easier. It boils the difficulties down to ones we've largely already solved.

Even just having the ability to put a probe to, say, Uranus or Neptune without having to do a whole bunch of gravity assists, and still get there in a reasonable amount of time, is good reason. Those two planets are very unexplored, and Triton may have a subsurface ocean. But we won't really know until we go there.

Plus, even having unmanned stations on the moon (like very large radio telescopes on the far side, like Arecibo and FAST, built into craters) means we'll need to haul a bunch of stuff up to the Moon. Having NTR-propelled craft means we'll be able to send more up there, and we could refuel them in Earth orbit. When we need to retire them, send them on a trajectory into the Sun.


amitym t1_j25qr2o wrote

So what you're saying is that permanent heavy orbit to orbit shuttles are the application?


dittybopper_05H t1_j28l6lg wrote

Earth orbit to lunar orbit, sure.

But you could also also use them for other things. The engines are about twice as efficient as chemical rockets for solid core designs, and since the fuel is generally hydrogen and no oxidizer is needed, that simplifies refueling, and also means you can loft that much more fuel per launch, because hydrogen is the lightest element, all other things being equal.

But you could also use something like that for maintenance of geosynchronous satellites, something we simply don't do now. And for even higher missions. Imagine being able to service the Webb Space Telescope like we've done with the Hubble Space Telescope. Having a near-Earth tug capable of getting astronauts to the Moon and back would also allow missions like that.

I kind of get the impression that you're not really imagining the possibilities here. Kind of like looking at a Wright Flyer in 1904 and asking "What use is it?", not seeing that something like that just opens the door for further development and that the jobs will be attracted to the application.

Heh, kind of reminds me about how the "killer app" for personal computers back in the early 1980's was organizing your recipes.

In short, if you build it, creepy ghost players will emerge from the maize.


amitym t1_j2a246f wrote

No, I'm kind of making fun of you because you are saying the same things I am.


Shrike99 t1_j25jiv9 wrote

>Sure you can make one that's ⅓ of mass, but that doesn't help much if you will still end up needing 3 of them. You know

The three final engine designs in the SNTP program all had thrusts of ~45,500lbf - about 80% of NERVA's 55,500lbf, while weighing between 3000lb and 4200lb - only about a tenth of NERVA's 40,000lb.

The best all around design was probably the partial flow expander, which offered an isp of around 935s and weighed 3300lb for 45,700lb of thrust. Two of those would weigh 6600lb - only 1/6th as much as a single NERVA, while producing ~65% more thrust and ~11% better isp.


PhD_Pwnology t1_j24kwh1 wrote

It's now obsolete technology for interstellar travel. Don't want it powering anything that orbits in space so that kinda of limits where it would be useful.


christiandb t1_j25oipr wrote

we want to get to a “safer” way of getting to the stars. Currently we are strapping a controlled bomb onto our asses and shooting ourselves up into space Making that nuclear is a step in the wrong direction

instead thinking explosive, maybe looking into different methods of propulsion and lift are in order. There are examples all around us of how to use this dimension in ways that are away from fire, we have to start thinking outside the box instead of rehashing and making things more intense the previous


doctorcrimson t1_j238a1f wrote

A lot of it fell out of popularity when it became very clear that electrogravitatics theories were false.


acelaya35 t1_j247gvr wrote

OP is referencing an engine that produces actual thrust from fuel. It has nothing to do with Electrogravitics.


doctorcrimson t1_j24cjhd wrote

Yes but nuclear powered rockets and transport in general were fawned upon by generations before the 1970s. I'm just sort of alluding to the sad context of humanities shattered dreams.


simcoder t1_j22lavc wrote

I think we should limit the amount of nuclear material we put it orbit. I think RTGs are crucial for some applications and we should spend our nuclear material budget on stuff like that rather than nuclear bomb engines and the like :P


TK-741 t1_j22xbpf wrote

This seems like something that would require a few initial rocket stages based on conventional technologies for getting free of Earth’s gravity. This is something I would expect to only be used when well clear of Earth/the Moon


toodroot t1_j237ber wrote

The Russians flew a bunch of nuclear reactors in low earth orbit, for radar satellites. There were multiple accidents, one of which smeared radioactive debris all over northern Canada. One hopes someone has learned something.


dern_the_hermit t1_j22ztsz wrote

Nuclear material is great for probes sent to the outer reaches of the solar system, where A: solar becomes less effective, B: you need stronger broadcasts to transmit data, and C: the danger of errant nuclear material is cosmically unlikely.