Will SpaceX ever go nuclear propulsion?

[simonbp]

I know this is quite speculative, but following reading 'The Martian' by Andy Weir, and SpaceX's push for Mars, got wondering, is there any merit to go from chemical rockets to nuclear at some point in the future?

I'm sure Elon Musk fantasizes about such a possibility; but will the AEC and the White House allow it?

The Atomic Energy Commission? Which hasn't existed since 1975? I dunno, I guess he'll also have to deal with the Department of War and NACA...

Even if SpaceX were really gungho about nuclear (which they aren't), the immediate issue would be testing. While KIWI and NERVA proved the concept in the 1960s, they were not very reliable and would require extensive testing to reach a point where you would even consider using them on a crewed vehicle. Plus, there is literally nowhere on Earth today where you would be allowed to do open-air tests of a nuclear rocket, as was done at Jackass Flats. The testing would have to be done in a closed facility, which would be regulated even more than a commercial power reactor. Which is say, by the time the paperwork is complete, you'll be dead.

And that's not even considering that are far better options. SpaceX's favored approach is very big chemical rockets and ISRU, which has no regulatory issues. Likewise for solar electric, which completely proven technology (i.e. Dawn). If you really, really want to use fission, nuclear electric is always available, and requires considerably less testing (especially if using a solid state reactor, like Los Alamos has recently been pushing).

There is very little future for nuclear thermal rockets.

[Robotbeat]

Sometime in the 22nd century, if attitudes about nuclear power haven't changed on Earth (likely would have... Unless we have more Chernobyls or nuclear wars), then Mars may be a great place to test nuclear rockets, the only place with both atmosphere and people where NIMBY isn't a concern (Mars has so much radiation on the surface, colonists will have long forgotten irrational fears of minuscule doses).

Mars also wouldn't have a century's worth of regulations for nuclear power. There'd be freedom enough to innovate without much pushback or fear.

[Vultur]

SpaceX isn't even going to use LH2/LOX for MCT, despite the better specific impulse, for reasons of practicality. I don't think there's much chance of them using NTRs.

Unfortunately, nuclear stuff is way over-regulated and irrationally feared.

[R7]

Mars may be a great place to test nuclear rockets, the only place with both atmosphere and people where NIMBY isn't a concern (Mars has so much radiation on the surface, colonists will have long forgotten irrational fears of minuscule doses).

It's generally a bad idea to spew radionuclides around where you live.

[ArbitraryConstant]

Mars has so much radiation on the surface, colonists will have long forgotten irrational fears of minuscule doses.

I fail to see how this suggests dispersing long lived fission products into the food supply.

[Vultur]

Mars may be a great place to test nuclear rockets, the only place with both atmosphere and people where NIMBY isn't a concern (Mars has so much radiation on the surface, colonists will have long forgotten irrational fears of minuscule doses).

It's generally a bad idea to spew radionuclides around where you live.

People on Mars will live in sealed environments anyway; and Mars is big, they could do it far from the colonies if the risk was enough to warrant it.

Mars has so much radiation on the surface, colonists will have long forgotten irrational fears of minuscule doses.

I fail to see how this suggests dispersing long lived fission products into the food supply.

Presumably they are growing food in sealed greenhouses; how is it getting in the food supply?

And  NERVA-types don't release radionuclides unless something goes wrong, so there probably wouldn't be that much.

nuclear power is needed no matter what given that once you want to go past mars solar power becomes very large and difficult due to diffusion of the suns light.

SpacexX isn't talking about past Mars yet, only to Mars. And solar is quite practical at Mars.

still the best even for a colony on starting given the size of a solar field

Why is that a problem? Use thin films -  you will indeed need a very big field, but the cells are so light that that's fine. No one else is using the land.

he also isn't a fan of space based solar power

That's IIRC because he considers it inefficient for producing power on Earth compared to Earth-based solar (due to converting electricity to microwaves and back). I don't think that's relevant for using the power in space.

then compare to how much space and mass is need for solar just to keep the iss running.

Solar panel technology has advanced quickly, and they're not building MCT yet. I don't think the power/weight of ISS arrays is a fair comparison.

[sheltonjr]

Besides space, Nuclear Power is another hobby of mine and I hope someday they will team up.

Nuclear power has so many advantages but due to politics and regulations, I believe we will not see it until Gen 3 of space exploration. And I believe the addition of nuclear power is what will separate Gen 2 from Gen 3.  Gen 1 being 1950-Now, Gen 2 is Nu-Space, SpaceX, Blue Origin, Planetary Resources, SNC, Bigelow.

Molten Salt Reactor (MSR) was shelved before its prime due to politics with the Nixon and Carter administrations, but is now making a come-back.

Kirk Sorenson with FLIBE Energy, Developing a small 50 MW scale LFTR reactor for the military. LFTR is a great terrestrial power reactor, but its advantages that drive some complexity is not required for space applications.

MIT, Transatomic. Is developing a MSR reactor that uses the used fuel from current light water reactors creating power and reducing nuclear waste. Added complexities of fuel processing are not easily done in space and are not required.

China has a MSR in the works. UK is also investigating them.

Terrestrial Energy of Canada is using Oil Sands Tax money to fund the development of small low enriched uranium plants that will be used for generating steam to for extracting more oil from the oil-sands. This will be pretty close to what we need for space applications.

In 10-15 years hopefully a couple of these will have operational test reactors and production reactors in operation. Regulatory issues overcome and safety proven.

Hypothetical reactor modeled after the Airfcraft Reactor Experiment.

Aircraft Reactor experiment Statistics:
Size:        3ft diameter, 3ft tall
Power:            2.5 MWatts Thermal
Fuel Temp:   1600F, 870C
Fuel:       177 lb of U235, 25 lb/ft3, 93.4% Enrichment
Fluid:      1153 lbs.
Fuel Usage:   1.5g/day at max power

I would also develop supercritical CO2 turbines and power conversion technology to reduce the size and weight of converting all that heat to electricity.

The reactor would weigh about 5-8MT for the reactor/systems and shielding mass.

The reactor would launch cold, never used with fuel in a low reactivity frozen state. Loss of payload would add almost no radioactivity to the environment. The system can be tested with non-radioactive fluids before launch.

Once loaded with fuel,  1 Kg will provide almost 2 years of power at full power generating 2.5 thermal MWatts and 1.25 MW of electrical power if required. It will not normally be at full power.

2.5 MW Thermal, would give about 1.25 MW of electrical power. The high temperature makes dumping the heat into space easier. The waste heat can also be used for heating and materials industrial uses. Examples include creating fuel. The reactor is fully self regulating. The less power that it uses the less it reacts.

1.25 MW can run 5 200MW HiPEP, VASIMR, Hall Effect thrusters will still 250KW of power for the ship.

1.25 MW of full time electricity and waste heat can help a Moon/Mars Colony or a Space Station grow at a much faster rate than using solar power.

Elon's plans are before this will be available and I believe it will be doable using Methane and solar, but it will become easier and grow quicker once nuclear in space is available.

[Robotbeat]

Yeah, ISS solar arrays have very poor specific power, like 10-25 W/kg depending on if you count the truss. It's 1980s tech. It goes to show just how far solar tech has come! Modern arrays like Ultraflex get 10x better, 150W/kg. And 1000W/kg effective has been demonstrated on IKAROS solar array (also had solar cells).

[Nindalf]

Hence, HEU is the only fuel to actually fly in space, and the only fuel anyone is even talking about flying.

HEU is certainly good, but Pu-239 and U-233 are better, and even more exotic fuels such as isotopes of Curium, Americium, and Californium are proposed for very lightweight systems.

There is zero point talking about thorium until you're on the surface and trying to build a reactor from native materials.

Thorium is also interesting from a safety and security perspective.  You can launch some minimal amount of HEU on one very careful launch, or ship it in a few separate amounts each too small to form a critical mass, and then ship unlimited amounts of thorium, which is a low-concern substance.  Once you're out on the moon, or beyond Earth orbit, there's not much worry about spills or theft, so there's little concern if you're breeding fuel out there.

While you could also launch natural or depleted uranium as your low-concern fertile material, if you want to make a small, low-maintenance breeder reactor, thorium-uranium has many advantages over uranium-plutonium, such as superior neutron economy, permitting the use of a moderator.

One of the interesting features of the thorium fuel cycle is that Pa-233 has a half-life of about a month.  So you can charge up a thorium-containing mass in the base reactor, and then you can take it away to use as an RTG and stay warm through lunar nights or long water-seeking excursions into craters of eternal darkness, or just to have a heat source for crew quarters in base (or at the other end of a deep space tether, with crew quarters at one end, and a nuclear reactor in the counterweight) with less of the radiation management concerns than a direct connection to the reactor, like cavemen taking stones from the campfire to warm their beds.

Then when it's not hot anymore, you bring it back to base and the U-233 can be leached out and separated with selective ion exhange (like a water softener), to replenish the reactor and accumulate fuel for other reactors (such as NTRs).  If you don't need the fuel surplus, you can do something like put a bismuth-containing mass in place of one of the thorium ones to make a polonium power source for longer away missions.  Similarly, separating the Pa-233 to make portable optoelectric nuclear batteries or more compact and intense warmers is also possible.  You could even run your main reactor at a low temperature, with no heat engine, as a transmutation plant, and just use the decay for power (might make sense if you can't remove the heat efficiently during, for instance, the lunar day).  Nuclear fuel is so energy dense that even this seemingly-gratuitous wastefulness would still provide excellent amounts of useful energy per increment of fuel mass shipped from Earth, and the convenience of radioisotope power sources in space is already well-established.

The point is, with a breeder reactor, you can get a lot more mileage out of the sensitive nuclear materials you launch from Earth, by letting you get similar value out of less sensitive materials, plus potential bonuses.

Molten fluoride salts are a bit spicy for a reliable space power system, though.  Of all the possible breeder reactors, I can't see LFTRs being chosen for space.

I think a moon base would be a good place to learn to do fission fragment reactors, and to breed fuel for them (possibly including the exotic fuels I mentioned before, with much lower critical masses).  Thrust-augmented dusty plasma fission fragment reactors are a very interesting form of nuclear propulsion (similar to VASIMR, but the argon is ionized and then heated further by direct impact of fission fragments, instead of having all the power go through an electrical system, so the power and thrust can be far higher).  This could realistically make trips between Earth and Mars somewhat shorter in the best case, and reasonable between "windows" defined by chemically-achievable delta-V, so there can be a steady stream of traffic rather than periodic bursts.  Similar decay-driven propulsion schemes also interesting, due to the lack of troublesome, penetrating neutron radiation, and the much lower mass of the system, which doesn't need a moderator and has no minimum critical mass.

I find this sort of advanced nuclear propulsion much more appealing than NTRs.  The specific impulse is in an entirely different class from chemical rockets, not just a little better, and it doesn't require liquid hydrogen for best performance.

If something this good becomes available, I can't imagine SpaceX would ignore it.  But you can't really plan for it at this point, either.

[Robotbeat]

Besides space, Nuclear Power is another hobby of mine and I hope someday they will team up.

Nuclear power has so many advantages but due to politics and regulations, I believe we will not see it until Gen 3 of space exploration. And I believe the addition of nuclear power is what will separate Gen 2 from Gen 3.  Gen 1 being 1950-Now, Gen 2 is Nu-Space, SpaceX, Blue Origin, Planetary Resources, SNC, Bigelow.

Molten Salt Reactor (MSR) was shelved before its prime due to politics with the Nixon and Carter administrations, but is now making a come-back.

Kirk Sorenson with FLIBE Energy, Developing a small 50 MW scale LFTR reactor for the military. LFTR is a great terrestrial power reactor, but its advantages that drive some complexity is not required for space applications.

MIT, Transatomic. Is developing a MSR reactor that uses the used fuel from current light water reactors creating power and reducing nuclear waste. Added complexities of fuel processing are not easily done in space and are not required.

China has a MSR in the works. UK is also investigating them.

Terrestrial Energy of Canada is using Oil Sands Tax money to fund the development of small low enriched uranium plants that will be used for generating steam to for extracting more oil from the oil-sands. This will be pretty close to what we need for space applications.

In 10-15 years hopefully a couple of these will have operational test reactors and production reactors in operation. Regulatory issues overcome and safety proven.

Hypothetical reactor modeled after the Airfcraft Reactor Experiment.

Aircraft Reactor experiment Statistics:
Size:        3ft diameter, 3ft tall
Power:            2.5 MWatts Thermal
Fuel Temp:   1600F, 870C
Fuel:       177 lb of U235, 25 lb/ft3, 93.4% Enrichment
Fluid:      1153 lbs.
Fuel Usage:   1.5g/day at max power

I would also develop supercritical CO2 turbines and power conversion technology to reduce the size and weight of converting all that heat to electricity.

The reactor would weigh about 5-8MT for the reactor/systems and shielding mass.

The reactor would launch cold, never used with fuel in a low reactivity frozen state. Loss of payload would add almost no radioactivity to the environment. The system can be tested with non-radioactive fluids before launch.

Once loaded with fuel,  1 Kg will provide almost 2 years of power at full power generating 2.5 thermal MWatts and 1.25 MW of electrical power if required. It will not normally be at full power.

2.5 MW Thermal, would give about 1.25 MW of electrical power. The high temperature makes dumping the heat into space easier. The waste heat can also be used for heating and materials industrial uses. Examples include creating fuel. The reactor is fully self regulating. The less power that it uses the less it reacts.

1.25 MW can run 5 200MW HiPEP, VASIMR, Hall Effect thrusters will still 250KW of power for the ship.

1.25 MW of full time electricity and waste heat can help a Moon/Mars Colony or a Space Station grow at a much faster rate than using solar power.

Elon's plans are before this will be available and I believe it will be doable using Methane and solar, but it will become easier and grow quicker once nuclear in space is available.

50% thermal to electrical efficiency? That's incredibly optimistic (unless you have multiple stages, which is really heavy). More like 20-30% because otherwise your radiator gets REALLY heavy. You are dumping the waste heat into the vacuum of space using radiative transfer only. Gets WAY easier if you can dump into a river or at least into the atmosphere (like Mars).

And heck, even if you DO get 1.25MW out of an 8mT reactor, that's only 150W/kg, about the same as EXISTING ultraflex arrays! (Near Earth, at least.) Plus, you forgot the mass for the radiator, which is big.

...in-space power is and will remain dominated by solar power until you get past Mars (I'd say all the way to Jupiter, actually). Surface power is another story (less sensitive to mass, can set up behind a hill for shielding, can dump waste heat to the atmosphere, plus solar would need batteries and would need to be over-sized by about 4 times due to shadowing, plus another 2x due to Mars distance, etc), but even there, it's not an open-and-shut case for nuclear. You can pack a LOT of thin-film solar arrays for deployment on the ground, plus lithium sulfur batteries are improving stuff a lot. Frankly, I'd use both if I were a colony planner. If I were funding-limited and wanted to get a mission started ASAP, I'd use solar + batteries, even on the ground.

In space, it's hard to see why you'd want nuclear power since you get basically a full view of the sun unobstructed night or the atmosphere (and even in low orbits, your "night" lasts for just 45 minutes and is all very predictable, so you only need a very small battery). There's a reason why NOBODY uses fission for satellites any longer, and it's not because of namby pamby environmentalists.

[ArbitraryConstant]

Hence, HEU is the only fuel to actually fly in space, and the only fuel anyone is even talking about flying.

HEU is certainly good, but Pu-239 and U-233 are better, and even more exotic fuels such as isotopes of Curium, Americium, and Californium are proposed for very lightweight systems.

Exotic fuels can work, however unlike the above HEU is safe until the reactor is turned on which is a useful property for something being launched by rocket...

If something this good becomes available, I can't imagine SpaceX would ignore it.  But you can't really plan for it at this point, either.

Yeah, it's not easy being a nuclear startup. Harder even than space launch.

[ArbitraryConstant]

Presumably they are growing food in sealed greenhouses; how is it getting in the food supply?

Via nutrients collected from outside.

Solar panel technology has advanced quickly, and they're not building MCT yet. I don't think the power/weight of ISS arrays is a fair comparison.

Indeed, the pace of innovation here is extremely high.

[macpacheco]

I just wanted to point out that there are a number of nuclear power variations. My favorite is the LFTR/VASIMR combination. Liquid Flouride Thorium Reactors were researched in the 1960's but despite very promising results, budget cuts and the decision to pursue the Fast Reactor approach killed the project. Read all about it at http://energyfromthorium.com/ This reactor promises much higher safety, low cost, and almost no long term nuclear waste. For space travel, it has advantages of relatively small size/mass but faces the same radiation challenges regards crew protection. Read about VASIMR ion drive here: http://www.adastrarocket.com/aarc/space-propulsion

I know my views are contrary to most here, but I think the best way to build the MCT is as a space-only interplanetary LFTR/VASIMR powered craft that goes from Earth Orbit to Mars Orbit and back again, never landing and being served by small rockets to deliver passengers and cargo to/from the planet's surfaces. I suspect it might be more cost effective if these orbits were above LEO, above the Van Allen belts.

Forget about nuclear rockets. I'm no nuclear engineer, but I have indeed spent hundreds of hours studying water/sodium/salt cooled nuclear reactors, neutron flux, neutron budgets (looking for a real solution to climate change, that can be quickly implemented). Bottom line, nuclear reactors are very difficult to scale down, and specially to slim down weight wise to be viable for space propulsion. So unless you are advocating some sort of single stage nuclear only rocket (where they propellant weight savings might justify a large reactor), or some very large spaceship that will have to be built in space and transit between earth and mars only (no landing), it just doesn't make sense.
A viable nuclear rocket would be a task many times more challenging than Skylon/Sabre development. Very similar to the challenges in the pre cooler slimdown, but you need to deal with neutron leakage. A nuclear reactor isn't like a flame, it needs a significant critical mass of fissile material to achieve criticality.
At some point nuclear reactors will be needed in Mars. That's almost a sure thing (solar radiation is much weaker in Mars due to distance to the Sun), but its more likely the reactor will be entirely shipped in parts as a payload instead.
I believe the BFR strategy discussed so far will make more sense instead. Make a huge rocket able to send its cargo until it land in Mars, without any refuelling, transfer between a earth to LEO and LEO to Mars separate vehicles.
Take a look at this:
  http://selenianboondocks.com/2010/06/ssto-ntr-bad/
Yes, the same Dr. Kirk Sorensen that just posted on this thread. On of the world's experts on molten salt / Thorium reactors.
I'm just an amateur of nuclear tech. Dr Sorensen actual knows stuff deep down.

[inventodoc]

If you are serious about getting people around the solar system, including Mars, then you've got to get serious about nuclear propulsion. Period. There are too many benefits. Even simple thermal nuclear rockets double ISP over hydrolox.  VASIMIR derivatives with solar might also work one day.

[Robotbeat]

If you are serious about getting people around the solar system, including Mars, then you've got to get serious about nuclear propulsion. Period. There are too many benefits. Even simple thermal nuclear rockets double ISP over hydrolox.  VASIMIR derivatives with solar might also work one day.

I've often found that whenever someone ends a statement with the word "period," they inevitably are glossing over a bunch of important issues.

For instance, the Isp is double, but you also explode the dry mass because you need much larger tanks (tank mass is proportional to volume) and NTR engines are much heavier than the otherwise-equivalent chemical rocket engine. Also, NTR is much more expensive and harder to reuse. And (a minor note), you need a LOT more hydrogen (oxygen you get included if you're doing electrolysis and nearly-free from Earth's atmosphere), which takes more energy to generate or water to mine (on the Moon or Mars or whathaveyou). But really, the increased difficulty of reuse in my mind makes NTR not worth it at all.

This is always glossed over... NASA architectures always show disposable NTR stages. Who (besides NASA with Apollo-funding-on-steroids) could possibly afford to throw away nuclear reactors like that? Chemical stages, if you do docking etc with them, aren't terribly difficult to reuse in principle, so they're a far more cost-effective solution. Not only are they much cheaper to develop, but they're surely going to be far cheaper to build per unit and almost certainly much easier to reuse plus their propellant costs (if that becomes significant) are much less and the overall SIZE of the stage will be much smaller with chemical (because liquid hydrogen is basically the least dense liquid).

Also, while I think Solar Electric Propulsion is awesome, don't become enamored with VASIMR. There are a lot of other electric propulsion solutions out there that are less complicated and even potentially higher performing, not to mention more mature and proven.

[ArbitraryConstant]

If you are serious about getting people around the solar system, including Mars, then you've got to get serious about nuclear propulsion. Period. There are too many benefits. Even simple thermal nuclear rockets double ISP over hydrolox.  VASIMIR derivatives with solar might also work one day.

The SpaceX approach for their first generation transport seems to be an abundant chemical strategy at enormous scale. This seems hard to avoid since just solving the problem of getting that number of people to orbit implies very large scale launches.

This is audacious, but I'm curious where other approaches realistically would start winning the trades if launches at this scale were possible. The scale would be huge in space terms, but still minor compared to other human activities. A ton of methane is a lot cheaper than a kilogram of nuclear reactor or solar panel.

[Robotbeat]

Actually, the scale that Elon Musk talks about (80k/year to Mars) wouldn't be miniscule compared to other human activities. It'd require an MCT construction line equivalent to a large airliner manufacturer. You can only reuse each MCT about 10-15 times over 30 years or so, so you need to be REALLY efficient at producing them, i.e. you'd need to build about 100 of them a year while refurbishing/preparing another 1000. Plus you have all the cargo required, so that could be several hundred more needing to be manufactured each year (might think of a cleverer way of getting cargo to Mars without needing a dedicated MCT for each synod), plus a bunch of BFR cores (probably can reuse them more than the MCTs, but still need to make a lot of them). Boeing produces 500 737s a year, and it's the most popular jet in the sky, so this would be nearly at that level. Which is good, because SpaceX will probably need to figure out how to reduce the cost of an MCT to about $50-100 million (not per flight, per unit), about that of a 737.
...that's not actually THAT outlandish. The cost per kg of dry mass for a 737 is about the same as for, say, a Delta IV rocket. But satellites usually are about 10x the cost per dry mass of a launch vehicle, but with mass production, that doesn't seem like an impossible gap.

...unless you're building it with a nuclear reactor in it. In that case, forget it! Won't happen. Will explode the cost and the weight. Good for Mars surface power, bad for Mars rockets.

[ArbitraryConstant]

Also, while I think Solar Electric Propulsion is awesome, don't become enamored with VASIMR. There are a lot of other electric propulsion solutions out there that are less complicated and even potentially higher performing, not to mention more mature and proven.

Honestly, with the kind of delta-v SpaceX is talking about here... I'm not sure any of the solar or nuclear electric schemes currently contemplated would come out better. All of those assume launch is expensive and leverage greatly increased specific impulse. They hope to decrease trip time by doing more delta-v than we can afford to do with chemical. But, high specific impulse has extraordinary power needs. If launch is cheap, the complexity becomes expensive, and Mars is close enough that there's no time to accrue greater total delta-v at low power.

To get around this a crazy increase in specific power is needed. Nuclear thermal has the issues you mention. Another idea might be zapping the solar panels with a monochromatic laser tuned for their band gap at hundreds of suns radiance. If this could get a few days at high thrust that might be worth it. It's hard to think of anything else that would do it even potentially that doesn't require science fiction technology.

[guckyfan]

...unless you're building it with a nuclear reactor in it. In that case, forget it! Won't happen. Will explode the cost and the weight. Good for Mars surface power, bad for Mars rockets.

Worth more than just a like.

People cling to concepts they liked before the concept of reusable BFR and MCT came up. So we see popping up cyclers, L-point deployment, nuclear. All complex and expensive and not necessary when cheap launch capacity is available.

[guckyfan]

To get around this a crazy increase in specific power is needed. Nuclear thermal has the issues you mention. Another idea might be zapping the solar panels with a monochromatic laser tuned for their band gap at hundreds of suns radiance. If this could get a few days at high thrust that might be worth it. It's hard to think of anything else that would do it even potentially that doesn't require science fiction technology.

Exotic science fiction technology will be required to build a society in the vast empty void of the asteroid belt. Not doable without fusion drives IMO. But Mars is near enough to go all chemical.