New Spacex Engine has to be nuclear

[ChrisWilson68]

This is yet another of the many threads I'd put in the category of someone posting "I think X is a good idea, therefor SpaceX must be doing X soon".

No.  Just because you think X is a good idea doesn't mean it's likely SpaceX is doing it soon.

[MATTBLAK]

SpaceX or indeed anyone building a nuclear engine?! That'll be the day...

[RotoSequence]

SpaceX or indeed anyone building a nuclear engine?! That'll be the day...

Wasn't Marshall's contract with BWXT Nuclear to continue developing a nuclear thermal propulsion system renewed?

[envy887]

Doesn't nuclear propulsion schemes largely negate your specific impulse gains with dry mass growth?

I've been trying to get more information on this topic. Nuclear engines have a thrust to weight ratio that is about 1/20th that of chemical rockets. But the chemical rockets need to carry a lot more propellant mass. In the end the nuclear rocket wins in a theoretical calculation for a Mars mission

It's not just the engine mass. Hydrogen NTR used a propellant with a bulk density 14 times worse than water, which means it requires huge and heavy tanks.

[wes_wilson]

Given the current regulatory environment and Shotwells interest in eventually taking SpaceX actually interstellar, I suspect they would leapfrog Nuclear to focus on Antiproton Capture.

I agree, this. 

Or fusion. 

(And I assume OP meant fission when saying nuclear)

[MATTBLAK]

SpaceX or indeed anyone building a nuclear engine?! That'll be the day...

Wasn't Marshall's contract with BWXT Nuclear to continue developing a nuclear thermal propulsion system renewed?

I'd heard something like that. But wake me up when they actually begin testing the thing - either on the ground or in flight...

[KelvinZero]

One thing that Elon Musk has specifically mentioned is multiple depots. An obvious way to exploit high ISP drives without adding any more requirements to your Starship, whether nuclear SEP or whatever, would be to raise depots slowly to the necessary orbits. I like the idea of a highly eliptical orbit that skims past the earth, so a couple of tankers can be used sort of like boosters, getting maximum Oberth effect then detaching just before nearest approach to aerobrake and land while the ship does it's own burn, also exploiting Oberth effect.

[Norm38]

Let's say SpaceX decides they want to develop a nuclear upper stage (or interplanetary tug).  Logistically, CAN they?  Wouldn't the government (and not just the US's) throw up a bunch of red flags?  Maybe it would be similar to the way companies like GE can design/build/sell nuclear reactors? 

Not if you build it on Mars.   

[raketa]

Doesn't nuclear propulsion schemes largely negate your specific impulse gains with dry mass growth?

I've been trying to get more information on this topic. Nuclear engines have a thrust to weight ratio that is about 1/20th that of chemical rockets. But the chemical rockets need to carry a lot more propellant mass. In the end the nuclear rocket wins in a theoretical calculation for a Mars mission

It's not just the engine mass. Hydrogen NTR used a propellant with a bulk density 14 times worse than water, which means it requires huge and heavy tanks, bring number of engine to magic 42 :-)

SS will have lot of methane for landing.
Methane could be used to produce hydrogen, you need heatup to 700-1000C, to produce it.Nuclear plant could easy deliver that.
Nuclear engine using heat fuel was tested in 70, just have to be improved. Something could be done in 10 years, no break through required.
Nuclear engine could be seventh engine on SS and use only on orbit to speed up to Mars, Titan Europe .

[raketa]

Given the current regulatory environment and Shotwells interest in eventually taking SpaceX actually interstellar, I suspect they would leapfrog Nuclear to focus on Antiproton Capture.

I agree, this. 

Or fusion. 

(And I assume OP meant fission when saying nuclear)

My concept didn't required any breake through, just to improve already existing or used to exist technology.

[raketa]

This is yet another of the many threads I'd put in the category of someone posting "I think X is a good idea, therefor SpaceX must be doing X soon".

No.  Just because you think X is a good idea doesn't mean it's likely SpaceX is doing it soon.

I predict Elon call his company boring company, check my thread.
Elon wants to go behind Mars in future, without nuclear power plant will not happen. Every nuclear propostion has biggest obstacle how to radiate heat produce by reactor.
I got idea that SS skin design  to withstand heat during landing, could play additional role to be powerful radiator for nuclear power plant.
This is reason i think next step for Spacex will be go nuclear and i think to get biggest pay off from this technology is use to produce electricity propulsion.
This way you increase %5 efficiency of such source to several 10%.

[john smith 19]

There is also nuclear electric with ion thrusters

I think direct conversion of heat propulsion is  more efficient and also way to cool down reactor, that will be one the issue deal with.
Ion thruster could  use just electricity and you have to deal with 95% heat to radiate. If most heat is expel and use for propulsion, it will easier to radiate through skin of SS.

Direct conversion IE Thermionic converters are less than 10% efficient and need very high temperatures to work.  They score in terms of reliability as they have no moving parts.

Do you mean nuclear thermal, where the coolant is the propellant? Or nuclear electric, where you face the problem that you are dealing with true radiators IE heat exchangers who can only lose heat by radiation? This is a field that could be improved quite a lot. What's needed is a high efficiency emitter at the operating temperature  of the coolant. This suggests some sort of approach tuned to give a peak emission wavelength corresponding to that temperature. My instinct is little tufts of carbon fiber or pits of the right dimension (like those on an old CD) would be options.

[Lampyridae]

Nuclear engines may be fine for government-bankrolled Mars missions where they are dependent on getting access to space with Oldspace pork barrel rockets, but it's pointless for commercial space because nuclear reactors are not cheap. Especially when the alternative is Raptors coming off of a production line.

[MATTBLAK]

In-space, cryogenic fuel transfer and Propellant Depots are literally the future. Anything more advanced is the future also - but the medium-to-far future.

[ZChris13]

Doesn't nuclear propulsion schemes largely negate your specific impulse gains with dry mass growth?

I've been trying to get more information on this topic. Nuclear engines have a thrust to weight ratio that is about 1/20th that of chemical rockets. But the chemical rockets need to carry a lot more propellant mass. In the end the nuclear rocket wins in a theoretical calculation for a Mars mission.

But there are many other considerations:
1. The total cost of placing the propulsion system into space.
2. Maintaining cryogenic H2 for a long duration.
3. Materials properties when irradiated with neutrons over time.
4. Materials properties when exposed to hot H2 and hydrogen plasma over time.

I foresee SpaceX's aversion to all things elemental Hydrogen continuing into the future, even if they go down the nuclear thermal route. The bulk density is just too poor, which results in a large dry mass penalty and poor thrust to weight ratio.

Let's say SpaceX decides they want to develop a nuclear upper stage (or interplanetary tug).  Logistically, CAN they?  Wouldn't the government (and not just the US's) throw up a bunch of red flags?  Maybe it would be similar to the way companies like GE can design/build/sell nuclear reactors? 

Not if you build it on Mars.   

This really depends on the regulatory environment of Mars, which has it's own thread and I don't think revising that topic here would be a good idea.

[sevenperforce]

Nuclear is attractive, but it is not automatically the most efficient option. In addition to the many reasons you don't want to use it as a launch engine (political and public concerns as well as abysmal T/W ratio), there are significant instances where biprop chemical rockets would outperform. Let's consider a fast transit to Mars packing 4 km/s out of LEO. Since we will assume that you don't want to land on the nuke, we'll make an apples to apples comparison and talk about getting into a nominal low Martian orbit. A vehicle like Starship can aggressively aerocapture at Mars and then aerobrake in multiple passes to the desired orbit. A nuclear rocket, on the other hand, cannot. Keeping the nuke well away from your crew during burns will require some sort of long truss or heavy shielding or other superstructure that will weigh as much or more as the heat shield and control surfaces on Starship but not permit any aggressive aerocapture. So while Starship enters Martian orbit for free, a nuke must carry 1.1 km/s in additional dV to brake propulsively. Any subsequent aerobraking will be much less aggressive and take much longer than for Starship, so it actually takes more time. If you want to circularize propulsively as well, rather than spend a week aerobraking, that jumps to 2.7 km/s. Additionally, the dry mass penalty is substantial -- I will say 20% m₁ mass growth to account for both the greater tankage volume and the heavier engine. So even if lifting liquid hydrogen into LEO is no more costly than lifting methalox (it's much more expensive, both in the context of actual price and with respect to the bulk density issues), the nuke will have to be  to be pushing a specific impulse of 780 seconds just to break even. And that's without additional considerations like the cost of getting the nuke into orbit, the cost of the nuke itself, the operating lifespan, the need to service the engine and reprocess the fuel, the extra descent/ascent infrastructure you need at Mars.

It is more efficient for the moon, of course, where propulsive braking is non-negotiable. Even here, however, the descent-ascent infrastructure needs to be considered.

Where nukes become game-changing is if you end up with LH2 production capacity on the moon AND regular shuttle/tug flights between the moon and other destinations.

[Lampyridae]

Where nukes become game-changing is if you end up with LH2 production capacity on the moon AND regular shuttle/tug flights between the moon and other destinations.

...and then there's the possibility of orbital elevators on the moon, slings and even mass drivers.

[savantu]

SpaceX is working on nuclear propulsion since at least 2016. Tom Mueller involvement currently is related to nuclear propulsion.

[Nomadd]

There is also nuclear electric with ion thrusters

I think direct conversion of heat propulsion is  more efficient and also way to cool down reactor, that will be one the issue deal with.
Ion thruster could  use just electricity and you have to deal with 95% heat to radiate. If most heat is expel and use for propulsion, it will easier to radiate through skin of SS.

Direct conversion IE Thermionic converters are less than 10% efficient and need very high temperatures to work.  They score in terms of reliability as they have no moving parts.

Do you mean nuclear thermal, where the coolant is the propellant? Or nuclear electric, where you face the problem that you are dealing with true radiators IE heat exchangers who can only lose heat by radiation? This is a field that could be improved quite a lot. What's needed is a high efficiency emitter at the operating temperature  of the coolant. This suggests some sort of approach tuned to give a peak emission wavelength corresponding to that temperature. My instinct is little tufts of carbon fiber or pits of the right dimension (like those on an old CD) would be options.

Stirlings can be close to 25% efficient.

[kevindbaker2863]

This will be available in ten years