How do nuclear powered space craft generate thrust?

[JLA727]

I've heard talk of some of the probes that NASA has planned for the future.(I can't remember what the mission was) just that they said Nuclear powered and that it would be pretty fast. My question is, If's nuclear powered.how would that propell a space craft? Is it from making electriity that would power some kind of engine that makes thrust like an ION engine?? You can't make thrust directly from a nuclear powered craft can you? Sorry I don't know hardly anything about this topic but it really interests me. Thanx J.A.

 

[Drakkith]

Well, we currently already have nuclear powered spacecraft in the sense that they use the heat from a decaying radioactive power source to provide electricity for the onboard electronics.

As a source of thrust, a nuclear power source could provide the power needed to propel the fuel source. An ion drive ionizes its fuel and propels it out the engine at a very very high velocity, much higher than normal rockets do. This allows us to use less fuel, which reduces the cost and mass of the spacecraft

 

[IsometricPion]

Perhaps you are referring to http://www.nustar.caltech.edu/uploads/files/harrison_spie2010_7732_27.pdf" the Nuclear Spectroscopic Telescope Array. However, I found nothing that indicates that this telescope has a nuclear power source. It seems highly unlikely that there will be anything nuclear on this telescope since it already has a solar panel and is meant to observe x-rays (and I doubt a nearby source of high energy radiation would be conducive to this purpose). The design does not seem to call for a nuclear power source (in the schematics I didn't see anything that looked like a reactor or a thermoelectric generator).

While NASA has toyed with the idea before (ref.http://trajectory.grc.nasa.gov/aboutus/papers/AIAA-93-4170.pdf" and related concepts.

As far as producing thrust, I think one of the above ideas involves using a nuclear reactor to vaporize liquid H₂. The large change in volume and pressure cause by the vaporization and high temperatures would provide the source of thrust. On the other hand, the Project Orion involved detonating nuclear bombs behind the ship. So, there are lots of things you can do with nuclear reactions to produce propulsion (including what you proposed, though I don't know how efficient it would be).

 

[Ryan_m_b]

I haven't got much to add to IsometricPion's excellent response but I did just stumble across this proposed Russian mission to put a nuclear powered crewed vessel into Mars orbit. However like most dramatic space ventures I'm not holding my breath, the history of manned space travel since the 80s onwards has been a formulaic one that goes something along the lines of bold predictions followed by design review followed by budget cuts followed by redesign followed by cancellation followed by new bold predictions that set a later date.

The problem in my opinion is that manned space travel is not something that you can make a market out of and is hideously expensive. Therefore it requires a substantial budget of a wealthy country on a continual basis, this only occurs when significant public and political will is behind it which has been lacking for decades. What would be nice (again in my opinion) is if various space organisations were combined into a larger one that was funded my many countries at once along with significant private sector involvement. Until we've got the will to invest significant resources into manned space travel again (like in the Apollo era) I think the formula is doomed to continue.

 

[Cosmo Novice]

The problem in my opinion is that manned space travel is not something that you can make a market out of and is hideously expensive. Therefore it requires a substantial budget of a wealthy country on a continual basis, this only occurs when significant public and political will is behind it which has been lacking for decades. What would be nice (again in my opinion) is if various space organisations were combined into a larger one that was funded my many countries at once along with significant private sector involvement. Until we've got the will to invest significant resources into manned space travel again (like in the Apollo era) I think the formula is doomed to continue.

I couldn't agree more - the technical and economic requirements are immense and only a realistically resource sufficient, international effort can make any real headway. There needs to be sufficient financial reward of public motivation for governments to undertake such largescale economically demanding projects - especially in the current financial era.

 

[DaveC426913]

You might want to read up on radioisotope thermoelectric generators and radioisotope heater units. These are used on space probes for heating and for electricity.

 

[Ryan_m_b]

I couldn't agree more - the technical and economic requirements are immense and only a realistically resource sufficient, international effort can make any real headway. There needs to be sufficient financial reward of public motivation for governments to undertake such largescale economically demanding projects - especially in the current financial era.

Definitely. I've never accepted the private sector commercialisation of space argument, even with the boom in companies offering private space services it is all reliant on government spending on space. Part of the problem is that in this day and age people ask about the economic benefit for everything, I think this is a very bad thing as we are potentially in a situation where we loose sight of the kind of endeavours that mean so much more than stimulating economies.

This is why the space race was a very good thing in my opinion and I strongly hope that we may see another one soon.

 

[Astronuc]

I've heard talk of some of the probes that NASA has planned for the future.(I can't remember what the mission was) just that they said Nuclear powered and that it would be pretty fast. My question is, If's nuclear powered.how would that propell a space craft? Is it from making electriity that would power some kind of engine that makes thrust like an ION engine?? You can't make thrust directly from a nuclear powered craft can you? Sorry I don't know hardly anything about this topic but it really interests me. Thanx J.A.

For missions to Mars, there were plans to develop nuclear thermal rockets (NTR), in which hydrogen would be passed through the core and expelled through a nozzle, and for nuclear electric systems in which a compact fast reactor core would produce thermal energy which would be converted into a electricity, which would power magnetoplasmadynamic thrusters.

The NTR is direct thrust and gets higher specific impulse higher than chemical systems, but comparable thrust. It burns for a few days then cuts off while the craft coasts from Earth orbit to Martian orbit. The problem is the mass of propellant required, and that propellant must be supplied from earth.

Electric and MPD propulsion achieve higher specific impulse at lower propellant flow rate, but at the coast of thrust, so the acceleration is low, but over months.

An ideal system might be a hybrid system.

The specific power is a critical parameter to consider for a propulsion system. One wants to to maximize the specific power.

A good book on the subject is To the End of the Solar System: The Story of the Nuclear Rocket by James Dewar
https://www.amazon.com/dp/189495968X/?tag=pfamazon01-20

 

[qraal]

I've heard talk of some of the probes that NASA has planned for the future.(I can't remember what the mission was) just that they said Nuclear powered and that it would be pretty fast. My question is, If's nuclear powered.how would that propell a space craft? Is it from making electriity that would power some kind of engine that makes thrust like an ION engine?? You can't make thrust directly from a nuclear powered craft can you? Sorry I don't know hardly anything about this topic but it really interests me. Thanx J.A.

Aside from detonating small nuclear devices for high-thrust, there are two low-thrust, direct nuclear energy systems - Carlo Rubbia's electromagnetic rocket and the Fission Fragment rocket. Rubbia's design runs a very, very hot reactor (3000-5000 K) and channels the electromagnetic radiation from its glowing structure for propulsion. Basically it's a nuclear fission Photon Rocket. Such systems have very low thrust (200 N) for obscene power levels (30 GW.)

Fission fragment rockets release fission fragments for their exhaust. In theory they're as capable as fusion rockets, but fissionable materials have to be made in a form they can sustain nuclear fission in a diffuse form, or else the whole lot goes critical too quick and literally explodes.

Finally there's the http://www.npl.washington.edu/av/altvw56.html" , which I have linked to John Cramer's much more eloquent discussion. Very high performance, in theory.