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NASA Wants to Send Nuclear Rockets to the Moon and Mars

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Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#11

Post by toxican »

typeformer wrote: post #9

UFO's are real, the government just admitted it (someday they may even admit recovered ET craft), and yet the media is failing so hard at diving in deeper. Until the headline is "NASA now has working vehicles than that can warp spacetime" I just can't be bothered to get excited.

They admitted to encountering the literal definition of UFO -- "Unidentified Flying Object", which in no way at all proves or even suggests alien activity. If you want to get annoyed with the media, direct it at them convincing people that "UFO" = aliens

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#12

Post by everdev »

typeformer wrote: post #9

UFO's are real, the government just admitted it (someday they may even admit recovered ET craft), and yet the media is failing so hard at diving in deeper. Until the headline is "NASA now has working vehicles than that can warp spacetime" I just can't be bothered to get excited.

Unidentified != Alien

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#13

Post by logfromblammo »

Arrezz wrote: post #2

How big is the added risk of toxic waste? I'm not sure how much waste is produced in relation to propulsion energy given but it must be quite small? And I imagine that during travel in space you could just dump that waste out into space considering the vastness of it all.

The risk is that in a catastrophic launch failure (read: exploded rocket), the radioactive materials could be dispersed downrange.

The solution--if that's really a problem--is to use the same escape systems used for crewed launches to eject the nuclear fuel with a parachute and emergency beacon, and keep it all inside a durable shielded container until the craft needs to start up the nuclear engine.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#14

Post by ianai »

Symmetry wrote: post #10
Arrezz wrote: post #2

How big is the added risk of toxic waste? I'm not sure how much waste is produced in relation to propulsion energy given but it must be quite small? And I imagine that during travel in space you could just dump that waste out into space considering the vastness of it all.

Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reactor stop working. Conventional reactors breed a bit of plutonium too as U238 captures neutrons but most aerospace reactors want to be as light as possible and so use highly enriched Uranium. So after your trip the engine will be quite radioactive but, as you poin…

I’m increasingly of the opinion that nuclear for space should be mined and built in space. Just launch the infrastructure needed to bootstrap the process.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#15

Post by logfromblammo »

everdev wrote: post #12
typeformer wrote: post #9

UFO's are real, the government just admitted it (someday they may even admit recovered ET craft), and yet the media is failing so hard at diving in deeper. Until the headline is "NASA now has working vehicles than that can warp spacetime" I just can't be bothered to get excited.

Unidentified != Alien

UFO = ( classified human-built experimental aircraft | meteorological oddity | optical illusion | camera malfunction | intentional hoax ) & !( extraterrestrial artifact )

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#16

Post by Robotbeat »

api wrote: post #3
Arrezz wrote: post #2

How big is the added risk of toxic waste? I'm not sure how much waste is produced in relation to propulsion energy given but it must be quite small? And I imagine that during travel in space you could just dump that waste out into space considering the vastness of it all.

I don't know for certain but I'm fairly sure that the idea is that you don't activate the reactor until it's in space. Before a reactor is turned on the fuels are less radioactive. It's once you turn it on that radioactivity increases dramatically and you get all the nasty decay products and such. So not zero but not as much as you might think. Personally I don't like the idea. Environmental concerns are real, but th…

Why is this downvoted? This is informative and (in my opinion) basically correct.

And while I agree that in the near term, refueling via chemical rockets is a far cheaper (and even higher performance) way of solving this problem, I do support the research because someday we'll want to go even beyond refueling of chemical rockets. When you get REALLY high transfer times between Earth and Mars, the higher Isp makes a significant difference.

To explain: Conventionally, it takes about 6-8 months to get to Mars. Nuclear thermal rockets can shorten this time for the same mass in LEO to like 3 or 4 months. HOWEVER, agreeing with what api said, you can get the same exact speedup by using refueling with conventional rockets (and aerocapture/braking/direct-entry). It increases the required mass in LEO, but if you have cheap (especially reusable) rockets, then cost to launch more mass to LEO is not a major factor compared to the cost of a nuclear thermal rocket. And this is exactly what SpaceX has proposed: (see slides 19 through 22) http://www.spacex.com/sites/spacex/files/making_life_multipl...

But the Isp (exhaust velocity) advantage is maintained. The rocket equation is exponential: mass full = (empty mass)*e^((mission delta-v)/(exhaust velocity))

So eventually, when mission delta v is much higher than exhaust velocity, the mass ratio explodes. So a factor of 2 improvement in Isp is worth the extra cost, even if you have reusable rockets. The exponential curve eventually beats even the cheap, brute-force approach, if you want transfer times of on the order of 1 month.

It's also the kind of work NASA should be doing. Private industry is doing a really good job reducing the cost to orbit, so NASA can focus on these longer-term problems.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#17

Post by Bud »

ianai wrote: post #14
Symmetry wrote: post #10

Earlier quoted context omitted.

Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reactor stop working. Conventional reactors breed a bit of plutonium too as U238 captures neutrons but most aerospace reactors want to be as light as possible and so use highly enriched Uranium. So after your trip the engine will be quite radioactive but, as you poin…

I’m increasingly of the opinion that nuclear for space should be mined and built in space. Just launch the infrastructure needed to bootstrap the process.

Um, uh, um, uh...where to start?

"Mined" from where? How?

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#18

Post by GlenTheMachine »

logfromblammo wrote: post #13
Arrezz wrote: post #2

How big is the added risk of toxic waste? I'm not sure how much waste is produced in relation to propulsion energy given but it must be quite small? And I imagine that during travel in space you could just dump that waste out into space considering the vastness of it all.

The risk is that in a catastrophic launch failure (read: exploded rocket), the radioactive materials could be dispersed downrange. The solution--if that's really a problem--is to use the same escape systems used for crewed launches to eject the nuclear fuel with a parachute and emergency beacon, and keep it all inside a durable shielded container until the craft needs to start up the nuclear engine.

Effectively, they already do that. Although the United States doesn't launch reactors, we do on occasion launch radioisotope thermoelectric generators (RTGs). These use a core of sub-critical plutonium surrounded by thermocouples, which turn the heat into electricity. These are used for probes going to the outer solar system, where solar panels aren't effective enough.

Anyway - there is certainly a concern with the plutonium in RTGs being dispersed by a launch failure. The engineering that goes into designing the protective system for RTGs is extensive; they each have their own miniature heat shield, and are surrounded by iridium and carbon blocks. Tests show that they can indeed survive the explosion of the launch vehicle.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#19

Post by ianai »

Bud wrote: post #17
ianai wrote: post #14

Earlier quoted context omitted.

I’m increasingly of the opinion that nuclear for space should be mined and built in space. Just launch the infrastructure needed to bootstrap the process.

Um, uh, um, uh...where to start? "Mined" from where? How?

The moon? Asteroids? Or even just ship up unrefined ore such that a catastrophic failure can’t threaten the population.

Re: NASA Wants to Send Nuclear Rockets to the Moon and Mars

#20

Post by joelthelion »

ianai wrote: post #14
Symmetry wrote: post #10

Earlier quoted context omitted.

Whenever you're splitting Uranium atoms the results will tend to be radioactive. The results will build up in the fuel over time and eventually make the reactor stop working. Conventional reactors breed a bit of plutonium too as U238 captures neutrons but most aerospace reactors want to be as light as possible and so use highly enriched Uranium. So after your trip the engine will be quite radioactive but, as you poin…

I’m increasingly of the opinion that nuclear for space should be mined and built in space. Just launch the infrastructure needed to bootstrap the process.

"just"
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