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Nuclear-Powered Rockets Get a Second Look for Travel to Mars




 
 
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  #1  
Old December 23rd 20, 11:20 PM posted to sci.space.policy
[email protected][_2_]
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Posts: 20
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars


Are nukes the future of space travel?

"For all the controversy they stir up on Earth, nuclear reactors can produce
the energy and propulsion needed to rapidly take large spacecraft to Mars
and, if desired, beyond. The idea of nuclear rocket engines dates back to the
1940s. This time around, though, plans for interplanetary missions propelled
by nuclear fission and fusion are being backed by new designs that have a
much better chance of getting off the ground.

Crucially, the nuclear engines are meant for interplanetary travel only, not for
use in the Earth’s atmosphere. Chemical rockets launch the craft out beyond
low Earth orbit. Only then does the nuclear propulsion system kick in.

The challenge has been making these nuclear engines safe and lightweight.
New fuels and reactor designs appear up to the task, as NASA is now
working with industry partners for possible future nuclear-fueled crewed
space missions. “Nuclear propulsion would be advantageous if you want to
go to Mars and back in under two years,” says Jeff Sheehy, chief engineer in
NASA’s Space Technology Mission Directorate. To enable that mission
capability, he says, “a key technology that needs to be advanced is the fuel.”"

See:

https://spectrum.ieee.org/aerospace/...travel-to-mars


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  #2  
Old December 28th 20, 03:10 PM posted to sci.space.policy
David Spain
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Posts: 2,901
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars

On 12/23/2020 6:20 PM, wrote:
“Nuclear propulsion would be advantageous if you want to
go to Mars and back in under two years,” says Jeff Sheehy, chief engineer in
NASA’s Space Technology Mission Directorate. To enable that mission
capability, he says, “a key technology that needs to be advanced is the fuel.”"


I think the key thing to keep in mind here is that by fuel they mean
what and how constructed is the fissionable material in the reactor. For
now we can forget fusion unless you are using fission-fusion-fission
bombs for propellant ala the nuclear Orion type spacecraft, which I
don't think is under serious re-think at least now with all the arms
treaties in place. So what exactly makes up the best FISSIONABLE
material, how is it constructed and clad are all research items. There
are pre-existing examples of how to build a Nuclear Thermal Rocket. In
the 1960's the NERVA project (long since defunct) developed a working
prototype rocket engine that was actually tested in the desert decades ago.

My main point is that it is important when talking about a nuclear
rocket to distinguish between FUEL (reaction-able (i.e. fissile)
material) vs. PROPELLANT. One of the easiest propellants to feed a
nuclear thermal rocket is water. Water is so handy in space it's hard to
overemphasize its importance. In fact if water is super flash heated in
a reactor it might also be possible to dissociate it and then combust
the hydrogen and oxygen gases for additional propulsion, although
chemically you are still not going to get the ISP you would from just
flashing the water into extremely high pressure steam and jetting it out
the nozzle. The other nice characteristics of water in space is that it
provides a very good radiation barrier for that cone-of-safety between
the crew compartment and the reactor, doesn't require cryogenics to
store (although it might require some heating to maintain a liquid state
at *reasonable* pressures), and can be electrolytically converted into
hydrogen and oxygen for combustion for other purposes.

The other means of nuclear propulsion is nuclear electric. Where the
reactor provides enough electricity to power an ion propulsion system
that ultimately probably also uses water as the the source propellant,
but a far far smaller quantity. Nuclear ion is low thrust but can be
sustained for a much much longer period of time, allowing to the
spacecraft to reach tremendous velocities given enough time. Sort of the
high mileage version of nuclear propulsion vs the drag racer that is
nuclear thermal. I view nuclear electric as a much much harder task,
certainly in my view more mechanically complex. Maybe a second
generation of nuclear propulsion?

Dave


  #3  
Old December 28th 20, 06:13 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars?

In article ,
says...

Are nukes the future of space travel?

"For all the controversy they stir up on Earth, nuclear reactors can produce
the energy and propulsion needed to rapidly take large spacecraft to Mars
and, if desired, beyond. The idea of nuclear rocket engines dates back to the
1940s. This time around, though, plans for interplanetary missions propelled
by nuclear fission and fusion are being backed by new designs that have a
much better chance of getting off the ground.

Crucially, the nuclear engines are meant for interplanetary travel only, not for
use in the Earth?s atmosphere. Chemical rockets launch the craft out beyond
low Earth orbit. Only then does the nuclear propulsion system kick in.

The challenge has been making these nuclear engines safe and lightweight.
New fuels and reactor designs appear up to the task, as NASA is now
working with industry partners for possible future nuclear-fueled crewed
space missions. ?Nuclear propulsion would be advantageous if you want to
go to Mars and back in under two years,? says Jeff Sheehy, chief engineer in
NASA?s Space Technology Mission Directorate. To enable that mission
capability, he says, ?a key technology that needs to be advanced is the fuel.?"

See:

https://spectrum.ieee.org/aerospace/...travel-to-mars

I'm still skeptical of nuclear propulsion the near term. Hydrogen is
the reaction mass of choice for nuclear (highest ISP), but liquid
hydrogen is bulky, requires large tanks, and must be kept at very low
cryogenic temperatures. Long term storage of liquid hydrogen in space
is a technology not yet developed.

To get the necessary hydrogen into the stage you're going to need to
perfect in orbit cryogenic refueling. That's a technology which would
also be beneficial to a conventional liquid fueled rocket engine.

In-situ propellant generation at Mars requires you find water to crack
into H2 and O2. With nuclear, most of the O2 will go to waste (you only
need so much O2 for breathing). Also, if you find water, that could
also be used to make liquid methane and liquid oxygen. Liquid methane
and liquid oxygen aren't as deeply cryogenic as hydrogen and are
therefore easier to store on Mars.

I think you see where I'm going with this. In the short term, liquid
methane and liquid oxygen based chemical propulsion is a lot easier and
can get the job done for Mars missions. That's not to say that nuclear
won't have a place in the future, I just don't want to put nuclear on
the critical path to Mars.

Jeff

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All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #4  
Old January 15th 21, 02:53 AM posted to sci.space.policy
[email protected][_2_]
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Posts: 20
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars?

Looks like the British are taking an interest in the concept too:

"Rolls-Royce and the UK Space Agency have signed an agreement to study the
application of nuclear energy in space exploration. The first contract between
the two organizations, the project will examine how nuclear energy can both
power spacecraft and be used for deep-space propulsion.

As humanity becomes more of a spacefaring species, there is a growing need
for power systems and propulsion engines that are closer in scale to their
terrestrial counterparts. There's a limit to what can be done with chemical
rockets and small robotic spacecraft operating in low-Earth orbit, and these
limits are being very rapidly reached."

See:

https://newatlas.com/space/rolls-roy...r-power-space/

  #5  
Old February 9th 21, 06:23 PM posted to sci.space.policy
Douglas Eagleson[_2_]
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Posts: 15
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars

On Monday, December 28, 2020 at 10:11:01 AM UTC-5, David Spain wrote:
On 12/23/2020 6:20 PM, wrote:
“Nuclear propulsion would be advantageous if you want to
go to Mars and back in under two years,” says Jeff Sheehy, chief engineer in
NASA’s Space Technology Mission Directorate. To enable that mission
capability, he says, “a key technology that needs to be advanced is the fuel.”"

I think the key thing to keep in mind here is that by fuel they mean
what and how constructed is the fissionable material in the reactor. For
now we can forget fusion unless you are using fission-fusion-fission
bombs for propellant ala the nuclear Orion type spacecraft, which I
don't think is under serious re-think at least now with all the arms
treaties in place. So what exactly makes up the best FISSIONABLE
material, how is it constructed and clad are all research items. There
are pre-existing examples of how to build a Nuclear Thermal Rocket. In
the 1960's the NERVA project (long since defunct) developed a working
prototype rocket engine that was actually tested in the desert decades ago.

My main point is that it is important when talking about a nuclear
rocket to distinguish between FUEL (reaction-able (i.e. fissile)
material) vs. PROPELLANT. One of the easiest propellants to feed a
nuclear thermal rocket is water. Water is so handy in space it's hard to
overemphasize its importance. In fact if water is super flash heated in
a reactor it might also be possible to dissociate it and then combust
the hydrogen and oxygen gases for additional propulsion, although
chemically you are still not going to get the ISP you would from just
flashing the water into extremely high pressure steam and jetting it out
the nozzle. The other nice characteristics of water in space is that it
provides a very good radiation barrier for that cone-of-safety between
the crew compartment and the reactor, doesn't require cryogenics to
store (although it might require some heating to maintain a liquid state
at *reasonable* pressures), and can be electrolytically converted into
hydrogen and oxygen for combustion for other purposes.

The other means of nuclear propulsion is nuclear electric. Where the
reactor provides enough electricity to power an ion propulsion system
that ultimately probably also uses water as the the source propellant,
but a far far smaller quantity. Nuclear ion is low thrust but can be
sustained for a much much longer period of time, allowing to the
spacecraft to reach tremendous velocities given enough time. Sort of the
high mileage version of nuclear propulsion vs the drag racer that is
nuclear thermal. I view nuclear electric as a much much harder task,
certainly in my view more mechanically complex. Maybe a second
generation of nuclear propulsion?

Dave



Thank you for clarifying the meaning of fuel in a reactor engine.

The nuclear engine powered aircraft designs used air as fuel.

In space a duel use fuel is as you said. Chemical fuel,
reactor thermal and/or electric boosted.

I vote for simple hydrazine plasma boosted. The reactor
design needs plasma cooling though. Radiant heating
lowers the allowed power density.

Putting some kind of radiators on the reactor is allowed.
The shield using fuel is maybe an option, but what happens
on approaching the Earth with low tanks.

Think big and have a thousand foot long ship and use
water to shield. This is human supply water. Coming back
with empty water tanks will have a lower ship mass to
return with. Lowering the engine power demands. And
the crew radiation dose. Added hydrazine shielding
is a bonus.


  #6  
Old February 9th 21, 09:13 PM posted to sci.space.policy
David Spain
external usenet poster
 
Posts: 2,901
Default Nuclear-Powered Rockets Get a Second Look for Travel to Mars

Douglas Eagleson writes:

On Monday, December 28, 2020 at 10:11:01 AM UTC-5, David Spain wrote:
On 12/23/2020 6:20 PM, wrote:
“Nuclear propulsion would be advantageous if you want to
go to Mars and back in under two years,” says Jeff Sheehy, chief engineer in
NASA’s Space Technology Mission Directorate. To enable that mission
capability, he says, “a key technology that needs to be advanced is the fuel.”"

I think the key thing to keep in mind here is that by fuel they mean
...


[explanation of Nuclear Thermal vs Nuclear Electric propulsion elided
for brevity ...]


Thank you for clarifying the meaning of fuel in a reactor engine.

The nuclear engine powered aircraft designs used air as fuel.


That would be quite a trick of transmutation. I think (again) you meant
propellant, since the heat was intended to be derived from a nuclear
fission fuel in a reactor as opposed to combustion of a
hydrocarbon-based jet fuel.

https://en.wikipedia.org/wiki/Nuclear-powered_aircraft

For a feel of what a nuclear powered jet aircraft would look like see
the uncannily weird and at the same time, semi-accurate water propelled
SST featured in the first episode of the made for TV adapatation of the
Phillip K. Dick novel, "The Man In The High Castle" (Amazon Prime
Video). Note the cooling steam coming off the engine moderators as it's
parked on the tarmac. Stay goodly distance back.... :-)

In space a duel use fuel is as you said. Chemical fuel,
reactor thermal and/or electric boosted.

I vote for simple hydrazine plasma boosted. The reactor
design needs plasma cooling though. Radiant heating
lowers the allowed power density.

Putting some kind of radiators on the reactor is allowed.
The shield using fuel is maybe an option, but what happens
on approaching the Earth with low tanks.


Well you can siphon off water from multiple tanks if you are expending
water as propellant. The cone of protection narrows as you empty tanks,
with the one closest to the crew compartment being consumed last. That
would be for nuclear thermal or NTR. Nuclear electric would use a closed
cooling system and the only time water would be expended is during
thrust. And only a very small amount comparied to NTR. The trick is
keeping the reactor cool. In the original design of the interplanetary
nuclear electric ion-propelled spaceship Discovery (2001 A Space
Odyssey), the ship had giant fins that extended away from the reactor
compartment to allow radiational cooling into space. The fins were
deleted in the final design because many thought it made the vaccum-only
spacecraft look too much like it had aerodynamic fins. An obvious
pseudo-scientific non-sequitur. Keeping the reactor far away on the
x-axis of the spacecraft helps as well. Even without the radiative fins,
I've always thought Discovery made for a pretty decent spacecraft
design.


Think big and have a thousand foot long ship and use
water to shield. This is human supply water. Coming back
with empty water tanks will have a lower ship mass to
return with. Lowering the engine power demands. And
the crew radiation dose. Added hydrazine shielding
is a bonus.


I like water because as you pointed out above it's triple
use and non-cryogenic. Propellant, bio-hydrate and a (derivative) fuel
source, assuming you have nuclear electric.

Dave
 




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