Nuclear Powered Spacecraft

I'm sure the fuel, payload, and the engine that's about two storeys tall will all together weigh less than an average man in a spacesuit.
 
Byeman said:
no sense in risking things on flying on SLS.
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Musk doesn't do hydrogen. Less risky than Starship for now.

Right now, we have--what--three cores in the pipeline. Put a 10 year manned BEO moratorium due to Orion problems.

This could be a windfall for the DARPA NTR guys.

If you are going to do NTR---you want as much hydrogen as you can get.

As New Glenn comes on line--then kill SLS if you wish.
 
publiusr said:
1. Musk doesn't do hydrogen. Less risky than Starship for now.

2. Right now, we have--what--three cores in the pipeline. Put a 10 year manned BEO moratorium due to Orion problems.

3. This could be a windfall for the DARPA NTR guys.

4. If you are going to do NTR---you want as much hydrogen as you can get.

5. As New Glenn comes on line--then kill SLS if you wish.
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1. no, it isn't. Don't need hydrogen anyways.
2. SLS will be gone by then
3. They don't need SLS
4. Not true.
5. Just do it now.
 
Number 4 ...if you go to the expense of an NTR, you might as well have the biggest LH2 tank you can find.
 
Scott Kenny said:
Right.

And to make 0.85m/s/s on 101newtons of thrust the spaceship weighs how much?

F = m * a, 101=m*0.85, 101/0.85=m, m=118.8kg.
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Indeed, but you scale the engine and the fuel relative to the size of the ship. So for a 101kg probe and 1m/s^2 you need 59kg/day of fuel and for a 10t ship you need 5.9t of fuel.

The fuel is obviously included in that mass but the ship gets lighter as the fuel is used. Space travel requires a lot of fuel but now do the same calcs for an Isp of 450s and get back to me.

Helicity are claiming up to 160,000s Isp unless it's a misprint, and 1,000N thrust:

www.nextbigfuture.com

Helicity Space Fusion Propulsion Funded by Lockheed Martin | NextBigFuture.com

Helicity Space, a commercial space company developing in-space propulsion and power technology based on fusion power, announced an investment from Lockheed
www.nextbigfuture.com www.nextbigfuture.com

The ISP would be 7000 to 160000.

The “large” system would get to 55-1000 newtons of thruyst with 30 plasma guns and convert about 100 kilowatts into 1-2 megawatts of power. The very large systems with 170 plasma guns could reach gigawatts of power and tens of thousands of newtons of thrust.
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1715247850364.png

 
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Forest Green said:
Indeed, but you scale the engine and the fuel relative to the size of the ship. So for a 101kg probe and 1m/s^2 you need 59kg/day of fuel and for a 10t ship you need 5.9t of fuel.
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You're talking a 12 day mission and the launch weight doesn't have mass for 12 days.

Do you see the problem?
 
Scott Kenny said:
You're talking a 12 day mission and the launch weight doesn't have mass for 12 days.

Do you see the problem?
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I would agree for the 15,000s Isp Pulsar design. You get ~1 day acceleration at 1m/s at best. Start mass 129.5% of average mass, finish mass 70.5%. With the 160,000s Isp of the Helicity design, then you can get nearly 11 days with the same mass of fuel. But hey, 86.4km/s or 864km/s is still a shed load better than the 11km/s you get with LH2/LOx.

It's 140m miles to Mars, or 224m km. 86.4km/s gets you there in 30 days theoretically.

224m / (86.4 x 3600 x 24)
 
Bimodal NTR gets you there in 45 days:
www.nasa.gov

New Class of Bimodal NTP/NEP with a Wave Rotor Topping Cycle Enabling Fast Transit to Mars - NASA

Nuclear Thermal Propulsion (NTP) is identified as the preferred propulsion technology for manned missions throughout the solar system. The
www.nasa.gov www.nasa.gov
www.nextbigfuture.com

Optimized Nuclear Thermal Rocket for 45 Days to Mars | NextBigFuture.com

Nuclear Thermal Propulsion (NTP) is the preferred propulsion technology for manned missions throughout the solar system. The state-of-the-art NTP cycle is
www.nextbigfuture.com www.nextbigfuture.com

More

If Helicity isn't blowing smoke---then use theirs for gas/ice giants and such.

NTRs are good enough for Mars, chemical for Luna.
 
160,000 Isp and 1,000 N is frankly insane numbers but similar to fission fragment rockets.

Ammonia is good especially if you get hot enough to dissociate molecules, methane is even better as you get more hydrogen atoms and a lighter carbon atom. Water is the worst of the 3 but it is the easiest to find and work with. Lithium is also an option.
 
publiusr said:
Bimodal NTR gets you there in 45 days:
www.nasa.gov

New Class of Bimodal NTP/NEP with a Wave Rotor Topping Cycle Enabling Fast Transit to Mars - NASA

Nuclear Thermal Propulsion (NTP) is identified as the preferred propulsion technology for manned missions throughout the solar system. The
www.nasa.gov www.nasa.gov
www.nextbigfuture.com

Optimized Nuclear Thermal Rocket for 45 Days to Mars | NextBigFuture.com

Nuclear Thermal Propulsion (NTP) is the preferred propulsion technology for manned missions throughout the solar system. The state-of-the-art NTP cycle is
www.nextbigfuture.com www.nextbigfuture.com

More

If Helicity isn't blowing smoke---then use theirs for gas/ice giants and such.

NTRs are good enough for Mars, chemical for Luna.
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How is an engine with less than a quarter of the Isp only taking 50% longer than one with 15,000?

A novel Wave Rotor (WR) topping cycle is proposed that promises to deliver similar thrust as NERVA class NTP propulsion, but with Isp in the 1400-2000 second range. Coupled with an NEP cycle, the duty cycle Isp can further be increased (1800-4000 seconds) with minimal addition of dry mass.
Click to expand...
 
Stan Borowski might be the one to ask.

The first time I heard of an NTR/NEP combo I figured it would limp back empty under NEP after dropping off astronauts.

Rubbia thinks it could take two weeks:

To Mars in Two Weeks?

www.scientificamerican.com www.scientificamerican.com

NTR/NEP combos might be best for power generation.....less of a stretch than Fusion.

When Rubbia first mentioned Am 242, we didn't have the technology level we do now.

Time for a revisit?
 
Desertfox said:
Isp is fuel efficiency, it has nothing to do with time. Thrust is what determines how fast you get there.
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Scott Kenny said:
Significantly more thrust.
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That gives faster acceleration but you still only get a delta V proportional to the Isp for a given mass of fuel, quarter the Isp with X kg of propellant gives quarter the delta V. It only takes 1 day of acceleration with the 15,000s Isp fusion example to reach a speed that gets to Mars in 30 days. Some of Helicity's designs make similar thrust to NTPs but with a much greater Isp.

1715416707673.png

publiusr said:
Stan Borowski might be the one to ask.

The first time I heard of an NTR/NEP combo I figured it would limp back empty under NEP after dropping off astronauts.

Rubbia thinks it could take two weeks:

To Mars in Two Weeks?

www.scientificamerican.com www.scientificamerican.com

NTR/NEP combos might be best for power generation.....less of a stretch than Fusion.

When Rubbia first mentioned Am 242, we didn't have the technology level we do now.

Time for a revisit?
Click to expand...
Am 242 is an order of magnitude or two more expensive than Pu 239.
 
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Michel Van said:
Bad News
Zubrin Nuclear Salt water rocket doesn't work
this analysis find that a modestly sized design leaks so many neutrons,
once the water starts boiling that it becomes impossible to reach the gigawatts needed for drive to work.
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Ouch, that sucks!

On the other hand, it's good that NSWRs don't work, because the only useful place for them as described by Zubrin is in ludicrous-speed missiles. 50 tons of missile boosting at some 283m/s/s at start, burnout at some 3000sec later at 422m/s/s. God have mercy on whatever it hits.

And now I need to pester some Navy Nukes, to see if they can translate this into something that I can understand. The math involved is WAY over my head.
 
From my understanding, anything above critical is an increasing reaction rate, which is bad/dangerous in power generation.
 
Scott Kenny said:
And "prompt supercritical" = kaboom.
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As far as I understand the NSWR, that's the point.

A rocket engine is a barely-contained kaboom. A nuclear reaction creates a high-energy kaboom. So, barely containing it creates a really high performance rocket.

How to actually do this is left as an exercise for the reader. Preferably one conducted on a different celestial body.
 
Yellow Palace said:
As far as I understand the NSWR, that's the point.

A rocket engine is a barely-contained kaboom. A nuclear reaction creates a high-energy kaboom. So, barely containing it creates a really high performance rocket.

How to actually do this is left as an exercise for the reader. Preferably one conducted on a different celestial body.
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In the sense that it's a development off of the Orion pulsed nuclear blast drive, yes.

But you cannot make a continuously-detonating nuclear blast, even using uranium saltwater.
 
publiusr said:
Maybe squirt-gun pulses?
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Then you need a pusher plate or whatever to absorb the pulses.

The idea with the NSWR was that it provided truly continuous thrust so didn't need the heavy pusher plate and shock absorbers.
 
I was thinking really heavy ablatives…old transmissions have intricate channels—I was thinking, as layer were lost to ablation, new “holes” would be uncovered.
 

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