Are nuclear engines really low thrust at sea level? Why?

[wumpus]

14 hours ago, DDE said:

Sure, but at that point system complexity and dead weight start to go out of control. A few minor additions and you can break out the nuclear-electric drive, with, what, 15 times the Isp?

It might have 15 times the Isp, but nowhere near 1/15th the thrust.  Pulsing the coolant through an open loop system appears to work well enough.  Expect any good sized spacecraft to already have a closed loop coolant system (like the ISS's that I used as the example for closed loop cooling), adding something like a nuclear plant on board will likely require increasing the power of such a thing if only thanks to heat migrating from the engine.

[mikegarrison]

never mind

Edited November 10, 2018 by mikegarrison
someone already discussed it.

[DDE]

5 hours ago, wumpus said:

It might have 15 times the Isp, but nowhere near 1/15th the thrust.  Pulsing the coolant through an open loop system appears to work well enough.  Expect any good sized spacecraft to already have a closed loop coolant system (like the ISS's that I used as the example for closed loop cooling), adding something like a nuclear plant on board will likely require increasing the power of such a thing if only thanks to heat migrating from the engine.

Plugging the cooling for a 1000 K-something system into the same loop as your 293 K habitat is highly unwise.

[Arugela]

On 10/23/2018 at 4:14 PM, Shpaget said:

Wikipedia has some data on actual NERVA engine that was built and tested

• Diameter: 10.55 meters (34.6 ft)
• Length: 43.69 meters (143.3 ft)
• Mass empty: 34,019 kilograms (74,999 lb)
• Mass full: 178,321 kilograms (393,131 lb)
• Thrust (vacuum): 333.6 kN (75,000 lbf)
• ISP (vacuum): 850 seconds (8.3 km/s)
• ISP (sea level): 380 seconds (3.7 km/s)

ISP is not bad at all, but maybe a bit heavy.

I would love .44 thrust at sea level.(380/850=26.8235..) That would be 27 thrust on the ground. That would be fantastic for landings on foreign bodies also. It would make them much more useful.

I'm going to presume the in game engine is based on being empty as it doesn't contain it's own fuel sources. 60/3tons is 20. 850/(74999lbs/2000)=22.66696889 which is very similar to thrust to weight of the in game engine.

If you reduce 27 down from the difference in thrust to weight of the engine(20/22.6669=0.8823*26.8235=23.667).So, I don't see why we can't have a 24ish thrust sea level nuke in game. It would make sense. I think that is still less than before the nerf. Or was that the number before the nerf?

I'm assuming the full weight is non radioactive fuel sources equivalent to the LF or OX in game.

Or did I do that wrong. I think I mixed thrust and ISP. That comes out the same regardless doesn't it?

Edited November 11, 2018 by Arugela