TyMoore - 12/2/2007 2:48 PMIf we allowed peak radiator temperature of 1000 K, dissipating 600 MWt (full reactor power,) would require a total of 10,580 m^2 of radiating surface.

lambda0 - 12/2/2007 1:30 PMQuote... we use MPD. ISP is ten times lower, so exhaust mass should go up x100 in order to use the same amount of energy.Reactor power: 1MWReactor mass: ~500kgExhaust, m/s: 100000 (ISP ~10000)Exhaust, kg per sec: 0.0002 (200 mg)Thrust: 20 kg*m/s^2 (20N)Acceleration: 0.04 m/s (40mm/s)T/W ratio: 0.004Above numbers are incorrect because (a) conversion efficiency is not taken into account and (b) MPD thruster's own mass is assumed to be zero. I suppose I should divide those numbers at least by four in order to compare it to the first set of numbers (remembering that realistic numbers for both "engines" are even lower).So far it doesn't look too bad - hey, 1 centimeter/second acceleration is not so feeble. In one month it gives you ~25 km/s delta-v (and will consume 500 kg of propellant, so... less than 25km/s , but still...).Where am I wrong? How much lower are "realistic" numbers?This reactor mass is not realistic, I think it should be at least 10 or 20 times higher with current technology. And you cannot compare directly the mass of nuclear reactor that generates electricity to the mass of a nuclear thermal thruster (such as the fission fragments reactor): the first one is much heavier because of all the equipment necessary to generate electricity.

... we use MPD. ISP is ten times lower, so exhaust mass should go up x100 in order to use the same amount of energy.Reactor power: 1MWReactor mass: ~500kgExhaust, m/s: 100000 (ISP ~10000)Exhaust, kg per sec: 0.0002 (200 mg)Thrust: 20 kg*m/s^2 (20N)Acceleration: 0.04 m/s (40mm/s)T/W ratio: 0.004Above numbers are incorrect because (a) conversion efficiency is not taken into account and (b) MPD thruster's own mass is assumed to be zero. I suppose I should divide those numbers at least by four in order to compare it to the first set of numbers (remembering that realistic numbers for both "engines" are even lower).So far it doesn't look too bad - hey, 1 centimeter/second acceleration is not so feeble. In one month it gives you ~25 km/s delta-v (and will consume 500 kg of propellant, so... less than 25km/s , but still...).Where am I wrong? How much lower are "realistic" numbers?

vda - 13/2/2007 6:36 AMQuoteTyMoore - 12/2/2007 2:48 PMIf we allowed peak radiator temperature of 1000 K, dissipating 600 MWt (full reactor power,) would require a total of 10,580 m^2 of radiating surface.Why radiate full reactor power? Aren't we planning to run our reactors for electricity and/or direct production of exhaust - which takes part of power output?

Tom Ligon - 12/2/2007 3:19 PMThe p-B11 reaction produces almost all of its energy as three alpha particles, and so can, in principle, use direct conversion to produce high voltage DC, with very little waste heat.

...We'd all like a lot higher performance, but I think NERVA at least gives a benchmark to work from. Any closed cycle nuclear electric system, including reactor, power conversion, radiators, and thrusters, needs a net performance significantly better than NERVA to be worthwhile.

I am not up on state of the art of thermionic power systems, but NASA seems to like 'em. http://ntrs.nasa.gov/search.jsp?N=4294927215

Tom Ligon - 13/2/2007 3:23 PMCould a fission reactor be used to excite charged particle emissions and use that to produce electric power directly?

Tom Ligon - 14/2/2007 1:38 PM...Someone here, I think, suggested Bussard's present machine, even if it could not hit breakeven, might be a good neutron source for causing controlled fission in, for example, U235 or plutonium, or perhaps even U238. This has me wondering, if it were possible to use some strong neutron source to conduct this reaction, and if fast or at least epithermal neutrons were the goal, reactor temperatures could be substantially higher....

Tom Ligon - 13/2/2007 11:58 PMThat link didn't say much. Nice Isp, but what kind of acceleration? In-system, it would sure be nice to hit 1/3 gee or so.