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I found a very interesting and detailed General Atomic study on nuclear pulse propulsion spaceship.
http://www.projectrho.com/public_html/r … 09vIII.pdf
In the paper there is also a 20 meter diameter 10 men spaceship for a mission in the moons of Jupiter, but I failed to find any information about the power source during the coasting. Given that in Jupiter system a solar array has to be huge, I suppose such a spaceship has to be powered by a 400-500 KW nuclear reactor, but it might be very difficult to find a place for it.
Do you have any information?
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SAFE-400 can be scaled up to provide 400kWe from 1.6MWt, but as designed and tested 4 reactors would also provide 400kWe. The cores aren't much bigger than small propane tanks, but weigh quite a bit. Figure about 1,000kg to 1,200kg per complete unit (core, some shielding, and radiators). You'd want some redundancy.
A 1MWe LENR, while perhaps not as compact as SAFE-400, would have a lower mass because it requires no shielding and fewer radiators. Even if you have to refuel the reactors every 6 to 12 months, the fuel amounts to a few kg's of material at most. If EMDrive only works as well as it works in the labs, then reasonable transit times are achievable with 1MWe, there's on radioactive power sources or debris from low yield nuclear explosions to contend with, and a craft that could carry a dozen or so people is the sort of thing that two or three SLS flights could reasonably put into orbit.
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SAFE-400 can be scaled up to provide 400kWe from 1.6MWt, but as designed and tested 4 reactors would also provide 400kWe. The cores aren't much bigger than small propane tanks, but weigh quite a bit. Figure about 1,000kg to 1,200kg per complete unit (core, some shielding, and radiators). You'd want some redundancy.
A 1MWe LENR, while perhaps not as compact as SAFE-400, would have a lower mass because it requires no shielding and fewer radiators. Even if you have to refuel the reactors every 6 to 12 months, the fuel amounts to a few kg's of material at most. If EMDrive only works as well as it works in the labs, then reasonable transit times are achievable with 1MWe, there's on radioactive power sources or debris from low yield nuclear explosions to contend with, and a craft that could carry a dozen or so people is the sort of thing that two or three SLS flights could reasonably put into orbit.
Safe 400 is enough. An Orion-drive spaceship needs it only to power life support and other systems while coasting. During propulsion she uses a few amount of shock absorber compressed gas to run a turbine with a generator. The problem is about where the reactor has to be locate: you cannot put it aft, behind the pusher plate because it would be destroyed by detonations. If you put it somewhere between the first stage shock absorbers and the second stage, it would be impossible to use a shadow shield and the reactor would have to be shielded 360 square degrees, resulting in a very heavy case. A solution may be to mount it on the nose, using a long lightweight carbon truss to distance it from the habitat. But there are no plan for it in GA documents.
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The problem we have with manned flight with a reactor is shielding mass....
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The problem we have with manned flight with a reactor is shielding mass....
Yes. In the document is indicated a main power supply for an 8 man/540 day Mars mission, which weight 3,470 kg, but it's not indicated if it is a solar array or a nuclear reactor. A life support for 8 men needs almost 20 KWe (15 KWe/man), that in a Mars mission might be suppied by a solar array, but there is also a bigger ship for a 20 man/910 day Jupiter mission, which needs almost 50 KWe, that must be supplied by a nuclear reactor.
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Why not look at a modification of the compact nuclear steam-turbine-electric plants they use in US Navy submarines? They generate multi-megawatts of power, with a demonstrated safety record unsurpassed by any other entity. For a nuclear pulse propulsion ship, the weight of the shielding is not an issue. Higher ship size and mass is just larger Isp and delta-vee.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Why not look at a modification of the compact nuclear steam-turbine-electric plants they use in US Navy submarines? They generate multi-megawatts of power, with a demonstrated safety record unsurpassed by any other entity. For a nuclear pulse propulsion ship, the weight of the shielding is not an issue. Higher ship size and mass is just larger Isp and delta-vee.
GW
Thanks GW,
Where do you put it: distanced on a truss on the top of the nose with a shadow shield or in the propulsive module with a 360 square degree shield?
Happy new year!
Last edited by Quaoar (2016-12-31 03:32:11)
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Heat engines have to get rid of waste heat. In Rankine cycles this means condensing the working fluid. If your heat engine generates 200 kW you would be looking at a heat source of around 500kW and a sink for about 300kW. That is a big radiator in space, where you cant get rid of waste heat any other way.
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Well, in the subs, they put it inside the pressure hull in its own shielded compartment, and put the steam turbine and generator and motor equipment in an ordinary engine room. Cooling in the sub just uses seawater, so Elderflower is correct: we are looking at a huge radiator somewhere. Maybe some of that heat could be put to work doing something else.
A pulse propulsion ship is a big item, so maybe the outer skin could be put to work as the radiator we need. I doubt there's enough for a big power plant, though.
Here's a really odd thought. Electricity can be produced from radioactive decay. In a pulse propulsion ship, the pusher plate is a big steel item that gets heavily irradiated. It should be fairly radioactive. I wonder if there's a way to extract at least a little electricity from that otherwise "waste" radiation?
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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You could extract heat from a pusher plate- you might have to extract heat to keep it from melting. This heat could be used to power auxiliaries using a heat engine, but you still have to radiate it away somehow. After its use in a heat engine the waste heat's temperature will be lower than the temperature of the pusher plate so it will be more difficult to radiate it away- your radiator gets bigger.
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You could extract heat from a pusher plate- you might have to extract heat to keep it from melting. This heat could be used to power auxiliaries using a heat engine, but you still have to radiate it away somehow. After its use in a heat engine the waste heat's temperature will be lower than the temperature of the pusher plate so it will be more difficult to radiate it away- your radiator gets bigger.
Project Orion study says that contact time between propellant and pusher plate is so short that heat transfer is minimal and the plate directly radiates it away between the pulses without overheating and melting. To avoid any ablation it's sufficient to spray a thin film of oil on the pusher plate between the pulses. The shock absorbers are open-cycle cooled by the same ammonia gas that propels the pulse units.
So GW suggests to put the reactor in a shielded compartment in the propulsive module and use the outer skin of the module as a radiator.
Happy new year to all
Last edited by Quaoar (2017-01-01 04:16:42)
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Use of the vehicle skin as a radiator has limitations. You have to orientate your radiator so that the sun isn't shining on it. A skin radiator would mean that the vehicle would have to be pointing at, or away from, the sun for effective heat dissipation. A separate set of panels can be arranged edge on to it. My point was that these are going to be big.
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Use of the vehicle skin as a radiator has limitations. You have to orientate your radiator so that the sun isn't shining on it. A skin radiator would mean that the vehicle would have to be pointing at, or away from, the sun for effective heat dissipation. A separate set of panels can be arranged edge on to it. My point was that these are going to be big.
An Orion spaceship is supposed to spin during coasting for artificial gravity, so radiators are a big problem: a solution may be a folding panel parallel to the spin plan or a panel fixed at 360° on the outer skin, with an electro-chromatic coating, which turns to white during isolation and black during shadow period.
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Use of the vehicle skin as a radiator has limitations. You have to orientate your radiator so that the sun isn't shining on it. A skin radiator would mean that the vehicle would have to be pointing at, or away from, the sun for effective heat dissipation. A separate set of panels can be arranged edge on to it. My point was that these are going to be big.
Which would require zone valve control to each radiator, additional cyculator pumps, temperature sensing ect to actively make it work...Other methods to expand into the sun lit side is with sun shades simula to what Sky Lab had to do.....These could also be panelized to allow for movement over sun lit sides versus deep space.....
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Panellised like venetian blinds, I assume, Spacenut. That might work but adds complication to open and close the blinds at the right times.
There may still be an issue with available radiator area. The larger the area the cooler you can run the panels and the lower the heat rejection temperature from your heat engine. This has a big effect on its peak efficiency.
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It is my understanding that a spacecraft without power gets very cold. That certainly seemed to happen on Apollo 13, even in direct sunlight.
A big Orion pulse-propulsion ship is going to have a big space inside, one big enough to put a garden park in it. Why not dump at least some of the waste heat in there by conventional convective means, to keep the living spaces comfortably warm?
Reducing the waste heat to be dumped to space reduces the size of the necessary radiator.
Any wastes that cannot be recycled will be dumped in space. Heat them up with some more of the waste heat by conventional convection, before you dump it.
Just some odd thoughts.
GW
Last edited by GW Johnson (2017-01-09 15:55:53)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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