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Last time somebody posted some numbers of specific masses on a thread. I was looking for tht and reacted. It was really off-topic in that thread, so yet I can´t found. It was about specific masses and efficiency of solar panels.
Who can help?
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It depends on the technology you assume. There was an article yesterday on Space.com or Spacedaily.com that spoke of new solar cells that are 50% efficient converting sunlight into electricity. Six months ago an article spoke about new technology that yields 40%. The best you can get now is 33% but it's really 25% after a few months because the cells degrade.
The Helios aircraft had the 33% solar cells all over its wings and the wings massed about 3.5 kg per square meter, I think. But some of that mass was the structure of the wings. I think Robert Dyck has cited 2 kg per square meter on this Forum.
Mars Direct assumed the old 10-12% efficient solar cells and concluded that solar power was way too heavy for a Mars mission. But if 50% solar cells are really possible and they mass 2 kg/m2, then 1 square meter--2 kg--can give a peak power output of 250 watts. Divide that by pi (3.14) and you get the average power output over an entire 24.6 hour day: about 80 watts, or 40 watts per kilogram. If you need 100 kw of power, that's 2,500 kg of panels, which is less than the projected mass of a nuclear reactor! But you still have to deal with dust storms and such.
So right now I don't think solar can compete with reactors, but it might in twenty years.
-- RobS
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Ooo...I like!
Let's just assume that the best we can get to Mars is the 25% efficient kind. For 100kw it would weigh 5 tonnes. That is about as much as Zubrin's proposed reactor.
Using solar could get us to Mars quicker by avoiding any regulations against nukes in space, not to mention the development time.
Since the solar panels would be primarily engaged in fuel production for the ERV, we wouldn't need to send any extra batteries (just enough for emergencies). Instead of charging a battery the panels could just keep topping off the methane and oxygen tanks.
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So right now I don't think solar can compete with reactors, but it might in twenty years.
Dont forget that reactors will be improving also. And since the reactors are more complex and less efficient, they should have more room for improvement.
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Martian solar cells would have to produce more energy than 100kW to compete with a 100kW reactor...
-Mars gets about 1/3rd of the sunlight as on Earth, cutting the efficency severely.
-Solar cells don't operate at night, requiring a powerful, heavy and robust energy storage system to get you through the frigid night.
-Since they need storage, you have to produce the energy for the storage and for mission demands during the day, which will increase the wattage needed considerably (perhaps double).
-Storage systems don't have that great an efficency... batteries, fuel cells, and flywheels have energy loss going and coming that a nuclear system would not. More things to go fatally wrong.
-Nuclear system like a SAFE-300 NaK/He cooled reactor can hit 33% efficency in theory, which means a 100kW electric reactor makes 200kW in heat which could be used to catalyticly make rocket fuel or otherwise supplant electric means for heating.
-Nuclear systems will work even if you have a year-long dust storm, no problem.
Advantage: Nuclear. And the "regulatory headache" will be a small issue... a reactor fueled with U235 is not substantially radioactive until after its activated, and would be an even smaller health threat than Cassini's Plutonium RTGs. The science will prevail over the enviro-nuts without too much trouble I think.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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