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From the comment section:
I wrote to Ad Astra some months back and asked if they could use oxygen as a fuel, and the response I got was yes. The microwave heating process works for pretty much anything as long as the frequency is tuned for the fuel chosen.
Seems like the flexibility in fuel use is a plus for this type of propulsion.
It uses less fuel, that's a plus.
The minus appears to be getting rid of all that heat.
Bob Zubrin has been very critical of VASIMR.
quote:
No electric propulsion system — neither the inferior VASIMR nor its superior ion-drive competitors — can achieve a quick transit to Mars, because the thrust-to-weight ratio of any realistic power system (even without a payload) is much too low. If generous but potentially realistic numbers are assumed (50 watts per kilogram), Chang Diaz’s hypothetical 200,000-kilowatt nuclear electric spaceship would have a launch mass of 7,700 metric tons, including 4,000 tons of very expensive and very radioactive high-technology reactor system hardware requiring maintenance support from a virtual parallel universe of futuristic orbital infrastructure. Yet it would still get to Mars no quicker than the 6-month transit executed by the Mars Odyssey spacecraft using chemical propulsion in 2001, and which could be readily accomplished by a human crew launched directly to Mars by a heavy-lift booster no more advanced than the (140-ton-to-orbit) Saturn 5 employed to send astronauts to the Moon in the 1960s.
If VASIMR is a hoax, it is just another example of mismanagement of the space program.
I get the feeling that politics is playing too much of a role in space policy. One administration proposes and develops a technology, then the next administration junks it. The back and forth between administrations is very damaging towards any long term goal of achieving anything worthwhile in space.
Update:
The 50 watt per kilogram mentioned in the Zubrin quote puzzles me. A 100 MW LFTR is claimed to fit on a flat bed truck. If that's true, it would unlikely to weigh more than 100,000 lbs, or about 45k kilograms. Let's just say for the sake of argument that the entire thing, including all fuel and so forth, could give you a 50 MW for 50k kilograms. That's 1000 watts per kilogram!
Something doesn't square here and I just don't get it. If you could put up a LFTR in space, as I mentioned in an earlier post, the VASIMR power requirements could be met. Dissipating the heat is another question.
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