A mission trajectory study estimated that a VASIMR-powered
spacecraft could reach the red planet within 40 days if it had a
200 megawatt power source. That's 1,000 times more power than what the current
VASIMR prototype will use, although Ad Astra says that VASIMR can scale up to
higher power sources.
The real problem rests with current limitations in space
power sources. Glover estimates that the Mars mission scenario would need a
power source that can produce one kilowatt (kW) of power per kilogram (kg) of
mass, or else the spacecraft could never reach the speeds required for a quick
trip.
Existing power sources fall woefully short of that ideal.
Solar panels have a mass to power ratio of 20 kg/kW. The Pentagon's DARPA
science lab hopes to develop solar panels that can achieve 7 kg/KW, and stretched
lens arrays might reach 3 kg/KW, Glover said. That's good enough for VASIMR to
transport cargo around low-Earth orbit and to the moon, but not to fly humans
to Mars.
Ad Astra sees nuclear power as the likeliest power source
for a VASIMR-powered Mars mission, but the nuclear reactor that could do the
job remains just a concept on paper. The U.S. only ever launched one nuclear
reactor into space back in 1965, and it achieved just 50 kg/kW.
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