Ad Astra’s Variable Specific Impulse Magnetoplasma Rocket needs 200 Megawatts of power for a 40 day trip from Earth to Mars, but the power source needs a high needs a high power to weight ratio power source as well
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.
Stretched Lens Array
Stretched Lens Array Squarerigger
Stretched Lens Array (SLA)/SquareRigger enables giant space solar arrays in the 100 kW to 1 MW class, with spectacular performance metrics (300 to 500 W/kg specific power, 80 to 120 kW/m3 stowed power, and operational voltages above 1,000 V) in the near-term (2010) to mid-term (2015).
In the longer term (2020-2025), with constantly improving solar cell efficiencies and incorporation of new nanotechnology materials into the lens and radiator elements, SLA’s technology roadmap leads to 1,000 W/kg solar arrays, as shown above.
Nuclear Powered VASIMR
A nuclear reactor has a very large amount of energy per unit mass, in fact a reactor core has the highest energy density of any useful energy source on earth. This high energy density and scalability make nuclear reactors an ideal power source in space. A nuclear powered spacecraft could dramatically shorten human transit times between planets (less than 3 months to Mars) and propel robotic cargo missions with a very large payload mass fraction. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse (less than 1000 seconds). A VASIMR® propelled, nuclear powered spacecraft promises to make fast human missions a reality.