(Image: A concept of a VASIMR-powered space craft. Credit: Ad Astra Rocket Company)
Seen by many to be the “great red hope,” VASIMR has the potential to shorten a six month journey to the red planet to about 40 days.
Unfortunately it looks like brighter minds have weighed in on the realities of VASIMR, and have concluded that the technology has more in common with Star Trek than reality.
Another concern is that for a Mars mission, VASIMR would have to use a nuclear power system that doesn’t exist yet. Mars Society president Robert Zubrin warned that mission designs that used VASIMR had unrealistic expectations about the mass of such reactors. The largest space nuclear power systems, the Topaz nuclear reactors developed by the former Soviet Union, generated 10 kilowatts and had a specific power, or alpha, of 100 kilograms per kilowatt. NASA had hoped to get alpha down to 65 kg/kW with its now-cancelled Prometheus program, and Zubrin said that if one is “quite optimistic” an alpha of 20 kg/kW was possible. The VASIMR-based Mars mission concepts, he said, assume an alpha of 1 kg/kW. “That’s like steel with the weight of Styrofoam,” Zubrin said. “It has no relationship with reality.”
Assuming an alpha of 20 kg/kW, Zubrin said, means that a reactor that generates 200 megawatts would weigh 4,000 tons. (By contrast, the VASIMR mission architectures with the 39-day travel times had assumed an overall mission mass of approximately 600 tons.) Moreover, the best travel time you could get with this much more massive system is six to eight months, comparable with conventional chemical propulsion systems, Zubrin claimed. “The numbers don’t add up,” he said. (The Space Review)
If humanity can not find a way to shorten the trip to Mars, then future explorers face the risk of being too weak to walk the crimson soil due to the effects of micro gravity.
While humanity could always resort to portable magnetic fields, heavy shielding and a steady diet of fish (as omega-3 can keep bones strong in micro gravity), finding ways to shorten the trip is probably wiser if we want to see Mars colonized within our life times.
Hopefully someone else can come up with a reasonable solution that doesn’t include our grandkids earning their grey hairs wondering why we never set foot on Earth’s nearest planetary neighbor (after Venus that is).