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Robert Zubrin throws down the gauntlet to Franklin Chang-Diaz over VASIMR

NASA (public domain)

Thursday, Mars Society President Dr. Robert Zubrin issued a challenge to a debate to Dr. Franklin Chang-Diaz, former astronaut and president and CEO of Ad Astra to a debate. The debate is not whether or not astronauts will go to Mars. The debate will be about how they will go to Mars. "Resolved: Electric Propulsion in an Enabling Technology for Human Mars Exploration.” Chang-Diaz would make the affirmative argument. Zubrin will make the negative argument.

The argument boiled down to its essential is about a mode of propulsion. Chang-Diaz is working on a plasma rocket engine called VASIMR which he claims will make trip times to and from Mars far less than conventional chemical rockets. Zubrin not only disputes that this is possible, but even desirable.

Chang-Diaz asserts that the radiation hazards inherent in interplanetary flight makes a quicker population system a vital pre requisite for missions to Mars. He has touted his VASIMR engine, which he has been working on for a number of years, as a solution to that problem. Zubrin responded that these assertions are false.

“First, the roughly 60 Rem cosmic ray dose that would be received by astronauts over the course of a round-trip Mars mission using 6 month transits involves about a 1 percent risk of cancer later in life, and has already been experienced by half a dozen cosmonauts and astronauts who have conducted extended stays on the ISS or Mir without any radiological causalities. Second, it is thus the case that interplanetary transits faster than six months are not necessary or even desirable, because the six month transit to Mars also provides the crew with a two-year free return trajectory, which would be lost if a faster outbound transit were attempted. Therefore if a superior propulsion system, like nuclear thermal rockets, were available that could, in principle, speed up the transit, competent mission planners would use it to increase the payload, and thus the redundancy of mission critical systems, while keeping the transit time the same, as this would do far more to increase both the safety and capability of the mission. Thirdly, it is simply not true that Dr. Chang Diaz’s VASIMR drive or any other electric propulsion system is capable of enabling the quick trips that Dr. Chang Diaz promises. Such claims are based on assuming nuclear electric power systems with 10,000 times the power and 1/100th the mass per unit power as any that have ever been built. In reality, using realistic numbers, electric propulsion systems would require much longer transit times to the Red Planet than what we can already do today.”

Zubrin is the progenitor of the Mars Direct concept. In essence it involves using resources on Mars as much as possible to create rocket fuel on site to supply astronauts when they visit the Red Planet. In this way expeditions to Mars would not have to bring all of the fuel needed for a return trip to Earth. The concept has been widely praised and has been incorporated by NASA to a certain degree in its Mars mission planning.

Chang-Diaz, who is of Puerto Rican and Chinese decent, is a former NASA astronaut and has flown on seven space shuttle missions. He retired from NASA in 2005 and founded Ad Astra to develop the VASIMR plasma rocket system which he worked on as a NASA employee, Besides his business enterprise, he is also an Adjunct Professor in Physics and Astronomy at Rice University,

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