Robert Zubrin says he wants a debate:
“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.”
Zubrin says he wants to debate Chang-Diaz, the inventor of the VASIMR electric propulsion engine, about whether electric propulsion makes sense for traveling to Mars. Zubrin, who came up with the Mars Direct idea, is stuck on the notion that using chemical rockets is the only way to go to Mars for our first trip there. But if you dig deeper you will see that this offer to debate might be more aptly called a hoax of a debate.
If I was Franklin Chang-Diaz I wouldn’t debate Zubrin. The first time Zubrin publicly criticized the idea of the VASIMR – to me he turned this into a rather personal attack on Chang-Diaz. In 2011 Zubrin gained press attention by claiming the VASIMR is a “hoax”. By calling it a hoax he implies that Chang-Diaz is being deceitful when saying that the VASIMR is a superior way to travel to Mars when compared to chemical rockets. However, with the right power system the VASIMR really can get you to and from Mars faster than chemical rockets.
In 2011 Zubrin did his best to make the VASIMR seem unimportant. He wrote:
“VASIMR, or the Variable Specific Impulse Magnetoplasma Rocket, is not new. Rather, it has been researched at considerable government expense by its inventor, Franklin Chang Diaz, for three decades. More importantly, it is neither revolutionary nor particularly promising. Rather, it is just another addition to the family of electric thrusters, which convert electric power to jet thrust, but are markedly inferior to the ones we already have.”
So along with saying Chang-Diaz is committing a hoax – Zubrin also says his baby is ugly! That is one heck of a way to win friends and debating partners. It is no wonder that Chang-Diaz has not publicly said much regarding Zubrin’s comments over the past 3 years. I think he understands that, in light of Zubrin’s disparaging attitude, that Zubrin is not acting worthy of engaging.
When Zubrin says that the VASIMR is “markedly inferior to the ones we already”, he is misleading. There are no megawatt-class electric propulsion engines anywhere near ready to go to space even as test prototypes. They are all only concepts and early prototypes here on Earth competing to become significant development projects one day. Chang-Diaz is the leader because he has an engine concept and a vision big enough to lead to the first megawatt-class production electric propulsion engine. Scroll down at this link to see a table of common power levels for existing ion thrusters and for electric engine prototypes being tested.
In 2011 Zubrin also added:
“But wait, there’s more. To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
The Topaz was a Soviet reactor last sent to space in 1988. That is a long time ago, and it is well known that the kg per kW of reactor system output electric power can be greatly reduced provided that this is given some priority for research. Zubrin very well knows this. It’s ironic that he accuses of Chang-Diaz of trying to pull a hoax, when Zurbin claims: “There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
The Topaz was 32 kg per kW (kW of electric output power). But in recent research, for example in this 2011 NASA research paper, researchers believe that with new technology it’s reasonable to assume that 2 kg/kW is possible. And here is a paper that says: “These advanced reactors at the conceptual design level have potential for the generation of tens to hundreds of megawatts of power in space with specific mass of about 1 kg/kW.” Thus, 1 to 2 kg/KW nuclear power systems are feasible, it’s just a matter of time and investment money.
Let’s see what Chang-Diaz actually said in his paper about travel times to Mars and what is needed for kg/kW for the power system that would power the VASIMR:
“Using 12 MW of power and a total specific mass for the entire power and propulsion system of a challenging, but presently realizable 4 kg/kW, allows for a scenario with a crewed one-way mission time of approximately 3 months, and a round-trip mission time of approximately 10 months (including 1 month stay on Mars). Assuming advanced technologies that reduce the total specific mass to less than 2 kg/kW, trip times of less than 60 days will be possible with 200 MW of electrical power. One-way trips to Mars lasting less than 39 days are even conceivable using 200 MW of power if technological advances allow the specific mass to be reduced to near or below 1 kg/kW.”
This seems very up front and open regarding the potential of the VASIMR and what is needed for the power system. Chang-Diaz is hiding nothing and he’s giving a matter of fact description of what is possible “assuming advanced technologies” for the power system. There is no hoax in sight.