Bob Zubrin and Al Globus on VASIMR and SBSP

[bananas]

Two apparently unrelated articles:
1) Bob Zubrin points out that a nuclear-powered VASIMR Mars mission is unrealistic because it won't meet the 1000:1 watts/kg power-to-mass ratio needed.
2) Al Globus points out that solar power is approaching the 1000:1 watts/kg power-to-mass ratio needed to make SBSP cost effective.

Obvious conclusion: a six-week solar-powered VASIMR Mars mission is realistic.

http://spacenews.com/commentaries/110711-vasimr-hoax.html

Wed, 13 July, 2011
The VASIMR Hoax
By Robert Zubrin

“Critical to deep space exploration will be the development of breakthrough propulsion systems.” — U.S. President Barack Obama, Kennedy Space Center, April 15, 2010

The Obama administration claims that it is developing a new breakthrough propulsion system, known as VASIMR, which uniquely will make it possible for astronauts to travel safely and quickly to Mars. We can’t go to Mars until we have the revolutionary VASIMR, they say, but just wait; it’s on the way, and once it arrives, all things will be possible.

Washington is a city known for its smoke and mirrors, but rarely has such total falsehood been touted as a basis for science policy.

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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.

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The Mars Society is holding its next international convention in Dallas, Aug. 4-7, 2011. Currently, we have a panel scheduled, titled: “VASIMR: Silver Bullet or Hoax.” I invite Chang Diaz and a colleague to come and take two of the four spots on it and defend the practical value of their concept in formal public debate.

Let the truth prevail.

http://blog.nss.org/?p=2807

Space Solar Power May Be within Our Grasp

According to National Space Society Director Al Globus, the development of thin-film solar cells may bring the reality of space solar power closer than ever.

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Space solar power using crystalline photovoltaics is expensive because the mass is high and launch costs tend to dominate. Industry people measure the effectiveness of a solar cell by its specific power, or output per weight. The unit of measurement is Watts per Kilogram (W/kg). The goal is to achieve 1000 W/kg. Recently, thin-film photovoltaics have exceeded this critical point. Very thin (10-25 micrometers) metallic substrates can achieve and exceed the required specific power targets.

According to Globus, this may bring space solar power within our grasp. Thin-film solar cells currently in use in space on the Ikaros solar sail achieve approximately 1,250 W/kg for power generation. However, this does not include the rest of the system (power beaming, ground receivers, etc.). Using current day technology, a thin-film based PowerSat could probably achieve around 275 W/kg. If we assume a reasonable R&D program to develop the basic technologies, it appears that 1,380 W/kg can be achieved in a reasonable time scale.

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This entry was posted on Wednesday, July 13th, 2011 ...

[bananas]

1. More info at Next Big Future

some technical info at http://nextbigfuture.com/2011/07/zubrin-trashes-vasimr.html