Sunday, July 17, 2011

Responding to Zubrin about VASIMR

Just like Harold Hill in "The Music Man," author and Mars Society President Robert Zubrin sees trouble ("right here in River City") which can only be nipped in the bud by making us "aware of the caliber of disaster indicated."

Music Man Ya Got Trouble by WarnerBrosOnline

Zubrin, the author of "The Case for Mars: The Plan to Settle the Red Planet and Why We Must" has singled out the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) electro-magnetic thruster for spacecraft propulsion, the Ad Astra Rocket Company (which is presently involved in researching and commercializing the VASIMR) plus former astronaut and current Ad Astra President/ CEO Franklin Chang-Diaz, who is credited with being the inventor of the technology.

Robert Zubrin, sizing up the situation,
So where's the trouble?

According to the July 13th, 2011 Zubrin written editorial on the Space News website titled "The VASIMR Hoax" the current focus on new technologies (especially VASIMR) is postponing, not facilitating space exploration and "only useful as a smokescreen for those who wish to avoid embracing" real initiatives which could begin now, using existing technology as previously outlined by Zubrin in his May 14th, 2011 Wall Street Journal editorial "How We Can Fly to Mars in This Decade—And on the Cheap."

Franklin Chang-Diaz has a different assessment.
And this latest editorial doesn't just have a title packed with hyperbole.

Zubrin also explicitly calls VASIMR a "total falsehood" which "must be exposed."

Best of all, the only way for the truth to prevail is for the people to attend a panel discussion titled: “VASIMR: Silver Bullet or Hoax" at the next Mars Society international convention in Dallas this August.

Say again?

Did Bob Zubrin actually get away with free advertising for his upcoming conference in a Space News editorial? Is this why the Wall Street Journal didn't run the latest Zubrin editorial?

Of course, the real story is far more complex

For example, electric space propulsion systems (of which VASIMR is just one of many and perhaps not even the best) need lots and lots of electricity. Zubrin is indeed correct when he states that:
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 (era) Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. 
But while Zubrin is also correct in his assessment that the current administration is "not making an effort to develop a space nuclear reactor of any kind" he omits to mention past and current efforts by the US and others, some of which are outlined in the November 3rd, 2009 Wired Science article "Russia Leads Nuclear Space Race After U.S. Drops Out."

Of course, we can't forget that there are also substantial difficulties testing electrical propulsion units. The physics of magnetic nozzles are a complex mash-up of theory and guesswork which often provides unreliable predictions at variance from any measured, real world performance.

For example, according to colleagues familiar with the testing requirements, a magnetic nozzle test requires a test volume that's large enough for the plasma to fully separate from the magnetic field "so as to insure that the outer fringes of the field aren't dragging on the plasma and killing most of the thrust that the inner parts of the field are producing."

This means you need a huge vacuum chamber to perform any sort of accurate test of an electrical propulsion engine and the chamber needs to be capable of a very high vacuum during the test since even small amounts of residual gas can mess up electric-thruster testing.

Or you could test the engine in space, which is big and has vacuum pretty much everywhere. However, the only place presently available for testing in space is aboard the International Space Station (ISS), which has been considered and hinted at by the US and NASA, but is not yet formally scheduled for the VASIMR.

But we can't forget about the ion thruster developed for the the Japan Aerospace Exploration Agency (JAXA) "Hayabusa" mission, which is a small scale, low powered electrical propulsion engine similar to VASIMR that has demonstrated its feasibility during interplanetary flight under real world conditions for over a thousand hours of continuous use during its seven year mission to retrieve a sample from the small near-Earth asteroid 25143 Itokawa.

An earlier battle of competing technologies.
And Hayabusa isn't unique. The NASA launched Dawn spacecraft which has just entered orbit around the asteroid Vesta, uses xenon ion thrusters pioneered during the Deep Space 1 probes, a part of the NASA New Millennium Program focused on testing high risk technologies.

There are others as well.

All of which means that VASIMR is certainly not a hoax, but it does suggest that perhaps Chang-Diaz is also a bit more optimistic in his claims for this specific electrical propulsion system than the existing evidence warrants.

In essence, both Zubrin and Chang-Diaz are exaggerated their present case. Why would they be doing this?

When the British National Space Centre (later the UK Space Agency) bumped up against competing claims regarding the capabilities of the Reaction Engines "Skylon" pilotless, reusable space plane several years ago, they set up a series of proof-of-concept engineering assessments to validate assumptions and figure out what the actual capabilities and bottlenecks were.

Skylon passed and ended up with increased funding but if it hadn't passed the review, then it would have lost funding, which is what should happen with grown-ups operating in the real world of science and engineering.

But that doesn't seem to be happening in the US, where the idea of Bob Zubrin calling out Franklin Chang-Diaz for the modern day equivalent of a public gunfight at high noon for perpetrating a "hoax" doesn't seem to strike anyone as being silly.

We seem to be entering a new era where showmanship, entertainment, political glad-handling, pork-barreling and hyperbole will each be necessary in order to suitably move forward new technologies in a world where science and engineering are starting to take a backseat to bread and circuses.

Maybe we do have trouble.


From: Michael Jensen

Hi Chuck. You bad-mouthing the circus now?  ;-)

The way I see it, people are so bombarded these days with everything, it takes circus stuff to get their attention. Many people don't even see the point of space exploration given all the problems we have at home or when faced with whole populations dying of hunger.

Of course, I don't want to go down on the record as somebody against space exploration, which is how that might sound, or to come across as being naive about its benefits.

What it comes down to (as I explain to everybody I end up on this topic with) is that each individual person has some limited range of interests that truly get them fired up and it is within this range of interests that society is best served by having them occupied.

There are plenty of people to serve every conceivable need and the rocket scientist has just as justifiable a place in society as the medicine man, the plumber, the folks providing communications equipment for pro-democracy demonstrations or even the "music man."

So lets let Zubrin be Zubrin and the same for Chang-Diaz.

Editors Note: I'm posting comments manually so don't be shy. Send your questions, queries, concerns and comments to


  1. I am familiar with Bob Zubrin's work. Getting to Mars 'Old School' isn't that appealing. Spaceflight technology has done a lot of progress... any politician who sits on The Office of Science & Technology Committee has a tendency to wonder if a program will be obsolete before it can be implemented? Mars missions aren't going to be like Moon flights; you need more margins on performance. Zubrin would be happy if you could go to Mars to stay... but exploration is the key to NASA missions. You have to return alive, and it's not a tough sale to get to Mars 6 times faster than convention means. There is no crash program to finance + cost overruns... thats why a lot of policy is going this direction. Bob Zubrin is an expert on how to get to Mars with what we have... but doing something like this has many more options than just one expert's plan! Ad Astra is an applied plasma technology company that does more than build 'test engines'... and they go hand in hand with product development & customer needs. There is a finish line with what any enterprise accomplishes, let's see what happens...when Mars or any other objective is approached, it's done with planning and resolve... maybe that's what this is really about.

    1. "Obsolete before it can get implemented..." The space industry is inovating at a snails pace commpared to the rest of the world. The real issue is Congress has stopped writing checks to Nasas never ending apitite for funding. As a result Nasa restructured their budget and almost had to cut the James Webb out of existence. The scarry thought is that Nasa may continue to see budget constraints as the Government fights itself over its uncontrollable debt and financial collapse.

  2. When you break it down though, Zubrin's pretty much dead-on correct.

    The 200 megawatts VASIMR would need to make a 39-day run to Mars would require literally *thousands of tons* of nuclear reactor and heat-radiating fins. Put another way, 200 megawatts is enough to power a medium-sized CITY.

    The other way to supply power would be solar panels. But even with 50 percent sunlight-to-power conversion efficiency, you're talking roughly 100 ACRES of solar panels. More, actually, because the sun is weaker at Mars' distance from the Sun... you only get 43 percent as much sunlight as you do at Earth's orbital distance.

    VASIMR is a nice technology, but the application of it that Chang-Diaz has been talking up- fast transit times to relatively near planets (Mars)- is very wrong-headed and currently wildly impractical.

    Where VASIMR would make sense is on voyages to the outer planets (where a lower-power/thrust implementation would have a lot more time to accelerate the vessel), and as a low-speed, high-efficiency cargo transporter to Mars.

    But manned missions to Mars? They're much better served by NTP (Nuclear Thermal Propulsion) engines, which are proven (NERVA built and tested 'em 50 years ago), are twice as efficient as current chemical rockets, are high-thrust, and yet don't require thousands of tons of nuclear reactor or hundred of acres of solar panels.

    Zubrin's anger with VASIMR, other than its wild current impracticality, is that it increases the cost of any manned mission to Mars ASTRONOMICALLY, which in the current budgetary environment essentially kills any chance of such a mission, if ppl buy into Chang-Diaz's line that you can't go to Mars without his engine.

    Chang-Diaz, while admirable as an entrepreneur, has been VERY irresponsible in his salesmanship job for his pet technology, and he may yet set back any timetable for a manned mission to Mars via the confusion he has sown.

  3. I've turned the editorial above into a longer article focusing more on the showmanship aspects which was published in the Space Review as "VASIMR and a new war of the currents" at

    Feel free to check it out.

  4. RZ is always saying the same damm thing he's over confident it's almost so annoying we barely know what he propose and where's he will find the money or fundraisers who will back his ideas? unseen yet !!
    2nd .it's well known that this fella it's very intransigent and usually comes with very mad ideas in the scientific community that usually confuse everyone even himself! much has to be investigate with the actual rovers and spacecraft that we got there ....PERIOD DEAL WITH IT!!


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