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A next-generation plasma rocket being developed by former NASA astronaut Franklin Chang Diaz called the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) has been touted as a way to get astronauts to Mars in weeks rather than months, as well as an innovative, cheap way to re-boost the International Space Station. But in a biting commentary posted on Space News and the Mars Society website, “Mars Direct” advocate Robert Zubrin calls VASIMR a “hoax” saying the engine “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,” adding, “There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
The VASIMR uses plasma as a propellant. A gas is ionized using radio waves entering into a plasma state. As ions the plasma can be directed and accelerated by a magnetic field to create specific thrust. The purported advantage of the VASIMR lies in its ability to change from high impulse to low impulse thrust as needed, making it an ideal candidate for a mission beyond low Earth orbit.
Chang Diaz’ company, the Ad Astra Rocket Company successfully tested the VASIMR VX-200 plasma engine in 2009. It ran at 201 kilowatts in a vacuum chamber, passing the 200-kilowatt mark for the first time. “It’s the most powerful plasma rocket in the world right now,” said Chang-Diaz at the time. Ad Astra has signed a Space Act agreement with NASA to test a 200-kilowatt VASIMR engine on the International Space Station, reportedly in 2013.
The tests would provide periodic boosts to the space station, which gradually drops in altitude due to atmospheric drag. ISS boosts are currently provided by spacecraft with conventional thrusters, which consume about 7.5 tons of propellant per year. By cutting this amount down to 0.3 tons, Chang-Diaz estimates that VASIMR could save NASA millions of dollars per year.
For the engine to enable trips to Mars in a reported 39 days, a 10- to 20-megawatt VASIMR engine ion engine would need to be coupled with nuclear power to dramatically shorten human transit times between planets.
Zubrin is the president of the Mars Society and author of the book “The Case for Mars: The Plan to Settle the Red Planet and Why We Must.” He has long touted the “Mars Direct” approach of getting humans to Mars to create a sustainable human settlement. The plan includes a series of unmanned and human flights to Mars using existing technology, as well as “living off the land” on Mars by creating rocket fuel to return to Earth, and using underground reservoirs of water on Mars.
In his commentary on VASIMR, Zubrin says, “existing ion thrusters routinely achieve 70 percent efficiency and have operated successfully both on the test stand and in space for thousands of hours. In contrast, after 30 years of research, the VASIMR has only obtained about 50 percent efficiency in test stand burns of a few seconds’ duration.”
On the ‘39 days to Mars’ claim, Zubrin says VASIMR would need to couple with a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram, while 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.
Zubrin has invited Chang Diaz to a formal public debate the VASIMR at a Mars Society convention in Dallas next month.
Read Zubrin’s commentary on Space News or the Mars Society website.
More info: Ad Astra Rocket Company
These sorts of debates are tiresome. Debating is not science or engineering. Test it and there will be nothing to debate about, it either works and is efficient by the numbers or it is not. There is no opinion, just math and math doesn’t lie or exaggerate.
In an ideal world you would be right but this is not an ideal world. We have seen both in the commercial world and in politics that often the best way is not chosen but the best publicized is. I have no idea where Zubrin gets his information from on this matter however it seems to me that he wants to put it out there that waiting for the perfection of the VASMIR system will only delay further a Mars exploration program that can be performed now with existing technology. I do not know by this article if Zubrin thinks that getting the VASMIR up to it’s claimed performance numbers is impossible. He only says that the engine has not reached those numbers yet and there are systems out there out performing VASMIR right now. When I look at Space Shuttle program, which cost Billions and never did what they claimed it could do in the world of cheap and routine access to space I can understand Zubrin’s animosity towards a future possibility and pie in the sky claims vs a current technology that is a certainty.
In an ideal world you would be right but this is not an ideal world. We have seen both in the commercial world and in politics that often the best way is not chosen but the best publicized is. I have no idea where Zubrin gets his information from on this matter however it seems to me that he wants to put it out there that waiting for the perfection of the VASMIR system will only delay further a Mars exploration program that can be performed now with existing technology. I do not know by this article if Zubrin thinks that getting the VASMIR up to it’s claimed performance numbers is impossible. He only says that the engine has not reached those numbers yet and there are systems out there out performing VASMIR right now. When I look at Space Shuttle program, which cost Billions and never did what they claimed it could do in the world of cheap and routine access to space I can understand Zubrin’s animosity towards a future possibility and pie in the sky claims vs a current technology that is a certainty.
“These sorts of debates are tiresome.”
If you find it tiresome, why are you chipping in with your two cents worth ?
“Test it” “no opinion, just math”
Testing it, and doing the math are not the same thing, so which do you mean ?
Testing it would mean building it and flying it to Mars to see how long it takes.
Zubrin says the math shows it isn’t suitable for getting to Mars.
Oh, Zuby, I really enjoyed your book. Very exciting and inspiring, but using this silly debate to attract attention is not helping.
The VASIMR works, and in principle is should be able to perform. It has the advantage of having a throttle. One can increase the specific impulse of the device and reduce the thrust, or conversely increase thrust and decrease specific impulse. It is a bit analogous to a transmission on a car.
Also clearly to run this in the 10-megawatt domain you are going to require a nuclear reactor. It does open up the question of nuclear power in space, but it has some distinct advantages over a standard nuclear rocket engine. Primarily the propulsion system is not the reactor itself. The VASMIR is an electrically driven plasma device and the power supply is separate. This avoids the issue of radioactive plumes and the rest.
LC
“The VASIMR works, and in principle is should be able to perform.”
It works? You mean it does something? Yes it does.
Perform? Perform what? Get to Mars quickly ? No way.
It works on the lab bench. The first ion propulsion systems were of that sort. The concept is workable as a laboratory instrument.
LC
The problem is the power density requirement for the source of electrical power. The VASIMR to be tested on the ISS will only run for short periods after charging up for a longer period of time, and that is enough for boosting the orbit now and again, but a fast spaceship to Mars requires serious, continuous power production running non-stop for weeks. We do not have such a power source yet, period.
I´m Costarrican and I´m so glad to know Franlin Chang Diaz was born in Costa Rica. It is a real proud for us. We are so grateful for his work in Liberia helping out physics students, providing them of advanced and new knowledge.
I´m Costarrican and I´m so glad to know Franlin Chang Diaz was born in Costa Rica. It is a real proud for us in this country and we are so grateful for his work in Liberia, Costa Rica, helping out physics students, providing them of advanced and new knowledge they will need throughout their careers.
¡¡¡ VIVA FRANKLIN, VIVA COSTA RICA !!!
For me, he just crossed over into the UFO-logists and Nibiru camp. Dumb publicity stunt.
To need a lot of electric power to run that VASIMR engine. That amount of power cannot be provided by solar cells, so you may need a nuclear reactor of some megawatts. A nuclear reactor in space needs shielding and cooling. Sufficient shielding adds a lot of mass to the craft, and the problem of cooling a powerful reactor in space is still unsolved.
But power is not the only problem. You need propellant for the engine, and the more and the faster you accelerate, and the higher the mass, the more you need.
There is one way to get away from shielding without much extra mass. Shield the reactor on the side facing the inhabited side of the ship and put the reactor on a string. The distance can act as a shield in of itself for radiation drops by the inverse square of the distance.
There is one way to get away from shielding without much extra mass. Shield the reactor on the side facing the inhabited side of the ship and put the reactor on a string. The distance can act as a shield in of itself for radiation drops by the inverse square of the distance.
I think his underlying point is that this is become a part of the current administrations shell game for space.
They are fronting this new technology as the future of space travel, but they haven’t done anything to actually advance it. They haven’t flown the engine, they haven’t started work on the reactor, they haven’t even declared mars as a firm destination for any mission.
They want to do an asteroid mission but they’ve killed the big rockets, they haven’t written contracts to fly commercial, they’ve taken out the shuttle, and they’ve set the replacement vehicle deadline so that nothing has to materialize until Obama is almost through with his second term.
Its just being abused as another campaign promise they have no intention of fulfilling.
Its a promising technology, but the odds are its never going to fly at this rate.
Zubrin is right to call them on it.
I don’t think this is a matter of politics. The VASIMR may develop in the same way the chemical rocket did. That started out small, such as Goddard’s little rocket, and from there evolved over a few decades into larger systems. The VASIMR has been around since the 1990s, and evolved out of some technology for accelerating plasmas. Obama made the statement about new technology just a little over a year ago, and VASIMR had been on the lab bench for years before then.
The politics of manned spaceflight has a bipartisan cynicism. GW Bush proposed a return to the moon in the wake of the mars rovers and to also defray attention from the torture at Abu Ghraib and GITMO and other problems which caused GW’s second term to disintegrate. Kennedy proposed a man on the moon for political traction as well, and in part to step up to the Soviet challenge. This tends to have an element of flag waving to it, which unmanned instrumentation and space science does not quite deliver on.
Whether for instrumentation and scientific probing of space or maybe manned spaceflight a robust system is required. It has been my thought that the VASIMR is a likely candidate for this. It will require a nuclear power system, which has questions with regards to technical reliability, safety and the like. However, if we want to get a spacecraft to the outer planets quickly, or if we want to probe the region of the universe .01-.1 light years out we will need something of this sort.
LC
If it was just the Vasmir then I’d agree its a matter of time before we get our new ships. But I see this as a follow on to Nerva and the atomic Orion concept from the 60’s. They’ve had the keys to going faster for a while and have no intention of using them.
Even if its seen as a bipartisan failure, Zubrins point still stands.
We can go at any time. We just can’t find the will to go, and holding out a warp drive like a carrot on a stick is continuing decades of administrative dishonesty towards manned spaceflight.
The Orion program involved detonating atom bombs at the back of a spacecraft. The open air test ban, which prohibited nuclear bomb tests in space, put an end to that. The early nuclear reactor rocket program was also cancelled out in part because of issues with radioactive releases and safety. It also fell under Nixon’s hatchet which dismantled the Saturn-Apollo program, where by 1972 it appeared the entire manned space program was going to be cancelled permanently. Vice President Agnew pushed for the shuttle program and this is what sustained the manned space program. Nixon cancelled out the lunar manned space program and future developments such as NERVA because there was a much bigger money black hole; the Vietnam War. Curiously, we face a similar situation with the Iraq-Afghan wars, which have recently been cited as consuming more treasury than WWII!
NASA and the manned space program were never set up with any idea of generating a permanent human presence in space, or for even really doing science. The whole program was a cold war show case meant to demonstrate American pre-eminence over the Soviet Union. We conducted six lunar missions, seven if you consider Apollo 13 which had to return without landing, and by 1971 the logic was that “we won,” and the space race (as it was called for a time) was like a war that concluded successfully. The troops come home.
The GW Bush administration was not friendly to space science. The current Congress threatens to defund the space weather sat program, which will have expected consequences. The Obama administration is facing dire economic conditions and a Congress that is willing to default the nation over the debt and budget constraints. Obama threw the return to the moon program away and signed the executive order to end the Shuttle program. So these are not conditions at all conducive to space programs of any kind. Space science programs are all being down graded or cancelled out, and the JWST is in danger. The US has pulled out of the gravity wave LISA program recently, and I suspect the Inquiry rover on Mars may be the last US mission of any kind to Mars.
It sucks living in a declining civilization, but that is something we have to get used to.
LC
I agree, but then why do we let politicians get away with making a promise we know they wont keep?
We let them have the good press on the front page and, when they disappoint us on page ten, we quietly slink away and sulk about the downfall of society.
What we should be doing is, just as publicly, showing everyone when a politicians promise turns out to be another dead end.
Embarrassing a few politicians with some big headlines is going to do alot more for manned space than just accepting the fate they’ve written for it.
This country has a political system that only PT Barnum could have invented. The whole thing is a circus show. The two-party system did emerge because of the winner take all approach to elections laid down in the Constitution. This has lead to a system where the two parties are ultimately manipulated by financial and corporate power. Campaign support is given by corporate interest proportionate to the immediate interests. It is a little known fact that Obama got about twice the corporate dollars McCain did. The reason is that a Democrat is more likely to turn on the Keynesian levers and switches to keep the financial ship afloat. Obama then followed on with GW Bush started with the bailouts in 2008-9. Now that the financial industry is back on even keel, forget about the rest of us, they want to trash him out and get a GOP-er in. Republicans are generally given more dollars when things are good, and the financial-corporate sector runs behind the skirts of a democratic administration and Congress when things go sour. “We the People” are basically reduced to a sort of audience attending this Punch and Judy show or circus.
Abraham Lincoln in a funny way turned the dial up with the Republicans. He used his federal powers to contract war production. This was something that Jefferson Davis envied considerably. However, Lincoln saw back then the growing influence of corporate and banking power in the federal government and its grip on the new Republican Party. Remember, the Republican Party used to be the “liberals.” Lincoln wrote various warning about this, similar in character to Eisenhower’s warning about the military industrial complex.
The simple fact is that we have a media driven circus for a political system. Orwell was right in that people have bad memories about things, and which ever party can tell the biggest and most persistent lie will manage to win. This was something that Goebbels wrote as well. We really do not have actual debates or political discussions with any oratorical merit, but rather TV-electronic sound bites and news reports about what Sarah Palin twittered today, and equally puerile nonsense. The whole system is a frekking joke.
LC
Very nice summary. I like the parallel comparison to how Nazi Germany used the emerging mass media so effectively to enthrall and public with lies while their leaders drove that nation down a mad path to ruin. It was not long ago when the big corporations realized their vision for America and that was the robber baron era of the late 19th century. Workers were essentially slaves living on corporate plantations forced even to buy essential goods from corporate stores. The U.S. was a third world nation then. How quickly we forget. Looking at the latest Rupert Murdoch example such corporate powers now purchase the mass media outlets, and only a fool would say they are not manipulating them to suit their fancy. Combine that with pandering and selfish power-hungry politicians willing to take corporate donations to stay in power and then turn around and put their interests in front of the good of the nation and you have a recipe for decline.
I also appreciated your tracing of corporate flip-flopping of donations between the various parties. It explains why Clinton was pro-Nafta, which at the time made no political sense to me whatsoever. It is completely clear that the big corporations have seized power over the last 20-30 years and shipped wealth and industry overseas to get their slave labor (sometimes literally via prison workers in China) and maximize profits while allowing the nation to fall into ruin. Our leaders have not only failed to punish this treachery with hefty taxes, fines, or even prison, they have in many cases subsidized the effort. By not investing in science and attracting the best and brightest to America we are past nailing the coffing and digging the grave, but we are now throwing dirt on it. The way out of the robber baron era was led by science and revolutionary innovation by the likes of Edison and Tesla. Scientists of this ilk in the future will be flocking to places like China and the E.U. considering curernt trends.
Probably the most insightful essay on this topic was written by Umberto Eco
http://www.pegc.us/archive/Articles/eco_ur-fascism.pdf
LC
The Orion program involved detonating atom bombs at the back of a spacecraft. The open air test ban, which prohibited nuclear bomb tests in space, put an end to that. The early nuclear reactor rocket program was also cancelled out in part because of issues with radioactive releases and safety. It also fell under Nixon’s hatchet which dismantled the Saturn-Apollo program, where by 1972 it appeared the entire manned space program was going to be cancelled permanently. Vice President Agnew pushed for the shuttle program and this is what sustained the manned space program. Nixon cancelled out the lunar manned space program and future developments such as NERVA because there was a much bigger money black hole; the Vietnam War. Curiously, we face a similar situation with the Iraq-Afghan wars, which have recently been cited as consuming more treasury than WWII!
NASA and the manned space program were never set up with any idea of generating a permanent human presence in space, or for even really doing science. The whole program was a cold war show case meant to demonstrate American pre-eminence over the Soviet Union. We conducted six lunar missions, seven if you consider Apollo 13 which had to return without landing, and by 1971 the logic was that “we won,” and the space race (as it was called for a time) was like a war that concluded successfully. The troops come home.
The GW Bush administration was not friendly to space science. The current Congress threatens to defund the space weather sat program, which will have expected consequences. The Obama administration is facing dire economic conditions and a Congress that is willing to default the nation over the debt and budget constraints. Obama threw the return to the moon program away and signed the executive order to end the Shuttle program. So these are not conditions at all conducive to space programs of any kind. Space science programs are all being down graded or cancelled out, and the JWST is in danger. The US has pulled out of the gravity wave LISA program recently, and I suspect the Inquiry rover on Mars may be the last US mission of any kind to Mars.
It sucks living in a declining civilization, but that is something we have to get used to.
LC
In an ideal world you would be right but this is not an ideal world. We have seen both in the commercial world and in politics that often the best way is not chosen but the best publicized is. I have no idea where Zubrin gets his information from on this matter however it seems to me that he wants to put it out there that waiting for the perfection of the VASMIR system will only delay further a Mars exploration program that can be performed now with existing technology. I do not know by this article if Zubrin thinks that getting the VASMIR up to it’s claimed performance numbers is impossible. He only says that the engine has not reached those numbers yet and there are systems out there out performing VASMIR right now. When I look at Space Shuttle program, which cost Billions and never did what they claimed it could do in the world of cheap and routine access to space I can understand Zubrin’s animosity towards a future possibility and pie in the sky claims vs a current technology that is a certainty.
In an ideal world you would be right but this is not an ideal world. We have seen both in the commercial world and in politics that often the best way is not chosen but the best publicized is. I have no idea where Zubrin gets his information from on this matter however it seems to me that he wants to put it out there that waiting for the perfection of the VASMIR system will only delay further a Mars exploration program that can be performed now with existing technology. I do not know by this article if Zubrin thinks that getting the VASMIR up to it’s claimed performance numbers is impossible. He only says that the engine has not reached those numbers yet and there are systems out there out performing VASMIR right now. When I look at Space Shuttle program, which cost Billions and never did what they claimed it could do in the world of cheap and routine access to space I can understand Zubrin’s animosity towards a future possibility and pie in the sky claims vs a current technology that is a certainty.
I don’t understand why propulsion is an issue in getting to Mars. Yes chemical rockets are less efficient and require huge amounts of mass, but couldn’t you just use chemical rockets to fire a bunch of containers into space with just fuel? That way, you’d have all the fuel you wanted, whether it’s chemical fuel, ion drive fuel or fuel for a VASMIR. Once in space, moving that fuel around (i.e. to Mars) shouldn’t be such a big deal. It could all be waiting for humans once their interplanetary craft arrives at Mars. You could even send food, water, spare parts and the landing craft ahead of time, so it’s in a nice floatilla, sailing above Mars ready for the humans to land and return to Earth.
Seems like there are 2 real issues. The first is $. We won’t be seeing a Mars mission in my lifetime with the US debt at $14 trillion and climbing. It’s going to take longer to pay off that debt than it would for me to walk to Mars. I don’t think that the US Congress will approve a budget that includes $ for Mars anytime soon. The second major issue is ensuring that humans survive the journey and are able to function once they are on Mars, with radiation and muscle/bone atrophying being the major issues that have yet to be addressed.
Can you imagine the uproar when everyone suddenly realizes a nuclear reactor will be launched into space to power this thing? I can remember the hysteria when Cassini launched with a relatively safe Plutonium isotope power generator.
— CHAS
I have to wonder about Bob Zubrin sometimes.
On the one hand, he’s unquestionably a genius, a planetary science zealot, and a leading light in the PR fight to get humans off planet.
But on the other, a lot has been spent (by him and others like him) on sociological studies and experiments on just how humans react to being couped up in a spaceship for 6-8 months getting to Mars. Not to mention his books… which are all about how to get to Mars cheaply using current tech only.
Why do I get the impression he’s just protecting his own theories by denying the possibility of something that rips through all of that?
“Why do I get the impression …”
Uh, because you find it easier to jump to such a conclusion than actually trying to understand the math.
I have to wonder about Bob Zubrin sometimes.
On the one hand, he’s unquestionably a genius, a planetary science zealot, and a leading light in the PR fight to get humans off planet.
But on the other, a lot has been spent (by him and others like him) on sociological studies and experiments on just how humans react to being couped up in a spaceship for 6-8 months getting to Mars. Not to mention his books… which are all about how to get to Mars cheaply using current tech only.
Why do I get the impression he’s just protecting his own theories by denying the possibility of something that rips through all of that?
“A gas is ionized using radio waves entering into a plasma state” Radio waves? But the phone companies keep telling us that radio waves are non-ionizing radiation.
why is he ridiculing the issue with such inconclusive statements. He sounds like a man of politics with elections plans. This in no way serves the greater goal of uniting efforts in order to accelerate the exploration of space. Hope Dr. Zubrin fixes it by offering aid to improve the technology rather than bashing it. Moral support for the scientists is considered as aid too.
Some men have big dreams, and some have big mouths.
They are mutually exclusive.
Dr. Chang is building his dream.
His critics are building hot air.
Hot air will not rise to the challenge of Mars.
VASIMR will.
“Hot air will not rise to the challenge of Mars.
VASIMR will. ”
Have you got any evidence that it will ?
Last August at the Human Spaceflight Forum held at the Columbia Memorial Center in Downey (directly across form what is now Downey Studios but what was the assembly facility of Apollo and the first home of Shuttle manufacture) Dr. Zubrn said much the same… he is not a stupid man, he IS controversay and gets on some folk’s nerves at times but he ain’t stupid. Plus I believe that it is NOT his intention to hold up work on long duration human flights and is instead his sincere passion to get things off of the perpetual “paper rocket” phace an into actual resutls. But then, i have seen him a few times and spoken with him a few times and also beden in atendance with Dr. Chang Diaz has done sessions (NewSpace 2010 in Silicon Valley, was my most recent), and have to say that the very smar Chang Diaz didn’t really make it out as solid and right-around-the-corner a technology as some of the hype has implied.
All this is my opinion frommy experiences wth the people involved though.
You may want to actually hear Dr. Zubrin speak his full mind on VASIMIR, without the SpaceNews Editorial limitations. You can do so at this video page of the August 2010 Human Spaceflight forum on smithvoice.com (if the upcoming link gets blocked just hit that site and use the search box at the top for the work Zubrin, you should see it in the list.
I’m not a scientist… but Zubrin, a very passionate man to be sure, truly appears to be more into getting humans flying with tech that flys than some others who have great big ming-vase tech concepts that may one day be great but aren’t in the bag in our lifetimes.
Zubrin, John Rose (Boeing), Dean Davis (Boeing), Jeff Greason (XCOR), Mark Hopkins (Rand & NSS), Buzz Aldrin (God), all on the form in this uncut video at
http://www.smithvoice.com/downey-human-space-forum-video
Just adding more for those who didn’t read the SpaceNews Editorial personally or want to hear the full Zubrin logic on the matter.
VASIMR will work exceptionally well in deep space, but in the atmospheric environment, during takeoff, phase-shift plasma turbine can work better. http://www.youtube.com/watch?v=GSkxPghXTCg
Whoa! Where did that come from? I see in the comments that Zubrin’s argument is at least one year old; but the technology and the NASA push for new technology (including nuclear reactors) is older than that.
Sadly it is fairly useless to try to model an individual’s behavior such as strategy as it rarely can be tested. Instead I can note that I would have been more keen to listen if this had come from someone else than a passionate advocate for the sufficiency of (mostly) traditional technology. (Say a person for which the goal is primary.)
Is VASIMR a hoax? No, it works demonstratively. Is VASIMR for interplanetary crafts a hoax? No, it is unclear if it can achieve that market, and I believe the project has been upfront with this as it is delivering demonstrators instead of dreams.
The rest is politics, which can be deferred to the hoaxers … excuse me, politicians, and the vote box. And some pushers and doers. Zubrin is mostly a pusher, Diaz is mostly a doer. Frankly I prefer the later, even if both have their place.
Also, it is clear that Zubrin is comparing apples with pears:
– Efficiency should be compared for mature and comparable technology. In VASIMR’s case, chemical rockets (CR).
I think CR can but dream of achieving ~ 50 % efficiency, isn’t it more like ~ 10 %!?
– Power source should be compared with similar high mass long duration missions. There NASA has routinely proposed nuclear power.
– The radiation analysis is interesting if true. However, my impression was that the risk assessment discussed was a newer result of research!?
I don’t know if Zubrin, an “aerospace engineer and author” has actually been involved in this research. Maybe he is the hoax.
– Aside from the question of radiation, still unsolved in Zubrin’s approach is:
1) Landing manned craft on Mars, a problem that VASIMR isn’t set up to solve nor has an intended market that revolves around it as Zubrin’s advoccacy is.
2) Good enough closure of biosphere environments. Today’s ~ 70 % is claimed to be insufficient for Mars trips, VASIMR or not. IIRC ~ 90 % is the necessary target.
At the end of the day, manned space is more than “the case for Mars”.
Zubrin:
“The argument that we must go much faster to avoid cosmic rays is demonstrably false, as proven not only by standard radiation risk analysis — which estimates about a 1 percent cancer risk for the 50 rem dose that astronauts would receive on a Mars round trip — but by the fact that about a dozen astronauts and cosmonauts have already received such a cumulative cosmic ray dose during repeated flights on the international space station or Mir, and, as expected, none of them have evidenced any radiological health effects.”
This is from the Wikipedia entry on radiation health threats during space missions:
“Average exposure on the ISS is a rate of 150 mSv per year, though crew rotations are shorter than that.[10] Astronauts on Apollo and Skylab missions received on average 1.2 mSv/day and 1.4 mSv/day respectively.[10]”
[10 is a NASA ref.]
A day on ISS averages ~ 0.4 mSv, a day on Moon missions ~ 3 times that. Zubrin isn’t far off, so his space angle model with Earth as shield may be correct.
Achieving 50 rem = 0.5 Sv, which is subclinical, takes ~ 3.5 years on ISS with the average dose and ~ 1.1 year on a Mars mission.
Presumably Zubrin’s Mars missions of ~ 2 years do have a substantial radiation problem. If a crew rotation of ~ 0.5 year accumulates 50 rem from episodic events such as CMEs during 1-2 stays, it would mean 300 ~ 600 rem on a Mars mission.
“Doses of 200 to 1,000 rem will probably cause serious illness with poor outlook at the upper end of the range.”
There are some serious issues with the power required for the VASMIR. It’s worth researching and but it’s technology readiness is too low for anything soon. Elon Musk has my bet for getting there first.