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VASIMR and the Nuclear Question

It’s safe to say that Franklin Chang-Diaz knows what he’s talking about when he discusses the space experience. An astronaut who has logged seven flights and over 1600 hours in space (a period that includes three spacewalks), Chang-Diaz has been making even more impressive news in recent times with his Ad Astra Rocket Company, where the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) is under development. It’s heartening to think of VASIMR undergoing space-based tests, a future that is now in the cards with the news that NASA has plans to test the VASIMR engine aboard the International Space Station.

We naturally think long-term here, but VASIMR’s uses in potential missions to Mars (Chang-Diaz talks about a 39-day trip to the planet!) and beyond will first have to be shaken out in near-Earth orbit. But ponder a VASIMR gradually becoming operational, mounting missions to communications satellites that are now economically all but unreachable. Indeed, VASIMR sets up the potential for servicing a wide range of space technologies, keeping them viable even as we move back to the Moon and find the need to service and re-supply a colony there, a tricky and expensive process with chemical rockets.

This is heady stuff that’s coming in the short term. Here’s what Chang-Diaz told an interviewer late last year, when asked about timelines for the technology:

We are on a fast track to complete the first flight-like VASIMR prototype, the VX-200 by early 2008. This device will be in all ways identical to the flight engine but will not fly. We plan to complete the characterization of this prototype by mid 2008 and begin the design of the VF-200-1 and the VF-200-2, the first flight engines, which will be ready for flight in late 2010 and 2011 respectively. By 2012 we expect to have both engines operating in space in two different venues. By the middle of the next decade we plan to fly more powerful engines in a lunar cargo vehicle, which is presently in our drawing boards. This vehicle could enable economically sustainable re-supply services to the Moon colonies and also be used to access space resources such as water and metals on comets and near Earth asteroids. By the end of the next decade, Ad Astra plans to begin construction of a lunar rocket test facility that will enable us to fully test the very powerful VASIMR rockets needed for missions to Mars and beyond. These rockets require a vacuum and a suitable facility large enough is not practical to build on Earth.

Using plasma heated by radio waves and channeled magnetically, VASIMR offers major benefits in fuel efficiency and thrust in a system that can be adapted for robotic cargo missions as well as faster manned operations. The ISS would not only provide the venue for early testing in space but also point to a major future use, the maintenance of large structures in orbit without burning far more inefficient rocket fuel to do the job. At the ISS, the plasma drive would draw its power from solar panels, but the kind of output needed for a mission to Mars would inevitably demand an onboard nuclear powerplant.

Thus we circle back to the nuclear issue, an obvious political problem that has plagued the development of space systems designed for operations far from the Sun. Remember the fear inspired by Cassini’s 1999 Earth flyby on its way to Saturn? Cassini’s radioisotope thermoelectric generators (RTGs) have to be used in venues where the Sun’s rays are weak, but anti-nuclear activists spoke of an environmental catastrophe if the craft hit the Earth. The obvious success of the mission has only put the nuclear question on hold rather than answering it. Mars in 39 days is a grand concept, but it means a nuclear option is in play that will generate more than its share of renewed protests. Brace yourself.

Comments on this entry are closed.

  • John Hunt August 11, 2008, 11:25

    Perhaps what we need is a new space race.

    What if US & EU scientists who support nuclear engines in space were to petition Russia and China to open up the field? Both are probably more risk tolerant than the US or EU. As they develop engines which are more robust than ours then our narrative will change. “Oh no, we’re falling behind the Russians and Chinese”. This won’t silence the anti-nuclear crowd but it will place them in the clear minority. An politicians care about the majority. It can make the difference come election time.

  • John Hunt August 11, 2008, 11:35

    So how about VASAMIR for interstellar missions? Data I have seen on it indicate the following:
        Effective (m/s) = 10,000 – 300,000
        Thurst (N) = 400 – 1,200
        Time to Alpha Centauri = (as little as) 4,387 years
    4,400 years is too long for a scientific probe but possibly within the survival time of equipment and frozen cells.

    My sense is that one of the big issues would be adequate power. Perhaps VASIMIR could be powered by a combination of beamed masers while it accelerates from one side of the solar system to the other followed by fission power.

  • Dave Salt August 11, 2008, 15:46

    This all sounds great, but I have to wonder who is going to develop the necessary power source that would enable such advanced missions (e.g. a 39-day trip to Mars)?

    Dr Chang-Diaz’s analysis, published in March 1995 (NASA TP-3539), assumed a system with a specific power of 6kg/kW and was described as “somewhat optimistic” but even this could only perform a 90-day sprint mission with a 15% payload mass fraction.

    The real key to enabling such advanced space missions is — and has always been — the availability of an energy source with sufficiently low specific power. Unfortunately, this requires nuclear systems employing gas-core fission or nuclear fusion — solid core fission just isn’t good enough — and the technology challenge (and cost!) of fielding these are orders of magnitude greater than the VASIMIR “thruster”.

    I’m all for developing advanced propulsion systems — for instance, I really like the work Andrews Space did on Mini-MagOrion (http://www.andrews-space.com/content-main.php?subsection=MTA2) — but we really need to put the technical challenges into perspective before trying to sell it as a serious future option.

  • Dave Ketchledge August 11, 2008, 17:52

    As a nuclear engineer with more than 20 years in the industry and in submarine sized power plants, VASMIR can work and should get attention in a development program. VASMIR greatly reduces the flight time to all the planets. And reduction of both solar radiation exposure and cosmic rays is strongtly affected by the time traveling in deep space. And the improvement in payload mass to Mars is worthy to consider.

    Many people have concerns with nuclear power. But facts should play more than hysterical Hollywood claims of dangers. The US Navy has operated nuclear power plants in the 80+ MW range for decades without a single incident that could led to a core failure. Three Mile Island was costly to clean up, but no one was killed or injured. Cherynobal was an isolated case, when the plant management violated the core protection system, violated procedures and the plant manager had no nuclear power experience, he came from the coal powered industry. The containment of that reactor was little more than a tin shack. Again a bad foreign design.

    A new reactor core has little radiation until it is taken critical. Thus a VASMIR system would be in orbit before starting the VASMIR propulsion system.

    A gas cooled reactor with a graphite moderator can provide good safety margins and run a gas turbine to make power while in zero gee as well.

    Radition doses from the core could be cut by at least a factor of 1000 by 6 feet of LH2. Each two feet of LH2 cuts dose a factor of 10.

    The challenge is to assembly both the power plant and interplanetary craft in orbit. Yet our skill on ISS and the Shuttle / Hubble show this can be achieved.

    Consider that the average nuclear submariner spends two years in propulsion engineering and lives for months at sea, makes a voyage to Mars more than practical. The recent press on the mental impacts of these trips months away from Earth is not supported by facts.

    VASMIR should be developed to support a long term deep space access. And the power plant design would be best served by taking what has been gained in the 50 years in undersea experience.

  • kurt9 August 11, 2008, 18:33

    I agree with everything that Dave says here. I will also add that there was a refinery explosion and fire in Brazil that killed 220 people the same week that the Three Mile Island incident occurred. Its an easy guess as to which one the media covered.

    I believe the typical mission of a Trident boat is 60 days. 60 days in a sub without seeing polluted air (Gene Hackman says he doesn’t trust air he can’t see). So, astronauts should be able to handle 60 day trips to Mars without any psychological problems.

    The Cherynobal reactor was of a “positive void” design that would never have been built in the West. I do not consider it representative of modern nuclear power.

  • Adam Crowl August 11, 2008, 19:47

    Hi Dave Salt & Dave Ketchledge

    Dave Salt’s comments are very pertinent – space-power is HARD. The chief problem is that systems can only lose waste heat via radiation, thus limiting the feasible power-levels and efficiency, due to needing a hot radiator relative to the core. A lot of clever designs have been proposed, but the higher power end of things are always heavy. That’s a pain for spacecraft performance.

    At the same time Dave Ketchledge’s comment rightly notes the USN’s superlative performance record with nukes – they can be run safely, efficiently and be compact. In fact a lot of similarities exist between space nukes and submarine reactor designs – high temperatures, high burnup fractions, and advanced fluid cooling systems.

    But how do we get from A to B? The Mini-Mag Orion design shares several features with VASIMR – magnetic nozzles and so forth – but it requires pulse units that use even material more fissile than U235, and more radioactive. Curium or Calfornium are not passively safe like a uranium core that hasn’t been activated, and they’re damned expensive too.

    Gas-core nukes have a lot of appeal, but the US experience with them is even less than the Russians. They’re not a near-term technology, though they’re vigorously promoted by Dr. Steve Howe and others. Would proper testing need to be done in space? Magnetic confinement of uranium plasma will be tricky, and the “lightbulb” material needed for the heat exchanger is still ill defined.

    Even less developed is Zubrin’s Nuclear Salt-water rocket, but its potential is huge.

    But better energy conversion materials will make the heat disposal burden less – perhaps that’s a better target for improvement? Efficiencies of 85% of the Carnot Limit are claimed for one solid-state converter recently in the news. It’s hoped to be able to operate at 1300 K. With a radiator at 600 K and 200 MWe power then the radiator area is ~16,000 m^2 – not too heavy given proper design. Liquid metal droplet radiators for example, with the attractive feature that liquid sodium can be used for both the core and radiator.

  • James M. Essig August 11, 2008, 23:22

    Hi Folks;

    I have to agree that nuclear fission reactors in space can be operated safely.
    Although I have have no experience within the nuclear power industry, my father was a nuclear engineering duty officer who at times had day to day contact with the late Admiral Rickover. My father was familiar with the 688 class nuclear attack submarines, and his work in the field of nuclear propulsion systems, and his personal desire for more wide spread commercial nuclear electrical power generation convinced me as a teenager that space based nuclear power can be made safe. The fact that nuclear submarine crews stay submerged for months at a time, even when charged with the potential of deploying the most destructive weapons systems man has developed, yet remain cohesive, cerebral, and unfailingly disciplined leads me to believe that a Mars mission travel time of 39 days under nuclear power is highly doable.

    I can even envision long tem space arks that could reach our nearby stellar neighbors in a few thousand years could be powered by non-other-than nuclear fission. The VASIMR engine give us the opportunity of jumping out of our solar system. A plan to use VASIMR engines to thrust huge rotating colony space craft on multi-thousand year journeys to all of the star systems within a 50 light year radius of Earth would no doubt be a huge governmental, commercial, and scientific enterprise, but do we as a human civilization gifted with the technology that can make this happen have the courage to marshal our global resources and jump off out of our solar system! I cannot see what better way to unit the human race than the developments of such an agenda with the full technological expertise of the Earth’s militaries, civilian space agencies, aerospace companies, universities, government labs at the encouragement of the leaders of all of the Earth’s major religions.

    There are about 1,600 stars within 50 LY of Earth and with optimized Isp and sufficient nuclear fuel reserves, all of these stars should be reachable within 10,000 years with VASIMR powered space craft.

    The VASIMR engine is a concrete development than can make all of this happen. We would like to have efficient fusions rockets, Interstellar Ramjets, beamed energy powered craft, fusion runway craft, and matter antimatter rockets, but we do not yet have such. However, we have a technology which could in theory be powered by fusion, matter/antimatter, beamed energy, and interstellar hydrogen and helium thus permitting much higher gamma factors that that possible with fission reactor powered craft.



  • david lewis August 12, 2008, 10:12

    If a suitable power source can be developed then this may be the system that can get us to the sun’s gravitational lens. So maybe 20-25 years, or less if a space race does develop, before we can really peer into the working of another solar system.

    This would work well with kepler which would identify worlds that have the potential to be earth like, combined with observations to try and sample the light from that world’s atmosphere. Those worlds that indicate water in their atmospheres would be prime candidates for a probe to the sun’s gravitational lens for observation.

    A 300 km/s exhaust would, if your probe is 97 percent fuel, reach speeds of 1/300 of that of light. At least according to the calculator at ducksandrockets website. 97 percent fuel might sound extreme but if you can refuel from some resource in space then it might not be so extreme at all.

    Or, more reasonably, 90 percent fuel would allow speeds of 1/435 that of light.

    80 percent would be 1/621 that of light.

    Assuming the engines can last long enough to burn such an amount of fuel, a nuclear power plant, and the ability to fuel from something like a comet, scaled up vasimir engines could get a probe to the centauri system in less than 2000 years. Still not good enough, but a large step up from the voyager probes.

  • Darnell Clayton August 12, 2008, 13:24

    This technology looks promising, and could ultimately be the deal breaker that allows us to settle on Mars (as well as the lunar worlds of both Jupiter and Saturn).

    Any estimates as to when this technology will mature for human spaceflight?

  • James M. Essig August 12, 2008, 13:38

    Hi Folks;

    Note that although the VASIMR rocket is stated as having a maximum exhaust velocity of 300,000 m/s, I would not be surprised to see improved versions or concepts thereof capable of much higher exhaust velocities, and then so with efficient power source to thrust energy conversion mechanisms.

    One possibility for increased effective power source and fuel energy density would involve nuclear fusion, especially wherein the fusion fuel would somehow be extracted from the interstellar medium such as by any improved magscoop, ISR scoop, or other collection mechanism.

    An ideal energy source might entail extracting energy from the zero point fields to power the rocket wherein the reaction mass is collected from the interstellar medium.

    It occurred to me that perhaps elements within the so-called Island of Stable Super heavies that are proposed to exist by nuclear chemists might produce more exothermic reactions than known traditional fission fuels or perhaps have longer decay chains thus leading to effectively greater energy density per unit of fission fuel. One problem with using any such fuels is that they might be hard to produce at least initially. Some folks might say that current Uranium and Plutonium Isotopes offer about as much fission energy as we can get per unit of fuel mass, but we really do not know for sure what all of the properties of these so-called super heavies will be discovered to have. It should be interesting if we actually find stable super heavies. I am banking on the hope that such elements/isotopes will be found with machines such as the planned Rare Isotope Accelerator.

    Either way, the VASIMR engine is truely a revolutionary technology, which no doubt can and probably will be improved upon, and which I hope will lead to a revolutionary improvement in the art of manned spaceflight.



  • Dave Salt August 12, 2008, 16:26

    When talking about VASIMIR’s ability to support deep space missions, such as a 39-day trip to Mars, you really need to understand the demands it places on the power source in terms of specific power (kg/kWe). I’d recommend reading W.E. Moeckel’s paper entitled “Comparison of Advanced Propulsion Concepts for Deep Space Propulsion” (Journal of Spacecraft & Rockets, Vol.9, No. 12, December 1972, pp 863-868) in order to get a basic understanding of the associated issues and challenges.

    The power source for something like VASIMIR, or any other type of electric propulsion, will have to be on the order of 1kg/kWe to support such a mission but the best I’ve seen for an extremely advances solid-core system is just over 20kg/kWe. Russia’s Topaz 2 reactor only had a specific power of 166 kg/kWe while Topaz 3, which was an advanced version, could only muster 75 kg/kWe. So, in order to meet these requirements, you’re talking about systems based upon radically different technologies that have yet to be demonstrated in the lab, let alone a flight-weight prototype.

    The bottom line is that the work done on VASIMIR is akin to developing an electric motor for a mid-sized car and hoping that someone else will develop the battery… except in this case the battery has to weigh about 100kg and be able to run the car at full power continuously for more than a month!

    On the matter of VASIMIR’s ability to provide very high exhaust velocities (e.g. 300,000 m/s), I’ll note that this is actually a disadvantage for missions within the solar-system — around 30,000 m/s would be far more optimum — and would only be useful for inter-stellar missions.
    (N.B. With respect to extracting zero-point energy, you may as well throw in warp-drive or even worm-holes if you really want to consider “advanced” space propulsion systems :-)

    A physicist once said of VASIMIR that “it is transparently a fusion rocket built by people who can’t manage the fusion part”. Unfortunately, I have to agree.

  • philw1776 August 12, 2008, 18:28

    Kepler is not a viable vehicle to ID Earths for better examination with space telescopes because Kepler will find most of its targets at vast LYs distances. It stares at a region of the Milky Way in Cygnus and watches for magnitude dimming occultations.

  • Adam Crowl August 12, 2008, 18:28

    Hi All

    VASIMR is fundamentally an electric space drive and is thus power-limited. It’s performance envelope overlaps with the low-end of fusion drives – it is essentially the plasma handling system of a fusion drive. That’s it’s origins and it’s also hoped to eventually lead to a full fusion system in time.

    But as an electric drive how far can we push it? Geoff Landis has analysed laser-powered ion drives versus laser-sails and found they were more efficient up to about 0.2c. That’s encouraging. VASIMR is more efficient than ion drives, so it might get up to 0.25-0.3c. The power levels would be extreme, but at least the power source is at home.

  • John Hunt August 13, 2008, 3:37

    VASIMR is more efficient than ion drives… The power levels would be extreme, but at least the power source is at home.

    This may be true in theory. From a practical standpoint there is the issue of focusing a beam for a great distance. Having to construct a 300 km fresnel lens beyond Saturn (as in Starwisp) is a deal killer for me. Can VASIMIR be accelerated via a laser (or maser) beam to a 5,000 years or less mission in a runway able to be reached by a focused beam? For discussion sake lets say we use 50% of the electric power of Earth (so 1 terrawatt).

  • philw1776 August 13, 2008, 10:36

    Folks have touched on the Elephant In The Room and that’s the public fear of nuclear power exaggerated to the max by so-called environmentalists. In Germany for example the Greens are so powerfull that germany plans to de-commision nuclear power plants. They will be replaced by coal burning plants. As long as the radical environmentalists have a stranglehold on the media and the politicians, no space nuclear program will fly. NERVA in the late 60s was over a generation ago. Thank you “China Syndrome”.

  • Adam Crowl August 15, 2008, 8:11

    Hi John

    For low speed probe missions the launch track doesn’t have to be all that long. For example to get to 0.005c (1500 km/s) at 10 m/s^2 takes a distance of just 0.752 AU. Thus the laser focussing unit only needs to be relatively small. Ridiculous transit speeds like 0.5 c need ridiculously large Fresnel lenses because the beam is being used to deccelerate at the destination and re-accelerate a vehicle for a return trip. Thus it needs to be focussed across many light-years (Forward’s original destination of choice was Epsilon Eridani) and is correspondingly gargantuan.

    According to Bob Zubrin’s analysis a 1,000 ton 323 km radius sail-probe boosted to 0.15 c over a distance of 806 AU needs a laser focuser just 100 metres across. Such a vehicle is kind of heavy and big because it was manned. A dielectric sail with a nano-probe might be feasible for under 1,000 kg, thus requiring a much lower power level, especially with a lower transit speed. A carbon mesh sail with an areal mass density of 5g/sq.m and a maximum operating temperature of 2700 K would accelerate at 1 m/s^2 if the payload massed as much as the sail. Thus it would accelerate to 1,500 km/s over just 7.52 AU, need 600 GW of beam energy, and a smallish lens.

    Of course if we could make a very, very thin sail, then some serious performance would be possible for a purely solar sail. Matloff & Mallove’s “Starflight Handbook” mentions one design for a solar-sail probe designed to reach 4,500 km/s – definitely unmanned as it boosts at 700 gee initially. Matloff’s more recent musings focus on a more feasible 1,000-1,500 km/s even for manned vehicles. Pretty impressive for no propulsive power input at all!

  • Eric August 15, 2008, 9:15

    How in the world can anyone think Coal burning powerplants are more “green” friendly than Nuclear power? Furthermore, when are people going to open their eyes and realize, “yes nuclear bombs are bad, the technology itself has potential to do far more good than the desruction that could have ever been wrought by the negatives of nuclear power”…

    I just don’t get it.

  • fra August 23, 2008, 11:15

    if only vasimir engine would permit the human colonization of moon (meaning some bases for science research and not town like in scifi movies) and fast robotic exploration of solar system (months instead of years to reach outer planets), then vasimir would be a great succes tecnology.
    i think that we have to be realistic and don’t have to think to vasimir for interstellar missions

  • Joe Cooper August 30, 2008, 15:39

    I love the potential of VASIMR here. I think the destigmatization of nuclear power will _have to_ happen when oil supply wanes. This could also be applied to systems already in development.

    Constellation, for example. Constellation involves the Orion spacecraft, Altair lunar lander and an “Earth Departure Stage”. I’m imagining a nuclear-electric Earth Departure Stage built with VASIMR that could allow Orion+Altair missions waaay out and yonder. How long to Enceladus or Europa with this thing?

    Simple hydrogen reaction mass could be refilled anywhere in the outer solar system.

    If NASA went nuclear, this sort of thing could allow some really ambitious missions within NASA’s post-Apollo budget.

  • ljk December 14, 2008, 21:49

    NASA and Ad Astra Rocket Company sign an agreement to
    test flight the VASIMR rocket engine aboard the International
    Space Station (ISS):


  • Breaking news July 24, 2009, 0:03

    The Newscientist magazine has just stumbled across this old story and are now trying to present it like some kind of scoop!

  • ljk July 27, 2009, 12:59

    Today’s Videos: VASIMR Full Throttle

    Video: Ad Astra VASIMR Full-Power, Full-Field Firing

    “This image shows our achievement of full-power full-field for the 1st stage of VASIMR. In addition, here are some recent video posts documenting this achievement with our new superconducting magnet. The maximum magnetic field within the core of VASIMR is around 2 Tesla, about the same as most MRI machines.”

    Nonreimbursable Space Act Agreement Between Ad Astra Rocket Company and NASA, signed 5 Dec 2008.

    “This Agreement becomes effective upon the date of the last signature below and shall remain in effect for a period of four (4) years from the date of the last signature.”


  • ljk October 7, 2009, 23:38

    Plasma Rocket Could Travel to Mars in 39 Days

    PhysOrg.com Oct. 6, 2009


    A 10- to 20-megawatt plasma rocket could propel human missions to Mars in just 39 days, whereas conventional rockets would take six months or more, according to AdAstra Rocket Company. (Ad AstraRocket Company)

    The company’s VASIMR technology uses radio waves to heat gases such as hydrogen, argon, and neon, creating hot plasma. Magnetic…


  • ljk September 8, 2010, 1:28

    VASIMR: hope or hype for Mars exploration?

    An advanced electric propulsion concept known as VASIMR has won support from some, including NASA leadership, for its potential to greatly reduce the travel times for human Mars missions. Jeff Foust reports that some Mars advocates are skeptical, at best, of the ability of this system to match expectations.


  • tom July 12, 2011, 0:53

    I’m am not impressed with the anti-nuke movement… how many of these folks are going to Iran to organize protests? Yeah, I guess these people have a sense of reality after all. Anyway, everything about VASIMR is going the right direction. Finding mass to power rating for this propulsion unit will be a lot of work and planning. Frankly, I hope the commercial applications will exceed the governments hold of funding. If financing isn’t the issue, a 2018 mission to Mars and the outer planets will be feasible. I’d like to see Ceres and Crythmne have a manned mission?

  • ljk July 12, 2011, 23:52

    Zubrin Challenges Chang Diaz to Debate VASIMR

    posted 8 hours ago by Michael Stoltz [ updated 8 hours ago ]

    In a major Op-Ed article entitled “The VASIMR Hoax” printed in the July 11, 2011 edition of the industry weekly Space News, Mars Society President Dr. Robert Zubrin denounced the claims advanced by the proponents of the VASIMR propulsion system who state that it is the key technology required for enabling human missions to the planet Mars, and invited VASIMR inventor Dr. Chang Diaz to defend his claims in open public debate.

    Whether Dr. Diaz and/or an associate agrees to participate or not, the debate panel, entitled “VASIMR: Silver Bullet or Hoax?”, will be held on the afternoon of Thursday, August 4, 2011 at the Fourteenth Annual International Mars Society Convention, Embassy Suites Hotel, Dallas, Texas.

    In order to register for the Mars Society convention, which will run from August 4-7 and feature over 50 other papers, panels and debates, please click here.

    To read the full text of Dr. Zubrin’s Space News article, please click here.

    Full article here: