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NASA aims for space tests of Mars-in-a-month plasma drive

270hp Star Wars-esque blue glow engine for the ISS?

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NASA will work with a firm started by a former astronaut to build a spaceworthy plasma drive capable of revolutionising travel beyond Earth orbit. However it appears that the space tests may not take place aboard the International Space Station (ISS) as had been planned.

The VX-200 blasting Argon at full bore in ground trials. Credit: Ad Astra Rocket Co

The blue glowing engine exhausts in Star Wars are actually quite realistic, it turns out

The Ad Astra Rocket Company, headed by Dr Franklin Chang Díaz. has already built an experimental prototype version of its Variable Specific Impulse Magnetoplasma Rocket (VASIMR). The VX-200, (VASIMR eXperimental 200 kilowatt) unit works fine in a vacuum chamber on Earth. Now Ad Astra has announced an agreement under which it will work in partnership with NASA to produce the VF-200 flight version, which has long been planned for installation aboard the International Space Station.

According to the Ad Astra announcement:

NASA will support Ad Astra’s efforts to mature the design of the 200 kW VF-200 VASIMR flight demonstrator. This support includes, among other things, engineering design on two of the VF-200 flight demonstrator’s subsystems, integration support and structural engineering of interfaces with a launch vehicle and a potential flight platform (eg ISS or free flyer).

The VASIMR works by squirting stuff out of its exhaust just as a normal rocket does: the difference is that it does so much more violently, hurling its argon reaction mass out as a plasma hot as the interior of the Sun and moving at better than 50 kilometres per second. This means that VASIMR gets a lot more poke out of a given mass of propellant than ordinary chemical rockets possibly can: though unlike them it needs electrical power to work.

The radical rocket was invented by Chang Díaz, who is a plasma physicist by training and who has seven Shuttle missions in his logbook from his days as a NASA astronaut. He considers that it is far more fuel-efficient even than existing ion engines, already used in satellites and space probes for orbital maintenance and manoeuvring.

The VASIMR isn't any use for getting into space in the first place as its power-to-weight ratio is small: the VX-200, the size of a small car, can only produce enough thrust to lift half a kilogramme or so off the ground.

Once in orbit, however, a VASIMR comes into its own. A normal rocket will burn up any practical amount of fuel very quickly: thus it can be used only in brief bursts. A spacecraft driven by such means must spend almost all its time coasting along unpowered. Thus a journey to Mars, for instance, would take 6 months for a conventional spacecraft.

A VASIMR, however, can keep on exerting its relatively tiny push for weeks on end without using any more juice, gradually boosting a ship up to terrific speeds that would never be possible with a chemical rocket. VASIMR ships could get to Mars in just 39 days.

That's for the future: but in the meantime there's the International Space Station, which needs to regularly fire up its normal rocket thrusters in order to maintain its orbit. Several tons of fuel are shipped up to the ISS every year for this purpose aboard Russian Progress (and now European ATV) supply capsules at huge expense.

If the space station gets the new VF-200, however, the plasma drive's more efficient use of fuel could do the same job with less propellant, so allowing more payload to reach the ISS on a given number of supply flights. It had been loosely planned that the VF-200 would be installed on the station in 2014 - perhaps travelling up atop a Falcon 9 rocket from Elon Musk's famous startup company SpaceX, hired for the occasion under NASA's new commercial launch arrangements.

The station is a good fit for VASIMR as it has vast solar-panel arrays - the largest ever placed in space* - and thus there is considerable electrical power available on board, up to 250 kW. The station could muster enough juice at times to run the VF-200 at full bore and really try it out properly.

But now we learn that the VF-200 may not in fact go to the station, but instead fly in some other "flight platform". This could be bad news for a really comprehensive test programme, as today's spacecraft don't have enough juice to really put a 200 kW machine through its paces. Even powerful communications satellites don't generally dispose of more than 15 kW or so. A large, costly (and correspondingly heavy, thus expensive to launch) solar array would probably be required for any "free-flyer" non-ISS option.

The other option for long-term power generation in space is nuclear, but this too is so far quite limited in output. Soviet radar-ocean-reconnaissance satellites carried Topaz reactors which could generate several kilowatts of electricity: they were the most powerful nuclear units so far flown. US nuke boffins have developed a space reactor, the SAFE-400, that could produce 100kW of electricity (two of these and the VF-200 could easily be lifted right up to geosynchronous transfer orbit by a SpaceX Falcon 9) but it has never been used.

The fact is that even the launch of comparatively simple and low powered radioisotope-decay power units (as opposed to reactors proper) often draws a lot of technofear protest, and the bureaucracy and expense associated with spaceflight-rated nuclear technology is immense. Chang Díaz has always suggested - in common with most serious analysts - that flight beyond Earth orbit, or anyway beyond the Earth-Moon system, can't ever become a serious activity without the use of nuclear power. Even so, his chances of getting a nuclear powerplant for the inaugural VF-200 trial flight would seem slim.

For now, it's probably best for plasma-rocket fans to hope that in fact NASA will find room for the VF-200 aboard a supply flight to the ISS. ®

Bootnote

*These are a large part of the reason that the ISS needs to refuel so much. The huge panels, ploughing through the not-quite-vacuum of low Earth orbit, exert a small but significant drag on the station, continually slowing it down and thus tending to make it fall out of the sky.

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