NASA Plans Test of New Plasma Drive

Sallust writes "Flightglobal has an interesting article about the testing of a new electrically powered plasma engine called the Vasimir. It's being developed by former astronaut Franklin Chang-Diaz and promises to greatly reduce the time and fuel required for interplanetary journeys. According to the article: 'The Vasimir involves the injection of a gas such as hydrogen into an engine that turns it into a plasma. That plasma is then energised further using radio signals as it flows through the engine, a process controlled by electromagnetic waves from superconducting magnets. Accelerated and heated through this process the plasma is focused and directed as exhaust by a magnetic nozzle. Vasimir is many times more efficient than conventional chemical rockets and far less fuel is needed.' The developers are finalising an agreement with NASA to fit a scaled-down version of the engine to the ISS to conduct operational tests. There is also a concept video on YouTube suggesting a journey time for a manned craft to Mars on the order of 60-70 days."

Comments

plasma exit velocity?

[oldspewey]

Neither summary nor TFA give any indication of the velocity of plasma exiting the engine. How does it compare with chemical rocket? Ion drive?

Re:plasma exit velocity?

[Intron]

We can guess that it is similar to the DS-1 Ion drive which propels Xenon ions at 30 km/sec.

Re:plasma exit velocity?

[bodino]

Wiki - the source of all knowledge - has some good details.

http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket

Re:plasma exit velocity?

[AKAImBatman]

VASIMR (Variable Specific Impulse Magnetoplasma Rocket) is a variation on the Magnetoplasmadynamic thruster (MPDT) that has been in development for a decade or two. These thrusters are coveted for their rare combination of high specific impulse (i.e. efficiency) and thrust to weight ratio (power). Such a combination makes them ideal for manned missions, as they allow space craft to fly under constant, high powered thrust. This is the "holy grail" of space travel because it cuts down the TIME in flight significantly. Thus the summary's mention of a 90 day flight time to Mars. (Normal flight time using a minimal Hohmann Transfer is ~1.5 years.)

Obviously, the exact thrust numbers depend upon the rocket. However, the VASIMR rockets have a range of specific impulses from 3,000 to 30,000 seconds. You can see how that compares to Ion Thrusters here. Chemical rockets tend to top out at 500 seconds and thus don't even place when compared to VASIMR or Ion thrusters. The only reason why we want to keep using chemical rockets once we have better thruster technology is that all these new technologies lack the thrust to weight ratio to get a rocket off the ground. i.e. They are only good for space travel. Atmospheric flight need not apply.

Re:plasma exit velocity?

[HRogge]

Ion drives use electromagnetic fields to accelerate particles with an accelerator. Most times they use heavy atoms like xenon.

VASIMIR makes plasma from light elements like hydrogen and then use electromagnetic fields to heat the plasma... by controlling the temperature you can change the thrust/momentum the engine creates.
(at least that's what I heared).

Re:plasma exit velocity?

[avandesande]

From wiki:

Current VASIMR designs should be capable of producing specific impulses ranging from 3,000 to 30,000 seconds (jet velocities 30 to 300 km/s). The low end of this range is comparable to some ion thruster designs. By adjusting the manner of plasma production and plasma heating, a VASIMR can control the specific impulse and thrust. VASIMR is also capable of processing much higher power levels (megawatts) than existing ion thruster electric propulsion designs. Therefore it can provide orders of magnitude higher thrust, provided a suitable power source can be provided.

Re:plasma exit velocity?

[GleeBot]

Actually, the main reason to have a variable Isp (specific impulse) engine is because there's a direct trade-off between Isp, and energy.

Note that momentum transfer increases linearly with velocity and mass, but kinetic energy increases linearly with mass and with the square of velocity. Thus, to make a given amount of mass go faster requires a lot more energy.

A more concrete example: You want to impart a total impulse of 2MV. You can either get it throwing out a mass M at 2V (mass efficient), or by throwing out a mass 2M at V (energy efficient).

In the first case, you use 1/2 M (2V)^2 = 1/2 M 4V^2 = 2MV^2 energy, while in the second case, you use 1/2 2M V^2 = MV^2 energy, or half as much, for the same total impulse. This only gets worse the bigger the velocity difference gets.

Often, the limiting factor in electric propulsion technologies like these is the power supply, not the thruster. Generally, to get the max Isp all the time you'd need a power supply so massive (like a nuclear reactor) as to completely throw off the mass fraction.

So generally, the way these systems are proposed to be operated is with a fixed power budget, and switched between mass efficient, low thrust mode (for long term delta-V), and mass inefficient, high thrust mode (for certain maneuvers).

New, it is not

[ivanthered]

The VASIMIR has been in developement since 1979.
http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket

I wonder where they will get the 200 kW to drive it from?

-------------
http://borislegradic.blogspot.com/

Re:New, it is not

[qoncept]

I'm sure in 1979 they could walk in to any corner drug store and buy plutonium, but this is 2008. No, no, the only thing that could generate that kind of electricity is a bolt of lightning, but unfortunately you never know when or where it's going to strike.

Re:Nice to see fact moving faster than fiction

[spun]

Fact is often capable of moving faster than fiction, it just takes a collective decision to make it so. We could have been to Mars already, just like we could be feeding everyone in the world. We just don't care enough.