VASIMR Ion Engine Could Cut Mars Trip To 39 Days

An anonymous reader writes "It would take about 39 days to reach Mars, compared to six months by conventional rocket power. 'This engine is in fact going to be tested on the International Space Station, launched about 2013,' astronaut Chris Hadfield said. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) system encompasses three linked magnetic cells. The 'Plasma Source' cell involves the main injection of neutral gas (typically hydrogen, or other light gases) to be turned into plasma and the ionization subsystem. The 'RF Booster' cell acts as an amplifier to further energize the plasma to the desired temperature using electromagnetic waves. The 'Magnetic Nozzle' cell converts the energy of the plasma into directed motion and ultimately useful thrust."

Comments

Re:I'm dizzy.

[ageoffri]

39 * 2 = 78 days for round trip to Mars in the article which is less then 3 months. The 39 days is one way just to get there.

Actually...

[denzacar]

It already is.

Re:"A new NASA rocket engine"

[sh00z]

Also, correct me if I'm wrong, but ain't VASIMIR developed private company, not by NASA? Sure, NASA is working together with Ad Astra Rocket Company, but does NASA really deserve all the fame?

This started as a NASA project, at the Advanced Space Propulsion Laboratory at the Johnson Space Center.

Dr Franklin R. Chang Diaz (the other former astronaut involved, and not mantioned in this Canada-centric article) took the project to private industry in 2005

Re:I'm dizzy.

[TheRaven64]

Depends on how much he weighs. The drive provides a force of 0.5N. A typical car plus passengers masses around 1000kg. F=ma, so, 0.5 / 1000 gives him an acceleration of 0.0005 m/s/s (ignoring friction and air resistance). 800 miles is a little under 1,300 km, or 1,300,000m. Assuming a stationary start, and accelerating for the whole time, we get sqrt(2s/a), which is around 51,000 seconds, or around 14 hours. Of course, after that time he'd be going quite quickly, so he'd probably want to be slowing down for the second half of the journey which increases the total travel time to about 20 hours.

Ion drives are not (yet) fast. They provide a much lower acceleration than conventional rockets, which is why no one is talking about using them to get to orbit. They use a lot less propellant to produce this thrust than an equivalent chemical rocket though, which means that they can provide this thrust for longer. After 14 hours, the car would be going at 25m/s. Not particularly fast; a chemical rocket can get to that speed in a couple of seconds. After a week it would be going at over 300m/s, which is a lot more respectable.

Your distance from earth to mars looks sensible, and makes the average speed 16.3km/s. Assuming linear acceleration and deceleration (which is incredibly wrong when we're talking orbital mechanics, because this would be a transfer orbit so you'd actually be accelerating for most of it), that would mean that the top speed would be 32.6km/s and you'd spend half of the time accelerating to this speed and half slowing down from it. That gives a delta v of just under 0.02m/s/s, which means that either they have more than one ion engine on the craft, or they are using something that weighs a lot less than a car. At that acceleration it would take just over 3 hours to travel 800 miles, which is close to what the grandparent said. I'm not sure where you get your 1.7km/s/s from, but I I think you dropped a 'k' somewhere in your calculations.

Re:No quite yet.

[Interoperable]

then you could just use it as a conventional nuclear rocket (i.e. superheated steam).

The VASMIR can accelerate a neutral gas to much, much higher velocities than a steam driven rocket would. This means significantly more impulse per unit mass so the fuel weight would be dramatically reduced. Sure the reactor is heavy but it still packs a much higher power density than combustibles so all in all a VASMIR can pull off an excellent power to weight ratio for an extended acceleration.

Re:Tag as SLASHVERTISEMENT

[Creepy]

Actually, I've found the latest VASIMR progress quite interesting, but that article seemed more intent on promoting Canada than feeding news. Heck, the ISS mission has been known since 2007.

A google search was also able to come up with an article with a lot more meat. This explains that the project is working towards 200MW ion rockets (MUCH more powerful than the earlier .3kW), would be powered by a cheap nuke drive instead of solar panels, and they believe it's doable by 2020. Similar info is in PopSci this month.

Now if they could just get that dense plasma fusion device (see Slashdot yesterday) to power the craft instead of fission, that would be cool... yeah, I know I'm pipe dreaming again, but I can't help it.

Re:No quite yet.

[ZombieWomble]

There's a bit of a confusion of terms here - nuclear reactors do have some degree of a size restriction, but neither the Pioneer or Voyager programs used nuclear reactors as their power source. They both used radiothermal generators (RTGs) - that is, they derived their power from the heat generated by the decay of a nuclear isotope, rather than a fission reaction.

This latter kind of generator is pretty much infinitely scalable, as you say, but aren't so efficient for big power demands - most of the RTGs in the probes you mention provide a few hundred watts, even when new.

For these thrusters, you're talking about burns of 10 MJ or more, which would require a vastly bigger RTG (or, more likely, a true reactor as the scaling would make it the more efficient choice) to get a reasonable pulse rate out of it.