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Plasma Rocket Successful Full Power Test
Matt_dk writes "VASIMR is a new high-power plasma-based space propulsion technology, initially studied by NASA and now being developed privately by Ad Astra. A VASIMR engine could maneuver payloads in space far more efficiently and with much less propellant than today's chemical rockets. Ultimately, VASIMR engines could also greatly shorten robotic and human transit times for missions to Mars and beyond."
In theory, we could always do that, in practise I don't think we'll ever do that. Getting anywhere really fast burns a ton of extra energy, plasma drive or not. Most of the really long-distance missions haven't accelerated to that speed, they've done a slingshot trip around jupiter or something like that. Even on a Mars mission we're really just waiting for Mars to be in the right position to leap orbit and minimize the rocket use, not plotting a course or going from full impulse to full stop in seconds like you see on Star Trek. It would still cut a lot of costs but the cheapest route is still the slow one.
Live today, because you never know what tomorrow brings
OK, this is a classic plasma rocket - ionize an inert gas (here argon) and push it out with an electric field (not done in this test). So what are the numbers? How much argon are they using per unit thrust? How much electric power does this take. Is 200KW the input, or the output?
You still have to carry reaction mass; that's the argon. So you can't just keep boosting as long as you have power.
It's not a bad idea, but it's not clear how good the implementation is.
The same incorporates "variable specific impulse" so you have to use a range.
3,000 seconds is comparable to a ion motor.
30,000 seconds is better than the predicted Isp of the Orion nuke-bomb drive.
I thought it seemed fairly straightforward.
1. the hotter the flame, the more thrust you have and the more efficient the thrust. Your limit is when it's hot enough to melt the rocket's nozzle.
2. Since it's a plasma, you can control it with a magnetic field, to the point that its heat won't affect the rocket's nozzle.
More efficient=less fuel needed. In addition to keeping the heat away from the metal, being able to control it with a magnetic field means you don't have to have a moveable nozzle to steer the thing, making it possibly simpler than traditional designs.
Free Martian Whores!
>The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 >mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are >obvious. But ion engines can potentially eject mass at much higher speeds.
Hmm. Traveling at 1000mph relative to what? The aether?
Keep in mind that unless you are doing something like a Bussard ram scoop that is collecting material enroute, the only thing you have to be able toss out the back of your vehicle is reaction mass you have brought with you.
So your top "speed" is limited to exhaust velocity. All of these more exotic propellant systems are about increasing the efficiency of throwing the mass to increase the velocity of the vehicle.
The problem with these propulsion systems is that none of them are strong enough to be able to push against the 9.8 m/s^2 acceleration that we have on the ground here on Earth, so they are only useful once you get into space. They are highly efficient but overall only give relatively low amounts of acceleration.
Their advantage is that they can be operated for long periods of time... days, weeks, months, or even years potentially. Over time, even a modest acceleration adds up to a huge velocity change and can be significant in terms of travel to distant places like the outer planets of the solar system or even Mars. You can even take trajectories other than a modified Hohmann transfer orbit in this case between planets.
If you toss out a huge amount of mass at low velocities, your reaction mass is gone. Tossing that mass out at a significant fraction of the speed of light... well, you don't have to be using all that much reaction mass in order to be getting some real benefit in terms of changes in velocity.
BTW, I just don't see huge efficiencies with solar arrays being used to generate the electricity needed to run these exotic motors. The mass of the panels themselves quickly start to become a major issue as you scale up the thrust to make them useful, not to mention that travel beyond the Earth (aka to Mars or the outer solar system) results in significantly reduced amounts of solar energy that would even hit the solar panels.
For satellite station keeping (rather than using hydrazine or other chemical thrusters) this is an option as you need the power anyway for vehicle operations and can temporarily shut down some high energy consumption activities in exchange for maneuvering the vehicle. Typically the on-board fuel is one of the things that limits the lifetime of satellites... particularly things like spy satellites who want to use thrusters to vary their orbital characteristics and make it much more unpredictable about where they might be in the sky at any given moment. Geosync satellites could also take advantage of this as a huge expense is simply getting the satellite from low-earth orbit to a higher altitude, but it doesn't have to be done immediately and can take several months if necessary... or to correct for drift from their position once they get to the correct altitude.