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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."
No stated in this article.
But I'm pretty sure the engine discussed will need to be roughly 100x more powerful to make that 39 day trip a reality.
No, not really. Hauling the fuel for chemical rockets into orbit is expensive, so mostly they do hard burns to get the right speed and direction, then they coast most of the trip. VASIMR doesn't need the heavy fuel, as it is solar powered, so it provides constant thrust. Apparently days of constant acceleration makes a difference.
- doug
VASIMR doesn't need the heavy fuel, as it is solar powered, so it provides constant thrust
Ummm, no. Or, rather, technically yes, but not really. In a chemical rocket, fuel and reaction mass are the same thing. The fuel burns, expands, and flies out of the back. With an ion engine, they are separate. The fuel is anything that can produce electricity (e.g. solar or nuclear plants) and the reaction mass is something that you've ionised. This still has mass, and still has to be carried with you until you throw it out of the back, irrespective of where the power comes from.
The important thing to remember is that all of these are reaction drives. They work according to the principle of conservation of momentum. When you throw some mass out of the back of your space ship, the space ship gains the same amount of momentum as the thing you throw out of the back. You can double the momentum that you gain from your engine by either doubling the speed of the ejected reaction mass, or by doubling the amount you throw out. With conventional rockets, the speed is limited by the rate of reaction, which is fairly fixed. With an ion drive, the speed is limited by the amount of power you put in.
You still need to carry the propellant, but if you can throw it out at ten times the speed then you need a tenth of the amount. If you need a tenth of the amount, then your space ship will mass a little over a tenth as much, and so the speed that it gains from this change in momentum will be almost ten times as much.
In theory, you could use a small glass of water, accelerated to a significant fraction of the speed of light, as your propellant for an entire trip to Mars and back. In practice, there is a limit to the speed to which an ion thruster can accelerate the ions it's throwing out and so you still need quite a large amount of propellant.
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Imagine if we could do a close flyby on another solar system!
A close flyby at 0.5C might not be as exciting as you'd think.
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