Re: Ion Propulsion

Michael M. Butler (butler@comp*
Mon, 09 Jun 1997 00:58:33 -0700

At 07:26 PM 6/8/97 -0600, you wrote:

>>A tunable plasma engine designed by MIT is being tested by NASA.


>>It can reduce the one way trip to Mars to 2.5 months and

>>allow a round trip of 7 months duration.

Isn't constant thrust drive a wondrous thing?

>To heat up the gas, a microwave oven of sorts is used, powered by 10

>megawatts of power supplied by a nuclear reactor.

This is basically magnetic resonance induction heating, and yep, it is a fair thing to call it a microwave oven; though you do need to tune it, as is mentioned elsewhere; I'm probably stating the very obvious ("Shut up, Peggy, Shut Up!").


>The spaceship will be surrounded by several huge tanks filled with liquid

>hydrogen, similar to those used by the shuttle at launch. The tanks will

>shield the crew from dangerous solar emissions and, at the same time,

>provide good insulation against heat.

This last is almost certainly a misquote of what the MIT chaps said. The tankage will have to include good superinsulation (ganged layers of Al-sputtered Mylar held inches apart), pointed toward the sun, or the boiloff loss during the voyage will be excessive. Even so, I'd be interested in seeing what the design tradeoffs would be in using e.g. methane instead of H2. Don't know if the residual carbon would gunk everything up.


>In a trip to Mars, Chang-Diaz said, the ion engine would accelerate the

>spaceship for half the distance and then decelerate it until it can settle

>into an orbit around the red planet prior to a landing.


See also the ion drive ships in Disney/Von Braun's _Conquest of Space_...

>Electricity during the tests will be supplied by a series of batteries.

>Chang-Diaz believes that once proven in a Mars mission, the ion engine will

>propel man further out, to Jupiter, Saturn or even Pluto.

Humbler use in Earth orbit is also a winner; previous "high-efficiency" designs such as the Russian ones used nogoodnik propellants like cadmium.

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