Sunday, August 19, 2012

Micro thrusters

A couple of years ago Paulo Lozano came up with a single-power supply method of accelerating ions for a micro-satellite propulsion system. A liquid salt seeps through porous metal to the tips of tiny needles where an electric field sprays them away. Last week he announced progress with a postage-stamp sized system that generates 50 microNewtons of force from 500 needles fed from a reservoir. The idea is to have a simple (no piping) system capable of adjusting micro-satellites' (1kg!) orbits. You can't use such tiny thrusters to land, or make big changes; just small adjustments.

The press release is exasperatingly vague on the details, such as how fast the ions are emitted, whether the polarity is reversed from time to time to avoid static charge buildup(*), and how long the thrusters can currently operate. And the release says things like "The researchers envision a small satellite with several microthrusters, possibly oriented in different directions." "Possibly?" You mean "obviously" Ack. I haven’t been able to get at the conference proceedings for details.

50 microNewtons isn’t a lot, but if you’re patient it can do quite a bit for you. For a 1kg micro-satellite, in a day it would change the speed by 4.3m/sec. In 20 days it could change the orbital speed by 1%, which can make interesting differences in the orbit. Or it could rotate the satellite to a new angle, provided there were counter-thrusters to stop the rotation. See "obviously" above.

Of course sooner or later you run out of fuel, but in the meantime you have an uncomplicated rocket. I look forward to hearing more about that.

(*) "Reverse the polarity" sounds like Star Trek technobabble, but suppose you're firing off the positive ions. Your craft will gain a net negative charge, which has two bad effects: it pulls you backwards towards that positively charged cloud and thus reduces the thrust, and it adds some sideways complications as you travel through the Earth's magnetic field. Neither are huge effects here, but then neither is the thrust. So it would make sense to change the polarity of your needles and eject the negative ions for a while, and use the whole fuel supply. The reports were cagy about the nature of the salt, but probably the negative and positive ions are different enough that you could only optimize for good thrust with one variety and the other wouldn’t be quite as useful.

1 comment:

Texan99 said...

In freefall you can make use of tiny forces exerted over long periods, if necessary, like being able to whisper is a very quiet room. Pretty cool.