Hi Phil, KA9Q What you describes using both magnetorquers ,momentum wheels and CCD video cameras for the attitude control system is what was made on AO40 but it was a big satellite and not a microsatellite.
73" de i8CVS Domenico ----- Original Message ----- From: "Phil Karn" <[email protected]> To: "R Oler" <[email protected]> Cc: "Amsat BB" <[email protected]> Sent: Friday, August 26, 2011 6:54 PM Subject: [amsat-bb] Re: some exceedingly clever technology > On 8/24/11 8:11 PM, R Oler wrote: > > > > http://onorbit.com/node/3709 > > Thrusters are necessary for orbit control, but for attitude control > (which I think we really need) you'd *really* prefer something that > doesn't consume a fuel. > > These attitude control systems come in basically two types: > magnetorquers and reaction wheels. Magnetorquers exchange angular > momentum with the earth by acting on its magnetic field, but they tend > to be slow, imprecise and require complex control and sensing systems > including a magnetometer far enough from the spacecraft to get away from > its own magnetic fields. > > Reaction wheels come in two kinds: momentum wheels and control moment > gyros. Momentum wheels change speed while control moment gyros don't. > The latter seem much more common in spacecraft but I'd investigate both. > They're good for quick, accurate pointing like you'd need to keep an > antenna pointed down or a solar panel pointed at the sun. > > Having both a magnetorquer and a set of wheels can be advantageous as > the magnetorquer can be used occasionally to dump accumulated angular > momentum from the wheels should it build up from small external torques. > > Controlling attitude also means measuring it, and for this I keep > thinking about small, cheap CCD video cameras. If we could build good > enough sunshades we could snap pictures of star fields and look them up > in a database. If you can match multiple stars in an image, then a > single image could fix the attitude of the spacecraft. But I'd want to > put a camera on each surface if possible. They could also sense the sun > and the earth, though that's not as simple as it might seem. The sun > usually overloads a CCD and produces streaks while the earth is very > large in LEO. It might be possible to recognize the limb of the earth > and get better precision that way. A lot would depend on the software > processing these images, and it would be a challenge to write. > > -Phil, KA9Q > > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
