[amsat-bb] Re: some exceedingly clever technology
This is what the KiwiSAT - ADAC - experiment will investigate. http://www.kiwisat.org/science.html Terry, ZL3QL. - Original Message - From: Phil Karn k...@philkarn.net To: R Oler orbit...@hotmail.com Cc: Amsat BB Sent: Saturday, August 27, 2011 4:54 AM 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 AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
[amsat-bb] Re: some exceedingly clever technology
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 k...@philkarn.net To: R Oler orbit...@hotmail.com Cc: Amsat BB amsat-bb@amsat.org 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 AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
[amsat-bb] Re: some exceedingly clever technology
This is exactly the kind of low tech solution that we need to use in amateur sats to have orientation and orbital control. But, I worry that if we did demonstrate control, would we be allowed to be in control since the craft could then become a weapon in the hands of the wrong person. Gregg W5GGW On 8/24/2011 10:11 PM, R Oler wrote: http://onorbit.com/node/3709 Robert G. Oler WB5MZO Life member AMSAT ARRL NARS ___ Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB@amsat.org. 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
[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 AMSAT-BB@amsat.org. 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
