Recovering from a Coplanar Orientation

If a thinsat goes without control for a long time it will end up coplanar with its equatorial orbit. That is, the plane of the thinsat will match the plane of the orbit, with the solar cell face pointing towards the north. If this occurs during winter, the solar cell will always be pointing away from the sun.

Fortunately, a thinsat still receives light reflected from the earth, which has a moderate albedo, about 0.3. If the thinsat is warm enough to operate the thrusters, the reflected light from the earth will be enough to operate low power circuitry to drive them. The transmitters and high power processors will be turned off, for the few minutes it takes for the thinsat to point its face towards the sun. The back of the thinsat will be very low albedo, high emissivity, so sunlight on the back will keep it reasonably warm, perhaps 260K rather than the normal 330K.

The biggest problem is at the equinoxes, when a coplanar orientation points the thinsat edge-on towards the sun. At that point, the only source of light and heat is the reflection from the earth filling 6.7% of the sky at 250K and about 190 watts of light per square meter. That will keep the thinsat at perhaps 150K, and it will have to orient at that temperature.


Coplanar (last edited 2013-02-17 05:32:34 by KeithLofstrom)