An Attitude Control System for the Advanced Orbiting Solar Observatory

The scientific objectives of solar research require ever increasing accuracy requirements for orbiting observatories. To speak of "seconds of arc" is now quite common among engineers designing control systems for scientific spacecraft. One such spacecraft is the Advanced Orbiting Solar Observatory (AOSO). The attitude control subsystem for the AOSO must meet a number of stringent performance requirements. For instance, it must have a pointing accuracy of +/- five seconds of arc to observe the smallest sun spots, and it must also have the capability of raster scanning to map phenomena emanating from the sun's surface. The AOSO control subsystem needs to be considerably more accurate than the over-all observatory requirements, because of possible misalignment of experiments. The key component affecting its accuracy is the fine sun sensor. A number of concepts using a mosaic of detectors were investigated and rejected because of high power requirements and developmental problems. It became apparent that there would be moving parts in the AOSO fine sun sensor. Several workable designs, meeting most of the control subsystem requirements, came to the surface. The sensor that will be used for AOSO was conceived by the combined efforts of Minneapolis-Honeywell and Republic Aviation Corporation.