Horizon scanner flight experiment on engineering test satellite IV

The horizon scanner test project is one of the four experiments on the Engineering Test Satellite IV launched on the 11th of February, 1981. The scanner was originally designed for an earth horizon attitude sensor utilizing a pyroelectric infrared detector (PbTiO3). The scanning mechanism is controlled by a quartz Phase-Lock-Loop and a direct drive motor sustained by a dry-lubricated bearing. The preflight test and analysis procedures are briefly described together with the operational schedule during the mission duration. Some of the obtained results are summarized.