Laser Reference Sensor Alignment Estimation Using Reference Signal Observations

The Laser Reference Sensor is the central instrument in the Ice, Cloud, and land Elevation Satellite laser pointing knowledge system, simultaneously observing the altimetry laser, stars, and a reference signal in a single instrument coordinate frame. The reference signal is intended to provide direct observations of the alignment between the Laser Reference Sensor and the Instrument Star Tracker. The reference signal failed early in the mission and a method was developed to partially replace it by comparing two attitude time series: an attitude filter time series for the Instrument Star Tracker and a pure-gyro time series for the Laser Reference Sensor. Only the Instrument Star Tracker and gyros are used in the replacement method, with the gyros tracking the Laser Reference Sensor attitude in order to make the relative motion of the Instrument Star Tracker observable.