In-Orbit Instrument-Pointing Calibration Using the Moon as a Target

A method was developed for in-orbit measurement of the relative pointing of spectrometer channels, and the relationship between the spectrometer channels and the spacecraft coordinate system. In this innovation, individual scans of the Moon, from the three channels, were used to determine the position of the center of the Moon, with respect to channel-specific coordinates. Comparing the coordinates of the center of the Moon, obtained from individual channels, yields the relative pointing between the channels. Comparing the coordinates of the center of the Moon in one of the channels with the Moon ephemerides and with the spacecraft coordinate measurement, using the onboard star tracker, yields the relative orientation of the channel optical axes with respect to the spacecraft coordinates.