Attitude Determination from Light Curves

T HE unscented Kalman filter (UKF) [1,2] has been used extensively in spacecraft attitude determination based on standard in situ measurements using gyro-based models for attitude propagation [3,4] and, more recently, in orbit determination from groundbased angles and range measurements [5]. In the latter application, the filter is unable to track changes in attitude, because these changes affect the nonconservative forces, which are subtle as compared with the dominant gravitational forces. (i.e., becoming manifest in positional data over long time scales). Attitude changes must be modeled and tracked to properly account for the nongravitational forces experienced by the object. In thisNote,we describe for thefirst time the use of the UKF in attitude determination from ground-based brightness measurements (i.e., light curves), which are very sensitive to attitude variations. This novel application of the UKF allows for the possibility of more accurate and precise orbit determination by exploiting multi-data-type fusion, combining both astrometric and photometric observationswithin the samedata-reduction process [5].