ALTIMETER RANGE PROCESSING ANALYSIS FOR SPACECRAFT NAVIGATION ABOUT SMALL BODIES

The impact of using altimeter range measurements as an observation type for navigation of spacecraft about small bodies is evaluated. The altimeter range measurements can supplement or replace the standard optical landmark and Deep Space Network (DSN) radiometric tracking. Navigation of spacecraft orbiting small bodies, like asteroids, can be challenging since the a priori physical characteristics of the central body can have larger than normal uncertainties. The addition of the altimeter range data into the orbit determination problem can be used to alleviate the increased uncertainty in the dynamics of the spacecraft, due to uncertainties in the gravity model of the body. Additionally, the altimeter data can be used to speed up determination of a more accurate gravity field model. An advantage of the altimeter data is that the measurements can be taken continuously, without the sunlight restrictions of optical landmark tracking, or the station visibility restrictions of DSN tracking. The specific cases analyzed include both orbital operations and close approaches with landing scenarios. The orbital cases include circular and ellipti