Abstract
Summary This paper describes two systems being developed under USAF contract to provide self-contained navigation for earth orbiting spacecraft. One system, called the Space Sextant, uses angle measurements between the moon and second magnitude (or brighter) stars in a Kalman Navigation Filter to estimate vehicle position and velocity. The other system, called the Passive Ranging Interferometer System (PRAIS), also uses a Kalman Navigation Filter, but it measures angles to existing radiometric landmarks and signal time of arrival from some of these landmarks with special characteristics. Both system designs are described in some detail, and on ground testing and simulation data are provided.
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