Stellar Compass

The Stellar Compass™ software analyzes digital images of the stars taken by a camera like the one to the left, to determine which direction the camera is pointing (vehicle attitude). This technology is used by spacecraft for navigation, either while in orbit or while in transit to another planet, such as Mars.

The Stellar Compass software's first full-fledged mission was on the joint NASA-Strategic Defense Initiative Clementine flight to the Moon in 1994. Some information about the role of the star tracker on that mission is available online from the National Space Science Data Center.

After its first flights, the software was substantially polished and refined over the next few years, including moving from the SAO to the Hipparcos star catalog, integrating the QUEST algorithm for quaternion refinement, incorporating correction for stellar aberration, adding a high-speed track mode capability and a command and automated test layer with a fully-documented API and software ICD. The code is written in C, and runs under several real-time operating systems, including VxWorks, on big-endian CPUs such as SPARC or the RAD6000 (PowerPC).

The software was flown on the following missions with star cameras like the one pictured to the left: NASA's Mars Climate Orbiter, Mars Polar Lander, Mars Odyssey 2001 and the Stardust comet sample return mission, as well as General Dynamics' (formerly Spectrum Astro's) MightySat II.

The Mars missions all ran in "track mode" most of their way to Mars. In that high-rate "all-stellar" attitude measurement mode, the camera produced roughly 2.6 million images per month.

A paper describing the overall operation and flight performance of the Stellar Compass was published in Advances in Astronautical Sciences, Guidance and Control 2000 (AAS 00-005), (2000) 104, 73-90.

The next page has some additional details about the use of the Stellar Compass on the Stardust mission, along with a sample image from one of its star cameras.