The Surface Attitude Position and Pointing (SAPP) software, which runs on computers aboard the Mars Exploration Rovers, tracks the positions and attitudes of the rovers on the surface of Mars. Each rover acquires data on attitude from a combination of accelerometer readings and images of the Sun acquired autonomously, using a pointable camera to search the sky for the Sun. Depending on the nature of movement commanded remotely by operators on Earth, the software propagates attitude and position by use of either (1) accelerometer and gyroscope readings or (2) gyroscope readings and wheel odometry. Where necessary, visual odometry is performed on images to fine-tune the position updates, particularly on high-wheel-slip terrain. The attitude data are used by other software and ground-based personnel for pointing a high-gain antenna, planning and execution of driving, and positioning and aiming scientific instruments.

This work was done by Khaled Ali, Charles Vanelli, Jeffrey Biesiadecki, Alejandro San Martin, Mark Maimone, Yang Cheng, and James Alexander of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Software category.

This software is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-41876.