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Sunday, September 26, 2010

Mars Sojourner

The Mars Pathfinder spacecraft was Launched from Kennedy Space Center on December 4, 1996. It took the Pathfinder about seven months to get to Mars. Once on Mars, the Pathfinder deployed a telerobotic rover named Sojourner. Sojourner was be humanity's first attempt to operate a remote control vehicle on another planet, its primary function being to demonstrate that small rovers can actually operate on Mars. The constraint of the mission was that there was only a once-per-sol (a sol being a day on Mars) opportunity for command and telemetry transmissions between the lander and earth operators. Communications with the rover were not done in real-time because of the approximately 11 minute light-time delay in receiving the signals. Therefore Sojourner needed to be able to carry out its mission with a form of supervised autonomous control where move commands were sent to the rover ahead of time and Sojourner then navigated and safely traversed the rugged Mars terrain to these locations on its own.

In order to further justify such a mission, the Sojourner was responsible for conducting a series of experiments which validated various technologies for an autonomous mobile vehicle. Some of these experiments included deploying an Alpha Proton X-ray Spectrometer (APXS) on rocks and soil to determine the elemental composition and constrain the mineralogy of rocks and other surface materials present at the landing site; imaging the lander, using IMP, as part of an engineering assessment after landing; Mars terrain reconstruction from imagery; basic soil mechanics; dead reckoning sensor performance and path reconstruction; and testing ultra high frequency (UHF) link effectiveness graphed as a function of location by logging data transfer errors.

The Sojourner telecommunications system was a two-way wireless UHF radio link between the Lander and the Rover. This link was used to send commands from Earth to the Rover and receive images and data from the Rover. The Rover communications were not done directly because the Micro rover radio had a signal range similar to a walkie- talkie. The rover's wheels and suspension used a unique system with no springs. Rather, its joints rotated and conformed to the contour of the ground, providing the greatest degree of stability for traversing rocky, uneven surfaces.


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