Sojourner was Mars Pathfinder's robotic miniature Mars rover, and explored Mars for around three months. It had front and rear cameras and several science experiments. It was designed for a 7 Sol mission with possible extension to 30 sols. It was active for 83 sols, until the base station had its last communication with Earth on 3:23 a.m. Pacific Daylight Time on Sept. 27, 1997. The rover needed the base station to talk to Earth, despite still functioning at the time communications ended. The final resting place of Sojourner is still not known as of 2012, although the proposed Mars Geoscience Imaging at Centimeter-Scale (MAGIC) orbiter might be able to find it.
The rover's name, Sojourner, means "traveler", and was selected in an essay contest won by a 12 year old from Connecticut, USA. It is named for Sojourner Truth (Isabella Van Wagener).
It had solar panels and a non-rechargeable battery, which allowed limited nocturnal operations. Once the batteries depleted, it could only operate during the day. The batteries were lithium-thionyl chloride (LiSOCL2) and could provide 150 watt-hours. Additionally, 0.22 square meters of solar cells could produce a maximum of 15 watts, depending on conditions.
Its CPU was a 80C85 with a 2MHz clock, addressing 64 Kbytes of memory. It had four memory stores; the previously mentioned 64 Kbytes of RAM (made by IBM) for the main processor, 16 Kbytes of radiation-hardened PROM (made by Harris), 176 Kbytes of non-volatile storage (made by SEEQ), and 512 Kbytes of temporary data storage (made by Micron). The electronics were housed inside the Warm Electronics Box inside the rover.
It communicated with the base station with 9600 baud radio modems. The practical rate was more like 2600 baud with a theoretical range of about half a kilometer. The rover could travel out of range of the lander, but its software would need to be changed to that mode. Under normal driving it would periodically send a "heartbeat" message to the lander.
The Alpha Proton X-ray Spectrometer (APXS) was nearly identical to the one on Mars 96, and was a collaboration between the Max Planck Institute for Solar System Research in Lindau, Germany (formally known as the Max Planck Institute For Aeronomy) and the University of Chicago in the United States. APXS could determine elemental composition of Mars rocks and dust, except for hydrogen. It works by exposing a sample to alpha particles, then measuring the energies of emitted protons, X-rays, and backscattered alpha particles.
Sojourner operations were supported by Rover Control Software, which ran on a Silicon Graphics Onyx2 supercomputer back on Earth, and allowed command sequences to be generated using a graphical interface. The rover driver would wear 3D goggles supplied with imagery from the base station, and move a virtual model with the spaceball controller, a specialized joystick. The control software allowed the rover and surrounding terrain to be viewed from any angle or position, supporting the study of terrain features, placing waypoints, or doing virtual flyovers.