Spirit's Solar Panels Stuck Towards Southern Sky
The rover team had hoped to shift Spirit's position within the sand trap so that the solar panels would be pointed northward, since during the winter the Sun remains in that part of the sky. The solar panels need to collect photons from the Sun in order to provide the rover with enough energy to sustain operations. If the rover can not get enough sunlight, it will go into hibernation mode. The risk is that hibernation could cause the rover mechanisms to become damaged by the extreme Martian cold.
Drives since Sol 2145 (Jan. 15, 2010) moved Spirit 34 centimeters (13 inches) south-southeastward. However, a counterclockwise yawing of the rover during the drives prevented it from reducing its southerly tilt.
On Sol 2169 (Feb. 8, 2010), the rover's last drive before winter, the team changed the angles of the rover's suspension system but this did not produce a hoped-for improvement to the overall tilt of the solar array. Spirit will spend the coming winter tilted 9 degrees toward the south.
Spirit's parking positions for its previous three Martian winters tilted northward. Engineers anticipate that, due to the unfavorable tilt for this fourth winter, Spirit will be out of communication with Earth for several months. The team does not plan further motion of the wheels until spring comes to Spirit's location beside the western edge of a low plateau called Home Plate.
The rover team is commanding Spirit to make additional preparations for the Mars southern hemisphere winter season. This week the rover team is uploading schedules to Spirit for when to communicate with Earth or with the orbiting Mars Odyssey during the rest of this year and into 2011. Spirit will use these schedules whenever it has adequate power to wake up. Spirit will take a set of "before" images of surroundings from the parked position this week, for comparison with images in the Martian spring to study effects of wind. Images toward the south will also aid preparations for possible future drives, although, with only four of its six wheels still working, the rover is not expected to move farther than short repositioning drives. Other preparations for winter will include putting the robotic arm into a position for studies of atmospheric composition when power is available and changing the stow positions of the high-gain antenna and panoramic camera to minimize shadowing of the solar panels.
Spirit is more than six years into a mission originally planned for three months on Mars. The rover has returned invaluable information about the Martian environment, both past and present. Its twin, Opportunity, is exploring an area halfway around the planet and closer to the equator. Opportunity's equatorial position provides it with enough sunlight to continue operations during the winter.