Inch by power-conserving inch, drivers on Earth have moved the Mars rover Spirit to a spot where it has its best chance at surviving a third Martian winter -- and where it will celebrate its fourth anniversary (in Earth years) since bouncing down on Mars for a projected 90-day mission in January 2004. Meanwhile, researchers are considering the implications of what Cornell's Steve Squyres, principal investigator for NASA's Mars Exploration Rover mission, calls "one of the most significant" mission discoveries to date: silica-rich deposits uncovered in May by Spirit's lame front wheel that provide new evidence for a once-habitable environment in Gusev Crater.
SPIRIT UPDATE: Final Winter Haven Selection Near - sol 1398-1403, December 17, 2007:
To make the most of waning sunlight during the approach of Martian winter, Spirit's handlers have returned to "Mars time." This means their working hours coincide with the Martian day, as they did for the first three months after the rover landed on the red planet. Because a Martian day is about 40 minutes longer than an Earth day, Mars time can coincide with all hours of the day and night on Earth. The alarm might go off the same time one day, 40 minutes later the next day, an hour and 20 minutes later the next day, and so on. Spirit's solar power levels continue to drop, with solar array energies recently ranging from 293 watt-hours to 254 watt-hours, depending on the vehicle's orientation relative to the Sun. (One hundred watt-hours is the amount of energy needed to light a 100-watt bulb for one hour.) All members of the rover science team -- drivers, engineers, and scientists -- are evaluating data to select a place where the rover will attempt to survive another Martian winter, focusing on areas that will tilt the rover's solar panels to the north more than 25 degrees. They will select a final location from a narrowed list of choices based on proximity to the rover's current position and the characteristics of the terrain, with an eye for accessibility as well as continued exploration in the spring. Spirit reached the northern edge of "Home Plate" after driving 13.24 metres on Martian day, or sol, 1397 (Dec. 8, 2007). Three Martian days later, on sol 1400 (Dec. 11, 2007), Spirit finished collecting reconnaissance images of the northern exposure of the elevated plateau. During the past week, rover planners got a special visit from two Tuskegee Airmen, the first black pilots to serve in the U.S. military. The pilots shared stories about serving in World War II while learning about rover operations.
Sol-by-sol summary: In addition to receiving morning instructions directly from Earth via the high-gain antenna, sending evening data to Earth at UHF frequencies via the Odyssey orbiter, and measuring atmospheric dust levels with the panoramic camera, Spirit completed the following activities: Sol 1398 (Dec. 9, 2007): Spirit drove 6.5 metres in a path nearly parallel to the northern edge of Home Plate. The rover acquired post-drive images with the hazard avoidance cameras and a mosaic of images with the navigation camera.
Sol 1399: Spirit drove 7.19 metres toward a small promontory to acquire images of the slopes below. The rover acquired post-drive images with the hazard avoidance cameras and a mosaic of images with the navigation camera. The following morning, Spirit acquired a series of navigation camera images to complete a 360-degree view of the rover's location after completing the drive.
Sol 1400: Spirit nudged 0.75 metre closer to the edge of Home Plate for a better view of what lay below. The rover acquired post-drive images with the hazard avoidance cameras and a mosaic of images with the navigation camera.
Sol 1401: Spirit took a break from driving and acquired images with the panoramic camera before turning around to back down the steep slope where the rover will spend the winter. After turning, the rover's solar arrays blocked the view of the slope by cameras on the rover mast assembly. Following the manoeuvre, Spirit acquired two image mosaics with the panoramic camera.
Sol 1402: Spirit acquired a pre-drive image of a pointy rock known as "General B.O. Davis" before backing up 2.5 meters and turning 180 degrees. The rover acquired post-drive images using the hazard avoidance cameras and a mosaic of images using the navigation camera. The following morning, Spirit monitored dust on the panoramic camera mast assembly and completed a systematic ground survey and a survey of rock clasts with the panoramic camera.
Sol 1403 (Dec. 14, 2007): Plans called for Spirit to approach the edge of Home Plate backward and acquire post-drive images with the hazard avoidance cameras as well as an image mosaic with the panoramic camera.
Odometry: As of sol 1402 (Dec. 13, 2007), Spirit's total odometry was 7523.31 metres.
SPIRIT UPDATE: Spirit Scouts "Home Plate" for Safe Haven - sol 1390-1397, December 14, 2007:
Spirit has arrived at the north edge of "Home Plate." The rover will spend the next few Martian days, or sols, scouting the edge of Home Plate and acquiring images of the slopes to determine the best site for "Winter Haven 3," where Spirit will try to survive another season of minimal sunlight. Once the team selects a site, Spirit will drive down the north-facing edge of Home Plate and manoeuvre into position to achieve the highest northerly tilt possible. Power levels are dropping rapidly, partly because the sun continues its retreat north on its way to winter solstice, and partly because the landscape tilts slightly southward near the rim. Drive sols are so precious and few, the team has been working long hours and weekends to make the most of the remaining sunlight.
Sol-by-sol summary: In addition to receiving morning instructions directly from Earth via the high-gain antenna, sending evening data to Earth at UHF frequencies via the Odyssey orbiter, and measuring atmospheric dust levels with the panoramic camera, Spirit completed the following activities:
Sol 1390 (Nov. 30, 2007): Spirit drove in search of Winter Haven 3 and acquired post-drive images with the navigation camera. Spirit acquired full-colour images, using all 13 filters of the panoramic camera, of the low, sandy area nicknamed "Tartarus." The rover surveyed Tartarus with the miniature thermal emission spectrometer and surveyed the horizon with the panoramic camera.
Sol 1391: Spirit continued to drive in search of Winter Haven 3 and acquire post-drive images with the navigation camera. The rover assessed atmospheric opacity caused by suspended dust with the navigation camera. Spirit acquired a mosaic of images with the panoramic camera and monitored dust accumulation on the rover mast assembly.
Sol 1392: Spirit drove in search of Winter Haven 3 and acquired a post-drive image mosaic and a rearward-looking image mosaic with the navigation camera.
Sol 1393: Spirit continued to drive in search of Winter Haven 3. Spirit acquired a post-drive image mosaic and a rearward-looking image mosaic with the navigation camera. The rover also completed a survey of rock clasts and a systematic ground survey with the panoramic camera.
Sol 1394: Spirit drove in search of Winter Haven 3 and acquired post-drive and rearward-looking image mosaics with the navigation camera. Spirit also acquired an image mosaic of Home Plate with the panoramic camera.
Sol 1395: Spirit drove in search of Winter Haven 3 and acquired post-drive images with the navigation camera. Spirit acquired a mosaic of panoramic camera images of a target known as "Hummock" and a rearward-looking mosaic of navigation camera images.
Sol 1396: Spirit continued driving in search of Winter Haven 3. The rover acquired post-drive and rearward-looking image mosaics with the navigation camera. Spirit completed a survey of rock clasts and a systematic ground survey with the panoramic camera.
Sol 1397 (Dec. 8, 2007): Plans called for Spirit to continue driving in search of Winter Haven 3, acquire post-drive images with both the navigation and panoramic cameras, and conduct a systematic ground survey as well as acquire spot images of the sky with the panoramic camera.
Odometry: As of sol 1397 (Dec. 8, 2007), Spirit's total odometry was 7495.15 metres.