PATHFINDER TO LAND ON MARS FRIDAY
If everything goes as scheduled, about 10 a.m. on Friday morning, July 4, a "meteor" will flash across the Martian sky. This meteor will really be a spacecraft carrying Pathfinder with its small rover vehicle, completing a 310 million mile journey from Earth that began on December 4, 1996. Its preprogrammed descent to the Martian surface marks the resumption of our exploration of the Red Planet.
During the next two minutes a parachute and then rockets will slow Pathfinder's speed to zero. As it slows, the lander, Pathfinder, will be lowered on a tether and large airbags will be inflated to cushion the lander's fall as it is released from about 40 feet above the surface. The rockets will carry the parachute and harness clear of the lander as it bounces and rolls to a stop. Then the airbags will slowly be deflated and partially retracted. Pathfinder will next determine its orientation, right itself if it is not sitting on its bottom, and unfold the petal-shaped covers that form a tetrahedron around its instruments and the on-board rover. After all this is accomplished, about 3 ½ hours after its descent began and with Earth well up in the Martian sky, Pathfinder will begin to radio information back to us.
The nominal location for set-down is an elliptical region 60 miles wide and 120 miles long centered at Martian longitude 32.8 degrees west and latitude 19.5 degrees north. The landing site is 527 miles southeast of the 1976 landing site of Viking 1, in the ancient flood plain Ares Vallis. This location was chosen because geologists -- or rather areologists -- believe a "grab bag" of rocks and soil materials was carried here eons ago by flood waters flowing into Chryse Planitia when liquid water existed on Mars's surface. Even though they will lack information on the exact origin of the flood-borne rocks and soil they expect to find, space scientists believe they can still learn a great deal about Mars from the diverse materials deposited here.
Pathfinder's first photography task will be to take a black and white image of parts of the lander, the small rover vehicle named Sojourner, the ramp leading off the petal on which Sojourner is stowed, and the terrain and airbags. This image will help scientists decide the best direction to send Sojourner as it begins its exploration of Mars. Next a high resolution, panoramic color image will be taken of the Martian surroundings. The first image is expected here about 6:30 p.m., 8 ½ hours after Pathfinder's landing, and the color panorama will follow in about a half hour. A little more than 11 hours after landing Sojourner will drive down the ramp onto Mars and take a black-and-white image of the lander. Its first color image will be taken about 25 minutes after that. Scientists on Earth will see Sojourner's first image about 10:45 p.m., but the color image will not be transmitted back to Earth for a few days, perhaps on July 7. You can stay informed at http://mpfwww.jpl.nasa.gov/mpf/news.html.
During its first week on Mars Pathfinder's main activity will be to support the primary mission of Sojourner. The rover will stay within 100 yards of the lander taking photographs and using its alpha proton x-ray spectrometer to make chemical analyses of surface materials it encounters. The extreme cold on Mars is expected to cause fairly rapid deterioration of Sojourner's electronics. If the rover is still functioning well after its 7-day primary mission its mission will be extended and will include getting detailed images of the lander and the bouncing path it took as it came to rest. It may even venture over Pathfinder's horizon if it performs extremely well in this extended mission. The primary mission for Pathfinder, monitoring atmospheric properties and weather conditions, is planned to last 30 days and will demonstrate a relatively inexpensive system for missions that include surface landings on Mars.
