On to Mars

The launch of Mars Pathfinder was scheduled for 2 December 1996 at 2:09 a.m. with a mere two-minute window in which to launch. The long-range forecast, however, did not look good, predicting high winds and rain, so the launch was scrubbed and rescheduled for 3 December at 2:03 a.m. The following day, JPL mission members returned to the most advantageous spot to watch the launch: Jetty Park across from Patrick Air Force Base. Just one minute before launch, a software problem in one of the ground computers monitoring telemetry from the Delta stopped the countdown. The problem could not be resolved in time and the launch was rescheduled yet again, this time for 4 December at 1:58 a.m. As the count passed the T-minus 30-second mark on this latest attempt, heart rates started climbing. Finally, the Delta II with Mars Pathfinder lifted off from launch pad C17-A. The exhaust plumes of the Delta's solid and liquid rocket engines were almost blinding as it rapidly climbed into the dark early morning sky over Cape Canaveral. Observers cheered and clapped, and soon the rocket was gone, on its way to Earth orbit. The Delta's PAM-D stage would then send it on its trajectory to Mars. Months of unremitting effort, stress and sometimes frustration gave way to tears as some JPL members openly cried in relief.

Pathfinder's destination was Ares Vallis, an ancient flood plain in the northern hemisphere of Mars. Despite being a technology demonstration mission, Pathfinder would still perform science once safely on the planet's surface.

"Ares Vallis is particularly interesting to geologists because it drains a region of ancient, heavily cratered terrain that dates back to early Martian history, similar in age to the meteorite Allan Hills 84001, which contains scientific evidence suggesting that life may have begun on Mars billions of years ago,'' said Dr. Matthew Golombek, Pathfinder Project Scientist, prior to the successful launch. "By examining rocks in this region, Pathfinder should [be able to] tell scientists about the early environment on Mars, which is important in evaluating the possibility that life could have begun there.''

On 4 July 1997, the spacecraft performed the first series in a total of forty-one pyrotechnic events, and jettisoned its cruise stage. It entered the Martian atmosphere at more than 7,400 meters per second, at the start of its Entry, Descent and Landing (EDL) phase. Heat shield aerobraking would slow the spacecraft to roughly 400 meters per second before parachute deployment approximately eight to ten kilometers above the surface of Mars. This was the most anxious time for the engineers at JPL, but it was also being closely watched by each of the NASA centers around the country as well as NASA Headquarters. This was very much a high profile mission for NASA. Due to the distance between Mars and Earth, signals from the spacecraft would take more than ten minutes to reach the tracking and

A sophisticated airbag deployment system was developed by JPL to cushion the landing of Pathfinder and protect the spacecraft from boulders and rocks by bouncing and rolling across the surface of Mars until coming to a stop. The airbags were then deflated and retracted underneath the lander. (NASA/JPL-Caltech)

A sophisticated airbag deployment system was developed by JPL to cushion the landing of Pathfinder and protect the spacecraft from boulders and rocks by bouncing and rolling across the surface of Mars until coming to a stop. The airbags were then deflated and retracted underneath the lander. (NASA/JPL-Caltech)

receiving stations, but finally, the tracking station in Madrid, Spain reported, "Comm, this is Madrid. I see a weak signal ...'' All the EDL events had occurred perfectly. For a few brief seconds, there was pandemonium in the Mission Support Area (MSA) on the second floor of building 230 at JPL. Then, just as quickly, order returned as they waited for the next critical signals. The tetrahedral airbag system had actually come to a rest with the lander right side up - a one-in-four chance. The most dangerous part of the mission had passed. Pathfinder was on Mars!

Over the next several hours the airbags were deflated and retracted under the lander, and the lander's solar panels, or petals, were deployed. "We have lockup!'' it was announced in the MSA, indicating the first signals from the lander's Low-Gain Antenna. Cheers went up. "We have rover data!'' elicited more cheers. The mission was already going better than many had dared to hope, but there was much yet to happen for the next technology demonstrations to occur. Data came in indicating that the tilt of the lander was only two degrees, a very positive sign that deploying the rover Sojourner would be that much easier. Another critical milestone was the alignment of the High-Gain Antenna with Earth. The Imager for Mars Pathfinder (IMP) had to properly locate the Sun and lock onto our solar system's star in order for the High-Gain Antenna to properly position itself toward Earth. Without this antenna, data and images would have to be transmitted through the Low-Gain Antenna at drastically reduced bit rates, diminishing the scientific return and health data of the lander and rover. The IMP locked onto the Sun then moved to survey the landing site, the High-Gain Antenna reoriented itself toward Earth, and the first images from the spacecraft started to appear on JPL monitors. The atmosphere inside the MSA was positively electric. All eyes were on the monitors as each image appeared. The Imager had a narrow field of view, and over the next several hours, JPL received images which were then digitally pieced together to form a mosaic. This included a panorama to determine the extent of airbag retraction, images of each end of the lander to determine the best direction for Sojourner's deployment, and an image of the area near the lander, the horizon and the Martian sky.

Examination of the images determined that the airbags had not retracted sufficiently to permit proper deployment of the rover's ramps. This had been anticipated, however, and a program was sent up to the lander to lift the petal with the rover approximately 40 degrees, activate the airbag retraction mechanism again and lower the petal. When the next group of images was received, the effort had proved successful, but all was not well. The lander was not communicating with the rover. All communications to and from the rover were done through the lander and if this problem could not be resolved, there would be virtually no mission on the surface. Until there were full communications between the rover and the lander, Sojourner could not be deployed.

Over the next twelve hours, communication between the rover and lander was reestablished, and rover deployment was set for the next Martian day (known as a sol). Over the next seven sols, Sojourner would perform a number of technology experiments to gain information that could be applied to future planetary rovers. This included terrain geometry reconstruction from lander and rover imaging, basic soil mechanics by studying the degree of sinkage of each rover wheel, path reconstruction by dead reckoning and track images, vision sensor performance, and rover thermal characteristics between the Martian day and night. In addition, the rover would conduct a series of experiments to validate technologies for an autonomous mobile vehicle, employ its Alpha Proton X-ray Spectrometer (APXS), and image the lander as part of the engineering assessment after landing. It would have a nominal seven-sol mission. If it continued to perform well, the rover's mission would be extended.

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