The Design of Pathfinder
The Mars Pathfinder mission was initiated in 1992 and was originally designed as the first in a network of landers, known then as the Mars Environmental SURvey (MESUR). It was designed to be a technology demonstrator mission of a new low-cost landing method — parachutes and airbags — instead of the convention rocket-powered landing that was done by the previous Viking landers. Although the overall MESUR program was cancelled, Pathfinder went ahead as the first mission in a new “Discovery” class of low-cost, high science return missions. The Near-Earth Asteroid Renzevous mission (NEAR) is also a Discovery mission, as are Stardust and the Mars Global Surveyor. (As an aside, all the current Mars missions are not in the Discovery category anymore, they are known as the Mars Exploration Program handled by the Mars Exploration Directorate at JPL).
Mars Pathfinder would carry a lander and (for the first time) a rover to the Red Planet. The entire cost of the program would be $265 million to build, test, and operate the lander & rover, and also pay for the Delta 2 launch vehicle. This was less than 1/10 the cost of the previous Viking program of the 1970s.
The lander would carry a stereoscopic digital camera, named the IMP or Imager for Mars Pathfinder, which had a much greater resolution than the TV cameras Viking had. It would also carry a complete meteorology package which could measure the temperature, pressure, and wind at different heights above the surface.
The rover, named “Sojourner” after the Civil War-era abolitionist Sojourner Truth, was the size of a microwave oven, and carried an Alpha Proton X-Ray Spectrometer which could analyse the elemental compostion of rocks & soil at the landing site. It was controlled remotely by an earth-based operator (with a 10 minute time delay), but the rover also had some autonomous control, and could negotiate obstacles with a set of laser pointers and some insect-like artificial intelligence.
Pathfinder was launched on December 4, 1996 and cruised for 7 months through space. When it reached Mars, it entered the Martian atmosphere. During the 4 minute Entry, Descent, and Landing sequence, a heatshield protected the lander from a fiery descent, 41 explosive bolts fired in the correct sequence, a 24-ft diameter parachute deployed on time, a radar found the ground and told the other systems just when to execute, a long cable deployed and the lander rappelled down it to be protected from rocket firings, all of the airbags inflated exactly 8 seconds before landing, a rocket fired and cut the cable, and the lander survive a hard impact with the ground. It bounced several times and landed perfectly on its base panel. After it rolled to a stop, the airbags retracted and the petals opened to witness the Martian sunrise.
The lander had been radioing back to Earth its progress, and the engineers at JPL were jumping up and down and hugging each other. CNN broadcast it to the world. America was on Mars again, after 21 years.
After the cheering at JPL subsided, the serious work of deploying the rover began. The airbags had not totally deflated, and were partially covering both ramps the rover could use to drive off the lander. A decision was made to raise the lander’s petal, retract the airbags some more, and see if the ramps were cleared. It worked, and on Sol 2 (a Sol is a Martian day, 24 hours and 45 minutes) of the mission, the rover Sojourner had a “Neil Armstrong moment” as it rolled off the lander and left tire tracks on Mars, the first time a rover had done so.
Pathfinder’s camera sent back wonderful pictures of the Martian surface. The mission engineers and managers continued the Viking custom of naming the rocks seen in the panoramas, and soon a series of familar cartoon character names such as “Yogi”, “Ren”, “Scooby Doo”, and “Mermaid” came forth. The rover drove in a circle around the lander, taking rock and soil measurments with its APXS instrument. Other than a few communication glitches, everything performed flawlessly and NASA told mission managers that Pathfinder was an “100% success”.
The rover was designed to last for a week, and the lander for a month. In fact, both of them lasted over three months, out to Sol 83. The lander finally died on September 27 when its battery power was expended. The rover was still working at the time. In the event of a communication failure, it was designed to circle the lander, trying to reestablish communications. If we ever get to go back to the landing site, we may see that the rover continued to drive around the lander, like an orphan whose parents have just collapsed.
Pathfinder sent back 2.6 billion bits of data, including 16,000 lander images and 550 rover images. The rover performed 20 chemical analyses of rocks and soil. Pathfinder discovered “dust devils” which travel along the surface, kicking up dust into the air. The mission also took a picture of the red sky with blue clouds, and a Martian sunset. Pathfinder bolstered the evidence that Mars was once a warmer, wetter planet, and therefore the possibility that life existed, and may still exist, remains feasible. Scientists will be studying the data from Pathfinder for many years to come.
Pathfinder has certainly left a mark on NASA, and the space agency has dedicated itself anew to Mars exploration. JPL’s Mars Exploration Program was founded after Pathfinder’s landing, and will be sending missions to Mars during every Earth-Mars opportunity (which occur once every 22 months). The failed Mars Polar Lander and Mars Climate Orbiter were intended to be the follow-up missions, but with the successes of the Mars Exploration Rovers, we are now back on track with the surface exploration of the Red Planet!
Shortly after landing, JPL renamed the lander the Sagan Memorial Station after noted astronomer and former Viking project manager Carl Sagan, who died in December 1996 before seeing Pathfinder’s images from Mars.