After operating on the surface of Mars three times longer than expected and returning a tremendous amount of new information about the red planet, NASA's Mars Pathfinder mission is winding down.
Flight operators at NASA's Jet Propulsion Laboratory, Pasadena, CA, made the announcement today after attempting to reestablish communications with the spacecraft over the last month. With depletion of the spacecraft's main battery and no success in contacting Mars Pathfinder via its main or secondary transmitters, the flight team cannot command the spacecraft or the small rover named Sojourner that had been roving about the landing site and studying rocks.
"We concede that the likelihood of hearing from the spacecraft again diminishes with each day," said Pathfinder Project Manager Brian Muirhead. "We will scale back our efforts to reestablish contact but not give up entirely.
"Given that, and the fact that Pathfinder is the first of several missions to Mars, we'll say 'see you later' instead of saying goodbye," he said.
At the time the last telemetry from the spacecraft was received, Pathfinder's lander had operated nearly three times its design lifetime of 30 days, and the Sojourner rover operated 12 times its design lifetime of seven days.
"I want to thank the many talented men and women at NASA for making the mission such a phenomenal success. It embodies the spirit of NASA, and serves as a model for future missions that are faster, better, and cheaper. Today, NASA's Pathfinder team should take a bow, because America is giving them a standing ovation for a stellar performance," said NASA Administrator Daniel S. Goldin.
Since its landing on July 4, 1997, Mars Pathfinder has returned 2.6 billion bits of information, including more than 16,000 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and extensive data on winds and other weather factors. The only remaining objective was to complete the high-resolution 360-degree image of the landing site called the "Super Pan," of which 83 percent has already been received and is being processed. The last successful data transmission cycle from Pathfinder was completed at 3:23 a.m. Pacific Daylight Time on Sept. 27, which was Sol 83 of the mission.
"This mission has advanced our knowledge of Mars tremendously and will surely be a beacon of success for upcoming missions to the red planet," added Dr. David Baltimore, president of the California Institute of Technology, which manages JPL for NASA. "Done quickly and within a very limited budget, Pathfinder sets a standard for 21st century space exploration."
The Mars Pathfinder team first began having communications problems with the spacecraft on Saturday, Sept. 27. After three days of attempting to reestablish contact, they were able to lock on to a carrier signal from the spacecraft's auxiliary transmitter on Oct. 1, which meant that the spacecraft was still operational. They locked on to the same carrier signal again on Oct. 6, but were not able to acquire data on the condition of the lander. At that time, the team surmised that the intermittent communications were most likely related to depletion of the spacecraft's battery and a drop in the spacecraft's operating temperatures due to the loss of the battery, which kept the lander functioning at warmer temperatures.
Over the last month the operations team has been working through all credible problem scenarios and taking a variety of actions in attempting to recover the link with Pathfinder. With all of the most plausible possibilities exhausted, the team plans to continue sending commands and listening for a spacecraft signal on a less frequent basis.
"Basically we are shifting to a contingency strategy of sending commands to the lander only periodically, perhaps once a week or once per month," said Mission Manager Richard Cook. "Normal mission operations are over, but there is still a small chance of reestablishing a link, so we'll keep trying at a very low level."
Although the true cause of the loss of lander communications may never be known, recent events are consistent with predictions made at the beginning of the extended mission in early August, Muirhead said. When asked about the life expectancy of the lander, project team members predicted that the first thing that would fail on the lander would be the battery; this apparently happened after the last successful transmission September 27.
After that, the lander was expected to begin getting colder at night and go through much deeper day-night thermal cycles. Eventually, the cold or the cycling would probably render the lander inoperable. According to Muirhead, it appears that this sequence of events has probably taken place. The health and status of the rover is also unknown, but since initiating its onboard backup operations plan a month ago, the rover is probably circling the vicinity of the lander, attempting to communicate with it.
The rover, which went into a contingency mode on Oct. 6, or Sol 92 of the mission, had completed an alpha proton X-ray spectrometer study of a rock nicknamed Chimp, to the left of the Rock Garden, when it was last heard from. The rover team had planned to send the rover on its longest journey yet -- a 165-foot (50-meter) clockwise stroll around the lander -- to perform a series of technology experiments and hazard avoidance exercises when the communications outage occurred. That excursion was never initiated once the rover's contingency software began operating.
Now known as the Sagan Memorial Station, the Mars Pathfinder lander was designed primarily to demonstrate a low-cost way of delivering a set of science instruments and a free-ranging rover to the surface of the red planet. Landers and rovers of the future will share the heritage of spacecraft designs and technologies first tested in this "pathfinding" mission.
Part of NASA's Discovery program of low-cost planetary missions, the spacecraft used an innovative method of directly entering the Martian atmosphere. Assisted by a 36-foot-diameter (11-meter) parachute, the spacecraft descended to the surface of Mars on July 4 and landed, using airbags to cushion the impact. The spacecraft's novel entry was successful.
Scientific highlights of the Mars Pathfinder mission are:
* Martian dust includes magnetic, composite particles, with a mean size of one micron.
* Rock chemistry at the landing site may be different from Martian meteorites found on Earth, and could be of basaltic andesite composition.
* The soil chemistry of Ares Vallis appears to be similar to that of the Viking 1 and 2 landing sites.
* The observed atmospheric clarity is higher than was expected from Earth-based microwave measurements and Hubble Space Telescope observations.
* Dust is confirmed as the dominant absorber of solar radiation in Mars' atmosphere, which has important consequences for the transport of energy in the atmosphere and its circulation. Frequent "dust devils" were found with an unmistakable temperature, wind and pressure signature, and morning turbulence; at least one may have contained dust (on Sol 62), suggesting that these gusts are a mechanism for mixing dust into the atmosphere.
* Evidence of wind abrasion of rocks and dune-shaped deposits was found, indicating the presence of sand.
* Morning atmospheric obscurations are due to clouds, not ground fog; Viking could not distinguish between these two possibilities.
* The weather was similar to the weather encountered by Viking 1; there were rapid pressure and temperature variations, downslope winds at night and light winds in general. Temperatures were about 10 degrees warmer than those measured by Viking 1.
* Diversity of albedos, or variations in the brightness of the Martian surface, was similar to other observations, but there was no evidence for the types of crystalline hematite or pyroxene absorption features detected in other locations on Mars.
* The atmospheric experiment package recorded a temperature profile different than expected from microwave measurements and Hubble observations.
* Rock size distribution was consistent with a flood-related deposit.
* The moment of inertia of Mars was refined to a corresponding core radius of between 807 miles and 1,242 miles (1,300 and 2,000 kilometers).
* The possible identification of rounded pebbles and cobbles on the ground, and sockets and pebbles in some rocks, suggests conglomerates that formed in running water, during a warmer past in which liquid water was stable.
Engineering milestones of the mission included demonstrating a new way of delivering a spacecraft to the surface of Mars by way of direct entry into the Martian atmosphere. In addition, Mars Pathfinder demonstrated for the first time the ability of engineers to deliver a semi-autonomous roving vehicle capable of conducting science experiments to the surface of another planet.
The Mars Pathfinder mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. The mission is the second in the Discovery program of fast track, low-cost spacecraft with highly focused science goals. JPL is managed by the California Institute of Technology, Pasadena, CA.