Mars Lander Starts Winter Shutdown
This image, taken by Phoenix's Surface Stereo Imager (SSI) on Saturday, Oct. 19, 2008 (sol, or Martian day, 142) shows Martian dirt piled on top of the spacecraft's deck and some of its instruments. In the upper-left are several wet chemistry cells of the lander's Microscopy, Electrochemistry, and Conductivity Analyzer (MECA). In the lower right is the Thermal and Evolved-Gas Analyzer. The excess sample delivered to the MECA’s sample stage can be seen on the deck in the lower left portion of the image.
Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute

As the sun sets on NASA?s Phoenix Mars Lander, both literally and figuratively, mission engineers are beginning to shut down some of the spacecraft?s instruments and heaters to conserve what little energy it has left.

The Phoenix lander, originally slated to run for 90 days after its May 25 touchdown on the red planet, has completed its fifth month of exploring the surface of the Martian arctic. Over the course of its mission, the lander dug up samples of dirt and the rock-hard ice layer underlying the surface of Mars' arctic plains and analyzed them for signs of past potential habitability.

But as the Martian northern hemisphere transitions from summer to fall, the spacecraft is generating less and less power as the days grow shorter, reducing the hours of sunlight reaching its solar panels.

To keep Phoenix chugging along for as long as possible, mission controllers will gradually shut down four survival heaters over the next few weeks, one at a time, to conserve power. The heaters keep the lander and its instruments within their tested operational temperature range.

"If we did nothing, it wouldn't be long before the power needed to operate the spacecraft would exceed the amount of power it generates on a daily basis," said Phoenix Project Manager Barry Goldstein of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "By turning off some heaters and instruments, we can extend the life of the lander by several weeks and still conduct some science."

Engineers sent commands to disable the first heater on Tuesday. That heater warms Phoenix's robotic arm, robotic-arm camera and Thermal and Evolved-Gas Analyzer (TEGA), which bakes samples and "sniffs" the vapors given off to help determine the samples' composition. Shutting down this heater is expected to save 250 watt-hours of power per Martian day.

The Phoenix team has parked the robotic arm on the ground, with its thermal and electrical-conductivity probe (TECP) ? located on the wrist of the arm ? stuck into the dirt. The TECP will continue to measure soil temperature and conductivity (or how heat and electricity move through the surface dirt), as well as atmospheric humidity near the surface. (The probe does not need a heater to operate and should continue sending back data for weeks.)

The robotic arm won't be digging up any more dirt samples though.

"We turn off this workhorse with the knowledge that it has far exceeded expectations and conducted every operation asked of it," said the robotic arm's co-investigator Ray Arvidson, of Washington University in St. Louis.

Phoenix finished scooping up all its samples last week and mission scientists were working to analyze them before Phoenix's time is up.

As power levels continue to drop, Phoenix engineers will gradually turn off the other three heaters. The second heater serves the lander's pyrotechnic initiation unit and is expected to add four or five days to the mission's lifetime. The third warms the lander's main camera and meteorological instruments. The electronics that operate those instruments should generate enough heat to keep them, and the camera, functioning for awhile.

The fourth heater ? one of two survival heaters that warm the spacecraft and its batteries ? would be shut down in a final step. This would leave only one survival heater to run out on its own.

"At that point, Phoenix will be at the mercy of Mars," said Chris Lewickie of JPL and the lead mission manager.

Engineers are also preparing for solar conjunction, when the sun is directly between Earth and Mars. This will happen between Nov. 28 and Dec. 13 and will block radio transmission between the spacecraft and Earth. No commands will be sent to Phoenix during that time, but downlinks from Phoenix will continue through NASA's Odyssey and Mars Reconnaissance orbiters.

For now, mission controllers are uncertain whether the fourth heater will be shut down before or after conjunction.

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