Posted: October 29, 2008
Engineers are gradually shutting down some of Phoenix’s instruments and heaters in an attempt to prolong its lifetime as the Martian summer rapidly fades away.
It’s a vicious circle: as the days get shorter and the hours of sunlight rapidly decline Phoenix is generating less power, but at the same time it requires more power to allow it to maintain enough heat to operate as temperatures fall.
"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," says Phoenix Project Manager Barry Goldstein. "By turning off some heaters and instruments, we can extend the life of the lander by several weeks and still conduct some science."
After a successful five months of digging and scraping Martian soil, the robotic arm operations have ceased, however, the TECP will have enough power to continue to measure humidity, conductivity and temperature changes in and around the soil for the coming weeks. Image: NASA/JPL-Caltech/University of Arizona/Texas A&M University.
Over the next few weeks, engineers will send commands to Phoenix to gradually shut down its survival heaters in an attempt to squeeze the last morsels of science out of the already highly successful mission. However, as each heater is shut down, so the electronics of the system will slowly fall outside their limits of operation and key science instruments will be lost one by one. By the end of the mission, it is expected that the lander will have just enough power to keep the main camera and meteorological instruments operational.
The first heater will be disabled by the end of today, and will save 250 watt-hours of power per Martian day. This particular heater warms Phoenix's robotic arm, the robotic-arm camera, and the Thermal and Evolved-Gas Analyser (TEGA), an instrument that “bakes and sniffs” Martian soil to determine its volatile ingredients. The robotic arm has therefore come to its final resting place on a patch of representative Martian soil, and no further soil samples will be collected. The Thermal and Electrical-Conductivity Probe (TECP), located on the wrist of the arm, has been inserted into the soil and will continue to measure soil temperature and conductivity, along with atmospheric humidity near the surface. The probe does not need a heater to operate and should continue to send back data for several more weeks.
"We turn off this workhorse with the knowledge that it has far exceeded expectations and conducted every operation asked of it," says Ray Arvidson, the robotic arm's co-investigator. Throughout the mission, the lander's robotic arm successfully dug and scraped Martian soil and delivered it to the onboard laboratories for analysis.
When power levels necessitate further action, Phoenix engineers will send commands to disable a second heater, which serves the lander's pyrotechnic initiation unit. The unit has been redundant since landing, and disabling its heater is expected to add four to five days to the mission's lifetime. The third heater in line to be disabled is heating the main camera - the Surface Stereo Imager, and the meteorological suite of instruments, but the electronics that operate the meteorological instruments should generate enough heat on their own to keep most of those instruments and the camera functioning for some time.
In the final step, Phoenix engineers may turn off a fourth heater, one of two survival heaters that warm the spacecraft and its batteries. This would leave one remaining survival heater to run out on its own. "At that point, Phoenix will be at the mercy of Mars," says Chris Lewicki, lead mission manger.
Engineers are also preparing for solar conjunction, when the Sun is directly between Earth and Mars. Between 28 November and 13 December, Mars and the Sun will be within two degrees of each other as seen from Earth, blocking radio transmission between the spacecraft and Earth. During that time, no commands will be sent to Phoenix, but daily downlinks from Phoenix will continue through NASA's Odyssey and Mars Reconnaissance orbiters. Nearer the time, Phoenix engineers will decide whether to disable the fourth heater before or after conjunction. The mission is expected to fade into permanent hibernation by the end of the year.
Oct 22 Phoenix completes soil delivery read more
Oct 08 Phoenix digs into darkness read more
Sep 30 Phoenix sees falling snow read more
Sep 29 Phoenix peeks under a rock read more
Sep 12 Dust devils pay visit to Phoenix read more
Sep 05 Phoenix's vapour quandary read more
Aug 26 Phoenix digs into extended mission... read more
Aug 06 Martian salts analysed for habitability... read more
Aug 01 Phoenix tastes water on Mars read more
Jul 29 Sticky situation for Phoenix read more
Jul 22 Phoenix in 24-hour monitoring assignment read more
Jul 17 Phoenix rasps frozen layer... read more
Jul 11 First success with Phoenix soil probe... read more
Jul 10 Phoenix struggling with icy payload read more
Jul 03 Next Phoenix bake could be last read more
Jun 30 Phoenix soil could support life read more
Jun 23 Frozen water confirmed on Mars read more
Jun 19 Bright chunks must have been ice read more
Jun 17 First results from Phoenix bakery read more
Jun 12 An oven full of sand read more
Jun 10 Clumpy Martian soil challenges Phoenix read more
Jun 06 Closest view ever of Mars sand read more
Jun 03 Phoenix scoops up Martian soil read more
Jun 02 Phoenix sees possible ice read more
May 30 Phoenix flexes robotic arm read more
May 28 HiRISE captures Phoenix descent read more
May 26 Spectacular new colour view of Mars read more
May 23 Phoenix prepares for Mars landing read more
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