081029 Falling power forces first Phoenix heater shut down

Top Stories

		Double asteroid belt in Solar System clone ...Spitzer observations have discerned two rocky asteroid belts and an icy outer ring surrounding our Sun’s doppelgänger Epsilon Eridani that could have been shaped by evolving planets.. read more Fireball captured by Canadian cameras ...for the second time this year The University of Western Ontario’s Meteor Group has captured rare footage of a meteor streaking across the sky and possibly falling to the ground... read more ESA gravity mission slips to 2009 ...the launch of Europe’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) has slipped to February 2009 due to ongoing technical faults with its launcher.. read more

Spaceflight Now +

		Subscribe to Spaceflight Now Plus for access to our extensive video collections! How do I sign up? Video archive STS-120 day 2 highlights Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights. Play STS-120 day 1 highlights The highlights from shuttle Discovery's launch day are packaged into this movie. Play STS-118: Highlights The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation. Full presentation Mission film STS-120: Rollout to pad Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission. Play Dawn leaves Earth NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt. Full coverage Dawn: Launch preview These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter. Launch \| Science Become a subscriber More video

Falling power forces first Phoenix heater shut down
BY DR EMILY BALDWIN
ASTRONOMY NOW

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.