NASA's
Phoenix Mars Lander went into an inactive "safe mode" late Tuesday triggered by
deteriorating weather conditions. The spacecraft also unexpectedly switched to
its second set of redundant electronics and shut down one of its batteries.
As the
Martian northern hemisphere, where Phoenix
landed on May 25, transitions from summer to fall, the amount of sunlight
available to the lander has dwindled and temperatures at Phoenix's
landing site have been steadily dropping.
The
spacecraft's declining health is no surprise to mission managers, who had
planned way in advance for this seasonal change. Phoenix's primary mission
ended in late August.
"This
is a precarious time for Phoenix," said Phoenix Project Manager Barry
Goldstein of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "We're in the bonus round of the extended mission, and we're aware that the
end could come at any time. The engineering team is doing all it can to
keep the spacecraft alive and collecting science, but at this point
survivability depends on some factors out of our control, such as the weather
and temperatures on Mars."
In recent
days, temperatures have fallen significantly, dipping down overnight to minus 141
degrees Fahrenheit (minus 96 degrees Celsius) and only reaching minus 50
degrees Fahrenheit (minus 45 degrees Celsius) during the day, the lowest
temperatures so far for the mission. This weather brought on a "low-power
fault" on Phoenix, presumably a failure that the spacecraft detected and
responded to by entering its power-saving safe mode.
To make
matters worse, a mild dust storm blowing through Phoenix's north polar landing
site, along with accumulating water-ice clouds in the atmosphere, has reduced
the amount of sunlight reaching the spacecraft, further hindering recent attempts
to keep it up and running for as long as possible.
Phoenix has been operating in the Martian
arctic for more than five months, digging
up samples of dirt and rock-hard subsurface water ice and analyzing them
for signs of past potential habitability. Phoenix finished gathering its
remaining samples last week.
All of the
lander's science activities have been put on hold for the next several days to
allow the spacecraft to recharge and conserve power. Mission controllers won't
try to resume normal operations before the weekend.
The ability
to communicate with the lander has not been affected, but the team decided to
cancel communication sessions on Wednesday morning in order to conserve power.
On Tuesday,
the mission announced
plans to turn off four of the spacecraft's heaters, one at a time, to
conserve power for the remainder of the mission. The low-power faults late on
Tuesday prompted engineers to shut down two heaters instead of one as
originally planned.
One of
those heaters warmed the electronics for Phoenix's robotic arm, robotic-arm
camera, and Thermal and Evolved-Gas Analyzer (TEGA), which bakes samples and
analyzes the vapors given off to determine the samples' composition. The second
heater served the lander's pyrotechnic initiation unit, which hasn't been used
since landing.
Mission controllers hope that switching off
the two heaters will preserve enough power to keep the lander's camera and
meteorological instruments running.
The
engineering team anticipates that Phoenix will essentially serve as a
meteorological station once its power supplies dip enough that most instruments
can no longer be run and kept within their optimal temperature range. Mission
planners previously predicted that Phoenix would no longer have enough power
for any operations by the end of November/beginning of December. But just when
the lander will truly die is uncertain.
"It
could be a matter of days, or weeks, before the daily power generated by Phoenix is less than needed to operate the spacecraft," said JPL mission manager Chris
Lewicki. "We have only a few options left to reduce the energy
usage."
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