Space Forum / Space Science / August 2007

http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20070731a.html

Mars Exploration Rover Status Report: Concern Increasing About
Opportunity
Jet Propulsion Laboratory
July 31, 2007

Rover engineers are growing increasingly concerned about the
temperature
of vital electronics on NASA's Mars Exploration Rover Opportunity
while
the rover stays nearly inactive due to a series of dust storms that
has
lasted for more than a month.

Dust in the atmosphere and dust settling onto Opportunity's solar
panels
challenges the ability of the solar panels to convert sunlight into
enough electricity to supply the rover's needs. The most recent
communication from Opportunity, received Monday, July 30, indicates
that
sunlight over the rover's Meridiani Planum location remains only
slightly less obscured than during the dustiest days Opportunity
survived in mid-July. With dust now accumulating on the solar panels,
the rover is producing barely as much energy as it is using in a
very-low-power regimen it has been following since July 18.

Keeping Opportunity's activity to a minimum has reduced the amount of
energy going into the rover's electronics core, reducing the amount of
heat that comes from the electronics components themselves during
normal
operation.

"The overnight low temperature of Opportunity's electronics module has
been dropping since we implemented the very-low-power operation, even
though the outside environment is actually warmer during this dust
storm," said John Callas, rover project manager at NASA's Jet
Propulsion
Laboratory, Pasadena, Calif. That temperature has dropped to minus 35
degrees Fahrenheit (minus 37 Celsius), within about 3 Fahrenheit
degrees
(about 2 Celsius degrees) of triggering survival heaters to turn on.
Those heaters could push the rover's total use of electricity higher
than what the solar panels produce, soon depleting the batteries.
"This
is energy Opportunity does not have to spare," he said.

To forestall the survival heaters from turning on, the rover team has
altered Opportunity's daily regimen to keep the electronics active for
a
longer period each day. This, too, could put the rover through some
negative-net-energy days if the sky does not begin to clear.

Callas said, "This means there is a real risk that Opportunity will
trip
a low-power fault sometime during this plan. When a low-power fault is
tripped, the rover's systems take the batteries off-line, putting the
rover to sleep and then checking each sol to see if there is
sufficient
available energy to wake up and perform daily fault communications. If
there is not sufficient energy, Opportunity will stay asleep.
Depending
on the weather conditions, Opportunity could stay asleep for days,
weeks
or even months, all the while trying to charge her batteries with
whatever available sunlight there might be."

Spirit, meanwhile, is also accumulating some dust on solar panels
under
a sky at Gusev Crater that remains nearly as dusty as the worst Spirit
has recorded.

"We will continue to watch the situation on Mars and do all we can to
assist our rovers in this ongoing battle against the environmental
elements on the Red Planet," Callas said.

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