Re: How is martian dust cleaned off the solar panels of the Rover?

Dear Harold,

The short answer is "It isn't"!  That is, Sojourner has no provision for
actively clearing dust off its solar cells.  However, this is an important
question that was considered before launch by the Pathfinder Project.
Studies of of the amount of dust expected, based on what is known about the
martian winds and atmosphere, indicated that not enough dust would
accumulate during the expected lifetime of Sojourner to cause a serious
reduction in electric power from the solar cell array.  While the wind
velocities on Mars can be high, the _density_  of the atmosphere (number of
kgm per cubic meter) is less than 1% that on Earth.  Thus the wind forces
tend be be low, and dust accumulation slow. An exception might occur during
the occasional major dust storms on Mars, which would have the potential to
knock out the rover's power.  Fortunately, these are rare, especially
during this part of the martian year.

Remember, the basic mission of the Pathfinder rover was only 7 sols (Mars
days, 1 sol = 24 hrs 37 min).  The Extended Mission, one month long, was
just completed on August 3.  Thus we can say that in fact, the estimates
were valid, and dust was not a problem:  as predicted!  An important
consideration for Mars Pathfinder, as for all space missions, is balancing
the risks of failure against the cost of preventative or protective
measures.  The idea is to do the basic mission objectives, as inexpensively
as possible.  Much of the art of engineering space missions comes in making
the right compromises about questions of just this kind.

Eventually, since Sojourner will continue to be operated for some time,
something may cause either the rover or its martian lander ground relay
station to fail.  Accumulated dust, either on the lander or the rover, is
one possible cause of failure.  Others are a failure caused by the extreme
temperature variations on Mars, weakness in the batteries with age, or some
other cause.  In any event, since the major mission objectives are
accomplished, dust accumulation itself (as well as other equipment failure
modes and processes) is of real interest in planning future missions to
Mars.  There are actually experiments on both the rover and lander designed
to measure the amount and characteristics of any accumulated dust.

Most of this information can be found in the Mars Pathfinder FAQ
(Frequently Asked Questions) on the
Pathfinder Web site.
(This is the main JPL URL for Pathfinder, but due to the heavy volume of
request there are many mirror sites. Pick a mirror site near you, and click
on "Live From Mars" for the FAQ.)

Cheers

Bill Wheaton