Planning the Final Sols
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View image a) (15 kB) or
larger image b) (40 kB) or learn about other sol 21 images.
As time goes by during the actual Mars Exploration Rover mission,
Mars will move around the sun in its elliptical orbit, floating farther and
farther away from the Earth and farther and farther from the sun.
The increases in distances cause decreases in power and communication
abilities. "Many things conspire against us," says
Scott McLennan, Professor of Geochemistry at State University of New York
at Stony Brook. "The rover receives less and less power to operate
on Mars, so we get less and less data to do our research."
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Scott Mclennan |
On Mars, the performance of the rover will slowly degrade as the
mission goes on. The details of this process will depend on exactly
where it lands. There are a number of reasons for this. One important
reason is that the solar panels become increasingly covered in dust on
the arid Martian surface: winds on Mars scatter dust across the
landscape and subsequently layer over any object on the ground -- in
this instance, it covers the rover. Another factor is that both the length
of day and the angle of the sun change as the season changes. The
average season on Mars lasts approximately 175 Earth days. Since
the mission is scheduled to last 90 sols, which equals approximately
93 Earth days, the position of the sun in the Martian sky changes significantly
and thus affects the amount of power available to rover operations. As
the mission nears its end, this diminished performance begins to dominate
the strategic operational planning of the scientists.
For the FIDO test, this process is being simulated in a rather
dramatic manner. This can be seen in the accompanying chart
(image 1a). For the first 14 sols of the test (remembering that the test
began on Sol 7) the scientists had 90 minutes on each sol for the
FIDO rover to accomplish the tasks that were requested by the
scientists. However, beginning on Sol 21, the time available began
to decrease dramatically. By the end of the FIDO test, Sol 26, only
30 minutes will be available. This rate of decreased performance is
much greater than what will be expected on Mars but will provide good
training for the science and engineering teams. The graph's linear drop
after Sol 20 shows the imposed constraints upon the FIDO team and
attempts to simulate, in a more severe manner, the crippling effects the
environment and planetary positions has on rover communications
and operations.
Other aspects of diminished performance are also being incorporated
into the test. For example, in order for the rover to operate on the
following sol, a critical amount of data must be returned to the FIDO
science and engineering teams in time for planning the subsequent
sol. Examples of the type of data that are critical include navigation
images and engineering information to ensure the rover is
"healthy" and ready to operate. This critical data does not
include any images of targets of opportunity or any scientific data.
The amount of this "critical" data that will be available will also
decrease towards the end of the mission, from about 13 to about 11
megabits per sol. This degradation of communication from the rover to
the FIDO team is analogous to the situation on Mars with the actual
rover. As Mars traverses its orbit around the sun, it gets further from
Earth. The rover will be unable to increase power to its communications
array, and the amount of resources will only decrease over time. In
summary, as the mission moves into the final stages, the FIDO team
will face an increasingly complicated set of conditions within which they
must plan and operate the rover's activities.