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Planning the Final Sols


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."

Scott Mclennan

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.

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Last Updated: 17 August 2002

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