NASA rover managers increasingly anxious with state of Opportunity

William Atkins
Wednesday, 01 August 2007 21:20

Science - Space

Mars Exploration Rover (MER) managers are growing very concerned with the low temperature of the electronics onboard Opportunity as Martian dust storms continue to assault the rover.

According to information reported on the NASA Mars rover website from John Callas, NASA Jet Propulsion Laboratory rover project manager: "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."

The nightly temperature of Mars has descended to around -35 degrees Fahrenheit (-37 degrees Celsius). Such a low temperature is within approximately three Fahrenheit degrees (or about two Celsius degrees) of automatically turning on special heaters to compensate for the cold weather.
 
With Opportunity primarily inactive (in very-low-power mode) during the Martian storms that have continued for over one month, the extra electricity needed for the heaters will probably remove any excess energy stored in its batteries, and place the rover into a more likely scenario of placing itself in hiberation (sleep) mode.

Callus states, "This is energy Opportunity does not have to spare.”

The dust storms that have descended upon Opportunity prevents the majority of sunlight from reaching the probe’s solar panels, so it cannot generate nearly as much of electricity as on a normal day on Mars.

As of July 30,2007, MER mission managers report that the storm has not lessened in intensity, with sunlight inpinging on the solar panels only slightly more than the worst conditions experienced in the middle of July. As of the end of July, Opportunity has generated over 200 watt-hours of energy per day, which is up from its low of 128 watt-hours during the worst of the storm.

Another problem for Opportunity is the fact that dust is gathering on the solar panels, which makes it even more difficult to convert the Sun’s rays to electricity on order to power the probe. In the past, small dust storms actually helped to clear the solar panels of dust. But, with so much dust swirling about the rover, it is increasingly obscuring the panels.

NASA engineers are attempting to delay the electric heaters from turning on by keeping the electronics turned on for longer periods of time. However, such actions places more energy consumption onto the probe. 

If a certain minimum very-low-power state is reached, Opportunity was turn itself off and attempt to generage electricity from sunlight. Eventually, if enough energy is generated it will turn itself back on.

In addition, both rovers, Opportunity and Spirit, contain eight radioisotope heaters that help the electrical heaters maintain the electronics and batteries at their nominal operating temperatures. On very-low-power day, which has occurred most of the time over the last month, these radioisotope units use the decay from plutonium-238 to generate about one watt of heat per day.