火星尘暴不减

美国宇航局７月３１日发布消息说，“机遇”号火星车目前所在的火星地区尘暴未见减弱，火星车核心电子器件温度过低的问题日益突出，其状况越来越让项目专家担忧。

美宇航局说，“机遇”号最近一次与地球进行通信联络是在７月３０日。从传回的信号来看，尘暴仅比７月中最为恶劣的时候稍有缓解。


近一个月来，火星上尘暴遮天蔽日，“机遇”号太阳能电池板上的尘土越积越多，电池板供电也越来越微弱。为节省电力，地面控制人员已将火星车与地球的联络降到最低。如今电池板每日提供的电力仅够火星车勉强“存活”。


目前，可供给火星车核心电子器件的电力严重缩减，“机遇”号电子器件的夜间低温已经降至零下３７摄氏度。按照设计，当这一温度低至零下４０摄氏度时，火星车的“救生加热器”会自动启动，这将使本已微弱的电力供应状况雪上加霜。


为延缓“救生加热器”启动，地面控制人员刻意让“机遇”号的电子器件在白天运转时间延长一些，以提高夜间温度。由于这样做也需要多耗用一些电力，“机遇”号目前在用电方面几乎是“捉襟见肘”。


项目科学家介绍说，如果尘暴再不减弱，按照目前“拆东补西”的办法，“机遇”号可能很快就会进入“低电自检”程序。届时，火星车控制系统会让火星车进入睡眠状态，然后检查是否还有足够电力重新激活。如果显示电力不足，“机遇”号会维持这种睡眠状态。直到阳光充足、电池板重新恢复时，火星车才可能醒来。


美宇航局称，位于火星另一面的“勇气”号所处区域尘暴近来也更加严重，该火星车太阳能电池板上已到处蒙尘。

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.

Image right: This is a view from Mars Reconnaissance Orbiter of the dust storms around Spirit and Opportunity. Image credit: NASA/JPL/MSSS
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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.