NASA鈥檚 Mars rover Spirit is stuck in what appears to be loose soil, but engineers hope to free it quickly so it can reach a safe spot to ride out the approaching winter.
For the past two weeks, Spirit has been heading to the northern end of a 90-metre-wide raised plateau called Home Plate. The region boasts relatively steep, northern-tilting slopes that would maximise the sunlight falling on the rover鈥檚 solar panels during winter in the planet鈥檚 southern hemisphere (see Mars rover Spirit to head north for the winter).
Mission scientists had hoped it would arrive on a safe slope by 1 January 鈥� a deadline made all the more critical because the rover鈥檚 power is already depleted due to dust on its solar panels. 鈥淭here鈥檚 more dust on Spirit now because of the dust storms a few months ago,鈥� says rover team member Ken Herkenhoff of the US Geological Survey in Flagstaff, Arizona, US. 鈥淭hat鈥檚 making this [journey north] more urgent.鈥�
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But within the past few days, the rover has become stuck. 鈥淣ow, winter is getting closer and closer, Spirit has been bogged down in loose soil and we鈥檙e trying to move out of that area,鈥� Herkenhoff told New 杏吧原创.
Switchback strategy
On Monday evening, NASA engineers uploaded commands to the rover to try to set it moving again. 鈥淲hat they鈥檙e planning is to turn the rover in place then attempt to drive, then turn it in the other direction and try driving forward again and sort of switchback across the slight slope we鈥檙e trying to get up,鈥� he says. The rover has been driving backwards ever since its right-front wheel seized up in mid-2006.
So far, the strategy appears to be working, but the progress is slow 鈥� on Monday night the rover moved just 0.5 m, says Herkenhoff. That鈥檚 because the rover can only drive for about 30 minutes at a time before using up too much of its limited battery power.
鈥淲e鈥檙e planning another short drive again today [Tuesday], but we鈥檙e not really out of the water yet,鈥� he told New 杏吧原创. 鈥淲e鈥檙e trying to climb an 11掳 slope in loose soil, and dragging that right-front wheel behind us, that鈥檚 a tough slope to climb.鈥� He says team members will work through the weekend to try to free the rover.
Meanwhile, another NASA spacecraft, the Mars Reconnaissance Orbiter, has taken the first good multi-colour image of Spirit from space.
The spacecraft鈥檚 HiRISE (High Resolution Imaging Science Experiment) camera 鈥� the most powerful ever sent beyond Earth orbit 鈥� has previously imaged the rover, but only in one colour. That鈥檚 because it can only image objects in all three of the colours it can detect if they are located in the central 20% of its field of view.
鈥楶ushing the limits鈥�
鈥淗aving colour is very useful,鈥� Herkenhoff says, explaining that different colours on the planet鈥檚 surface may be due to different types of rocks or different coatings on the rocks. 鈥淲e can compare the colour information from HiRISE from orbit with colour data taken from the surface [by the rover]. It allows the surface observations to be put into context and allows us to plan where we want to go next.鈥�
He says HiRISE is sending back terabytes of data, despite the fact that soon after it started operating it experienced noise in some of its detector channels. The problem stems from errors in converting the electrical voltage in the camera鈥檚 CCDs to digital data in the form of binary code.
Such 鈥榓nalogue to digital conversion鈥� has been used in space many times before. 鈥淏ut what鈥檚 new about HiRISE is that it鈥檚 a very complex camera, using 14 CCDs instead of just one typically, all operating at a very high rate and really pushing the limits of some of these devices,鈥� he says.
Cool down
To reduce the errors, mission planners heat the camera from its normal operating temperature of about 18 to 32掳C. But engineers do not want the camera鈥檚 electronics to get too hot for fear they will become damaged, so they have to cool the camera down for about 30 minutes after each image.
鈥淭he downside is it takes longer for the camera to cool down between images,鈥� Herkenhoff says.
Recently, mission members have been taking one large image during every two-hour orbit the spacecraft makes, so that 鈥渨hen the orbiter鈥檚 on the back side of Mars, for that hour, there鈥檚 plenty of time to cool down so we can take another big image on the next orbit鈥�, he says.
Engineers are also studying whether or not the camera can safely operate at higher temperatures, which would reduce the amount of time needed to cool it between images.
Mars Rovers 鈥� Mars is full of surprises; learn more in our continually updated .
