Mars's top camera suffers failing eyesight
Detectors may all grow old before their time.
The High Resolution Imaging Science Experiment (HiRISE) on board Mars Reconnaissance Orbiter, the newest and most powerful craft to arrive at the red planet, has lost its peripheral vision. And its colour vision is fading too.
Seven of HiRISE's 14 detectors are sending back spurious data, the mission team reports, and one of the four colour detectors has stopped working completely. This has led to only a 2% loss of signal so far, which doesn't sound too bad. But the problem looks set to hit all of the detectors eventually.
"We do think it's a systematic problem for all of them," says Alfred McEwen, HiRISE's principal investigator, who is based at the University of Arizona, Tucson. "It's going to be a real irritant as it worsens."
HiRISE is famous for having provided some of our most stunning views of Mars to date, including a snap of Victoria Crater with the Mars rover Opportunity perched on its the edge (see picture). Pictures continue to be sent back from the craft, which started its scientific survey of the planet in November 2006. It was late in that same month that mission scientists first noticed problems with its eyesight.
Ringing in the eyes
The problem lies in the electronics needed to convert what the detectors see into digital data for transmission back to Earth.
The detectors convert the photons that they spot to an electronic waveform, which is converted to a digital signal by measuring the peaks and troughs of the wave. In the broken detectors, extra peaks and troughs are somehow being introduced, causing what McEwen calls a "ringing" in the signal. "We don't know where the ringing is coming from," he says.
But warming up the electronics (by keeping them turned on for longer) before taking images helps the problem. This temperature effect might also explain why the detectors on the cold peripheral edges of the array were the first to pack up.
The aim now is to slow the deterioration of the detectors, which it is hoped will buy more time for the camera. McEwen is confident that HiRISE will last for the nominal mission length of two years, but for how much longer than that is unclear. Many other NASA projects, including the recently defunct Mars Global Surveyor (MGS), long outlived their official mission lengths.
HiRISE scientists are all disappointed, and uncertain about how to fix the problem, says McEwen. Hope that a cure will be found hasn't been ruled out, but may be wishful thinking, McEwen admits.
"We could do without [HiRISE], but we would have a lot less precision," says planetary geologist Nathalie Cabrol of NASA Ames and the Seti Institute in California. "It is a very central instrument," she adds.
The orbiter's "eagle eyes" have been very good for close-up examination of points of interest spotted by other craft, Cabrol says. Its continuing mapping project is meant to identify a landing zone for the next generation of Mars rovers, which will be designed to look for signs of life.
A previous high resolution NASA camera was lost with the demise of MGS. The best camera currently in orbit around the red planet is on Mars Express, which arrived in December 2003.
Problems with the Mars orbiter aren't confined to HiRISE's detectors. NASA has also announced that a second instrument, the Mars Climate Sounder, which routinely scans the martian atmosphere, has been temporarily stowed while a recurring problem is investigated.
Additional reporting by Geoff Brumfiel
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