Worrying behaviour from amnesiac Mars rover prompts plan to isolate faulty memory
Friday, January 2, 2015, 12:22 PM - Approaching the end of its 11th year exploring the surface of Mars, the memory problems plaguing NASA's venerable Opportunity rover are growing worse, so much so that it actually forgot to call home over the holidays!
"The problems started off fairly benign, but now they've become more serious - much like an illness, the symptoms were mild, but now with the progression of time things have become more serious," John Callas, the project manager for the Mars Exploration Rover mission at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif, told Discovery News.
"So now we’re having these events we call 'amnesia,' which is the rover trying to use the flash memory, but it wasn't able to, so instead it uses the RAM," Callas added. "It stores telemetry data in that volatile memory, but when the rover goes to sleep and wakes up again, all (the data) is gone. So that’s why we call it amnesia - it forgets what it has done."
According to the NASA JPL website, Opportunity's flash memory problems go back to at least August 2014, when the rover experienced a dozen different memory resets while on the edge of a large crater named Endeavour, which involved a recovery time of one or two days each. The team at JPL successfully performed a reformatting of Opportunity's memory in early September, which they hoped would correct the problem.
However, as the mission continued through the end of 2014, the flash memory failed again, prompting the team to put Opportunity in 'no-flash mode' on December 11. Then, as Discovery News reports, when the scientists and engineers went on Christmas holidays, and had left three days worth of work with Opportunity to do while they were away, it did fine on the first day on its own, but then stopped talking on day two.
Upon returning to work after the holidays, the team was able to recover a signal from the rover and it has continued on since, but as Callus told Discovery News, "we get very, very worried," when Opportunity stops talking.
Opportunity uses two types of computer memory while it goes about its work on Mars - 'volatile' and 'non-volatile' - both of which have their uses and benefits, as well as their limitations.
"The difference is non-volatile memory remembers everything even if you power off, in volatile memory everything goes away," Callas explained. "So volatile memory is like the traditional RAM you have in your computer; non-volatile memory uses flash memory technology."
One of the problems with using the non-volatile memory so much, according to Callas, is that you can only use it a certain number of times before you start to experience problems.
"It 'wears out' with use," he told Discovery News.
For comparison, it's like buying a 256MB flash drive back in 2005, to store your important documents and calendar reminders for each day, and you're still using the same one even now, in 2015. You're going to run into problems.
For Opportunity, though, there's no going down to the electronics store to pick up a much-needed upgrade. It has to work with what it has, and with no backups.
According to NASA, the problem with Opportunity's memory can be traced back to just one of its seven flash memory cells, and a new plan the team is working on is a set of commands that will completely isolate that cell, so that the rover will only store instructions and data on the other six.
Exciting discoveries ahead?
It's incredible that Opportunity has lasted as long as it has, given that it will celebrate its 11th anniversary on Mars on January 25, and it was originally sent to the Red Planet for only a 90-day mission. Even more impressive is the fact that the rover has survived this long with no backup parts - to keep the robot's weight down, to ensure a safe landing, the design did not incorporate any - but it is still in relatively good shape.
However, as Callus told Discovery News, "anything could fail at any moment."
"It's like you have an aging parent, that is otherwise in good health - maybe they go for a little jog every day, play tennis each day - but you never know," he said. "They could have a massive stroke right in the middle of the night. So we're always cautious that something could happen."
Opportunity is close to a new science target too, so failing now would be a serious blow to the mission.
Ever since its memory 'fix' back in September, the rover has been making a marathon jog - of 26.2 miles or roughly 42.2 km - along the rim of Endeavour Crater to a nearby valley the JPL team has aptly dubbed 'Marathon Valley'. Opportunity set a new off-world driving record on the way, but according to NASA, the valley may hold clues to Mars' past environment that are a much more important reason for the trek. By directly investigating the clay deposits exposed in this valley - already spotted and identified from orbit - Opportunity may confirm the findings of its cousin, Curiosity (roughly on the other side of the planet in Gale Crater). Not only do clays require the presence of water that's just right - not too acidic or alkaline - to form, but the deposits may have formed even before those in Gale Crater.