Monday, 5 January 2015

NASA’s Mars Rover’s Flash Memory Slowly and Steadily Wearing Out


Problems with NASA’s Mars Exploration Rover Opportunity’s flash memory have intensified over recent weeks

NASA’s Mars Exploration Rover Opportunity has been exploring the martian surface for over a decade now. The greatness of the achievement sinks in, only when told that the rover was originally supposed to survive for just 3 months. And as with every machine, even the Mars rover has undergone damage over time and this damage is leading to a loss of data collected by the Opportunity.

 

Flash Memory worn out

It’s primary mission it began in January 2004. But with its great successes, inevitable age-related issues have surfaced and mission engineers are being challenged by an increasingly troubling bout of rover “amnesia.”   Opportunity utilizes two types of memory to record mission telemetry as it explores the Meridiani Planum region. Sister rover Spirit, which sadly succumbed to the Martian elements in 2010 after 6 years of exploring Mars, used the same system. The two types of memory are known as “volatile” and “non-volatile.”
“The difference is non-volatile memory remembers everything even if you power off, in volatile memory everything goes away,” said Mars Exploration Rover Project Manager John Callas, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “So volatile memory is like the traditional RAM you have in your computer; non-volatile memory uses flash memory technology.”
As per procedure, all telemetry data is stored on the rover’s flash storage, so that when the rover powers down during night time on the planet, the data remains safe and secure, just like data remains on your computers of phones even after you shut it down.  However, such memory has a life time i.e. there is only so many number of times you can perform read/write operations on it before it starts wearing out. Because of this wear and tear, when the rover shuts down, all the data that is stored on the rover’s RAM gets erased.  After a decade of constant use, this wear and tear has become the source of lost data and unexpected reset events for the mission.

 

Oldman problems

“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,” added Callas. “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 … 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.”
Opportunity uses the Mars Odessy satellite to send back data to its handlers on earth. Every time Odessy made a pass near Opportunity (as per its revolution), commands were sent to Opportunity rover and the telemetry sent back to earth. However, if the satellite did not pass near the rover and data transmission was not possible, they noticed that some data was being lost. They found out that the rover was suffering from the flash memory error and was using the RAM to avoid flash memory altogether. And as the rover shut down, it erased all data stored on its RAM.
The flash memory problem has now grown even more problematic. As the rover fails to save data, its software forces the rover to restart. If a sequence of commands is sent to the rover, it will keep rebooting over and over again, forgetting what the previous command instructed the rover to do.
“Basically the rover stops what it was doing because it wasn’t sure what caused the reset,” said Callas. “So that interrupts our science mission on the surface of Mars.
“It’s like you’re trying to drive on a family trip — the car stalls out every 5 minutes. You don’t make much progress that way!”

 

Worries between Christmas celebrations

And now the rover team’s worst nightmare has reared its ugly head — Opportunity stopped communicating with Earth over the Christmas break. As the NASA team went into the Christmas holidays, a series of 3 sol (Mars day) plans gave the rover a sequence of commands to work on. On the first sol, the rover would operate as expected, but come the second and third sols, not only would the rover not execute the rest of the commands, it stopped talking to mission control. Fortunately though, the rover reconnected to the station and continued its operations as per commands.
“It seems the source for all these problems lead back to one particular bank of flash memory. 7 banks are used by Opportunity and it’s the 7th bank that is triggering the data loss, rover resets and communications glitches. Now the culprit has been identified, JPL software engineers have developed a technique that will force the rover’s software to ignore the 7th bank and utilize the other 6 apparently healthy banks. According to Callas, his team is probably a couple of weeks away from completing the software change so it can be uploaded to Opportunity.”

 

Surprised at the longetivity

Excluding the recent events, Callas has expressed surprise at how healthy and long lasting the mission has been.
“The rover has been amazingly healthy considering how much we’ve used it … we thought the mobility system would have worn out a long ago but it’s in great health.
“But anything could fail at any moment,” he said. “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, they could have a massive stroke right in the middle of the night. So we’re always cautious that something could happen.”

 

Milestone approaching

The Mars rover has also come very close to achieve two feats. The first being completing the distance equivalent to one entire Mars marathon. Marathon Valley is so-called as the location marks the distance the rover will have exceeded a marathon on Mars should it get there. Opportunity has traversed over 26 miles and currently holds the off-world record for any rover — robotic or driven by an Apollo astronaut.
According to orbital mapping of Marathon Valley, the location contains a variety of clay minerals that could have only been formed when Mars had an abundance of pH-neutral water on its surface. It has ancient geology spanning back to the Noachian era, much older than Gale Crater — where NASA’s Curiosity rover is currently exploring. Like Opportunity’s previous exploration of clay-rich deposits, studies of Marathon Valley could provide invaluable data as to the ancient, potentially habitable Mars environment.

 

Software Glitch

The engineers have identified that the 7th flash memory bank aboard rover is triggering the data loss. Opportunity has 7 banks of flash memory and now the JPL software engineers have developed a technique that will force the rover’s software to ignore the 7th bank and utilize the other 6 apparently healthy banks.

\According to Callas, his team is probably a couple of weeks away from completing the software change so it can be uploaded to Opportunity.

Resource : Discovery
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