Slashdot Mirror
NASA Switches Curiosity Rover To Backup Computer Following Glitch (extremetech.com)
NASA has switched its Curiosity rover over to its backup computer system after the main system started experiencing errors last month. "Many NASA spacecraft and surface missions have redundant systems built-in," reports ExtremeTech. "Once they've launched from Earth, there's no way to repair damage to critical systems, so it makes sense to double-up on the vital components. That includes Curiosity's computers, which were designed specifically for the harsh environment on Mars." From the report: The rover has a pair of identical brains running a 5-watt RAD750 CPU. This chip is part of the PowerPC 750 family, but it has been custom designed to survive high-radiation environments as you'd find on Mars or in deep space. These radiation-hardened CPUs cost $200,000 each, and NASA equipped the rover with two of them. Each computer also has 256 kB of EEPROM, 256 MB of DRAM, and 2 GB of flash memory. They run identical VxWorks real-time operating systems. When Curiosity landed on Mars in 2012, it used the "Side-A" computer. However, just a year later in 2013 (Sol 200), the computer failed due to corrupted memory. The rover got stuck in a bootloop, which prevented it from processing commands and drained the batteries. NASA executed a swap to Side-B so engineers could perform remote diagnostics on Side-A. In the following months, NASA confirmed that part of Side-A's memory was unusable and quarantined it. They kept Curiosity on Side-B, though. With Side-B experiencing problems preventing the rover from storing key science and engineering data, NASA switched Curiosity back to Side-A while it investigates the problem, which it can only do when the other computer is active. "NASA hasn't said how much of Side-A's RAM is bad, and it only had 256MB to start, but the team does intend to move Curiosity operations back to Side-B if possible," the report adds. "For now, the mission is functioning normally on Side-A."
it only had 256MB
What a strange use of the world `only`. 256MB is a lot, really a lot.
We could run our desktop computers with 256MB RAM at ease if we wanted to. As comparison: When windows 2000 was released (around 2000...) most computers only had around 64MB of memory, and that would already be a reasonable beefy computer. Windows 2000 liked a bit more, around 128, but would run on this 64MB just fine albeit a bit slow. And this same windows 2000 offered a desktop experience not much different from the (windows) desktops we are using today, including proper plug and play support, multimedia and whatever fancy you liked. When XP came a couple of years later, most people still hadn't updated to 256MB of memory.
Now, compare that to an embedded computer that does not have to waste any memory on fancy graphics, user interfaces and what more, and you will notice that 256MB is a lot. Really a lot. Try writing code to fill that up - a single human couldn't, even a whole team can't. Obviously it'll need some memory to store images etc, but this 2GB of flash is also a lot and comparable to what the first digital camera's came with..
And for those saying 'long time ago long time ago' - even today it's pretty common to write software that has no more than a single kilobyte of RAM memory available, for embedded purposes. With all the modern webcrap using gigabytes of memory for trivial tasks people seem to have lost the feeling for quantity. 256MB are more bits than i can count in my lifetime..
A glitch a day keeps the bugs away.
Your link is circular back to this same slashdot article, but a google search of your link title finds this:
https://www.militaryaerospace....
This is cool, thanks!
Also interesting:
An alternate approach that doesn't require expensive radiation hardening also seems to have worked with a half-day transition through the Van Allen belt. It will be interesting to see if their approach can stand up over time on a long mission.
"Every time I see an adult on a bicycle, I no longer despair for the future of the human race." - H. G. Wells
The RTG on the rover is "right-sized" to provide the necessary *average* consumption, as anything more would be wasting plutonium. However, since momentary consumption fluctuates, there's a battery buffer to smooth over the load profile.
Ezekiel 23:20
Or "developing specialized semiconductors with extreme testing requirelents and a sales potential in the (at best) double digits is extremely expensive."
Also, triple redundancy only helps to protect against SEE (Single Event Effects), those are cases where an ionizing particles changes some charge, and flips a bit in the memory. These are recoverable errors. The processor can reset the faulty bit, and continue normally.
The problem is that part of the cosmic radiation consists of heavy element nuclei, flying at near speed of light. These don't just flip some bits, they have enough energy to permanently dislocate atoms in the crystal silicon lattice. Due to this damage, the processor will get higher leakage currents, and will eventually stop working altogether as the damage accumulates.
Shielding is impractical, because a thin layer of metal (good enough to block gamma radiation), can't stop these highly energetic particles. Even if the particle hits the shielding, it doesn't stop it, instead you get a shower of secondary particles, still strong enough to cause damage. Radiation hardened processors use a different technology that is less sensitive to damage (at the cost of lower logic density)