It’s been a sleepy weekend for the new Mars rover. Though all hardware checks out, and looks to be in good shape after the landing, all is quiet on the surface. The team is performing a software update, replacing the cruise and landing code with the driving and experiments code. Then they’re giving the computer and code a thorough checkout… and then, the backup computer and code.
Why is this all necessary? Why doesn’t the rover computer have a big hard drive, that can store the whole mission sequence? Hard drives don’t make sense on these missions, just like they don’t make sense in your pocket anymore. Too big, too breakable, too much power draw (even with a “nuclear reactor,” such as it is). Apple shifted iPods to flash memory as soon as it was practical, and it couldn’t have been soon enough.
But that just pushes the question back one step: why doesn’t the rover have a big flash drive? I’ve got more memory in my phone than I know what to do with. Two answers.
First, the rover sees high radiation. On Earth, we’re shielded from most particle radiation, and the biggest thing my phone has to worry about is the pavement. Making chips smaller helps, by making falls and impacts less of a big deal. In space, however, tiny chips (and thus, tiny circuit traces) are worse. A tiny trace or electron well is now less able to absorb and shrug off a radiation hit. Older, clunkier chips are actually better in that way, and Moore’s Law does not hold in space. There are other things you can do about radiation, so chips do improve. Just, not as fast as phones and cameras and other gadgets.
Second, a probe’s systems must be thoroughly tested before one gets on the rocket, and shoves off. No one is going to spend all that money on a mission, and then not check their handiwork. And double-check, and triple-check… It takes about as long to do component, subsystem, system, and full-up spacecraft testing as it takes to build the thing in the first place. Thus, a space mission is pretty much built a year or two before it actually flies. This in turn means it’s designed three or four years before it flies… and this means the chips are years out of date compared to what’s on a truck at the time, heading to the electronics stores.
Compared to a quiet rover now, the new programming will be worth the wait. Did I mention it has a laser, for vaporizing interesting rock samples in its path?