A Martian Software Update
Friday, September 29, 2006
I follow the NASA sites on the Mars rovers just about every day. There is a raw imagery site, that I check out, and a mission updates page. Lately, as I posted a few months ago, the rover Opportunity has been approaching the large crater "Victoria" which is about the size of a full shopping mall and parking lot. They've been driving toward this crater for well over a year now!
So imagine my surprise when not more than about two days drive, maybe 100 yards away they stop the rover and do a software update!!! I mean, WTF??? Why not drive to the lip, take a picture, and *then* do the update?
Well, the answer came today. And it was a good answer.
The rovers were designed to have a mission life of 90 days. That's all. Three months was considered a very successful mission (and they had to drive something like 200 meters for their mission success parameters). Both (still healthy) rovers have now been on Mars for nearly three years. That's ten times longer than a very successful mission.
As I've said before, engineers always overstate the problem so I'm sure that most of the science and engineering team really hoped for a double mission. That would have been considered *wildly* successful before the mission started. I'm sure that if you asked the engineers what would be *beyond* their wildest dreams they'd have said a five-time mission. That is, extending 15 months and driving a full kilometer. I'm sure that would have been considered *maybe* possible, but way way way beyond anyone's dreams. (If for no other reason than everyone expected the solar panels to cake with dust, and didn't expect the Mars tornadoes which periodically cleaned them off!)
Well now, of course we're twice past the way way way beyond anyone's dreams point. As an indicator of how beyond everyone's dreams these missions have been the rovers have a kind of Y2K problem. When the missions were planned they had a task number for each day of the mission. The mission was supposed to last 90 days. Two digits. As evidence that engineers were really hopeful to get beyond that 90 day point they designed the rovers to have a three digit task number. Thus the rovers could, in the software, carry out tasks performed on the very optimistic one hundredth day of the mission.
Three digits. We're now approaching the nine hundred and ninety ninth day of the mission. 999 task days. Not even the over-engineer-the-problem engineers thought they'd ever need a one thousandth day. They only allocated three digits to the mission.
They stopped Opportunity because her clock was going to go beyond the capability of her software to function.
Ok, that's a good reason to stop.