2010-02-18

Opportunity Sol 382 (Spirit Sol 402)

We planned two sols yesterday, and we're planning three today -- for President's Day Weekend. Saturday, Sunday, and Monday are all going to be drive days.

And what drive days! Friday, we do one hour of blind driving followed by 2.5 hours of autonav. Saturday and Sunday are each four hours of autonav -- we'll just let the rover pick up where it left off the sol before, and continue to find its own way south. The combined total distance for the three sols might be 350m, possibly even more! As Justin Maki points out, we'll basically do two-thirds of our mission success driving in one weekend.

Fitting all this driving in is going to require some work. They'd originally planned to spend the rest of each sol doing some remote science, but our power situation is such that we can't. So the science team ruthlessly cuts science until the drive fits. We have to cut some of the post-drive drive-support imaging, but it's not a big deal. As long as we get the drive-direction FHAZ images, we'll be fine. And we'll get NCAMs on top of those, so we're gold.

The rover's continued (Saturday and Sunday) driving will be autonomous, but depending on what we see in the downlink, we could want to pull the plug. So we'll have to come in over the weekend, just long enough to evaluate the downlink and say whether we think it's safe for Opportunity to go on. Theoretically, we might decide on Monday that we need to re-plan the drive, but that doesn't look likely. Nobody wants to call the team in on a holiday anyway.

We plan the drive. We cross our fingers. We go home.

But not before saying goodbye to Julie Townsend, who's moving on to other work. She hugs Art and tells him she's had the time of her life. "I know what you mean," he says. "You work on something like Pathfinder, and you think nothing will ever be like that again. And then something like this comes along."

3 comments:

Emily said...
This comment has been removed by the author.
Emily said...

Maybe I just missed it, but did you ever explain the difference between 'blind driving' and autonav?

Scott Maxwell said...

I don't know, either. :-) So here's a short description of autonav.

The rover takes an image of where she wants to go using a stereo pair of cameras -- on Spirit, usually the HAZCAMs; on Opportunity, the NAVCAMs. Since it's a stereo pair, the rover can build up a 3-D model of the world and evaluate it for geometric hazards.

Too big a rock? Too deep a ditch? Then go around it; else, go straight ahead.

That's autonav. For blind driving, we just tell the rover, "trust me." No imaging, no modeling of the world; we just drive.

We'd use autonav all the time except that the rover's brain is slow. The rovers have a 20MHz CPU -- about 100 times slower than a box you buy off the shelf at a Best Buy -- because old, slow parts with big fat transistors do better in high-radiation environments such as Mars. Building up that 3-D image and reasoning about it takes time -- we drive something like 90m/hour when blind driving, but as little as 10-30m/hour on autonav.

Typically, then, when we're going for distance, we drive blind to the edge of what we can see from the starting-point images, and then we have the rover drive on autonav from there. The extra distance might be gained slowly, but without autonav, we wouldn't get it at all.