2011-02-07

Spirit Sol 746

We're not starting until 11:00, but I'm in at 09:00, and it turns out John has been here a while already. "Need any help working out the drive?" I ask him.

"Drive's already done," he shrugs.

Which is reasonably close to the truth. All the drive-related data came down yesterday, so we've already got enough to plan, and John's roughed out the approach already. He's got us climbing up the side of Home Plate to a patch of coarse-grained outcrop the scientists are slavering over. When we get up there, our pitch is going to be over 20 degrees. Hillary, all over again.

OK. When we were at Hillary, what did we wish we'd had? Wiggle-cams, for one thing. Higher-precision data at the end of the drive, for another. So we include that stuff in this sequence.

Speaking of drives, the Opportunity drive Frank and I planned Friday crapped out: we backed up a meter, turned, and tripped the hyper-ultra-paranoid suspension limits during the turn. So we're not where we wanted to be. What makes this more painful is that we knew the bogies had hit 5.5deg coming in here, and the limits we've been using were 6deg -- so we knew this might happen, discussed it, and decided not to mess with the limits. Now I kind of wish we had (though Ashitey points out that maybe it's better we didn't: we're supposed to be conservative like this while we get used to this new hover-stow driving).

Having screwed up both Spirit and Opportunity drives in the last week or so, it's hard not to feel like I'm in something of a slump. I hope that tomorrow's data shows I'm out of it.

[Next post: sol 749, February 10.]

2 comments:

Emily said...

Hi,
I looked in the glossary but if it's there I missed it: what are suspension limits (the ones that are apparently hyper-ultra-paranoid)? If you ever explain them I've missed it.

Scott Maxwell said...

The rovers have a rocker-bogie suspension, which consists of two parts.

The first part leads to the two front wheels and is called the rockers; the rockers are connected through the transaxle in such a way that as one side goes up, the other goes down, or vice versa.

The second part is the bogies, connecting the middle and rear wheels. These are connected middle-to-back on each side but not through the transaxle. That is, each middle wheel is connected to its rear wheel, but the left side is not connected to the right side.

The suspension limits are limits on the angles through which these two basic parts (the rockers and the bogies; we unfortunately can't distinguish the left from the right bogies) are allowed to articulate. For example, we might say that the differential (the amplitude of the articulation of the rockers) is allowed to go up to five degrees, while the bogies can range from -8 to +10 degrees. (All angles are chosen such that a vehicle at rest on a flat table would have zero for all measurements.)

Since the suspension articulates in characteristic ways as we climb obstacles, well-chosen settings for the suspension limits are often our first line of defense against climbing something that's larger than we expect.