Opportunity Sol 627 (Spirit Sol 648)

This was one of the busiest days I've had lately. RP-1 shifts are usually busier than RP-2 shifts, but this one reminds me of the super-stressful days of the nominal mission. It's not as bad as that, but it's close.

Naturally, I loved every minute of it.

Yestersol's drive was another good one. It went only 35m, including 15m of autonav, mainly because we were limited by the lack of PCAM coverage. But at the end, we turned for comm, so we got a good downlink and are rarin' to go again.

Of course, our comm direction is basically north, and we have to drive basically south. So we have to do a nearly 180-degree turn, on a vehicle where large point turns are prohibited, and in a relatively confined space (due to ripples before and behind).

Our first approach is to drive backward down the current trough a bit past the point where we plan to hop the ripples, then do a series of sharp forward arcs that change direction and put us in the next trough over. (We have to end up heading forward at some point because we can't autonav backward as well when using the NCAMs -- their view of the nearby terrain is blocked by the rover deck.)

But this involves a bit too much uncertainty, so I bag it for a different approach. Counterclockwise arcs work well even with the stuck RF steering actuator and aren't subject to any rules-of-the-road limits, so I decide to use a bunch of those. First, we arc 75cm forward with a 22.5-degree counterclockwise heading change. Then we back straight up 50cm. We repeat this maneuver until we have the desired heading, then drive on -- straight -- for the rest of the sol.

Why not make the forward and backward arcs the same length? Because that would take us back and forth over the soil in the same spot too many times, and we're a bit worried about whether that will interfere with our traversability here. We had an experience like that in Endurance, and it left its mark. Of course, maybe it will just compact the soil and make driving better, not worse -- but if we always knew stuff like that, it wouldn't be exploration. So we try the asymmetric approach, and document it copiously with HAZCAMs as we go. And somesol soon, when those images get downlinked, we'll know whether this is a good or bad technique to use next time.

Other than that, this drive is not too remarkable -- about 30m blind, then switch to autonav. All through the sol, our TUL, Rich Morris works to free up more time, and when he's done, we have a whopping two hours and 47 minutes. This is a little embarrassing for me, actually, since if the slip checks work a little faster than they have been, we might actually complete the drive. That wouldn't be such a bad thing, although it would be a shame to waste any time.

Emily Eelkema's picture of the day is an image emailed to her by Ray Arvidson, a picture of the Rio Tinto. This is a naturally highly acidic river in Spain, so acidic that it's actually red. Some shallow pools of the stuff, the color of a nice Cabernet, take on a jelly-like consistency if you stir them. "That's Meridiani Planum, four billion years ago," says Ray. How appropriate. Even Mars's water was red.

And the Red Planet -- and with it, of course, our girls Spirit and Opportunity -- are about as close as they're going to get for a while. The one-way light-time is three minutes 52 seconds. Monday it will start rising again. Mars makes its closest approach at 8:52 PM Saturday -- tomorrow. Maybe I'll take Zenobia[1] outside with me and have a look at it.

[Next post: sol 655, November 5.]

[1] My cat, then. She was ornery and bossy and I loved her to pieces.

1 comment:

Anonymous said...

Hello Scot, I watched a documentary last night on the rovers. Some many people would be envious of your job. The time lag must be so frustrating and drving just a short distance such a challenge. Keep the blog going its great.