Opportunity Sol 398 (Spirit Sol 419)

The good news is, we did a record-setting blind drive on sol 396. The bad news is, we didn't mean to.

The problem stemmed from a mistake in a waypoint command. A waypoint is actually a "waydisc" -- an imaginary circle on the terrain. The rover drives until it's inside the circle, or until it runs out of time trying. The mistake they made yesterday was that they moved the circle away but forgot to make it bigger, so the rover had to drive farther to reach it. What was intended to be a multi-stage 100m drive with increasingly paranoid suspension checks turned into a single-stage 125m drive with relatively generous suspension limits.

That could have been bad. It's not that we mind making more distance than expected, it's that the mistaken command sent the rover beyond what we could see well in the available imagery. If there had been a rover-killing obstacle out there, we could have sent the rover to its doom.

Luckily for us, the terrain the rover was driving over had no such hazards. (Admittedly, such hazards are rare in this terrain. But as Andy says, we're paid to be paranoid. And brother, we earn it.) Indeed, it stopped only because it ran out of time; if it had been given a couple more minutes to drive, it would have reached the circle anyhow, despite its greater-than-intended distance, and proceeded to the next command. That would have compounded the problem.

Frank needs no reminder that he made a potentially dangerous mistake. It's actually worse for him, because he almost caught it. He and Khaled noticed yesterday that something was screwy with the simulation, but they found a different error -- the rover's initial position was set incorrectly -- and thought that explained what they were seeing.

We've all had days like this. Yesterday it was Brian's and Frank's (and Khaled's) turn. I've had my turns, and I don't need another; they can have mine. Because one of these days, we're afraid we're going to come in and have to tell a story a lot like this one, except it will end with, "and that's how we killed the rover." Before the day is out, I have an automated check in place that will catch us if we make that mistake again. But Murphy's law is merciless: the number of potential mistakes seems infinite.

I try to cheer Frank up. "Still, you set a new blind-driving record! And it's one we're never going to break, at least not on MER!"

"Just what I needed," he groans, "my stupidity enshrined for all time in the Guinness Book."

I'm not very good at cheering people up.

Because the rover timed out while striving for the waydisc, the sol-396 drive didn't go as far as intended, and the sol-397 drive (an automatic continuation drive meant to execute Sunday) noticed the leftover error and, properly, didn't go anywhere at all. So we haven't quite made it to Vostok yet; today's just another long drive.

And believe me, we check the waypoint.

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