The telecom guys also tell us today that we need to keep the rover from being pitched too far up -- we can only afford a nose-up pitch of 4deg or less. Now that we're close to Route66, it looks like this will not be possible; the rock sits at the top of a small hill, so when facing it we'll be aimed upward. As it turns out, there's not so much of a problem; the hazcam images exaggerate the slope of the hill, and when we measure it carefully, it's flat enough that we'll probably be OK.
The other consideration for the drive is to maximize science. The best case is to find a way to put the MB on a rock and the APXS pointing into the air. This will let them run the MB for long integrations during the day (when it's too warm for the APXS to generate useful data) and calibrate the APXS while it's cold, all without further moving the IDD or the vehicle -- and all while they're reprogramming the rover's brain. The only problem is that this is naturally difficult because of the orientation of the instruments on the IDD's turret. If we can't do this, we'll just do the APXS calibration alone (which is relatively easy; we just have to stick the IDD out in the air and point the APXS up), but we'd really like to be able to use both instruments.
To find a way to make this possible, I sequence a candidate drive, which Bob and I then spend two hours tweaking, so that we'll end up in just the right orientation relative to the rock. This would be easy if we were free to choose the final orientation of the vehicle (we're not; we have to be at 127.5deg, +/- 2.5deg) or if the rock face were a better shape. End result of two hours of tweaking: a 2.5deg heading change, and we cut the drive by 5cm. But hey, sometimes that can make all the difference. Even then, it's something of a crapshoot. We'll see how it goes.
At the beginning of the tweaking process, I realize we'll need to know the APXS's field of view in order to do this correctly. I think I know the answer, but there's a lot riding on this, so to be sure, I ask the APXS PUL, Rudolf Reider. This was the guy who spoke so passionately in favor of letting us "just drive" the other day -- and who was so dismissive of touch-and-go science. When I find him, he's in the middle of another argument against touch-and-go science, which I sit down and listen to for the entertainment value. I notice that he's literally wearing a belt and suspenders. Several minutes later, when Rudolf has vanquished his opponent, I get the number from him that I need: the APXS has a 60deg field of view, or a 30deg half-angle (to be precise, it's 28.8deg, he says). (Good thing I asked: I had the half-angle value in my head as the total field of view.)
I return to the sequencing room and tell Bob, "Hey, I asked Rudy about the APXS field of view --"
"60 degrees," Bob says, "a 30-degree half-angle."
"You bastard," I say, and he laughs.
"Actually, the half-angle is twenty-eight point something," he says.
"Twenty-eight point eight. Bastard."
He laughs again.
Courtesy NASA/JPL-Caltech. Just a little farther to Route66.
No comments:
Post a Comment