In the same drive, we broke the 2km mark. We didn't beat Opportunity's single-sol distance record, but that's not too surprising. Anyway, we beat the heck out of our old record, and that's pretty good.
So that's the good news. The bad news is, I can't go to SpaceOps to brag about it. The International Legal Affairs Office at JPL sat on my travel paperwork for a week, so it didn't get to NASA HQ and the State Department in time, so they disapproved it. So John Wright is going to present my paper for me, and I'm going to stay here and drive the rover.
Come to think of it, that's not such a bad deal.
Especially just after we landed, there were a lot of claims about records we'd set or broken. Many of these were reasonable, such as when we broke Sojourner's record for a single-sol traverse. But then there was growing pressure to think up more and more records in an effort to stay newsworthy, and after the first couple of months post-landing, that became harder and harder to do. We quickly moved into a phase of being tongue-in-cheek about it, and there we've stayed. I think Mark Adler's Mission Manager report from sol 123 is a brilliant example:
Sol 123 started off with Pancam and mini-TES observations for
near-field surveys, atmospheric studies, and localization.
Spirit then took a half-hour nap, followed by the day's drive.
This sol we had another 48 meter direct drive, the mid-drive
survey and localization remote sensing, and then 47 m of
driving using auto-navigation. The total was 95.2 meters,
bringing the mission total to 1830 meters. Nextersol, we
should break one Earth nautical mile, which is 1852 meters.
As we drive another kilometer and change to the base of the
hills, we will continue to bring you as many arbitrary
numerical achievements as we can come up with. Think of it as
the games you play on a long road trip so you don't keep
hearing "Are we there yet?". More numerical trivia: a
nautical mile, defined as the length of an arc-minute at the
equator, is almost exactly a kilometer on Mars! Keep that in
mind the next time you're navigating a boat down the Valles
Marineris.
[...]
Plan:
Continue on to the hills. "99 bottles of beer on the wall, ..."
We'd have enough time to sing the whole song today, if we wanted. This is because Opportunity delayed our downlink. Both rovers share the relay passes through Odyssey, and Odyssey is just a FIFO[1] -- that is, whatever got sent to it first, gets sent back to Earth first. Opportunity sent all of its data to Odyssey before we sent any of ours (luck of the draw, more or less), so all of their data will come down before any of ours does.
The upshot is that we're facing a lengthy delay. The downlink starts at 13:00 or so, but we're not going to get any of our data, Art tells me, until 14:30 at the earliest. As it happens, we actually don't get anything until 15:15 -- at very late start, considering that we were scheduled to be done by 18:00 or so.
One thing we do know is that yestersol's data included a slightly worrisome bit of drive data, as Mark Maimone explains to me. The rover keeps an eye on its current tilt as a way of protecting itself from flipping over. Indeed, the rover actually keeps two measurements of its tilt, one an instantaneous measurement taken eight times per second, and the other a "filtered" measurement, which sort of smooths out the instantaneous measurement over time. For an instant during yestersol's drive, the instantaneous measurement of the rover's tilt exceeded 20 degrees -- the limit we've currently set on the rover. Now, the instantaneous measurement can be fooled by the kind of quick short drop the rover experiences when, for instance, it finishes climbing over a rock and the wheels drop to the ground, and we don't want the rover to panic when this happens. So it has a rule that says to stop driving if the instantaneous measurement is over the limit twice in a row. It wasn't -- the measurement settled out by the time the next snapshot was taken -- but we were an eighth of a second away from losing the rest of the drive.
Mark takes the opportunity to complain about overly aggressive drives (his diagnosis of the problem), and while I haven't seen the drive sequence in question, I don't outwardly disagree with him. But it must be said that, in the end, the sequence worked fine. Since the smoothed tilt measurement was only 12 degrees, the 20-degree spike was surely spurious, and could have happened almost any time.
I came in early so I could hang out in the downlink assessment meeting -- I haven't been to one in a long time. (Since the downlink was delayed so long, I didn't need to be early, but of course I didn't know that.) The news in the meeting is good: we're 200m ahead of where we need to be to make it to the hills on schedule. Sometime soon, in the next week or so, they'll choose a spot to stop for a few sols and do some science -- dig a trench, IDD it, and generally hang out for two or three sols. The objective of the trench is said to be "ground truthing" -- confirming orbital measurements with measurements we take on the ground -- and getting MTES observations of the hills from 500m or so out. (I thought at first that it was a little early to be discussing that, then realized that we're only about 1km from the hills now, so we could reach that point as early as next week!) But I think the real reason is that the science teams are getting bored. All this driving is fun for us, but not for many of them.
I'm glad to hear one of the scientists voice what's been a minor annoyance for me: the meeting times are posted with very little notice. We typically haven't been finding out when we need to come in the next day until the day before. Say what you like about Mars time, at least it was predictable. Jim Bell's exact words are: "I would like to make a bitter complaint about people not knowing when meetings are going to be, even the next day." Of course, today was worse than usual because the delayed downlink delayed the meetings as well, and Jim seems to be mollified when Art points this out to him.
Larry Soderbloom leads a discussion of what to do when we get to the hills. The basic choices, which he illustrates by spinning that cool 3-D model around again, are to go uphill into the caldera-like thing or south into the dark basin. He still favors the southern region. It's got an ejecta blanket, a lava flow, or something like that -- whatever it is, the orbiting THEMIS instrument shows a high thermal inertia. Rocks.[2] In addition, the stratigraphy of the plain should be well exposed there -- we might be able to drive up to a rock wall and see sedimentary layers, or anyway that's the geologists' fantasy. There's also a set of seven or so terraces -- huge natural steps carved into a hill. The whole area is "loaded with interesting stuff," in his words.
So Larry's worked out a basic traverse to that region from the "spur" we're currently aiming for; the path is about 625m long, and goes up a hill on the way, so we'll get a pretty good view of the whole area. The route also takes us past some "megaripples," some kind of huge sand-dune-like things.
I've missed those meetings.
Courtesy NASA/JPL-Caltech. A sample orbital map whose colors correspond to different predictions of surface materials. Spirit's been confirming those measurements, providing "ground truth," as she moves across the terrain.
While I was sitting in on the meeting, John was doing the hard part. I go take a look. It's a typical drive: a little zig-zagging around obstacles, then a lengthy autonav segment. Ho-hum.
Things get a little silly during the command approval meeting. We've all been there a long time, and for most of these people it's rather late to be working. John Grant briefly zones out looking at a screen saver in the corner and says, "Man, I'm freaked out by those rainbow-colored worms." I look at him strangely and say, "I don't see any rainbow-colored worms ...."
As has often been the case lately, there's not much science in the sol, mostly driving. When Art asks John Grant if science is happy with the plan, however, John says yes. And he adds: "When I came in Monday morning, all Ray said to me was, 'Keep driving, Grant!'" (He says the last part in a mock-gruff voice. John was clearly talking to Grumpy Ray.) And so we shall.
Footnotes:
[1] Computer lingo: First In, First Out. The line you stand in at the grocery store is a FIFO: the first person in line gets served first, and so on.
[2] Rocks take longer to absorb heat than soil does, but they also take longer to bleed the heat back out when the sun goes down. This property of being slow to absorb and slow to release heat is known as a high thermal inertia. It lets you tell from orbit whether an area is mostly rock or mostly soil: measure the temperature of the same area at different times of day and night, and from there it's easy.
As a side note, I am fascinated and awed that it's possible to figure out stuff like that -- and even more fascinated and awed that we can put a chunk of metal in the sky of a planet a hundred million miles away and have it tell us about that planet's surface from hundreds of kilometers above. We live in an age of wonders.
No comments:
Post a Comment