Phoenix sol 4 press briefing: unstowed arm, full panorama, and weather
Posted by Emily Lakdawalla
29-05-2008 15:38 CDT
So I anticipated last night two of the main messages of today's press briefing: the completion of the initial reconnaissance panorama, which was taken in only one color and at a quarter the full resolution of Phoenix' camera, and the successful unstow of the arm. Here's their better-quality version of that first panorama.Why do they bother getting a panorama that's black and white and is only 25% of the full resolution of the camera? Because they can take it and get it down to Earth very quickly; it'll take them a few weeks to build up a full-resolution color view. This one took them only a few days. By taking it in only one color instead of three, they cut the necessary data volume by a factor of three. A bigger savings was achieved by cutting the resolution by a factor of four, returning the individual images for the mosaic at a pixel size of 256 by 256 instead of the native resolution of the camera, 1,024 x 1,024. By doing that, they cut the necessary data volume by a factor of 16. So this panorama is (1 divided by 3 divided by 16, or 1/48, or about 2%) of the size, measured in terms of data volume, of the eventual three-color panorama that they will take. Never mind the fact that if they want it in stereo, they'll have to take an identical panorama through the camera's other eye.
The next major news was the safe deployment of the robotic arm. Here's an animation of that process, which I was able to put together from the raw images on the Phoenix website, actually from the useful zipped-up batch-downloadable versions from James Canvin's website.Robotic Arm Flight Software Lead Matt Robinson was "ecstatic" that the arm unstow had gone as easily as it did. Both of the two deployment events -- unlatching the forearm launch restraint and the elbow launch restraint, which held the arm in a safe position during all the shocks and jolts of launch and landing -- went flawlessly. Robinson said they have actuated (that is, moved) all four of the arm's joints, and all of the data they are receiving from the arm "looks comparable to the data taken during test runs." That is, everything looks normal. "All the joints are healthy, and we're rarin' to go," he said. He said the next steps are to do more checkouts on all the individual joints, to evaluate their performance at the temperature extremes at Phoenix' landing site, both hot and cold.
Then there are several things they'll have to do before they can touch the ground. The first thing is to evaluate the lander's stability. The lander has three footpads, only one of which has been photographed to date. The other two are invisible from where the mast-mounted camera sits, so the only way to image them is with the camera on the robotic arm. One of them they can see with the robotic arm out in the air, but to see the third foot, they will need to snake the arm underneath the lander. But they'd better not try to do that before they take a look underneath the lander to see if there's a big rock under there. It's not likely, but it would be lousy to find a rock by bashing the arm into it. So they are going to poise the arm below but outside the lander, in an area they've imaged already, and check. I asked during the Q and A segment whether they plan to use the arm camera for stereo imaging. The arm has only one camera, but you can pretend it has two eyes by taking one image, then shifting the arm slightly to take a second (I do this trick all the time with my own digital camera to get stereo images; see my post on the MSL "scarecrow" rover to see a couple of those). Peter Smith said yes, they do plan to do that, and they have a visualization tool that makes it easy. Anyway, all of this arm-moving activity is going to take several days. Things are going great but they did lose a day of arm activity because of the Mars Reconnaissance Orbiter communications snafu (which doesn't seem to have been solved yet, or at least they didn't report that it was solved this morning), so we're still looking at early next week for the first soil touch to take place.
Here's an animation of the other unstow event. Since Phoenix is a sessile lander, the major motion events to make animations of will be these arm movements. I think they're pretty cool.Barry Goldstein reported that as of today, they have completed the initial engineering characterization, finding all of Phoenix' vital systems working within normal parameters. They've now moved on to the science instrument characterization phase, and are nearly done with that. Once they're done with characterization, they can move on to digging.
Peter Smith showed a map of the workspace, with some of the names that I mentioned yesterday labeled. They're going with a theme of fairy-tale characters and folk tales to name the rocks, soil patches, topographic features, and other stuff within the robotic arm's workspace.I asked Mark Lemmon to explain what "National Park" means to the team. He said that they are reserving that area until they have learned everything they can about it before disturbing it, and (probably more importantly) until the science team has achieved some consensus on an explanation for the various features -- rocks, topographic highs and lows, and so on. The "national park" won't be left undisturbed for the whole mission; in fact, by mission's end, it will probably be a "mess," as Mark put it. But for now, he said, they'll take more pictures and carefully take their first soil sample before they begin to make decisions about what to do with the reserved space. Probably the space will be divvied up among different kinds of investigations. "but we have to figure out just where and in what order. That way we don't decide we need a sample of stuff we just tossed on the rubble pile last week!" Sounds like a good plan to me!
Mark also explained the plans for the upcoming imaging campaign: they are going to start taking more color data, at higher resolution, possibly even in stereo. They are also beginning to identify high-priority targets for detailed images. I'm sure they'll image each of the visible large rocks at high resolution, and also the backshell and parachute.
Last but not least, Jim Whiteway gave a weather report, stating that the Canadian meteorological instrument is working great, and that the lidar it uses to analyze the opacity (dust content) of the atmosphere is up and running. He said they've observed dust lofted up to heights of three kilometers. I've just added the Phoenix Weather Widget to my iGoogle page, and it tells me that the weather report for sol 2 (I'm guessing the two-sol data lag will be common, because they take the data one sol, return it the following sol, and have it processed and ready for posting online on the sol after that) was the same as for sol 1: min and max temperatures of -30 and -80 Celsius (-112 and -22 Fahrenheit), sunny, with light dust.
One of the cutest features of the meteorological instrument is a little telltale mounted on top of the tall meteorological mast. It blows back and forth in the wind on Mars. A tilted mirror below the telltale shows which direction the wind is blowing, and how far the telltale has been blown off of vertical; it also shows the sky color directly above the mast, and as you can see, it's darker than the color of the sky closer to the horizon (same as it is on Earth, for the same reason; near the horizon, there's a longer path through the atmosphere, more space along which air molecules and dust can scatter light and make things look brighter). I asked Whiteway how to interpret the telltale images, and he told me that the Sol 1 image showed that the wind was blowing at about 15 miles per hour (24 kilometers per hour), and blowing the telltale toward the northeast (toward the lander). I took that Sol 1 image and annotated it below; I very much hope that I have not messed up the labels showing the directions. Note that if the telltale is being deflected toward the northeast, then the wind is out of the southwest.I also asked Peter Smith about their current thinking regarding where the rocks at the landing site came from, and he was fairly noncommittal, essentially saying it's too early to be definite. He did point out as interesting that the rocks were "flat, almost like paving stones" and that their color tends to be lighter than the surrounding soil, which is unusual.
Since there were very few questions from the press, I decided it shouldn't offend anybody to take the time to thank the Phoenix team for so openly sharing their raw image data with the international community of space enthusiasts on the Internet. He replied that "Involving the world in this mission is one of my highest goals, and the way to do that is not hold on to data, but to put it right out on the Web so that the world can enjoy it as we do." Good man.
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