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Characterization continues

by Mark Lemmon

March 18, 2008 - We’ve made it to the wee hours of sol 5 on simulated Mars. Things continue to go well for the test, but we’ve been uncovering issues that we will have to solve or potentially deal with during the real mission -- that’s why we do this, of course. Sol 3 was a milestone for us -- it was the first sol we used all instruments of the payload. All worked well. We’re looking ahead to
another on sol 5 -- the first touch of the surface with the robotic arm.

On sol 3 we completed the panorama of the landing site. We even arranged to get that down quickly. We also got just enough of the sol 1 images of the potential dig area to decide where to go ahead with the tests of the robotic arm. There’s still much we haven’t seen and are desperate to see soon, but we do not feel quite so blind.I mentioned before that we have a data problem. There is urgent data on the lander that hasn’t come down yet, and while we try to get it we have to proceed with activities that generate more and more urgent data. It is all a question of priorities, but right now we have to play some tricks to recover from a couple early mistakes (umm, learning opportunities).

I should introduce the concept of “critical path.” So far, the Phoenix lander, as simulated, has flown across the inner solar system, survived a brutal entry and landed safely. However, we’re trying to understand and use this robot from another planet, with limits to our insight into what its condition is. Ultimately, in order to succeed, we need to be able to dig a hole, retrieve samples, and deliver them into our chemistry experiments. What does it take to do that? Well, we need a working arm, the ability to dig and sample with it, and working instruments ready to receive soil and ice samples. Characterization phase is about demonstrating that we have all that, and solving any problems that come up while doing so.

So, sol 0 Phoenix landed and automatically deployed some items. The camera imaged the biobarrier. That’s step one on the critical path -- getting the RA ready to sample is the hardest and slowest task we have. On sol 1, we imaged the area the arm will need to dig, and got images to show there is no rock waiting at just the wrong place for the next moves. Having verified the biobarrier is not blocking the arm, on sol 2 we deployed the arm. That worked. On sol 3 the RA needed to do some characterization of how it performs when hot or cold. It also helped RAC
take a picture of MECA’s microscopy tongue, which had collected dust during entry. On the critical path, the RA moved to a safe area in front of the deck, and imaged one of the footpads.

The lander has three footpads. One is partially visible to SSI on sol 0. The other two are not. We will not initially know if one of them is perched precariously on a rock. If the lander slips dramatically while the RA is digging, that could be the end of the arm. From safe places to go (as
seen by SSI), the RA can position the RAC to see more of the first footpad and then to see the second. From near the first footpad (under the deck), RAC can see the third. But the RA cannot go there right away -- what if it runs into a rock? So, sol 3 is used to image the blind spot.

Sol 4 was supposed to be used to image both of the other footpads. The one under the lannder proved difficult. The terrain was tricky, and it was not clear if RAC would be pushed into the ground during the move. So, the move was cancelled and a less risky image was taken (showing where the thrusters hit the surface, where the testbed team -- aka, elves -- had left a nice blackened bone).

For sol 5 we had to make a non-flight choice. The plan is to touch the surface. But we see footpad 2 up on a rock (thanks, elves), and don’t see 3 (OK, the testbed doesn’t even have #3). Rather than waste a day or two, we were allowed to continue. We certainly do not expect everything to be tilted against us in this particular way -- but we could still be delayed while worrying about stability.

I’ll describe the rest of the path to sampling martian material with the RA later. In the meantime, TEGA (with one sol to spare compared to the RA) has proceeded, and we have a nice movie of the protective cover retracting (the elves left pictures of the TEGA team behind the covers).
In addition to the “touch test” tomorrow, TEGA will open the door for the oven to be used when we have a sample.

We are starting to get the ability to drop in some extra observations. We have to be careful. We expect to have solved our data problem by the end of sol 5 (check back later…). But we are not there yet. We will do a mix of flight-like activities and activities that help us make good choices after the test. For instance, we’ll be looking into a version of the workspace
imaging with much less detail and data volume to help avoid the data problem.But we’ll also practice some thing we might choose to do on a real sol 6 or 7, like color imaging or using all of SSI’s filters (and yes, the other instruments get to play, too).

Well, I have to go now. I hate it when it is just starting to get light at bed time… But the Martian sols march on, compared to Earth time, and we’re sending sequences off to Mars after 4 am now.