No mission update for the week ending December 29, 2001.

We've made good progress with the latest round of Mini-TES testing. After all the problems we had with Mini-TES 2 not working right when it was tilted, we decided a few weeks ago that we had better pull Mini-TES 1 out of storage and make sure that it was okay. We shipped it up to Santa Barbara (carefully!), and the guys there have spent the last couple of weeks checking it out. It's fine, as it turns out... everything works as it should. So now we know that both instruments for both rovers will behave themselves properly no matter how we tilt them. We don't want to fly instruments that won't work right if the rover is parked on a hill!

Everybody on the project is going to take a well-deserved rest for the coming week, so the next weekly update will be after the first of the new year. Happy holidays to one and all.

A long-standing problem with the rover's arm was solved this week. The arm's job is to place several of our instruments onto martian rocks. Time on Mars is a precious commodity, so to keep from wasting time we'll often use the arm at night. But it gets really cold at night on Mars. So the motors on the arm need to have heaters on them, allowing the arm to move properly even when it's really cold out.

The problem is this: What happens if we make a mistake and leave the heaters on in the daytime? The answer, unfortunately, is that the motors could get overheated -- cooked, really -- and be permanently damaged. Not good. For awhile there, it looked like maybe we were going to have to use much weaker heaters, which would have been safe but which would not have worked well at night. Instead, someone at JPL came up with a very slick design in which the motors are automatically protected from overheating by a thermostat. If a heater goes on at night then everything is fine, but if we leave it on accidentally in the daytime, the thermostat will automatically shut it off. So we can use the arm at night after all.

Oh yes, and I almost forgot... the Mission System Critical Design Review was a big success!

It's time for yet another big Critical Design Review. This one is the Mission System CDR, scheduled for Tuesday through Thursday of this coming week. A project like MER is divided into two big parts, called the Flight System and the Mission System. The Flight System is the hardware... the stuff that actually goes to Mars. The Mission System is the stuff on the ground, back here on Earth. It's just as important as the Flight System, because it's everything that makes the Flight System work. Computers. Software. People... lots of 'em. People to train the people. And so forth. For the past week (and for many weeks before that), a huge amount of our time and effort has been spent getting ready for a big review of the design of the MER Mission System. And now it's time to do it. Let's hope it goes as well as our other CDRs have gone.

The Mini-TES saga continues. We found out some time back that the instrument wasn't quite working right when we tilted it in certain directions. That's a big deal, because the rover won't always park on level ground! It has been a long road to track this one down, but we seem to be almost there. Part of it was a problem with some wiring, but that wasn't all there was to it. There was also a subtle problem in the electronics. We've been testing the living daylights out of the instrument in Santa Barbara lately, and with some minor tweaks to the electronics design it now seems to be behaving itself nicely at every crazy angle the rover could find itself at.

The instrument we've been doing this to has been our second Mini-TES... the one that's still not finished. So now, just to be safe, we have to test the one that we built a couple of years ago and make sure that it works properly at all angles too. This coming week, we're going to ship it (very carefully!) from JPL up to Santa Barbara, and make real sure that it's behaving itself as well.

There's been bad news about our cameras lately, but there's been some really good news too. Two weeks ago we were dealing with problems with the electronics for Pancam and the Microscopic Imager, and we're still dealing with them. But this past week we got the first really good look at the CCD's that we'll use for our cameras, and they're incredibly good. CCD stands for "charge coupled device", and it's the detector that lies at the heart of a digital camera -- the device that forms the image, just as film does in a film camera. When CCD's are built, it's typical for them to vary in quality. So normally you build a bunch of them, and then put a lot of work into picking the few best ones to fly. It didn't quite work that way with the CCD's for our cameras. We built a whole bunch of them, alright, but now that we've checked them out, we've found to our surprise they're nearly all about as close to perfect as a CCD can be. The camera guys on our team are scratching their heads now over which ones to fly, because they can hardly even tell them apart. There are bad problems and good problems to have, and this one's a good problem!

We've had a hang-up with our cameras lately. The lenses are fine, the detectors are fine, and all the mechanical pieces are fine. But we're having some difficulties with the electronics. Both of our cameras, Pancam and the Microscopic Imager, use the same electronics design. We got all our electronics boards built a couple of weeks ago, but when we looked at them carefully we realized that there was a problem. It's simple stuff, really: the points where we have to attach little parts called resistors to the boards are spaced too close together, and the resistors won't fit. So now we have to have another set of boards built, which is going to delay our camera schedule a couple of weeks. This isn't a particularly big deal; stuff like this happens all the time. But it's the kind of thing you spend a lot of time worrying about when you get to this stage in a space project.

We learned something very interesting about the RAT in the past couple of weeks. The RAT is our Rock Abrasion Tool, and we'll use it on Mars to grind into rocks so that we can see what's inside them. In all the RAT tests that we had done until now, the grinding produced a lot of dust. Not only that, but the dust formed a kind of "plume"... rising almost like smoke as we'd grind away at the rock. This isn't good, since the dust in the plume could contaminate some of our instruments. To prevent contamination, we've put a "skirt" around the RAT, to catch the dust.

Just recently, we did our first tests of the RAT in a special chamber that creates Mars-like environmental conditions. The very good news is that we saw no dust plume at all! Mars has a much less dense atmosphere than Earth does, and apparently the dust particles that the RAT creates are large enough that the martian atmosphere can't suspend them. We'll still need a dust skirt, since the RAT could always stir up martian dust, which we know is very fine. But now we know that the dust created by the RAT itself is unlikely to create much of a problem for us.

Landing sites were a big focus again this week. We settled on our landing sites in general terms at a meeting a couple of weeks ago. We're down to four prime sites and two backups now, and they're all really good. But it's not enough to pick the general areas where we think we might want to land. Mars Global Surveyor is up there taking pictures of these sites for us, and we need to tell them exactly where to take those pictures so they know where to point their camera. So this week we dialed in the exact positions of the sites, and passed them along to the Mars Global Surveyor folks. Now we have to be patient for a few months while MGS gets those shots for us. Fortunately we've got until next spring before we have to "downselect" to the final two sites.

Mars Odyssey is in orbit! The orbit insertion maneuver took place early this week, and it went flawlessly. This is a huge step forward for NASA's Mars exploration program, and our congratulations go out to the Odyssey team. Odyssey will map Mars for several years, providing new information about what the planet's surface materials are made of.

Odyssey is more than a scientific spacecraft. It's also a communication satellite, and that's what makes it big news for us. Once our rovers are on the martian surface, Odyssey will fly over each one twice per day, collecting data from them by radio and relaying it to Earth. We'll get roughly half of our data through Odyssey, so it feels very good to have it safely in it's natural environment -- in orbit around Mars.

This was a huge week for us. We began this project over a year ago with something like 185 possible landing sites for our rovers. Now we're down to the Final Four. There was a big landing site selection meeting this week, and dozens of scientists who have spent their careers studying Mars were there. The four sites that came out on top are the Meridiani "Hematite" site, Melas Chasma in the Valles Marineris, Gusev Crater, and a place called Athabasca Vallis in the Elysium region. They're all great sites! Check out our landing site page for more on all of them except Athabasca. (Athabasca was a bit of a dark horse, and we don't have a map of it ready yet. We'll provide an update with details soon.)

We have a big week ahead of us, too. On Tuesday evening, the Mars Odyssey spacecraft is scheduled to go into orbit around Mars. This is a terrific new science mission, and it also will be a key communication satellite for our rovers once we get there in 2004.

The guys at Raytheon found and fixed our Mini-TES problem this week. It was what we expected: a cable had been put in the wrong place, and it caused a sensitive part of the instrument to bend very slightly when we turned it rightside-up. It wasn't much of a bend, but it was enough to cause the trouble we were seeing. We opened the instrument up, re-routed the cable, fastened everything back together, and then ran it through its paces sideways, upside-down, and rightside-up. And now it works right no matter which way we're tilted.

So now it's on to the next problem... whatever that turns out to be!

Probably the most exciting thing going on this past week has been the progress on our cameras: Pancam and the Microscopic Imager. These were problem areas for awhile, but they really seem to be coming around. On a payload this big there's bound to be something that lags behind everything else, and for us it has been the cameras. But the camera work has really been going well lately. All of the mechanical parts -- things like camera housings -- are now done. All of the electronics boards should be done in another week and a half. And the lenses are basically done too. So it's not going to be too long now before we can start putting some real Mars cameras together... and taking real pictures with them.

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