Mars Exploration Rover Status
27 Dec 2002
(Source: Cornell University)
Week Ending December 21, 2002
Thermal vac testing on our first rover is done, and we survived it. We have a very tired team!
A test like this requires use of a very big, very complicated facility. So you don't run it just 8 or 12 hours a day... it's a round-the-clock operation. We've all just finished almost two weeks of irregular and very long shifts, but it was worth it. We got some great data, and we sure learned a lot about one of our new rovers.
Over the next few weeks I'll post here several of the data products that we collected during the test. Here's a first one for starters. To give us something interesting and challenging to look at in the test chamber, Dick Morris from Johnson Space Center put together a really nice test target with lots of rocks on it. Before we're done with our testing, we're hoping to look at every rock on this target with every one of our instruments. The image was taken by Pancam, and shows color close-ups of two of the rocks. We've got some spectacular Mini-TES data on this target, which I'll post next time.
For now, though, I'm going to go sleep for a week!
Week Ending December 14, 2002
We're deep into thermal vac with the MER-2 rover now, and so far it's going great. "Thermal vac" is short for thermal vacuum testing, and it's one of the toughest tests we have between now and launch.
We started on Thursday with the rover in the test chamber, all folded up the way it'll be when we land. We took the pressure and temperature in the chamber down to just what they'll be like on Mars. And then we put the rover to work. Out came the solar panels. Up went the mast and the antenna. The rover stood up, swung its wheels into place, released its arm, and was ready for action.
One of the first things we did once the rover was ready -- and one of the first things we'll do on Mars -- was take a whole bunch of pictures. There are a lot of lights in the test chamber, so the central post doesn't cast just one shadow here like it will on Mars. But this gives a real sense of what our sundial pictures will look like.
Of course, what we're really going to Mars to take pictures of is Martian rocks. We didn't have any Martian rocks to put in the test chamber, but we did cut some nice slabs of a bunch of different Earth rocks and take some pictures of them as well.
Thermal vac isn't over yet... in fact, in many ways it's just getting started. We'll be at it all this coming week too: testing the rover's arm, taking more pictures, and -- especially -- putting Mini-TES to work.
Week Ending December 7, 2002
This week it's been all about preparation for one of the biggest tests we have in front of us before we launch.
The motto you try to follow in this business is "test as you fly, fly as you test". In other words, test everything on the ground just like you plan to fly it, and then fly it that way. Coming up over the next couple of weeks is one of the most important test-'em-like-we'll-fly-'em events of the whole MER program. It's called the "surface thermal vacuum test". In this test we take the whole MER-2 rover, put it into a big space simulation chamber, take the atmosphere down to martian pressure, and take the temperature down to martian temperature. And then we make the rover do just about everything it knows how to do. We can't drive it, because there isn't enough room in the chamber. But we do everything else, and that's a lot. Every instrument gets tested under conditions just like we'll experience on Mars.
To tell the truth, you'd have to be nuts not to feel just a little nervous before a test as important and complicated as this one. But we've been preparing for months, and we think we're ready. We'll find out soon.
Week Ending November 30, 2002
We've just made our last major design decision, and now our RATs have teeth. We settled most of the design details for our Rock Abrasion Tool (RAT) a long time ago. In fact, the two flight RATs are built, tested, and at JPL. But we've left one thing open for a long time, and that's the exact design of the "business end" of the RAT... the grinding heads that will actually contact the rock and grind their way into it.
We've known pretty much since the start that we were going to make the grinding heads using diamonds, since diamonds are the hardest materials we can possibly use. But finding the best way to use diamonds has been a very long research project. ("Diamonds are forever", as we put it.) We've tried grinding heads encrusted with tiny diamonds. We've tried big single diamonds. We've tried diamonds coated with nickel. All of these have worked, but they don't all work equally well. We have no idea how hard martian rocks are going to be, so we have to find the material that works the very best.
And now we seem to have found it. The best grinding heads of all have been ones that are made of a hard resin with lots of fine diamond grit mixed in with it. The great thing about these bits is that they sharpen themselves. Even diamonds wear out after awhile. But the way this resin works, it's strong enough to hold the diamonds in place only for awhile. Then, after they've been used awhile the worn diamonds pull out and the resin wears away... exposing fresh, sharp diamonds underneath. After a lot of testing, we've built about a dozen of these bits, and we've now shipped them out to JPL to go into the two flight RATs.
Week Ending November 23, 2002
We dodged a bullet this week. We made a mistake a long time ago, and we just realized it very recently. It was almost too late.
Our Microscopic Imager has to have a dust cover. After all, if you're going to be waving a sensitive scientific camera around on the surface of the dustiest planet in the solar system, it makes sense to have a cover to keep the lens clean. And the cover has to be transparent. We use a motor to open and close it, and the motor is a very reliable one. But even so, if it fails for some reason, we want to be sure we still can take pictures.
When you use materials in space there are some special things you need to think about. One of them is called "outgassing". Some materials, when they get exposed to the vacuum of space, can outgas -- meaning that stuff that would stay totally solid in the Earth's atmosphere actually evaporates a bit. That can be bad news if the stuff that evaporates condenses again someplace else... like onto the lens of a camera.
We were dead certain that the transparent material we were making our dust covers out of was immune to outgassing, but we were wrong. We finally did a good test last week just to be on the safe side... with no camera present, of course. And lo and behold, a bunch of crud evaporated off of the cover material and condensed again right next to it, making a real mess. If that happened in flight, we'd have a useless camera on our hands.
So just remove the cover and change to another material, right? Not so simple. Right now the dust cover is on the camera, the camera is on the MER-2 rover's arm, and the rover is all folded up and almost ready to go into a vacuum chamber for a test! Problem is, when the rover is folded up like that, it takes a couple of days of work to unfold it and get the arm out where you can get at it. And days in the schedule are the most precious thing we have right now. So we really didn't want to waste two days fixing a problem -- especially a problem that never should have happened in the first place.
And then a small miracle happened. Lori Shiraishi and a couple of the other mechanical wizards at JPL looked real hard at the thing, and somehow managed to come up with a special tool that let them snake their way in there, get to the cover, and get it off the camera. If they weren't mechanical engineers, I think they'd be safe crackers. So the cover is off now, and we can go ahead and put the rover into vacuum chamber and test it safely. In the meantime, we can build some new dust covers. And you can bet they'll be made of something that we know doesn't outgas!