Martian Chronicles VI: Good Problems
Three spacecrafts are now hurtling toward the Red Planet to look for evidence that it might once have been wet enough to sustain life. Orbital projections of where Europe’s Mars Express and the two NASA Mars Exploration Rovers (MER) are right now, can be continuously monitored over their half-year journeys. Experiments performed by the MERs will help to determine whether water might have once existed in volume on the red planet. The two Mars Exploration Rovers are targeting what imagery indicates might have been ancient dry lake beds and other geologically interesting sites in early 2004.
|A simulated image of the new Mars rover carrying the Athena science instruments.|
The Martian Chronicles series gives an inside view of what it takes for scientists to deliver a complex mars mission. The journal entries are from Cornell’s Steve Squyres, the Principal Investigator for the Mars Exploration Rovers’ scientific package called Athena. The chronicles begin sequentially from the beginning of July 1999, four years before launch, and will culminate in the dramatic landing of the twin rovers on Mars in January 2004. The expected mission time roaming the red planet is ninety days, from January to April.
The chronicles include an insider’s view of hardware tests and site selection to problem solving and science planning on the surface of Mars.
August 11, 2001
We had a little bit of a scare this week. A problem popped up early in the week that looked pretty stupid, but maybe also real. Our payload includes several magnets, whose job it is to gather magnetic mineral grains from the martian atmosphere. We’ll look at these minerals with the instruments, including our Mössbauer Spectrometer. The Mössbauer, as it turns out, is built with a fair amount of magnetic metal in it. This metal gets attracted to the magnet, of course, when we bring the instrument close to it.
|Martian polar cap|
Credit: NASA/ JPL/ MSSS MOC
Early in the week, some calculations suggested that the arm that the Mössbauer is mounted on might not be strong enough to pull the Mössbauer back off the magnet once it has touched it! Imagine going all the way to Mars, using the Mössbauer to look at the magnet sometime early in the mission, and then getting it stuck there. Not good. We spent a couple of days worrying about it before concluding that we can fix things by making a pretty simple change in the way the arm is controlled for that one maneuver.
August 18, 2001
We’ve been having a lot of reviews lately… projects like this one tend to attract a lot of attention! But this coming week is the review of all reviews: the Project Critical Design Review. It literally is the review of all our other reviews, actually. We’ve had reviews of just about everything you can imagine on this project, from some of the smallest electronic parts all the way up to the whole spacecraft. Every piece of the payload has been through it too, of course, most of them several times. And now it all comes together this week at a three-day review of the whole MER project. It’s no fun… preparing for these reviews is a lot of work. But reviewers from outside the project bring a fresh perspective, and that means that they sometimes catch things that we don’t. Once this review is behind us, though, we’ve got to really step on the gas. Assembly and test of the first spacecraft begins in February, just five and a half months from now.
August 25, 2001
The Critical Design Review is done. It was a long review and it made for a long week, but we’ve got it behind us now. Of all the things that we talked about at the review, the one that got the most attention was our schedule. It’s tight. Missions to the planets aren’t like other space missions. You can only launch when the alignment of the planets is right. Miss a launch opportunity to Mars and you have to wait 26 months for the next one. Our launches are in the summer of 2003. That’s almost two years away, but two years is a very small amount of time for all the work we need to get done. So we’re going to be watching our schedule very closely. One thing that’s certain is that the pace isn’t going to ease up at all, any time between now and the end of the mission.
September 1, 2001
Our biggest problem this past week has been working out the details of how our Pancam and Mini-TES instruments will work together. The Pancam cameras sit right at the top of the tall mast at the front of the rover. The reason that the mast is so fat is that it also acts as a periscope. Mini-TES sits down inside the rover and uses some mirrors near the top of the mast to get almost the same view of the world that Pancam does.
|Martian basin and drainage|
Credit: NASA/ JPL/ MSSS MOC
It’s that "almost" that’s the problem. The Mini-TES mirrors actually sit a little bit below the Pancam cameras, so they don’t quite have the same vantage point. Also, we couldn’t get everything to fit inside the lander until we turned the Mini-TES mirrors around so that they look in exactly the opposite direction from Pancam. So this means that we have to swing the mast around 180 degrees to look at the same object with both instruments. The tricky part of all this is building the hardware and software so that when we tell Mini-TES to look at something that Pancam has already seen, we don’t miss it, even by a little bit. We’re making progress, but this one is going to keep us busy for awhile.
September 8, 2001
This was one of those weeks where so much was going on that it’s hard to decide what to write about. We’re getting into real hardware testing now, and things are starting to get intense. I guess the biggest events of the week were the final preparations for two critical tests. One is the first vibration test of our new APXS design. In a "vibe" test, you shake a piece of hardware to simulate the vibrations it’ll experience during launch. (Read more about this on our science bite page.) We’re going to vibe the APXS in Berlin next week, and they’re working very hard over in Germany to get ready for it.
The other big test we prepared for this week is the first "thermal vacuum" test of our latest Mini-TES instrument. In a thermal vac test, you put the hardware into a chamber with no air in it to simulate space, and then run it through its paces at the kinds of temperatures it’ll experience in flight. This one’s going to happen in Santa Barbara, and they’re working really hard there as well.
September 15, 2001
Like everyone else, our focus this week was on the tragic events in New York, Washington and Pennsylvania. Our hearts go out to all who suffered.
September 22, 2001
Credit: NASA/ JPL/ MSSS MOC
We’re testing hardware now. It started this week, with vibration tests on an engineering model of our APXS instrument. An engineering model is a piece of hardware that is pretty much identical to what we’re going to fly, but that we can test pretty severely to make sure the design is good. We took the APXS to a test facility in Berlin this past week, and shook in three different directions at levels more violent than anything we should see in flight. We’ve still got a little more shaking to do, but so far nothing has broken. The APXS uses a new design that we’ve never tested before, so it’ll be real good to have this set of tests behind us.
September 29, 2001
When you start testing hardware is when you start finding problems, and we hit one this week. Believe it or not, it was with Mini-TES, which has been the smoothest-running part of the whole payload until now. It’s a weird problem. The instrument works fine when it’s lying on its side, but goes bad when we turn it rightside-up! The guys in Santa Barbara took it apart this week to figure out what’s wrong, and it looks like they found the problem. It seems to be a simple one: some wires are routed wrong, in a way that pulls the mirrors a tiny bit out of line when the instrument is rotated. We should know for sure this week if that was the problem. If it is it’s an easy fix, but it will have taken us three weeks to track it down and take care of it. Good thing Mini-TES was thirteen weeks ahead of schedule before this happened!
October 6, 2001
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.
October 13, 2001
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.
|Sculpted mesa-like rocks|
Credit: NASA/ JPL/ MSSS MOC
So now it’s on to the next problem… whatever that turns out to be!
October 20, 2001
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.
October 27, 2001
|Frost on one side of embankment|
Credit: NASA/ JPL/ MSSS MOC
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.
November 3, 2001
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.
November 10, 2001
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.
|Mars from orbit |
Credit: NASA/ JPL/ MSSS MOC
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.
November 17, 2001
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.
November 24, 2001
Credit: NASA/ JPL/ MSSS MOC
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!
December 1, 2001
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.
December 8, 2001
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.