Martian Chronicles V: Cutting Metal
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.
February 24, 2001
The guys at Honeybee Robotics have been making a lot of progress lately on the Rock Abrasion tool, also known as the RAT. The RAT is the one really new invention on our payload for 2003, so we’re devoting a lot of attention to making sure we get it right. We held a Preliminary Design Review for it several weeks ago, the result of which was a thumbs-up to go forward with the detailed design work.
The mechanical design of the RAT is pretty far along now, and much of the focus this past week has been on the electronics that go with it. This thing has a lot of wires, and we’re building a full-scale mockup of it to help us figure out exactly where to run them all. We’re also testing what are called "breadboard" electronics — electronics that do the same things that the final version will, but that are built so that they’re easy to take apart and change while we’re still figuring out how to get it all to work.
March 3, 2001
We made a really major change this week: We added a dust cover to the Microscopic Imager. That may not sound like a big deal, but at this stage of the game, it is. The reason we did it, obviously, is that Mars is a very dusty place, and we were worried that at some point we might accidentally push the microscopic imager into the dirt. The reason it’s a big deal is that it adds more complexity to an already complex system: another motor, more wires, the mass of the cover, the software to make it all work, the testing to prove that it works, and so forth. But it was the right thing to do, and now we feel comfortable that we’ll be able to keep that lens as clean as we need it to be.
March 10, 2001
We had a very good week… one of those weeks where you make progress on a dozen different things at once. We’ve now got a design for the door that will protect the APXS from dust. We’ve almost got the design worked out for the "contact sensor" that will tell us when the Mössbauer Spectrometer has touched a target.
|The Mössbauer Spectrometer electronics. |
Credit: Johannes Gutenberg University
The new Pancam electronics are coming together. And we seem to have finally decided how we’re going to keep the insides of the Mini-TES as dry as they need to be in the humidity of Florida when it’s time to launch. That’s the good news. The bad news is that we’re going to have to keep making progress at close to this pace if we’re going to make it to the launch pad in time.
March 17, 2001
We had a great week! On Wednesday, we pulled Mini-TES 1 out of storage and fired it up in what is called an "aliveness test". This is just what it sounds like: a test to see if the instrument is still alive. We didn’t expect anything bad, but any time you pull five million bucks worth of hardware out of storage after nine months, there’s a little bit of anxiety the first time you hit that power switch. As it turns out, there was no cause for worry — Mini-TES 1 works just as well now as it did the last time we used it. It’s a good thing, too, since it’s going to have to go in one of the rovers. Now all we have to do is build another Mini-TES to go in the other one…
March 31, 2001
The big event this past week was our first test of Mars Exploration Rover operations. We did it using the FIDO rover, which is an early prototype of the rovers we’ll be launching in 2003. The test was a pretty wild experience: a couple of dozen scientists and engineers spending two solid days in a detailed simulation of everything we’ll do once the MER rovers are on Mars. We learned a lot! We’ll have to do it a lot more, too. The way to train for space flight has always been to do plenty of simulations ahead of time, and this project is no exception. Our next test will be two weeks from now.
April 7, 2001
This was a landmark week for our project: the Mars Odyssey orbiter was launched! Odyssey is a great mission by itself, and it’s also very important to our rovers. The rovers can transmit some of their data directly to Earth, but a lot of it — including many of the best pictures — will be relayed to Earth by an orbiter overhead. And Mars Odyssey is that orbiter. The launch was picture-perfect. The weather was as good as it gets, and Boeing’s Delta II rocket gave Odyssey a flawless ride. So Odyssey’s on its way to Mars now, and should be waiting there for us when we arrive in 2004.
April 14, 2001
This week we finished up our second operations test with the FIDO rover. Just like two weeks ago, we spent Thursday and Friday simulating four martian days of rover operations. These past two tests have taken place with the rover in the "Mars Yard" at JPL… an outdoor facility that looks like a little bit of Mars. The test this week went really well, and we feel now like maybe we’re ready for something bigger. We’d better be. Just two weeks from now we’ll begin a 10-day test with the rover somewhere out in the desert.
Credit: NASA JPL
April 21, 2001
We made a little change to the payload this week. The RAT is a very cool little machine, and we expect it to work really well. There’s just one problem. While we’re confident that the RAT will be able to grind into hard martian rocks just fine, we’re worried about soft rocks. The grinding wheels on the RAT are a little like sandpaper, and when we grind into really soft rock we’ve found that they can get "gummed up". It’s simple, really — tiny particles of rock get caught between the little diamonds that do the grinding, and if too much of that happens the RAT just can’t work well any more. It’s a low-tech problem, and we’re using a low-tech solution: putting a stiff wire brush on the rover that we can use to clean the RAT off after each use.
Who says rocket science is complicated?
April 28, 2001
Rocket launches are pretty violent events, with lots of noise and lots of vibration. All of our hardware has to survive launch, so we spent a lot of time thinking about how to make sure our designs are sturdy enough to take it. The real proof, though, is testing. This past week our APXS instrument faced its first vibration test. Vibe tests can be a little scary. You put the instrument on a "shake table" that vibrates it as violently as a launch will (or even harder). Sometimes things break. The APXS passed with flying colors, though, so it looks like we’ve got a solid design.
May 12, 2001
We conducted an enormously successful test this past week with the FIDO rover. This is a prototype of the MER rovers, and we used it to simulate twenty days worth of rover operations on the surface of Mars. The rover itself was in the Mojave Desert, and we operated it "in the blind" from the Jet Propulsion Laboratory, just as we will with the real rovers at Mars. We investigated a number of rocks and soils, took lots of images and spectra, and drove over 120 meters. Most importantly, we learned a lot about how we’ll operate the MER rovers in 2004.
May 19, 2001
The Rock Abrasion Tool (a.k.a. The RAT) passed an important milestone this week: its Critical Design Review. We still have one or two odds and ends to work out, but with this review behind us now it means that we’re ready to start building the real RATs that will go to Mars.
May 26, 2001
We’ve had a little bit of a problem lately. Our rovers are big machines, and they each have to be folded up in a complicated way to fit inside their lander. After landing, we need to fold out lots of important pieces: the wheels, the antenna, the camera mast, and so forth. Each of these pieces needs to be held firmly in place before it folds out, so that vibrations during launch and landing don’t do any damage. The difficulty is figuring out how to release each piece.
The usual way you do this on a spacecraft is with what’s called a "pyro": a little explosive device. Pyros are very simple and reliable. Problem is, this rover is folded up so tight that we’d have to set these little explosions off right next to our instruments, and some recent calculations have suggested that the shock might be so great that instruments could be damaged.
June 2, 2001
We’ve got another problem on our hands this week. We did some calculations a while ago, and they showed that if we were ever to point Mini-TES at the sun we could damage the instrument. That’s not bad news scientifically… there’s no reason we’d want to look at the sun with Mini-TES anyway. But what if we did it accidentally? We could have a toasted spectrometer on our hands.
So now we have to figure out how to keep such an accident from ever happening. It shouldn’t be hard… it’s easy to calculate where the sun will be in the sky, and we’ll just make sure that we don’t point Mini-TES in a dangerous direction. But it’s one more thing to put in the software, and time is getting tight. As of this week, we’re less than two years away from launch.
June 9, 2001
The star of the show lately has been Mini-TES. We learned a lot when we built the first one, and we’re using what we learned now as we build Mini-TES 2. Not only are we weeks ahead of schedule, it’s starting to look like a real instrument. It’ll be on its way to Mars in just two more years.
The other Mini-TES news is that we’ve figured out how we’re going to keep from pointing it at the sun accidentally, which we were worried about last week. The best answer turns out to be the simplest one. The rover always knows roughly which way it’s pointed, and also what time it is… which means that it can figure out where the sun is. So we keep Mini-TES pointed away from where the rover thinks the sun is, and we keep it far enough away that even if the rover’s off by a little, Mini-TES will be safe anyway.
June 23, 2001
|The Pancam CCD housing assembly. Here the Pancam CCD itself is covered by a protective piece of orange Kapton tape.|
The slang that’s always used in the space business to mean that you have started building some hardware is to say that you’ve started "cutting metal". Well, we’ve started to cut metal on all our cameras now, literally. The drawings of all the metal parts for Pancam and the Microscopic Imager were completed last week, and they’ve now been sent to the machine shops for the building to begin. These are the same machine shops that will be cutting metal for both rovers before long, so we figured we’d better get our order in early! It shouldn’t be long before we have the real flight camera bodies in our hands.
June 30, 2001
We’ve had a problem come up regarding two of our instruments: the Mössbauer Spectrometer and the APXS. The sensor heads for both of these instruments sit right next to one another, on the end of our instrument arm. The problem is that the Mšssbauer spectrometer has a little bit of radioactive material in it (it’s cobalt-57), and the APXS electronics are sensitive to radiation. We did a test this past week with the two instruments together, and it appears that the APXS electronics are indeed having some radiation problems. The solution is going to be to protect the APXS with a little bit of radiation shielding, using a material called tantalum
July 14, 2001
Mini-TES 2 is now a real instrument! Well, maybe not quite, but we’re getting there. We hooked the electronics up to the optics and the motor last week. It still has a long way to go, of course. Right now the electronics boards are "fanned out", which means that they’re hanging out where they’re easy to get to, rather than tucked neatly inside the Mini-TES box where they belong. And we still have more pieces to put inside the box before the instrument is really done. Most importantly, there’s enormous amount of testing that still has to happen. But what was just a bunch of parts a few months ago is now starting to look very much like a real scientific instrument.
July 21, 2001
It’s always something. We just came across a dumb little problem that could have caused a lot of headaches in the months ahead. There are an awful lot of cameras on this rover… ten on each. Most of them are in pairs, but how do we keep them all straight? In going through our documents this week, we realized that there was a lot of potential for confusion. There’s one pair of cameras on the front of the rover, pointing forward. Another pair is on the back, pointing backward. Four more are on top of a rotating mast. So how do we name the cameras in each pair? Camera 1 and camera 2? If so, which is which? Port and starboard, like on a ship? If so, then what about the ones that rotate?
|Each "eye" of the Pancam carries a filter wheel that gives Pancam its multispectral imaging capabilities.|
It sounds trivial, but this is the kind of thing that can lead to wiring mistakes and all kinds of other goofups if you’re not careful. We decided to keep it simple… name the cameras in each pair left and right, as if they were eyeballs in somebody’s head. That way it’s clear which is which, no matter which direction the cameras point. So three years from now when you see a martian picture from the rover’s "Left Rear Hazcam", there shouldn’t be any question about which camera really took the picture
July 28, 2001
It’s CDR time. CDR stands for Critical Design Review, and it’s a pivotal event in the life of any space mission. No project team does its work without a lot of help. MER is no exception; in fact, we seem to be getting more help than most. A Critical Design Review can be one of the most helpful events of all. At a CDR, we bring together a panel of outside experts, and we have them go over everything we’re doing.
Their questions can cover anything from the detailed design of the smallest component to the overall health of the project. Actually, we don’t have just one CDR, but a whole series of them, culminating in the Flight System CDR this coming week (that’s a review of the whole spacecraft, including the instruments), and the Project CDR a couple of weeks after that. We’ve spent months getting ready for this, and we’re really hoping it’s going to go well.
August 4, 2001
Believe it or not, our biggest worry this week has been ghosts. Or, to be more specific, we’ve been worried about what are called "ghost images".
One of the most important jobs for our Pancam camera will be to take pictures of the sun. Part of the reason we’re going to do this is to figure out how dusty the martian atmosphere is: the more dust there is in the sky, the darker the sun will look. The really important reason, though, is to figure out which way is north. Mars doesn’t have a magnetic field, so we can’t use a compass to figure out directions. Instead, we use Pancam to see where the sun is in the sky, and then use that information to work out which way is which.
Taking pictures of the sun isn’t all that hard: we just have to give Pancam special dark filters. They’re sunglasses for our rover, really. But even with the filters, all that sunlight can sometimes bounce around inside the camera in funny ways, creating the "ghost images" we were worried about. But after lots of good work by the optics experts at JPL this week, we’ve concluded that it shouldn’t be a problem. So we’re not afraid of ghosts any more.