Flying a Science Lab to Mars
|Artist conception of Mars long-range science laboratory.|
Even before the Mars Science Lander (MSL) touches down descending from its hovering mother ship like a baby spider from an egg case the first of a slew of cameras will have started recording, capturing and storing high-resolution video of the landing area.
The MSL landing will represent a first, says Frank Palluconi, MSL project scientist. After entering the Mars atmosphere- like Viking and MER but with a potential landing zone about one fourth the size – he says, MSL will show its stuff. "It completes the descent down to the ten-meter [33-foot] level, or so, where the descent vehicle hovers, and it lowers the rover on a tether down to the surface. By that time, the rover has erected its wheels, so it lands on its mobility system. And then the tether is cut and the descent stage flies away and is no longer used. It crashes."
In addition to the obvious advantages of such a soft landing, hovering and the tether drop are possible to model mathematically, unlike the airbag landing the MER vehicles used. Tethered descent is also scalable, Palluconi says, whereas the much smaller MERs were pushing the envelope of the airbag system’s capability.
Eyes on Mars
Shooting will begin as soon as the heat shield drops from the MSL descent stage. The Mars Descent Imager will take video in megapixel resolution, comparable to modern consumer digital video cameras. Aimed straight down, this camera will provide a spider’s eye view of the landing area– a very wide angle at first– and continue shooting until the rover touches down on Mars.
|Sundown on Mars, Pathfinder mission.|
Landing videos will be transmitted to Earth by the rover when it becomes fully functional. This visual information, showing the landing area and its surroundings in fine detail, along with the fact that the rover will land on its wheels– no tricky navigation off of a landing vehicle needed– will allow project scientists to begin working the rover much sooner.
Once the rover’s mast rises and all systems are go, the real work will begin. As with MER, a mast-mounted, two-eyed camera system will feature prominently. The MastCam, like the descent imager and an arm-mounted close-up camera, is being designed and built by Malin Space Science Systems in San Diego, CA. All three rely on similar full-color, high-resolution subsystems. MastCam takes the basic setup found on the MERs twin cameras that will allow scientists to assemble 3D images and refines it considerably. MastCam has twin 10x optical zoom lenses, the same power as found in high-end consumer digital cameras on Earth. This will allow the camera to take not only wide-angle panoramas but also zoom in and focus on fist-sized rocks a kilometer (0.6 miles) away.
MastCam also shoots high definition video, a first for Mars. Both stills and video will be captured in full color, just like with earthbound digital cameras. In addition, MastCam will use a variety of specialized filters. Several members of the Malin Space Science Systems scientific team contributed to the various camera designs, including director James Cameron (Titanic, The Abyss, Aliens), a co-investigator on the MastCam science team.
Photograph, Vaporize, Analyze
The MSL mast will also hold a unique hybrid optical instrument, never before flown to Mars. Called the ChemCam, this telescopic tool takes close-ups with a field of view of about 30 cm (1 foot) at ten meters (33 feet) distance. But that’s just the first step for ChemCam. In step two, eerily reminiscent of the heat rays described in War of the Worlds, a powerful laser will focus through the same telescope at the target. The laser can heat a spot about a millimeter (0.04 inches) in diameter to nearly ten thousand degrees Celsius (18 thousand degrees Fahrenheit). The heat blows away dust, breaks off molecules, breaks up the molecules and even breaks apart atoms in the rocky target.
|Schematic of major mission events during entry, descent and landing.|
Credit: NASA/JPL/ Cornell University/ Dan Maas
As a result, the target emits a spark of light. ChemCam can analyze the spark’s spectrum, identifying what elements– carbon or silicon, for example –the target contained. Called Laser-Induced Breakdown Spectroscopy, or LIBS, this technique is widely used on Earth but will be a first for Mars, says Roger C. Wiens, a planetary scientist at Los Alamos National Laboratory and the principal investigator on the ChemCam project. "LIBS is being used in a number of facets on Earth. For example, a company that makes aluminum uses it to check the composition of their aluminum alloy in the molten state."
Going into space is a different story. Seven years in the making, ChemCam will make MSL much faster than MER at choosing targets, Wiens says. "The Opportunity rover landed in a small crater and here in front of us sat a rock outcrop, which is the first one we had seen on Mars up close and personal. And it was less than ten meters away. [With the ChemCam] we could have immediately analyzed that rock before actually even driving the rover off the pad, and told them that here sits a sedimentary rock outcrop right in front of you. Instead, it took a number of days, and they drove up to the rock and actually sampled it with the contact instruments before they really determined that it was a sedimentary rock outcrop." With its long optical reach, ChemCam can analyze objects out of reach of the rover’s mechanical arm, even overhead.
|Empty nest view back to landing petal from the mobile Opportunity rover, which has ventured to the crater’s rim|
In addition, ChemCam will be able to do some chemical analysis of small parts of rock samples, before they are crushed and transported to MSL’s internal analytical instruments.
"I think this instrument is going to see a lot of use," Wiens says, "because we can take a lot of data rapidly. So one of the great things is that we can get a much larger database of rock samples than some of the in-situ techniques. I think it’s going to be an exciting instrument to build and fly."
Palluconi sees MSL as an intermediary step between MER and the direct search for life on Mars. "I would regard MSL as being kind of a transition mission between the more conventional aspects of planetary exploration, which involve geology and geophysics and, in the case of Mars –because of its atmosphere, the climate and weather– to ones in the future which will make direct searches for life. So the overall objective of MSL is to make a habitability assessment of the area that the vehicle lands in on Mars."
The Near Future
Because NASA decided only in December 2004, which of many scientific instruments proposed for MSL will actually fly, all of the scientists whose projects were chosen are scrambling to put the finishing touches on their instruments. "The mission is in phase A, which is a definition phase, so it’s really the earliest formal phase of the mission," Palluconi says. "Right now the principal work on the science side is figuring out where to place the instruments on the rover, how to meet their thermal needs, how to ensure that they have the fields of view they need and that their other requirements are met. Of course, the vehicle itself is being designed at the same time and the design is being refined. So there’s quite a bit of work to do and we’re probably just about a year away from the preliminary design review, which on the 2009 launch schedule would occur next February."
Some aspects of the Mars Science Laboratory remain up in the air. Many of the MSL scientific instruments require plenty of power. The proposed source of that power, a radioisotope power supply, requires presidential approval, which lies in the future. And in March 2005, NASA began considering the possibility of flying two MSL rovers in 2011 instead of one in 2009.
Mars Odyssey recently detected water ice near the surface in the high latitudes, and in 2007 the Phoenix Mars Lander will investigate those regions. This August, the Mars Reconnaissance Orbiter will be launched. What it discovers will determine the fate of the Mars Science Laboratory, which is scheduled for launch in 2009 or 2011.