NASA Tech Briefs recently spoke with Doug McCuistion, Director of the Mars Exploration Program, and Michael Meyer, lead scientist for the Mars Exploration Program and Program Scientist for the Mars Science Laboratory (MSL). We talked about what NASA hopes to find, the technologies used onboard, and how the two-year mission is expected to progress.
NASA Tech Briefs: What are the science objectives for the Mars Science Laboratory?
Michael Meyer: The overarching goal of the Mars Science Laboratory and rover Curiosity is to understand whether Mars has ever been, or is capable today, of supporting microbial life. So that’s another way of saying we want to determine the habitability of Mars. There are other things that can be discovered by Curiosity as it roves about, but that’s the overall goal and how it was designed. NTB: Why was Gale Crater selected as the landing site?
Meyer: Over the past five years, the science team got together, people proposed what they considered were very interesting landing sites, and then there were discussions about how interesting it is to everybody else. As we narrowed it down, we also got into how safe it is, does the landing ellipse fit inside a good place, and are there rocks.
The science community had to be self-policing about what it could actually do and what it could reasonably speculate. This is one of the things we really benefit from — the amount of information we got from having a Mars program. We ended up picking Gale Crater because it has Mount Sharp in the middle — this huge mound that should have an extensive history of Mars starting from more than three billion years ago to whatever Mars is like at present.
NTB: This is the first time since the Viking landings in 1976 that NASA has used throttleable engines for landing a Mars spacecraft. Why was this method chosen for MSL?
Doug McCuistion: The engines are a new design based on a heritage unit. Because of the throttleable nature and the amount of thrust we can get from these, they make a great engine for orbiters for certain Mars orbit insertions as well. So, we’ll use these again, maybe next time on an orbiter.
There were a lot of things chosen because of the additional mass of MSL. Airbags max out around 200 kg, so the airbag technology couldn’t handle a rover of this mass. So we had to come up with a new technique. The concept was a larger parachute to get more drag, and obviously a larger entry shell that reduces our speed and also is volumetrically necessary. But once we got done with the parachute, the replacement for the airbags had to be something that could handle a 1,000-kg rover underneath it, to be able to take out both horizontal and vertical velocities. So instead of putting the engines underneath it like Viking, we decided to put the engines on top.
NTB: Curiosity is NASA’s largest and most complex rover. Other than size, how does it differ from Opportunity and Spirit?
McCuistion: It’s very different — probably the two biggest differences are the payload capability and the power source. Essentially, the plutonium 238-powered radioisotope thermal generator is a constant power source, regardless of time of day. We’re not dependent upon solar energy any longer. We’ve got a constant feed of power, with a constant output of about 110 Watts. That gives us a great capability to charge batteries overnight, to be able to rove farther, and to be able to last longer on the surface by design. That’s a fantastic capability because of the power source. For the instruments, we’ve gone from less than 6 kg of instruments to over 80 kg of instruments, comparing the MER (Mars Exploration Rover) rovers to the MSL rover.
Meyer: The key difference is that Curiosity is a roving analytical laboratory. There are two instruments in the interior of the rover that are major instruments. For Spirit and Opportunity, all of the instrumentation was remote and contact instruments, while Curiosity has two analytical instruments inside.
On the interior, we have an instrument called CheMin (Chemistry and Mineralogy), which is an x-ray diffraction/x-ray fluorescence instrument that measures the distance between atoms. This is the same kind of instrument you’d have in a laboratory. Mineralogy is important because it tells you the environment in which the rock was formed. The other instrument is SAM (Sample Analysis at Mars), and that’s a gas chromatograph mass spectrometer. This gives you composition — it tells you what things are made out of. It’s not the elements, but also the smaller compounds. SAM can also measure isotopes. In addition, SAM has what’s called a tunable laser spectrometer (TLS), which is a spectrometer that can measure certain things to an extreme degree. It can measure carbon dioxide, water, and also methane, which is probably the one we’re most excited about.
The other instrument that’s unique is the ChemCam (Chemistry and Camera suite), which is a laser-induced breakdown spectrometer. It fires a laser, creates a plasma, and then uses a spectrometer to look at the plasma and tell what the composition is. It’s a remote sensing instrument, so you don’t have to place the instrument against whatever you’re interested in. You can do it within 7 meters of the rover.
NTB: Are there other minerals you’re looking for besides carbon and methane?
McCuistion: This mission is highly unusual in that we’ve already targeted minerals that we see from orbit. We see sulfates and we see clays, both of which are minerals that form in water, and they also represent slightly different environments. Clays form in a neutral environment with a pH around 7, while sulfates tend to form in more acidic environments and you also find them, at least on Earth, in environments where the water is drying out. Those are good indicators that we’re going to go to a place where we have mineral deposits that were laid down when Mars was warmer and wetter, and mineral deposits that were laid down when Mars was drying out. As you go further up Mount Sharp, we’ll find things that are indicative of modern Mars, which is cold and dry.