LCROSS (Lunar Crater Observation and Sensing Satellite), which will travel to the moon aboard the launch vehicle for the Lunar Reconnaissance Orbiter (LRO), will test for the presence of water beneath the lunar surface by crashing a pair of heavy impactors into one of the permanently shadowed craters at the Moon's South Pole. The impact will create a plume of debris that can be analyzed for the presence of water using specialized instruments. Dr. Anthony Colaprete, who is an expert on the Martian climate system, is principal investigator for the LCROSS mission.
NASA Tech Briefs: You are NASA's principal investigator for the Lunar Crater Observation and Sensing Satellite, also known as LCROSS. Tell us about that project and what it's designed to do.
Dr. Anthony Colaprete: LCROSS is a secondary payload to the Lunar Reconnaissance Orbiter (LRO). It is to launch later this year on an Atlas 5 rocket to the moon. The physical purpose for the LCROSS mission is to investigate a permanently shadowed region at the South Pole of the Moon.
About 10 years ago the Lunar Prospector spacecraft detected enhanced hydrogen concentration at the poles of the Moon and there's speculation that this enhanced hydrogen is in the form of water ice trapped in the lunar dirt. The LCROSS mission principally is to excavate some of this lunar dirt from one of these permanently shadowed craters, lift it into sunlight so we can see it, and investigate whether or not this enhanced hydrogen is in the form of water, or some other mineral form, and to broadly understand what the characteristics of the lunar dirt is in one of these permanently shadowed craters. Since we've never been to the poles of the moon, we just want to understand more broadly if it is similar to what we saw at the Apollo landing sites, for example.
NTB: The plan is to crash both parts of the LCROSS spacecraft, first the 2-ton rocket booster, followed later by the command module, known as the "shepherding spacecraft," into a crater on the Moon. How fast will they both be traveling at the moment of impact?
Dr. Colaprete: They'll both be moving at approximately 2.5 kilometers per second.
NTB: The impact of the rocket booster is expected to create a plume of debris that could rise as high as 40 km above the surface of the moon. The shepherding spacecraft will then fly through this debris and analyze it for traces of water using a sophisticated array of onboard instruments, correct? Won't the heat generated by the crash alter the properties of some of the elements in that debris?
Dr. Colaprete: A small portion. It's kind of a fallacy that impacts are hot. Certainly parts of the impact are hot, but the vast majority of the material that is lifted up from the lunar surface is going to be at approximately the temperature it was before the impact.
In one of these permanently shadowed craters it's very cold; it's about 200 degrees below zero Centigrade. The portion of the impact that will be hot — as high as 1500 degrees Celsius initially — is primarily the rocket itself and the material that comes into immediate contact with the rocket, and that's really a fairly small area of the overall amount of dirt that's excavated. What does the excavation is the percussion, the sound wave, if you will, that travels through the lunar dirt, rebounds, and then lifts the dirt up, kind of like a drop of milk falling into a cup. You have this really small bead of milk, but what is lifted up is due to the percussion, or the reverberation of the sound waves that move through the milk. The same kind of thing happens on the moon. As the impact penetrates the lunar dirt, it will generate sound waves that travel through the lunar dust, they will rebound off the more dense dirt down below, and then reverberate and move back upward, lifting material with them up into the sunlight.
The material that's lifted is not going to be perturbed very much. That's actually one of the chief requirements that we have on this mission; the booster rocket, the one that hits first, we purge, we clean, we dry out, literally, in space for several months so that it's very clean and pristine and free from as much contamination as possible. Then we have instruments that actually detect how much of it has either vaporized or heated so that we can understand what portion of our signal or our observations may be contaminated. That's a consideration we've taken into account, but we really don't think it's going to amount to more than maybe five-hundredths of a percent of the total material that's thrown up that will be altered or contaminated by the initial impact.
NTB: Why is finding some trace of water on the Moon so important to NASA?
Dr. Colaprete: It's important for a couple of reasons. The first reason is it would be a pivotal decision point in our exploration plans. Finding water on the Moon can have great ramifications in terms of how we plan our next steps for going to the Moon and beyond. Water is a fantastic resource. It can be split to make usable oxygen, drinkable water, and probably most important, it can be used to make rocket fuel. It costs a lot of money to bring anything into space; being able to find a resource like water outside of Earth's gravity provides the potential for mining that water, mining that resource, utilizing it, and becoming more productive on that planetary body.
The Moon is an excellent first step towards, say, Mars, or other bodies beyond in that it's nearby. We can practice a lot of our techniques for living off the land, for In Situ Resource Utilization, and so on and so forth. Finding water on the Moon will allow us to mature our concepts of engineering and really allow us to build the confidence to live off the land and use other planetary resources.
The other side of the coin, so to speak, is the scientific value. We're going to a place that has not seen the light of day – sunlight – for maybe 3-billion years, so they're fantastic time capsules. Any volatiles that may have traveled to the Moon, either in the form of impacts from asteroids and comets, or even just captured solar wind particles, may migrate to these cold traps at the Poles of the Moon and be trapped there for billions of years. Understanding how this material got there and what this material – this hydrogen – is composed of, actually is understanding how our solar system, the Moon/Earth system and just the general interplanetary system itself, was formed and evolved over the last 3 or 4 billion years. So it's like a time capsule that we can look at and study and use as a laboratory to better understand the formation of Earth.
NTB: In the event you do find water on the Moon, how does NASA plan to extract it and process it in quantities sufficient enough to be of any use?
Dr. Colaprete: Well that gets back to my point regarding the importance of finding water in the form of water ice at the poles. There is hydrogen elsewhere on the Moon. Even in the equatorial region, there's hydrogen bound in various mineral types. The difference is that the amount of hydrogen is much less than what has been observed at the poles by maybe a factor of a hundred. And it's also important in that it's in a different form; it's found in mineral matrices and it takes much higher temperatures to liberate that hydrogen, to extract it. You'd have to scoop up a lot of dirt, put it in an oven, raise the temperature to about 800 degrees Celsius to drive off the hydrogen and oxygen, and make use of it. If it's in the form of water ice, then it's very easy to liberate the hydrogen and oxygen. It takes much, much less power – about a thousand times less power – and if it's at the concentrations we expect – about 1-percent or 2-percent by weight – that's a hundred times more, at least, than what's in the equatorial region.
So you have two things working for you. You have a lot more of it, and it's a lot easier to extract and utilize. The more difficult problem is that this water presumably exists in these permanently shadowed craters that are 200 degrees below zero Celsius. So you'd have to devise a mining operation that could operate at these extremely cold temperatures, and there are plenty of plans to do exactly that with large dozers and other apparatus that thermally mine the water. All you have to do is raise the regolith and the water will start to sublime out of it and you capture that and you can draw it back to a processing plant that's in the sunlight, which is a little easier to cope with. But the first step is to just identify that the hydrogen we see is, indeed, water. That's what LCROSS is all about.
There's no other mission that will be able to do that. The LRO spacecraft will be able to refine our understanding of the hydrogen maps, but nothing on the LRO spacecraft, or any other international mission for that matter, will be able to unambiguously identify the form of that hydrogen. LCROSS will be able to do that.
NTB: This isn't the first time NASA has tried this. In 1999 they crashed a spacecraft called the Lunar Prospector into Shoemaker Crater near the Moon's South Pole and found nothing. So why do it again? What's different about this attempt?
Dr. Colaprete: Well, Lunar Prospector was the spacecraft that started all of this. It's the spacecraft that discovered this enhanced hydrogen.
The Lunar prospector spacecraft was an orbiter; its purpose was to map the mineralogy of the Moon. It was relatively small – about 160 kilograms or so – and it was in a lunar orbit. It was never conceived to be an impactor, but when it came to the end of its life it was going to impact the Moon anyway, so the controller said, "Let's do an experiment. Let's crash it into Shoemaker Crater." That's one of these permanently shadowed craters.
Lunar Prospector, being very light and in orbit, came in at a grazing angle, only at about 7 degrees or so above the surface. In doing so, a lot of its energy was imparted very near the surface; it might have even skipped across the surface. Therefore, it didn't excavate very much material. Indeed, no material was seen being excavated. It wasn't that we didn't see any water; we didn't see anything.
LCROSS, by more than a factor of 10, is more massive. The primary impactor is about 2200 kilograms, and it sends that impactor at a much steeper angle – greater than 60 degrees from the horizontal surface. That allows the energy of the impact to more efficiently couple with the surface and, therefore, excavates more material.
Also, we have this follow-on spacecraft that, at impact, is only 600 kilometers away observing with a suite of nine instruments that are specifically designed to look at the impact and look for water. As you mentioned earlier, this follow-on spacecraft even flies through the ejecta plume before making an impact itself. So the LCROSS mission has been specifically designed in much the same way the deep impact mission was specifically designed to impact the body and make measurements of the ejecta plume and remnant materials. We feel we're going to have a much, much better chance of actually observing the ejecta and that's the first step to making the measurements.
Also, being as close as we are, we'll have much, much greater sensitivity. Lunar Prospector was only observed from Earth assets, whereas we'll be able to observe really up close and personal. This has been demonstrated recently. A year-and-a-half ago or so, the European Space Agency's SMART-1 spacecraft also crashed into the Moon at the end of its life. It crashed about 27-degrees south of the equator, not in the polar regions, but investigators from the LCROSS team and others tried to observe that impact and had success. The Canada-France-Hawaii Telescope on Mauna Kea did, indeed, observe the flash and the ejecta cloud come up from that spacecraft. Like Lunar Prospector, it was never designed to be an impactor. It was relatively small – a couple hundred kilograms – and also came in at a grazing angle, maybe 2 or 3 degrees above the horizontal. So we feel that LCROSS is going to have a much, much greater chance of success in terms of creating an ejecta cloud that's observable.
NTB: What types of instruments will be onboard the shepherding spacecraft to observe and analyze this debris plume?
Dr. Colaprete: We have five cameras, three spectrometers, and a special photometer. The five cameras include a visible camera, which is to provide color context imagery so we know precisely where we hit. We have two near infrared cameras that look at wavelengths where water is visible…water ice in particular. What we do with the two cameras is we actually have them looking at two different parts of the wavelength spectrum sensitive to water and by differencing the two images we can actually make a map of where water ice is.
Then we have two mid-infrared, or thermal, cameras. They look at temperatures. They will measure the temperature of the plume and the expanding particle cloud and remnant crater, if there's any heat left in that crater after impact. We have two of those cameras to work in the same way as the near-infrared cameras. They have filters that look inside and outside of portions of the spectrum that are sensitive to water vapor, so we can difference those images and look for water vapor.
We also have two near-infrared spectrometers. Near infrared spectrometers are very sensitive to water ice and water vapor. We have one that looks down at the impact itself, looking for water ice in the ejecta cloud, and then we have one that looks to the side towards the sun, so as we fly through the ejecta cloud we can monitor how the sunlight is absorbed or scattered away by the ejecta cloud particles. That's a very sensitive technique to look for various small amounts of water vapor or water ice.
Lastly, we have an ultraviolet visible spectrometer that also looks down at the ejecta cloud and it will be looking at the emission lines from the impact flash, and also scattered light off the ejecta clouds from which we can derive the mineralogy and characteristics of the particles in these ejecta clouds.
Then there's one last instrument, the Total Luminescent Photometer, which is an instrument built here, by Ames, and it is a very, very fast photometer. It actually measures the flash of the impact itself. The flash lasts only a couple hundred milliseconds, but depending on the brightness and shape of that flash – and by shape I mean the shape of that light curve over time – you can tell how far you penetrated, how strong the material you entered was, even if there was water subliming as you impacted, so this instrument is designed to make very, very precise measurements of very faint signals very quickly. It measures a thousand times a second as the impact occurs.
NTB: Has NASA set a launch date and chosen a point of impact yet?
Dr. Colaprete: Right now the baseline launch date is October 28, 29 and 30th. That's our first 3-date window. Then there are approximately 3-date windows every two weeks going through 2008.
Since we are a secondary payload to LRO, we have to be ready to go whenever they go, so we have picked an impact site for each launch date depending on the geometry of the Earth, Sun and Moon. The geometry of a particular impact site can differ from launch date to launch date. For our first October 28 launch date, the impact site is a large crater named Faustini. It's approximately 30 to 32 kilometers across and it's probably about 3 to 3.5 billion years old. We will impact an area approximately a kilometer across inside that crater.
For October 29 it remains the same; our impact site is still Faustini, but on October 30 we move to a different crater — Shoemaker, the one where Prospector impacted. We do this shift primarily due to illumination changes. As the Sun, Earth and Moon geometries change, we maximize, or optimize, the illumination of the ejecta cloud and our ability to observe it from Earth. So for every different launch date we look at several different craters and we pick the one that's best.
NTB: You are also heavily involved in studying Martian climate and the formation of clouds around that planet. What have you learned from those studies?
Dr. Colaprete: I am currently doing both numerical and laboratory measurements with a colleague here at NASA Ames on the formation of water ice clouds under Martian conditions. Actually, I got into the LCROSS project – or I put in the proposal – a couple of years ago based on work with the NASA Ames General Circulation Model where I was simulating the climate effects of an impact on the Martian climate. So I learned a lot about impacts and what they would do, and I extended that to the Moon, and that's how LCROSS came to be.
What we're studying now is how clouds form under these very, very cold, rarified air conditions on Mars. We've discovered some very interesting things that are not only relevant to Mars, but very relevant to Earth. It turns out that at these cold temperatures – and by cold I mean about 100 to 110 degrees below zero Centigrade – it becomes much, much more difficult to form a cloud. While these temperatures seem ridiculously cold on Mars, they're typical, and on Earth, quite often, in the stratosphere and even more likely in the mesosphere, you see these kinds of temperatures regularly. But we still see clouds in these regions.
On Mars we see clouds very frequently. So what we've been working on is trying to really understand what it takes to form these clouds, and then turning those laboratory measurements into constraints for general circulation and climate models on Mars. What we found is the clouds probably have a very difficult time forming. Much of the water vapor will not go into clouds on Mars and overall cloud particles will probably be larger and, therefore, make the atmosphere drier because they can fall out of the atmosphere more quickly. So what we're predicting is a drier atmosphere than previous models predicted, based on these laboratory measurements, and as it turns out a lot of the new observations of water vapor and water clouds, from the missions that are currently orbiting Mars, seem to suggest that previous observations were overestimating the total water amount. The Martian atmosphere may actually be drier than we first thought, and for water-based clouds, the formation process may be a little more complicated and less understood than we once thought.
But that's science – for every question you answer, two more pop up.
NTB: In addition to your science projects, I understand you've also formed a working group at NASA's Ames Research Center to try to generate new business and further maximize the use of Ames' equipment and facilities. Tell us about that effort.
Dr. Colaprete: That's at the Instrument Working Group. A few years back a number of us who had an affinity for both instrumentation and science thought that better communication within the center and across the agency could really assist in bringing individuals with particular facilities, equipment, ideas, and so forth, together to capitalize on those new connections. So what we've done is build a grassroots campaign to start reenergizing the instrumentation groups here at NASA Ames by bringing together earth scientists, space scientists, planetary scientists, life scientists, etc., all with very similar experience or hardware that otherwise weren't talking with each other. We got individuals from each of those groups as representatives, we pulled them together, and we talked about what we can do to increase our communication, and out of it came a workshop, what we call the Instrumentation Workshop. They were center-wide, all day, where people presented what they were working on and just got people talking with each other.
On top of that, working with our management here, we awarded several small, internal research grants to various groups who had proposed various ideas. We try to help select, internally, good ideas and foster those ideas with a little bit of seed money and engineers' time. For example, a scientist may have a great idea, but they don't have the means to actually turn that idea into a real instrument or a real mission concept, so what we do is we help identify the good ideas and work with our management to support those, either through engineering time or facility time, to bring those ideas to a more mature status. And I'm glad to say that's worked in many cases where we've been able to get field instruments built, or new instruments have gone out and actually been awarded time or additional support funds from outside of NASA Ames, and that's really the point. Get these things built up so that they could go out and find their place on a mission, or in a field study, or wherever. And it's worked out pretty well.
LCROSS came in kind of at a good time because a lot of those connections were built just before LCROSS started up, and we managed the entire payload here for LCROSS and built one of the instruments, so it worked out really well. A number of those connections were made among the facilities, the engineers, and the scientists, and I think that contributed greatly to the overall success of delivering the LCROSS payload on time and under budget.
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