October 22, 2010
Strange Lunar Brew
Bullseye on the Moon -- the LCROSS impact site
A year ago, the LCROSS (Lunar CRater Observation and Sensing Satellite) mission team announced the detection of water in the impact plume produced after the Centaur separated from the Lunar Reconnaissance Orbiter (LRO) and crashed into the Moon. We now have more detailed information on the water and some other substances detected during that event. Some of these elements and compounds were expected, others are very strange indeed.
Because the spin axis of the Moon is perpendicular to the plane of its orbit with respect to the sun, the Moon’s poles get grazing solar illumination. This means that the floors of craters and low areas are in permanent shadow and extremely cold. The DIVINER instrument on LRO measured these temperatures for the first time and found some areas as cold as 25 Kelvin (25° above absolute zero, -273° C), making them colder than the estimated surface temperature of Pluto. Because these areas are so cold, any molecule or atom of a volatile substance that gets into them is trapped. These dark areas are referred to as “cold traps” where, over very long periods of time (billions of years) significant amounts of these elements and compounds might accumulate.
Since water is one of the most abundant compounds found in the Solar System, we expected some accumulation of it at the lunar poles. It was on this basis that scientists have been searching for water ice on the Moon for the past 20 years, using a wide variety of techniques, including spectral reflectance, radar, neutron and gamma-ray sensing and ultraviolet imaging – all techniques done remotely from space. Landing at the poles and surveying the lunar surface to actually see what was there, was next on the list.
A plan to soft-land a long-lived rover near the poles and conduct an extended surface mission surveying polar resources was discarded when the Ares rocket became the focus of NASA’s lunar return effort. A smaller mission was improvised to hurl an impactor (the spent upper stage of the rocket that launched the Lunar Reconnaissance Orbiter) into the polar deposits so the spacecraft could analyze the material shot off into space from the collision. Although this is still “remote sensing” of the deposits, at least the material would be ejected out of the dark, cold regions into open space where we might get a look not only at the water but also some other volatile substances that might be there.
The LCROSS team’s published data from the mission reveals a cold witches’ brew deep inside Cabeus crater. The finding of significant lunar water has confirmed data from earlier missions, while the ejecta plume from the LCROSS impact reveals more modest amounts of a variety of other substances. The Near-IR spectrometers on the LCROSS shepherding satellite detected abundant water (H2O) but also hydrogen sulfide (H2S), ammonia (NH3), methanol (CH3OH), methane (CH4), ethylene (C2H4) and sulfur dioxide (SO2). The uv-vis spectrometer found carbon dioxide (CO2), sodium, silver, and cyanide (CN). Aboard the distant LRO spacecraft, the ultraviolet LAMP imager detected hydrogen (H2), nitrogen, carbon monoxide (CO), sodium, mercury, zinc, gold (!), and calcium. But water, present in quantities between 5 and 10 weight percent, is the most abundant volatile substance present.
In lunar terms, this is a very odd association of materials. Whereas we had found these elements and compounds in the returned lunar rock samples (some in vanishingly small quantities), the presence of significant amounts of ammonia and methane is significant; these gases are common components of cometary nuclei. One idea about the origin of water ice at the poles of the Moon is that it is derived largely from comets, which have continually hit the Moon over geological time. An alternative model suggests that most of the volatiles of this cometary debris are lost to space and the water and hydroxyl (OH) molecules found on the lunar surface come instead from the interaction of solar wind hydrogen with metal oxides in the lunar soil. In this model, heat provided by micrometeorite impact causes the solar wind hydrogen to reduce the metal oxides into native metal (like Fe0) and OH, which attaches itself to mineral faces. This hydroxyl is widespread over the lunar surface and was mapped by the Moon Mineralogy Mapper on the Chandrayaan-1 spacecraft over a year ago.
The newly published LCROSS data showing large amounts of volatiles normally associated with comets strongly suggest that at least some of the lunar water is of cometary origin. However, the detection of large amounts of free hydrogen (H2) in the ejecta plume supports significant preservation of solar wind hydrogen in the cold traps as well. It appears that both sources contribute to the water on the Moon and more analysis is necessary to determine which process is responsible for what fraction of the deposits. The clear message of the new work is that the processes and history of lunar volatiles are complex and poorly understood. Once again, the Moon shows us that its history, as well as its current state, is richer and more nuanced than we had thought.
The LCROSS results indicate that a variety of useful substances are present in the polar cold traps. Water is our principal object for future resource extraction, being one of the most valuable and readily available substances for spaceflight imaginable (i.e., a life-support consumable, a medium of energy storage and rocket propellant). However, both ammonia and methane have a variety of industrial uses, as well as being ready sources of nitrogen and carbon, two elements essential for the support of human life. Sulfur is also a useful element and appears to be present in fair quantity as both native sulfur and sulfide. Some reports suggest that the high concentration of mercury makes lunar water unusable; this impression is incorrect. Impurities can be removed from harvested polar water easily through the technique of fractional distillation, a common industrial process on the Earth for hundreds of years.
Some of the components of the polar suite are perplexing. For example, silver (Ag) shows a very strong peak in the uv-vis spectra. In lunar samples, silver is extremely sparse, occurring at the parts per billion level. Mercury (Hg) is also rare in lunar samples but it is a very volatile substance and the processes that preserve volatiles in the cold traps would work to increase and concentrate mercury at the poles relative to equatorial areas of the Moon. But silver is not volatile (its melting temperature is about 1000° C), so why would it concentrate at the poles? With such bizarre associations, scientists will be looking over this new data with keen interest. To determine the composition, physical nature and distribution of these deposits, a robotic surface rover needs to be sent into the polar cold traps to take detailed measurements.
Just after it has been relegated to a “been there, done that” status, the Moon again shows us we have a lot to learn about its history, physical state and the potential value of its resources. We must take the initiative to learn more as the Moon is crucial in developing and advancing a sustainable space faring infrastructure.
October 7, 2010
The Authorized Version
Congress disposes....
NASA’s new authorization bill (S.3729) was passed by Congress before they cleared out of town and will soon be signed by the President, codifying into law the federal government’s formal abandonment of the Vision for Space Exploration. In its place is a mish-mosh of platitudes, entitlement programs, pontificating blither about “unique” missions, commercial aerospace welfare and most significantly, an utter lack of direction for our national space program.
I’ve already heard the reaction to the sentiments above, as the space blogosphere has hashed and rehashed space access, space direction and space pork and now is left with – what? Defensively, we’re told, “The new bill does too have direction!! We’re going to Mars! We’re going to a near-Earth asteroid!! We’ll develop new, “game-changing, leap-ahead” technologies to make spaceflight easier and cheaper – that will take us there sooner! The commercial sector will develop new, ultra-affordable launch vehicles to allow the movement of humanity into space!” They will just … “Make it so.”
A statement that “Mars is the ultimate destination” is not programmatic direction, but rather an exhausted platitude, unsupported by any facts in evidence. We do not now have the technology, the will or the national wealth to expend on a human Mars mission and will not for decades. The idea that some new “magic beans” technology will spontaneously arise to enable a human mission is technically illiterate. The quasi-religious belief by some in the efficacy of “New Space” efforts to provide routine and inexpensive access to LEO is touching, but unsupported by any evidence. It is certainly true that many NASA programs have cost more and taken longer than promised or planned, but that’s been the nature of the space business since its founding 50 years ago. At least NASA had a track record of building and flying spacecraft, under a variety of difficult technical and fiscal conditions. But for now, NASA’s manned space workforce has been told to make tracks for other employment.
The likely effect of the proposed new “direction” for NASA by this administration has been apparent to many of us for some time now – the end of human spaceflight by this nation. Although some of us suspect that this shattering of a national capability is all quite deliberate, motives do not matter at this stage. The new authorization bill makes some significant changes to the administration’s proposal. The only pertinent question is, can pieces of the space program be picked up and re-assembled again, sometime in the future after years of destructive non-activity? It is in this vein that I want to examine some of the language of the new authorization bill.
The most prescriptive part of the new authorization is its language dealing with a new NASA-developed heavy lift launch vehicle (HLV) and a Multi-Purpose Crew Vehicle (MPCV), replacements for the now-terminated Project Constellation. The launch vehicle description reads as though the authors of the bill had some solution (or range of solutions) in mind, a surmise supported by the requirement that the agency use “existing Shuttle parts and infrastructure to the maximum extent possible.” The specific requirement is for a vehicle with a payload capacity of 70 to 100 metric tonnes to LEO, capable of growth to 130 mT, including a possible “Earth departure stage.” It is further specified that this vehicle be capable of launching the MPCV into orbit and to supply cargo and crew to the ISS.
The crew vehicle description is a little more vague, as befits a spacecraft with no defined mission. Although it is specified that the MPCV shall be capable of conducting missions beyond LEO, its primary mission seems to be crew and cargo delivery to the ISS. In addition, it must be capable of supporting “rendezvous, docking, extra-vehicular activity” and “servicing of assets” in “cislunar space” (interesting wording that). The bill goes on to define the intent of this provision in another section (804) related to making space-based telescopes (like the James Webb telescope at Earth-Sun L-2) serviceable by humans. But by using the term “cislunar,” it may well be that something else might be lurking in the background.
The prefacing language in the bill (the seven “findings” of the Senate) is even more interesting (Section 301a). Cislunar space is mentioned in 4 of the 7 provisions of the prefacing section; human lunar surface presence is mentioned in 3 of those 7 sections. Strange language for an authorization bill that “abandons the Moon as a destination,” as claimed in many press reports. What should we make of this unusual language and phrasing?
I think that the bill’s provisions for a NASA-developed HLV and crew spacecraft reflect a fundamental ambivalence on the part of Congress for the “new direction” adumbrated by the administration last spring. It would seem some healthy skepticism exists as to whether a purely commercial solution to human LEO access is possible or even desirable. In addition, although the President is now famous for remarking that a return to the Moon is pointless because “we’ve been there,” someone on the Hill fortunately recognized the lack of understanding embodied in that statement.
The bill’s wording about human access to “cislunar space,” as well as the mention of “in situ resource utilization” indicates that some in Congress are not blind to the wealth of knowledge recently acquired showing that the poles of the Moon contain abundant water – material useful to those countries willing to go after it in order to achieve affordable space faring capability and routine access to cislunar space, where all advanced countries’ satellite assets reside.
In short, I detect in the new authorization bill the hand of someone in the bowels of the committees – a staffer perhaps – who has perceptively salvaged a slender thread of capability for the use of some future national leader, one that supports a robust American space program. I note that the authorization calls for a report in 90 days on how the agency proposes to implement the new plan. Somebody will be watching them.
