Early last Friday, the public and families of employees at Ames Research Center in California, where the LCROSS mission was conceived, built and operated, camped on the lawn in an all-night vigil. NASA’s educational outreach and public relations push about the pending lunar impact event was very effective, having reached a wide audience in the weeks leading up to the much hyped event. Alas, the promised giant plume of impact debris was invisible from Earth, leaving a receptive public feeling cheated and disappointed.
The understanding that a high-velocity impactor can yield important information about planetary composition and state is very old. The first probes to the Moon (both Soviet and American) were impactors. We know that when something strikes a planetary surface at high speed, target material is thrown up into space, some of it vaporized by heat generated in the energy of the impact. By studying this impact ejecta, we learn about the composition of the target object.
I didn’t post on it earlier, but as the LCROSS mission has successfully concluded, I think it is a good time to examine this mission, how it came about, and the lessons that hopefully it has taught NASA about public appeal and its involvement with space.
LCROSS was not originally a part of the robotic precursor program for lunar return. Initially, the Lunar Reconnaissance Orbiter (LRO) spacecraft was to be launched on a Delta II. By the end of 2005 it had outgrown its booster and was forced onto the much larger Atlas V booster where it had surplus payload margin. The Associate Administrator for the Exploration Systems Mission Directorate (ESMD) Scott Horowitz, decided to use this margin to fly an additional small spacecraft (called a secondary payload) that would address the raging debate about whether water ice exists at the poles of the Moon. Horowitz looked to NASA’s field centers for a small payload that would provide data about this contentious and nagging issue.
Although a variety of small missions were proposed, including survivable hard landers and small “hoppers,” the idea of slamming the Centaur upper stage into the Moon and examining the resulting ejecta plume was selected as LCROSS in April 2006. It was considered a low-risk, low-cost concept, as the used Centaur upper stage had no value and would have been steered into a solar orbit anyway. A small satellite was built to track the Centaur impact, measure the properties of the ejected plume and with luck, would “settle” the issue of water on the Moon.
A serious defect in this mission concept was that it presupposed that we understood the Moon well enough to identify in advance the most likely site for ice on the Moon. Lunar investigators knew from previous data that water ice, if present, was not present everywhere – it had a patchy, heterogeneous distribution because the permanent shadow around the poles (where the ice would be stable) is itself patchy. Moreover, the remote sensing data of the time was ambiguous as to which shadowed locales contained ice, if any.
In March of 2006, because of these uncertainties, those who had worked on the robotic precursor program laid out a sequential, incremental strategy to first map the deposits from orbit and identify the best candidate sites for ice. Following orbital mapping, we would soft-land with capable rovers and map and test the surface composition at a minimum of about 20 different sites. Although this strategy is more costly than a simple impactor mission, it would have provided us an unequivocal answer to the ice issue; we would know without doubt whether there is or is not water ice at the poles of the Moon. Moreover, rovers would collect information on the possible presence, physical nature and setting of other volatile substances (such as ammonia and methane) that have resource value. In other words, we would have collected the critical strategic information needed to locate, prospect, harvest and use lunar water.
Instead, the mission chosen and flown and heavily advertised by NASA as a citizen participation viewing event to find water on the Moon, could not answer key questions about polar water. If LCROSS detects water, we still won’t know where all the ice deposits are located, what other species might be present, what its physical state might be, and how it is distributed laterally and vertically in the surface regolith. If LCROSS detects nothing, it won’t prove that water doesn’t exist on the Moon, only that the wrong site was selected. In other words, after this mission, we will still know next to nothing about the material that will enable and advance permanent, sustainable economic presence on the Moon.
An impact plume wasn't the only thing missing. Hopefully, NASA will recognize the real discovery of LCROSS – mission hype is a poor substitute for shortcomings in programmatic logic.