Moon Society Hails Completion of
Very Successful SMART-1 Moon Mission

2006.09.05 When the European Space Agency's budget Moon probe SMART-1 was launched almost three years ago on September 27, 2003, the media focus was almost entirely on its unique mode of propulsion. Indeed, the probe's small ion engine, producing a very gentle but constant thrust, took over a year to corkscrew its way to the point where the Moon's gravity took over on November 13, 2004. Only 61.5 kg (123 lbs) of fuel was used in getting the 305 kg (671 lb) craft into position to start studying the Moon. When you have more time than money, this is evidently a good way to go.

In a remarkable feat of miniaturization, its 7 powerful instruments accounted for just 19 kg (42 lbs.) of that mass. But, read on. The mission team found a way to turn the rest of the probe's mass into an valuable instrument as well.

The first lunar probe since Lunar Prospector (1998), the ESA probe's goals belied its small size: "... to return data on the geology, morphology, topography, mineralogy, geochemistry, and exospheric environment of the Moon in order to answer questions about planetary formation accretional processes, origin of the Earth-Moon system, the lunar near/far side dichotomy, long-term volcanic and tectonic activity, thermal and dynamical processes involved in lunar evolution, and water ice and external processes on the surface."

Indeed this "little probe that could" built upon the achievements of the Clementine and Lunar Prospector missions, endeavoring to fill in critical gaps in our knowledge of the Moon. When the mission scientists are finished analyzing all the data returned, our picture of the Moon and the geographical disposition of its key resources will be much less sketchy.

China's Changé 1, India's Chandrayaan 1, and NASA's Lunar Reconnaissance Orbiter will take this process even further in the remaining years of this decade.

In the spirit of getting the last drop out of the bottle, even SMART-1's final impact crash on the Moon was controlled to occur on a previously unexplored area of the Moon's Nearside currently in darkness, so that the flash and splashout from the low angle impact might reveal data about the crash site previously unknown or only surmised. The probe's entire bulk would serve as one final instrument of investigation.

This is the third attempt, and the second successful one, to derive useful knowledge from a spacecraft impact. Lunar Prospector's splashout revealed nothing of note on July 31, 1999. The Deep Impact probe to comet Temple I, however, told us much about the comet's surface when a detachable part of it was hurtled on a collision course that impacted the comet on July 4th, 2005.

The Beijing Declaration issued by the attendees of this years International Lunar Conference, ILEWG 8, on July 27th this year, calls for all nations and agencies sending probes to the Moon to use the opportunities provided by their craft's final impact on the Moon's surface to maximize science return. This is a very positive step.

To date, in addition to craft intended to crash land, or soft land on the Moon such as the Rangers and Surveyors, all craft in lunar orbit (Except Clementine which at the end of its lunar mission was redirected elsewhere) have crash landed on the Moon. This happens because lunar orbits are temporary. Perturbations by Earth cause the perilune, the point of an orbit closest to the lunar surface, to gradually decay until, inevitably, it intersects the lunar surface on a very low, almost tangential angle. This was the inevitable fate of NASA's Lunar Orbiters, as well as of the Apollo Lunar Ascent Modules, abandoned in orbit after each moonwalker crew reentered the Apollo Command Module for the trip back to Earth.

Some of these impacts will have occurred on the Moon's farside, where they could not be observed from the Earth. But prior to Lunar Prospector and SMART-1, there had been no attempt to control the point of impact so that the flash and splashout could be observed. These opportunities were not pursued.

It is good to see that this mission plan deficiency has now been corrected and that splashout science is now a part of all future missions. Splashout science gives us a chance to sample sites on the Moon other than those visited by the Apollo and Lunakhod missions, filling in gaps, and giving us a greater degree of confidence in our picture of the Moon.

Future targets will include permanently shaded craters near the Moon's poles. One of these was indeed the target of Lunar Prospector. It was hoped that the impact would occur in a water-ice laden area, confirming the water-ice interpretation of Lunar Prospector's finding of excess hydrogen near the poles. The negative results of that first experiment did not prove that there are no water-ice reservoirs there. The probe could have crashed into an ice free rock outcrop for example. It was a matter of luck at best.

Impact splashout science has emerged as an elegantly simple and cost-effective substitute for expensive "sample return" missions. An orbiter releases an impact probe, and the orbiter's instruments analyze the splashout remotely, or even by flying through the plume. Such a budget sampling mission has been proposed for Europa.

As our various space programs mature, inventive, ingenious minds are finding new ways get the most bang for the buck.

The Moon Society congratulates The European Space Agency and the SMART-1 team for a splendid effort.