Europe's first mission to the moon is due to crash-land in a cloud of dust and rock Sunday, ending a three-year voyage that gathered data about the lunar surface and tested a new engine intended to propel future spacecraft to Mercury and other planets.
The European Space Agency's SMART-1 should hit its target on a volcanic plain called the Lake of Excellence at 1:41 a.m. ET, skimming low as it makes its final approach at 4,475 mph.
Observatories on earth will try to capture images of the impact and the resulting debris cloud, and European space officials hope their study of the debris will provide information about the minerals present at the impact site.
Even before the mission ends, however, ESA is already celebrating the main goal — a successful test of the ion engine they hope to use for future interplanetary missions, such as the BepiColombo joint mission to Mercury with Japan's space agency slated for launch in 2013.
"The prime object of this mission was to test the ion propulsion," mission manager Gerhard Schwehm told The Associated Press.
"This is a very efficient means to get a spacecraft over large distances with a very small mass of fuel. It worked really well."
Instead of burning rocket fuel, the PPS-1350 engine from French aerospace firm Snecma generates a stream of electrically charged atoms called ions. That creates minuscule amounts of thrust — roughly enough to hold up a postcard.
Riding that small, steady push, SMART-1 made it to the moon in 14 months, gradually accelerating and raising its orbit around the earth until it was high enough to be grabbed by the moon's gravity.
It was launched into earth orbit using an Ariane 5 rocket from the European spaceport in Kourou, French Guinea, on Sept. 27, 2003.
By contrast, the first mission to put humans on the moon, NASA's Apollo 11, took 76 hours to reach lunar orbit in 1969, hurled by a Saturn 5 rocket.
Mission on the cheap
SMART-1, a cube measuring roughly a yard on each side, took the long way — over 62 million miles instead of the direct route of 217,000 to 250,000 miles.
But ESA did it for a relatively cheap $140 million and on only 176 pounds of xenon fuel. NASA's Deep Space 1, launched in 1998, also used an ion engine.
ESA flight controllers and scientists at mission control in Darmstadt, Germany, honed their skills in managing the different rhythm of spaceflight with ion propulsion, where the continuous thrust requires more careful monitoring than coasting after the one-time impulse from a rocket.
"It's different in how you operate the spacecraft in your operations center," Schehm said. "You have to determine your orbit more frequently."
Although the moon has already been explored by U.S. astronauts, ESA says SMART-1 gathered valuable information as it orbited.
Its miniaturized X-ray and infrared spectrometers probed the mineral content of the surface to better understand the distribution of elements over the entire moon, not just the small areas explored by astronauts.
The information could increase scientists' understanding of how the moon's surface evolved and help test a theory that the moon originated when another astronomical body slammed into the Earth.
The spacecraft has also been taking high-resolution pictures of the surface with a miniaturized camera.
The mission has contributed to ESA's cooperation with India's space program, which will use SMART-1's spectrometers on its Chandrayaan-1 moon mission slated for 2007 or 2008.
ESA officials say the planned crash site at the Lake of Excellence — at coordinates 43.5 degrees west and 36.4 degrees south — will be in darkness and not directly lit by the sun's rays at the time of impact, though there will be some illumination from light reflected from earth, or earthshine.
Geographic features on the moon are named lakes and seas — such as the Sea of Tranquillity, where Apollo 11 landed — even though they are in fact dry.
If the debris cloud from SMART-1 rises more than 12 miles and reaches sunlight, it may appear as a bright spot against the darkness visible using an amateur telescope or binoculars.
The moon will be visible from North and South America and the East Pacific at the moment of impact, but not from Europe.