Europe's lunar orbiter to impact the moon Sunday
BY STEPHEN CLARK
Posted: September 2, 2006
A European space probe is just hours away from a violent crash into the lunar surface that ground-based scientists hope will help answer debated questions about the Moon's sub-surface.
The exact timing of the impact remains unknown, but European Space Agency officials say their most recent estimates place the event at 0542 GMT (1:42 a.m. EDT) Sunday morning.
The 630-pound SMART-1 craft is wrapping up almost two years in orbit around the Moon. During the mission, the probe was tasked with testing new technologies that officials hope to include on future spacecraft. In addition to its role as a testbed, SMART-1 employed several instruments for science observations.
Because of dwindling propellant reserves, managers decided in favor of an end-of-mission plan for SMART-1 that would give scientists a final opportunity to gather important data about the Moon that cannot be easily replicated by other missions. Otherwise, the probe would have been left to crash uncontrolled into the lunar surface because it is trapped in orbit by the Moon's gravity field.
Other recent spacecraft deliberately crashed into the Moon include NASA's Lunar Prospector in 1999 and Japan's Hiten demonstrator in 1993.
Engineers at SMART-1's control center in Germany have been planning and executing a series of precise maneuvers since June to place the craft on a collision course with the Moon on Sunday.
The thruster firings have left SMART-1 on a near-perfect trajectory, and the projected impact time is less than a minute from predictions released in July.
On Friday, SMART-1 went into an unexpected safe mode, during which most spacecraft and payload operations ceased. ESA says the ground team successfully restored the probe's functions about six hours later.
Last week, analysis of three-dimensional digital images revealed that uneven terrain near the expected crash site could lead to an impact one orbit earlier than planned at around 0038 GMT Sunday (8:38 p.m. EDT Saturday).
SMART-1 is targeting an impact in a region dubbed the Lake of Excellence in the mid-southern latitudes of the Moon's nearside.
The recovery of SMART-1 from the safe mode was crucial to perform last-minute burns of the craft's thrusters on Friday and Saturday to raise the low point of its orbit by just under 2,000 feet.
"While impact may still occur earlier due to uncertainty in terrain elevations, the possibility of this happening has been reduced as much as possible based on the information we now have," said SMART-1 project scientist Bernard Foing.
Scientists want the spacecraft to make its explosive send-off on the later opportunity due to better viewing conditions for an army of astronomers stationed at observatories in Chile, Arizona, Hawaii, and a number of other locales.
Amateur astronomers are also called being called upon to use their telescopes to attempt to see the impact or its aftermath. The most ideal viewing conditions are expected to be in North and South America where the waxing quarter Moon will be high in the sky.
Images from the telescopes could include a cloud of debris excavated by the high speed crash for scientists to analyze to determine the chemical composition and physical properties of the material.
See our earlier story for more details.