Impact of lunar orbiter seen by observatory in Hawaii
BY STEPHEN CLARK
Posted: September 5, 2006
Europe's first probe to the Moon went out with a bang this weekend as it deliberately plunged into the lunar surface in a final attempt to gather useful science data. The impact was seen from at least one ground telescope, and more observations of the crash site could come soon.
SMART-1 hit the Moon at a very oblique angle - comparable to that of a commercial airliner on final approach to a runway, according to European Space Agency officials. About the size of a typical washing machine, the craft was expected to collide with the surface at a speed well over 4,000 miles per hour.
Officials had called upon a large group of professional and amateur astronomers around the world to observe the Moon around the expected impact time. Scientists stationed at observatories across the globe trained their eyes on the Moon, and astronomers at the Canada-France-Hawaii Telescope were the first to submit a sighting live to SMART-1's control room in Germany.
Perched atop Mauna Kea in Hawaii, the observatory's 11.8-foot telescope detected the impact flash using a wide-field infrared camera.
Several optical and radio telescopes, Sweden's Odin satellite, and countless amateur astronomers were also looking for signs of the crash. Reports from these observers are still being sought and analyzed.
"We have a lot of work still to do," said Pascale Ehrenfreund, the SMART-1 impact ground campaign coordinator. "We have to collect all the data. We have to process the data correctly and try to interpret them in terms of impact physics, in terms of lunar science - and also what happened to the spacecraft.
"I think it will help as a guide for future impactors on the Moon," she said. "We are very happy and grateful for the participation worldwide of all the professional and amateur astronomers."
Analysis of other data from ground observations is also expected to reveal whether bits of rock and dust were thrown high enough above the lunar surface to be illuminated by sunlight. Post-impact observations of the crash site later this week will look for signs of a fresh ejecta blanket.
Instruments aboard SMART-1 were also gathering data and beaming it back to Earth in the final days and hours of the mission.
The crash ended SMART-1's three-year mission that tested a number of cutting edge technologies that engineers hope to apply to future probes. The craft featured a solar-electric ion propulsion system that slowly boosted it out of Earth orbit following its launch in September 2003.
The Moon's gravity captured SMART-1 into lunar orbit in November 2004, where it was set to begin a six-month mission to serve as both a testbed and science platform. Good spacecraft performance allowed managers to extend the mission by more than a year to this summer, when it was planned to make an uncontrolled impact on the Moon's far side where the crash would not have been visible to observers on Earth.
A two-week series of thruster firings in late June and early July raised the probe's orbit and delayed the looming lunar impact until September 3. The orbit change also moved the site of the crash to an ideal location on the Moon's near side.
Several last-minute maneuvers were conducted last week to reduce the chances of SMART-1 smacking into the Moon an orbit earlier than expected. Analysis of high-resolution images of the impact zone revealed rough terrain that could be high enough to cause the craft to crash before the planned time.
In its final few circuits around the Moon, SMART-1 was flying at just a few miles above the lunar surface as it reached the low point of each orbit. Controllers feared high mountains could stand in the way of the probe and cause an early impact.
SMART-1 also went into a sudden safe mode last week, severely curtailing most spacecraft and science activities for about six hours. Ground teams devised a quick fix to the situation so the end-of-mission plan could continue, and no other problems were reported before the last communications from the craft were received in the mission's final moments.
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