SMART-1 Lunar Mission: Operations Close to Moon Impact

摘要

The spacecraft orbit around the moon has been optimized for science successfully, both during the nominal mission phase and the extended mission phase. Coverage of a large part of the lunar surface—especially the South Pole regions— was achieved, at low altitudes and with good illumination, including opportunities for multiple observation of the same surface area. Closer to the moon it became more difficult not to violate platform and payload constraints. The Mission Control Team commanded a solar panel offpointing in May 2006 to lower the solar panel temperatures. At low altitudes there was a concern for long blinding periods of both startracker cameras (at the same time), and a special spacecraft pointing had to be implemented to clear at least one of the two startracker cameras. There have been two main reboost phases during the science mission around the moon. In the first one, the electric propulsion engine was used to prepare the spacecraft orbit for the extended science mission, using all of the remaining pro-pellant for the electric propulsion engine. In the second reboost phase, the hydra-zine subsystem was used in an innovative way to do a series of small △V maneuvers. Without the second reboost phase, the spacecraft would have impacted the moon on the far side, away from ground contact and visibility. Only 30 h before moon impact, a correction maneuver was executed (using the hydrazine thrusters), to maximize the probability of impacting as planned on the morning of 3 September at 05:42 UTC. Without this correction maneuver, the probability of impacting the rim of the Clausius crater, one orbit before the nominal impact, was high. On 3 September, early in the morning at 05:42 UTC, SMART-1 ended its journey in the Lake of Excellence at 34.4°S latitude and 46.2°W longitude. Loss of signal was confirmed by the ESA ground station and several radio telescopes around the world. The impact was observed in infrared by the CFHT, offering a stunning image of the SMART-1 impact.The SMART-1 legacy is a wealth of data, to be analyzed in the months and years to come. SMART-1 has mapped large and small impact craters, studied the volcanic and tectonic processes that shaped the moon, unveiled the mysterious poles, and investigated sites for future exploration—a precious contribution to lunar science, at a time when the exploration of the moon is once again getting the world's interest.