June 26, 2006

SMART-1 Enters its Final Days Orbiting the Moon


SMART-1, Europe's successful first Moon mission, is scheduled to end on 3 September 2006, impacting on the Moon's surface in a disposal plan similar to that of many earlier lunar missions and almost three years to the day after its 2003 launch.

The recently started manoeuvre campaign aims to avoid having the spacecraft intersect with the Moon at a disadvantageous time from the scientific point of view, as it would have naturally about 17 August if left alone. Instead, this 'extension' to mission operations will provide new opportunities for low-altitude scientific observations and give optimum science returns during and after the spacecraft's controlled impact on the Moon.

In preparation for mission end, spacecraft controllers at ESOC, ESA's Spacecraft Operations Centre in Darmstadt, Germany, have started a series of thruster firings to give a 'delta-velocity,' or change in velocity, of approximately 12 metres per second. This will raise the orbit perilune (point of closest passage over the Moon) by about 90 kilometres, and will shift the impact to 3 September.

"The shift in date, time and location for Moon intersection is also optimised to favour scientific observations from Earth," said Gerhard Schwehm, ESA's SMART-1 Mission Manager. "Projections based on the current orbit indicated that the spacecraft, if left as is, would impact the Moon on the far side, away from ground contact and visibility. The new location is on the Moon's near-side, at mid-southern latitudes."


"The manoeuvre strategy consists of a series of reaction-wheel off-loadings combined with about three hours of intermittent thrust centred at apolune (point of furthest distance from the Moon) during the next 74 orbits," said Octavio Camino, Spacecraft Operations Manager at ESOC.


"We use asymmetric firing of the attitude thrusters to produce a small velocity variation aligned with the flight direction. This will change the orbit by an accumulative effect," added Camino.



SMART-1 is the first in a series of 'Small Missions for Advanced Research and Technology' in which elements of the platform and miniaturised payload technology have been conceived as a demonstration for future scientific missions and an early opportunity for science. SMART-1 used an innovative ion-propulsion system powered by a small quantity of onboard Xenon and solar energy to generate electricity used to ionise the fuel to travel to the Moon.

After a 27 September 2003 launch, SMART-1 spiralled out over a 14-month period until being captured by the Moon on 15 November 2004, thus successfully achieving the primary objective of demonstrating solar electric propulsion during interplanetary travel. In addition to helping prove new technology from the perspective of satellite design, the mission has also provided an opportunity to develop new ways of conducting ground control operations based on both increased satellite autonomy and improved tools for ground automation.

The wealth of scientific data from SMART-1 are still being processed and analysed. Thanks to SMART-1, scientists all over Europe and around the world will have access to the best-resolution surface images ever taken from lunar orbit, as well as a better knowledge of the Moon's minerals. For the first time from orbit, SMART-1 detected Calcium and Magnesium using an X-ray instrument. It measured compositional changes from the central peaks of craters, volcanic plains and giant impact basins. The camera studied impact craters, volcanic features and lava tubes, and monitored the polar regions.


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SMART-1 Mission