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Smart-1: Smackdown in the Lake of Excellence

August 25, 2006

The European Space Agency's Smart-1 mission ends on September 3rd 2006. Appropriately for such a successful mission, its final resting place will be an area of the Moon known as the 'Lake of Excellence'. During its 3-year lifespan, Europe's first mission to the Moon has advanced both lunar science and the technology that underpins it.

UK participation in Smart-1 was funded by the Particle Physics and Astronomy Research Council with additional funds from the British National Space Centre. PPARC CEO Professor Keith Mason hailed the mission's success "Smart-1 has been amazingly successful, both in proving new technologies that will help shape how Europe explores space in the future and in dramatically increasing our understanding of the Moon. With Smart-1 UK and European scientists and engineers have made a significant contribution to future international lunar exploration programmes."

Scientific Success Smart-1's scientific instruments have subjected the Moon to new scrutiny and worked so well that the mission was extended by an additional year. The UK instrument D-CIXS (a demonstrator compact X-ray spectrometer) has obtained mineral maps of the Moon's composition, looking at the distribution of calcium, magnesium, aluminium, silicon and iron. These will help to determine if the Moon was formed from terrestrial debris after a collision or mostly from a planet-sized object that crashed into the Earth.

Professor Manuel Grande of the University of Wales, Aberystwyth who leads the D-CIXS instrument said "By measuring the X-rays emitted when the Sun shines on the Moon, we can analyse the chemical composition of the surface. We then compare the abundances of key minerals to those found on the Earth to understand how much of the Moon's material came from our planet originally."

D-CIXS plays an important role in understanding the Moon and gives us new insight into whether the samples brought back from manned missions are typical of the lunar surface or not. Manuel Grande said "Where we can make comparisons with American and Russian landing sites, the agreement is good, which gives us confidence when we look at the data from areas of the Moon that have not been visited by humans."

D-CIXS has proved so successful that an enhanced version (called CIXS) is now under construction to fly on the Indian Chandrayaan mission to the Moon in 2007/8.

Smart-1's camera AMIE has also added greatly to our understanding of the Moon. Previously, the best digital maps of the Moon were from the US Clementine mission with a resolution of 200 m. At its best, Smart-1 mapping reveals features 40 m across.

Professor Bernard Foing, ESA Project Scientist for the mission said "Smart-1 has shown new views about the origin, evolution, and shaping processes of Earth's satellite. The analysis of data and the experience from the mission will be instrumental in planning future lunar exploration."

Technology Success Smart-1 was designed to test new technologies for exploring space as well as to conduct science. It is Europe's first mission to use an ion engine instead of chemical combustion to reach its destination. Smart-1 made the trip from Earth orbit to lunar orbit using gravitational assistance and an ion engine that created a very slow gentle thrust from charged xenon. Whilst slower in the short term than a conventional engine, it uses very little fuel which means that it is an ideal technique for missions that have to travel a long way without carrying a large volume of fuel - such as ESA's forthcoming BepiColumbo mission to Mercury.

Smart-1 also tested new radio communications systems and miniaturisation of science instruments that ESA's hopes may be useful for future missions.

Impact With the mission extended a year longer than planned, Smart-1 has exhausted its supply of Xenon fuel. Without fuel, the Moon's gravity will bring it naturally into impact on the surface as has happened with lunar probes since 1959. ESA engineers are controlling the time and location of the collision in order to conduct a final scientific investigation. By ensuring that the impact can be watched from Earth, telescopes will be able to study the dust plume from the crash and analyse the composition of the surface of the Moon. The area of the Moon where Smart-1 will smackdown is called the Lake of Excellence (Lacus Excellentiae) which is in fact a plain not a lake.

UK software experts SciSys are a key part of the team controlling Smart-1. Alan Batten, Head of Space at SciSys said "Mission operations often go unnoticed in space programmes but Smart-1 has been a real interplanetary adventure for us, exploring techniques in spacecraft automation that have never been tried before in Europe. Having extended these operations as far as we can, we are now at the mercy of the laws of physics."

When it arrives at the Moon's surface, SMART-1 will be travelling at 2 kilometres per second. That's much slower than a natural meteoroid-for instance Leonid meteoroids arrive on the Moon at 70 kilometres per second. SMART-1 will go in at a glancing angle - like a ski jumper. SMART-1 may hit a steep hill at 7000 kilometres per hour, but what is more likely is that it will glide down over a flat part of the lunar surface, dropping 15 metres in the last kilometre of forward motion. At impact, its vertical speed will be only 70 kilometres per hour, which is less than some ski jumpers achieve.

The impact will not be damaging to the Moon which has frequently been struck by harder impacts from meteorites. All the elements found in Smart-1 also occur naturally on the Moon.

Particle Physics & Astronomy Research Council