January 26, 2005
SMART-1’s First Images from the Moon
ESA -- SMART-1 captured its first close-range images of the Moon this January, during a sequence of test lunar observations from an altitude between 1000 and 5000 kilometres above the lunar surface. The first four days after being captured by the lunar gravity were very critical. There had been the risk, being in an 'unstable' trajectory, of escaping the Moon's orbit or crashing onto the surface. Because of this, the electric propulsion system (or 'ion engine') started a thrust to stabilise the capture.
SMART-1 entered its first orbit around the Moon on 15 November 2004. It has spent the two months following spiralling down to the Moon and testing its array of instruments.
The first four days after being captured by the lunar gravity were very critical. There had been the risk, being in an 'unstable' trajectory, of escaping the Moon's orbit or crashing onto the surface. Because of this, the electric propulsion system (or 'ion engine') started a thrust to stabilise the capture.The ion engine was switched on until 29 December, allowing SMART-1 to make ever-decreasing loops around the Moon. The engine was switched off between 29 December and 3 January 2005 to allow scientists to start observations. At this point, the AMIE camera took the close-up lunar images. The engine was switched off again to optimise fuel consumption on 12 January, and SMART-1 will spend until 9 February making a medium resolution survey of the Moon, taking advantage of the favourable illumination conditions.
The first close-up image shows an area at lunar latitude 75° North with impact craters of different sizes. The largest crater shown here, in the middle left of the image, is Brianchon. The second largest, at the bottom of the image, is called Pascal.
At low illumination angles, the crater shadows allow scientists to derive the height of crater rims.
"This image was the first proof that the AMIE camera is still working well in lunar orbit," says AMIE Principal Investigator Jean-Luc Josset of Space-X.
The composite images shown here were created to show larger-scale features. The first mosaic shows the complex impact crater Pythagoras and the strip of images (bottom) was produced from images taken consecutively along one orbit.
Starting with this mosaic, SMART-1 scientists expect to build up a global medium-resolution context map, where high-resolution images later observed from lower altitude can be integrated.
SMART-1 is the first of ESA's 'Small Missions for Advanced Research in Technology'. It is heading for the Moon using revolutionary propulsion techniques and carry a battery of miniaturised instruments.
Over 30 years after the last Apollo mission visited the Moon in 1972, there is still much that we do not know about our nearest satellite. For example, how was it created? What role did it play in the formation and evolution of Earth? SMART-1 may help to answer these questions.
As scientists demand more from space missions travelling to other worlds and beyond, traditional rocket technologies are beginning to show shortcomings. In response to this need, ESA are developing a new type of engine, known as solar-electric propulsion, or an 'ion' engine, which could mark a whole new era of space exploration.
As well as testing new technology, SMART-1 will make the first comprehensive inventory of key chemical elements in the lunar surface. It will also investigate the theory that the Moon was formed following the violent collision of a smaller planet with Earth, four and a half thousand million years ago.
The main purpose of the SMART-1 mission is to flight-test the new solar-electric propulsion technology "“ a kind of solar-powered thruster that is ten times more efficient than the usual chemical systems employed when travelling in space. If all goes well, such a system could be providing the propulsion system for future ESA missions into deep space, such as BepiColombo.
However, in the process, the mission will be providing some fascinating science. For example, SMART-1 will be mapping the lunar surface chemical composition more accurately than ever before. Apollo spacecraft carried hand-held cameras to photograph the lunar surface. SMART-1 will be leading the way in the latest imaging techniques. Images taken from many different angles and X-ray and infrared detection work will allow scientists to draw up new three-dimensional models of the Moon's surface.
SMART-1 will be looking at the darker parts of the Moon's south pole for the first time. It will be mapping the so-called Peak of Eternal Light, an eerie mountaintop that is permanently bathed in sunlight, while all around are dark craters never touched by the Sun. These craters are believed to harbour water-ice in the lunar soil. SMART-1 will also help scientists to confirm if ice is present at the lunar poles, where the temperature never rises above "“170°C. Any water on the lunar surface would be very helpful in the creation of permanent bases on the Moon.
Solar-electric propulsion does not burn fuel as chemical rockets do; instead the technique converts sunlight into electricity via solar panels and uses it to electrically charge heavy gas atoms, which accelerate away from the spacecraft at high speed. This drives the spacecraft forwards. In a chemical rocket, the burning fuel creates gases which are expelled relatively slowly compared to ion thrusters. However, in an ion engine, the gas is ejected at high velocity, which makes it much more efficient and requires less fuel.
Ion engines are very important because their high efficiency makes previously impossible missions achievable. Since they do not need to carry so much fuel, ion engines release room for more scientific instruments. As technology continues to get smaller, the size of instruments decreases and the overall size and mass of the spacecraft decreases, further increasing efficiency.
Further away from the Sun, where the light is weaker, a new power source, such as a nuclear reactor, would be needed. This type of engine could take spacecraft to the Kuiper belt and even farther away. The Kuiper belt extends beyond the planet Pluto. It is a dream destination for many scientists because it contains comets that have been undisturbed since the formation of the Solar System. Beyond Pluto is a mysterious realm of magnetic fields and rarefied gases known as interstellar space. Solar-electric propulsion would make such a mission possible because an ion engine can run almost constantly, so that eventually it outperforms any chemical rocket on such long flights.
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ESA's SMART-1 Project Scientist Bernard Foing said, "A sequence of test lunar observations was done in January at distances between 1000 and 5000 kilometres altitude, when the electric propulsion was paused. We are conducting more survey test observations until the electric propulsion resumes from 9 February to spiral down further towards the Moon. SMART-1 will arrive on 28 February at the initial orbit with altitudes between 300 and 3000 kilometres to perform the first phase of nominal science observations for five months."