Map of the Lacus Excellentiae region on the Moon, showing the nominal SMART-1 impact orbit (central red line) and possible impact location at perilune on the lunar surface.
Credit: ESA/Clementine Project
SYDNEY, 22 August 2006: Europe's first successful Moon voyager is hurtling toward a spectacular crash landing, but will take pictures of uncharted lunar terrain before impact – potentially shedding light on some of the natural satellite's many mysteries.
On September 3, the SMART-1 probe will hurtle in at a glancing angle - like a skier jumping off a cliff into untouched powder.
The last observations before impact will provide new perspectives on the lunar landscape. The Advanced Moon micro-Imager Experiment camera on-board SMART-1 will send back three-dimensional images providing the scientists with a better understanding of the geological evolution of the Moon's surface.
Although the expected date of impact is September 3, scientists are unsure of exactly where and how the spaceship will land because of incomplete knowledge of lunar topography. Because the spacecraft is coming in at such a shallow angle, it could just as likely hit the surface on September 3 as collide with a hill up to a day earlier.
The expected area of impact is the ‘Lake of Excellence', a volcanic plain area surrounded by highlands. Scientists hope to see up close images of this area, which is thought to have a diverse mineral constitution.
While the impact will surely result in the obliteration of the SMART-1 craft, it has already served a long and fruitful life. The original mission called for only six months of service, although the mission was subsequently extended by a further year.
One of the primary purposes of the SMART-1 craft was to test an experimental solar powered ion propulsion engine along with gravity assist manoeuvres for space travel.
Although, several NASA probes, such as STARDUST, already use ion propulsion, SMART-1 represents the first time the European Space Agency has employed the technology.
According to Bernard H. Foing, SMART-1 project scientist at European Space Agency, ion engines are efficient and cheap. They use solar panels to convert sunlight into electrical energy and later propel ions derived from the propellent tanks that thrust and spaceship forward.
"The thrust per ejected mass can be 10 times higher than for chemical propulsion, requiring less fuel and allowing more payload or smaller launchers," said Foing.
In fact, the experimental ion engine and gravity assist manoeuvres were even more efficient than the scientists had predicted.
"When passing near a planet or moon, the spacecraft gains some excess velocity. We used this three times in 2004 to save fuel on the way to the Moon," he said.
But by March 2005, there was only seven kilograms of propellant left from the 84 kilograms at launch.
The engineers used all the remaining propellant to avoid a crash in September 2005, after employing the gravity assist manoeuvres to re-boost into a higher orbit. This alone gave the spacecraft an extra year in orbit, which proved to be a great benefit to Europe's space scientists and engineers.
However, it couldn't last up there forever.
It inevitably becomes a prisoner as the Sun, the Earth and irregularities in the Moon gravitational field bind it forever to a decreasing Moon orbit.
If SMART-1 avoids unexpected hills, the spaceship is expected to crash at 05:41 UT (15:41 AEST), which will be visible through large telescopes in south and northwest Americas and Hawaii and possibly Australia.
"We hope to see it with telescopes, imaging the dynamics of ejecta in Earth shine, or with binoculars if some dust reaches sunlight at 25 km altitude," said Bernard H. Foing. The engineers hope to obtain physical and mineralogical data on the crash site of the spacecraft.
Australians are encouraged to grab their binoculars to see the flash of the sunlit dust cloud formed by the soft impact.
Scientists hope the cloud's behaviour will provide information on impacts in general. Additional analysis of the light from the dust, using spectrographs in the telescopes, may detect materials dug up by the impact.
