Image: SMART-1
The SMART-1 probe, shown in this artwork, has been circling the moon since 2004.
By Senior space writer
updated 3/7/2006 12:21:34 PM ET 2006-03-07T17:21:34

Scientists are plotting out a “crash course” in learning what happens when a European lunar probe slams into the moon.

The European Space Agency’s SMART-1 spacecraft — now circling the moon — is headed for a planned early September impact with Earth’s celestial neighbor.

The ESA probe would plow into the lunar surface, giving it a glancing blow as it speeds in at nearly 5,000 miles per hour (2 kilometers per second).

SMART-1 is Europe’s first robotic lunar mission. The name SMART stands for Small Mission for Advanced Research in Technology

The spacecraft was launched on Sept. 27, 2003. Making use of its ion propulsion engine to slowly nudge it outward from Earth, the probe powered its way into lunar orbit on Nov. 15, 2004.

Outfitted with miniaturized instruments, SMART-1’s goal has been to gauge key chemical elements in the lunar surface, as well as look into the theory that the moon was formed following the violent collision of a smaller planet with Earth long ago.

ESA’s lunar probe completes a loop around the moon every five hours — but that’s about to end later this year.

Rehearsal mode
Engineers and scientists are now targeting SMART-1 for possible impact on the moon around Sept. 1-2. The current uncertainty range for the exact time of impact is 15 hours.

At the end of June, SMART-1 is slated to carry out two maneuvers. These will fine-tune the exact time of impact. Those slight thrust firings will lead to the spacecraft flying over the moon at its lowest point at below 186 miles (300 kilometers) in altitude.

In early July, the plan calls for assessing the success of the maneuver and determining the spacecraft’s orbit and expected impact time. Later that month, the probe will zip as close as 124 miles (200 kilometers) to the barren lunar landscape.

In early August, SMART-1 will make an overflight of its eventual impact site, racing over that area at an altitude of just 75 miles (120 kilometers), in what’s termed as “rehearsal” mode for the September run-in with the moon.

According to Bernard Foing, ESA's SMART-1 project scientist, an inventory is being made of the composition and mechanical properties of the spacecraft — including aluminum, copper, titanium and other materials, as well as the probe’s remaining hydrazine fuel.

That data will be used to support observations of what is kicked up from the moon itself on impact, contrasted to bits, pieces, and fuel tossed into the mix due to SMART-1’s high-speed slap.

Boom-and-bust finale
Here on Earth, skywatchers worldwide are getting ready for the projected Sept. 1-2 lunar boom-and-bust finale of SMART-1.

Foing told that he is now engaged in assembling a “coordinated campaign” of ground-based observations. This activity would support SMART-1 measurements and monitor the artificial crash — which would mimic, in a small way, an asteroid or comet hit on the moon.

Observatories around the world have indicated interest in watching the outcome from SMART-1’s collision with the moon, Foing has reported.

At impact, the ESA spacecraft will weigh a little more than 628 pounds (285 kilograms), punching the moon at a grazing incidence near 37 degrees south latitude. The near-side impact is timed so that it will be illuminated to assist in observations from Earth.

A current orbit simulation of the SMART-1 impact for Sept. 2 is at lunar longitude 44.54 degrees west and 36.22 degrees south, in Lacus Excellentiae, 10 degrees south of Mare Humorum. A far more refined target point will come as the event draws closer.

Crater-making crash
Back on July 31, 1999, the moon was on the receiving end of NASA’s Lunar Prospector.

That farewell fall of space hardware struck within a crater near the lunar south pole — in an attempt to detect water ice stirred up by the wallop. No visible debris plume was reported.

According to Foing, the hope is that those Earth-based observers intending to take part in September’s thump of the moon can make pre-hit predictions of SMART-1’s impact magnitude, cloud ejecta dynamics, exospheric effects and other observable manifestations brought about by the crash.

Coordinated measurements by observers here on Earth are high on the priority list, Foing noted. Impact observations would include: Infrared imaging of thermal flash; visible/infrared imaging of ejected clouds; hydrazine flame detection; post-characterization of ejecta; as well as the effects if lunar material is blasted high off the Moon’s surface.

In addition, Foing said, there is also the intent to conduct follow-up searches for the crater produced by SMART-1’s crash into the moon, through the sensor eyes of future lunar orbiters.

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