Clementine provided our first complete look at the lunar surface, including the poles.
The probe found evidence of ice in the bottom of a permanently shadowed crater at the Moon's south pole.

Key Dates

Jan. 25, 1994: Launch

Feb. 19, 1994: Entered lunar orbit

May 3, 1994: Departure for asteroid

July 20, 1994: Clementine propelled into heliocentric orbit

Aug. 8, 1994: Mission terminated

Feb. 20 & May 10, 1995: Contact with spacecraft briefly reestablished

In Depth: Clementine

Clementine was the first U.S. spacecraft launched to the Moon in over 20 years—since Explorer 49 in June 1973.

The spacecraft, also known as the Deep Space Program Science Experiment (DSPSE), was designed and built to demonstrate a set of lightweight technologies such as small-imaging sensors and lightweight gallium arsenide solar panels for future low-cost missions flown by the Department of Defense.

Specifically, Clementine was a technology proving mission for the DOD’s Brilliant Pebbles program for the Strategic Defense Initiative (SDI), which required a large fleet of inexpensive spacecraft. Clementine carried 15 advanced flight-test components and nine science instruments.

After launch, the spacecraft remained in a temporary parking orbit until Feb. 3, 1994, at which time a solid-propellant rocket ignited to send the vehicle to the Moon. After two Earth flybys, Feb. 5 and Feb. 15, Clementine successfully entered an elliptical polar orbit (about 270 × 1,830 miles or 430 × 2,950 kilometers) around the Moon on Feb. 19, 1994, with a period of five days.

In the following two months, it transmitted about 1.6 million digital images of the lunar surface, many of them with resolutions down to about 330-660 feet (100-200 meters). In the process, it provided scientists with their first look at the total lunar landscape including polar regions.

After completing its lunar mission goals during 297 orbits, controllers fired Clementine’s thrusters May 3, 1994, to inject it on a rendezvous trajectory (via an Earth flyby) with the asteroid 1620 Geographos in August 1994.

However, due to a computer problem at 14:39 UT May 7, 1994, that caused a thruster to fire and use up all propellant, the spacecraft was put in an uncontrollable tumble at about 80 rpms with no spin control. Controllers were forced to cancel the asteroid flyby and return the vehicle to the vicinity of Earth.

A power supply problem further diminished the operating capacity of the vehicle. Eventually, on July 20, 1994, lunar gravity took control of Clementine and propelled it into a heliocentric orbit.

The mission was terminated Aug. 8, 1994, when falling power supply levels no longer allowed clear telemetry exchange.

Surprisingly, because the spacecraft was fortuitously in the correct attitude to power up again, ground controllers were able to briefly regain contact between Feb. 20, 1995, and May 10, 1995.

On Dec. 3, 1996, the Department of Defense announced that Clementine data indicated that there was ice in the bottom of a permanently shadowed crater at the lunar South Pole. Scientists estimated the deposit to be approximately 78,500 to 157,000 cubic yards (60,000 to 120,000 cubic meters) in volume, or comparable to a small lake that is four football fields in surface area and about 16 feet (5 meters) deep. This estimate was very uncertain, however, due to the nature of the data.

An accounting of Clementine’s legacy should include the fact that methods developed for the project became the basis for NASA’s “Faster, Better, Cheaper” initiative which ultimately paved the way for the Agency’s Discovery program.

- Credit: NASA

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