Clementine - The Small Lunar Explorer that Produced Big Results

This is a final look at the Clementine DSPSE spacecraft, which is mated to its launch vehicle, the Titan 11G. here, the nose fairing is being lowered to enclose Clementine in her new home during launch. Credit: U.S. Navy.

Twenty-five years ago, on Jan. 25, 1994, the deep space program science experiment—better known as “Clementine”—was launched from Vandenberg Air Force Base, California.

Developed and built by the U.S. Naval Research Laboratory (NRL), Clementine’s primary mission was in-space testing of advanced technologies for high-tech, lightweight missile defense. The relatively inexpensive, rapidly built spacecraft constituted a major revolution in spacecraft management and design and also contributed significantly to lunar studies.

In addition to the scientific value, the mission presented clear benefits to the Department of Defense (DoD), with the intent of flying the craft past the near-Earth asteroid Geographos to provide a meaningful target against which to flight-qualify advanced lightweight missile defense technologies. Clementine’s high closing velocity on the asteroid, a cold body flying against a deep space background, presented a two-fold opportunity to test DoD missile-intercept applications and NASA space exploration requirements.

Fostering a New Era

In the early 1990s, NASA approached the Strategic Defense Initiative Organization (renamed the Ballistic Missile Defense Organization in 1994) proposing a joint NASA/DoD space mission that could prove beneficial to the future objectives and capabilities of both agencies. The purpose of the mission was to test new state-of-the-art technology and its ability to function and withstand prolonged exposure to deep space, and to determine the collaborative functionality of a major multiagency project.

Using Earth’s moon as a focal point, the mission would test lightweight sensory equipment, attitude control systems, and software. To accomplish mission goals Clementine required a multimode propulsion system, computers, inertial measurement units, and an array of cameras that included an ultraviolet/visible camera (UVVIS), near-infrared camera (NIR), high-resolution camera (HIRES), laser rangefinder (LIDAR), long-wavelength infrared camera (LWIR), and two star-tracker cameras designed and built by the Lawrence Livermore National Laboratory in Livermore, California.

Faster, Better, Cheaper

In early 1992, DoD and NASA selected NRL’s Naval Center for Space Technology (NCST) to build this spacecraft. Because of the sponsor’s funding limits and the timeline to rendezvous with Geographos, the Clementine mission became known in retrospect as an exemplar of the “faster, better, cheaper” management approach.

At a 1998 IEEE aerospace conference, Dr. Donald Horan, then chief scientist and director of the Clementine program, said “Some reasons why Clementine could be considered faster, better, and cheaper are inherent to the Naval Center for Space Technology. Clementine was the 81st satellite built by NCST since 1960 and, over the years, competition for space dollars had forced NCST to become efficient.”

NRL engineers eagerly accepted the challenge, developing the mission design, spacecraft engineering, spacecraft manufacturing, flight-logistics and flight operations in less than a two-year period.

To the Moon!

Formally considered the Deep Space Program Science Experiment, the project was soon dubbed Clementine, from the American folk ballad “Oh My Darling,” because the lightweight spacecraft would not only be “mining” the geology of the lunar surface, but carried only enough fuel to complete its mission before being “lost and gone forever.”

Demonstrating that smaller, highly capable satellites were obtainable at a cost below $100 million, Clementine was completed in 22 months at a cost of less than $80 million. It was launched aboard a Titan IIG rocket from Vandenberg Air Force Base. After two Earth flybys, Clementine entered lunar orbit on 19 February 1994 and was positioned into an optimal five-hour polar orbit to fully map the lunar surface.

In an FY1994 report to Congress, President Bill Clinton stated that among the nation’s notable achievements in aeronautics and space was the launch of the Deep Space Probe, Clementine. “The highly successful launch of the Clementine Deep Space Probe tested 23 advanced technologies for high-tech, lightweight missile defense,” he said. “The relatively inexpensive, rapidly built spacecraft constituted a major revolution in spacecraft management and design; it also contributed significantly to lunar studies by photographing 1.8 million images of the surface of the moon.”

Between 26 February and 22 April, Clementine was able to deliver the nearly two million digital images of the moon to the NASA Deep Space ground network and NRL’s satellite ground-tracking station located in Pomonkey, Maryland.

Images were quickly made available to scientists and the public using the then-nascent World Wide Web. However, in 1994, serving this amount of data challenged all but top supercomputer sites. To accomplish this task, NRL’s Center for Computational Science hosted the images and developed sophisticated data handling and caching strategies for distributing and retrieving the large data set across multiple storage subsystems. The resultant system enabled researchers, as well as K-12 students from around the world, to quickly browse the entire imagery collection and download selected subsets from even slow Internet connections, such as those served by dial-up modems.

After completing its two-month mapping mission orbiting the moon, the craft was designed to then use phasing loops around Earth and fly past the near-Earth asteroid Geographos. Unfortunately, after leaving lunar orbit May 3, an onboard computer glitch inadvertently caused a thruster to fire, expending the remaining fuel and leaving the spacecraft spinning in a geocentric Earth orbit.

A Legacy Not Lost

Although its attempt at flying past the asteroid failed, Clementine provided answers to many questions about the moon that remained from the Ranger and Surveyor unmanned programs and the Apollo-era manned missions. Observations included imaging at various wavelengths including ultraviolet and infrared, laser ranging altimetry, and charged particle measurements. These observations were for the purposes of assessing surface mineralogy, obtaining lunar altimetry, and determining the size, shape, rotational characteristics, surface properties, and cratering statistics of the moon.

When scientists further reviewed the data from Clementine, they made a major scientific discovery: the possible existence of ice within some of the moon's craters. In early 1998, NASA’s Lunar Prospector confirmed this discovery when NASA scientists announced that the spacecraft’s neutron spectrometer instrument had detected hydrogen at both lunar poles, theorized to be in the form of water ice.

Encouraged by the valuable data gathered by the Clementine mission and a new vision for space exploration, including a planned return to the moon for the purpose of eventual human missions to Mars, NASA launched the Lunar Crater Observation and Sensing Satellite and companion Lunar Reconnaissance Orbiter. The 2009 mission was launched to better understand the moon’s topography and composition and search for water ice in the dark shadows of one of the moon’s many craters.

NASA concluded that conditions in large areas of the lunar south pole proved favorable enough to accumulate water ice deposits and accommodate a series of other compounds such as sulfur dioxide, carbon dioxide, formaldehyde, ammonia, methanol, mercury, and sodium, further confirming critical discoveries of the Clementine mission.

Twenty-five years later, Clementine continues to inspire the quest for answers to our closest celestial body and serves as a benchmark for innovative lunar exploration and beyond. The mission offered many benefits to the U.S. space program—including its primary military mission to qualify lightweight technology—and returned valuable lunar data for the international civilian scientific community that exceeded mission science objectives. Its scientific observations have built the most comprehensive lunar multispectral geological map to date, demonstrating near-autonomous spacecraft operations and providing a pathway for reduced flight operations costs on many future DoD/NASA space collaborations.

Triptych of lunar images taken by Clementine satellite. To create this triptych, images taken individually by Clementine in 1994 were composed by NRL's Technical Information Division. Credit: NRL.
Triptych of lunar images taken by Clementine satellite. To create this triptych, images taken individually by Clementine in 1994 were composed by NRL's Technical Information Division. Credit: NRL.

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