Clementine – The Mission, Twenty Years Later

Clementine lifts off SLC-4W at Vandenberg AFB, January 25, 1994.

In the twenty years following the end of the Apollo program, the lunar science community tried to interest NASA in sending a robotic orbiter to the Moon to map its shape, composition and other physical properties.  Such a mission would not only document the processes and history of the Moon, but would also serve as an operational template for the exploration of other airless planetary objects through the collection of global remote sensing data and use of surface samples to provide ground truth.  The Lunar Polar Orbiter mission was proposed several times but never received a new start.  Its last incarnation was the Jet Propulsion Laboratory’s Lunar Observer, patterned after the ill-fated Mars Observer.  The non-advocate cost review of Lunar Observer came in at around $1 billion (1990 dollars).  Needless to say, it was passed over yet again.

Grandiose notions of ambitious human missions to Mars were advocated while NASA reeled from a series of mission failures and disasters, including the failed deployment of the Galileo spacecraft antenna, the mysterious disappearance of the Mars Observer spacecraft before orbit insertion, and the embarrassing fiasco of the Hubble Space Telescope, launched into space with an out-of-focus imaging mirror.  It was around this juncture that a panel was assembled to report to the White House on how to implement President George H.W. Bush’s Space Exploration Initiative (SEI).  I was a member of this Synthesis Group, led by astronaut Tom Stafford.  Although SEI never stood a chance, many friendships were formed among Synthesis Group participants and we continued to network long after the group had disbanded.

Dr. Stewart “Stu” Nozette of Lawrence Livermore National Laboratory was a Synthesis Group member and was involved in the Brilliant Pebbles (BP) program of the Strategic Defense Initiative.  The idea behind BP was to defend against ballistic missiles by launching swarms of small, inexpensive satellites, each capable of observing, calculating and plotting an intercept course to incoming missiles (the “brilliant”) and then rendering them inoperative by collision (the “pebble”).  These small, three-axis stabilized vehicles carried imaging sensors (both active and passive), in-flight computers and propulsion systems.  In short, they were small but fully capable spacecraft.

Stu’s idea was to fly a BP to some distant target in space.  Because he had an interest in using space resources, he devised a mission that would fly by an asteroid and possibly orbit the Moon.  Stu and I discussed these ideas and it seemed to me that a fairly significant mission might be built around these small spacecraft.  My colleague Dr. Eugene Shoemaker of the U. S. Geological Survey was brought into the mission study early in its planning.  Gene, a legend in planetary science circles and a member of the National Academy of Sciences, was actively researching asteroids and had done the original geological mapping of the Moon before Apollo.  His interest and involvement with the mission brought both prestige and credibility to the idea.

An agreement between NASA and the Strategic Defense Initiative Organization (SDIO) specified that NASA would provide the science team and the tracking support for the flight, and that SDIO would provide the sensors, spacecraft and launch.  The sensors had been developed at Livermore as part of the BP program, while the Naval Research Laboratory designed and built the spacecraft – later named Clementine.  Launch would be on a surplus Air Force Titan II rocket (the same vehicle used to launch the two-man Gemini missions in the 1960s).  Because the Titan II pad at the Cape had been dismantled, launch would be from Vandenberg Air Force Base near Lompoc, California.

Artistic rendition of Clementine in flight. Door opens onto sensor deck; communications antenna at bottom. The overall length of the spacecraft was about 1.5 meters.

The Clementine spacecraft would orbit the Moon for two months, map its color in 11 wavelengths in the ultraviolet, visible and near-infrared, measure its shape from laser ranging, and take other measurements as possible.  After this phase, Clementine would leave lunar orbit and fly by the near-Earth asteroid Geographos.  Program Manager Col. Pedro Rustan was a skilled, tough engineer who kept us to deadlines.  Stu became his deputy, coordinating many different activities, ranging from the science objectives, to spacecraft fabrication and testing.  The Science Team, twelve lunar scientists with varied expertise, was selected from individual proposals submitted to NASA; Gene was named the Team Leader and I was his deputy.  The assembled science, NRL and Livermore teams worked together planning mission operations.  The Science Team carefully selected filters for the imaging systems to allow us to identify lunar rock types in the color images.

The Clementine mission was remarkable for its short development cycle and cost.  Twenty-two months elapsed from project start to launch; typical NASA planetary missions took from 3 to 4 years.  In FY 1992 dollars, NRL spent about $60 million for the spacecraft and mission control center.  Livermore spent about $40 million on support services and on the production of the mission sensors.  The Titan II launch vehicle and services were supplied by the Air Force (valued at about $20 million), with an additional $10 million or so for avionics upgrades.  The NASA Science Team cost a couple million, and the Deep Space Network support was a few million more.  Totaling those numbers, I estimate that the mission cost about $140 million ($540 million in today’s dollars); for comparison, the then-recently lost JPL Mars Observer mission cost a bit over $800 million (over $2 billion in 2014 dollars).

Those cost numbers caused considerable controversy, with some in the scientific community whining that the massive “Star Wars” (SDI) program absorbed and hid much of Clementine’s cost.  In fact, the whole point of Brilliant Pebbles was to adapt cheap, rugged tactical sensors to deep space use and thus take advantage of the cost savings provided by mass production (as opposed to the custom builds of most space systems).  Moreover, there was nothing to stop NASA from using this same technology, other than a not-invented-here mindset and the still-prevalent tendency in the space science community to gold-plate scientific payloads.

The Clementine mission demonstrated the value of the so-called Faster-Better-Cheaper (FBC) paradigm.  The concept is not that cheap missions are inherently “better” but that by carefully restricting mission objectives to only the most essential information, we can fly smaller but capable missions that return 80-90% of the most critical data.  Sometimes resources are squandered attempting to achieve the last 10% of performance.  Maybe FBC should be renamed Faster-Cheaper-Good Enough.  The broad success of NASA’s Discovery program over the last 20 years (in which mission objectives are carefully defined and limited so as to control overall cost) is testament to the validity of the FBC concept.  In addition to its scientific return, Clementine flight-tested and qualified 22 new spacecraft technologies, including solid-state data recorders, nickel-hydrogen batteries, lightweight components, and low mass, low-shock, non-explosive release devices.  All of these technologies have been employed on dozens of subsequent missions, making many of these spacecraft lighter, more reliable and longer-lived.

On the morning of January 25 1994, less than 2 years after project start, members of Clementine’s team stood together on a cold, windy California beach, just a couple of miles from SLC-4W.  We watched the Clementine Titan II rise above a cloud of orange smoke and flame, arcing into the clear blue Pacific sky.  We followed its progress all the way through staging before losing sight of the vehicle.  I left Vandenberg excited about the mission ahead but my mood quickly changed with news from Science Operations Manager Trevor Sorensen that we were in danger of losing the spacecraft (erroneous commands had been sent to Clementine and the spacecraft was out of control).  Fortunately, we recovered from this particular disaster.  Things were not as fortunate for Clementine later on.^*

The “Batcave”, Clementine mission control center, in Alexandria VA

Working inside the Batcave (our mission control center, set up in a converted Alexandria VA National Guard armory), we waited for the first images from lunar orbit.  Designed to save fuel, Clementine had taken a month-long, leisurely looping trip to the Moon, arriving on February 19^th.  When the first image finally flashed on the screen, I immediately recognized the crater and just as quickly, forgot its name!  Quickly consulting the wall map, it was apparent we were looking at Nansen, a crater near the north pole.  At that moment, I had a strong personal sense of “presence” at the Moon – I was flying across a landscape as familiar to me as any on Earth.

Clementine images of the crater Tycho. At left is a map of the 1 micron absorption, the middle image is a false-color composite and the image at right is “true” color. The features evident on the crater floor appear related to the sheet of impact melt rock that lines the crater.

The mission became a regular series of work cycles, arranged around the collection and down-linking of data, verifying that it was good, and making initial scientific observations.  A couple of incidents in particular stand out.  One evening I noticed that the next orbit would pass over Tycho, the largest rayed crater on the near side of the Moon.  I alerted everyone in the Batcave’s Control Room that something incredible was about to appear.  Heads turned and audible gasps were heard when spectacular images of the floor and central peak of Tycho flashed on the big screen.  Another evening, Dave Smith, a science team member from NASA-Goddard, asked how much polar flattening I would expect for the Moon.  I said “almost none” – mainly because of the slow rotation rate of the Moon (once every 708 hours).  As the orbital ground tracks slowly marched westward across the far side of the Moon, we saw an astonishing falling off of topographic relief toward the south pole.  This relief was the rim and floor of the huge South Pole-Aitken basin (an impact crater over 2600 km across and more than 12 km deep).  Geologists had long known about this basin, but until Clementine mapped its topography, no one had fully appreciated its enormity and state of preservation.

Stu Nozette had an inspiration midway through the orbital mapping campaign when Clementine shifted the perilune (low point) of its polar orbit from 30° south to 30° north latitude.  Although Clementine did not carry any sensors for detecting water, we could improvise an experiment using the spacecraft’s radio transmitter to “look into” the dark areas near the poles, where water ice might exist.  Radio echoes from the Moon could be detected on the giant radio antenna dish at Goldstone in California’s Mojave Desert.  With some careful planning and commanding of the spacecraft by Radio Engineer Chris Lichtenberg, we successfully took bistatic radio frequency (RF) data of both poles during those phasing orbits.  Analysis would take many months but that experiment (something we had not considered in pre-mission planning) was a huge bonus.

The Batcave welcomed several distinguished visitors during the two months that Clementine orbited the Moon, including Astronauts John Young (a familiar face to members of the Synthesis Group and always a friend of lunar science) and Wubbo Ockels (a Dutch physicist at the European Space Agency).  Wubbo, encouraged by Clementine’s success, worked to generate enthusiasm for small, cheap lunar missions where he worked at ESTEC (the European space center in the Netherlands).  Congressmen Bob Zimmer and Jim Moran were impressed with our operation and pledged their support for future Clementine-like space efforts on the Hill.  Finally, the then-new Administrator of NASA, Dan Goldin visited – distributing lapel pins and offering encouragement to the worker bees.  Not all at NASA were enamored with the mission; some resented the attention it had drawn, particularly with regard to the inevitable comparisons with their own ongoing (and budget overrun) robotic missions.

Press conference on the publication of the Clementine bistatic experiment results in Science, December 1996.  Left to right: Pedro Rustan, Paul Spudis, Stu Nozette, Dwight Duston.

As Clementine finished its global mapping and prepared to leave the Moon, a Science Team press conference was scheduled.  With Clementine, we’d successfully returned to the Moon, made significant discoveries and mapped it globally.  At the last minute, NASA intervened and cancelled the briefing.  Several (mutually exclusive) excuses were given for its cancellation.  It was clear that some in the agency wanted to “keep a lid” on the mission and its success.  But in time, news of the discovery of “the most valuable piece of real estate in the Solar System” was revealed; in 1996, a press conference on the results of the Clementine bistatic experiment was held at the Pentagon to  announce our discovery of ice at the south pole of the Moon.  At the urging of the lunar science community, NASA agreed to fund a research program to use the abundant new lunar data acquired by Clementine.

The Clementine mission was highly influential and significant to a degree largely unrecognized today.  I expand on this notion in a companion post at the Once and Future Moon blog (Air and Space magazine), where I discuss the scientific and space-faring legacy of the mission.

^* The spacecraft was lost shortly after it left the Moon on its way to the near-Earth asteroid Geographos when firing thrusters became stuck, spinning Clementine out of control and eventually draining its batteries.  The spacecraft flew by the Earth and went into an orbit around the Sun, where it currently resides.