IT was 4:17 p.m. EDT July 20, 1969, and there were ``a bunch of guys about to turn blue'' in the Manned Spacecraft Center's Mission Control room near Houston, as one of them put it.
Lunar Excursion Module (LEM) Eagle, with astronauts Neil Armstrong and Edwin Aldrin on board, was overshooting its landing site, and the 120-second cushion its reserve fuel supply allowed was fast running out. Eagle landed 43 seconds later with 20 seconds' worth of fuel to spare. ``We're breathing again,'' mission control reported.
``We literally did [hold our breath],'' recalls Joseph Gavin, the now retired engineer who led the Lunar Module program at Grumman Aerospace Corporation (now part of Northrop Corporation). He adds: ``I always had a great deal of confidence that Armstrong would get it down. [But] as the time went on, the tension grew.''
Thus the grand human adventure of lunar exploration began with a now-famous cliffhanger. Not so well remembered is that the great scientific adventure of revolutionizing our knowledge of the moon began even before Neil Armstrong made humanity's first extraterrestrial footprint.
Mr. Gavin explains that Eagle overshot its target because the automatic- pilot system had a bad map of lunar gravity. The model of lunar structure that planners used was wrong. So the gravity map, which depends on how mass is distributed on the moon, was flawed. The misguided autopilot brought Eagle in too high. Eagle overshot its target by about four miles, and Armstrong had to fly it manually to avoid a field of boulders.
Armed with this knowledge, engineers revised the autopilot instructions. When astronaut Charles Conrad flew the second LEM four months later, he landed ``right on'' target, Gavin says.
Twenty-five years later, it is the revolution in our knowledge of the moon - not the fading memory of moon-walking astronauts - that is Project Apollo's enduring legacy. ``Apollo is not a model for space exploration,'' says space-policy analyst John Logsdon of George Washington University in Washington, D.C. He adds that ``we should not do things that way again.''
President John Kennedy's goal ``of landing a man on the moon and returning him safely to the earth'' within the decade of the 1960s was political. Only after it was decided how to upstage the Soviet Union in a space race was thought given to scientific objectives, Prof. Logsdon notes. He reflects what has become a general consensus among space planners when he explains that governments should first pick the scientific objective, then decide how best to accomplish it. Also, he adds, we should ``do it together'' as an international venture.
Apollo's scientific return has been bountiful, even though it was an afterthought. Seven missions headed for the moon between July 1969 and December 1971. One - Apollo 13 - had to turn back in April 1970 because of a ruptured oxygen tank. The other six returned with 382 kilograms (842 pounds) of material from both the rocky lunar highlands and the smooth lava-covered maria. They left behind robot instrument stations that included seismographs for studying moonquakes. Research using the Apollo samples and data is an ongoing scientific activity.
Maria Zuber - a geophysicist at Johns Hopkins University in Baltimore and the NASA Goddard Space Flight Center in Greenbelt, Md. - says that, for her, two major results stand out. They are new insights into the moon's origin and its early state.
Before Apollo, scientists endlessly debated whether the moon formed elsewhere and was captured by Earth, or formed from material a passing star pulled out of Earth, or whether Earth and moon formed simultaneously from the same primordial material. Apollo samples, which showed that Earth and its moon have some similarities in composition and some major differences, narrowed the options.
The moon, for example, has relatively little iron and hydrogen, indicating it didn't form from the same primordial material as did Earth. Adding it up, most lunar scientists now opt for a fourth theory. They believe it likely that an object the size of Mars struck the early Earth, knocking loose substantial parts of the outer layers of both bodies. This material then formed the moon. That's major insight No. 1, Dr. Zuber says.
Insight No. 2 is a theory unknown before Apollo. The mix of minerals in the moon samples and the surface structures on the moon strongly suggest that the early moon was covered by a thick layer of molten material. It would have been what geologists call a magma ocean created by the intense heating of the moon-forming impact.
Reviewing Apollo's scientific legacy in the current issue of Scientific American magazine, geologist G. Jeffrey Taylor of the University of Hawaii in Honolulu notes that scientists are using this previously unknown concept of an early magma ocean to explain features of other planets. ``It is changing the way scientists look at the evolution and early history of the solar system,'' he writes.
Apollo-based studies have confirmed that the moon has very little, if any, water. They have dated rocks of both the highlands and the lowlands, which has given insight into the nature of those surface areas and of the underlying lunar mantle.
The lunar surface has an area as large as North and South America combined. The six Apollo landings and several Soviet robot probes have sampled only an area about the size of the North American Midwest. Scientists want more information about the whole moon. And earlier this year, a small United States Department of Defense ballistic-missile-defense test-satellite called Clementine 1 gave it to them.
Launched Jan. 25, the $55-million, 220-kg (485-lb) craft sent back 1.6 million images during a two-month mapping period beginning Feb. 21. These provide the first detailed topographic map of the entire moon. They also provide information that geologists will use to construct a mineralogical map.
The National Aeronautics and Space Administration (NASA) put up no funds for the mission. But it did provide tracking. NASA-supported scientists such as Maria Zuber are working with the data.
IT will take a year or more to work up that data. However, Zuber says, a quick look shows that the height difference between high and low lunar topography is 40 percent greater than expected - a total surprise. She explains that this suggests the moon cooled more quickly than has been supposed in order to preserve such rugged topography. Also, she says there are hints that the moon may have fluid material somewhere in its interior. And a trivia item - the moon's radius is 2 kilometers smaller than previously listed.
These early findings show there still is much scientists don't know about the moon and its history, Zuber says. But the prospect for more moon missions is uncertain. Space planners agree that Clementine represents a low-cost, highly effective exploration technology. But with the wind-down of missile-defense research, that technology is an orphan. Policy-analyst John Logsdon says that ``whether or not there will be a Clementine 2 is a hot issue.''
Meanwhile, Japan is the only space-faring nation with an authorized lunar exploration project. The Japanese Space Activities Commission has approved plans to launch a lunar orbiting spacecraft in 1996. This follows a successful three-year test mission with the Hiten spacecraft launched Jan. 24, 1990. Hiten placed a test satellite - Hagoromo - in lunar orbit March 18, 1990. Hiten itself later entered lunar orbit and crash-landed on the moon April 10, 1993. Although the probes did little lunar research, they thoroughly tested relevant space-flight technology.
Europe also has lunar ambitions. The European Space Agency is drawing up detailed plans for a program that would begin with an unmanned lunar probe. It hopes to win approval for this initial step. Then both Europe and Japan anticipate evolving programs that would lead to manned lunar exploration. But in the US, any such planning isn't even on the back burner.
Noting this, Mr. Logsdon observes: ``At the time of the Apollo anniversary, it is ironic that Europe and Japan are talking about [lunar exploration] and the [US] military [not NASA] went off and did it.''