NASA - National Aeronautics and Space Administration

Chapter 9
1991 Edition

Apollo Continues

NASA selected a veteran space pilot, Charles "Pete" Conrad, to command Apollo 12, the second lunar landing attempt. Richard Gordon became the command module pilot, and Alan Bean filled out the crew as lunar module pilot. Bean had not previously flown in space.

The crew took up residence at KSC in mid-August 1969 for final preflight training. Prior to the crew's arrival at KSC, the launch team had worked on the rocket and the spacecraft. The first of the rocket stages had arrived March 9, six days after the Apollo 9 launch, Ascent and descent stages of "Intrepid," as the all-Navy crew dubbed the lunar module, arrived later that month. So did the command and service modules, named "Yankee Clipper."

With September came a change in KSC management. Petrone left the launch director's post to become the Apollo Program director at NASA Headquarters in Washington. His deputy, Walter J. Kapryan, succeeded him.

Apollo 12 rolled out of the Vehicle Assembly Building en route to the pad at daybreak on Sept. 8. The launch countdown had begun at 8 a.m. Nov. 7, and the clock had started at T minus 108 hours. The astronauts passed their final physicals on Nov. 10.

A problem developed at T minus 40 hours. One of two hydrogen tanks in Yankee Clipper's service module failed to chill down when the extremely cold liquid propellant was pumped aboard. Tanking continued until both tanks were 90 percent full. The quantity in tank number 2 continued to drop and frost formed on the outer shell.

This was interpreted to indicate either that the inner shell was leaking, allowing hydrogen to flow between the shells, or that a leak had occurred in the outer shell. The decision was made to remove the suspect tank and replace it with a tank from Apollo 13. Technicians worked around the clock to make the substitution and the countdown proceeded. The launch team also installed a small atomic generator fueled by plutonium238 which would provide power for the experiments the crew would leave on the lunar surface.

The crew entered Apollo 12 on the morning of Nov. 14. The weather had turned unpleasant during the night and rain fell intermittently. Dark clouds moved northeasterly across the launch site. Launch Director Kapryan kept in close touch with the KSC weather station, whose readings were supplemented by two aircraft flying through and just above the clouds over the spaceport. No lightning was reported. Heavy rain fell about an hour before launch. President and Mrs. Richard Nixon arrived 40 minutes before liftoff, joining other observers at a viewing site north of the Vehicle Assembly Building. Apollo 12 lifted off precisely on schedule at 11:22 a.m. EST.

At the 36-second mark into the flight, spectators saw two flashes of lightning streak to the ground on either side of the launch tower. Conrad reported: "We just lost the platform. I don't know what happened here. We had everything in the world drop out..."

Conrad was referring to the inertial platform that is the heart of the Saturn V navigation, guidance and control system. Apollo 12 never faltered. Kapryan later compared the power outage to a fuse blowout in a home, saying it protected vital electronic instrumentation from power overloads. The crew re-established the inertial platform and soon had power flowing in all systems.

Later, it was theorized that the vehicle plus its long flaming tail acted like a lightning rod, triggering static electricity in the cloud cover into lightning bolts.

After this incident, the mission became a textbook flight. On Nov. 19, having separated from Yankee Clipper, Intrepid entered a looping orbit which carried it down to the Ocean of Storms, landing within 600 feet (183 meters) of Surveyor 3, an unmanned lunar spacecraft, which had landed on the Moon two years before.

In all, Conrad and Bean spent 7 hours, 45 minutes working on the Moon, setting up scientific experiments, collecting lunar samples and pieces from the Surveyor, and photographing their landing craft and other objects of interest. They lifted off in the Intrepid ascent stage at 9:25 a.m., Nov. 20, and rendezvoused with the Yankee Clipper piloted by Dick Gordon. Clipper splashed down in the South Pacific at 3:58 p.m. on Nov. 24.

After quarantine the crew's first stop was KSC. When they returned Dec. 17, over 8,000 spaceport employees gathered inside the VAB to welcome them "home."

"The crew didn't consider the flight over until we got back here," Conrad told them, adding, "I'd just like to tell you, you all did a hell of a job for us."

World interest in the lunar landing program waned after the routine and highly successful Apollo 12 mission. It was dramatically rekindled by the plight of Apollo 13.

For the Apollo 13 mission, NASA selected space veteran James A. Lovell Jr., as commander, Thomas K. Mattingly II, command module pilot, and Fred W. Haise Jr., lunar module pilot. Mattingly and Haise would be making their debuts in space.

KSC began preparations for the mission in June 1969, when the first launch vehicle stage arrived. The astronauts named the command service module "Odyssey" and the lunar module "Aquarius." Their target on the Moon was Fra Mauro, a hilly area of major interest to scientists.

The rocket with the spacecraft atop was moved to Pad A in December 1969. From the beginning, the mission seemed jinxed. On March 25, 1970, the last day of the countdown demonstration test, a strange accident occurred. A large quantity of liquid oxygen used to chill down the liquid oxygen pumping system on the booster stage was emptied into a drainage ditch outside the pad perimeter fence-a routine procedure during tests.

Normally, ocean breezes dissipate the oxygen. However, on this morning there was a pronounced temperature inversion and no wind. A dense oxygen fog built up in the drainage ditch and overflowed onto a nearby roadway. A three-car security team, which had cleared the pad area, had stopped nearby. When one of the guards turned his ignition on, he heard a loud pop and flames sprang from beneath his hood. In rapid succession, the other two cars burst into flames. The three guards ran for cover. It was nearly an hour before the oxygen cloud dissipated and the fire could be brought under control.

The incident, which left three burned-out cars and a shaken security team, proved once again that ground operations were as fraught with unknown dangers as flying in space. KSC officials took immediate steps to eliminate the problem by changing operational and safety procedures and extending the liquid oxygen drainage pipes beyond the perimeter ditch into a marshy area further from the pad.

Another problem that arose during the testing appeared insignificant at the time but, in fact, was the beginning of what were to prove Apollo 13's most nerve-wracking hours. The number 2 liquid oxygen tank in the service module, one of two liquid oxygen tanks that feed the fuel cells which supply electrical power and life support systems on the Apollo, failed to empty completely during repeated tests. Only by energizing the tank's heater and venting the tank were crews able to empty its contents.

The problem was thought to be a loose filler tube in the tank. Replacement of the tank, however, would take two days and posed the possibility of damaging other vital equipment. Moreover, a loose filler tube would not threaten the mission since it had no effect on the flow of oxygen to the fuel cells.

After studying the problem, Apollo officials at KSC, Houston, Washington and the manufacturer's plant in Downey, Calif., decided to keep the defective tank. On April 5, the final countdown to launch was initiated. Two days later, the Apollo 13 jinx struck the flight crew.

Astronaut Charles M. Duke, Jr., a member of the backup crew, became ill with the German measles, or rubella. John Young and John L. Swigert Jr., who trained with him, had been exposed to possible contagion, as had the prime crew. Following tests, Dr. Berry announced that Lovell and Haise showed immunity to rubella, but Mattingly did not. Swigert, the backup command module pilot, was also immune.

NASA reviewed the alternatives. Delaying the launch would be costly. On April 10, it was announced that Swigert would replace Mattingly because it would be unwise to risk the possibility that the command module pilot might develop measles during the mission, particularly when he would pilot Odyssey around the Moon alone while his crewmates were on the lunar surface.

The terminal count began at 4:13 a.m., April 11. Liftoff occurred on schedule at 2:13 p.m. During the ascent phase, the center engine of the Saturn V's second stage cut off more than two minutes early, and, to compensate, the remaining four engines were burned 34 seconds longer than planned. As a further remedy, the engine of the third stage was fired an extra nine seconds during its orbital insertion burn.

Despite these minor problems, the early events of the flight proceeded with gratifying smoothness. Fifty-five hours into the mission, the crew entered the lunar module Aquarius. A telecast from space followed, lasting about 30 minutes. Then, disaster struck. All three astronauts heard a long bang. Swigert felt the spacecraft vibrate. Within two seconds, the master alarm sounded.

Mission Control was stunned by the terse words flowing over the radio link. "... Houston, we've got a problem here!" said the voice from space.

The nature and dimensions of the problem quickly became evident to the crew and Mission Control. Liquid oxygen tank 2 in the service module -- the tank found defective during ground tests -- had exploded, wiping out the fuel cells that supplied life-sustaining oxygen and electrical power for the command and service modules. There was a backup battery-powered electric supply in the spacecraft, but, under ideal circumstances, it had a lifetime of only 10 hours.

Lovell and his crewmates were nearly 240,000 miles (386,243 kilometers) out in space and 87 hours from home. The service module, including the main propulsion engine which was needed to get them out of lunar orbit and on the way home, was dead. The command module's 10-hour battery supply had to be reserved for the approach to the Earth's atmosphere, for the command ship alone carried the vital shield and parachutes for safe re-entry and splashdown.

Now that the mother ship was a partial wreck, the crew's hope for salvation rested with the life support systems of the lunar module--the spiderlike craft designed to accommodate just two astronauts, not three. Still linked to its crippled parent, Aquarius had to become a lifeboat in space.

Two major activities dominated the remainder of the mission: planning and conducting the mandatory propulsion maneuvers, utilizing the lunar module's descent engine substitute for the defunct service module engine; and managing the vital resources--oxygen, water, electricity, and the canisters of lithium hydroxide used to remove carbon dioxide from the cabin atmosphere--in the two spacecraft. Open communication lines between KSC and Mission Control in Houston carried advice and test requirements. The two Centers simulated the various maneuvers and conservation measures before directions were given to the flight crew.

A KSC team devised a means of recharging the command module's re-entry batteries from the lunar module's electrical system. Another KSC recommendation turned off the radar heaters to save electricity. Rockwell and Grumman engineers at KSC helped devise ways to transfer water from the portable life support systems designed for lunar surface activity into the lunar module's water coolant system.

One of the biggest problems was the removal of carbon dioxide from crowded Aquarius. KSC engineers, again duplicating activities at Houston, rigged a system that carried carbon dioxide-rich air from the lunar module through a hose into the command module's lithium hydroxide canisters. When the flight crew duplicated the procedure, carbon dioxide in the cabin immediately returned to tolerable levels.

The lunar module's descent engines performed beyond expectations, looping the two spacecraft around the Moon and into a trajectory that would bring them back to Earth 30 hours earlier than expected, and to the original target area in the South Pacific.

During the hectic voyage home, the astronauts lived in Aquarius, preferring its cramped confines to the chilly 52 degrees Fahrenheit (11 degrees Celsius) of the powerless command module Odyssey. Respect for the lunar module increased among ground and flight crews alike as its systems, designed to support two crew members, continued to sustain the three-man crew well past its two-day mission expectancy.

On April 17, the crew re-entered the command module and switched on its batteries, employing a phased power-up sequence to conserve electricity. Four and a half hours before re-entry, they jettisoned the service module and maneuvered their spacecraft to photograph the service module's condition. An entire panel of the service module housing had been ripped off by the explosion. An hour and a half from re-entry, the crew jettisoned their lunar module lifeboat. Mission Control radioed, "Farewell Aquarius, and we thank you."

Lovell added, "She was a good ship."

Odyssey re-entered the Earth's atmosphere 142 hours, 40 minutes and 47 seconds after the flight began, splashing down at 1:08 p.m. EST, 3.5 miles (5.6 kilometers) from the recovery ship.

NASA Administrator Dr. Thomas O. Paine ordered a Board of Review to look into the causes of the mishap and recommend corrective actions. After an inquiry, the board found that two thermostatic switches, which controlled electrical feed to heaters in the service module's number 2 oxygen tank, probably welded permanently in a closed position when activated during the countdown demonstration test at KSC in March. Switch failure was blamed on a change of manufacturer specifications in voltage to the switch-a change which somehow went unnoted over a period of time. Because of the inoperative switch, temperature and pressure rose in the tank when activated during flight; wiring insulation apparently ignited and more pressure was created. The result was a fire and rupturing of the tank. The review board recommended that all potential ignition sources a combustible materials be removed from oxygen tanks in the future. These precautions were taken before Apollo 14 left Earth.

When the Apollo 13 flight crew returned to KSC to speak to some 7,000 employees in the VAB, they presented the Center with an armrest from Aquarius as a permanent token of appreciation. It had been removed from the lunar module before the module was jettisoned.

Astronaut Lovell told the assemblage, "We're proud to come back today and tell you, 'thank you.' I think the mission matured the space program a little, because people were perhaps getting a bit complacent about what we do."

The crew for Apollo 14 was announced in August 1969. America's first astronaut, Alan B. Shepard Jr., was named commander of the flight.

His crewmates would be Lunar Module Pilot Edgar D. Mitchell and Command Module Pilot Stuart A. Roosa. Both had joined NASA in 1966 and were experienced research pilots. It would be the first trip into space for both.

The launch was first targeted for October 1970, with the Littrow region of the Moon as the destination. Apollo 13's difficulties, however, forced changes in the flight plan as well as modifications to the spacecraft. The launch was postponed, first to December 1970 and then to Jan. 31, 1971--the 13th anniversary of the launch of the first U.S. satellite, Explorer 1. The rugged Fra Mauro highlands, Apollo 13's intended target, became the crew's new destination.

While the astronauts devoted their time to rigorous training, launch crews at KSC modified the spacecraft modules, checked them out, and tested and assembled the Saturn V stages. A Saturn V rocket had more than three million parts. Of particular concern to KSC engineers was the center engine of the rocket's second stage. During Apollo 13's flight, the second stage had experienced severe oscillations, known as the pogo effect, forcing an early shutdown of the center engine. Although the stage's remaining engines had burned longer to compensate for the loss, NASA officials did not want any more pogo. Engineers made several changes in the stage's engine systems to dampen the oscillations. including a cutoff device to shut down the center engine in case the other changes failed to correct the problem.

Apollo 14 was moved from the Vehicle Assembly Building to the launch site on Nov. 9, 1 970. The countdown proceeded uneventfully until the sky clouded over and rain fell. Two aircraft carried instrumentation which measured electrical fields in the clouds and fed data into the Launch Control Center. Launch Director Walter Kapryan, following procedures established after the Apollo 12 lightning incident, called a hold around eight minutes before ignition to await more favorable weather. It was the first time an Apollo launch had been delayed. When the aircraft indicated danger from lightning had passed, Kapryan resumed the count. Apollo 14 lifted off at 4:03 p.m. EST, less than an hour behind schedule.

Three and a half days later the crew prepared for lunar descent. This was accomplished through a maneuver quite different from that executed by either Apollo 11 or 12. For those missions, the command ship ventured no closer than 70 miles (113 kilometers) from the surface and the lunar module separated at that altitude to begin the descent. The hilly terrain of Fra Mauro called for a steeper descent for the Apollo 14 lunar module, "Antares." The command service module, "Kitty Hawk," therefore approached the Moon within 10 miles (16 kilometers).

Antares landed on a slope of 18 degrees, just 87 feet (27 meters) north of the chosen site. The touchdown occurred at 4:18 a.m. EST on Feb. 5. After rest and preparations, the two men opened the hatch, climbed down to the surface and set up the Apollo Lunar Surface Experiments Package (ALSEP). The crew deployed a two-wheeled cart and began collecting samples, with Shepard describing the terrain samples.

Before entering the lunar lander, Shepard caught the world -- and Houston -- by surprise. He produced three golf balls from his pressure suit and, using the handle of a geological tool as the driver, swung at the balls. He missed the first but sent the others soaring above the terrain.

"There it goes," he commented, "miles and miles and miles."

Actually, Shepard estimated later, the first ball went about 200 yards (183 meters) and the second 400 yards (366 meters).

Apollo 14's splashdown marked the completion of the world's 40th manned space flight, the 24th flight for the United States. It restored public confidence in Apollo-Saturn equipment.

The 12-day Apollo 15 mission was designed to increase knowledge of the Moon's history and composition, plus the evolution and dynamic interaction of the Sun-Earth system.

NASA selected David Scott to command the expedition. Scott was command module pilot on the Apollo 9 mission in March 1969. His crew included Command Module Pilot Alfred M. Worden, and Lunar Module Pilot James S. Irwin.

A unique Moon vehicle, officially designated the lunar roving vehicle, but informally called the "rover," was to be used for the first time on this mission. It was fabricated by Boeing under contract to the Marshall Space Flight Center.

The rover was 10 feet, 2 inches (310 centimeters) long. Two 36-volt batteries powered tiny motors which drove each wheel. The vehicle folded into a compact unit mounted on the side of the lunar module for the trip to the Moon.

The crew set up residence at KSC in March 1971. Checkout and training for the rover had to be fitted into the schedule for the first time. A trainer vehicle equipped with tires in lieu of the mesh-type wheels of the Moon buggy was provided for familiarization driving. KSC built a traverse route, promptly dubbed "Rover Racetrack," adjacent to the lunar surface training site. During a demonstration for the press, a few reporters tried their hand with the rover trainer, guiding the vehicle through the astronauts' crater-pocked sandpile. Their enthusiastic response carried over into next day's newspapers.

The crew named the Apollo command ship the "Endeavor," and the lunar module "Falcon." Target area for the mission was the rim of the canyonlike Hadley Rille in the Apennine Peaks, one of the highest lunar mountain ranges.

Beginning with Apollo 15, lunar landing missions became longer and more complex. Modifications to the spacecraft and crew support systems allowed the astronauts to double their stay time on the lunar surface. The weight devoted to lunar surface experiments also doubled. The new requirements placed a burden on KSC spacecraft and rocket engineers, especially in the area of scheduling. As one engineer commented, "... every time we powered up the ship for a major test, somebody would come down with a special requirement for their instrument."

The Apollo service module, which supplied propulsion, electrical power and environmental support for the crew, became a scientific platform as well. KSC spacecraft engineers installed experiments in a new scientific instrument bay added to the module. The gear included several kinds of cameras, a laser altimeter, spectrometers and a small satellite which would be ejected in lunar orbit. The latter could relay information on the Earth's magnetosphere and its interaction with the Moon, the solar wind, and the lunar gravity fields. These experiments were controlled by Worden as he flew Endeavor while his crewmates explored the lunar surface.

Apollo 15 rolled out to the pad on May 11. In the weeks that followed, launch crews faced an old nemesis--lightning. During the flight readiness test in June, lightning struck the mobile service structure and mobile launcher, knocking out some ground support equipment. Schedules had to be revised to permit retesting of all spacecraft systems. Ten days later lightning struck again, with the same results. Damaged electrical components were replaced and spacecraft systems checked once more. During spacecraft propellant loading on July 2, a third strike caused some tests to be repeated. Lightning continued to play havoc with ground crews during final countdown, forcing Kapryan to delay moving the protective service structure from the pad until the evening before launch.

Apollo 15 lifted off precisely at 9:34 a.m. EDT, July 26. Following a routine trip to the Moon, Falcon began powered descent to the lunar surface at 6:04 p.m. EDT, July 30. Twelve minutes and 20 seconds later, Commander Scott reported, "Okay, Houston, Falcon is on the plain at Hadley."

During their lunar stay, the astronauts spent almost as much cumulative time on the Moon's surface as had all six astronauts who preceded them. The rover's performance delighted both the crew and its designers. This new mode of transportation greatly increased the astronaut's area of reconnaissance. Before liftoff, Scott positioned the rover so that its television camera could view the ascent from the surface. As Falcon's ascent stage rose, the familiar strains of the Air Force song were heard over the communications system.

Splashdown occurred Aug. 7 at 4:45 P.M., north of the island of Oahu. The impact was greater than normal because one of the three 84-foot (26-meter) diameter main parachutes failed to open properly; however, the crew was not injured. Unlike previous crews, the Apollo 15 crew was not required to spend time in quarantine.

For Apollo 16, the eighth journey to the Moon, NASA selected the Descartes region as the landing site. The choice offered the first opportunity to explore the lunar highlands, which cover about three-fourths of the lunar surface.

Navy Capt. John Young, who had flown three times in space, was selected as the commander for this mission. Thomas Mattingly, command module pilot, had been scheduled to fly on the Apollo 13 mission, but had been replaced because of exposure to measles. The final crew member was Charles Duke, the lunar module pilot.

KSC's launch team began preparing the Saturn V stages in September 1971, while the lunar, command and service modules underwent combined systems testing. The rover was installed on the descent stage of "Orion," as the crew dubbed the lunar module, in November. The Command/service module was called "Casper."

Rollout occurred Dec. 13, and preparations continued for a March 17, 1972, launch. Then problems cropped up in rapid succession, making the date less certain.

Young and Duke found that their pressure suits did not allow sufficient freedom of movement, requiring modifications and retesting throughout January.

Then, factory technicians in Downey, Calif., discovered that an explosive device used to separate the command/service modules would malfunction under certain conditions. The problem could be corrected, but full-scale testing would be needed to verify the solution. A second and more serious problem cropped up immediately afterward. A fuel tank bladder in Casper's service module was inadvertently overpressurized and had to be replaced. On Jan. 27, Apollo 16 was returned to the Vehicle Assembly Building for the necessary repairs and modifications. It was the first time a flight-ready Saturn V had been removed from the pad. NASA announced a new launch date of April 16.

Working overtime and weekends, the KSC team completed the repairs in less than two weeks. Apollo 16 was returned to the pad Feb. 9. Prime backup crews took part in a simulated flight test Feb. 25, when a subsatellite which would be launched in lunar orbit was installed.

Launch countdown began at 8:30 a.m., April 10. At T minus 5 hours, 51 minutes, a gyroscope in the Saturn's instrument unit shifted abnormally for two seconds. Kapryan requested a detailed analysis. The results indicated that a shift occurring in flight would not adversely affect the mission. Countdown proceeded to liftoff at 12:54 p.m. EST, April 16.

Casper and Orion swung into orbit around the Moon a little more than 74 hours after launch. The lunar module Orion touched down in the Moon's Descartes region 860 feet (262 meters) northwest of the planned destination. Orion rejoined Casper in lunar orbit on April 23.

The crew splashed down in the Pacific at 2:45 p.m. EST, only 0.3 nautical miles (0.6 kilometers) from the planned site.

Apollo began, and Apollo ended.

The sought-after goal of a manned lunar landing had been reached. Apollo 17 was the last mission of the program and the last visit of men to the Moon for an unknown number of years. Understandably, pride was mixed with regret among the employees of aerospace companies and NASA's manned space flight organization.

The landing site for the final mission was Taurus-Littrow, named for the Taurus Mountains and Littrow Crater situated in a mountainous region of the Moon, southeast of the Serenitatis Basin. Three massifs, or rounded hills, surrounded the relatively flat target area. It was one of the most difficult landing approaches of the entire program.

Capt. Eugene Cernan, U.S. Navy, was selected to command the mission. He had flown on Gemini 9 in 1966, and was lunar module pilot on Apollo 10. Geologist Dr. Harrison Schmitt, to be his companion on the Moon, was the first NASA scientist-astronaut assigned to an Apollo mission. Navy Cmdr. Ronald E. Evans, who would also make his debut in space, was chosen as command module pilot.

At sunrise on Aug. 28, 1972, Apollo 17 atop its Saturn V was moved to Pad A.

Launch operations followed the routine established in earlier missions. Minor hardware changes, tailored to the mission's requirements, went smoothly. During pad tests, one scare arose which threatened to postpone the launch for a month. An oxidizer tank in the command module was accidentally overpressurized and it was feared the tank's bladder had been ruptured. Tests showed the bladder intact, and the mission stayed on schedule for an early December launch.

Morale at the spaceport remained generally high despite budget cuts in the space program and a severe reduction in personnel-over 50 percent in Apollo launch operations. For most companies, KSC contracts would continue through the Skylab and Apollo-Soyuz missions. For the 600 members of the Grumman team, however, Apollo 17 would be the last flight for their stepchild, the lunar module. Throughout the lunar landing program, the team had gained an excellent reputation among all personnel at the center. The astronauts lauded their efforts, especially the crewmen of Apollo 13.

The Grumman crew, anxious to assure the Apollo 17 astronauts of their continued support and dedication, posted a large sign at the lunar module working level at the pad. It read: "This may be our last but it will be our best."

NASA Administrator James Fletcher said the slogan "should be the watchword for the entire Apollo team." It was. Morale never became a significant problem--a tribute to effective civil servant and contractor leadership and to the personal pride of the launch team members.

The launch of Apollo 17 was scheduled for 9:53 p.m., Dec. 6, the first nighttime Apollo launch. At T minus 30 seconds, the countdown suddenly slopped. Kapryan explained it to the press later: "At 2 minutes, 47 seconds before ignition, the automatic sequencer failed to provide the command to pressurize the S-IVB (third stage) liquid oxygen tank. Firing room monitors immediately observed this and took steps to perform the pressurization by manual command. At the time cutoff occurred, at 30 seconds, the stage was up to pressure and everything was normal.

"The problem was that since the terminal sequencer did not give the command, the electronic logic circuitry said that it had not happened, and so the computer stopped the count. It did not take very long to determine that we should bypass the command system, pressurize the tank manually, and continue to ignition . . . But we also had to get assurance that all functions which must occur in the last 30 seconds would indeed work properly. We wanted to avoid, at all costs, a cutoff after igniting the five engines of the first stage."

At the Marshall Space Flight Center, engineers ran through the latter phase of the countdown several times, and determined that the bypass would work.

The countdown was finally resumed, and launch occurred at 12:33 a.m., Dec. 7, 1972. The launch could be seen from hundreds of miles away. Observers in Miami', northern Florida, Georgia, and points even farther away reported seeing the plumes of flame as Apollo 17 roared into space.

Apollo 17 entered lunar orbit on Dec. 10. The next day Evans guided "America," as the command/service module was called, to a low point in orbit. Cernan and Schmitt backed away the lunar module, "Challenger." Challenger touched down on the Moon at 1:55 p.m., Dec. 11.

The astronauts explored the lunar surface during three separate excursions, collecting samples and deploying experiments. At the end of their lunar sojourn, the crew uncovered a plaque on the leg of the descent stage of the lunar module that would remain on the Moon. The plaque showed a picture of the world with a view of the Moon between the two hemispheres. It stated: "Here Man completed his first exploration of the Moon, December 1972. May the spirit of peace in which we came be reflected in the lives of all mankind." The plaque was signed by the astronauts and President Nixon.

Challenger lifted off at 5:55 p.m. EST, Dec. 14, and rendezvoused with America. Before leaving lunar orbit, the crew turned on the television camera so that Mission Control could see the dark side of the Moon. Splashdown in the Pacific occurred on schedule at 2:24 p.m., Dec. 19.

What did Apollo accomplish? Scientists consider it an exciting and highly profitable exploration program. So much data was returned by the astronauts and the experiments they planted on the lunar surface that many years of analysis, evaluation and study will be required to fully digest this priceless legacy.

By studying the Moon, we have learned how to go about the business of exploring other planets. Apollo proved that we could apply to another world the methods used to understand our own. Equally important, Apollo brought about better ways of studying Earth. Because of the rarity of lunar samples, techniques were developed to measure extremely small samples, weighing only 0.00003 ounce (0.00085 gram). Also, we can now measure the ages of terrestrial rocks more accurately than before Apollo.

From geology to medicine to architecture, the extraordinary demands of space programs -- Apollo in particular -- spurred innovative efforts that reached into virtually every scientific and technological discipline. How this vast storehouse of new knowledge is used for the benefit of mankind is covered in Chapter 17 of this book.

What matters most about what we have learned from the Moon, in the view of many, is what it tells us about Earth--the "spacecraft" that carries over four billion of us--and the Sun, that great energy source so essential to our survival. From lunar clues as large as mammoth craters and as small as tracks etched by atomic particles into tiny crystals of soil, science is beginning to piece together the history of the solar system.

That understanding, as Apollo 17 astronaut Harrison Schmitt commented, is needed "so that we can start to tackle this long-term -- 50-, 100-, 200-year problem -- the problem of preserving and protecting the environment of Earth."