1969: First Half

Apollo’s successes in the seventh and eighth missions augured well for a manned landing on the moon during 1969. But program executives were not complaisant about even these demonstrations of the command and service modules and the Saturn V. Nor did they exhibit any tendency to depart from a systematic step-by-step plan and to stampede toward a lunar landing earlier than scheduled, although President Kennedy’s deadline year had arrived.

Frank Borman’s Apollo 8 crew in its flight near the moon had met no major obstacles, but the need for trailblazing missions had not lessened. Associate Administrator for Manned Space Flight George Mueller in Washington wrote Center Director Robert Gilruth in Houston after Apollo 8 to remind him, “It is essential that we not rest on our laurels, for we have yet to land on the moon.” Gilruth foresaw few chances for resting. Only three days of the new year had passed when John D. Stevenson, Director of Mission Operations in Washington, projected five Apollo flights for 1969, with launches on 28 February, 17 May, 15 July, 12 September, and 10 December. This schedule was essentially the same race-with-the-decade timetable outlined a year earlier.¹

Schedules and Lingering Worries

NASA had scheduled six missions in 1968 but had found only four necessary (see Chapter 10) (see Chapter 11). The agency could also omit a flight in 1969, if the crew of the G mission listed for 15 July could touch down, stay awhile, and leave the moon safely. The intervals between following launches might then be as long as six months to assimilate more of what had been learned before going on to the next mission. But until the first landing took place, Mueller and his management council still planned to launch a mission every two and a half months.²

NASA Headquarters continued to emphasize schedules, even while worrying lest something be overlooked in meeting the deadline. To avert this possibility, Washington kept adding specialized administrative layers, and Gilruth shortly complained to Mueller that too many Headquarters review teams were investigating one thing or another about the mission.³ In addition to administrative actions, two technical suggestions surfaced at Headquarters. The first, tinged with conservatism, was to land an unmanned lunar module on the moon before a manned vehicle touched down. Mueller told Acting Administrator Thomas Paine that modifying the lander for unmanned flight would take too long and would, in the end, give very little in return for the costs in time and money. The second idea, proposed by Apollo Program Director Samuel Phillips, was to ship the command and service modules to the Cape already assembled and mated, rather than separately. Houston’s Apollo Spacecraft Program Manager George Low informed Phillips it would save time at Kennedy but would add time at Downey. It would also cost an extra million dollars.⁴

Good reasoning lay behind this paradox of both hurrying and holding back. Ever-present desk and wall calendars kept reminding the managers that time was running out, yet they had to guard against another terrible tragedy in the program. Two areas, however, were viewed with satisfaction - program costs and spacecraft weights. Both North American and Grumman were operating within fiscal 1969 financial limits. And, although fire-related changes in the command and service modules had increased the weight significantly, NASA and North American had reversed this trend in the latter half of 1967. In the succeeding months, the command module’s bulk had actually been whittled down. Lunar module weight, however, did not stabilize until mid-1968, and that machine still had some lingering technical troubles.⁵

One of the more exasperating problems was the electrical wiring in LM-3. Kennedy Space Center engineers had complained about the vehicle ever since its arrival in Florida in June 1968. In late January 1969, Low asked Martin L. Raines, reliability and quality assurance chief in Houston, to find out just how bad the wiring was. Raines told the Apollo manager that he had found hundreds of splices in the vehicle, but it could still fly safely. Most of the broken wiring, Raines said, was caused by the low tensile strength of the annealed copper wire. The wiring in LM-4, ticketed for Apollo 10, should cause fewer problems, since a high-strength copper alloy would be used.⁶

Another recurring lander ailment was stress corrosion, or metal cracking. Grumman had no structural failures during testing, but the cracks worried both NASA and contractor engineers. A number of fittings were replaced in LMs 3, 4, and 5; by the end of January 1969, the vehicles for Apollo 9 and 10 were considered ready for launching. If problems arose later, more fittings could be changed on LM-5 as it passed through its testing program.⁷

Operational as well as component problems raised some issues during this period. For example, what would happen to the electrical systems in the spacecraft when the two vehicles docked? Ground tests at Downey and the Cape revealed that there would be little electromagnetic interference. A larger question centered on flying the lunar module after the vehicles separated. About a year before the Apollo 9 mission, astronaut Charles Conrad had commented to Bill Tindall, a leading Houston mission planner, that the lander would be hard to handle when a large amount of the propellant had been used and the descent stage had been dropped off. At a flight program review in October 1968, Phillips asked about the problems of steering the lightweight ascent stage manually. Gilruth directed Warren J. North and Donald C. Cheatham to find out what the difficulties would be. North and Cheatham reported that docking would require precise control but that this and other guidance tasks had been successfully simulated at Bethpage, in Houston, and at Langley.⁸

Perhaps the biggest concern before Apollo 9 was the docking maneuver. A 1972 report revealed that there was little confidence in the docking system in early 1969. At a January program review, Phillips said that problems encountered during probe and drogue testing worried him. On several occasions, when the command module’s extendable probe had nuzzled into the lander’s funnel-shaped drogue, the capture latches had failed to engage. In other tests, they had only partially caught, raising the specter of “jack-knifing” and possible damage to one of the spacecraft, probably the lunar module. Phillips was also concerned that the sharp edges on the probe might scar the drogue when the craft were reeled together and prevent airtight sealing of the 12 latches on the command module docking ring. Low asked his deputy, Kenneth Kleinknecht, to investigate. On 14 January, Kleinknecht and six others^* from the Manned Spacecraft Center went to Downey to see what was being done about correcting 17 known problem areas. North American personnel responded to each criticism to the satisfaction of the team.⁹

Although the spacecraft occupied the center ring of concern, Marshall Space Flight Center focused on a nagging item a little lower in the stack. Borman and his crew aboard Apollo 8 had been grateful when the second (S-II) stage of the Saturn V finished thrusting and dropped away. Although the launch had been neither particularly painful nor dangerous, it had shaken them up and bounced them about. Launch vehicle engineers concluded that the shaking had been a form of pogo, since the pulsing engines had increased the vibrations. The Marshall and Rocketdyne troops pounced on the problem, trying out various fuel-feeding combinations through the propellant valve. Another suggested cure was to increase the pressure to the inlet of the oxidizer pump. Time was too short for tests of this method before the scheduled launch, and there were some objections; but the managers decided to raise the pressure in the propellant tanks a little and hope for the best. The crew on Apollo 9 might very well encounter just as much pogo as the crew of the preceding flight, but that was not enough to delay the launch.¹⁰

A Double Workload

Apollo 9 gave the Kennedy launch preparations team its first opportunity to simulate the launch of a lunar landing mission all the way through liftoff. (Apollo 8, with only the command and service modules aboard, represented just half the spacecraft preparation task.) This time - in addition to checking, stacking, and rechecking the multistage Saturn V - the team had to get two spacecraft ready for flight and launch them. The beehive of activities, employing thousands of persons, grew more frenzied as hardware for several missions began arriving regularly from the factories. For example, before Apollo 8 left its launch pad on 21 December 1968, all the pieces of Apollo 9 and some of the parts for Apollo 10 were already in Florida.

LM-3 arrived from Bethpage in June 1968. By the end of September four altitude chamber tests of the ascent stage had been run, to check the environmental control system and the operation of many components under simulated vacuum conditions of space. During this time, engineers and technicians examining the descent stage found dimples (small depressions formed during welding) in the oxidizer lines. Since the dents were within accepted limits, they caused no problems. Elsewhere, other workers were stacking the S-11 stage on top of the S-IC in the huge Vehicle Assembly Building.¹¹

The ascent and descent stages of the lander were then joined, tested, and taken apart again. When inspectors found cracks in the ascent stage engine, a heavier engine was substituted. The command module and the service module arrived from Downey the first week in October, and the North American Cape team, even with all its experience, had trouble fitting them together. When the attitude-control-thruster quad sets were attached to the service module, a cracked quad was found. While that was being evaluated, the command module and the lunar module were brought together for a docking test. The command module was then moved to the altitude chamber for tests similar to those the lunar module had undergone, and the lander was hauled into a hangar for the installation of such components as the rendezvous radar, antennas, and pyrotechnics. From time to time, the command and service modules, the lunar module, or the launch vehicle were either a few days ahead of or behind the schedule. In mid-December, however, Mueller told Paine that all vehicles were on time.¹²

On 3 January, the big stacked vehicle lumbered on its carrier out of the assembly building and crawled toward Launch Complex 39. While flight simulations, linked with the control center in Houston, and all the normal jobs at the pad - cabin leak checks, electrical power tests, and component operations, among others - were going on, some engineers were working on technical problems that had cropped up during previous missions. One was the fogging spacecraft windows, particularly the round one in the hatch door. Samples of contaminants from CSM-101 and CSM-103 were studied, and the hatch window from 101 was tested by subjecting it to the hot and cold extremes met in space. Some thought a better method for curing the glass might eliminate the fogging, but others, analyzing the residue from thruster firings, were not at all sure that the space environment was the problem. If firings from the reaction control thrusters (which steered the spacecraft) were smudging the windows, there might never be a solution.¹³

As the work progressed, the accumulated information was fed into the management reviews. The certification review, which covered all flight hardware (including suits), was held at NASA Headquarters on 7 January. Flight readiness reviews were later conducted for each of the vehicles - command and service modules, lunar module, and Saturn V - and then confirmed before Apollo Director Phillips. On 28 February, all hardware problems had been solved, all questions answered. Everything was ready for flight - except the pilots. All three astronauts had head colds.^{* 14}

The Mission and the Men

When James McDivitt, David Scott, and Russell Schweickart had received their Apollo flight assignment in late 1968, they were faced with an even more complicated mission than the one they contemplated in early 1969. Inspired by the Gemini VII and VI rendezvous mission in October 1965, when one spacecraft was launched to catch up with another that had been sent into space a dozen days earlier, some NASA officials wanted to use this concept to check out lunar module and command module docking operations in earth orbit. Most Apollo mission planners wanted to avoid the extra tasks required for launching each vehicle on separate Saturn IB boosters, and by 1969 the big Saturn V rocket was all set to boost both spacecraft into earth orbit in a single launch. Although McDivitt and his crew would not have to search for the lunar module in the vastness of space for the rendezvous, this was almost the only thing that made it an easier mission.

From the perspective of early 1969, the manned shakedown cruise of the lunar module, even in earth orbit, was a venturesome journey. The thought of mission commander McDivitt and lunar module pilot Schweickart’s flying away from the command module in this machine, which could not return to earth through the atmospheric shield, was a little frightening. In an emergency, however, command module pilot Scott could steer his ship to a rendezvous with a stricken lunar module. NASA officials hoped this would not be necessary; they wanted a smoothly operating lunar module that could simulate many of the steps in the lunar orbit mission.¹⁵

Flight planners had another key objective for Apollo 9: checking out what might almost be called the third spacecraft in the program (a combination of the extravehicular space suit and the portable life support system - the PLSS, or backpack). As a matter of fact, this was the only flight scheduled for the backpack before the lunar landing mission, making it of prime importance in finding out how the equipment worked in the space environment. The commander and the lunar module pilot, wearing their extravehicular garments, would crawl through the tunnel from the command module into the lunar module. Then Schweickart, after donning the backpack and attaching a nylon-cord tether to his suit, would move through the open front hatch and step out on the porch. Finally, he would use handrails to climb over and crawl into the open command module hatch. Schweickart’s tasks also included collecting experiment samples on the spacecraft exterior and standing in foot restraints (called “golden slippers”) on the lunar module porch to take photographs and operate a television camera.¹⁶

This was a well-seasoned crew. McDivitt, a member of the second group of astronauts, chosen by NASA in September 1962, had been commander of Gemini IV, a trailblazer in its own right. It had included what was then considered long-duration flight, a rendezvous experiment, and a highly successful extravehicular exercise. Scott and Schweickart were members of the trainee group picked in October 1963, and Scott had been a crewman on Gemini VIII when it made the first docking in space. Although Schweickart had not flown a mission, he had participated heavily in the experiments program and in spacesuit testing. For two years the three men had been working as a team. By the time McDivitt’s crew was finally ready for flight, it had spent 7 hours in training for each of the 241 hours it would spend in space. At a news conference, McDivitt quipped that he hoped all this training did not imply that the crewmen were slow learners.¹⁷

Because there would be two craft in simultaneous flight, Apollo 9 revived a practice that had been discarded almost four years earlier - call signs, or names, for spacecraft. Gordon Cooper had encountered trouble selling the name Faith 7 for his Mercury-Atlas 9 craft to NASA officials. If anything happened, they dreaded the thought of the almost inevitable headline: “The United States lost Faith today.” During Gemini, these same leaders had turned down Gus Grissom’s selection of “Molly Brown” for Gemini-Titan 3, which alluded to both the unsinkable characteristics of an American heroine and the loss of his Liberty Bell 7 during Mercury. His second choice, “Titanic,” was equally unwelcome. After that, missions were simply called by the program name and a number: Gemini IV, Apollo 7. But a single designation, such as “Apollo 9,” was no longer enough. Flight control would have to talk to McDivitt and Schweickart in the lunar module, as well as Scott in the command module. McDivitt’s crew named the lander “Spider,” for its long thin legs and buglike body. When North American shipped the command module to Florida, its candy-wrapped appearance and shape suggested the tag, “Gumdrop.”¹⁸

Apollo 9: Earth Orbital trials

For the 19th flight of American astronauts into space, Vice President Spiro T. Agnew, representing the new administration of Richard Nixon, sat in the firing control room viewing area on 3 March 1969. He and other guests listened to the countdown of the tall Saturn-Apollo structure several kilometers away at the edge of the Florida beach. Fully recovered from their stuffy heads and runny noses, McDivitt, Scott, and Schweickart lay in the mixed-atmosphere cabin of CSM-104. Breathing pure oxygen through the suit system, they tried to adjust an inlet valve that seemed to have two temperature ranges - too hot and too cold. That was their only problem. Less than one second after its scheduled 11:00 a.m. EST liftoff time, Apollo 9 rumbled upward.¹⁹

In Houston, where more than 200 newsmen had registered to cover the mission, Flight Director Eugene F. Kranz and Mission Director George H. Hage^* watched the displays on their consoles while McDivitt and CapCom Stuart Roosa called off the events of the launch sequence. There were the usual vibrations but, on the whole, the Saturn V’s S-IC stage gave the crew what McDivitt called "an old lady’s ride" - very smooth. The big surprise came when its five engines stopped thrusting. Feeling as if they were being shoved back to the earth, the astronauts lurched forward, almost into the instrument panel. The S-II second stage engines then cut in and pressed them back into the couches. Everything went well until the seven-minute mark, when the old pogo problem popped up again. Although the oscillations were greater than those of Borman’s flight, McDivitt’s crew lodged no complaints. At 11 minutes 13 seconds from launch, the S-IVB third stage kicked itself and the two spacecraft into orbit 190 kilometers above the earth.²⁰

Upon reaching the orbital station, the trio remembered Borman’s warning against jumping out of the couches too quickly and flitting about in the weightless cabin. The men avoided sudden head turns, made slow deliberate movements, took medication - and still felt dizzy. But they were able to go about their duties, checking instruments and extending the docking probe. After more than a circuit, 2 hours 43 minutes into the mission, Scott lit the pyrotechnics that separated the command and service modules from the S-IVB stage and began one of the critical steps in the lunar-orbit concept. He fired the thrusters and pulled the command ship away, turned the ship around, fired again, and drew near what he called the "big fellow." Then he noticed that the command module’s nose was out of line with the lander’s nose. Scott tried to use a service module thruster to turn left, but that jet was not operating. The crew then flipped some switches, which started the thruster working, and at 3 hours 2 minutes the command module probe nestled into the lunar module drogue, where it was captured and held by the latches.²¹

After docking, McDivitt and Schweickart began preparing for their eventual entry into the lunar module. First, they opened a valve to pressurize the tunnel between the two spacecraft. With Scott reading the checklist aloud, McDivitt and Schweickart removed the command module hatch and checked the 12 latches on the docking ring to verify the seal. Next they connected the electrical umbilical lines that would provide command module power to the lander while the vehicles were docked. McDivitt checked the drogue carefully and found no large scars. Meanwhile, Schweickart glanced out the spacecraft window and failed to see the lunar module in the darkness, which scared him. "Oh, my God!” he exclaimed, "I just looked out the window and the LM wasn’t there.” Scott laughed and said it would be "pretty hard [not to] have a LM out there . . . with Jim in the tunnel.” McDivitt put the hatch back in place until time to transfer into the lander. About an hour later, an ejection mechanism kicked the docked spacecraft away from the S-IVB. Apollo 9 backed away, and the Saturn third stage, after firing twice, headed for solar orbit.²²

McDivitt’s crew then turned to another trailblazing task - firing the service module propulsion system. Astronauts had in the past used one vehicle to push another into higher orbit,^** but never a craft as big as the lander. Some six hours into the mission, they made the first test burn, which lasted five seconds. Flight controllers in Houston considered this the most critical of the docked service module engine firings. Scott must have agreed with them, because he exclaimed, "The LM is still there, by God!” The engine had come on abruptly, McDivitt later said; with the tremendous mass, however, acceleration was very slow - it took the whole 5 seconds to add 11 meters per second to the speed. Sixteen hours after this short burst, a second propulsion system ignition, lasting 110 seconds, included gimbaling (or swiveling) the engine to find out whether the guidance and navigation system’s autopilot could steady the spacecraft. The autopilot stilled the motions within 5 seconds.²³

The crewmen grew more and more confident that they could handle their machines. And that was a good thing, since they next had to make a 280-second burn, to produce an added velocity of 783 meters per second. This lightened the service module’s fuel load by 8,462 kilograms and made it easier to turn the vehicles with the reaction control jets. The firing also altered the flight path and raised the apogee of the orbit from 357 to 509 kilometers, to provide better ground tracking and lighting conditions during the rendezvous. Scott later reported that they had the sensation that the docked vehicles were bending slightly in the tunnel area, but the maneuver produced oscillations only one-third to one-half as large as they had expected from training. As the big engine fired, McDivitt commented, "SPS . . . is no sweat.” The astronauts were growing so used to the propulsion system that they hardly mentioned its fourth burn. Perhaps they were thinking of their next trailblazing chore, when two of them would crawl into the lunar module and check out its systems.²⁴

After they woke in the morning^*** and ate breakfast, McDivitt and Schweickart put on their pressure suits. Schweickart suddenly vomited. Fortunately, he kept his mouth shut until he could reach a bag. Although he did not feel particularly nauseated, both he and McDivitt became slightly disoriented when getting into their suits. For a few seconds, they could not tell up from down, which gave them a queasy feeling. Scott, already dressed, removed the command module hatch, the probe, and the drogue from the tunnel so his colleagues could get into the lunar module. Schweickart slid easily through the 81-centimeter tunnel, opened the lunar module hatch, and went next door in the first intervehicular transfer in space. After he had flipped all the necessary switches, Schweickart reported that the lander was certainly noisy, especially its environmental control system.

McDivitt followed Schweickart into the lunar module an hour later. Within a brief time, a television camera had been unstowed and their activities were being beamed to the earth. Then they shut themselves off from Scott by closing their hatch while he was sealing himself off from Spider. A key event in lunar missions would be the deployment of the landing gear. A second or two after Schweickart pushed the button, the lunar module’s legs sprang smartly into place. After the vehicles separated, the lunar module would flip over so the command module pilot could make sure all four legs were in the proper position.

Then Schweickart was sick again, and McDivitt asked for a private talk with the medical people. Although the news media were quickly informed of Schweickart’s problem, this request for a "private” discussion was like waving a red flag, causing repercussions and a spate of unfriendly stories.^**** On this second occasion, the impulse to vomit came on just as suddenly as as it had earlier, while Schweickart was busy flipping switches. Afterward, he felt much better and moved around the cabin normally, but he had lost his appetite for anything except liquids and fruits for the remainder of the voyage.²⁵

As soon as he was sure the systems were operating properly, McDivitt asked Scott to put the command module into neutral control, so he could check out the lunar module’s steering system. McDivitt then operated the small thrusters to get the docked vehicles into the correct position for firing the lunar module’s throttleable descent propulsion system. Seconds after starting the large descent engine, McDivitt shouted, "Look at that [attitude] ball; my God, we hardly have any errors.” Twenty-six seconds later, at full thrust, he reported that errors were still practically nonexistent. In fact, things were going so smoothly that halfway through the 371.5-second exercise, the commander felt hungry - not an uncommon sensation with him. So he ate before crawling back into the command module. Schweickart stayed behind to shut everything down and straighten up the cabin before joining the others in Gumdrop. The lander appeared to be a dependable machine.²⁶

After Schweickart had vomited on two occasions, McDivitt was doubtful that the lunar module pilot would be able to handle his chores outside the spacecraft. The commander recommended to flight control that this exercise be limited to cabin depressurization. Flight control agreed that the extravehicular activity would consist of one daylight period, with Schweickart wearing the portable life support system and the lunar module umbilical hoses,^# and with both the lunar module and command module hatches open. On the fourth day of flight, working his way into the lander to get it ready, Schweickart felt livelier than he had expected. By the time he had put on the backpack, McDivitt was ready to let him do more - to stand on the porch at least. Flight control told the commander to use his own judgment. So McDivitt fastened Schweickart to the nylon-cord tether that would keep him from floating away from the spacecraft.²⁷

Once Schweickart had entered this "third spacecraft,” to become essentially a self-contained unit, flight control ran a communications check with PLSS, as they first called him. The four-way conversation - between Spider, Gumdrop, PLSS, and the Houston control center - was much clearer than they had expected. Lunar module depressurization also went smoothly. Schweickart could tell that his backpack was operating, since he could hear water gurgling while he watched his pressure indicator. He was quite comfortable. McDivitt had to use more force than he had anticipated to turn the hatch latch handle and more strength to swing the hatch inside. He was very careful to keep the door pushed back, fearing it might stick closed, leaving Schweickart outside.²⁸

Once the lunar module hatch was opened, Scott pushed the command module hatch outward. Schweickart, who now called himself Red Rover because of his rust-colored hair, enjoyed the view and did so well outside on the platform in the golden slippers that McDivitt decided to let him try out the handrails. Hanging on with one hand as he moved about, he took photographs and found that the handholds made everything easier than it had been in simulation, even in underwater training. He did not go over and visit Scott in the command module, but both pilots retrieved experiment samples from the spacecraft hulls. Scott and Schweickart also took pictures of each other, like tourists in a strange country. Originally scheduled to last more than two hours, the extravehicular period ended in less than one, partly because they did not want to tire Schweickart after his illness and partly because they had plenty to do to get ready for the next day’s pathfinding activity, the key event of the entire mission: the separation and rendezvous of the lunar module and the command module. With the door closed and their life-sustaining outside equipment off, McDivitt and Schweickart recharged the backpack, tidied up the cabin, and returned to the command module.²⁹

On both occasions when they had transferred to the lander, the pilots had been behind the schedule. On 7 March, they got up an hour earlier than usual. They also obtained permission from flight control to move into the lunar module without helmets and oxygen hoses, which made it easier to go through the checklist and to set up the module for the coming maneuvers. Soon both spacecraft were ready. When Scott tried to release the lunar module, however, it hung on the capture latches. He punched the button again and the lander dropped away. McDivitt watched the widening distance between the two craft. Spider then made a 90-degree pitch and a 360-degree yaw maneuver, so Scott could see its legs.³⁰

After drifting around within 4 kilometers of the command module for 45 minutes, McDivitt fired the lunar module’s descent propulsion engine to increase the distance to nearly 23 kilometers. The motor was smooth until it achieved 10-percent thrust. When McDivitt advanced the throttle to 20 percent, the engine chugged noisily. McDivitt stopped throttling and waited. Within seconds, the chugging stopped. He accelerated to 40 percent before shutting down and had no more problems. McDivitt and Schweickart checked the systems and fired the descent engine again, to a 10-percent throttle setting; this time it ran evenly. As they moved off in a nearly circular orbit 23 kilometers above the command module, they had no trouble seeing Gumdrop, even after the distance stretched to 90 kilometers. From the command module, Scott could spot the lander as far away as 160 kilometers with the help of a sextant. Estimating distances was difficult, but the radar furnished accurate figures.

This new orbit, higher than that of the command ship, created the paradox associated with orbital mechanics of speeding up to go slow. Being higher above the earth (i.e., farther out from it) than the command module, the lander took longer to circle the globe. Spider gradually moved away, trailing 185 kilometers behind Gumdrop. To begin the rendezvous, McDivitt and Schweickart flipped their craft over and fired the thrusters against the flight path to slow their speed enough to drop below the command module’s orbital path. Below and behind the command module, they would begin to catch up. They fired the pyrotechnics to dump the descent stage and leave it behind. The firing produced a cloud of debris and caused their blinking tracking light to fail. McDivitt commented that staging was "sort of a kick in the fanny . . . but it went all right."³¹ The distance between the lander and the command module soon shortened to 124 kilometers. McDivitt blipped the ascent engine for three seconds to circularize their orbit and begin a chase that would last for more than two hours. As the gap between the two craft narrowed, McDivitt spotted a very small Gumdrop at 75 kilometers.

About an hour after the ascent engine firing, McDivitt and Schweickart lit off their spacecraft’s thrusters. "It looks like the Fourth of July,” McDivitt commented, and Scott responded that he could see them very clearly. When the thrusters stopped, however, Spider, without its tracking light, was hard for Scott to spot. At that point, remembering the problem they had breaking away, McDivitt told Scott to make sure the command module was ready for docking. As he approached the other craft, the commander turned his machine in all directions so Scott could inspect its exterior. More than six hours after leaving the command module, McDivitt settled the lander firmly back into place and then reported, "I have capture.” The 12 latches on the docking ring caught the lunar module and held it fast. Another stretch of the trail to the moon had been blazed. The lunar module could leave the command module, find its way back to it, and dock safely.³²

Even before crawling back into the command module, McDivitt said he was tired and ready for a three-day holiday. Another 140 hours would pass before touchdown in the Atlantic, but the crew had achieved more than 90 percent of the mission objectives. There were still things to do, such as making more service module engine burns (a total of eight throughout the flight) and jettisoning the ascent stage. Ground control radioed a firing signal to park the lunar module in a 6,965- by 235-kilometer orbit. The crew watched the departing craft a while and then settled down to the more mundane tasks of checking systems, conducting navigation sightings, and taking pictures.³³

After 151 revolutions in 10 days, 1 hour, and 1 minute, Apollo 9 splashed safely down in the Atlantic, northeast of Puerto Rico, on 13 March 1969, completing a 6-million-kilometer flight that had cost an estimated $340 million. Less than an hour later, the crew was deposited, by helicopter, aboard the carrier U.S.S. Guadalcanal. Then the debriefings and celebrations began. At a ceremony in Washington, with an address by Vice President Agnew, lunar module development leaders Carroll Bolender of the Manned Spacecraft Center and Llewellyn Evans of Grumman were given the NASA Exceptional Service Medal and NASA Public Service Award, respectively. NASA officials were stimulated by the path-breaking voyage of Apollo 9. They were now ready for the final rehearsal, a mission that would take Apollo back to the vicinity of the moon.³⁴

Setting the Stage

From a technical standpoint, Apollo 10 could have landed on the moon. It probably would have - with some offloading of fuel to shed a little weight - had the flight been scheduled for the last few weeks of the decade. There were, however, good reasons for waiting until the next mission for a landing. Only two lunar modules had flown, and both those flights had been in earth orbit. NASA managers wanted to see how the lander’s guidance and navigation system would behave in the moon’s uneven gravity fields while the craft was within rescue range of the command module. Further, helium ingestion, which had caused Spider’s descent engines to chug, would have to be investigated before a lunar module landed on the moon. Flight control also wanted a chance to review operation, tracking, and communications procedures of both vehicles while they were actually in the vicinity of the moon. The crews and controllers had been through many simulations, but it would take a real mission to give them the confidence they needed. Apollo 10 was to be a dress rehearsal, complete with a cast that included a lunar module capable of a lunar landing.³⁵

The basics of the mission plan had been conceived in the spring of 1967. When, the next autumn, Low and his men outlined the alphabetical sequence of the route to the moon, Apollo 10 was assigned the “F” role, a lunar-orbit flight with all components. Toward the end of 1968, the mission planning and trajectory analysis people in Houston, led by John Mayer, Tindall, and Carl Huss (all veterans dating back to Mercury), buckled down to work out the refinements.

One feature was a two-phase lunar-orbit insertion maneuver introduced on Apollo 8. The vehicle would begin the first revolution of the moon in an egg-shaped orbit, to avoid an unsafe pericynthion (known in earth orbit as a perigee - that is, the lowest point). If the service module engine fired too long and slowed the speed too much on the first burn, that part of the circuit must not be so low that the spacecraft would crash into the lunar surface. On Borman’s mission the engine had fired for an excess of almost five seconds. On the next burn, to circularize the orbit, the duration of the firing was adjusted to keep the craft a safe distance above the moon. “Weren’t we smart?” Tindall asked his colleagues, when this became a standing procedure for Apollo 10 and the lunar landing missions that followed.

As first planned, the lunar module on Apollo 10 would simply pull away from the command module and return for rendezvous and docking; but in December 1968 Tindall and the mission planners began campaigning to put the descent propulsion system through a real test down near the surface, where the landing radar could be fully checked. Moreover, they plotted the path so the lunar module crew could fly close enough to look for landmarks and take pictures of the site selected for the first landing. Tindall wanted them to go even farther - almost to touchdown - and then to fire the ascent engine to get back to the command module in a hurry, as though there had been an emergency. He had a fair hearing, he later said, but the mission planners did not think they had enough experience in the lunar environment to attempt this maneuver on the lander’s first moon flight. Tindall reluctantly agreed. And there were many more procedures to be decided on and worked out before the flight plan became “final” in April 1969.³⁶

When LM-4 arrived in Florida during October 1968 (the descent stage on the 11th and the ascent stage on the 15th), the Kennedy Space Center inspection team led by Joseph M. Bobik found it was a much better machine than LM-3; they had very little to grumble about. NASA was also quite satisfied with CSM-106^* and with North American’s performance in its checkout and delivery to the Cape on 25 November 1968.³⁷

Although the contractors had shipped excellent spacecraft, preparations at Kennedy did not go lickety-split from the assembly building to the launch pad. Staying out of the way of Apollo 9 preflight activities delayed testing several days. And during maintenance to the Launch Control Center, the electrical power was cut off to replace a valve. The Apollo 10 launch vehicle’s pneumatic controls sensed the power cutoff, opened some valves (the normal failure mode for these components), and dumped 20,000 liters of fuel (RP-1 - similar to kerosene) on the pad. Besides losing the propellant, the fuel tank bulkhead buckled. Technicians applied extra pressure to the tank, which removed all but a few wrinkles. Later the vehicle preparation team lowered a man inside to inspect the tank; he could find no further damage. Tests of the stage through the first week in May 1969 revealed no loss of structural integrity.³⁸

Actually, neither spacecraft nor booster preparations held up the launch a single day, although adjustments in the launch date for other reasons probably helped the hardware teams to maintain schedules. On 10 January, NASA changed the anticipated sendoff from 1 to 17 May to fit the lunar launch window (optimum position of the moon in relation to earth for this mission) and to provide more time for crew training. Then on 17 March Phillips postponed the liftoff till the second day of the launch window (to 18 May), so the crew could get a better look at candidate landing sites.³⁹

LM-4 and CSM-106 went through their flight readiness reviews on the same day, 11 April, with very nearly the same men passing on the lunar module in the morning and the command and service modules in the afternoon. During the lander review, a suggestion was made that the descent engine’s chugging during McDivitt’s flight might have been a form of pogo, but Low told Phillips that Faget’s engineers had found no such indication. On 16 May, Phillips assured Mueller that all hardware would be ready for the mission two days later.⁴⁰

On 13 November 1968, NASA had announced that the prime crew for Apollo 10 would be Thomas Stafford, John Young, and Eugene Cernan, with Gordon Cooper, Donn Eisele, and Edgar Mitchell as backups, and Joseph Engle, James Irwin, and Charles Duke as the support team. Coming from understudy roles on Apollo 7 in the leap-frogging crew selection methods that had evolved during Gemini, the Stafford group was the first all-veteran crew sent into space by the Americans.^** Stafford had flown two missions (Gemini VI and IX), Young two (Gemini III and X), and Cernan one (Gemini IX).

The Apollo 10 crew had about 5 hours of formal training for each of the 192 hours it would spend on the lunar-orbital trip. Completely satisfied with the training program (“down to the nth degree,” as Stafford later said), the crew was especially pleased with the time spent in the simulators. Putting Stafford and Cernan in the lunar module simulator and Young in the command module trainer and then linking them with mission control provided situations remarkably like those faced during actual missions. They had four or five such sessions in the Houston simulators. When they arrived at the Cape, they would practice rendezvous maneuvers in no other way. During the more than 300 hours each man spent in the simulators, other tasks - such as reentry, launch abort, transearth injection, and translunar injection - were also studied. That this was a veteran crew was readily apparent in later remarks about such training aids as planetariums (Cernan said they had been looking at the stars for five years) and the centrifuge (Stafford said he had not been in one since Gemini III).⁴¹

Stafford’s crew picked its flight patch in March. The patch displayed two craft flying above the lunar surface, with a Roman numeral X and the earth in the background. The astronauts also selected their call-signs, “Charlie Brown” for the command module and “Snoopy”^*** for the lander. Julian Scheer, NASA’s public affairs administrator, greeted these nicknames, as well as those of Spider and Gumdrop for Apollo 9, with raised eyebrows. He wrote Low that something a little more dignified should be picked for Apollo 11, the mission scheduled for the first lunar landing.⁴²

Apollo 10: The Dress Rehearsal

On 18 May 1969, a king,^* some congressmen, other distinguished guests, and a hundred thousand other watchers waited at scattered vantage points around the Cape area. At 49 minutes past noon, Rocco Petrone’s launch team sent Apollo 10 on its way to America’s second manned rendezvous with the moon. Humming along at first like a Titan II, or so its Gemini-experienced crewmen felt, the gigantic Saturn V first stage suddenly slammed Stafford, Cernan, and Young forward and backward, until the cabin dials blurred before their eyes. Stafford tried to tell chief Flight Director Glynn Lunney’s mission control team when the first stage of the vehicle dropped off but he could not squeeze the words out. When the remainder of the stack steadied, the S-II second stage (already firing) had the same pogo tendencies. The three astronauts had begun to wonder if the vehicles would hold together, especially the lunar module below them, when the S-IVB third stage fired, growling, rumbling, and vibrating as it shot into earth orbit.⁴³

During the systems review period, the ride smoothed. Lunney checked the men at the monitors in the control room and they all voted to fire for translunar injection. Stafford’s crewmen considered not wearing their helmets and gloves but “chickened out,” as Young phrased it, and put them on. They probably found the extra garb comforting when the S-IVB fired, because the third stage again groaned and shook. None of the three were confident of being able to continue the trip much longer, and Cernan wondered how the mission could be safely aborted at this point in space. The guidance system kept Apollo 10 on a steady course, however, and they were on their way.⁴⁴

When Young pulled the command module away from the S-IVB, the crew saw the panels that had housed the lunar module drift away. After the command module was flipped around, it was 45 meters away from the third stage, about three times farther than intended, but it would take only a little extra gas to get back for docking. As the CM moved around, the mission controllers on the ground watched the maneuvers, in “living color.”

Television had worked so well on other Apollo flights that NASA had decided to put a color system on Stafford’s command module. Weighing only 5.5 kilograms, the Westinghouse camera included a 7.5-centimeter monitor to show the astronauts what they were transmitting. Now flight controllers watched along with the crew as Charlie Brown, perfectly aligned with his target, pulled up to Snoopy, latched onto him, and drew him out of his doghouse. Shortly thereafter, with signals to Houston through the big antenna dish at Goldstone, California, a vast populace saw a color view of a large portion of their western hemisphere from thousands of kilometers in space.⁴⁵

After checking tunnel, latches, and docking probe, the crewmen had a light workload as they coasted toward the moon. They were grateful for even such small jobs as firing the thrusters to make slight corrections in spacecraft attitude, but this was so seldom necessary they began to wonder if the jets were working. On occasion, however, when nothing was firing, the whole stack shimmied. They later speculated that this may have been caused by fuel sloshing. When making optical navigational sightings, the crew had trouble acquiring enough stars for an accurate reading. Without the optics, the men could see no stars at all for a long time. Finally, Stafford spotted a few dim orbs after he had traveled 190,000 kilometers into space. But not much navigating was needed; the course was so true that the service module propulsion system was used only once, to add 15 meters per second to their speed, at 26 hours into the voyage. This firing put the spacecraft on a lunar path that would lead the crew over the exact spot where the first landing might be made. The rest of the time the astronauts studied the flight plan, slept, ate, and beamed five excellent television transmissions back to the earth.⁴⁶

Stafford, Cernan, and Young were the first Apollo pilots to be free from illness during the mission, although Cernan experienced a slight vestibular disturbance. Like all their colleagues who had flown before, once they unbuckled from the couches they had a stuffy feeling in their heads. This lasted for 8 to 10 hours for Stafford and Young; Cernan gradually lost the sensation over the next two days. He practiced “cardinal head movements” that the medics thought might help overcome his slight feeling of nausea. Although he was able to do the exercise for more than four minutes at a session by the seventh day of flight, when he returned to earth he lambasted the procedure, saying it must have been designed to bring on illness rather than to alleviate it.⁴⁷

The crew slept well, although thruster firing bothered Cernan the first night. Later, when they were circling the moon, the men were glad that McDivitt’s crew had suggested they carry a sleeping bag apiece. The spacecraft grew cold once the windows had been covered to darken the cabin for sleeping.

One major complaint the astronauts registered was about their water supply. They were supposed to chlorinate it at night; because of an error in procedures passed to them by flight control, Stafford had a double dose of chlorine when he took a drink during the first breakfast of the trip. This was unpleasant, but it posed no major problem. Something else in the water supply did. When earlier crews had complained about gas in the water system, a new water bag was designed, with a handle the crew could use to whirl the bag around to separate the gas from the water. It did not work. The gas settled to the bottom of the bag and then remixed with the water when the crew members tried to drink. The gas worried them; they could envision getting diarrhea, which would have been difficult to cope with during flight. They did have gas pains and cramps but, fortunately, nothing more.⁴⁸

Poor water quality may have affected their appetites, for the astronauts on this flight were not big eaters. On occasion, they skipped meals. Stafford estimated they had enough food to last for 30 days. Not all the blame could be laid on the water, however; the food was still no epicurean delight. Back on earth in early May, Donald D. Arabian, chief of the Apollo Test Division, had tried a four-day supply of their rations. Arabian claimed to be “somewhat of a human garbage can,” but even he lost his desire for food on this diet. The sausage patties, for example, tasted like granulated rubber and left an unpleasant taste. With all the difficulties of preparation, Arabian added, by the third day continuing the test was a chore. He did like the items that were closest to normal table foods. Stafford’s crew also found some of the newer dishes that could be eaten with a spoon quite palatable. But the men dreaded reconstituting the dehydrated meals, knowing that the water contained so much gas.⁴⁹

Unlike Borman’s crew, which could not see the moon with the unaided eye until the spacecraft was almost upon it, Stafford’s group spotted it on the second day of flight. On the earth, it looked like a waxing crescent, but Stafford and Young, with the help of earthshine, could see almost a full moon. Although the moon was much bigger at 200,000 kilometers above the earth, landmarks on the lunar surface still could not be picked out. Cernan also asked flight controllers if they thought he could really recognize the S-IVB stage 5,600 kilometers away, because that was what he thought he was seeing. The CapCom told him that the men in the control room were nodding their heads yes and that the distance between the two vehicles actually measured 7,400 kilometers.⁵⁰

When Apollo 10 reached the lunar vicinity on 21 May, the controllers informed the crewmen that at one time or another more than a billion persons had watched their televised activities. But interest now focused on the exact moment when their craft would shoot around the moon and lose communications with the earth. At 74 hours 45 minutes into the mission, flight control predicted that loss of signal would come at 75 hours, 48 minutes, 24 seconds. The controllers had already determined that the ship would reach the moon 11 minutes later than scheduled, since there had been only one midcourse correction, rather than two. Its trajectory would be 110 kilometers above the lunar surface.⁵¹

The crew was impressed by the lunar landscape, although Stafford insisted it looked like a big plaster of Paris cast. The three found it almost incredible that someone back on earth had been smart enough to place them within 110 kilometers of the moon - but there they were. They caught just a glimpse of the surface a minute before they fired the service module engine to go into lunar orbit, an activity that required all their attention. The six-minute retrograde maneuver seemed interminable, just as it had to Borman’s group, but the engine kept firing and their confidence in it kept growing. When the engine finally shut down and they were sure that it had done its job, Stafford and Cernan had time to look at the lunar surface. They likened one area to a volcanic site in Arizona. Finally Stafford forced his attention back inside the cabin and told his crewmates that he thought the best thing to say when they got back in radio contact was, “Houston, tell the earth we have arrived.”⁵²

Stafford, Young, and Cernan were fascinated by how much more slowly they seemed to travel around the moon than they had around the earth. They liked the slower pace, because on the first circuit they would pass directly over the area where Apollo 11 was due to land two months later. They had barely rounded the corner before Stafford and Cernan began describing the physical features down the highway they called “U.S. 1,” leading to the landing site. By the third circuit, the world was sharing the view on color television. Watchers could see the gray, white, black, and brownish tints of the landing site, which seemed to be free from boulders, providing a smooth landing field.⁵³

Six hours after reaching the moon, Cernan and Stafford began getting the lander ready. The hatches, probe, and drogue were easily removed. As he entered the lunar module, Cernan was greeted by a snowstorm of mylar insulation, apparently sucked into the vehicle through a vent from the tunnel. The insulating material had come loose in the tunnel, and the crewmen had spent some time capturing and cleaning it up in the command module. Now they had the same job to do in the lunar module.

Cernan had floated head down through the tunnel into the lunar module. Because the two spacecraft were locked together from top to top, his own private world had a new orientation. He later commented that the best way to handle this psychologically was to slide through the hatch, look around, and then mentally assign an arbitrary up and down. Once he had accepted the new environment, he had no problems in checking, hauling in equipment, and getting things in order. The crew had intended to leave the passageway to the lander open after returning to the command ship, but the hardware was too bulky. It was simpler, and quite easy, to put the probe and drogue back into place.⁵⁴

Flight control had planned to let the crew sleep until the last moment on 22 May, when Stafford and Cernan would leave Young and fly the lander down near the lunar surface. But, after playing “The Best Is Yet to Come” and sounding reveille, ground control found that the astronauts had stealthily risen, eaten breakfast, and quietly begun work on the flight plan checklist. Cernan removed the encumbrances from the tunnel and zipped over into the lunar module to get everything ready, while Young helped Stafford with his suit (a five-minute job even with assistance).^** Cernan then came floating back into the command module and jumped into his suit. When flight control heard from them at the start of the tenth circuit, the two pilots were in the lander and closing off the tunnel.⁵⁵

When Stafford and Cernan were ready for undocking, however, they found that the lunar module had slipped three and a half degrees out of line with the command module at the latching point, possibly because of loose mylar collecting on the docking ring. It might also have happened when Young, during docking, had forgotten to turn off the service module roll thrusters and flight control had been tardy in reminding him of the task. Whatever caused the problem, the crew feared separating the two craft might shear off some of the latching pins, possibly preventing redocking. Stafford and Cernan would be stranded in lunar orbit with no way back except by going out the lander hatch and making their way to the command module hatch - a dangerous undertaking. But Low, who was in the control room at the time, told Flight Director Lunney that as long as the misalignment was less than six degrees they could go ahead and undock.⁵⁶

Just before Apollo 10 rounded the corner to the back of the moon, flight control passed the good news to Stafford. The two crewmen in LM Snoopy heard a “pow” as they broke free. Young, all alone in what now seemed to be an unusually large command module, turned on the television camera so the flight controllers back on the earth could help him inspect the lander. Meanwhile the lunar module landing gear had deployed and was in place. The lander’s systems checked out well, especially the radar, the abort guidance system, the antennas, and the pressurization of the descent propulsion system. Everything looked good, and everybody was ready to go. Telling Young not to get too lonesome and not to go off and leave them, Stafford and Cernan announced that they were ready to go down and snoop around the moon.⁵⁷

Young had used his service module thrusters to pull Charlie Brown nine meters away from the lunar module for the inspection. He then gave the same jets a spurt to thrust downward toward the moon until the two vehicles were three and a half kilometers apart. Stafford and Cernan were ready to try, for the first time, another of the operations with a significant Apollo abbreviation so cherished by the engineers - descent orbit insertion, or DOI. At nearly 100 hours into the mission, Stafford started the descent engine at minimum thrust - which slowly built up past 10 percent - and then 15 seconds later he increased it to 40 percent for 12 more seconds. The engine ran smoothly, with none of the chugging experienced on McDivitt’s ride. Young tracked the burn optically and told the lunar module crewmen that they were moving away from him at more than 20 meters a second. Cernan did not think they were going that fast. “It’s a very nice pleasant pace,” he said. Now they could get a close look at a proposed landing site in the Sea of Tranquility, where Apollo 11 might set down in July.⁵⁸ Stafford and Cernan had studied hard for what they were going to do. In a T-38 aircraft, they had simulated this trajectory above the earth. They had pored over charts and maps of the site, and they had scrutinized the area during their hours in lunar orbit. So the astronauts traveled easily down the approach path, calling out the names of craters, rilles, and ridges as they went along. They appeared to be traveling exactly over the track they wanted, reaching a low point of 14,447 meters above the surface. They took many pictures; then Stafford’s camera failed as the film started to bind. He described the landing site as much like “the desert in California around Blythe.” If a lander touched down on the near end, it would have a smooth landing, he said; but, if it wound up at the far end of the zone, extra fuel would be needed for maneuvering to a clear spot. Their landing radar worked perfectly when they tested it, and the pilots remarked that they had no visibility problems with lighting and sun angles.⁵⁹

Young caught sight of the lunar module at a distance of 120 kilometers; Snoopy appeared to be running across the lunar surface like a spider. At other times, using a sextant, he spotted the craft as far away as 550 kilometers. An hour after the first descent burn, Stafford and Cernan fired the engine again, to shape the trajectory for their return to the command module. Shoving the throttle forward for 40 seconds and 100 percent thrust, Stafford was happy to note that there was still no chugging. Young tried to see the flames from the engine but could not. Although the lander’s speed had increased by 54 meters per second, the crew again had the impression that acceleration was slow. During these activities, the lunar module had a “hot [open] mike,” which was fine with Young, since it kept him informed of what was happening in the lander. But whenever he talked, he had a feedback of his own voice. Somebody would have to fix that before the next mission, he said.⁶⁰

After Stafford’s camera failed, he and Cernan had little to do except look at the scenery until time to dump the descent stage. Stafford had the vehicle in the right attitude 10 minutes early. Cernan asked, “You ready?” Then he suddenly exclaimed, “Son of a bitch!” Snoopy seemed to be throwing a fit, lurching wildly about. He later said it was like flying an Immelmann turn in an aircraft, a combination of pitch and yaw. Stafford yelled that they were in gimbal lock - that the engine had swiveled over to a stop and stuck - and they almost were. He called out for Cernan to thrust forward. Stafford then hit the switch to get rid of the descent stage and realized they were 30 degrees off from their previous attitude. The lunar module continued its crazy gyrations across the lunar sky, and a warning light indicated that the inertial measuring unit really was about to reach its limits and go into gimbal lock. Stafford then took over in manual control, made a big pitch maneuver, and started working the attitude control switches. Snoopy finally calmed down.⁶¹

For this first lunar module flight to the vicinity of the moon, the pilots were supposed to use the abort guidance system instead of the primary guidance system, to test performance in the lunar environment. The abort system had two basic control modes, “attitude hold” and “automatic.” In automatic, the computer would take over the guidance and start looking for the command module, which was certainly not what the crew wanted to do just then. In correcting for a minor yaw-rate-gyro disturbance, the pilots had accidentally switched the spacecraft to the automatic mode, and the frantic gyrations resulted. From Cernan’s startled ejaculation to Stafford’s report that everything was under control took only three minutes. Flight control told the crewmen they had made an error in switching, but the system was fine. They could fire the ascent engine. After the firing, the lander flew what Stafford called a “Dutch roll,” yawing and pitching and snaking along. When the engine shut down, however, to the crew’s surprise the attitude and flight path to the command module were correct. From a maximum distance of 630 kilometers, the thrust from the ascent engine moved the lunar module to within 78 kilometers of the mother ship.⁶²

As the lunar module approached, Young saw it through his sextant at a distance of 259 kilometers. Stafford and Cernan got a radar lock on the command module shortly after the insertion burn and watched with interest as the instrument measured the dwindling gap between the vehicles and demonstrated the theories of orbital mechanics in actual practice. Cernan especially liked the steady communications that kept both crews aware of what was happening. After watching the command module from as far away as 167 kilometers and then losing sight of it at sunset, the lunar module pilots saw Charlie Brown’s flashing light with their unaided eyes at 78 kilometers. At last, the two craft were only eight meters apart, and the relative speed between them was zero. Stafford did find the ascent stage a little difficult to hold steady, just as Conrad had suspected, but Young slid the probe smoothly into the dead center of the drogue. Stafford rammed the lunar module forward, and the capture latches closed with a loud bang.⁶³

Stafford and Cernan had been gone for more than eight hours, and they were ready to get back into the command module and rest. Transfer ring equipment and closing the tunnel were easy. When all three were settled in, they cut the lander loose. Flight control then fired the ascent engine to fuel depletion (249 seconds) and sent the lunar module into solar orbit. The crew watched it move away; Snoopy was soon out of sight. Stafford and his crew went back to tracking landmarks on the surface below for the upcoming lunar landing mission.⁶⁴

After 31 circuits, the crew fired the service module engine to begin the return to the earth. On 26 May 1969, Apollo 10 streaked through the early morning darkness like a shooting star, to splash down in the Pacific 690 kilometers from Samoa and only 6 kilometers from the prime recovery ship. The journey had taken 192 hours, 3 minutes, 23 seconds. A helicopter picked the crew up and carried them to the U.S.S. Princeton within the hour. This fantastic voyage was over and had revealed absolutely no reason why Apollo 11 could not negotiate the final few kilometers to the lunar surface. The trail had been blazed.⁶⁵