In the annals of space history, few dates are more important than July 1969, when Neil Armstrong and Buzz Aldrin took humanity’s first steps on the Moon. However, their triumphant landing on the Sea of Tranquillity was by no means guaranteed at the dawn of that momentous year. Following the deaths of three astronauts in a launch pad fire, the Apollo spacecraft did not even undertake its first manned test in Earth orbit until October 1968, yet President John F. Kennedy’s goal was met within just nine months. Forty-five years ago this week, the crew of Apollo 10 cleared the final hurdle for the historic landing, bringing their spidery lunar module close to the Moon … and leaving a question on many lips: Why did they not land? In reality, the race with the end of the decade was so close that astronauts Tom Stafford and Gene Cernan might indeed have been the first men to leave their bootprints in ancient lunar dust.
As early as September 1967, NASA outlined a series of seven critical steps, labeled “A” through “G,” to enable the first piloted landing on an alien world. First would come unmanned tests of the Apollo spacecraft (“A” and “B”), followed by manned tests of the command and service module (“C”) and lunar module (“D”) in Earth orbit. Next, an “E” mission would fly into a highly elliptical orbit, with an apogee of 4,000 miles (6,400 km), to demonstrate re-entry systems from close to lunar-return velocities. The “F” voyage—later to become Apollo 10—would then perform a full dress rehearsal in orbit around the Moon and would involve a pair of astronauts descending to within 9 miles (15 km) of the surface, clearing the way for the “G” mission: the landing itself.
Much of this plan changed in August 1968, when the E mission was unofficially cancelled in favour of an audacious new expedition known as “C-prime”: a manned flight into lunar orbit, aboard Apollo 8, to be launched in December … a mere four months away. By the time Frank Borman, Jim Lovell, and Bill Anders returned triumphantly from Apollo 8, only a dozen months remained in which to meet Kennedy’s challenge. The D mission (Apollo 9) went smoothly in March 1969, but as the weeks wore on Gene Cernan began to wonder if his flight, the F mission, might instead be transformed from a dress rehearsal in lunar orbit into a full-blown landing. Tom Stafford, the commander of Apollo 10, had the same thoughts, but unlike Cernan he was decidedly unhappy about them.
Early in 1969, George Mueller, NASA’s head of the Office of Space Flight, hinted strongly that Apollo 10 might make the first lunar landing, but Stafford expressed many reservations. “Tom was not so adamant about being first on the Moon,” wrote Cernan in his autobiography, The Last Man on the Moon. “He never looked at it that way. He wanted to do what was the best thing to do to have a co-ordinated, planned program.” Instead of embracing Mueller’s suggestion, Stafford replied that if Apollo 10 was retasked to perform the landing, “this flight crew won’t be on it.” In Stafford’s mind, there was simply too much work to be done and too many unknowns remained before such an enormous step could be taken.
The main problem was that Apollo 10’s Grumman-built lunar module (“LM-4”) was overweight. Grumman engineers knew that LM-4 was earmarked for either an Earth-orbital or lunar-orbital test flight, rather than a landing, and therefore had not subjected it to their Super Weight Improvement Program. The next lunar module, LM-5, on the other hand, was slated for a first shot at the landing and was significantly lighter. “The option, then, was to postpone Apollo 10 for a couple of months until [LM-5] was ready,” wrote Deke Slayton, the head of Flight Crew Operations. “When you added up what we would gain, as opposed to what we would lose, the decision was pretty easy.” On 24 March 1969, Apollo Program Manager Sam Phillips made the final announcement: The F mission would fly as planned.
Over the years, speculation has been rife that if Apollo 10 had taken place closer to the end of 1969, “adjustments” could have been made to enable LM-4 to accomplish a landing. A little offloading of fuel to shed weight could have helped, but in reality other problems remained which simply had to be resolved. One of these was the phenomenon of “mass concentrations”—”mascons”—which take the form of large positive gravitational anomalies, caused by excess distributions of mass, on or just beneath the lunar surface. Areas of such concentrations included the enormous impact basins of Imbrium, Serenitatis, Crisium, and Orientale, and the effect of mascons upon satellites could be truly profound, even altering their orbits so dramatically as to cause them to crash.
Mascons were first reported in the journal Nature in August 1968 by Jet Propulsion Laboratory (JPL) scientists Paul Muller and William Sjogren, who had studied data from the unmanned Lunar Orbiters. Sometimes, the orbiters diverged from their predicted positions by up to 10 times more than they should have done, and NASA quickly realized the importance of knowing where the mascons were situated and how great an influence they exerted. By the end of the year, using data from three equatorial Lunar Orbiters and two polar ones, it was possible to compile a near-complete gravitational map of the Moon’s near side. Apollo 8 did not carry a lunar module, so its ability to investigate the mascons was somewhat limited, leaving Apollo 10 as the only mission to observe how the spidery lander’s guidance and navigation systems might perform in this situation.
When Stafford, Cernan, and John Young were named as the crew of Apollo 10 in November 1968, NASA described their mission as encompassing a range of options, “from Earth-orbital operations to a lunar orbit flight”. When it became clear that Apollo 8 would perform a flight to the Moon, Apollo 10 began to take shape as either a lunar-orbital voyage or a landing. Early plans called for the lunar module to simply undock and fly in formation with the command and service modules, but trajectory analyst Bill Tindall advocated a more expansive program of tests. He wanted to the lunar module to fly close to the surface—as close as 9 miles (15 km)—to rehearse the approach to the point at which a landing mission would begin its Powered Descent. This would permit an all-up test of the descent engine, the landing radar, and the rendezvous radar. Tindall even proposed a “fire in the hole” ignition of the ascent engine at low altitude to simulate an abortive descent, but on this last point he was overruled, on the grounds that Apollo 10 was already filled with tasks and another would overburden the crew.
Although he would not be landing on the Moon, Cernan remained philosophical. “Our pathfinder role,” he wrote, “meant launching aboard a Saturn V, flying a quarter of a million miles in space and leaving John in Moon orbit, while Tom and I took the lander on a sweeping flight near the lunar surface. No one had ever done that before.” One of Stafford and Cernan’s tasks, during their descent, was to observe the leading candidate landing point for Apollo 11. Known as “Site 2,” it lay close to the Moon’s equator, about 62 miles (100 km) east of the crater Sabine, in the relatively flat Sea of Tranquillity.
Even in the late spring of 1969, riding on the coattails of Apollo 8’s success, many wondered why Stafford, Young, and Cernan could simply not take a chance: After traveling all the way to the Moon, with all the necessary hardware in place, why not land? However, others cautioned that the software and procedures needed as the lunar module descended in a precise, sweeping arc, under the thrust of its throttleable descent engine, had still to be verified. Two years earlier, managers decreed that half a dozen different docking modes had to be demonstrated, ahead of a landing. “So far,” wrote Deke Slayton in his autobiography Deke, co-authored with Michael Cassutt, “we had demonstrated exactly one.” The drive to reach the Moon was already proceeding at break-neck pace and had already been daring accelerated by Apollo 8 and the cancellation of the E mission. To skip another step and attempt a landing so soon was too rash to risk.
One of the lessons carried over from Apollo 9 was the need to impose individual callsigns on the lander and the command and service modules. The choice of “Gumdrop” and “Spider” by the Apollo 9 crew went down like a lead balloon with some NASA managers … until Stafford’s men revealed their selection: “Charlie Brown” for the command and service module and “Snoopy” for the lander! It was not just a bit of fun. For years, NASA had awarded “Snoopy pins” to its staff in recognition of their outstanding work. “The choice of Snoopy was a way of acknowledging the contributions of the hundreds of thousands of people who got us there,” wrote Tom Stafford in his autobiography. “Once you had Snoopy, Charlie Brown couldn’t be far away.”
Originally scheduled to fly on 1 May 1969, Apollo 10 slipped until the 17th in order to best “fit” the lunar launch window and allow additional training time for the astronauts. Another 24-hour delay was effected to allow Stafford and Cernan to benefit from closer levels of sunlight to those Apollo 11 would encounter when they made their low pass over Site 2. The mission would also make history as the Saturn V’s first, and only, liftoff from Pad 39B. (However, the pad was kept in reserve throughout the remainder of the lunar program, lest a disaster wipe out its sister, 39A.) In the weeks preceding Apollo 10, the “newness” of 39B was apparent. As Stafford watched his Saturn V roll out in mid-March, he could not help thinking of the many workers still putting finishing touches to the new pad. As the giant rocket arrived at the launch complex, the paint was barely dry on the umbilical tower. …
Training of the prime crew and their backups—Gordon Cooper, Donn Eisele, and Ed Mitchell—was feverish as launch neared. Not until he was placed into pre-flight quarantine, in early May, could Stafford finally appreciate the enormity of the mission he was about to undertake. On the evening of the 16th, the crews had dinner with Vice President Ted Agnew and James McDonnell, founder of the aerospace giant which had built NASA’s Mercury and Gemini spacecraft. Late on the following afternoon, driving a little too fast back to the Cape Kennedy crew quarters after seeing his family, Cernan was pulled over by a deputy sheriff.
An absence of papers in his car’s glovebox, an iffy-looking military driving licence which, it seemed, never expired and an unlikely-sounding name aroused the officer’s suspicions. Fortunately, a timely intervention by launch pad leader Guenter Wendt saved the day. Sharing a quiet “word” with the disbelieving cop, Wendt finally satisfied him that all was well. No, said Wendt, unfortunately “Mr. Kurnin” could not accompany the officer to the police station, because—motioning toward the distant Saturn V—he had somewhere important to go tomorrow. …
The second part of this four-part article will appear tomorrow.
Missions » Apollo »