Even Moon Landings Need Dress Rehearsals

Last month, amateur British astronomer Nick Howes announced that he will soon take up the hunt for Snoopy – not the cartoon Beagle whose mission will always be to take down the Red Baron in a dogfight, but Apollo 10’s lunar module of the same name. The ascent stage of the spacecraft was sent into orbit around the sun after it had served its purpose, and its thought to still be out there. Armed with his astronomer’s tool kit – namely looking for a moving dot against a background of stars – and a knowledge of the area where Snoopy might be, Howes hopes to recover the lost artifact of the Apollo program. (The Apollo 10 crew pats their mascot on the nose on their way out to the launch pad. 1969.)

Howes might accomplish something else, too: he might reignite interest in one of the most commonly overlooked missions of the Apollo program. Apollo 10 rarely makes an appearance in the history books. More often that not it is mentioned in passing, lumped into the pre-Apollo 11 missions that form the stepping stone to the moon. And so I thought I’d tell its story in a little more detail – and Snoopy’s while I’m at it. This probably won’t be news to anyone who has studied the space program in detail, but for the more casual reader, I hope this illustrates just how interesting the Apollo missions that didn’t land on the moon really were. (Right, Snoopy after the Red Baron gunned him down.)

When the Apollo program began manned flights in 1968, a number of question marks punctuated the journey from Cape Kennedy to the lunar surface. Tensions, too, were high after the loss of the Apollo 1 crew. The command and service module had been largely redesigned, and had yet to be proved. So did the hardware on the lunar module. Both the CSM and LM used specialized software that hadn’t been tested yet. No man had made the trip outside Earth orbit to reach the moon. (Jim Lovell practices using the stars as points against to align the spacecraft on the way to the moon on Apollo 8. One of the many challenges checked off a long list before an attempted landing. 1968.)

In an effort to negate as many unknowns as possible, every Apollo flight leading up to the first landing aimed to take at least one of these unknowns out of the equation. In October of 1968, Apollo 7 thoroughly checked out the CSM in Earth orbit. In December of that year, Apollo 8 took a CSM into orbit around the moon – the LM was unfinished, but the mission did answer question about the software that would guide Apollo to the moon. In March of 1969, Apollo 9 took a full spacecraft – LM and CSM – into Earth orbit. The crew tested each spacecraft and worked out the details of rendezvous between the two vehicles.

All that was left was to take it all to the moon.

But there were still unknowns, questions about how the spacecrafts would behave in lunar orbit. The conditions on and around the moon are just not replicable on Earth. Testing the pieces of the puzzle in Earth orbit wasn’t entirely satisfactory when a manned lunar landing was at stake. (Left, Dave Scott steps out of Apollo 9′s CSM “Gumdrop”. The mission checked many LM/CSM tests off the lunar landing checklist. 1969.)

For one thing, the moon isn’t a uniformly weighted; its mass is more dense in some areas than others. This makes its gravitational pull uneven, and no one was sure how a manned spacecraft would fare close to the surface, or how the programming the engineers had devised for a lunar mission would hold up. If their calculations were wrong, it could be a very bad day for NASA with the loss of a crew around the moon.

The moon lack of atmosphere was also a potentially troubling factor. While this made landing much easier – no atmosphere makes landing significantly easier than landing on a body with a thin atmosphere – it provided the astronauts and their spacecraft with no natural protection from solar flares. It was plausible that some solar phenomena could wipe out a missions communication during a critical mission phase. It wasn’t a situation NASA wanted to run into during the first attempted landing.

The moon’s surface was also presented an unknown. Satellites and landers had given NASA some information about the surface, but the topography was still a bit of a mystery. Only Apollo 8 had been close enough for detailed observations; it orbited the moon just 60 miles from the surface. NASA felt more reconnaissance about the planned landing sites would be indispensable before attempting a landing. Features observed from afar might look different up close, especially if the sun’s angle was different and created oblong and unfamiliar shadows across a landing site. NASA wanted as much information about this alien environment as possible before sending men to its surface. (One of Apollo 10′s images of the Sea of Tranquility. There were multiple points in the area NASA was considering for a landing. Apollo 10′s images helped make the final choice. 1969.)

There was a feeling, too, that the Saturn V could use another shakedown before sending men to land on the moon. Only Apollo 8 had used the titanic rocket to leave Earth’s orbit and there was some concern about its performance. A failure of the rocket at any point would render a lunar mission impossible; another test to make sure it was really up to a lunar flight made a lot of people happier.

There was no better way to test the spacecraft’s programming, observe the planned landing sites, and generally test the whole lunar landing package than with a dry run. This was Apollo 10’s task. It would do a dress rehearsal of a lunar landing, running through every stage of the mission except the one little detail of actually landing on the surface. Getting as many question marks out of the way could only increase the chances of success on the first landing attempt. (The crew pose in front of their Saturn V launch vehicle. 1969.)

On May 18, 1968, Commander Tom Stafford, CM pilot John Young, and LM pilot Gene Cernan lifted off from Cape Kennedy. The Saturn V performed flawlessly. One day after launch, the crew had extracted the LM and were on their way to the moon. A single midcourse correction burn during the translunar journey put Apollo 10 in the exact flight path NASA was planning for Apollo 11. NASA’s attention to detail was astounding. The moon was at the same point in orbit as it would be when Apollo 11 approached the moon that the shadows on the lunar surface were exactly as the next mission would see them.

Three days after launch, Apollo 10 arrived at the moon. A controlled burn of the CSM main engine slowed the spacecraft enough that it entered into orbit 60 miles above the lunar surface. Four days after launch, Stafford and Cernan transferred into the LM, Snoopy. Around the far side of the moon during the twelfth, the LM separated from the CSM, call sign Charlie Brown. They emerged as two separate spacecraft on the other side. (Snoopy and Charlie Brown lent support in mission control throughout Apollo 10′s flight. 1969.)

At this point, the focus shifted to the LM; Charlie Brown stayed in a circular orbit 60 miles above the surface. To simulate a landing, Snoopy entered into a highly elliptical orbit. At it’s furthest it was about 70 miles from the lunar surface. At its closest, it was a only a little over 8 miles from the surface.

The question at this point in the mission – at least by those looking back in retrospect – is why didn’t they just land. And what would have happened if Stafford and Cernan had just decided to go all the way to the surface? The latter was never a likely course of events. NASA’s astronauts were not only well trained, but disciplined in their training. Their mission was a dry run of a landing, and that is what they would do. But had they landed, what would have happened? Death, for one thing, and not a metaphorical death to their careers. Snoopy was well stocked with consumables for the mission, but it was under-fueled. The crew didn’t have enough fuel on board to get back up to and dock with the CM from the lunar surface. (Above, Stafford and Snoopy share a moment.)

On March 13, 1969, Peanuts paid tribute to Apollo 10 with this comic strip featuring Snoopy as an astronaut.

With no possibility of a lunar landing, the eight-mile distance from the surface was a perfect analogue. At this altitude, the LM’s descent radar becomes a reliable guide and a check of the hardware and programming in situ was necessary. This altitude was also far enough from the surface that the CSM could safely descend and rescue the LM if it got into trouble.

But the lunar-orbiting Snoopy didn’t need Charlie Brown’s help. The spacecraft achieved its orbit easily. It passed over one of the possible sites for the first landing to gather radar information and take pictures to help the next crew recognize their intended landing point. The information also had applications in planning later landing profiles. (During one of Apollo 10′s TV transmissions, the crew hold up a picture of Snoopy. 1969.)

Snoopy and Charlie Brown spent only six hours working independently from one another. To simulate lunar orbital rendezvous as closely as possible, the LM crew fired Snoopy’s ascent engine to meet Charlie Brown in orbit. Achieving orbital rendezvous was a vital manoeuvre. If the characteristics differed form an Earth orbital rendezvous, there would be a serious kink in the Apollo program. And a couple of stranded astronauts.

To find John Young in Charlie Brown, Stafford and Cernan relied on Snoopy’s abort guidance system. This was a vital instrument that needed to be tested in lunar orbit to make sure the programming worked away from home – if it didn’t, a new emergency abort measure would be needed for subsequent missions. (Left, Apollo 10′s Snoopy in lunar orbit. 1969.)

As soon as the ascent engine fired, Snoopy began tumbling. The crew exchanged confused profanities as their spacecraft’s radar searched in vain for an absent Charlie Brown. The cause of the problem was later determined to be a mis-set switch. The abort guidance system functioned in two modes – attitude hold and automatic. The latter was not what they crew wanted, it gave control to the computer and had it search for the CSM, but automatic is what they’s got. It took three minutes for the astronauts to regain control, but once they did the crew moved through a textbook lunar orbital rendezvous.

They’d proved the engineering behind a lunar mission was sound. With the crew reunited in the CSM, the LM’s useful life span was over. All that was left was to jettison Snoopy and send it off into the void. The spacecraft had one terminal operation. Mission control remotely fired the ascent engine until its fuel was depleted. The burn lasted 239 seconds. Snoopy gained speed, and Apollo 10 watched as its LM left the moon’s gravity and entered into a heliocentric orbit. (Right, a lighter moment with the Apollo 10 crew who speaks, sees, and hears no evil.)

The crew spent a final day around the moon. For 30 orbits they observed, tracked, and photographed sites on the lunar surface after which they fired the CSM’s main engine again to head home. With only one mid-course correction, Apollo 10 splashed down on target in the Pacific Ocean on May 26. (Left, Apollo 10′s splashdown.)

The relief within NASA was almost tangible in the wake of Apollo 10’s return. The mission was wildly successful and had taken out almost every unknown associated with a lunar mission. All that was left for the Apollo 11 crew to test was the landing; aside from that one little mission objective, Apollo 10 had done it all.

The Earth as seen by the Apollo 10 crew. 1969.

Suggested Reading/Selected Sources

W. David Woods. How Apollo Flew to the Moon. Springer. 2009.

Charles Murray and Catherine Bly Cox. Apollo. South Mountain Books.

Tom Stafford and Michael Cassutt. We Have Capture. Smithsonian. 2002.

Gene Cernan and Donald Davis. Last Man on the Moon. St. Martin’s Griffin. 2000.

Paul Dickson ed. Apollo Expeditions to the Moon. Dover. 2009.

Comments

  1. Kelly Tieu says

    Hi, I’m in a high school debate team, and i need to quote you for one of my debate, is it possible for you to email me your qualifications and real name?

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