Apollo: The Race to the Moon (59 page)

Actually, Don Arabian’s anomalies team later determined that Yankee Clipper—Apollo 12’s command module—was hit twice by lightning, once 36.5 seconds after launch at an altitude of 6,000 feet, when it discharged the cloud it was flying through, and again 16 seconds later, at an altitude of about 14,000 feet, when it triggered a cloud-to-cloud bolt. Each time, the lightning acted on Yankee Clipper in two ways, as Arabian later described to a visitor (accompanied by a vivid reenactment of the crew’s reaction and the sound of the alarms). First, the lightning itself, a jolt of 60,000 to 100,000 amperes, flowed through the metal exterior of the Apollo stack from top to bottom. The only damage it did, however, was to destroy some external instrumentation for measuring temperatures and R.C.S. reserves, none of which was critical. Because of the way the Apollo stack was electrically grounded, the direct charge did not penetrate the spacecraft itself. In addition, however, the lightning induced electromagnetic fields within the stack. Induced voltages and currents, powerful but not nearly as devastating as a direct jolt, raced through the electrical circuitry and, among other things, knocked the fuel cells off line and caused the guidance platform to begin tumbling. As it turned out, the shocks were not powerful enough to destroy the circuits.

The reason Twelve was able to get to orbit was that the guidance system for the Saturn V, buried within the Instrumentation Unit at the top of the S-IVB stage, was unaffected by the lightning. If its platform had tumbled, the Saturn would have gone out of control within a few seconds. Part of the reason the spacecraft was so affected by the lightning while the Saturn was not involved the spacecraft’s greater exposure—it was positioned like the tip of a lightning rod—and part of it was luck, as Arabian emphatically pointed out. Neither the launch vehicle nor the spacecraft had been designed with lightning in mind.

Once in orbit, the crew was preoccupied first of all with getting the guidance platform realigned. The platform was at the heart of the Inertial Measuring Unit (I.M.U.), a metal sphere about the size of a beach ball located beneath the center couch of the command module. Within the I.M.U.’s casing were three nested spheres called gimbals. The gimbals, each controlled by a gyroscope, functioned like a gimbal in a boat that lets a table surface remain unaffected when the boat heels. At the center of the three gimbals was the platform—the table surface—which had been aligned before launch. From the moment of launch, each movement in the spacecraft was measured by accelerometers and registered in the guidance system, which added that movement onto the previous movements it had recorded. In other words, the guidance system always knew where it was relative to some specific zero point. When the main power buses went out during launch, the gimbals lost their balance, as it were, and the result was that the platform physically tumbled.

The crew of Apollo 12 had to realign the platform through star sightings taken on board Yankee Clipper, a task that was never easy but was particularly difficult when the spacecraft was not (as for sightings during a nominal mission) in deep space with lots of time. The crew, already busy checking out the spacecraft, had somehow to work in the star sightings during the half of each orbit when they were in the earth’s shadow. With much effort, and at nearly the last opportunity, Command Module Pilot Dick Gordon succeeded, and the onboard guidance system could take over from the Instrumentation Unit in the S-IVB stage that had been doing all the work up until then. This left the Apollo’s managers still confronting the larger question: Should Twelve proceed to the moon?

As EECOM, the man responsible for the environmental and electrical systems, Aaron was once again the man on the spot. This time it wasn’t just Gerry Griffin coming to him, but Chris Kraft, descending from the fourth row. “Now, young man,” Aaron remembered Kraft saying to him, “you’ve got an hour and a half to figure out whether that spacecraft’s ready to go to the moon or not.” They could take no longer than that, because they couldn’t let the spacecraft continue in earth orbit longer than three revolutions. On each revolution, the earth was changing position under them; after three orbits, the ground stations would be unable to track the burn, emergency recovery vessels would be in the wrong parts of the world’s oceans, and the spacecraft itself would be out of position for the lunar trajectory needed to conduct the mission.

“[Kraft] really put it on me,” Aaron said. By this time, they were certain that the cause of Apollo 12’s problems had been lightning. But how does one determine in an hour and a half that a spacecraft struck by lightning is sound enough to go to the moon? It was not the kind of exercise for which the flight control team had ever trained. Griffin and Aaron didn’t have time to invent a procedure, so they decided to section out the piece of the flight-maneuver checklist that the crew would ordinarily have used before burning into lunar orbit. Their logic was that no maneuver in the flight was more critical than the L.O.I. burn—if the spacecraft was in good enough shape to pass the L.O.I. checklist, it was good enough to proceed out of earth orbit. They worked through the checklist with Conrad’s crew, testing the propulsion systems, gimbal systems, gyros, computers, counting down to the last few seconds before actually firing the S.P.S. Everything worked.

During that same hour and a half, the MOCR’s support network in SPAN, the MER, and at the North American Rockwell plant in Downey worked frenziedly to figure out whether the lightning had compromised any of the spacecraft’s systems. (Bethpage, Long Island, where Grumman was located, couldn’t do much except speculate: The LEM was still housed in the SLA, inaccessible.) Watching the data in the MER, Arabian reached the conclusion that the spacecraft looked fine except for the destroyed instrumentation, which had no bearing on the mission, and there was no reason not to continue. For Arabian, it was just one more instance where you examine the physics of the situation: “You do whatever the data say. All the systems seemed all right, so go ahead.”

The MER passed its recommendation along. To Bill Tindall, watching the data, it looked as if they had a normal spacecraft once they had reset the platform. But, it was later pointed out to him, a large and undesigned-for electrical charge had run through every circuit in Yankee Clipper. “Aaah—who cares?” Tindall replied, with a big laugh.

Griffin recalled that Kraft had tried to take some of the pressure off—“Don’t forget that we don’t have to go to the moon today,” he had said to Griffin. But the determinations that flowed to the flight director’s console all said the same thing. “We kept clicking off that checklist,” Griffin recalled, “and when we got to the end, we all kind of said, ‘Well, there’s this unknown about a few things—we don’t know where all that stray electricity may have run around in the cabin—but everything we can check looks okay. Is there any reason not to go?’ And we looked at each other and said, ‘Hell no, let’s go.’” Griffin turned around to Management Row and told Kraft that’s what they were going to do.

It was a unique test for senior management who were close enough to the day-to-day operations to have a reasonable technical grasp of the situation—specifically, the directors of Flight Operations (Kraft), Flight Crew Operations (Slayton), ASPO (McDivitt), and the Apollo Program itself (Petrone). They had never overridden a flight director’s decision during a mission, but never before had a strategic choice of this nature presented itself. There was an argument for terminating the mission no matter what the data said. The unknown in Griffin’s mind was in theirs as well. The spacecraft hadn’t been designed for the treatment it had gotten during launch. Why take a chance?

Kraft was in Houston; Slayton, McDivitt, and Petrone were at the Cape. They had been conferring over the phone lines. Apparently there was no argument and no agonizing. There was one awful possibility that they couldn’t check out with telemetry: Conceivably, the electricity had blown the pyrotechnics that operated the entry parachute system. But that was extremely unlikely, and—thinking back on it Petrone shrugged fatalistically—if that had happened, what difference would it have made to their decision about going to the moon? The crew wouldn’t have come back alive no matter what they did.

“We had a very short time to discuss it,” Petrone recalled. “But all of our minds were saying the same thing. You’re up! The big part of the mission had been accomplished, and everything was working, you’ve got the table lined up, everything’s pumping, everything looks good on board. Houston on the ground says, ‘Everything looks good here.’ So we all said, ‘Hey—obviously.’ No big discussion. Wasn’t needed. Once you’ve got all those other parameters falling in line—Let’s go.” So when Griffin told Kraft that he was going to go for T.L.I., Kraft just nodded.

But suppose the situation had been posed as a scenario on the ground, when writing mission rules. Under those circumstances, would Tindall’s Mission Techniques meetings have come up with a rule saying that if the spacecraft is hit by lightning and the electrical system goes down and the platform tumbles, our Standard Operating Procedure will be to conduct an hour-and-a-half check and, if nothing seems wrong, continue? Well, said an Apollo veteran, now a senior NASA manager, maybe not. Or suppose, twenty years later, after the Challenger accident, that a comparable situation were to occur with the shuttle. Would NASA go ahead with the equivalent of a translunar injection? He laughed aloud at that one. Not a chance. But this is now, he said. That was then.

When Apollo 11’s Eagle had landed on the Sea of Tranquility four months earlier, no one knew at first where it was. “We were all scrounched around trying to figure out where the hell it was,” Tindall recalled. “Kraft was there, and Sam Phillips was there, and they were talking to the scientists in the back room,” trying to pick up clues from Armstrong and Aldrin’s description of the terrain. “It was a comedy.” Phillips turned to Tindall, whose Mission Techniques determined the landing procedures. “On the next mission,” Phillips said firmly, “I want a pinpoint landing.” “So help me God,” Tindall recalled, “that’s what he said. I thought it was impossible.”

Tindall convened his lunar landing group. The task looked impossible, because the moon had proved to be unmanageably lumpy, in a gravitational sense. Mascons, uneven concentrations of the lunar mass, constantly introduced unexpected deviations into the Apollo lunar orbits. Their effects were too complex to be fully modeled.

After they had wrestled with the problem for a few meetings and rejected a few unworkable ideas, Emil Schiesser, a soft-spoken, intense young man who was one of MPAD’s experts on deep-space navigation, had an inspiration.

Scheisser pointed out that as the spacecraft came out from behind the moon, it was heading toward the tracking stations on earth. And, as everyone knew, this created a Doppler effect that was used for tracking the vehicle. The Doppler effect is the apparent change in the frequency of a light, sound, or radio wave as its source approaches or recedes, as in the changing pitch of the sound of a train as it approaches and then moves away. As the LEM continued on its circular orbit, it was no longer approaching the earth’s tracking stations, but was moving at an increasing angle relative to them until, as the LEM headed back around the moon again, it was moving directly away from the earth. During its entire period, measurements of the LEM’s Doppler effect from the earth showed a predictable pattern.

Now came Schiesser’s imaginative leap: Suppose that we forget about trying to model perfectly the effects of the mascons, he suggested, and concentrate instead on modeling what the shifts in frequencies should look like during the course of a landing at point X, from the time that the LEM appears around the edge of the moon until touchdown. With this predicted pattern of frequencies in front of us, we can watch what the actual frequencies are, and calculate the difference. Then we can use the difference between the predicted and the actual frequencies to decide how far off target we are. It was, Tindall reflected, “astounding”—simple and obvious after you heard it, as elegant solutions seem always to be.

No matter what the source of navigational errors—firing of the R.C.S. thrusters, or an imprecise burn—Schiesser had given them a way to determine precisely how much they needed to change the planned course of a descending LEM. Now what they needed was a way for the LEM to use that information to achieve the pinpoint landing that Phillips wanted. One option was to update the “state vector” in the onboard computer—the information required to compute the vehicle’s precise position and velocity. But a state vector is expressed in seven pieces of information, and asking the lunar module pilot to input seven new numerical nouns, each of them about eight digits long, during the middle of a lunar landing was far too unwieldy.

The group came up with an alternative. (“I didn’t, of course,” Tindall said quickly; “I never did anything. I just got the people together to do these things.”) Don’t try to tell the LEM where it really is, went this bright idea. Just tell it that the landing site has moved. If they found that the LEM was coming down 800 feet short of the landing site, they would tell the computer to land 800 feet farther downrange than it had planned. To implement this procedure required only one number—“Noun 69,” they decided to call this piece of crucial targeting data.

MPAD’s mathematicians went off to model the Doppler readings they needed for Apollo 12’s target. The computer people went off to modify the onboard computer’s software The flight operations people went off to devise crew procedures and begin simulations. Elegant as Schiesser’s procedure was in theory, it was far from simple to put into practice. The earth did not stand still while the tracking stations measured the Doppler effect; it rotated, and the effect of the earth’s rotation had to be taken into account. The tracking stations handed off from one to another as they rotated out of position, and each of them was at a different latitude; the effects of the angle at which they received the signals from the LEM had to be incorporated. The time measurements had to be so precise that only a nuclear clock was sufficiently accurate. And all of these changes had to be completed and practiced during the interval between the July landing of Apollo 11 and the November launch of Apollo 12.