Simple systems either work or fail. There is nothing in between. If the systems were lost, we had no real backup for many of them. However, repeated testing over the years had proved that their success rate was very high. I would rather fly a proven system than the space shuttle, for example, which has many computers that all have to talk to each other and then mutually agree. There is an analogy with flying multi-engine versus single-engine aircraft. It surprises people to learn that there are more accidents in multi-engines. If you lose your only engine, you quickly look for a place to land. If you have multiple engines, you may try to keep flying, which becomes increasingly difficult and dangerous. Simpler is often better.
Our computer was a good example of spacecraft simplicity. It was designed by MIT as a rudimentary piece of hardware. It was literally hardwired: you could zap it, turn the power off, and do pretty much anything else to it, and when the power came back on you were right back where you had been before. It had no silicon chips to burn out, was extremely reliable and virtually indestructible. Of course, simplicity came at a price: our computer had less storage memory than the average modern wristwatch.
Many of the tasks the computer needed to perform on an Apollo flight were already hardwired inside. The lack of storage capacity, however, prevented us from preloading all of the programs needed for the flight. For a simple thrusting maneuver, for example, we had to load in the data. The computer had no room at all for a particularly important program, called “Return to Earth.” The ground would need to send that one to us when we were in lunar orbit.
To navigate in space between Earth and the moon, we required two pieces of information. One was the attitude of the spacecraft compared to some fixed frame, such as the field of stars all around us. The attitude—in simple terms, which way we were pointed—was needed so that we could aim the craft during thrusting maneuvers and keep on course. The spacecraft had a set of gyroscopes to tell us. Attitude was not something we could otherwise know for sure in zero gravity, where there is no up or down. It was the equivalent of an attitude indicator in an airplane, which tells you if your wings are level. Crucially, we could also measure acceleration forces on the spacecraft, so we could gauge the accuracy of our engines when we fired them.
The other information we wanted was the precise location of the spacecraft in the Earth-moon system. We always needed to know exactly where we were. The team on the ground could track the spacecraft by precisely angling their large antennas, located on different parts of the globe. By measuring the precise timing of a return signal from the spacecraft and comparing the results, mission control could compute our location and speed with great accuracy.
Without constant checking, however, uncertainties about our position could grow larger over time. And no system was foolproof. Mission control’s calculations of our location would be useless if our radio failed and they could not share them with us. We also had one gyroscope set in the Apollo spacecraft, which we tested mercilessly before flight. Yet no matter how perfect we could make it, a little friction would always be acting on the gyroscopes. We needed to be able to calculate and correct any drift.
So, Dick and I focused on discovering our attitude and location with no help from the ground. We could be in lunar orbit with no working radio, and three lives depending on our own calculations to thrust the spacecraft out of lunar orbit in the right direction for a precise reentry into Earth’s atmosphere many days later. We needed at all times to be able to independently work out our state vector—that is, to find out precisely where we were within the Earth-moon system, how fast we were going, and what direction we were headed. We were navigators, and although we had some sophisticated equipment, Dick and I still had to master the same skills that ancient mariners once used to cross the oceans.
We would navigate using a sextant much like those used for centuries by seafaring navigators. The sextant was located in the equipment bay, at the bottom of the footpads where our feet usually rested. In space, an astronaut could float down there and have enough room to look through the optical equipment while in a standing position. We’d peer through a telescope with a wide field of view to locate stars we used as guide stars, then shift to a telescope with a much narrower field. By using the optics for sighting and the onboard computer to measure the line of sight to a star, then repeating that procedure with several stars, we could determine our exact attitude in space. By sighting on different stars and measuring their angles, the computer could average out the information.
Using that same equipment but this time using a split prism to form both a fixed and a movable line of sight, we could also precisely measure the angle between stars and the horizon of Earth or the moon. Their positions would look different against the starry backdrop as we traveled between the two, and these differences could be measured. The more sightings we made, the more accurately the computer could calculate our location and direction, until we knew precisely where we were.
It sounds complicated, but it was technologically simple. There were no science-fiction–like computers to tell us what to do and make enormous calculations on our behalf. We relied on skills learned in extensive training and memorized the stars that would surround us on our journey. If we lost our navigation computer or our gyroscope, we had an even more basic backup method. We could resort to a World War II–era gun sight. We could clip this optical device to the edge of a spacecraft window, look through it just as you would with a hunting rifle, and line up the crosshair with a known star. We would then know the direction of the spacecraft’s line of thrust, and that information was better than knowing nothing.
This all required a great deal of astronomical knowledge on our part, learning and remembering dozens of different stars that we could use to help us navigate. This knowledge was vital, however, in case we ever lost radio contact with the ground. We would head to the Griffith Observatory in Los Angeles, or the Morehead Planetarium in North Carolina, and use their planetarium domes to simulate the view of stars from space. Tony Jenzano, the planetarium director at Morehead, had a great way of training us. To begin, he would ask us to close our eyes. He would then spin the star field on the planetarium dome, ask us to open our eyes and tell him where we were. Over time, he would gradually decrease our field of view. It became increasingly harder to identify our position in the sky with fewer stars in our vision, so we really had to memorize them. Eventually he put us in a small box inside the planetarium with a ten-degree window cut into the front. Once again he’d spin the view and we would have to give him our position. Man, that was hard. But we were seeing the same view that would fill our spacecraft optics, so we had to master it.
The focus on astronomy meant that whenever I was flying anywhere in a T-38 at night, I spent far more time watching the stars than I did looking at the ground. On moonless nights, above the clouds and away from city lights, the star view from my cockpit was stunning, and all the more interesting because I could now name hundreds of those stars.
While I was spending time in Downey with Dick to ensure the Apollo 12 command module was ready and training with Dave and Jim in case we needed to fly the mission, other important events were taking place. After the success of the Apollo 9 mission, NASA felt confident about flying back to the moon in May of 1969. With Apollo 10, they sent both a command module and a lunar module. Some spectacular test piloting proved that NASA was ready to go all the way on the next flight: a lunar landing.