First Man

by James R. Hansen

  Intermittent voice communications with Gemini VIII happened a few minutes at a time as the spacecraft circled the globe on its easterly path. Relaying between the cockpit and Houston was a worldwide tracking network with stations on Ascension, a British island in the South Atlantic; at Tananarive in the Malagasy Republic, on the island of Madagascar off the east coast of Africa; at Carnarvon, in western Australia; at Kauai, the northernmost Hawaiian Island; and at Guaymas, in Mexico on the Gulf of California.

  Not until the astronauts were over Hawaii did they try to do much sightseeing. Armstrong, who was familiar with the Hawaiian Islands from his days in the navy and his sojourn at the Kauai tracking station during Cooper’s Mercury flight and Gemini III, was able to make out Molokai, Maui, and the big island of Hawaii, but a bank of storm clouds obscured his view of Oahu and Kauai itself. Approaching the Baja, Neil set his eyes on his old navy base in San Diego and exclaimed, “Oh! Look at all those ships!” Both men then started looking for the shoreline of Texas, hoping to see Houston and to pinpoint the location of their homes just east of the Manned Spacecraft Center. But the demands of the mission quickly interrupted the scenic interlude. The job at hand was to chase down the Agena, presently some 1,230 miles away from Gemini VIII and moving in a separate, higher orbit.

  The first task Armstrong needed to perform was aligning the spacecraft’s inertial platform, a fixed base, or “stable table,” that measured angles—and thus directions—in the void of space where all directions (up-down, right-left) are relative. In the Gemini spacecraft, the inertial platform consisted of three gyroscopes mounted at right angles to one other. As the spacecraft moved relative to the gyroscopes, the inertial measuring unit fed pitch, roll, and yaw angles to the onboard computer tracking the Agena via radar. Three accelerometers mounted in tandem with the gyroscopes measured the spacecraft’s reaction to thruster firings.

  A five-second burst of Gemini VIII’s forward thrusters would slow the Gemini spacecraft into a position where its orbital inclination—that is, the angle between the plane of its orbit and that of the equator—matched up precisely with the Agena’s. This critical moment came shortly before 1:15 P.M., at one hour and thirty-four minutes elapsed time into the mission, just as Armstrong and Scott crossed over the Texas coastline for the first time and headed out over the Gulf of Mexico.

  “A fundamental requirement of rendezvous,” Armstrong explains, “is to get your orbit into the same plane as the target’s orbit, because if you’re misaligned by even a few degrees, your spacecraft won’t have enough fuel to get to its rendezvous target. So the plan is to start off within just a few tenths of a degree of your target’s orbit. That is established by making your launch precisely on time, to put you in the same plane under the revolving Earth as is your target vehicle.” But no matter how precisely the two launches are timed, the angles of inclination in the resulting orbits of the two spacecraft invariably prove to be slightly askew. In the case of Gemini VIII, a .05-degree difference between its inclination and that of the Agena’s needed to be burned off.

  Even under ideal circumstances, chasing down a target in space required unusually keen piloting. Armstrong’s Apollo 11 crewmate Michael Collins was himself introduced to the dark mysteries of rendezvous while training for his own Gemini X flight of July 1966: “The pilot sees the Agena’s blinking light out the window, points the nose of the Gemini at it, and fires a thruster to move toward the Agena. For a short time all seems well, and the Agena grows in size. Then a strange thing happens: the Agena begins to sink and disappear under the Gemini’s nose. Then minutes later it reappears from below, but now it is going faster than the Gemini and vanishes out front somewhere. What has happened? When the Gemini fired its thruster to increase its velocity, it also increased its centrifugal force, causing its orbit to become larger. As it climbed toward its new apogee, it slowed down, so that it began to lose ground compared to the Agena. The Gemini pilot should have fired a thruster to move away from the Agena, causing him to drop down below it into a faster orbit, and begin to overtake it.” Complicate those tricky maneuvers by throwing in orbits of different shapes, or orbits not in the same plane, or difficult rendezvous lighting conditions, or the need to bring the orbits of the two spacecraft together in a great hurry—in other words, any number of real-world complications of spaceflight—and the demands of rendezvous grew exceedingly stringent.

  Without extensive simulator time, it is doubtful that any astronaut could ever have been truly ready to perform a space rendezvous. “Rendezvous simulation in Gemini was really quite good,” Armstrong notes. “We achieved fifty to sixty rendezvous simulations on the ground, about two-thirds of which were with some sort of emergency. That means that some part of the equipment was either malfunctioning or inoperative during the rendezvous. We completed the rendezvous in all of them but two. But in the two that we missed there were unplanned malfunctions of the simulation experiment, so we never really missed…What the ground simulations could not do well was simulate the visual field we would be experiencing. It was okay at night: the star field was pretty good and the relative motion against the stars was pretty good. But when the target was in daylight, it couldn’t do a very good job of reproducing that.”

  A guidance computer was needed to compute the location of the two spacecraft, to define the best transfer arc into the GATV’s orbit, and, during the final phases of rendezvous, to solve precise mathematical problems based on radar lock-on with the Agena. Built for NASA by Federal Systems Division of IBM in Oswego, New York, the Gemini guidance computer was among the world’s first computers to use digital, solid-state electronics for the purpose of assisting with the real-time guidance, navigation, and control of a flying machine. “This was a teeny-tiny computer,” Armstrong relates. Measuring nineteen inches long and weighing fifty pounds, the computer fit inside the front wall of the spacecraft. Within this compact unit, tiny doughnut-shaped magnets comprising the computer’s core memory stored 159,744 bits of binary information—less than 20,000 bytes—far less than even the very moderate storage capacity of the very first eight-inch floppy disks developed in the early 1970s, which was some 130,000 bytes. Adding only slightly to this capacity was a tape drive by which the astronauts could put alternate programs into the computer. Gemini VIII was the first space mission to benefit from the alternate-tape system. Even with what was then the most current computer technology, it was incumbent on the mission planners to reduce the complexities of rendezvous.

  Mathematical models, simulations, and early Gemini flight experiences determined that the optimal altitude difference between the two spacecraft was fifteen miles, and that the ideal transfer angle—the angular distance the Gemini spacecraft needed to traverse during its rise to the higher orbit of the Agena—was 130 degrees rather than the 180 degrees (or halfway around the globe) called for by the so-called Hohmann transfer. This was the classical method of transferring from one circular orbit to another circular orbit with the greatest efficiency, as suggested by German engineer Walter Hohmann (1880–1945) in his 1925 book Die Erreichbarkeit der Himmelskörper (The Attainability of Celestial Bodies). Employing the Hohmann transfer, as Armstrong explains, “you maneuver to perigee, your lowest point in an orbit, accelerate the vehicle, and then climb for half an orbit, arriving at the orbit of the target vehicle with essentially zero vertical velocity. That sounds good, but the disadvantage of the Hohmann transfer is that when you arrive at the target orbit, there is a lot of motion between your target and the stars in the background. You’re looking at the target and everything is moving behind it, so it’s difficult for you to know exactly how to control your own vehicle to make sure that you’re on the proper approach. What our mission planners worked out was an approach path that allowed us to arrive at the Agena when it appeared to be a great big star fixed in the middle of the background and things weren’t all going every which way. This technique used a little more fuel, but it gave us the advantage of having a much easier approach to our tar
get vehicle, because we didn’t have the background moving on us. With our target frozen against the star background, we could know we were on the right path. It automatically told us something important if the target started moving; it told us that we had a velocity component that we needed to take out.” As for the best lighting conditions, it was found through analysis and simulation that the Sun should be behind the Gemini spacecraft during its braking phase to rendezvous. From these stipulations, the mission planners worked backwards to design launch times, ascent trajectories, and orbital parameters that set up the optimum conditions for Gemini’s terminal phase of rendezvous leading to docking.

  From the time of the spacecraft’s first burn at one hour and thirty-four minutes into the mission (a period when the onboard computer operated in “catch-up mode”) to the point in time that the spacecraft began terminal phase (when the astronauts manually switched the computer back to “rendezvous mode”), it took approximately two hours and fifteen minutes. Armstrong and Scott then decided to eat what turned out to be their only meal in space. Some six hours had passed since they had eaten their prelaunch breakfast (filet mignon, eggs, toast with butter and jelly, coffee, and milk) back in crew quarters at the Cape. Schirra and Stafford in Gemini VI had not taken the time to eat early enough in their mission, leaving them hungry and in need of energy by the time they rendezvoused with Borman and Lovell in Gemini VII.

  Inside the meal packet labeled Day 1/Meal B was a freeze-dried chicken and gravy casserole. But a call from CapCom Jim Lovell in Houston, relayed through the tracking station at Antigua in the British West Indies, told the crew to get ready for their next burn—a phasing adjustment, or slight in-plane repositioning, requiring another platform alignment. Taking advantage of weightlessness, Armstrong and Scott used patches of Velcro to stick their packaged food on the ceiling of their spacecraft until the burn was complete. Retrieving their food half an hour later, the astronauts found the casseroles still dry in spots. Washing NASA’s humble entrée down with fruit juice, Armstrong next tried a package of brownies, only to have crumbs float all over the cabin.

  The next maneuver, a plane-change burn, came over the Pacific Ocean just before completing a second orbit, at 2:45:50 elapsed time. Punching the aft thrusters, Armstrong produced a horizontal velocity change of 26.24 feet per second, which brought Gemini VIII’s nose down, perhaps imprecisely:

  2:46:27 Armstrong: I think we overdid it a bit.

  Not until the spacecraft was over Mexico was Neil’s gut feeling confirmed. Lovell told him from the remote site line at Guaymas to add two feet per second to his speed by making another very short burn. As Scott later said, “It was…a pretty quick loose burn…without much preparation.”

  Armstrong explains how he and Scott brought Gemini VIII to the verge of the rendezvous: “We had gotten in plane and into an orbit where we were below the target vehicle so that we were traveling faster around the Earth than the target was, so we were catching him. Then we waited until we got to about one hundred thirty degrees behind the Agena. At that point we added some velocity and got into a transfer arc that was to take us up to the GATV orbit. When we got to this point we started making computations of our range and range rate to assure ourselves that we were on the right transfer arc. We did that both with the computer and manually with charts and also with the ground—all three ways. At intermediate points, we made small corrections based on the computations to improve our transfer arc, because it was impossible to get it exactly right. If we were off just a little bit, the errors got bigger. So we took the errors out and restarted the calculating. Knowing that it was inevitable that we would get a little bit out of plane (meaning that we would be going sideways when we got to the terminal phase of rendezvous), we made a number of fine adjustments on the way so we could hopefully arrive at the target with the target having zero relative motion against the stars and with us approaching at a reasonable rate that had us using a minimum amount of fuel in decelerating for final approach.”

  The terminal phase could not begin until Gemini VIII had a solid radar lock-on with the Agena. On the Agena was a transponder that answered the inquiring signal sent out by the Gemini spacecraft. The computer on board Gemini VIII measured the time it took for this signal to make a round-trip to the Agena and back. From this measurement, the Gemini computer twice calculated the range between the two vehicles, comparing the two transit times to deduce how quickly the spacecraft was closing on its target. Commander Armstrong kept range and range rates constantly in mind so as not to overshoot the target by closing in on it too fast.

  At 3:08:48 elapsed time, while over the United States and in direct communication with Houston, Armstrong reported, “We’re getting intermittent lock-on with the radar.” Thirty-five minutes later, with the spacecraft over Africa, Neil reported a solid radar lock:

  2:20P.M. This is Gemini Houston Control. About two minutes ago, NeilArmstrong called in over Tananarive and he was able to confirm at that time that radar lock had been established…. He said the range was 158 nautical miles. This is an all-important element of a rendezvous mission—the establishment of that radar link. The pilots say that if they had to lose any of the several things involved in a rendezvous mission—that is, the platform, the computer, or the radar—the one they would rather not lose is the radar.

  While still over Madagascar, Armstrong needed to perform another burn. The transfer arc in which Gemini VIII had been moving for the past couple of hours in order to catch up with the Agena had been elliptical, the pathway that was dictated, as Johannes Kepler explained, by the gravitational field of one body. At 3:40:10 after the launch, Armstrong nosed down his spacecraft and applied the aft thrusters. The burn resulted in a velocity change of 59 feet per second, which circularized Gemini VIII’s orbit and put it more precisely in plane with the Agena.

  It took a while before the crew could see its target. “It’s hard to do at night,” Armstrong explains. “We had the radar information giving us range, range rate, and position. At some point we knew we would see the target. But we had to be pretty close. According to the mission plan, what we wanted to do is be in the dark throughout 130 degrees of the transfer arc—or at least 125 degrees or so. Then at roughly ten miles out, the target would go into daylight. At that point it lit up like a Christmas tree. We could see it against that dark sky just like a gigantic beacon. When that happened, the star background became less important because we would be on a good trajectory, so we could make the final adjustments visually.”

  At 4:40 elapsed time, while over the Houston tracking station, Scott radioed the crew’s sighting of an object seventy-six miles distant that was gleaming in the sunlight. They assumed it was the Agena. Busy preparing for maneuvers necessary for Terminal Phase Initiation (TPI), Armstrong did not comment on the sighting of the target for another three and a half minutes:

  With the Agena located ten degrees above Gemini VIII, Armstrong needed to align the inertial platform once again, in preparation for one of his last translation maneuvers. In it Neil would pitch up the spacecraft’s nose some thirty degrees and cant the vehicle roughly seventeen degrees to the left. When that maneuver was completed successfully, he had time to take another look at the Agena:

  A few minutes later, the Agena vanished from view as it entered twilight, soon to reappear for the astronauts when the acquisition lights on the target vehicle, by command from Gemini VIII, blinked on:

  “Once we completed our transfer arc,” explains Armstrong, “we had to make final adjustments that would get us exactly into the same position and to the same speed as the Agena, so that we would be flying in formation. From that point, we did what was called ‘station keeping.’ This meant we stayed about one hundred fifty feet apart. We flew around the target but never got very far away from it. We had to stay in the same orbit as the Agena, because if we went astray by even just a little bit, the errors propagated. So we had to fly essentially in formation. Unlike with flying in formation with aircraft, whe
re you fly in the same direction as the target and have the nose of your airplane pointed just like the nose of the airplane with which you are in formation, that was not required in space.”

  High over the tracking ship Coastal Sentry Quebec (CapCom James R. Fucci), which was positioned near the Caribbean island of Antigua, the crew of Gemini VIII prepared to apply the brakes to their spacecraft so that it would not close too quickly on the Agena and fly right by it. Delicately, Armstrong handled the braking by intermittently firing his aft thrusters in very short bursts, while Dave Scott called out Gemini VIII’s range and rate:

  Two minutes and twenty-one seconds later came the glare of the Agena’s lights. Edging ahead at the glacial pace of five feet per second, a pace by which it would have taken a track athlete twenty-four seconds to run forty yards, Gemini VIII bore down on the Agena.

  At this critical point in the rendezvous, Houston reported that, “all in all, the pilots are acting extremely ‘ho-hum,’” and that the crew had to be “urged to say a bit more about their situation.” The news from Mission Control was misleading, as Armstrong’s excitement was clearly evident:

  Two minutes later, CapCom Lovell, who had kept quiet so as not to bother Armstrong and Scott during the critical braking phase, broke in and asked the crew for an update on the rendezvous. Dave Scott knew that Armstrong deserved center stage: