Automation in the Gemini Program

Less heralded than the human controls but equally important for the technical learning of spaceflight and its implications for Apollo was a new type of human-machine interaction, subtly importing the chauffeurs versus airmen dichotomy into the orbital realm. Most of Gemini's rendezvous and reentries relied on programs running on a digital computer.

Intuitive piloting alone proved inadequate for rendezvous. Following Grissom and Young's successful demonstration of manual maneuvering on Gemini III, on Gemini IV astronaut Jim McDivitt attempted to rendezvous with a spent booster. He envisioned the task as ''flying formation essentially in space,'' but quickly found that his aviation skills would not serve him in this situation. Schedule and some other unexpected parameters constrained the first attempt at rendezvous, so McDivitt employed ''a brute force technique where instead of assuming that we were in orbit we just assumed that we were flying across the earth like in an airplane.''62 McDivitt turned around to attempt a practice rendezvous with his spent booster stage, but found that as he thrusted toward the target, it inevitably moved away. After McDivitt spent a significant amount of maneuvering fuel, flight director Chris Kraft (working for the first time from the new mission control center in Houston) called off the exercise, in favor of Ed White's historic space walk (the first for an American). The human image of White floating through space overshadowed the disappointing experiment in orbital flying.

Afterward McDivitt attributed the problem to poor lighting, but he was facing something new. Orbital dynamics created a strange brew of velocity, speed, and range between two objects and called for a new kind of piloting. Catching up to a spacecraft ahead, for example, might actually require flying slower, to change orbit. ''It's a hard thing to learn,'' observed Deke Slayton, ''since it's kind of backward from anything you know as a pilot.'' A NASA investigation concluded that training had been inadequate, and that the entire program had underestimated the subtlety of the rendezvous task.63 Gemini IV taught an important lesson: pilots could not rendezvous by eye.

A successful rendezvous would require more than keen eyes, stable hands, and cool heads. It would require numbers, equations, and calculations. It would require simulators, training devices, and electronics. Running them would be another Gemini novelty: an onboard digital computer, first flown on Gemini III. This machine, manufactured by IBM, had 4,096 words of 39-bit memory. It collected data from a variety of sources, including the spacecraft's inertial measuring unit and could display calculations and quantities on a variety of displays.

For every phase of flight, the pilots shared control with their new companion. On ascent, the computer served as backup for guidance of the launch vehicle. If the primary system in the booster failed, the astronaut could switch over the control to the cockpit, or the Gemini computer could take command automatically. During rendezvous, the computer collected data from the ground, from the astronauts, and from sensors on board the spacecraft. It calculated commands and trajectories and displayed thrust and orientation that the astronauts should fly. Astronauts interacted with it by means of a mode switch that selected a variety of programs, a numerical keyboard and display, and an IVI or ''incremental velocity indicator'' that displayed ''velocity to be gained'' for thrusting maneuvers. The astronaut fired the thrusters with his stick, keeping his eye on the IVI, which measured accelerations and counted down in velocity, indicating zero when it was time to stop. The astronauts used the computer in a simulator on the ground to practice and to develop a variety of procedures for rendezvous.64

The computer had seven operating modes, corresponding to seven programs and seven functions. During pre-launch, it performed some self-diagnostics. In ''ascent'' mode, it provided backup guidance to the Titan booster and could take over if the rocket's computer failed.65 In ''catch-up'' mode, it provided pointing commands and velocity increments to the crew to begin the rendezvous. In ''rendezvous,'' it took data from radar and the inertial platform to calculate the velocity changes required for rendezvous, and drove the IVI display to zero as the astronaut gave thruster commands. In ''reentry'' mode, the computer solved the reentry equations and displayed data for the crew to follow when flying manually.

Beginning with Gemini VIII, the computer included a magnetic tape storage system that allowed the crew to read in programs and orbital parameters, a necessary feature since the computer programs had grown in size with the increasing sophistication of the missions and could no longer fit into the memory. Neil Armstrong and David Scott first used this procedure while their spacecraft was spinning, reading in the reentry program for their emergency landing.66 Heroic action now involved not only controlling the spacecraft but also loading code into a digital machine.

For rendezvous, the crew used data from their digital computer and checked them against a printed chart, which served as an analog computer like a slide rule (a practice continued on Apollo). Usually, the ground staff computed the necessary mid-course or catch-up maneuver numbers and called them up by voice. On Gemini X Michael Collins computed the maneuvers on board, using a combination of the onboard computer and star sightings from the optics, a difficult and frustrating process that did not produce accurate results.

Once the accurate data was calculated and displayed in the cockpit, the actual maneuvering became an ordinary, mechanical task, the pilot serving as a human servo-mechanism and following the computer's instructions. In Apollo, these maneuvers would require no manual thrusting, but would be controlled by the computer from beginning to end based on a series of keypunches.

The computer also commanded the reentry maneuvers, indirectly, through the crew, or directly, in an automatic mode. When coming in from orbit, at about 400,000 feet, the astronaut manually kept the spacecraft aligned with the horizon, when the computer began indicating roll commands for the astronaut to follow. Or, in automatic mode, the computer commanded the attitude system directly.

By Gemini XI, the computer automatically steered the spacecraft and landed within three miles of the target with no crew input, a feat repeated on the final Gemini XII flight. ''Reentry of the Gemini spacecraft was successfully controlled both manually and automatically,'' concluded the project's final report. Which mode was desirable depended on the complexity of the task, the number of control commands, and the desired accuracy of the landing spot.67

Jack Funk, a member of the Space Task Group who specialized in trajectories, recalled that the astronauts slowly realized that the dynamics of flying in space were so complex, as were the numerous systems aboard the craft, that anything that helped them manage the chaos would extend their ability: ''Instead of having a battleship with 6,000 crew on board, you just have a small craft with a computer which is your big crew that does all the work for you.''68 Aaron Cohen, a control engineer who would play a central role in developing the Apollo system, believed that ''the piloting, the man interface with the computer, the display, and the techniques of how he used it,'' stood out as the major contribution of the Gemini program.69

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