The Lessons of Gemini 8

The plight of Gemini 8 seemed desperate enough while it tumbled out of control on its high orbit. Last week, when the perils of that wild ride were reviewed at a Houston press conference, Astronauts Neil Armstrong and David Scott seemed to have come even closer to disaster. Their firsthand account, and further interpretation of telemetered data, supplied frightening new details about Gemini's troubles; to make the danger even more dramatic, there were the remarkable color snapshots and motion pictures brought back to earth by the astronauts.

Shot by a camera through the spacecraft's window, the movie films first showed the Agena target vehicle sailing serenely through space (see opposite page) as the Gemini maneuvered carefully around it in a masterly exhibition of spacecraft control. Pictures of the docking process (see succeeding pages) reflected Gemini's cautious approach and clearly showed the green lights on the Agena's instrument panel signaling that all was well. Despite their silence, the pictures seemed to give the sound of a solid, satisfactory thump as the two vehicles mated firmly in space.

Then came the first dizzying and unexpected vision of the earth below, seeming to spin, and the sudden, explosive separation of the two spaceships. Finally, as the freed Gemini began to roll faster and faster, the camera recorded the alternating brightness of reflected sunlight and the darkness of outer space sweeping in accelerating flashes across the craft's nose until the film ran out.

A Futile Attempt. The vivid pictures were more than a record of near disaster; they were a testament to the skill and resourcefulness of the astronauts and the value of NASA's intense training program, which taught them not only to master the complexities of a properly operating Gemini spacecraft, but to expect--and to cope with--the unexpected.

When the Gemini capsule is operating properly, its attitude in orbit can be changed by firing strategically placed thrusters that can roll the vehicle, yaw its nose to one side or the other, or pitch it up or down. Once thrusters have been fired to change the orientation of the craft, however, other thrusters--pushing in the opposite direction--must be fired to stop the motion at the desired point. In the absence of an atmosphere to slow it down by friction, the spacecraft would continue any attitude-changing maneuver indefinitely unless reverse thrust were available to stop it.

It was while Gemini 8 was docked with the Agena that the joined vehicles suddenly began to tumble as if some attitude-control thrusters had gone amuck. Since the Gemini's thrusters were turned off and the Agena's could be seen firing, Armstrong assumed that it was the Agena controls that were at fault. After cutting off the Agena thrusters, he struggled for 10 minutes to bring the joined ships under control. Then he undocked, still unaware that the real trouble was a short circuit in Gemini's electronic control system that had caused its No. 8 thruster to begin firing intermittently. The Agena's thrusters--weaker than Gemini's--had been firing automatically in a futile attempt to stabilize the two orbiting spacecraft. Once cut loose from the Agena's stabilizing thrusters, the Gemini immediately increased its roll rate under the continuing push of No. 8, which now had even more effect because it was no longer turning the combined mass of the two ships, only the Gemini itself.

Re-Entry Endangered. As the roll rate increased to a terrifying one revolution per second, Armstrong realized that Gemini was at fault; he quickly threw circuit breakers that cut off the flow of fuel and oxidizer to all of the attitude thrusters, including No. 8. The roll--with no friction or counterfiring thruster to stop it--continued undiminished. It was at this point that Armstrong resorted to the independent reentry rocket system to bring Gemini back under control. Once the vital re entry control fuel had been tapped, however, Gemini's ability to make a successful re-entry was endangered and it was necessary to return to earth as quickly as possible.

Had Gemini been within range of a tracking station when trouble began, ground controllers could have immediately diagnosed the problem and told Armstrong how to solve it. But the spaceship was in a dead zone between stations, and in all its maze of instruments, none was designed to report when thrusters were firing. Though the short circuit might have required early termination of the mission anyway, such on-board instrumentation would have enabled Armstrong to bring Gemini under control much more quickly.

Coriolis & Nystagmus. As it was, according to NASA's Dr. Charles Berry, both Armstrong and Scott began to experience two conditions brought on by their rapid rotation: 1) the coriolis effect, a complete loss of orientation caused by the effects of rotation on the inner ear, and 2) nystagmus, an involuntary rhythmic motion of the eyes. Had either or both those effects be come severe enough, the two astronauts would have been unable to see or operate their controls. They might well have perished.

The malfunction might have been even more serious had it occurred when Scott was taking his scheduled walk in space. Some experts believe that outside the spacecraft Scott would have quickly spotted the firing thruster and warned Armstrong in time for him to shut off its propellant. Others are convinced that the rolling Gemini would have whirled Scott around in space at the end of his 75-ft. tether, eventually slamming him against the spacecraft and probably causing fatal injuries.

Shaken by the near tragedy, but determined to put its lessons to good use on the remaining four Gemini flights, NASA officials last week continued to sift telemetry data to pinpoint the location and determine the cause of Gemini 8's short circuit. They indicated that they will probably include new attitude-thruster instrumentation on future flights. And as if to demonstrate their confidence that the U.S. space program will continue on schedule, they designated Space Veterans Virgil Grissom and Edward White and Rookie Roger Chaffee as crew members on the first three-man U.S. space mission--an earth-orbiting flight late this year in the Apollo moonship.

This file is automatically generated by a robot program, so reader's discretion is required.