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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Agena target vehicle | 3/3 | https://en.wikipedia.org/wiki/Agena_target_vehicle | reference | science, encyclopedia | 2026-05-05T12:50:42.429195+00:00 | kb-cron |
After the failure of the first GATV, NASA commissioned McDonnell to develop a backup docking target minus the Lockheed Agena rocket, the Augmented Target Docking Adapter (ATDA). This consisted of the Gemini docking collar and an attitude control propulsion system based on the Gemini Reentry Control System. The ATDA was 10.9 feet (3.3 m) long, with a mass of 1,750 pounds (794 kg). A few questions were raised about the compatibility of the ATDA with the Atlas booster, since it had much lower mass than the GATV, potentially throwing off the launch vehicle's aerodynamics and calibrated settings. However, Convair assured McDonnell that it would pose no technical issues with the booster. A second GATV launch failure occurred on May 17, 1966, as Gemini 9 astronauts Tom Stafford and Eugene Cernan sat on their pad awaiting launch. The Atlas–Agena lifted smoothly into a cloudy sky, vanishing from view around T+50 seconds. Shortly before Booster Engine Cutoff (BECO), the guidance control officer announced that he had lost contact with the booster. Telemetry indicated that Agena staging had taken place on schedule at T+300 seconds. The Agena continued transmitting signals until T+436 seconds, when all telemetry ceased. Hidden behind clouds, the Atlas's B-2 engine gimbaled hard to right starting at T+120 seconds and remained fixed in that position, flipping the launch vehicle 216° around and sending it back towards Cape Kennedy. This rotation had made it impossible for ground guidance to lock on. Radar stations in the Bahamas tracked it heading north and descending. Vehicle stability was gradually regained following BECO, however it had pitched approximately 231° from its intended flight path. Both vehicles plunged into the Atlantic Ocean 107 nautical miles (198 km) downrange. The Agena's engine did not activate since the proper altitude and velocity had not been attained, preventing the guidance system from sending the start command. While the exact cause of the engine gimbal control loss was not found, telemetry indicated that a short-to-ground occurred in the circuit for the servoamplifier output command signal, which may have been caused by cryogenic leakage in the thrust section. Substantiating this theory were abnormally low thrust section temperatures starting at T+65 seconds. The source of the cryogenic leakage was not identified. The loss of the lock on the ground prevented normal engine cutoff signals from being transmitted to the Atlas; BECO was generated by the staging backup accelerometer, SECO at T+273 seconds due to LOX depletion, and VECO and Agena staging from a backup command generated by the missile programmer. Aside from the flight control system, all Atlas systems functioned properly. While Convair accepted responsibility for the launch failure, Lockheed engineers expressed concern about telemetry data that indicated a servo failure in the Agena, leading to doubts as to whether the stage would have still operated properly if the Atlas hadn't malfunctioned. However, the true cause of failure surfaced when the Air Force released film taken by tracking cameras at Melbourne Beach, Florida, which showed the Atlas pitching over and heading downward. It was then determined that the Agena's servo malfunction was caused by passing through the Atlas's ionized exhaust trail. The Gemini 9A modified mission launch was rescheduled for June 1, 1966, using the ATDA. However, the shroud that protected the docking adapter during launch failed to separate, due to lanyards being incorrectly secured with adhesive tape. Gemini 9A was launched on June 3, and when in orbit, the crew observed that the shroud of the ATDA had partially opened and was described by Stafford as "looking like an angry alligator". Docking was not possible, but the rendezvous maneuver was practiced instead.
== Flight statistics ==
== In popular culture == Gemini 8's docking with the Agena was shown in episode 1 "Can We Do This?", of the 1998 HBO miniseries From the Earth to the Moon, and in the 2018 Neil Armstrong biopic First Man. Gemini 8's docking with the Agena featured in the short science fiction drama DARKSIDE produced by nrgpix as an entry to the London Sci Fi film festival 2020.
== References ==
This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.
== External links == Gemini 6/Agena target vehicle 5002 systems test evaluation (PDF) December 1965 Gemini 6 Agena Target vehicle Gemini 8 Docks with Agena Video On the Shoulders of Titans, Project Gemini, NASA history