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The '''Agena Target Vehicle''' ('''ATV''',{{IPA|ədʒiːnə}}), also known as '''Gemini-Agena Target Vehicle''' ('''GATV''') was an [[uncrewed spacecraft]] used by [[NASA]] during its [[Project Gemini|Gemini program]] to develop and practice orbital [[space rendezvous]] and [[docking and berthing of spacecraft|docking]] techniques, and to perform large [[orbital maneuver|orbital change]]s, in preparation for the [[Apollo program]] lunar missions.<ref name="ShuttleAgenaEx" />
The spacecraft was based on [[Lockheed Aircraft]]'s [[RM-81 Agena|Agena-D]] upper stage rocket, fitted with a docking target manufactured by [[McDonnell Aircraft]]. The name 'Agena' derived from the star [[Beta Centauri]], also known as Agena.
The combined spacecraft was a {{convert|26|ft|m|adj=on|sigfig=3}}-long cylinder with a diameter of {{convert|5|ft|m|sigfig=3}}, placed into [[low Earth orbit]] with the [[Atlas-Agena]] launch vehicle. It carried approximately {{convert|14021|to|14054|lb|kg}} of propellant and gas at launch,<ref>[https://nssdc.gsfc.nasa.gov/nmc/
The ATV for [[Gemini 6]] failed on launch on October 25, 1965, which led [[NASA]] to develop the Augmented Target Docking Adapter (ATDA) as a backup, a smaller spacecraft consisting of the docking target fitted with an [[attitude control]] propulsion system, but lacking the Agena orbital change rocket. The ATDA was used once on [[Gemini 9A]] after a second ATV launch failure on May 17, 1966, but failed as a docking target because its launch shroud failed to separate.
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A second GATV launch failure occurred on May 17, 1966, as Gemini 9 astronauts [[Thomas Patten Stafford|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 {{convert|107|nmi|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.<ref>"Atlas SLV-3 Flight Evaluation Report, Vehicle 5303" Convair June 27, 1966.</ref><ref>{{cite web |url=
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.
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| October 25, 1965 <br> 15:00:04 UTC
| October 25, 1965 <br> 15:06:20 UTC
| [
| N/A
| Atlas-Agena exploded during launch. <br>Gemini 6A achieved first rendezvous with [[Gemini 7]] instead.
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| May 17, 1966 <br> 15:12:00 UTC
| May 17, 1966 <br> 15:19:00 UTC
| [
| N/A
| Failed to orbit.
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==External links==
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750069069_1975069069.pdf Gemini 6/Agena target vehicle 5002 systems test evaluation (PDF) December 1965]
* [
* [https://web.archive.org/web/20140802173529/http://www.maniacworld.com/Gemini-VIII-Docks.htm Gemini 8 Docks with Agena] Video
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780012208_1978012208.pdf ''On the Shoulders of Titans, Project Gemini''], NASA history
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