Agena target vehicle

Agena Target Vehicle used on the Gemini 8 mission		Gemini 8 spacecraft about to dock with the Agena.

An Atlas-Agena launches with the Agena for Gemini 6 in which it fails

The Agena Target Vehicle (ATV) was an unmanned spacecraft used by NASA during its Gemini program to develop and practice orbital space rendezvous and docking techniques and to perform large orbital changes, in preparation for the Apollo program lunar missions.

Operations

An Atlas launch vehicle launches GATV-5006 into orbit for the Gemini 11 mission.

Each ATV consisted of an Agena-D derivative upper rocket stage built by Lockheed and a docking adapter built by McDonnell. The Agena was launched from Cape Canaveral Air Force Station Launch Complex 14 on top of an Atlas booster built by the Convair division of General Dynamics. The Agena first burn would occur shortly after shroud jettison and separation from the Atlas over the Atlantic Ocean. Over Ascension Island, a second burn would place the Agena into a low circular orbit.

The McDonnell Gemini spacecraft would then be launched from Launch Complex 19, as soon as 90 minutes later. Both countdowns would proceed in parallel and required close synchronization. The Gemini would rendezvous and dock with the Agena as soon as Gemini's first orbit toward the end of the program.

The Gemini astronauts would then fly the combined spacecraft in a stabilized mode and perform a number of experiments:

• Using the Agena's attitude control system to stabilize the combination, which saved the Gemini's propellants
• Extra-vehicular activity to perform practice work on a tool panel. This required installing handrails on later flights to prevent excessive astronaut exertion.
• Refiring the Agena engine to raise the spacecraft's apogee. Gemini 11 reached a record of 739.2 nautical miles (1,369.0 km). The modified Bell 8247 engine was qualified for up to 15 restarts.
• Undocking, unreeling a 50-foot (15 m) nylon tether between the capsule and the Agena and flying in a "dumbbell" configuration with the Agena below the astronauts, to check the gravitational effect on the formation stability in uncontrolled mode. This technique is now known as Gravity-gradient stabilization.
• Using a similar tether and a few thruster bursts to rotate the two craft around each other as an early test of artificial gravity.
• After rendezvous with its own ATV, Gemini 10 performed a second rendezvous with the ATV from Gemini 8.

After the Gemini capsule separated for the last time, the Agena remained in orbit for a short time and was used to verify the command system.

The first GATV was launched on October 25, 1965 while the Gemini 6 astronauts were waiting on the pad. While the Atlas performed normally, the Agena's engine exploded during orbital injection. Since the rendezvous and docking was the primary objective, the Gemini 6 mission was scrubbed, and replaced with the alternate mission Gemini 6A, which rendezvoused (but could not dock) with Gemini 7 in December.

Augmented Target Docking Adapter

The ATDA in orbit as seen from Gemini 9A.

A backup vehicle for the ATV, known as the Augmented Target Docking Adapter (ATDA), was constructed by McDonnell from the docking target and the Gemini reentry attitude control thruster assembly for use if the primary ATV failed. The ATDA was designed to allow docking, but lacked the propulsion capability of the Agena rocket. On May 17, 1966, Gemini 9 astronauts Tom Stafford and Eugene Cernan were sitting on the pad awaiting the launch of their GATV. But once again, things went awry. The Atlas lifted smoothly into a cloudy sky, vanishing from view around T+50 seconds. Shortly before BECO was supposed to occur, the guidance control officer announced that he had lost contact with the booster. Telemetry indicated that vernier and sustainer cutoff occurred at T+300 seconds and Agena staging had taken place. The Agena continued transmitting signals until T+436 seconds, when all telemetry ceased.

Meanwhile, hidden behind cloud cover, the Atlas's right booster engine gimbaled to hard right at around T+120 seconds. The launch vehicle flipped 216 degrees around and began flying back towards Cape Canaveral, and in doing so had rotated into a position where it was impossible for ground guidance to lock on. Radar stations in the Bahamas indicated that it was heading north and descending. Atlas engine cutoff and Agena staging occurred on schedule, and both vehicles plunged into the Atlantic Ocean. The cause of the failure was unclear, but telemetry indicated that a short-to-ground occurred in the circuit for the servoamplifier output command signal, possibly due to a LOX leak in the thrust section.

Flight statistics

Target	Gemini mission	Launched	Reentered	NSSDC ID	Mass	Comments
GATV-5002	Gemini 6	October 25, 1965 15:00:04 UTC	October 25, 1965 15:06:20 UTC	GEM6T	7,190 pounds (3,260 kg)	Atlas-Agena exploded during launch. Gemini 6A achieved first rendezvous with Gemini 7 instead.
GATV-5003	Gemini 8	March 16, 1966 15:00:03 UTC	September 15, 1967	1966-019A	7,000 pounds (3,200 kg)	Achieved first docking, but mission soon aborted due to stuck Gemini thruster. ATV later used as secondary target on Gemini 10.
GATV-5004	Gemini 9	May 17, 1966 15:12:00 UTC	May 17, 1966 15:19:00 UTC	GEM9TA	7,170 pounds (3,250 kg)	Failed to orbit.
ATDA No. 02186	Gemini 9A	June 1, 1966 15:00:02 UTC	June 11, 1966	1966-046A	1,750 pounds (790 kg)	No Agena rocket. Successful rendezvous, but no docking due to shroud separation failure.
GATV-5005	Gemini 10	July 18, 1966 20:39:46 UTC	December 29, 1966	1966-065A	7,000 pounds (3,200 kg)	Boosted Gemini 10 to 412-nautical-mile (763 km) apogee.
GATV-5006	Gemini 11	September 12, 1966 13:05:01 UTC	December 30, 1966	1966-080A	7,000 pounds (3,200 kg)	Boosted Gemini 11 to record 739.2-nautical-mile (1,369.0 km) apogee. First demonstration of artificial gravity created in microgravity.
GATV-5001A	Gemini 12	November 11, 1966 19:07:58 UTC	December 23, 1966	1966-103A	7,000 pounds (3,200 kg)	No apogee boost due to defective Agena engine. Performed tether experiment.

See also

• Project Gemini
• RM-81 Agena

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 8 Docks with Agena Video