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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Agena target vehicle | 2/3 | https://en.wikipedia.org/wiki/Agena_target_vehicle | reference | science, encyclopedia | 2026-05-05T12:50:42.429195+00:00 | kb-cron |
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 detaching from their respective Gemini capsules, Agena target vehicles continued to execute post-mission operations under ground control. For instance, GATV 5003, post-separation from Gemini 8, underwent extensive systems testing. Its main engine was fired nine times, and it executed 5,000 commands, surpassing the contractual requirement of 1,000. This allowed a detailed assessment of its command and communication systems. The vehicle was eventually placed in a 220 nmi (410 km; 250 mi) circular decay orbit, facilitating its observation during the Gemini 10 mission. Similarly, GATV 5005 performed three orbital maneuvers post-Gemini 10 separation, including adjustments to study temperature effects in varying orbits and executing 1,700 commands, some of which were relayed from Gemini 10. The first Gemini-Agena Target Vehicle (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. An investigation into the failure concluded that it was most likely caused by design modifications to the GATV versus a standard Agena D stage. The Agena D was designed to have its engine restarted just once while the GATV would need to be restarted five times. While a standard Agena D pumped oxidizer into the combustion chamber first and then followed with the fuel, the GATV was modified to do the reverse because the normal start method had a tendency to leak oxidizer. While this would not be a problem for the Agena D with its single restart, the multi-restart GATV would eventually lose all of its oxidizer before the stage's operating life (which would last weeks instead of hours) could be completed. Unfortunately, pumping the fuel into the combustion chamber first caused the engine to backfire and rupture from mechanical shock. It was found out that Lockheed engineers did not properly test the GATV to root out this problem (it had been tested at a simulated altitude of 21 miles up when actual Agena engine start would occur at around 75 miles up). The solution to the problem was switching back to the normal oxidizer-first engine start and also testing the GATV in appropriate conditions. Bell Aerosystems, the manufacturer of the Agena's engine, were also instructed to perform further ground-level tests.
== Augmented Target Docking Adapter ==