Augmented Target Docking Adapter Agena target vehicle

the atda in orbit seen gemini 9a.

after failure of first gatv, nasa commissioned mcdonnell develop backup docking target minus lockheed agena rocket, augmented target docking adapter (atda). consisted of gemini docking collar , attitude control propulsion system based on gemini reentry control system. atda 10.9 feet (3.3 m) long, mass of 1,750 pounds (794 kg). few questions raised compatibility of atda atlas booster, since had lower mass gatv, potentially throwing off launch vehicle s aerodynamics , calibrated settings. however, convair assured mcdonnell pose no technical issues booster.

a second gatv launch failure occurred on may 17, 1966, gemini 9 astronauts tom stafford , eugene cernan sat on pad awaiting launch. atlas-agena lifted smoothly cloudy sky, vanishing view around t+50 seconds. shortly before booster engine cutoff (beco), guidance control officer announced had lost contact booster.

telemetry indicated vernier , sustainer cutoff occurred @ t+300 seconds , agena staging had taken place. agena continued transmitting signals until t+436 seconds, when telemetry ceased. however, atlas s right booster engine had gimbaled hard right @ around t+120 seconds, flipping launch vehicle 216° around headed towards cape kennedy. rotation had made impossible ground guidance lock on. radar stations in bahamas tracked heading north , descending. atlas engine cutoff , agena staging occurred on schedule, , both vehicles plunged atlantic ocean 107 nautical miles (198 km) downrange. agena engine did not activate since proper altitude , velocity had not been attained, preventing guidance system sending start command. while exact cause of engine gimbal control not found, telemetry indicated short-to-ground occurred in circuit servoamplifier output command signal, may have been caused cryogenic leakage in thrust section.

while convair accepted responsibility launch failure, lockheed engineers expressed concern telemetry data indicated servo failure in agena, leading doubts whether stage have still operated if atlas hadn t malfunctioned. however, true cause of failure surfaced when air force released film taken tracking cameras @ melbourne beach, florida, showed atlas pitching on , heading downward. determined agena s servo malfunction caused passing through atlas s ionized exhaust trail.

the gemini 9a modified mission launch rescheduled june 1, 1966, using atda. however, shroud protected docking adapter during launch failed separate, due lanyards being incorrectly secured adhesive tape. gemini 9a launched on june 3, , when in orbit, crew observed shroud of atda had partially opened , described stafford looking angry alligator . docking not possible, rendezvous maneuver practiced instead.