The Agena target vehicle (or ATV) was an unmanned spacecraft that was in service to NASA in the mid-1960s. This vehicle was used for developing and practicing orbital rendezvous between spacecraft in the Gemini Program. This was an essential step in the preparation up to the Apollo program. The first successful docking of an Agena test vehicle to a manned spacecraft occurred on March 16, 1966 during the Gemini 8 mission. On approach, the crew of Gemini 8 photographed the vehicle's profile as it orbited over Earth.