The original Gemini 6 mission was to feature the first orbital docking to an Agena target vehicle. With Gemini 6 fully fueled on the pad and the crew in their seats, the Agena target vehicle exploded 6 minutes into its launch. Gemini 6 was canceled and replaced with Gemini 6A, which would rendezvous with the 14 day long Gemini 7 mission. The first launch attempt ended with a pad abort and emergency shutdown of the Titan II rocket's engines just 1.7 seconds before liftoff. The causes of the abort were quickly fixed and the mission launched three days later. The crew rendezvoused with the on-going Gemini 7 mission, marking the only time two crewed NASA spacecraft were in orbit together. This became the first time two spacecraft rendezvoused with each other in orbit.