After the flotation collar is attached, a hatch on the spacecraft is usually opened. At that time, some astronauts decide to be hoisted aboard a helicopter for a ride to the recovery ship and some decided to stay with the spacecraft and be lifted aboard ship via crane. All Gemini and Apollo flights (Apollos 7 to 17) used the former, while Mercury missions from Mercury 6 to Mercury 9, as well as all Skylab missions and Apollo-Soyuz used the latter, especially the Skylab flights as to preserve all medical data. During the Gemini and Apollo programs, NASA used for the astronauts to practice water egress.