CSM/SLA Separation

Separation of the CSM from the SLA is a fast but complex event. A train of explosive cords sever electrical connections between the Service Module and the S-IVB; they cut the metal structure joining the SM to the SLA to allow the spacecraft to come free; they cut the upper 75% of the conical SLA into four long sections which are now only joined to the S-IVB by spring loaded partial hinges at the centre of their lower edge; they set off pyrotechnic thrusters, mounted within the intact portion of the SLA, which force pistons to push on the outside edge of each SLA panel, causing them to begin rotating away from the enclosed Lunar Module. Once the panels have rotated about 45° from the centreline of the launch vehicle, the hinges disengage, allowing the springs within the hinge assembly to push the panels away at about 2.5 m/s, leaving the LM exposed on top of the Saturn's third stage.

An image from the Apollo collection regularly reproduced in books is of the S-IVB for Apollo 7, seen from the CSM, which clearly shows the panels still attached. The commander of this mission, Wally Schirra, was unhappy that one of the panels had not fully deployed and that they seemed prone to flexing. He cancelled a planned docking test for fear of a panel hitting the spacecraft and NASA subsequently arranged for SLA panels to be jettisoned completely away from the vicinity. (ap15fj)