IGM (Iterative Guidance Mode)

Up to now, the IU has been steering the vehicle according to a predetermined trajectory which minimises sideways movements though the air while tilting it along its flight azimuth. It has not been using any information about its position and velocity to alter its flight path. The control is "open loop." Dave Scott's call of "Guidance initiate," marks the point where the IU begins the IGM (Iterative Guidance Mode). The control loop is closed as the IU begins using position and velocity data to help it guide the vehicle to where it wants to get to - an accurate Earth orbit. (ap15fj)