HELIOS's first steps towards the sun

Details are presented on the design and performance of HELIOS, a joint German-USA solar probe launched (Dec. 10, 1974) into an elliptical orbit around the sun. The attitude control system and its components, control of the internal (air) atmosphere, antenna array, and in-flight control system of the probe are described. The configuration designed to minimize the distance between the center of gravity and the center of solar radiation pressure, the launch sequence, reorientation maneuvers executed, antenna deployment operations, and final maneuvers to get the craft into the required orbit configuration are covered.