The tubular, truss-type superstructure extended upward from the base hexagon. It provided support for the solar panels while latched under the shroud during the launch phase, and for the radiometers, the magnetometer, and the nondirectional antenna, which was mounted at the top of the structure. The superstructure was designed to be as light as possible, yet be capable of withstanding the predicted load stresses. The six magnesium chassis mounted to the base hexagon housed the following equipment: the electronics circuits for the six scientific experiments, the communications system electronics; the data encoder (for processing data before telemetering it to the Earth) and the command electronics; the attitude control, digital computer, and timing sequencer circuits; a power control and battery charger assembly; and the battery assembly. The allotment of weights for Mariner II forced rigid limitation in the structural design of the spacecraft. As launched, the weights of the major spacecraft subsystems were as follows: Structure 77 pounds Solar panels 48 pounds Electronics 146 pounds Propulsion 32 pounds Battery 33 pounds Scientific experiments 41 pounds Miscellaneous equipment 70 pounds Gross weight 447 pounds THE POWER SYSTEM Mariner II was self-sufficient in power. It converted energy from sunlight into electrical current through the use of solar panels composed of photoelectric cells which charged a battery installed in one of the six chassis on the hexagonal base. The control, switching, and regulating circuits were housed in another of the chassis cases. [Illustration: _This hexagonal frame, constructed of magnesium and aluminum, is the basic supporting structure around which the Mariner spacecraft is assembled._] [Illustration: _Plan view from top showing six magnesium chassis hinged in open position._] VIEW LOOKING AFT ASSEMBLIES HINGED IN OPEN POSITION SCIENTIFIC EQUIPMENT ASSEMBLY I COMMUNICATIONS ASSEMBLY II DATA ENCODER AND COMMAND ASSEMBLY III ATTITUDE CONTROL AND CC AND S ASSEMBLY IV POWER ASSEMBLY V BATTERY ASSEMBLY VI The battery operated the spacecraft systems during the period from launch until the solar panels were faced onto the Sun. In addition, the battery supplied power during trajectory maneuvers when the panels were temporarily out of sight of the Sun. It shared the demand for power when the panels were overloaded. The battery furnished power directly for switching various equipment in flight and for certain other heavy loads of brief duration, such as the detonation of explosive devices for releasing the solar panels.