[Illustration: _Mariner spacecraft with solar panels in open position. Note extension to left panel to balance solar pressures in flight._] The Mariner battery used sealed silver-zinc cells and had a capacity of 1000 watt-hours. It weighed 33 pounds and was recharged in flight by the solar panels. The solar panels, as originally designed, were 60 inches long by 30 inches wide and contained approximately 9800 solar cells in a total area of 27 square feet. Each solar cell produced only about 230 one-thousandths of a volt. The entire array was designed to convert the Sun’s energy to electrical power in the range between 148 and 222 watts. When a later design change required the extension of one panel in order to add more solar cells, it was necessary to add a blank extension to the other panel in order to balance the solar pressure on the spacecraft. In order to protect the solar cells from the infrared and ultraviolet radiation of the Sun, which would produce heat but no electrical energy, each cell was shielded from these rays by a glass filter which was nevertheless transparent to the light which the cells converted into power. The power subsystem electronics circuits were housed in another of the hexagon chassis cases. This equipment was designed to receive and switch power either from the solar panels, the battery, or a combination of the two, to a booster-regulator. CC&S: THE BRAIN AND THE STOPWATCH Once the Atlas booster lifted Mariner off the launch pad, the digital Central Computer and Sequencer (CC&S) performed certain computations and provided the basic timing control for those spacecraft subsystems which required a sequenced programming control. The CC&S was designed to initiate the operations of the spacecraft in three distinct sequences or “modes”: (1) the launch mode, from launch through the cruise configuration; (2) the midcourse propulsion mode, when Mariner readjusted its sights on Venus; and (3) the encounter mode, involving commands for data collection in the immediate vicinity of the planet. The CC&S timed Mariner’s actions as it travelled more than 180 million miles in pursuit of Venus. A highly accurate electronic clock (crystal-controlled oscillator) scheduled the operations of the spacecraft subsystems. The oscillator frequency of 307.2 kilocycles was reduced to the 2,400- and 400-cycle-per-second output required for the power subsystem. The control oscillator also timed the issuance of commands by the CC&S in each of the three operating modes of the spacecraft. A 1-pulse-per-minute signal was provided for such launch sequence events as the extension of the solar panels 44 minutes after launch, turning on power for the attitude control subsystem one hour after launch, and for certain velocity correction commands during the midcourse maneuver.