Heaters

Electrical heaters are provided in the forward RCS module and the OMS/RCS pods to maintain the propellants in the module and pods at safe operating temperatures and to maintain safe operating temperatures for the injector of each primary and vernier RCS thruster.

Each primary RCS thruster has a 20-watt heater, except the four aft-firing thrusters, which have 30-watt heaters. Each vernier RCS thruster has a 10-watt heater.

The forward RCS has six heaters mounted on radiation panels in six locations. Each OMS/RCS pod is divided into nine heater zones. Each zone is controlled in parallel by an A and B heater system. The aft RCS thruster housing contains heaters for the yaw, pitch up, pitch down and vernier thrusters in addition to the aft OMS/RCS drain and purge panels. The OMS/RCS heater switches are located on panel A14.

The forward RCS panel heaters are controlled by the fwd RCS auto A, B, off switch on panel A14. When the fwd RCS switch is positioned to auto A or B, thermostats on the forward left-side panel and right-side panel automatically control the respective forward RCS heaters. When the respective forward RCS panel temperature reaches a minimum of approximately 55º F, the respective panel heaters are turned on. When the temperature reaches a maximum of approximately 75º F, the heaters are turned off. The off position removes all electrical power from the forward RCS heaters.

The aft RCS heaters are controlled by the left pod auto A and auto B and right pod auto A and auto B switches on panel A14. When the switches are positioned to either auto A or auto B, thermostats automatically control the nine individual heater zones in each pod. Each heater zone is different, but generally the thermostats control the temperature between approximately 55º F minimum to approximately 75º F maximum. The off position of the respective switch removes all electrical power from that pod heater system.

The forward and aft RCS primary and vernier thruster heaters are controlled by the fwd and aft RCS jet 1, 2, 3, 4 and 5 switches on panel A14. When the switches are positioned to auto , individual thermostats on each thruster automatically control the individual heaters on each thruster. The primary RCS thruster heaters turn on between approximately 66º to 76º F and turn off between approximately 94º to 109º F. The vernier RCS thruster heaters turn on between approximately 140º to 150º F and off between approximately 184º to 194º F. The off position of the switches removes all electrical power from the thruster heaters. The 1, 2, 3, 4 and 5 designations refer to propellant manifolds. There are two to four thrusters per manifold.