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
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