Wax Motor Heaters

The wax motor that operates the CUBIC camera door is actuated by two redundant 10W heaters. The heater power is wired through the normally closed contacts of the TEC power relay and the normally open contacts of the heater power relay in series to ensure that the TEC and heater power cannot both be on simultaneously. This will prevent the possibility of an excess power drain by CUBIC . The heater power also passes through a relay controlled by the ICP, which requires a serial command to apply power. The ICP monitors the pressure on both sides of the door to prevent inadvertent door actuation on the ground, and monitors the wax motor temperature to ensure that the motor is not damaged by overheating. Finally, a relay selects between the redundant heaters. The circuit is shown in Figure 19.

  
Figure 19: Wax Motor Heater power circuit.

Actuation of the wax motor to open the experiment door requires:

• A Pulse Relay command to turn off the TEC.
• A Pulse Relay command to select the Wax Motor Heater.
• A Serial Command to turn on the Wax Motor Heater.
• Pressure inside the camera within 10 Torr of pressure outside the camera, or pressure inside and outside of camera less than 120 Torr.
• Wax Motor temperature below the value set by the WAXTEMP (SC42) serial command (default is 80 C).