THE DESIGN OF A REMOTELY OPERATED SHUTTER (ROS) FOR THERMAL VACUUM TESTING

摘要

Space-flight hardware is required to meet specific outgassing criteria under vacuum conditions in order to reduce the risk of contaminating sensitive optics and spacecraft components. Under certain circumstances, it is desirable to measure the contamination levels that are being released from all surfaces of the test payload. This certification is often accomplished with a Total Outgassing Measurement (TOM) box. The TOM box has one 103.2 cm2 (16 in2) opening and one 4.84 cm2 (0.75 in2) opening. The larger opening allows contaminants to easily escape the box during the hardware bakeout phase. The smaller opening provides a limited conductance path for outgassed contaminants during the certification phase. A Thermoelectric Quartz Crystal Microbalance (TQCM) monitors the contamination levels inside the box to provide the total outgassing measurement. During transition from the bakeout phase to the certification phase, the TOM box is reconfigured to close the larger opening. For previous certifications, the vacuum chamber was returned to ambient conditions and the larger conductance port was closed manually. The ROS system eliminates the need to enter the chamber by remotely closing the large TOM box opening. Substantial schedule and cost savings are achieved through the use of this system. The ROS system consists of three main components; a shutter, a motion actuator, and an actuator controller. Each of these components was selected or designed to operate in an extreme-temperature and vacuum environment while providing a high level of reliability. Different types of motion actuators were considered for driving the shutter. Design parameters for the actuator included material properties, force capability, reliability, and cost. The shutter door was designed to provide a reliable seal against the TOM box without creating an excessive amount of friction. The actuator controller was chosen for its simplicity and ability to provide the correct type of power. Once the design was finalized, the shutter was manufactured in-house and the actuator and actuator controller were procured. Performance and verification tests shall be performed on the completed system over the next month (Sept-Oct 2002). The final design is presented here.