Heritage Adoption Lessons Learned: Cover Deployment and Latch Mechanism  James W incentsen.  Abstract  Within JPL, there is a technology thrust need to develop a larger Cover Deployment and Latch  Mechanism (CDLM) for future missions. The approach taken was to adopt and scale the CDLM design as  used on the Galaxy Evolution Explorer (GALEX) project. The three separate mechanisms that comprise  the CDLM will be discussed in this paper in addition to a focus on heritage adoption lessons learned and  specific examples. These lessons learned will be valuable to any project considering the use of heritage  designs.  Introduction  Because of future JPL mission needs for meter class space telescopes, there was an internal technology  demonstration to develop a complete mechanism set for single-time deployable cover to protect the  optics. Because the task was tracked for a fast technology development, the decision was made to fully  adopt the GALEX cover deployment design early in the project cycle to save cost and schedule. For  reference, the baseline design aperture opening diameter was 0.83 m (32.7 in) and the outer diameter of  the instrument was 1.1 m (43.3 in) in diameter, roughly twice the size of GALEX.  CDLM Overview  The three mechanisms that comprise the CDLM are the Latch, Hinge, and two Energy Absorbers. When  the Latch releases the cover, two push off springs and the Hinge mechanism rotate the cover  approximately 4.66 rad (267 deg) and impact the crushable honeycomb filled Energy Absorbers.  Deployment time is approximately 3.4 seconds. The Hinge mechanism is un-dampened. After  deployment, the cover remains against the canister. An overview of the instrument and placement of the  mechanisms are presented in Figure 1.  Latch Mechanism  The Latch mechanism, attached to the cover, employs a Starsys paraffin thermal actuator as the prime  mover. An interfacing slotted Latch Arm is affixed to the Cover Ring. The Latch Arm is spring loaded to  rotate away from the aperture opening upon release. A detail view of the latch area is shown in Figure 2,  the Latch Arm is shown in Figure 3, and a cross section of the Latch mechanism is shown in Figure 4.  The Locking Piston passes through and retains the Latch Arm. The Push Piston has a small-diameter tip  and passes through the Latch Arm slot. To deploy the cover, the actuator heater is energized, which  translates both the Push Piston and Locking Piston, forcing the Locking Piston clear of the Latch Arm.  Once the Locking Piston is clear of the Latch Arm, the Push Piston slips through the Latch Arm as it  rotates. The mechanism locks open by means of torsion spring loaded arms that snap into a grove on the  Locking Piston. Microswitches sense the motion of the arms and provide telemetry of the mechanism  state.  Power to the actuator is discontinued once one of three criteria are meet: Hall effect sensors mounted on  the Energy Absorbers register a deployed cover (discussed later), PRTs mounted on the actuator reach a  maximum temperature, or a time limit circuit is exceeded. Both the temperature and time are based on a  look up table derived from thermal vacuum Latch test data. After power is terminated and the actuator  * Jet Propulsion Laboratory, Pasadena, CA  Proceedings of the 38th Aerospace Mechanisms Symposium, Langley Research Center, May 17-19,2006.  65