465 A Novel Release Mechanism Employing the Principle of   Differential Coefficients  of Thermal Expansion 

Clint Apland*, David Persons*, David Weir*, and Michael Marley*  

Abstract 

APL has developed a novel miniaturized release mechanism that can be used in CubeSats, NanoSats  and miniature space-borne science instruments. This miniature device is inexpensive, reusable, power-efficient, and doesn’t consume any flight parts. The principle of operation for the release mechanism is to use two parts that have complementary coefficients of thermal expansion (CTE).  Requirements, key  challenges, performance results and lessons learned are presented. Results from a total of 37 test actuations of the design under various environmental conditions demonstrated a robust device that performed reliably in a flight-like environment.   Introduction   While in the process of developing the first 3U CubeSats designed and built at APL, the authors became convinced they needed a unique release mechanism for use in restraining and releasing the CubeSat’s four solar array panels. Driven by power and volume limitations, the actuator developed in this original work is inexpensive, has a single moving part, generates no shock, uses little power, is re-settable, and does not consume any flight parts in its operation. In the process of qualifying the release mechanism, we revised the design twice to improve the performance, ease of operation and installation of the device, and to reduce the cost of producing the devices.   The CTE Release Actuator (CTERA) has successfully completed functional testing in vacuum, self-actuation testing and static load testing. It was tested under three power profiles representing those expected during flight. It has been tested in an actuator only configuration, as well as with a deployable structure representing a possible mission use.  The principle of operation for the release mechanism uses two parts that have complementary  coefficients of thermal expansion (CTE). The material with a low CTE is inserted into a hole in the material with the high CTE after the high CTE material is heated. Once the high CTE part cools, the low CTE part is trapped due to an interference fit between the two parts. The interference is sized for the retaining force desired from the actuator. The low CTE part, called the plug, is fastened to the part or assembly to be separated from the space vehicle. When the high CTE part, called the cup, is re-heated, the low CTE part is freed, just as a bolt would be freed from a separation nut.   Key challenges for the design included analysis to set the machining tolerances required, choice of the  mechanical surface properties of the two interfacing parts, finding low cost heaters with high watt-density that operate at low voltage, and testing various power profiles to minimize the power drawn by the device. A MathCAD design tool was developed for initial sizing of the interference fit, and later, using a test-verified release coefficient, to predict the release temperature under the influence of the kick-off spring.                                                                  * Johns Hopkins University Applied Physics Laboratory, Laurel, MD 

Proceedings of the 41st Aerospace Mechanisms Symposium, Jet Propulsion Laboratory, May 16-18, 2012