Figure 6. Frangibolt housing shown with  features used to avoid actuator damageSlot CushioningThrough the performed tests, we have seen significant differences in actuation times between tests with 9  and 10 VDC applied to the Frangibolt actuator. This result can be attributed to two factors. By observing  the electrical power equation ( /g1842=/g3023/g3118 /g3019), one can see that an increase in voltage has a squared effect on  the power applied. Therefore, a change from 9 to 10 VDC has a large impact on how quickly the  Frangibolt heats. Secondly, the faster the Frangibolt can be heated to its actuation temperature, the less  time there is available for heat to be lost to the environment.  Housing Design Testing showed that there is a significant kickoff force  caused from bolt fracture. This force can cause damage to the actuator insulation if allowed to impact edges of  the housing, as was observed. Care must be taken to ensure any Frangibolt housing design will provide clearance to the actuator and not cause damage from the reaction of the actuation. Figure 6 shows some of the features made in the housing to provide freedom of movement for the actuator. It was noticed that during actuation the heater wires that exit the housing were impacting the edge of the existing cut, causing the actuator to twist and inadvertently impact other edges. The slot shown in Figure 6b was extended so that the wires did not catch upon actuation and cause  damage. Additionally, all sharp edges were filed as to avoiding cutting of the actuator jacket. The addition  of cushioning to the inside of the actuator housing is another way to mitigate this issue. Although the tearing of the jacket does not impact the performance of the FD04, it was found that resetting the FD04  and subsequent actuations do cause tearing to propagate. Therefore, the actuator should be carefully inspected before and after each test. Conclusion Overall, testing of the radiation cover prototypes and Frangibolt implementation provided valuable insight, considerable knowledge, and a number of lessons learned regarding the thermal and mechanical sensitivity of the FD04 Frangibolt actuator. The prototype cover successfully opened 19 times at a range  of temperatures. It was confirmed that a clear relationship between actuation time and testing  temperature exists and is closely related to the established thermal path. Lessons were learned about  implementing the FD04 on an instrument like REXIS. The power applied has a strong impact on actuation time. Likewise, if power is applied to the Frangibolt post-actuation the heater can burn and smoke,  causing outgassing and contamination issues. The insulating jacket on the space-rated FD04 actuators is sensitive to impact so any housing around the actuator must be designed with that point in mind. The  REXIS ETU radiation cover design and test enabled characterization of this mechanism within the  relevant environments, and the lessons learned from these efforts will form the basis for a robust flight model radiation cover design. Acknowledgements This work was conducted under the support of the OSIRIS-REx program through research funds from Goddard Space Flight Center. TiNi Aerospace provided valuable technical support during the testing of  the FD04 actuators. The test effort was also made possible thanks to the help of the REXIS student team,  especially Mr. Harrison Bralower, Mr. Nhat Cao, Ms. Sara Falcone and Mr. Derek Barnes. 151