Spring/Damper Actuator Implementing the heritage Spring/Damper also proved to be considerably more complex than initially  planned. The first obstacle was thermal control. Viscosity of the Damper’s silicone working fluid was  strongly dependent on temperature. After much petitioning, it was finally agreed that the narrow operational temperature band should be actively controlled by the Instrument, while the survival limits  could be maintained with mechanical thermostats. Given the high criticality of the Dampers, both  redundant heater circuits and redundant thermostats were required. Power resistors were chosen as heaters due to their robustness and simplicity. Finding adequate surface area to mount all the thermal  control hardware dramatically altered the exterior of the Actuator from the heritage configuration (Fig. 6).  Roller Pin (Vernier Patterns)Spring Arbor Heritage  Actuator  Accumulator Spring Laminations Figure 6. Heritage vs. Aquarius Spring/Damper Actuator Heaters &  Thermostats  Because the Spring/Damper had flight heritage, there was extreme resistance to making any changes. The fluid dynamics within the Damper were considered especially sacred, mainly because there weren’t  any of the original developers around. This caused problems because design elements such as bearing  fits and spring sizings were not scrutinized adequately, as would be found at assembly. Additional weaknesses and design inconsistencies were perceived, but were not allowed to be addressed. Other  elements deemed inconsequential to the damping function, such as direction of rotation, o-ring seals,  bearing clamps, structural mounting, and output couplings were modified to facilitate assembly and tailored to the Aquarius implementation. Also, the heritage belleville springs used to generate fluid  pressure within the Accumulator were no longer available. Substitutes were found that happened to result  in a more constant fluid pressure  and were a better material choice. A lubricating PTFE coating on the  constant-torque Spring Laminations of the Spring Motor was no longer available, either. Qualifying an  acceptable substitute would take time, and application of the coating would complicate the fabrication  process. After reasonable investigation, the coating was assessed to be ineffective at solving the spring  buckling problem for which it had been implemented, and was eliminated from the design.  The Spring/Damper had to be sli ghtly decoupled from th e Axle, so that during launch the dynamic  motions of the Boom would not be transmitted and result in  extremely high loads. A torsionally-compliant  Driveshaft (Fig. 7) was designed, which meant th e deploying Reflector co uld behave more like a  pendulum. This was aggravated by the Damper having two damping regimes: low damping initially to  accommodate kick-off and stimulate first-motion, transitioning into higher damping to slow the deployment  and minimize end-of-travel impact. This transition had the potential to incite deployment oscillations. ADAMS software was used to model the deployment dynamics and tune the Driveshaft. This model was  later used as a basis for developing the complicated Gravity Off-Load Fixture (GOLF) that would be used  to support the Antenna during instrument-level ground deployments.  240