109 Design and Development of a Two- Axis Thruster Gimbal with   Xenon Propellant Lines  

Armond Asadurian* 

Abstract   A Two-Axis Thruster Gimbal was developed for a two deg ree-of-freedom tip-tilt gimbal application. This  light weight gimbal mechanism is equipped with flexible xenon propellant lines and features numerous  thermal control features for all its critical components.  Unique thermal profiles and operating environments have been the key design drivers for this mechanism which is fully tolerant of extreme space environment al conditions. Providing thermal controls that are  compatible with flexible components and are also capabl e of surviving launch vibration within this gimbal  mechanism has proven to be especially demanding,  requiring creativity an d significant development  effort. Some of these features, design driv ers, and lessons learned will be examined herein. 

Introduction   The construction of the Thruster Gi mbal is modular, as seen in the exploded view of Figure 1. It is  comprised of subassemblies in orde r to facilitate fabrication and as sembly and to allow subassemblylevel testing. This construction expedites the manu facturing process for the entire Thruster Gimbal  Assembly. The modular structural components of the gimbal are the Inboard Platform, the Outboard  Platform, and the Gimbal Ring, which is the intermediate gimbal member. Other modular components are the two Rotary Actuators and the Tubing Assembly.  The basic gimbal structure consists of the Inboar d and the Outboard Platforms joined together through  the Gimbal Ring. The Gimbal Ring is joined to the Inboard Platform on a single pivot axis through two sets of preloaded angular contact bearings. This articu lation is the Azimuth axis. Its two points of support  are the actuator output bearing set, housed within the Azimuth actuator, and the opposing bearing set,  housed in the yoke arm of the Inboard Platform. Bo th bearing sets are preloaded angular contact pairs,  providing rigid and accurate location of the Gimbal Ring.  The actuator bearing set is a duplex set preloaded to meet stiffness and load requirements, while the  bearing set on the opposite side is a more compli ant duplex set, to meet load and stiffness requirements  while accommodating any misalignments. This arrangem ent is duplicated on the orthogonal Elevation  axis. The Elevation actuator is mounted to the yoke arm of the Outboard Platform, with the gimbal ring  again attached to the actuator output member. The second bearing pair is again mounted in the opposite yoke arm, supporting the other side of the Outboard Pl atform on the gimbal ring. Orthogonality of the two  separate and independent axes is therefore established by the gimbal ring. This configuration forms a  true gimbal, with the axes intersecting at the center of the gimbal ring. The dimension from the interface  surfaces of the platforms to the rotational center lines is common, and therefore the gimbal axes are  located at a midpoint between the inboard and outboard platform interface surfaces.   The true gimbal configuration utilizing an open intermediate member (the Gimbal Ring) results in a large clear space on the central axis of the unit. This spac e is used to accommodate a set of flexible xenon  propellant lines, which are routed from the inboard in terface to the outboard interface. The size and shape                                                       

* Moog Chatsworth Operations, Chatsworth, CA 

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272