A laboratory apparatus called a "vacuum damper investigation and performance evaluation robot" ("V-DIAPER") affords capabilities for vacuum dynamic testing of torsional dampers. The apparatus was developed for original use in testing torsional dampers (rotary viscous dampers) that are destined to operate, in vacuum, as parts of rotary solar-panel-deployment and antenna-deployment mechanisms on spacecraft. The V-DIAPER can also be used to perform vacuum dynamic testing of torsional dampers designed for terrestrial use in vacuum or in air.
In the original application, for which the V-DIAPER was developed, each damper contains a paddle that, in operation, is rotated through a highly viscous liquid in a chamber. By virtue of the rotation, the liquid is forced through an orifice from the advancing side to the retreating side of the paddle; this action contributes a major portion of the damping torque. The flow of the viscous liquid in the clearance between the paddle and the chamber walls also contributes some damping torque. When the damper is placed in a vacuum, bubbles can form in the damping liquid. The bubbles cause local decreases in viscosity and thus intermittent sharp decreases in damping torque during rotation. The V-DIAPER was designed to facilitate investigation of the effects of the bubbles under realistic vacuum operating conditions.
The V-DIAPER (see figure) includes a motor and gearbox for rotary actuation of a damper under test. The damper is mounted inside a vacuum bell jar. The motor and gearbox are mounted outside the vacuum bell jar, and the output shaft of the gearbox is connected to the damper via a torque load cell and a vacuum rotary feed-through. The load cell provides measurements of the time-varying responsive damping torque, so that decreases in damping torque associated with incidence of bubbles and the recovery of damping torque after passage of bubbles can be studied in detail. Optionally, an x-ray camera can be used for visual observation of bubbles.
In the original application, the V-DIAPER was not used only to investigate the effects of bubbles; it was also used to confirm the effectiveness of corrective measures that were undertaken in an effort to eliminate bubbles. These measures consisted mostly of improvements in the techniques for filling and sealing the dampers.
This work was done by Brian Ottens and Alphonso Stewart of Goddard Space Flight Center. GSC-14093