WFPC2 Technical Instrument Report 01-01:
Shutter Jitter History Measured from INTFLATs
-A. Riess, S. Casertano, and J. Biretta
Apparent sporadic variations in the closed position of the two WFPC2 shutter blades were detected by examining the light reflected from the shutter in internal flats (INTFLATs). To characterize this phenomenon, we developed a simple algorithm to measure the history of the shutter jitter using INTFLATs. We found the position jitter in the direction of shutter motion to be minimal, indicating stable behavior. In contrast, the positions along the axis perpendicular to the direction of shutter motion exhibit greater jitter, and the amplitude of the jitter has been increasing with time. In addition, much larger sporadic departures from the nominal position are seen beginning in 1999 and continuing to the present time. We hypothesize that these variations in the closed shutter position result from mechanical wear and degradation. However, no direct connection between the jitter history and the shutter anomaly has been determined.