Locating the HRC Shutters

To locate the blades of the HRC's on board shutters, we performed four scans- one for each blade on both the I and S detectors(Scan of the +Y blade with the I and +Y blade with the S, Scan of the -Y blade with the I and -Y blade with the S). The data was then fit with a vignetting template derived from the on-orbit mirror model. Each data set is shown below with the best fits (the top elements in the figures are the +Y shutter).


For the I: we found that the fit significantly degraded with the inclusion of the data points at 77 and 79 degrees for the +Y fit, these points were excluded from the final solution. No such difficulties were found with the -Y data. The results of the fits indicate that the blades are 1.875 and 5.375 degrees closer to the center of the detector for the +Y and -Y respectively. This gives the blade positions to be 1076 and 1259 and 1020 and 1203 for the Leading/Trailing edges for the + and - shutters respectively.

For the S: The fits seem to indicate that the blade geometry is not the nominal. The solid line of the fits indicates the nominal blade vignetting profile. As you can see the data points for both + and - suggest that the blade is actually wider than nominal. Fitting only the front edge gives a good fit (the dotted line), while fitting only the back side (the dashed line) gives an equally good fit. After consultation with the IPI team, a "wider than nominal" blade was settled upon as being the most likely cause of the off nominal vignetting profile. To whit: the front edge of the blades is offset 2.125 and 5.1875 for the + and - blades respectively, while the back edges are only offset 1.4375 and 4.5 degrees closer to the center of the detector than nominal.

During the initial scans with the I, we had some concerns that there might be a secular trend in the flux from the source. We have plotted the unvignetted flux as a function of VCDU number (aka time) and find that within each scan (both scans are shown below) that there is no conclusive evidence for any change, although there is the possibility that over the course of the entire sequences of scans there was some change in the flux.

R. Hank Donnelly
Last modified: Tue Aug 31 04:31:56 EDT 1999