A.3 Transfer Mode Acquisition and Scanning

When the FGS is operated in Transfer mode, the acquisition is implemented in the same sequence as described in the previous section, with the exception that the FGS remains in CoarseTrack until a specified spacecraft time. Thereafter, the 486 slews the IFOV to the starting point of the first scan and steps it across the object along a diagonal path in detector space for a distance specified in the Phase II proposal. Each sweep across the target is referred to as a scan. After completing a scan, the 486 reverses the IFOV’s direction and scans the object again until the total number of scans (as specified in the Phase II proposal) has been completed. Every 25 milliseconds, the PMT data and star selector rotation angles are reported in the telemetry. The FGS samples the entire S-Curve and its wings with sub-milliarcsecond resolution. The interferogram can be reconstructed by post-observation data processing.