GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

Figure 11-1. Block diagram of TRE and associated aspects of the SRE systemThe telescope Readout System performed well during initial on-orbit checkout (IOC). Most of the templatesworked as intended. The detector balancing algorithm, which is intended to adjust the operating point of thedetector preamplifiers and the signal level at the A/D converter, underwent a minor adjustment to change thelimits of acceptable completion for the clamp adjustment. As a result of less than optimal automated adjustmentperformance, a CSTOL procedure was created, and used to make manual adjustments of the clamp commandlevel to optimize the voltage level at the A/D converter.11.2 Operational Performance and OverviewThe Operations personnel had little to monitor or change with the Telescope Readout Electronics. Most of thetimeline events were related to managing the CPU utilization by the SQUID/ST Software. Three specific areas ofinterest, other than initial power on and setup did require some operator intervention, and these are highlightedin the next few sections.11.2.1 Gain LevelsTwo overall signal gain levels were used during IOC, Gain 12 and Gain 11. These correspond to approximately870 and 615 V/V between the charge-locked loop preamp output and the A/D converter of the SRE. It has beendetermined that the lower gain level achieves good performance and is easier to adjust with the balancingprocedure. During Science, it was determined that there might be an advantage to using even lower gain levels.Table 11-1 lists the times of gain changes on the two sides from just after launch until the end of the Science datacollection on 15 August 2005. The gain changes during the post-Science calibration phase are not given in thetable.310 March 2007 Chapter 11 — Telescope Readout Subsystem (TRE) Analysis