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

Analog control loops on the electronics boards in the forward SREs are optimized to remove thermaldisturbances on annual time scales (i.e. bias drifts over the course of the year). There is no active temperaturecontrol at higher orbital (1.7 e-4 Hz) and roll (12.9 mHz) frequencies. However, the passive thermal attenuationof the FEE minimizes the thermal disturbances at roll to a few mK rms. Spectra for the FLL boards are shown inFigure 10-12 below. The other boards are similar.Figure 10-12. SQUID Electronics Temperature Control – On-Orbit10.4.3 SRE Temperature Control PerformanceThe three tables below summarize the SRE temperature performance on orbit. The measured thermal stabilityat roll combined with the measured on-orbit bias temperature coefficients gives the bias contributions due totemperature fluctuations at roll. The measured amplitudes of the thermal disturbances are as expected prelaunch.The temperature coefficients of the electronics are a factor of 10 larger than expected, while the SQUIDsensor temperature coefficients (BKT) are a factor of 10 smaller, keeping the end-to-end contribution asspecified. Further study of the on-orbit temperature coefficient measurement data may be required.Table 10-3. Thermal Power Density at Roll (C/(Hz))— Worst case estimateFLL DAC DAS BKT_ELEC BKTSQUID 1 0.02 0.02 0.04 0.02 0.00030SQUID 2 0.02 0.02 0.04 0.02 0.00030SQUID 3 0.02 0.04 0.05 0.02 0.00030SQUID 4 0.02 0.03 0.05 0.02 0.00030296 March 2007 Chapter 10 — SQUID Readout Subsystem (SRE) Analysis