The initial values used were identical to those used during ground testing. After early on-orbit tests showed that the gain of the MCPs was higher than expected on both segments, the voltages were lowered to return the gain to the prelaunch values. As described in Section 1.2.1
, exposure to photon events lowered the gain in the spectral region at the original lifetime position, so the voltage was raised on several subsequent occasions as shown in Table B.1
to keep the gain high enough to minimize throughput loss. The voltage has been adjusted as needed since then to keep the gain in the spectral region at acceptable levels.