Looking up at the back of the primary mirror array, you now see all the inductive edge sensor pairs that make up SAMS (the Segment Alignment Maintenance System). Each segment has 12 L-brackets, to which the actual sensors are bonded. These transmitter/receiver pairs talk to each other to monitor & decide on corrections to apply to the actuators that are attached to each segment's 3-point mount. In the past, the alignment would degrade over time as the mirror truss would contract differentially, causing the mirror stack to fall apart. But this closed loop system now maintains the alignment of the primary mirror array to superb precision over several days, in spite of large temperature & humidity changes. This greatly improves the efficiency & performance of the telescope, since we no longer need to waste an hour or two per night aligning the mirrors, & more significantly, the image quality is now both good & stable throughout the night.
|A glimpse behind the primary mirror|