Edge sensor design for the TMT

The Thirty Meter Telescope project will design and build a thirty-meter diameter telescope for research in astronomy at optical and infrared wavelengths. The highly segmented primary mirror will use edge sensors to align and stabilize the relative piston, tip, and tilt degrees of freedom of the segments. We describe an edge sensor conceptual design and relate the sensor errors to the performance of the telescope as whole. We discuss the sensor calibration, installation, maintenance, and reliability.