HET Technical Overview

The primary mirror is composed of 91 segments, each hexagonal in shape and 1 meter across. They form a large spherical surface having a radius of curvature of 26.164 meters. Each segment is positioned under computer control to yield a hexagonal primary mirror 11 meters in diameter with an area of 77.6 square meters.

Primary Mirror Array Maximum Diameter 11 meters Area 77.6 square meters Focal Length 13.08 meters Filling Factor ~96.6%

The mirror resides within an overall telescope structure that is made of welded steel and weighs 60 tons. It rotates on air bearings around the complete 360° horizon. It is fixed in zenith angle at 35° which along with the azimuth rotation allows it to access declinations from -10°20' to 71°40' (about 70% of the celestial sky from this latitude, but 81% of the scientifically useful airmass range < 2.5).

	The HET is a tilted optical Arecibo type telescope, which means that tracking of astronomical targets is achieved through moving a tracker optical package, which contains spherical aberration correction optics and instrument feeds, rather than the whole telescope. Tracking time across the 12° focal surface ranges from 0.75 hr. at the equator to 2.5 hr. at the north declination limit.

The HET is located at:
W 104 00 53.0
N 30 40 53.2
2026 meters above the geoid
on the WGS84 system

The HET is housed in a spherical dome 85 feet in diameter and standing 100 feet above the ground. A 2500 square-foot building houses maintenance and service equipment and the telescope control room. A 90 foot tower contains an interferometer at the primary mirror center of curvature which is used to align all the segments in piston, tip and tilt.