Hobby-Eberly Telescope

The Hobby-Eberly Telescope Project

Rainbow line

Completed outside of telescope.

Status of the Hobby-Eberly Telescope

Most major structural components of the HET are complete. The telescope is now in a system integration phase. First light is scheduled for late summer 1996 and science operations are expected to begin in mid 1997.

The Hobby-Eberly Telescope Project

The Hobby-Eberly telescope (HET) is a 9 meter telescope being built by an international collaboration between the University of Texas at Austin, The Pennsylvania State University and Stanford University in the United States and Ludwig-Maximilians-Universitaet Muenchen, and Goerg-August-Universitaet Goettingen in Germany. The HET is named in honor of its principal benefactors, Lt. Governor William P. Hobby of Texas and Robert E. Eberly of Pennsylvania. The HET employs a unique design that marks a fundamental departure from the usual paradigm for building large optical telescopes. The engineering approach adopted makes the HET a quality instrument which maximizes the scientific research capability and minimizes cost. The HET is currently nearing completion at the University of Texas McDonald Observatory near Ft. Davis Texas for a cost of ~$13.5 million; not including instruments.

General Features of the Design

Central to the HET design approach is specialization: the HET is tailored for spectroscopy, and in particular, fiber-coupled spectroscopy. By limiting observational flexibility, extremely cost-effective technical solutions are possible and these have been implemented in the HET. The HET has a spherical main mirror whose optical axis is tipped 35o from the zenith. The mirror and telescope are mounted on a frame which turns 360 o in azimuth. During an observation the telescope is fixed in azimuth and objects are tracked by moving a spherical aberration corrector to follow the reflected light. The angle of the primary mirror with respect to gravity is constant resulting in large cost savings in the mirror and mirror support systems. HET reflecting surfaces utilize enhanced silver coatings to maximize the amount of light that is delivered to the focal plane.

Technical Details

Primary Mirror: The primary mirror is composed of 91 segments, each hexagonal in shape and 1 meter across the flats. 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 complete primary mirror 11 meters in diameter with an area of 77.6 square meters. All the segments are supported on a steel mirror support truss which is kinematically mounted on the telescope structure.
Optical Design: The spherical figure of the large primary mirror is a major reason for the lower cost of the HET. The resultant spherical aberration does have to be corrected. This is done with a four mirror system that allows good images over a 50 mm diameter (~2 inch) focal plane that images four-arc-minutes of sky.
Telescope Structure: 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-degree horizon. It is fixed in zenith angle at 35 degrees which along with the azimuth rotation allows it to access declinations from -10o 20' to +71o 40'(about 70% of what a general purpose telescope at the same site would normally achieve).

Telescope structure.

Tracking: 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 12o focal surface ranges from 0.75 hr. at the equator to 2.5 hr. at the north declination limit.

Telescope foundation.

Enclosure and Facility: 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 both piston and tilt.

Completed outside of telescope.

Instrumentation: The incoming light is captured at the focus of the telescope and is relayed by a fiber optic cable to either a high resolution (20000< l/Dl <60000) or medium resolution (3000< l/Dl <18000) spectrograph which both reside in a temperature-controlled room under the telescope. Alternatively it can feed a prime focus low resolution (300
Science Capability
The technical approach taken with the Hobby-Eberly telescope leads to a powerful special purpose telescope. The telescope design has incorporated deliberate and considered trade-offs between cost and performance to achieve 8 meter-class capability in important areas within our $13.5 million costs. While we expect the HET will fulfill a wide variety of scientific missions we have not yet considered, it will be especially competitive when used with the following criteria in mind:

The following is a brief sample of scientific programs for which the HET is particularly well suited:

Program Management
The HET Project Manager is Thomas A. Sebring. The Project Scientist is Dr. Larry Ramsey. Dr. Frank Bash is the Director of McDonald Observatory. A board known as the Hobby-Eberly Telescope Board is formed of representatives from all partner institutions to govern the construction and operation of the HET. Dr. Greg Geoffroy, Dean of the PSU Eberly College of Science, serves as the Chairman of the HET Board.
Hobby-Eberly Telescope Board

Further Information
For further information on the science programs and anticipated telescope performance contact
Lawrence W. Ramsey, Hobby-Eberly Telescope Project Scientist
Department of Astronomy & Astrophysics
The Pennsylvania State University
5256 Davey Laboratory
University Park, PA 16802
Phone 814-865-0333 FAX: 814-863-3399
E-Mail: (Internet) lwr@astro.psu.edu

For more detailed information on the engineering implementation of the telescope systems contact

Thomas A. Sebring, Hobby-Eberly Telescope Project Manager
McDonald Observatory
University of Texas at Austin
RLM 15.308
Austin, TX 78712
Phone: 512-471-4322 Fax 512-471-7199
E-Mail: (Internet) sebring@astro.as.utexas.edu

(Compiled by Andrew Stephens)