General Telescope Data
From the blue McDonald Observatory booklet, 1986

Telescope Operation Manuals are here, although some of this material may be dated. Also check out the McD Observing Support Page.

36" | 30" | HET

2.7m (107") Harlan J. Smith Telescope


Primary Mirror
Diameter: 2.72m (107")
Focal Length: 10.68m (35')
f-ratio: 3.93
f/9 Ritchey-Chretien System
Focal length: 23.91m (78.4')
f-ratio: 8.8
Field angle: 61.5 arc min
Plate scale: 8.62 arc sec/mm
f/18 Cassegrain System
Focal length: 47.98m (157.4')
f-ratio: 17.65
Field angle: 31 arc min
Plate scale: 4.29 arc sec/mm
f/33 Coude System
Focal length: 88.43m (290.1')
f-ratio: 32.54
Field angle: 3 arc min
Plate scale: 2.32 arc sec/mm


Primary mirror weight: 7,800 lbs.
Primary mirror thickness: 12.5"
Primary mirror material: Fused Silica
Telescope tube diameter: 12'
Telescope tube length: 32'
Telescope weight: 160 tons
Polar Axis bearings: pressurized oil radial and thrust
Declination axis bearings: Preloaded roller bearings
Dome diameter: 76'
Dome weight: ~220 tons


Design: Charles Jones, Inc.
Construction started: April, 1966
Construction completed: October, 1968
Telescope contractor: Westinghouse
Optics: Davidson Optronics
Dome: C.H. Lovell Construction Co.
Cost: ~$7 million

2.1m (82") Otto Struve Telescope


Primary Mirror
Diameter: 2.08m (82")
Focal Length: 8.13m (26.7')
f-ratio: 3.90
Cassegrain System
Focal length: 28.53m (93.6')
f-ratio: 13.65
Field angle: 28 arc min
Plate scale: 7.25 arc sec/mm
Coude System
Focal length: 47.70m (156.5')
f-ratio: 22.9
Plate scale: 4.3 arc sec/mm


Primary mirror weight: 4,200 lbs.
Primary mirror thickness: 11.75"
Primary mirror material: Pyrex
Telescope tube diameter: 8', 8"
Telescope tube length: 27'
Telescope weight: 45 tons
Polar Axis bearings: ball radial and thrust
Declination axis bearings: Tapered roller bearings
Dome diameter: 62'
Dome weight: 115 tons


Construction started: 1933
Construction completed: 1939
Telescope and dome contractor: Warney & Swasey Co.
Optics: Carl Lundin
Cost: ~$375,000

0.91m (36") Telescope


Primary Mirror
Diameter: 0.918m (36.1")
Focal Length: 3.18m (125")
f-ratio: 3.5
Cassegrain (Dall-Kirkham) System
Focal length: 12.27m (483")
f-ratio: 13.42
Plate scale: 16.8 arc sec/mm


Primary mirror weight: 448 lbs.
Primary mirror thickness: 6.1"
Telescope tube diameter: 47"
Telescope tube length: 10', 2"
Dome diameter: 20'


Construction completed: 1956
Telescope contractor: Boller & Chivens,
Dome: McDonald Staff

0.76m (30") Telescope


Primary Mirror
Diameter: 0.767m (30.2")
Focal Length: 2.29m (90")
f-ratio: 3.0
Cassegrain System
Focal length: 10.3m (405")
f-ratio: 13.5
Field angle: 30 arc min
Plate scale: 20.0 arc sec/mm


Primary mirror weight: 260 lbs.
Primary mirror thickness: 5"
Primary mirror material: Fused Silica
Telescope tube diameter: 35.2"
Telescope tube length: 90"
Dome diameter: 20'


Construction completed: 1970
Telescope contractor: Boller & Chivens,
Dome: Ash Domes

11m (432") Hobby*Eberly Telescope

Also check out the unofficial (?) HET Website and the official HET Website


Primary Mirror Array
91 Identical, spheroidally curved, 1 meter hexagonal segments
Diameter: 11.1m tall, 9.8m across (437" x 386"); Effective aperture 9.2m (362")
Radius of curvature: 26.2m (85')
Focal length (Radius of curvature/2): 13.1m (43')
f-ratio: 1.4
Segment thickness: 2"
Segment material: Zerodur
Mirror coating: Silver with Silicon Dioxide overcoat, 0.1 micron thickness
Gaps between segments: 2.04% loss over complete array
Spherical Aberration Corrector (SAC)
4 element Gregorian with Invar supports, ULE mirrors, 19.3" diameter
Low, medium, high resolution spectrographs (LRS rides atop tracker, MRS & HRS in basement)
Basement optics receive signal via fiber optic cable from tracker
LRS field of view: 4 arc minutes
Mirror Alignment Recovery System (MARS): external 90' tower with laser/optics for segment alignment.


Fixed elevation angle: 55 degrees (zenith angle 35 degrees)
Primary mirror array (+mirror truss) weight: 13 tons
Telescope structure weight: 12 tons
Tracker weight: 7 tons
Total telescope weight: 80 tons
Dome diameter: 86'
Dome weight: 19.9 tons ( +4 tons of Al tape)
Mirror truss: 1747 struts, 389 nodes, weighs 12 tons, kinematically mounted within telescope structure.
Segment support: modified Hindle mount
Actuator motion: Stepper motors / screw capable of linear motions as small as 20 nm.
Total # of actuators (3 per segment): 273
Tracker motors: 10 (all working simultaneously)
Tracker payload capacity: 970 pounds
Azimuth pointing accuracy: 1.8 arc sec


Design: Concept from PSU 1984, UT/PSU Engineering 1992-1993
Construction started: March 1994
Construction completed: 1998 (Dedication October 8, 1997)
Mirror figuring: Eastman Kodak
First light: December 10, 1996 with 7 segments in place
First spectrum: September, 1997 with 21 segments in place
Partners: UT Austin, Penn State, Stanford (CA), Georg-August (Gottingen), Ludwig Maximilians (Munich)
Cost: ~$15 million

Additional HET Tech Info courtesy Jim Fowler

The tracker weighs 4 tons. Range of motion is plus/minus 8 degrees.
10 motors operate the tracker in X-Y-Z and Theta-Phi-Rho (rotation angles about X, Y, and Z, respectively).

Primary mirror cleaned once per month with CO2 (same as the 107)

Segment control:
Segments are moved by actuators (stepper motors) - the smallest motion possible with the actuators is .02 microns (20 nanometers), which is about the same wavelength of an X-ray photon. They are basically screw shafts, 35 threads per inch but are gear reduced down to 485:1, thereby allowing very small corrections. 3 motors per mirror.

SAMS (Segment Alignment Maintenance System):
$700,000 price tag.
There are 6 sensors per mirror, except for the edge segments. There are 480 sensors total. SAMS uses an active sensor on one segment, and a passive sensor on the neighboring segment. A resonant frequency is created between the segments by the RCL (Resistor/Capacitor/Inductance) circuits in both sensors. Segment shift (in various directions) is measured by quantifying the change in resonance between segments. SAMS segment corrections are made once/minute, and are controlled by electronics kept in the big white box (looks like a freezer with aluminum tape at the corners) on the platform beneath the truss. Usually the correction needed is within 0.1 to 0.2 arc seconds (5 - 10 microns).

MARS (Mirror Alignment Recovery System):
Uses a Shack/Hartmann detector to measure the focus of one segment and then set the sphere on that reference mirror. MARS sends white light to the entire array and then measures positions and makes corrections. HET staff use MARS once/night to set the mirror, and then uses SAMS
once/minute to hold the sphere throughout the night.

Low Resolution Spectrograph (LRS): Limiting magnitude ~23. Great for measuring galactic red shifts. Uses a 1K-1K chip.

Medium Resolution Spectrograph (MRS): Not completed yet, but all components are on site. Will be great for studying the loads of Brown Dwarf candidates being cranked out by other sites. Uses a 1K-1K chip.

High Resolution Spectrograph (HRS): Limiting magnitude ~19. In use today, for things like line profiles, planet searches... It's an Echelle spectrograph. Uses a 4K-2K (two 2Kx2K chips side by side) chip.

The Telescope Operator (TO) is responsible for telescope safety and driving. They make the call on closing.
The Research Astronomer (RA) is responsible for navigation and deciding where/what/when and quality control.

HET budget: $1.5 million per year, and a tiny staff. Keck, Gemini, etc have annual budgets an order of magnitude larger, and huge staff support. Cost to operate is something like 5K per night.