Transcript Telescope Design The Keck II Telescope

Telescope Design
The W.M. Keck (I & II) Telescopes
Jana Hunt & Kent Van
ME250 Precision Machine Design
April 8, 2003
Telescope Design
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Introduction/Purpose of Keck Telescope
Precision Engineering Applications
Keck Telescope Design
Dome and Building Design
Conclusion
W.M. Keck Telescope
• Type: Optical reflecting, Schmidt-Cassegrain design
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Uses the primary hyperboloid mirror to focus incoming light onto the convex circular secondary mirror which sends
the light back through a hole in the primary mirror to the eyepiece, located at the rear of the telescope…tertiary
mirror...
Sits on summit of Mauna Kea, Hawaii
Purpose: To gather light to help astrophysicists observe the universe.
Various instruments are attached to analyze gathered light
Material
Zerodur
Mount:
Altazimuth
Overall height:
24.6 meters
World’s Largest Reflecting Telescope
• Single piece large mirror would be extremely difficult to make & maintain
• Deflection is function of diameter (d) cubed
• Array of 36 hexagonal mirrors
– 1.8m across, 0.075 m thick
Vgd 3
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– Individually mounted and adjusted
48EI
– reduce deformation & mass of mirror
Primary Mirror configuration
Light path
Why is Precision Important for Keck
Telescopes?
Produce high quality image & reduce image blur
– Collimation - Alignment of optics
– Serrurier truss design- sets of vees gives parallel motion of upper and
lower tube - no miscollimation due to secondary tilt
– Adjust relative stiffness of the upper and lower tubes to maintain
adequate focus in direction parallel and perpendicular to optical axis
Hexagonal Mirror Segments
Passive Support System
– Axial Support (piston - x y z)
• Three 12-point wiffle trees w/flex rods epoxied to back of segment
– Radial Support (‘tilt’-x, spin-y, azimuthal-z)
• Radial Support Post
• .25m-diameter Flexible Diaphragm - permit small amount of tilt
and piston motion required by control system
Wiffle Tree Support
12-pt Wiffle Tree (x3)
Diaphragm &
Radial Support Post
Segment Fabrication
Stressed Mirror Polishing
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Forces and moments applied to Zerodur blank to form desired non-axisymmetric
shape
Sphere is ground and polished into blank, forces are removed
Polished surface deforms elastically into desired shape (provided no hysteresis)
Segment cut into hexagonal shape
Warping harnesses used to correct surface shape (reduced surface error to 90nm rms)
Ion-Figuring- ionized argon beam removed glass molecules from surface (15nm
rms!)
Surface Profile of Segment after Warping Harnesses are used
Mirror Sensors & Actuators
Controls compensates for small errors
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Requires active control system to maintain segments in proper alignment
Adjustments made 2x per second
Redundancy – 168 sensors, 108 actuators
Precision linear actuators
Dome Design
To protect telescope and help maintain
precision
– Important in maintaining
temperature stability
– Height, Width: 30.8 x 37 meters
– Moving weight: 635 tons
– Total air-replacement: 5 minutes
– Geographic stability and vibration
isolation pg9-2
W.M. Keck Telescope
• Conclusion (Kent)
– Review precision applications adapted on a larger
scale
– Summarize how/why precision engineering was
used for Keck telescope design
– 1080 segment (CELT) telescope being planned
?’s
References
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W. M. Keck Observatory. [Online] Available: http://www.astro.caltech.edu/mirror/keck/
Keck Telescope's adaptive optics let astronomers study volcanic activity on Io from armchair on
Earth. [Online] Available: http://www.berkeley.edu/news/media/releases/2002/06/03_keck.html
The Keck Telescope Space Craft SCIENCE Kit. [Online] Available: http://scikits.com/Keck.html
The Keck Telescope. [Online] Available: //www.ngst.nasa.gov/science/meetings/Keck.html
An Introduction to Interferometry. [Online] Available:
http://www.mtwilson.edu/Education/Presentations/Interferometry/
Kodak Supplies Optical Quality Mirrors to the W.M. Keck Observatory. [Online] Available:
http://www.kodak.com/US/en/government/ias/optics/ion.shtml
Nelson, Mast, and Faber. The Design of the Keck Observatory and Telescope (Ten Meter Telescope),
Keck Observator Report No. 90, January 1985
“Advanced Technology Optical Telescopes IV,” SPIE Volume 1236, 1990
Terry Mast and Jerry Nelson, Warping Harnesses for CELT. CELT Technical Note No. 6. [Online]
Available: celt.ucolick.org/reports/technote01_6.doc, February 2002
Terry Mast and Jerry Nelson, and Gary E. Sommargren, Primary Mirror Segment Fabrication for
CELT. [Online] Available: http://celt.ucolick.org/reports/report00_5.pdf
Appendix
• Mirror profile
• Improvement from use of active optics
• Interferometer plans
Figure 1: Decenter and tilt of secondary mirror and its effects
on image quality and image displacement (blur).
Mirror Alignment
• Active controls of mounts
required due to Earth’s
motion
– Adjustments made 2x per
second
– Adjustments to 4nm possible
• Adaptive optics installed on
Keck II
– 670 adjustments per second
– 10x focus improvement
Interferometer
• Future plans:
– Multiple telescopes become a massive interferometer
– Light combined at single point in tunnel
– Resolution angle improved as function of 1/D:
• Θ=λ/D
D