Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)


 
 
 
 
 
 
 
 
 
 

Photo credits: HET photo – McDonald Observatory; all other images – Center for Electromechanics, University of Texas @ Austin

Solidworks rendering of full telescope developed by CEM.

CEM was contracted to design, fabricate and test a new star tracker for McDonald Observatory’s flagship telescope, the Hobby-Eberly Telescope (HET), to conduct the Dark Energy Experiment (HETDEX).  HETDEX’s goal is to complete the largest survey of the universe ever attempted in order to unlock the mystery of dark energy.

The new 20-ton tracker glides along linear bearings on a steal hexagon structure 40 feet above the primary mirror.  The tracker must position the science instruments along a hemispherical focal plane within an accuracy of 5 microns.

 

 

Design / Solid Modeling:

  1. Tasked with the design and fabrication of the $250,000 tracker bridge, which serves as the backbone of the tracker.  The new bridge increased in mass by 4x but supports science payload with 7x mass increase. Design criteria:
    • Constructed of hollow structural steel (HSS) tubing.
    • Design driven by minimum natural frequency of 10 Hz.
    • Required to minimize bridge mass and light obscuration (defined as the amount of light being blocked by the tracker as viewed from above).
  2. Redesigned X-axis drive system:
    • Specified pair of 4 meter long, dual-drive, planetary roller screws.
    • Sized larger linear bearings due to mass gain and retrofitted to existing structure.
    • Incorporated additional degrees of freedom to the tracker support system to prevent binding if roller screws induced skew.

Analysis:

Initial installation of bridge onto the X-rails at CEM.

Performed multitude of finite element analyses utilizing beam meshing due to aspect ratio of thin-walled tubing.

  1. Natural Frequency: Achieved final first mode natural frequency of 9.40 Hz (goal was 10 Hz).
  2. Deflection: Exceeded goal of maximum delta deflection under science payload of 2 mm (1.51 mm predicted result).
  3. Stress: Maximum Von Mises stress was 48 MPa providing adequate factor of safety.
  4. Buckling: Final buckling load factor of -7.61.

Documentation:

  1. Primary participant in significant Failure Modes and Effects Analysis (FMEA) covering the entire tracker and subsystems.
  2. Created detailed documentation for assembly and maintenance for the X-drive systems.
  3. Created many engineering drawings for fabrication, significantly utilizing geometric dimensioning and tolerancing (GD&T).
  4. Required to maintain revision control using Solidworks PDM and in-house document change process.

Publications:

  1. M.S. Worthington, T.A. Beets, J.H. Beno, J.R. Mock, B.T. Murphy, B.J. South, and J.M. Good, “Design and development of a high precision high payload telescope dual drive system,” paper no. 7733-201, Proc. SPIE Astronomical Telescopes and Instrumentation, San Diego, CA, USA, June 27 to July 2, 2010. (PN 338)
  2. M.S. Worthington, N.T. Mollison, I.M. Soukup, J.J. Zierer, J.M. Good, S.P. Nichols, “Design and analysis of the tracker bridge for the Hobby-Eberly Telescope wide field upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, San Diego, CA, USA, June 27 to July 2, 2010, paper no. 7733-147. (PN 339)
  3. B.J. South, I.M. Soukup, M.S. Worthington, J.J. Zierer, J.A. Booth, and J.M. Good, “Wind Loading and Strategy for Deflection Reduction on HET Wide Field Upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, San Diego, CA, USA, June 27 to July 2, 2010, paper no. 7733-143. (PN 340)
  4. R.D. Savage, J.A. Booth, M.E. Cornell, J.M. Good, G.J. Hill, H. Lee, P.J. MacQueen, M.D. Rafal, B.L. Vattiat, K. Gebhardt, J.H. Beno, J.J. Zierer, D.M. Perry, T.H. Rafferty, C. Ramiller, C.A. Taylor III, T.A. Beets, R.J. Hayes, J.T. Heisler, S. Hinze, I.M. Soukup, J.R. Jackson, J.R. Mock, M.S. Worthington, N.T. Mollison, O. Molina, B.J. South, D.R. Wardell, and G.A. Wedeking, “Current status of the Hobby-Eberly Telescope wide field upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, San Diego, CA, USA, June 27 to July 2, 2010, paper no. 7733-149. (PN 347)
  5. G.J. Hill, J.A. Booth, M.E. Cornell, J.M. Good, K. Gebhardt, H. Lee, P.J. MacQueen, D.M. Perry, M.D. Rafal, T.H. Rafferty, C. Ramiller, R.D. Savage, C.A. Taylor III, B.L. Vattiat, L.W. Ramsey, J.H. Beno, T.A. Beets, J.D. Esguerra, R.J. Hayes, J.T. Heisler, I.M. Soukup, J.J. Zierer, Jr., M.S. Worthington, N.T. Mollison, D.R. Wardell, G.A. Wedeking, M.P. Smith, “Current status of the Hobby-Eberly Telescope wide field upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, Amsterdam, Netherlands, July 1-6, 2012, paper no. 8444-19.
  6. I.M. Soukup, J.H. Beno, C.E. Penney, T.A. Beets, J.D. Esguerra, R.J. Hayes, J.T. Heisler, J.J. Zierer, G.A. Wedeking, M.S. Worthington, D.R. Wardell, J.M. Good, J.A. Booth, G.J. Hill, M.E. Cornell, M.D. Rafal, “Testing, characterization and control of a multi-axis, high precision drive system for the Hobby-Eberly Telescope wide field upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, Amsterdam, Netherlands, July 1-6, 2012, paper no. 8444-147.
  7. R.J. Hayes, T.A. Beets, J.H. Beno, J.A. Booth, M.E. Cornell, J.M. Good, J.T. Heisler, H.J. Kriel, C.E. Penney, M.D. Rafal, R.D. Savage, I.M. Soukup, M.S. Worthington, J.J. Zierer, “Use of failure modes and effects analysis in design of the tracker system for the HET wide field upgrade,” Proc. SPIE Astronomical Telescopes and Instrumentation, Amsterdam, Netherlands, July 1-6, 2012, paper no. 8449-56.
  8. J.M. Good, J.J. Zierer, M.S. Worthington, G. Wesley, G.J. Hill, “Design of the HETDEX VIRUS support structure for the Hobby-Eberly telescope,” Proc. SPIE Astronomical Telescopes and Instrumentation, Montreal, QC, Canada, June 22-27, 2014, paper no. 9145-204.