Interior and Structure Seeing Nathan Dalrymple

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Interior and Structure SeeingNathan Dalrymple
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Outline

• Problem Definition
• Thermal Performance
• Seeing Performance

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Problem Definition

• Thermal mixing in interior flows and flows over
  structure
• Which enclosure concept has the least seeing?

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Retractable Issues

• Retractable
• Service platforms and structure not shaded
• No way to provide ventilation on calm days

Suns view
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Insolation on Structure

• No insolation on telescope structure for rotating
  enclosure
• Significant insolation on telescope structure for
  retractable

Protection v. Performance
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Insolation on Telescope Structure w/ Retractable
Enclosure

• Structure seeing is significant issue
• Telescope structure (OSS mount m1) 102 m2
  (1100 ft2) exposed area (equivalent to 11.4-m
  dome)
• Most (78) of this exposed steel is at or above
  the M1 level
• Low wind (0.5 m/s), un-cooled, white-painted
  surface temperatures can rise to 10 C above
  ambient air temperature
• Relatively high wind speeds are required for
  minimizing structure temperature via passive
  means 10 m/s (23 mph) required to get structure
  temp 2 C above ambient air temp
• 90 of time (or more), candidate sites have winds
  less than 10 m/s
• Need to actively cool structure or implement
  separate shading system

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Structure Thermal Performance and Seeing
Red MuSES performance Blue seeing (arcsec)
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Site Wind Speed Distributions
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How to Address Issue of Sunlight (Insolation) on
Structure

• Direct cooling on structure is problematic
• Separate, articulated shading device (e.g.,
  Sloan) not feasible, cost effective at ATST size
• Attached, cooled shades on soft stand-offs are
  best solution

Protection v. Performance
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Hybrid Issues

• Hybrid
• Entire floor and structure shaded from direct
  sunlight
• Vent gates allow passive wind cooling, thin
  boundary layers, and flush air volume
• Enclosure-mounted fans provide artificial
  ventilation on low-wind days or on days when
  external dust is present

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Hybrid Interior Ventilation

• Gemini volume flowrate 10 enclosure volumes/hour
  (150,000 m3/hr)
• This flowrate on the smaller hybrid gives V 0.2
  m/s average
• Directed flow can give V0.5 1 m/s over much of
  structure

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Summary

• Retractable requires active structure cooling or
  Sun shade to perform adequately
• Hybrid Configurable vent gates/louvers allow
  passive interior ventilation
• Can provide artificial flushing in hybrid concept
• Must weigh relative complexity of systems
• Hybrid dome is the shade
• Retractable must mount liquid-cooled Sunshades
  on structure

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Thermal Seeing Bottom Line

• Rotating Enclosure
• External shell seeing is sole issue
• Ambient air cooling of shell not adequate to meet
  spec (req gt4.5m/s)
• Chilled air system does meet spec
• Retractable Enclosure
• External shell seeing
• Ambient air cooling of shell not adequate to meet
  spec (req gt3.5m/s)
• Chilled air system does meet spec
• Structure seeing
• Passive cooling not adequate (req gt4.5m/s)
• Water cooled shade system required on mount
  structure