DECam

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DECam CTIO
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DECam CTIO

• DECam will greatly expand and extend wide field
  imaging capability at CTIO
• DECam makes new demands on Blanco image quality,
  reliability, efficiency and functionality.
• CTIO is responding by investigating and improving
  telescope performance, improving image quality,
  and upgrading telescope systems to adequately
  support DECam.
• DECam must also fit within the NOAO system as a
  facility instrument, the design reflects this.

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DECam CTIO CTIOs preparations, recent

• Radial support mechanism now understood
• 24 supports, 3 pivot points each complex,
  gravity-driven system.
• Supports were detaching from the primary due to
  mechanical interference and accumulated
  misalignments resulting from inadequate repairs.
• Primary mirror movement identified and
  (partially) resolved
• Broken radial supports generated imbalances in
  the radial support system
• Primary mirror movement in cell involved
  hysteresis and was unpredictable

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DECam CTIO CTIOs preparations, recent

• Primary mirror repositioned 2.3mm in z-direction
• Primary mirror is now centered in cell
• Coma was dominant and variable, is now the third
  most significant aberration and stable.

Image Quality obtained by the SuperMacho program,
2005B, airmass corrected, VR filter. 2005-09-05
to 2005-12-31, Blue pre-shutdown, red
post-shutdown, approx equal number (580)
exposures each.
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DECam CTIO CTIOs preparations, recent

• Radial support counterweights augmented
• Telescope flexure measured
• Movements of primary w.r.t. corrector no longer
  show hysteresis and are believed to be due to
  flexure.
• Aluminization chamber upgrade underway
• Two degree slew time reduction from 35s to 17s -
  feasibility established
• Telescope FEA model built, drawings supplied,
  design limits explored

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DECam CTIO CTIOs preparations, to do and
under way

• Complete radial support repairs
• Either complete review of repaired supports
  retune as necessary
• Or upgrade re-site all radial supports to
  virgin glass
• TCS upgrade
• Retire irreplaceable, obsolete components
• Move to modern, integrated system (Linux,
  ethernet, current gen PMAC, tape encoders)
• To incorporate supply observation telemetry
  metadata
• Cleanroom
• Coude room, required for assembly, testing
  future repairs

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DECam CTIO

• Significant upgrades will come with the
  instrument itself
• Alignment sensors and active alignment correction
• Contemporaneous focusing
• Active instrument cooling
• New corrector(better design, not damaged!)

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DECam CTIO Integration Community Use

• DECam is to be a facility instrument.
• DECam will replace Mosaic II and must offer the
  same functionality and similar flexibility
• f/8 secondary (top-end flip)
• DECam U band is limited by CCD response, Mosaic
  II by corrector transmission ? same efficiency
• Filters
• Must be able to use non-DES filters on non-DES
  nights
• 6 filter positions minimum, 8 preferred (Safe
  change procedure)
• Observing environment
• Observer interface
• Integration into NOAO Science Archive

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DECam CTIO Integration, Physical Envelope

• Installation integration considerations
• Mechanical limits (Instrument max mass 5 tons)
• Interfaces
• Assembly
• Mounting (DECam replaces the entire top-end,
  excluding top-rings and spider)
• Alignment (Hexapod)
• Commissioning
• Environmental conditions Temperatures, humidity,
  orientation changes, earthquakes
• Maintenance, spares, tooling, documentation
• Operations

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Documents in preparation

• Much of what has been discussed here is already
  incorporated in the design, and will be laid out
  in detail in the following documents
• Integration Plan
• Defines the interfaces between DECam, the Blanco
  Telescope and the outside world
• Installation Plan
• Defines procedures and responsibilities for the
  initial installation of DECam
• Operations and Maintenance plan
• Defines and documents the procedures and
  responsibilities for servicing DECam.
• Community use document
• Defines and documents the needs of the
  NOAO/Blanco community for DECam.

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DECam CTIO

• END

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Radial Support
One radial support, in below-mirror (compression)
position. M Primary mirror H H-bar attachment
to primary (old style) A Lever arm C
Counterweight D Cast bracket E Plug, fits into
socket (not shown) mounted on inside of
telescope barrel B Point of attachment to mirror
cell F Force vector radial support applies to
primary mirror G Gravity vector P Pivot points.

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Current H-bar design Strains are not uniform in
the pads
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New H-bar design
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2006 04 28 another spin around the pole
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4m TCS Upgrade Current TCS Rack
VME Chassis (Obsolete comms board)
VME Interface (Wire-wrap breadboarded components
)
Drive Interface (Wire-wrap and breadboarded compon
ents)
Power Supplies
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Existing Blanco TCS
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4m TCS Upgrade Rack Evolution
Proposed Rack
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Current TCS telescope control
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SOAR control model
In SOAR this is proprietary
IN ? PID ? OUT
Encoders
Motor Controller
Interlocks
Setpoint
Status
Motors
Position Status Telemetry
Setpoint
TCS App Kernel
GUI
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Planned Blanco TCS
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Shutter specifications

• Shutter performance requirements are based on the
  precision required to make calibrations via
  standard star observations
• The shutter should provide 1 percent uniformity
  at a 1 second exposure time.  (i.e. the actual
  exposure time anywhere on the CCD should not be
  more than 1 different from anywhere else at this
  exposure time).
• Shutter exposure time repeatability should be
  better than 0.005 seconds (5 milliseconds).
• Shutter exposure time accuracy should be such
  that the offset from the nominal exposure should
  be less than 0.05 seconds (ie 50 milliseconds)
• Absolute timing of an exposure should be measured
  to a precision of 10ms and recorded in the
  resulting image FITS header.
• The shutter should allow exposures from 1 second
  upwards. We will not test performance for shorter
  exposure times, but capability to take shorter
  exposures (e.g. down to 0.2 seconds) would be
  useful as goal, not a specification.
• Performance maintained -5C to 20C.
• Performance maintained after high duty-cycle
  tests,
• 7. Approximately 125,000 shutter movements will
  take place per year, Shutter MTBF and MTTR
  should be based on a 10-year lifetime.
  Monitoring and diagnosis of performance anomalies
  (Uniformity, Repeatability, Accuracy above) would
  be aided by suitably telemetry from sensors
  associated with the shutter mechanism.

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Community Filters

• Filter review panel recommends considering
• BVRI
• wide VR
• SDSS u
• Washington C
• DD 051
• Ha
• OIII
• SII

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DECam as community instrument

• DECam will replace Mosaic II in all respects
  therefore must be able to perform as Mosaic II
• f/8 function must be maintained
• DECam U band limited by CCD response, Mosaic II
  by glass ? same efficiency
• Shutter performance driven by standard star
  observations, minimum exposure time 1s
• Filters current concept is for 6, possibly 8.
• 4 DES, remainder for community
• Community/NOAO will have to purchase own filters
  beyond DES 4.

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DECam CTIO CTIOs preparations, previously

• High-quality primary, D80 at manufacture 0.25
• Active Optics
• 33-pad system, LUT driven, updated every few
  months
• DECam will provide in-line updates (via donut)
  possibly allowing us to close the loop during
  observations

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DECam CTIO CTIOs preparations, previously

• Thermal Environment improvements
• Dome ventilation doors at telescope level
• Dome covered with thermally insulated aluminum
  panels
• Air ventilation around primary mirror and
  telescope structure
• Better thermal management throughout the
  building, servo-control optimized system.