Version 1 (modified by trac, 16 months ago) ( diff )


This is where we will collect information and requirements about the diffuser that has been designed to be used with ARCTIC.

Project History and Personnel

The diffuser was funded by a scialog grant from the Research Corporation issued to Suvrath Mahadevan (Penn State), Leslie Hebb (NAPG) and John Wisniewski (OU) :


Joe H’s role was to build the rotator for the diffuser; his time was paid for out of ARC. Suvrath and his students built the diffuser. Leslie Hebb is now the ARC point of contact for the diffuser.

Science Objective

A 4" diffuser is placed in front of ARCTIC to spread the light out into a well-defined top-hat PSF. Looking at a target through the diffuser results in a lot of tiny speckles; the idea was to rotate the diffuser rapidly so that the speckles get blurred out, resulting in improved photometry. Do we know what the limiting magnitude of this system is? It was intended to be used on bright stars, but how faint can it go?

See attached presentation for a presentation of initial performance

Current Specifications

None known.

We should have a handle on the environmental specifications as well. (eg how cold must it operate, specifications on the glass, heat generation of motor, etc)


The diffuser was commissioned in September 2016, during which test observations of 16 Cyg A & B were conducted.

Preliminary Results

Brett Morris used it successfully on 1/22/17 and was able to observe a transit of WASP-85. Based on those preliminary observations (and maybe some others?) it seems likely that the diffuser will enable the observations of transits at a level that is a factor of a few (3?) worse than what Kepler has done - to be able to do this from the ground is very appealing. The ability to fully characterize the performance of the diffuser has been hampered by bad weather on most of the observing nights during which it was scheduled to be used.

Rotator Issues

[Non rotator issue, but required engineering just the same: had to replace bearing with a precision bearing - done by Bill]

Need a description of the various issues here. This is what I can recall...

  • Leslie tried to observe with it on 2/5/17 - nothing appeared out of the ordinary but they discovered it was not rotating; Candace was able to rotate it by hand but when commanded it to rotate, no sound of air being pumped through the lines
  • Candace tested it again on 2/7/17 and the diffuser stopped rotating. Bill got it working that day but it was clear that it was going to bind again.
  • Bill tested it again on 2/9/17 and it ran for 30 minutes without issue.
  • part of the diffuser sent to Jason at UW on 2/11/17 after Leslie was scheduled to use it (without rotation) on the night of 2/10/17
  • Leslie joined tech-o-con on 2/23/17 to discuss diffuser rotator issue
  • Jason 3-D printed a new static mount that mounts the diffuser to ARCTIC (made a copy without the bearing and motor); shipped back to APO; ready for operations (in non-rotating mode) on 3/8/17
  • rotator and bearing assembly stayed at UW; Jason to devise a test bench once the rotator/motor specs are defined

Rotator Solutions

Need to collect a set of requirements and then we can explore what would be involved to implement them.

  • Rotation and other Performance Specifications (here are some notional specs suggested by Mark - need to get science drivers from Leslie )
    • Target speed 10 rev/sec , no regulation beyond min/max
    • Minimum speed 5 revs/sec, maximum speed 15 revs/sec
    • Need indicator of status (if diffuser is in or not) in TUI
    • Need indicator of rotation state (rotating or not) in TUI
    • Operation temp range -10 deg F to 90 deg F
    • dust and moth resistant IP65
    • oilless
    • Less than 5 watt heat dissipation in front of optical path
    • Operational 0 to 100% humidity
    • Expected MTBF of >10 million revolutions
  • Control
    • TUI control for in or out plus status display
    • Tui control for spin or not plus status display
    • No spin if out
    • continuous Spin during sequence
    • Start spin 1 sec before first exposure
    • stop spin 1 sec after last exposure readout
  • Physical Size Constraints
    • Get from Bill?
  • Motor Types
    • Ed Leon has already begun looking at this. See his recommendations below in the Attachments section.
  • Estimated Costs
    • TBD
    • what have we already spent so far?
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