Title: Ground%20Based%20Observatories%20(GBO)%20All%20Sky%20Imager%20Design%20Stewart%20Harris%20-%20UCB
1Ground Based Observatories (GBO)All Sky Imager
DesignStewart Harris - UCB
2All Sky Imager
- Overview
- Use Camera/Lens design validated in Phase A
- Cooled CCD camera
- 16-bit A/D, USB interface
- All Sky Lens
- w/ telecentric filter cell
- Add USB extender
- USB cable extends from 5m to 50m using CAT5 cable
- Add Environmental Enclosure
- Requires heating / temperature control
- Provides flexible mounting interface
- Add Sun Shield
- Electrical Interface
- Unit Test
3All Sky Imager w/ USB I/F
Starlight Xpress MX716
4ASI Requirements
REQUIREMENT SYSTEM DESIGN
GB.ASI-1 FOV. The field of view of the ASI shall be greater than 170, full angle. Compliance. Yes
GB.ASI-2 Exposure Time. Shall have an exposure duration that is programmable with a maximum exposure duration of no less than 1 second. Compliance. Yes
GB.ASI-3 Spectral Response. Within passband of 400 to 700nm, shall provide detectable response when stimulated with a source radiance less than 10kRayleigh, at maximum specified exposure duration. Compliance. Expect minimum sensitivity lt 1kR (51 SNR)
GB.ASI-4 Spatial Resolution. Shall provide aurora onset localization with accuracy better than 100km (dMLTlt 1) Compliance. Raw ASI image will have gt 250 pixel resolution per image diameter. Thumbnails will have 0.5 binning.
GB.ASI-5 Viewport. Shall have heated dome viewport Compliance. Yes
GB.ASI-6 Cadence Shall have a programmable repetition interval, minimum interval of no less than 10 seconds Compliance. Have demonstrated cadence of 5s, and 3s appears to be feasible
5ASI Data Products
- ASI primary image 290 pixel diameter is binned
to 0.5 resolution (thumbnails) - Primary science data
- Level 1 ( 1kbps) (incl GMAG, housekeeping)
- Available via SAT comm, either Telesat
(Internet real-time) or Iridium (daily) - High resolution data
- Level 0 (180 kbps) recorded HDD
- Selective downloads via Satellite Internet
- Periodic manual collection via disk swapping
6ASI Enclosure Specifications
- ASI Enclosure
- Operate in external ambient 50º to 40ºC
- Maintain internal temperature at 20º 10ºC
- Requires about 150 W heating
- Heat dome to clear it of snow/ice
- Hermetically sealed unit w/ nitrogen purge
- Dessicant used for field repair
- Hermetically sealed electrical connectors
- Polycarbonate/acrylic dome
- Flexible mounting
7Prototype ASI Enclosure
8ASI Enclosure Performance
- Dome
- Stayed clear
- Some ice buildup on flange
- Heating
- Maintain 50 ?T using about 35W avg. heat power
- Total heating power available is 240W
9ASI Prototype Findings
- What we learned
- 5 second cadence produces a LOT of data
- Insulation must be tolerant to sun exposure
- Adopting Foil-face polyethylene air pillow wrap,
multi-layer wrap - Improvement to dome heating is desirable
- Sealing improvement needed
- Other minor issues
- Need to reduce length of housing
- Improve thermal coupling of thermistor to
mounting bracket - Orient camera such that top of image is North
- Various changes in fasteners / assembly
10Production Enclosure Design
Design Allison Park Group, Inc.
11ASI Sun Shield
- Background
- ASI must survive, without degradation,
non-operating exposure to daytime sun exposure - CCD is Sony Interline Transfer device ICX249AL
- Features microlens on each pixel, an organic
material subject to deterioration due to UV
exposure - All Sky Lens uses Peleng Fisheye f/3.5
- A/R coating exhibited discoloration after one
summer in Athabasca - Result
- Need internal sun shield
- Drives housing diameter and heat required
12Sun Shield Design
Retracted Position is the Fail-safe Position
13Sun Shield Prototype
- Status
- Just built
- Needs adjustment / balancing
- Solenoid drive circuit needs test
- Provides low power cont. duty drive
- Needs qualification test
14ASI Electrical Interface
ASI has two external interface connectors
Power
Data
15ASI Unit Test Summary
- Acceptance Tests
- FOV (gt170)
- Exposure Time (duration at least 1 sec)
- Spectral Response
- Produce detectable response to source radiance lt
10kR - Goal lt 1kR
- Passband 400 700nm
- 1 sec exposure duration
- Spatial Resolution (gt250 pixel image diameter)
- Verify point source response
- Cadence (better than 10s)
- Goal lt 5s
- Record dark and bias images (room temperature)
- Record response to standard source
- Pre-Shipment
- Focus adjustment and verification
- Alignment verification (top of image relative to
alignment datum) - Heater control functional test (incl thermistor
time response) - Solenoid functional test (iterations TBD)