Project name
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Acam |
Release
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Draft Date: |
PRINCE2
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Co Authors: |
Chris Benn / Kevin Dee |
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Owner: |
Don Carlos |
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Client: |
ING |
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Document Number: |
ACAM_HL_REQ |
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Document Location
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This document is
only valid on the day it was printed. Printed on July
2007. The source of the
document will be found at: http://www.ing.iac.es/~eng/private/projects/ACAM/ACamweb/documents/current/High_Level_Requirements.htm |
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Revision History
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Date of next
revision: ? |
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Revision date |
Previous revision date |
Summary of Changes |
Changes marked |
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22 Jul 07 |
N/A |
Document created
& updated. |
Kevin Dee |
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25 Jul 07 |
22 Jul 07 |
Requirements amended
& updated |
Chris Benn |
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Approvals
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This document
requires the following approvals. Signed approval forms
are filed in the project files. |
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Name |
Signature |
Title |
Date of Issue |
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Kevin Dee |
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Acam Project Manager |
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Chris Benn |
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Acam Project
Scientist |
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Don Carlos |
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Head of Engineering
ING |
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To summarise all
of the ACAM High level Requirements or Constraints and their status. |
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Reference |
Last up dated |
Requirement /Constraint |
Optimum Value |
Acceptable Value |
Comments |
Status |
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001 |
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Observing Modes |
High Resolution/Throughput Imaging 350nm-1000nm. Long Slit Spectroscopy. (1arcminute good PSF- make available up to 8 arcmin) |
High Resolution/ Throughput Imaging 360nm-850nm |
Wide field imaging is the primary mode in which the instrument must be
optimised for. Image quality 850-1000 nm is not critical but will probably be OK
anyway. |
Frozen. High Resolution/Throughput Imaging 350nm-1000nm. Low resolution Slit
Spectroscopy |
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002 |
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Unvignetted Field of View
(FOV) Diameter |
9.3 Arcmin (ref
122.7 mm dia @ telescope focus) |
8.3 Arcmin (ref
110.4 mm dia @ telescope focus) |
A larger field up to 11.8 arcmin would make use of CCD corners and
width on a 2k by 4k chip but
constraints in particular costs of optics and complexity of design and of
equal importance the weight of the
optics – which in turn would effect the total weight constraint of the
instrument force this value lower. |
Frozen 8.3 arcmin |
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003 |
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Image Quality Imaging Mode 80% encircled energy diameter |
380 - 1000nm <0.25” FOV r<4.15’ <0.5” FOV r>4.15 350 – 380nm <0.25” FOV r <1.0’ <0.5” FOV 1.0< r <4.15’ <1” FOV r >4.15’ |
380 - 1000nm <0.3” FOV r <4.15’ <1” FOV r >4.15’ 350 – 380nm <0.35” FOV r <1.0’ <0.7” FOV 1.0< r <4.15’ <2” FOV r > 4.15’ |
The image quality is relaxed as a function of field size in the UV
wavelengths, as the design complexity, cost for exotic glass types, number of
lenses all increase to facilitate the UV. Overall throughput across the
visible wavelengths should not be compromised to accommodate an improvement
in image quality across a large FOV for UV. |
? |
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004 |
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Spectral Resolution @ 600nm 0.75” slit |
380 – 1000nm R>1000 1 arcmin R=>500 Full Field 350 – 380nm R>500 1 arcmin |
380 – 1000nm R>500 1 arcmin R>200 Full Field 350 – 380nm R>250 1 arcmin |
The key requirement is that the on-axis spectroscopic resolution in
the visible range is attained. The resolution in the UV is less critical. In
the UV, the spectroscopic resolution is poorer (because the aberrations are
larger), but the impact of this on the science is small. Off-axis, the
spectroscopic resolution is also degraded, but the impact of this on the
science is again small, because most spectroscopy would be of single on-axis
targets. |
? |
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005 |
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Image Quality Slit Spectroscopy Mode 80% encircled energy diameter |
380 - 1000nm < 2 pixels on axis < 3 pixels full field 350 – 380nm < 2 pixels on axis < 4 pixels full field |
380 - 1000nm < 3 pixels on axis < 4 pixels full field 350 – 380nm < 3 pixels on axis Full field not required |
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? |
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Slit |
Slit slide Slit length = 8 arcmin Slit width arcsec = 0.5, 0.75,
1, 1.25, 1.5, 1.75, 2, 10 & out |
Slit slide Slit length = 5 arcmin Slit width arcsec = 0.5, 0.75,
1, 2, 10 & out |
At a minimum, one slit of size 1" x 8' should be provided, but
ideally, a choice of slit widths should be available e.g. 0.5, 0.75, 1, 2,
10". These could be mounted on a slide, leaving open the future
possibility of installing multi-slit masks. |
Frozen. 3 Slit Positions available, mounted in instrument at any one time
covering the 8.3 arc min field. Interchangeable Slit masks available = 0.5, 0.75, 1, 1.25, 1.5, 1.75,
2, 10 arc sec. Commissioning and diagnostic multi holed mask to cover full 8.3 arcmin
field. |
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Instrument Entrance aperture |
9.3 arc min |
8.3 arc min |
Instrument entrance aperture
to be fitted. |
Frozen @ 8.3 arc min |
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Pupil Aperture |
50mm |
>40 mm <70mm |
Larger pupils are worse for nb filters & increase the optical path
length. Small pupils increase the complexity of the design |
Currently 45 mm diameter. Driven by optical design |
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Camera Focus |
Re-focus of telescope
secondary for filter changes and different wave lengths. |
A focus translation stage in
the actual camera is an acceptable option. |
If there is a clear gain in
image quality in both imaging and spectroscopic modes by using a focus stage
in the camera – then this can be incorporated in the design. |
Frozen. Telescope re-focus required on filter changes. Slit refocus TBC after spectroscopic design is frozen. |
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Camera Optical length I.e. from telescope focus (which is close to the outer
diameter of the A&G box) to CCD. |
>600 mm |
<850 mm |
Making the instrument length
short reduces the effects on mechanical, thermal and optical stability.
Distance between certain optics must be maintained to accommodate and
optimise the use of a slit mask, filters, Grisms and a shutter. |
TBC. Driven by Optical design |
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Pupil exit distance to next
optical lens. |
>50 mm |
Half thickness of GRISM/VPH
plus 7.5 mm. |
NB filters & Grisms will
sit at pupil. Optical design optimizes by brining next optical component
close to pupil. Filter wheels & structure constrain this distance |
TBA. Between Optical
designer & Mechanical Engineer |
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Camera throughput |
350-380 nm >0.8 380-1000nm >0.8 |
350-380 > 0.6 380-100nm >0.75 |
Barr indicates that to get
an anti reflecting coating that covers 350-1000nm you may suffer losses up to
< 2% a surface. If you only consider 400nm -1000nm you can reach
<1% a surface. CaF2 due to its low
index basically act's as an AR coating all on its own and Barr do not
recommend coating it. |
? |
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Narrow band filters |
Allow for filter tilt to remove ghosting. Standard.8=Number of filters available. Up to 80 mm dia. 10mm thick. Special<8=Number of filters up to 120 mm dia x 12 mm thick. |
Allow for filter tilt to remove ghosting. Standard.6=Number of filters available. Up to 80 mm dia. 10mm thick. Special.<6=Number of filters up to 120 mm dia x 12 mm thick. |
Location: chosen to minimise
the *range*
of angles of incidence of incoming rays, to minimise the range of wavelength
shifts. A constant wavelength shift across the whole field is OK, a
difference between on-axis and edge of field is not. Astron's design the wavelength shift between
on-axis and edge of field happens to be ~ 5 A (i.e. ~ acceptable) for nband
filters both before *and* after L2/L3, but this may change with further
optimisation |
Frozen. Location @ camera pupil. Standard diameter of filters. 76 mm. Standard number of filters positions in instrument. 5 + 1 clear + 1
VPH. 6 position combinations of 76 mm NB filters & VPH/GRISMs + 1 clear Specials up to 110 Diameter. |
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Broad Band Filters |
Position in front of NB filters. 8 = Number of filters U B V R I Z clear 80 mm diameter 5 mm thick |
Position in front of NB filters. 7 = Number of filters U B V R I Z clear 80 mm diameter 5 mm thick |
Location: not critical, but ideally before the narrow-band filters, to
remove bulk of energy from beam before it gets scattered by the many layers
in the narrow-band filter. Positions: 7, almost always with U B V R I Z
filters. Diameter of filters: slightly larger than beam, to allow for tilting
to remove ghosts. The current 50-mm ones are almost large enough for Astron's
design. |
Frozen. Up stream of Narrow band filters. Filter Diameters 76mm. 6 filters + 1 clear. |
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VPH/ Grisms in Littrow Configuration. |
Same position as NB filters. 8 = number of Grisms 76 mm diameter thickness > 20 < 30 |
Same position as NB filters. 6 = number of Grisms Diameter plus 5mm on pupil diameter thickness < 50 |
VPH/Grisms which exploit the optimized imaging instrument |
TBC |
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Order sorting Filters |
Position in front of Broad
band filters. Number of filters 5 |
Filter slide. Position in front of Broad band filters. Number of filters 5 |
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Frozen. To be included with VPH/ grism for a standard set up |
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CAGB ACam science fold
mirror |
Size = 11 arcmin . Elliptical mirror size Minor axis = 190 Major axis =
270 coating optimised for λ range Surface finish λ/20 |
Size = 10 arcmin . Elliptical mirror size Minor axis = 190 Major axis =
270 coating Aluminium Surface finish λ/20 |
New coatings to be investigated. Mirror size set at 11 arcmins which
is constrained by the autoguider Patrol field |
Frozen @ 11 arcmins |
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Patrol Field |
Keep current patrol field |
Maximise fold flat with out
compromising ability to find adequate guide stars |
Ref. Document : CAGB
autoguider patrol field and fold flat.pdf |
Frozen @ 20% lose of original
Patrol field. |
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Calibration source |
Use current CAGB unit. Fold flat to feed light on axis into ACam is mounted on an off axis
rotation stage combined with the CAGB science fold mirror |
Use current CAGB unit. Fold flat to feed light on axis into ACam is mounted on an off axis
rotation stage combined with the CAGB science fold mirror |
This has been modelled and provides a cost effective and efficient
calibration source for ACam spectroscopy |
Frozen. Utilise current small auxport fold flat |
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Slit Acquisition |
It may be feasible using fold mirrors and some optics to use the
current acquisition TV camera pick up the back reflected light of the slit
unit which is on a 10 degree angle. |
The easiest & cheapest option for target acquisition is to view
the field in imaging mode, position the target on a predetermined pixel, then
switch to spectroscopic mode. |
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Fixed. Target acquisition is to view
the field in imaging mode, position the target on a predetermined pixel, then
switch to spectroscopic mode. |
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Camera Plate Scale |
0.25”/pixel |
0.25”/pixel |
Provides good sampling for best seeing 0.5” |
Fixed @ 0.25”/pixel |
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CCD |
E2V 2048x4100x15micron pixels. |
Marconi. 2047 x 4611 x 13.5 micron pixels. |
E2V same QE curve and fringe performance as the ISIS Red+ detector.
The central 2kx2k pixels can be windowed off to improve readout speed. |
Fixed. E2V order complete. Delivery July 2007. |
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CCD Fringing |
+/- 1% at 800nm |
+/- 1% at 800nm |
E2V meets fringing requirements |
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CCD cryostat window |
Flat window Distance from window to CCD >10mm< 12mm. Distance from window to preceding optical element. >10 mm Material should be fused
silica to avoid background radiation from the glass |
Active Window. Distance from window to CCD >10mm< 12mm. Distance from window to preceding optical element. >7.5 mm . Material should be fused silica to avoid background radiation from the
glass |
It is preferred to have a flat cryostat window in the optical design
to enable the CCD to be used at any focal station. This also means a standard
mounting arrangement can also be used. Image quality must meet requirements;
if this is not the case then an active window should be incorporated in the
optical design. Note consideration for the effects of vacuum and atmospheric
pressure across the window need to be addressed. |
Frozen. Active cryostat window. Distance from optical edge to CCD = >7.5mm |
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Weight of instrument Out of Balance Moment |
80 kg < 100Nm |
110 kg < 150 Nm |
Instrument must be counter
balanced to reduce the out of balance torque on the rotating cass cluster. |
TBC |
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Instrument Interface |
. Open aperture flange is
220mmÆ. Fixing 12 x M6 equispaced
on a PCD of 230mmÆ. |
Current auxport interface
flange. Open aperture flange is 220mmÆ. Fixing 12 x M6 equispaced
on a PCD of 230mmÆ. |
Current mount can be stiffened
to minimise flexure. |
Fixed. Current CAGB auxport
interface flange |
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Instrument Space Envelope |
Optical axis and interface
flange as datum. 600 mm (long) x 450 mm wide x 450 mm (high) |
Optical axis and interface
flange as datum. 850mm (long) x 600mm wide x 600mm (high) |
This excludes the actual
cryostat. NB. Electronics etc. can be mounted outside the space envelope after
considerations for collisions and outer balance forces have been taken into
account. |
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| 028 | 22-July-2007 | Focal plane Deflection | < 25 microns from optical axis at CCD in any observing orientation. | < 30 microns from optical axis at CCD in any observing orientation. | First pass flexure analysis indicates instrument structure can deliver 30 microns deflection through a 90 degree gravity vector change. More detailed analysis required, including, thermal, vibration and shock. | TBC. |
| 029 | 22-July-2007 | Focal Plane Tilt | < 0.06 mill-radians tilt from focal plane at any observing orientation | < 0.1 milli-radians tilt from focal plane at any observing orientation | First pass flexure analysis indicates instrument structure can deliver 12 arcsec tilt through a 90 degree gravity vector change. More detailed analysis required. | TBC |
| 030 | 22-July-2007 | Shutter | 100m diameter clear aperture prontor shutter - modified for air operation. Position after Pupil and next lens element. | 100m diameter clear aperture prontor shutter - modified for air operation. Position up stream of Broad Band filters. | Relative large aperture allows the shutter to be fitted in many positions in the camera. Instrument is designed to be light tight - essential down stream of shutter. | Frozen. Air operated. Up stream of Broad band filters |