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AUSTRALIAN
NATIONAL UNIVERSITY System Design Note 4.00 Created: 14 June 2000 Last modified: 14 June 2000 |
NIFS REQUIREMENTS ANALYSIS
Peter J. McGregor
Research School of Astronomy
and Astrophysics
Institute of Advanced
Studies
Australian National
University
Revision History
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Revision No. |
Author & Date |
Approval & Date |
Description |
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Revision 1 |
Peter J. McGregor 28 June 2000 |
John Hart 29 June 2000 |
Original document. |
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Contents
6 Optical
Alignment Error Budget
1 Purpose
This document describes the flow down of requirements from the Gemini Near-infrared Integral Field Spectrograph (NIFS) Functional and Performance Requirements Document (FPRD; SDN0003.02) to specific requirements for each NIFS sub-system.
2 Applicable Documents
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Document ID |
Source |
Title |
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RSAA |
NIFS Operational Concept Definition Document |
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RSAA |
NIFS Functional and Performance Requirements Document |
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RSAA |
Fringing Effects in the NIFS Science Detector |
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3 Introduction
The operational requirements of the Gemini Near-infrared Integral Field Spectrograph (NIFS) are defined in the NIFS Operational Concept Definition Document (OCDD; SDN0003.01). These operational requirements are combined with technical requirements in the NIFS Functional and Performance Requirements Document (FPRD; SDN0003.02). The NIFS FPRD defines the top level requirements for the instrument. The present document defines requirements for each sub-system of the instrument so that the top level requirements will be achieved in the final integrated instrument. These sub-system requirements are identified in various system error budgets.
4 Flexure Error Budget
NIFS is required to have a flexure of < 0.1 pixels for any 15° change in attitude. Image translation at the NIFS science detector will be caused by relative motion between the NIFS science detector and the NIFS On-Instrument Wavefront Sensor (OIWFS) detector. A flexure error budget can therefore be derived by tracing the effects of translation and rotation on each optical element between the NIFS OIWFS detector and the NIFS science detector. The resulting flexure error budget is presented in Table 1.
Table 1 is based on the following assumptions:
1. The spatial scale at the OIWFS detector is 0.17²/pixel with a pixel size of 18.5 mm.
2. The spatial scale at the science detector is 0.04²/pixel with a pixel size of 18.0 mm.
3. Flexure in the OIWFS optical path produces an erroneous OIWFS guide star centroid which erroneously translates the science object position. The focal plane scales are such that centroiding errors (in microns) at the OIWFS detector are amplified at the science detector by a factor of 4.135.
4. Translations are tested using offsets of 0.1 mm.
5. Tilts are tested using offsets of 1 mrad.
Table 1: NIFS Flexure Error Budget
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Component |
X Tra. Tol. (mm) |
Y Tra. Tol. (mm) |
Z Tra. Tol. (mm) |
a Rot. Tol. (mrd) |
b Rot. Tol. (mrd) |
g Rot. Tol. (mrd) |
X Tra. Bud. (mm) |
Y Tra. Bud. (mm) |
Z Tra. Bud. (mm) |
a Rot. Bud. (mm) |
b Rot. Bud. (mm) |
g Rot. Bud. (mm) |
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OIWFS
Det/Cam2/Prism/Col2 Ass. |
0.1 |
0.1 |
10.0 |
1.0 |
1.0 |
... |
0.414 |
0.414 |
0.149 |
0.372 |
0.372 |
0.000 |
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OIWFS Detector |
0.1 |
0.1 |
10.0 |
... |
... |
100.0 |
0.414 |
0.414 |
0.096 |
0.000 |
0.000 |
0.083 |
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OIWFS Camera 2 Assembly |
0.1 |
0.1 |
10.0 |
10.0 |
10.0 |
... |
0.414 |
0.414 |
0.124 |
0.021 |
0.021 |
0.000 |
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OIWFS Camera 2d |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.033 |
0.033 |
0.015 |
0.004 |
0.004 |
0.000 |
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OIWFS Camera 2c |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.021 |
0.021 |
0.013 |
0.017 |
0.017 |
0.000 |
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OIWFS Camera 2b |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.045 |
0.045 |
0.043 |
0.041 |
0.037 |
0.000 |
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OIWFS Camera 2a |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.074 |
0.074 |
0.068 |
0.004 |
0.000 |
0.000 |
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OIWFS Prism |
... |
... |
... |
... |
... |
100.0 |
0.000 |
0.000 |
0.000 |
0.000 |
0.000 |
0.124 |
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OIWFS Collimator 2 Assembly |
0.1 |
0.1 |
10.0 |
10.0 |
10.0 |
... |
0.422 |
0.422 |
0.149 |
0.087 |
0.083 |
0.000 |
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OIWFS Collimator 2b |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.058 |
0.058 |
0.027 |
0.000 |
0.000 |
0.000 |
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OIWFS Collimator 2a |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.017 |
0.017 |
0.012 |
0.021 |
0.021 |
0.000 |
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OIWFS Filter |
... |
... |
... |
10.0 |
10.0 |
... |
0.000 |
0.000 |
0.000 |
0.083 |
0.083 |
0.000 |
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OIWFS Camera 1 Assembly |
0.1 |
0.1 |
10.0 |
1.0 |
1.0 |
... |
0.414 |
0.414 |
0.175 |
0.045 |
0.045 |
0.000 |
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OIWFS Camera 1d |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.028 |
0.028 |
0.018 |
0.029 |
0.029 |
0.000 |
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OIWFS Camera 1c |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.003 |
0.004 |
0.001 |
0.050 |
0.050 |
0.000 |
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OIWFS Camera 1b |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.031 |
0.034 |
0.015 |
0.083 |
0.079 |
0.000 |
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OIWFS Camera 1a |
0.01 |
0.01 |
1.0 |
1.0 |
1.0 |
... |
0.050 |
0.050 |
0.023 |
0.013 |
0.008 |
0.000 |
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OIWFS Gimbal Mirror |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.124 |
1.406 |
1.282 |
0.000 |
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OIWFS Collimator 1 Assembly |
1.0 |
1.0 |
10.0 |
10.0 |
10.0 |
... |
0.622 |
0.620 |
0.381 |
0.744 |
0.744 |
0.000 |
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OIWFS Collimator 1b |
0.1 |
0.1 |
1.0 |
10.0 |
10.0 |
... |
0.240 |
0.244 |
0.103 |
0.070 |
0.040 |
0.000 |
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OIWFS Collimator 1a |
0.1 |
0.1 |
1.0 |
10.0 |
10.0 |
... |
0.178 |
0.182 |
0.062 |
0.165 |
0.165 |
0.000 |
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OIWFS Fold Mirror 2 |
... |
... |
1.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.910 |
0.580 |
0.869 |
0.000 |
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OIWFS Fold Mirror 1 |
... |
... |
1.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.821 |
0.646 |
0.530 |
0.000 |
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OIWFS Field Lens |
1.0 |
1.0 |
1.0 |
10.0 |
10.0 |
... |
0.115 |
0.115 |
0.036 |
0.018 |
0.041 |
0.000 |
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Pick-off Mirror |
... |
... |
1.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.790 |
0.098 |
0.116 |
0.000 |
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Focal Ratio Converter |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
... |
0.620 |
0.730 |
0.030 |
0.094 |
0.078 |
0.000 |
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Cold Stop Mirror |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.060 |
0.088 |
0.073 |
0.000 |
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Fold Mirror 1 |
... |
... |
1.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.063 |
0.074 |
0.043 |
0.000 |
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Fold Mirror 2 |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.160 |
0.066 |
0.055 |
0.000 |
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Triple Fold Mirror 1 |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.140 |
0.039 |
0.032 |
0.000 |
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Image Slicer Assembly |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
... |
0.040 |
0.010 |
0.020 |
0.020 |
0.010 |
0.000 |
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Pupil Mirror Array |
1.0 |
1.0 |
1.0 |
1.0 |
1.0 |
... |
0.580 |
0.720 |
0.050 |
0.039 |
0.032 |
0.000 |
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Field Mirror Array |
10.0 |
10.0 |
1.0 |
1.0 |
1.0 |
... |
0.100 |
0.100 |
0.090 |
0.000 |
0.000 |
0.000 |
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Triple Fold Mirror 2 |
... |
... |
1.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.120 |
0.080 |
0.069 |
0.000 |
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Collimator Mirror |
1.0 |
1.0 |
10.0 |
1.0 |
1.0 |
... |
0.590 |
0.700 |
0.080 |
0.610 |
0.505 |
0.000 |
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Triple Fold Mirror 3 |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.037 |
0.590 |
0.490 |
0.000 |
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Collimator Corrector |
10.0 |
10.0 |
10.0 |
10.0 |
10.0 |
... |
0.170 |
0.220 |
0.020 |
0.049 |
0.041 |
0.000 |
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Grating |
... |
... |
10.0 |
1.0 |
1.0 |
... |
0.000 |
0.000 |
0.010 |
0.520 |
0.520 |
0.000 |
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Camera Lens Assembly |
1.0 |
1.0 |
100.0 |
1.0 |
1.0 |
... |
1.000 |
1.000 |
0.000 |
0.088 |
0.017 |
0.000 |
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Camera Lens 1 |
0.1 |
0.1 |
100.0 |
10.0 |
10.0 |
... |
0.132 |
0.132 |
0.000 |
0.017 |
0.015 |
0.000 |
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Camera Lens 2 |
0.1 |
0.1 |
100.0 |
10.0 |
10.0 |
... |
0.052 |
0.052 |
0.000 |
0.069 |
0.071 |
0.000 |
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Camera Lens 3 |
0.1 |
0.1 |
100.0 |
10.0 |
10.0 |
... |
0.024 |
0.024 |
0.000 |
0.110 |
0.110 |
0.000 |
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Camera Lens 4 |
0.1 |
0.1 |
100.0 |
10.0 |
10.0 |
... |
0.071 |
0.071 |
0.000 |
0.034 |
0.033 |
0.000 |
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Camera Lens 5 |
0.1 |
0.1 |
100.0 |
10.0 |
10.0 |
... |
0.025 |
0.025 |
0.000 |
0.023 |
0.023 |
0.000 |
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Science Detector |
1.0 |
1.0 |
10.0 |
10.0 |
10.0 |
10.0 |
1.000 |
1.000 |
0.000 |
0.000 |
0.000 |
0.261 |
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RSS Total (mm) |
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2.123 |
2.235 |
1.581 |
2.133 |
2.064 |
0.301 |
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RSS Total (pix) |
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0.118 |
0.124 |
0.088 |
0.119 |
0.115 |
0.017 |
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RSS System Total (pix) |
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0.254 |
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5 Image Quality Error Budget
TBD.
6 Optical Alignment Error Budget
TBD.
7 Thermal Budget
TBD.
8 Mechanism Setting Speeds
TBD.
9 Grating Setting Reproducibility
NIFS will routinely be operated in a manner whereby calibration frames are obtained for each grating prior to observations commencing, and then gratings are freely interchanged during science observing. This places a tight constraint on the grating setting reproducibility. Acquisition of objects may also require the mirror on the grating wheel to be rotated into the beam. The original grating must then be repositioned to high accuracy.
The required grating setting accuracy is set by two factors. One is the required accuracy of the instrumental wavelength calibration. The other is the required accuracy of the instrumental flat field calibration. The centroids of emission-lines are expected to be determined to 0.1 pix from good signal-to-noise ratio spectra. The wavelength calibration should be stable to at least this level. Fringing in the NIFS science detector will be corrected by division by a flat field frame. Modeling shows that cancellation to better than 1% will only be achieved if the wavelength shift between the science spectrum and the flat field spectrum is less than ~ 0.2 pixels.
These considerations lead to the requirement that the NIFS grating setting reproducibility be at a level of 0.1 pix or better. This translates to an angular setting reproducibility at the grating of 3.1 mrad (based on 18 mm detector pixels and 288 mm camera focal length).
Appendix A: List of Figures
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Figure 1 |
figure.gif |
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