Since the NIFS CoDR, the following developments have occurred:
·
The
manner in which the thermal enclosures will be populated has been defined.
·
The
power requirements of components in the thermal enclosures has been defined.
·
Risks
identified at the CoDR have been investigated and some new risk areas have been
identified.
·
NIFS
will not be able to record out-of-focus images suitable for determining
non-common path phase errors between NIFS and ALTAIR.
NIFS meets the Gemini environmental heat load requirement. The maximum acceptable heat load that can be conducted into the instrument body is 50 W and the maximum acceptable heat load that can be convected into the dome is 50 W. The heat generated by the closed-cycle coolers is excluded from this budget. The majority of the heat generating electronic components will be mounted inside the two cooled thermal enclosures. The two items that need to be mounted on the cryostat are the OIWFS SDSU-2 detector controller and the spectrograph SDSU-2 detector controller. The OIWFS and spectrograph detector controllers generate ~ 45 W each and will be bolted to the cryostat. Both will be water cooled so only a small fraction of this heat will be dissipated at the cryostat.
NIFS meets the Gemini instrument mass requirement of 2000 kg. The mass budget for NIFS is presented in Table 24.
Table 24: NIFS Mass Budget
|
Item |
Mass (kg) |
Source |
|
|
|
|
|
ISS
Interface |
187 |
AutoCAD
solid model |
|
Main
Frame (and partial ballast) |
500 |
Estimate |
|
Vacuum
Jacket |
315 |
Young
et al. (1998) |
|
OIWFS |
147 |
Young
et al. (1998); includes cold work surface |
|
Spectrograph |
40 |
Estimate |
|
Detector
Controllers (2 of) |
10 |
Estimate |
|
Thermal
Enclosures (2 of) |
330 |
From
Gemini ICD |
|
Detector
Controller Power Supplies (2 of) |
15 |
Estimate |
|
IOC (2
of) |
40 |
Estimate |
|
ICS
Stepper Motor Drive Frame |
20 |
Estimate |
|
ICS
Sensor Interface Frame |
10 |
Estimate |
|
ICS
Temperature Controllers (3 of) |
15 |
Estimate |
|
ICS
Temperature Control Hardware |
20 |
Estimate |
|
Cabling
and Hoses |
50 |
Estimate |
|
Miscellaneous |
40 |
Estimate |
|
|
|
|
|
Subtotal |
1739 |
|
|
Ballast |
261 |
|
|
|
|
|
|
Total |
2000 |
|
NIFS meets the Gemini center of gravity requirement; ballast weights will be used to give NIFS the same center of gravity as NIRI.
NIFS meets the Gemini instrument volume requirement; it will occupy the same space envelope as NIRI.
NIFS will produce an optical wavefront error of 67 nm RMS which is less than the Gemini instrument allocation of 120 nm RMS. The optical image quality error budget is presented in §4.8.2.2.6.
NIFS meets the Gemini requirement of >15% system throughput, excluding ALTAIR. The throughput budget is presented in §4.15.2.
NIFS meets the Gemini requirement of an effective instrumental emissivity < 1% at wavelengths > 2.2 mm (§4.16) and an instrumental photon background less than one half of the detector dark current (§4.21).
NIFS will use an OIWFS guide star to provide closed-loop tracking and flexure correction. It is then necessary only to control open-loop mechanical flexure between the OIWFS detector and the science detector.
The mechanical flexure error budget between these detectors is presented in Table 25. The coordinate system is defined by the X, Y, and Z axes with the Z axis oriented parallel to the optical surface normal. The parameters α, β, and γ are rotation angles about the X, Y, and Z axes, respectively. The assigned translational and rotational tolerances are listed for each element, as well as the resulting image motion at the science detector. Individual image motions will add and subtract in a complex way dependent on the orientations of the optical components in the cryostat. This has been approximated by summing the image motions in quadrature.
Analysis of the spectrograph housing (consisting of the Cold Work Surface plate, the spectrograph skirt, and the spectrograph cover) shows that absolute positions of modules within the housing will be maintained to ~ 0.1 μm and their orientations will be maintained to ~ 0.3 μrad for a 15° change in orientation (§4.22). Generally, fixed modules are assigned these tolerances. Individual components within modules are assigned translational tolerances one order of magnitude lower than this value, and orientation tolerances lower by a factor of three. Components mounted in mechanisms are assigned larger tolerances.
Formally, NIFS does not meet the Gemini flexure requirement of < 0.1 pixel per 15° change in orientation; the NIFS quadrature sum is 0.132 pixels. The largest contribution to the sum is the angular tolerance on the OIWFS gimbal mirror (~ 1.4 μm of the 1.8 μm allowance assuming angular tolerances of 1 μrad). The OIWFS for NIFS is a duplicate of the NIRI design, so the design has not been re-analysed. The angular tolerance assigned to the OIWFS gimbal mirror is estimated based on consistency with our assignments to other mechanisms. The actual performance of the NIRI OIWFS is unknown.
The next most sensitive component is the spectrograph grating. This is assigned an angular tolerance of 1 μrad (as for the OIWFS gimbal mirror). This corresponds to an image motion at the science detector of 0.52 μm. The quadrature sum is fairly insensitive to this value; the tolerance can be doubled without significantly increasing the sum.
Table
25 demonstrates that the flexure performance of NIFS
will be critically dependent of the performance of the OIWFS gimbal mirror.
Table 25: Mechanical Flexure Error Budget.
|
Component |
Mechanical Tolerance |
Image Motion at Science Detector (μm) |
||||||||||
|
Translation (μm) |
Rotation (μrad) |
Translation |
Rotation |
|||||||||
|
X |
Y |
Z |
α |
β |
γ |
X |
Y |
Z |
α |
β |
γ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
OIWFS Det/Cam2/Prism/Col2 Ass. |
0.1 |
0.1 |
0.1 |
0.3 |
0.3 |
... |
0.414 |
0.414 |
0.002 |
0.112 |
0.112 |
… |
|
OIWFS
Detector |
0.1 |
0.1 |
1.0 |
... |
... |
50.0 |
0.414 |
0.414 |
0.010 |
0.000 |
0.000 |
0.042 |
|
OIWFS
Camera 2 Assembly |
0.05 |
0.05 |
0.1 |
0.3 |
0.3 |
... |
0.207 |
0.207 |
0.001 |
0.001 |
0.001 |
… |
|
OIWFS
Camera 2d |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.033 |
0.033 |
0.002 |
0.000 |
0.000 |
… |
|
OIWFS
Camera 2c |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.021 |
0.021 |
0.001 |
0.002 |
0.002 |
… |
|
OIWFS
Camera 2b |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.045 |
0.045 |
0.004 |
0.004 |
0.004 |
… |
|
OIWFS
Camera 2a |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.074 |
0.074 |
0.007 |
0.000 |
0.000 |
… |
|
OIWFS
Prism |
... |
... |
... |
... |
... |
50.0 |
… |
… |
… |
… |
… |
0.062 |
|
OIWFS
Collimator 2 Assembly |
0.05 |
0.05 |
0.1 |
0.3 |
0.3 |
... |
0.211 |
0.211 |
0.001 |
0.003 |
0.002 |
… |
|
OIWFS
Collimator 2b |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.058 |
0.058 |
0.003 |
0.000 |
0.000 |
… |
|
OIWFS
Collimator 2a |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.017 |
0.017 |
0.001 |
0.002 |
0.002 |
… |
|
OIWFS Filter |
... |
... |
... |
1.0 |
1.0 |
... |
… |
… |
… |
0.008 |
0.008 |
… |
|
OIWFS Camera 1 Assembly |
0.05 |
0.05 |
0.1 |
0.3 |
0.3 |
... |
0.207 |
0.207 |
0.002 |
0.014 |
0.014 |
… |
|
OIWFS
Camera 1d |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.028 |
0.028 |
0.002 |
0.003 |
0.003 |
… |
|
OIWFS
Camera 1c |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.003 |
0.004 |
0.000 |
0.005 |
0.005 |
… |
|
OIWFS
Camera 1b |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.031 |
0.034 |
0.002 |
0.008 |
0.008 |
… |
|
OIWFS
Camera 1a |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.050 |
0.050 |
0.002 |
0.001 |
0.001 |
… |
|
OIWFS Gimbal Mirror |
... |
... |
1.0 |
1.0 |
1.0 |
... |
… |
… |
0.012 |
1.406 |
1.282 |
… |
|
OIWFS Collimator 1 Assembly |
0.1 |
0.1 |
0.1 |
0.3 |
0.3 |
... |
0.062 |
0.062 |
0.004 |
0.022 |
0.022 |
… |
|
OIWFS
Collimator 1b |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.024 |
0.024 |
0.010 |
0.001 |
0.000 |
… |
|
OIWFS
Collimator 1a |
0.01 |
0.01 |
0.1 |
0.1 |
0.1 |
... |
0.018 |
0.018 |
0.006 |
0.002 |
0.002 |
… |
|
OIWFS Fold Mirror 2 |
... |
... |
0.1 |
0.3 |
0.3 |
... |
… |
… |
0.091 |
0.174 |
0.261 |
… |
|
OIWFS Fold Mirror 1 |
... |
... |
0.1 |
0.3 |
0.3 |
... |
… |
… |
0.082 |
0.194 |
0.159 |
… |
|
OIWFS Field Lens |
0.1 |
0.1 |
0.1 |
0.3 |
0.3 |
... |
0.012 |
0.012 |
0.004 |
0.001 |
0.001 |
… |
|
Pick-off Mirror |
... |
... |
0.1 |
1.0 |
1.0 |
... |
… |
… |
0.079 |
0.098 |
0.116 |
… |
|
Focal Converter Mirror |
0.1 |
0.1 |
1.0 |
0.3 |
0.3 |
... |
0.062 |
0.073 |
0.030 |
0.028 |
0.023 |
… |
|
Cold Stop Mirror |
... |
... |
0.1 |
0.3 |
0.3 |
... |
… |
… |
0.001 |
0.026 |
0.022 |
… |
|
Fold Mirror 1 |
... |
... |
0.1 |
0.3 |
0.3 |
... |
… |
… |
0.006 |
0.022 |
0.013 |
… |
|
Fold Mirror 2 |
... |
... |
0.1 |
0.3 |
0.3 |
... |
… |
… | ||||