1 Cryostat and OIWFS Duplication

 

1.1 Overview

 

A large part of the NIRI instrument is being duplicated to form the integration frame, cryostat, and OIWFS for NIFS. The duplicated NIRI components will be unmodified to the greatest extent possible. However, some changes are required to accommodate NIFS.

 

A description of the duplicate NIRI parts and any modifications has been included in §5 which describes the overall NIFS mechanical design.

 

This section discusses the approach to the duplication process, its progress, and the difficulties encountered to mid-February 2001. The current status of the cryostat and OIWFS duplication work is summarized in §9.5. Further information can be found in the Management Plan.

 

1.2 Changes Since CoDR

 

The NIFS plan as presented at the CoDR called for a subcontract with the University of Hawaii (UH) for the delivery of a fully operational cryostat and OIWFS to RSAA for integration with the NIFS spectrograph. This solution, although technically attractive, was considered too costly. The plan was revised so that most work will be carried out at RSAA. UH will still manufacture the OIWFS detector system and provide consultancies on the cryostat and OIWFS duplication under a subcontract from RSAA. UH will manufacture the OIWFS gimbal and filter wheel mechanisms under a Gemini NIRI contract variation.

 

Work at RSAA started immediately after agreement in principle was reached on the NIFS fabrication contract. By August 2000, RSAA had appointed two extra workshop staff members on temporary contracts to cope with this workload. A third joined two months later. To supervise the workshop effort and make the required changes to the NIRI design, the contract of a mechanical engineer was extended. It was envisaged that he would also lead the assembly and testing effort for the cryostat and OIWFS, but he unfortunately left RSAA mid-January. Efforts are underway to recruit new mechanical engineers.

 

Ordering of long lead time items was started in July 2000, but was suspended when RSAA financial commitments to NIFS reached US$200,000 while the NIFS fabrication contract continued to be delayed. By the time purchasing was resumed in December, several quotations had expired and their renewal caused further delays.

 

Difficulties obtaining “as built” information and other assistance from UH (UH staff who were involved with the NIRI mechanical design have either left or are too busy with other work) has led to RSAA having to take some fabrication risks in preference to risking further delays. The following serve as examples. Some parts have been fabricated which do not seem to appear in any assembly drawings. Fabrication subcontractors have been sent NIRI drawings with modifications described separately because the NIRI drawings have been provided in PDF format, not suitable for modification. Such procedures are more prone to errors than usual.

 

1.3 Description of Work

 

1.3.1 ISS Interface Plate

 

Figure 157 shows an exploded view of the NIFS ISS interface plate and vacuum jacket. The interface plate is at the top of the figure. The NIFS vacuum jacket and integration frame attach directly to the interface plate. Fabrication of the whole subsystem of the interface plate, its corner brackets, and the attached alignment system has been completed. Figure 158 shows these components as delivered by local subcontractor Craigie Engineering.

Figure 157: NIFS ISS interface plate (top) and an exploded view of the vacuum jacket.

 

Figure 158: ISS interface plate, key mount assemblies, and parts for the instrument to ISS alignment system.

1.3.2 Integration Frame

 

The NIFS integration frame is a large welded frame measuring 1300×1300×2100 mm (Figure 159). This frame is the largest NIFS component and supports the main counterweight, the thermal enclosures, cables and lines, the balance ballast, and forms the interface to the Gemini instrument handling equipment. The frame has also been fabricated by Craigie Engineering and has recently been delivered as shown in Figure 160. Just visible at the right edge of the photograph in the distance is the frame component for carrying the thermal enclosures, and the ballast. The NIFS weight estimate is approximately 120 kg less than the weight of NIRI, and extra ballast weights have been made to compensate.

 

Figure 159: The cryostat with integration frame and two electronics thermal enclosures.

 

 

1.3.3 Vacuum Jacket

 

All of the vacuum jacket components shown in Figure 157 are NIRI designs being duplicated for NIFS. The three large hexagonal forgings for the vacuum jacket were fabricated and rough machined by Lenape Forge, the same U.S. subcontractor who delivered these parts for NIRI. They are now with Broens Toolmaking, a Sydney subcontractor, for final machining. Delivery is expected mid March 2001. This subcontractor already has delivered the vacuum jacket endplates. Figure 161 shows the vacuum jacket center section in a partially machined state.

 

Figure 160: NIFS integration frame at RSAA.

 

Figure 161: The vacuum jacket center section partially machined.

Figure 162: NIFS cryostat large internal components, from the left, the science side radiation shield, the cold work surface plate with support tines, and the OIWFS Optable.

 

 

1.3.4 Cold Work Surface Plate

 

Figure 162 shows the large internal cryostat parts for NIFS. The Cold Work Surface plate is at the center of the figure with the titanium tines and pads attached. Two CWS plates will be manufactured. One will be used to speed integration and testing of the NIFS spectrograph, while the other will be installed in the cryostat to allow integration and testing of the vacuum jacket and OIWFS. As the NIFS spectrograph assemblies will attach directly to the CWS plate, the detailed design of the plate cannot be finalised until all spectrograph assemblies have been fully detailed. The CWS plate used for the OIWFS integration and testing will be fabricated earlier, and will not be able to carry the spectrograph. It will be exchanged for the complete CWS plate at the time of spectrograph integration into the cryostat.

 

1.3.5 NIFS Radiation Shields

 

The whole of the NIRI radiation shields and floating shields will be duplicated for NIFS, with only minor modifications. Figure 162 shows only the spectrograph radiation shield frame on the left, while Figure 163 shows machining of one of the base rings in progress.

 

Figure 163: Machining base rings for the hexagonal radiation shields at RSAA.

 

 

1.3.6 NIFS On-Instrument Wavefront Sensor

 

All of the NIRI OIWFS is being duplicated for NIFS, except the focal plane mask wheel and the focusing mechanism. Figure 164 shows some of the OIWFS components already fabricated at RSAA.

 

1.3.6.1 Optical Elements

 

The entire optical train of lenses, mirrors, prisms, and filters is being duplicated. The Shack-Hartmann prism will be manufactured by RSAA. All other optical elements will be obtained from Janos Technology and Optics for Research.

 

1.3.6.2 Optable

 

The OIWFS Optable is being fabricated by Superior Jig, the same US subcontractor who delivered this component for NIRI. The NIRI focal plane mask wheel slot and fittings in the optable have been deleted from the design. This will reduce scattered light inside the OIWFS optable and will also make it structurally stiffer. This intricate component is shown on the right in Figure 162.

 

1.3.6.3 Gimbal and Filter Wheel Mechanisms

 

Both the gimbal mirror and filter wheel mechanisms are being duplicated by UH under a NIRI contract variation. The mechanisms will be assembled at UH, but cannot be tested there.

 

1.3.6.4 Focus Mechanism

 

Analysis has shown that the focus mechanism can be replaced by a simple fixed focus unit that can be adjusted only by disassembly of the cryostat. The new focus unit is described in §5.5.3.3.2.

 

1.3.6.5 Detector System

 

With the exception of some of the internal cryostat wiring, the whole of the OIWFS detector system will be manufactured by UH under a subcontract from RSAA.

 

Figure 164: Aluminum parts for the vacuum jacket and OIWFS optical system.

 

 

1.4 Work at UH

 

ANU and UH are awaiting the finalization of a NIFS subcontract which formalizes the involvement of UH in the NIFS development and fabrication. The following paragraphs detail the UH work related to the cryostat and OIWFS.

 

1.4.1 OIWFS Detector

 

UH will fabricate, test, optimize, and deliver the OIWFS Detector Subsystem for NIFS. It will be an exact copy of the NIRI OIWFS Detector Subsystem. To be delivered are:

 

The following will be provided to UH:

 

1.4.2 OIWFS Mechanisms

 

Not as part of the ANU-UH contract, but under an amendment to the Gemini NIRI development contract, UH will fabricate and assemble the OIWFS Filter Wheel and Gimbal mechanisms.

 

1.4.3 Consultancies

 

UH will make available to ANU the services of competent staff with experience in the development of NIRI, for consultation to assist in determining details of NIRI design and fabrication, in modifying the NIRI design, and in the final assembly and alignment of NIFS. The contract contains provisions for travel of UH staff to visit ANU in association with the consultancies.

 

1.5 Current Status

 

Considering the delays mentioned in the introduction to this section, progress towards assembling the vacuum jacket and vacuum testing it has been reasonable. By the time of the CDR the vacuum jacket is expected to be assembled without the cryocoolers. The first cooldown with the cold work surface plate and radiation shields installed is planned for July 2001. The OIWFS can be installed soon after.

 

1.5.1 Long Lead Time Items

 

Table 71 lists the long lead time items for the duplication of the cryostat and support structure, together with their suppliers and delivery dates.

Table 71: Suppliers and Delivery Dates of Long Lead Time Items.

Item

Supplier

Status/Delivery Date

Integration frame

Craigie Engineering

Completed

ISS interface plate

Craigie Engineering

Completed

VJ forgings

Lenape Forge

Completed

VJ machining

Broens Toolmaking

mid March 01

Optable

Superior Jig

mid May 01

OIWFS Lenses

Janos Technology

mid May 01

Cryostat Window

Janos Technology

August 01

OIWFS Filters

OCLI

Supplier located

OIWFS Mirrors

Optics For Research

June 01

Gimbal Mechanism

University of Hawaii

June 01

Filterwheel Mechanism

University of Hawaii

June 01

OIWFS Detector Controller

Astronomical Research Camera

mid May

OIWFS Detector System

University of Hawaii

July 01

Cryocoolers

Leybold Cryogenics

end April

Cryocooler Bellows

Metal Flex Welded Bellows

mid June 01

 

1.5.2 Work at RSAA

 

Table 72 shows progress on the fabrication work at RSAA, related to the cryostat and OIWFS duplication, up to 2 February 2001. At that point in time, 64% of the parts fabrication work had been completed and approximately 1500 hours remained to be completed

 

Table 72: Fabrication Work at RSAA.

Item

Status

(% complete)

Window Assembly

65%

Window Cover

100%

Cryocooler System

73%

Spectrograph Radiation Shield

57%

OIWFS Radiation Shield

78%

Floating Shield

0%

Photon Shield

57%

CWS Plate

40%

Temperature Control Items

0%

OIWFS Field Lens Mount

95%

OIWFS Pupil Imager

100%

OIWFS Beam Folders

95%

OIWFS Detector Pack

69%

OIWFS Detector Mount

53%

OIWFS Detector Controller Mount

100%

Wiring Connector System

0%

Handling Equipment

0%

 

 

1.6 Cryostat and OIWFS Duplication Risks

 

1.6.1 Vibration Coupling From Closed-Cycle Helium Coolers

 

NIRI initially experienced substantial problems with vibration coupling from the closed-cycle helium coolers to the CWS plate, sufficient to smear out test images at the detector. It is understood that modifications to the NIRI cryocooler mounts reduced vibration to an acceptable level. The NIRI modifications have been incorporated in the NIFS design and more modifications have been made on the recommendation of Jeff Douglas to further reduce vibration levels.

 

1.6.2 OIWFS Repeatability

 

At the time of writing, no further information had become available on the performance of the NIRI OIWFS. The NIFS OIWFS is required to reliably set with an accuracy of < 0.005″ defined to be one tenth of the half slit width step that will be required to “sub-sample” spatially perpendicular to the slit as described in the NIFS Operational Concept Definition Document. The performance of the NIRI OIWFS will be closely monitored as NIRI is commissioned. The bench test results stated in ICD 1.9b/1.10 “GNIRS to Infrared OIWFS Interface Control Document” are not encouraging. Modifications to the current design may be required for NIFS.