Committee

Kim Gillies

Tom O’Brien

Jim Oschmann

Doug Simons

Summary

The Gemini Near Infrared Spectrometer, GNIRS, was reviewed from technical and management perspectives during the formal prefabrication review (PFR) held at NOAO’s headquarters in Tucson. This is a follow-up review from the Restart Review that was held during July 2000.

Overall the committee was impressed by the open and candid nature of the GNIRS team during the review. This represents a continuation of the good communication that has been evident since the project was restarted under new engineering and management oversight within NOAO. GNIRS continues to appear to be overall on-track from a technical and management perspective and we congratulate the entire GNIRS team for the impressive amount of detailed design work that has taken the project to its current level. That said, the design is somewhat behind the nominal schedule, which is not a good situation to be in during the early phases of a project. The reasons for the delays are reasonably well understood, though, and we believe the aggressive management approach described by the GNIRS project manager, Neil Gaughan, will be able to hold the project on its original delivery schedule.

Comments and Recommendations

· Mechanical

· The design philosophy of having

· A monolithic bench hogged from a single billet of 6061

· Active radiation shields

· Liquid nitrogen pre-cool system

· Active temperature compensation of the bench using a relatively simple control system

· Phytron cryogenic motors that are isolated from a light tight science channel

· A modular assembly of mechanisms to the bench which provide excellent access to key components

· A “bolt and go” approach to alignment, etc.

are all viewed as good design choices by the committee. We in fact believe this represents an optimal blend of technical approaches with the instrument.

· While it would have been better to have all of the prototyping work completed by the time of the PFR, experience gained with the prototypes to date has clearly been valuable to the project and we believe will lead to solid design choices in key risk areas for the instrument

· Given the current state of the flexure analysis, the committee can only comment that GNIRS appears to be “headed in the right direction” regarding flexure and early indications are positive but it is premature to assume that the aggressive 0.1 pixel flexure per 15º attitude change specification will be met by this design. Too little analysis was presented to make a definitive conclusion about meeting this spec and we anticipate a lot of work required to fine tune the bench design and incrementally increase the model’s complexity by adding additional loads, optics, mechanisms building in the influence function for all of the optics, etc.

· The GNIRS team should further develop the fall back plan of active flexure compensation, based upon LUTs, in the event the actual flexure of the system fails to meet spec by a large margin. Specifically, they should identify an optimal compensator in the system (e.g., XY detector stage, move the collimator, etc.) and determine if they have adequate space/mass budget available to retrofit a mechanism it proves necessary to provide flexure compensation.

· This does not mean we recommend a fundamental change in the design philosophy of the instrument, in the sense of building an extremely rigid opto-mechanical assembly.

· The GNIRS team may in fact find that, given the amount of effort expended in future FEA, an “early” decision about building in flexure compensation reduces risk and accelerates the production schedule.

· The thermal design looks good and indicates a large amount of performance margin. We therefore see no need to do a detailed thermal FEA, unless the GNIRS team thinks this is a useful exercise based upon the results presented.

· Overall the mechanism designs presented look good and we believe the problems identified in the prototypes will be solved.

· The GNIRS team should consider running ultimate lifetime tests using their prototypes after they are done using them to support the design effort – in effect running the mechanisms until they break to learn about the intrinsic weaknesses in the designs that wouldn’t emerge from the planned tests.

· The committee is concerned about the “prototype #1” option presented and anticipate that this may lead to premature wear on key bearing surfaces. We recommend instead going straight to prototype #2, as we believe it has a higher probability of meeting performance and lifetime expectations and has been proven to work in other cryogenic instruments. Going straight to prototype #2 therefore reduces risk and probably represents the fastest solution to the flexure problem identified in rotary mechanism.

· We do not see any need for additional prototype testing of the lens mount, given that this design has been used successfully in many other instruments and the lessons which would be learned from any more testing can no doubt be extracted from the experiences of others. We recommend contacting Klaus Hodapp to understand exactly what difficulties he has had with this design as a rapid means of closing out this effort.

· The modular design of the OIWFS assembly is good. If NOAO wants to pursue the idea of IfA installing elements in this module and testing it as a unit before it’s shipped, that should be explored quickly as OIWFS parts are scheduled to be built this summer at the IfA. Alternatively, Klaus and/or Jeff can come on-site and help integrate/test the parts within GNIRS.

· Consider the use of invar bushings on the bolts that “permanently” connect parts of the main bench as a means of providing increased cold preload on that critical joint.

· The software proposal for GNIRS is now “light years” ahead of what was presented at the Restart Review and we are much more confident now that the S/W portion of the system design is on track.

· We expect that the architecture described will be able to meet existing ICDs and support all key functionality from both standalone engineering and observatory operations perspectives. That said we remind the GNIRS team that they must conform to all principal system interfaces.

· The GNIRS team need to clarify what will be delivered in the engineering system, as this is a deliverable and Gemini would like to know if it requires additional expertise, software licenses, etc. beyond what we normally expect to be required to support our facility instrumentation.

· GNIRS needs to thoroughly document the S/W that operates below the proposed “thin EPICS layer”, again to permit long term support by Gemini’s software staff of GNIRS. This documentation is normally expected to exist in the form of the software maintenance manual, which is already a contractual deliverable.

· Management

· We suggest rectifying the discrepancy between CAS (Central Accounting) and Neil’s costs, by reporting in real dollar values to avoid in the future the confusion evident during the review. Specifically, we recommend reconciling the difference between accounting for scientists’ time between the cost schedules maintained. This will yield actual final total costs for various components of the program, which are arguably some of the most important metrics for gauging GNIRS status.

· The management approach is very thorough and we have confidence it will catch significant departures from projected costs, levels of effort, task schedules, etc. while mitigating action can still be effectively pursued.

· We believe GNIRS should release some parts, which are not very expensive or complex, for fabrication as quickly as possible to (1) test the entire off-site fabrication process with a vendor and (2) stimulate a change in the psychology of the team, from one of only designing to actually building the instrument.

· We applaud the use of staff dedicated to procurement management, inventory control, acceptance testing, as well as detailed weekly accounting of effort actually spent in the project.

· We suggest the use of an engineer independent of the GNIRS team (e.g., Earl Pearson) to double check drawings which depict key interfaces between the main bench and mechanisms and optical assemblies. A useful exercise may be to have him “reverse engineer” the location of the chief ray throughout the opto-mechanical assembly, and check if his analysis of its location matches what was used in designing the instrument.

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