3.1.1 Optics, Optical Corrector, Mechanical Systems

M. Johns, C. Claver

3.1.1 Optics, Optical Corrector, Mechanical Systems (1)

Findings & comments:

WBS tasks for the optical and opto-mechanical assemblies are complete with resource loading and documented cost estimates. The estimates appear to be conservative and contingency allowances take risk into account.

A review of the costs associated with telescope simulator testing at FNAL and on-site integration at CTIO is advisable.

No schedule problems were identified at this time. Progress is tracked through regularly spaced milestones, EV analysis, plus other metrics. Slack time is not explicitly added in the WBS.

Six of nine recommendations from the May 2007 joint DOE/NSF DES review have been fully addressed. Pending items include a stray light analysis, the design of the C1 lens cover, and finite element modal analysis of the combined DECam/telescope structure.

3.1.1 Optics, Optical Corrector, Mechanical Systems (2)

System engineering has improved within the DECam project with the hiring of a project scientist. System engineering documentation (requirements and interface documents) and configuration control are being implemented. These are critical for the success of the distributed opto-mechanical effort.

A FE modal analysis of DECam mounted in the telescope top ring is needed to validate the design of the cage, vanes and hexapod. The analysis may reveal potential problems in the design that result in lower modal performance and need to be addressed. It also provides the basis for specifying stiffness requirements for the hexapod assembly.

The plan for manufacturing and assembling the DECam optics is deemed adequate. Careful attention must be paid to fabrication and assembly tolerances to insure that optical performance meets error budget specifications.

3.1.1 Optics, Optical Corrector, Mechanical Systems (3)

The filter changer and shutter assemblies are being provided by U. Michigan. The assemblies will be purchased from Bonn and are based on scaled up versions of existing designs. The technical and schedule risk for these items is deemed to be low.

The Project will use a hexapod for positioning DECam within the cage assembly. The project has received engineering and fabrication cost estimates from a number of vendors. Hexapod development is on the critical path and the Project is requesting CD3A approval to go forward with early procurement. Hexapod stiffness requirements should be determined from the finite element modal analysis. The hexapod is ready for CD3A development pending the results of the FE modal analysis.

3.1.1 Optics, Optical Corrector, Mechanical Systems (4)

Advancing filter procurement one year will significantly reduce the risk of schedule slip. The procurement of filters is currently on the critical path.

The DECam project should evaluate the programmatic impact of the loss of a filter due to breakage and obtain a quote for the cost of providing spares.

The effect on image quality of a temperature differential between the DECam cage and ambient air should be analyzed and the specification and/or the thermal design of the assembly revised if necessary to comply with the image error budget. Current specifications allow the DECam cage assembly to be at a temperature up to 2° C different from ambient.

3.1.1 Optics, Optical Corrector, Mechanical Systems (5)

Recommendations:

1. Continue to develop the systems engineering controls prior to CD3B.

2. Complete the pending recommendations from the May review prior to CD3B.

3. Review the costs for DECam assembly & integration at FLAL and CTIO and provide a generous contingency to the budget and schedule for these activities. (Prior to CD2 baseling)

4. Perform an FE modal analysis of DECam in the telescope structure within 6 months.

5. Analyze the effect of a hot air plume caused by the cage assembly being at a temperature 2 degrees above ambient prior to CD3.

3.1.1 Optics, Optical Corrector, Mechanical Systems (6)

Recommendations:

6. Investigate the cost to provide a set of spare filters prior to CD3.

7. Develop a strategy to control the hexapod positioner in the required 5 degrees of freedom prior to CD3.

8. Proceed to CD2 with Opto-mechanical systems.

9. Proceed with CD3A procurement of the hexapod assembly pending the results from the FE modal analysis.