STUDY SUMMARY - IPMU

SUMMARY REPORT
WIDE FIELD FIBER-FED OPTICAL
MULTI-OBJECT SPECTROMETER (WFMOS)
ance, or 3) added risk. A list of descopes and trigger dates will be used to balance any cost overruns
within the framework of balancing risk in the instrument. The most important feature of this
approach is to implement the descope in a timely manner. Features maintained in the descope list
are:
• Descope options, with implementation approach
• The resulting acceptable reduced performance or risk position.
• The schedule milestones related to the required decisions.
• The budget impact if the options are exercised at the identified milestones.
• The survey success impact.
• Reserve Management.
This strategy has been used successfully on other projects that have faced similar cost caps
such as M3, recently delivered, and the Nuclear Spectroscopic Telescope Array (NuSTAR) project,
currently in Phase C/D. A formal process that may include a trade study to review the impact
and final approval from the management team is required to exercise the descope. The advisory
board may be involved if the change is significant and Gemini will be consulted on any
descope that affects a Level 1 or Level 2 requirement. The challenge is that the time to exercise a
descope effectively is often early and there is a tendency to want to defer in order to maintain all
features of the original design. A descope list will be developed further at the start of the study,
but at this time two high-level descopes are to reduce total number of positioners and to use
standard spectrograph CCDs instead of custom CCDs. For the positioners, there are several execution
dates: 1) start of positioner contract, 2) parts procurement, 3) positioner assembly, and 4)
bench assembly. At each stage, the cost savings decreases, but this allows the flexibility to maintain
the baseline design as long as possible. We can also generate multiple trigger dates in the
procurement of custom CCDs. Similarly, cost savings decrease with time, but the option retains
the advantages of the system for as long as possible.
Both of these descope options described effectively increase the survey time. Science goals
are still achievable, but the instrument is less efficient.
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