STUDY SUMMARY - IPMU

SUMMARY REPORT
WIDE FIELD FIBER-FED OPTICAL
MULTI-OBJECT SPECTROMETER (WFMOS)
5.0 Integration and Test
5.1 Integration Approach
Our history in delivering science instruments has enabled us to develop a systematic approach
to I&T where it is common to have subsystems developed and tested by different groups.
Emphasis on early validation at the subsystem level with clear definitions of interfaces allows
verification of functionality and identification of problems early and minimizes the problems encountered
when the instrument is finally assembled and tested as a system. Initial sub-system
level validation also provides early test data to confirm interfaces, especially data content and
form. The verification process of the instrument begins with the development of the Acceptance
Test Plan (ATP) to define the series of tests, inspection, and analyses used to validate the instrument
requirements. This plan will emphasize subsystem level tests and subassembly tests to verify
functionality and performance early and to identify any problems and minimize telescope
time for acceptance tests. At each stage we weigh the differences in response or performance
when simulating an interface against the complexity of higher level tests, time and personnel
necessary to debug higher level assembly tests, and finally telescope time at the full system level
to determine when each requirement should be validated.
The strategy in developing the ATP is:
• Develop tests with clear objectives and success criteria.
• Validate as many requirements as possible at the lowest level.
• Select representative tests to confirm tests at the previous stage after the next integration
step.
• Select simple interfaces and identify risks associated with use of simulators and support
equipment compared to a higher system-level test.
• Minimize telescope time for Acceptance Tests by identifying the minimal set of tests that,
in conjunction with previous tests and analysis, will fully validate the instrument.
An example of how this process works for the PFI is described in Section 2.14.6 of the Detailed
Design Document. A similar approach is developed for every assembly and subsystem.
These tests are defined as the design progresses to ensure features needed for I&T are built into
the software and hardware and the necessary laboratory facilities are available at the appropriate
time.
Examination of the instrument block diagram (Figure 3.2-1) shows this instrument can be integrated
along two paths: one involving the telescope-mounted hardware and the other for the
spectrograph, detectors and data pipeline. The software control system will be installed and
tested at both integration sites. All of this occurs prior to integration onto the telescope, and the
only test missed is the overall optical throughput, which can easily be calculated from individual
tests. These parallel paths will also be followed in the initial telescope installation work before
the final on-sky work commences. The advantages of this approach are minimizing the risk to
schedule by allowing parallel independent progress and flexibility for as long as possible and
maximizing the total resource available to the integration Phase by using two integration sites.
The full plan is detailed below and shown schematically in Figure 5.1-1. The System Software
will require careful management as modifications and bugs will be appearing simultaneously
from two sites/time zones.
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