In this section we discuss the engineering questions that need to be answered in the System Design phase and how we intend to approach the iterative process of requirements and system design development.
In terms of functionality, performance, cost and complexity, NGAO will be one of the most sophisticated AO systems attempted to date. Such a system requires careful planning and attention to requirements at the earliest stages of its design. In this regard the technical team for NGAO will continue to work closely with the science teams during the system design phase to ensure that NGAO is as scientifically productive as possible.
The technical team will follow the standard system design approach for new Keck instruments.
This approach features the development of top-level system requirements to satisfy science “test cases”. These science cases are the basis for establishing NGAO function and performance. A concept of operations will be developed to determine features necessary for NGAO including observing modes, calibrations methods and data processing. The system requirements must also consider the full lifecycle of the NGAO system including installation and operations. A series of trade studies will follow the requirements development leading to the NGAO architecture. This architecture will be evaluated for performance, cost and risk. The results of this evaluation will be used to revise the system requirements. Subsequent NGAO architectures will be developed and reevaluated.
To facilitate the evaluation of the NGAO system the technical teams will continue to develop and maintain the performance budgets discussed in section 4.3.2.
The technical teams will work in the early phases of system design on validating their analytical models and computer simulations that feed into these performance budgets. Technical team members will also strive to crosscheck each other’s models and analysis. The technical team members will document their work as a set of electronic documents easily available to other team members.
The science team members will determine a set of prototype science cases for each performance budget. The same science case would not necessarily be judged as key for all performance budgets. The prototype science cases would be similar to the science cases in Table 13. If the NGAO project is to make progress in the early phases of system design the technical team must be able to rapidly evaluate the performance of proposed NGAO architectures and receive feedback from the science teams. We proposed that a NGAO project scientist be appointed to coordinate with the NGAO PI on the science requirements and use case testing of any NGAO architecture.
An integrated effort between engineers and astronomers is necessary for a successful NGAO design. To be truly useful the performance budget will require input and supporting analysis from the science teams. Our teams will build on the relationships already in place between the science teams and technical team from the production of this proposal.
As the highest-level NGAO requirements begin to solidify the technical team will determine the system and subsystem level requirements for NGAO. These requirements will be used to guide the development of the NGAO architecture to the subsystem level. This architecture will include conceptual designs for all major systems to a sufficient level of detail to allow a cost estimate and a risk evaluation. These subsystems would be the same as discussed in the Point Design subsystems, although the exact details of the design could be radically different.
As part of this proposal the technical team has identified a series of trade studies that will need to be performed to support the development of the NGAO system (See Appendix: System Design Phase Trade Studies). This list will be the starting point for our trade studies in the System Design phase of this project. The following is an abbreviated listing of some of the highest priority trades studies that have been identified:
Consider the feasibility of upgrading one of the existing Keck AO systems to meet NGAO requirements.
Determine best way to support Keck interferometer operations when NGAO is operational.
Evaluate the performance impact of Rayleigh scatter on NGAO performance and consider various mitigation methods such as a pulsed laser.
Determine the relative cost versus benefits of alternate optical relay designs.
Consider the cost/benefits of an adaptive secondary mirror implementation.
Consider the cost/benefits of a stand-alone tip/tilt mirror as opposed to mounting another necessary optic on the tip/tilt stage.
Consider cost/benefits of different options for achieving the NGAO science goals in the K through M-bands.
In addition to a design concept for NGAO the technical team will manage the interface control between NGAO and its subsystems, primarily through interface control documents.
5 MANAGEMENT