David Buscher edited untitled.tex  about 8 years ago

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\section{Introduction}  The Automated Alignment System (AAS) and Back End Active Stabilization of Shear and Tilt (BEASST) together serve to align the beam trains in the MROI and to keep these aligned during the night. An design for the AAS has been developed to the level of went through  a Conceptual Design Review (CDR) andadditional development has been performed  since thento prototype  some subsystems of the AAS. have been prototyped.  We propose here a modification to the AAS concept  which will allow the existing goals to be met but which would allow while addressing  drifts in alignment during the nightto be addressed much  more robustly using BEASST. rapidly and robustly.  At the same time, some of the constraints on the BEASST system can be relaxed, allowing a more performant higher-performance  system to be built more quickly. \section{Functional requirements}  The function of the combined AAS and BEASST systems (hereafter collectively  referredto  asjust  ``the AAS'') AAS'' since they can be considered to be a single system addressing alignment needs)  can be briefly described as: \begin{enumerate}  \item When a new beam train is installed or configured, the AAS must allow for coarse (and possibly manual) alignment of the beam train to allow an alignment beam to pass between the beam combining area (BCA) and the unit telescope mount (UTM) without vignetting.  \item At the beginning of each observing night the beam train, night,  the AAS must align re-align  the beam train so that beams of starlight arriving at the beam combiners meet the tilt and shear error budget. \item During the night, the AAS must make fine adjustments to the alignment so that the tilt and shear error budget is maintained in the presence of thermal and other drifts (this requirement was originally delegated to BEASST). drifts.  \item When a new beam train is installed or configured, the AAS must allow for measurement of the "piston" term due to the optical path between the beam combiners and the telescopes. telescopes, in order to allow for rapid acquisition of stellar fringes.  \item At the beginning of the night, the AAS must allow the pathlength differences between the fringe tracker and the science instrument to be measured. measured so that these can be equalized.  \end{enumerate}  \section{Outline of the existing scheme}  \section{Proposed modification}  \section{Advantages and disadvantages}  \section{Recommendation}