The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly-segmented direct Gregorian configuration. Each mirror pair must be coaligned and co-boresighted. During operations, the alignment of the optical components will deflect due to variations in temperature, gravity-induced structure flexure of the mount, and, on a scale relevant to phasing, vibrations. The doubly-segmented nature and size of the GMT will create a novel set of challenges for initial assembly, integration, and verification and maintaining high-precision alignment of the optical elements during operations. GMT is developing a Telescope Metrology System that uses 3D laser metrology systems to decrease the complexity of alignment and increase observatory efficiency. This paper discusses the 4 subsystems of TMS as well as their operational modes.
A concurrent engineering approach to the design and analysis of a space-borne Electro-Optical (EO) sensor is presented.
A detailed design of an infrared telescope payload is developed by an interdisciplinary team of mechanical, structural,
thermal, and optical engineers using a Simulation Driven Engineering (SDE) software environment. The telescope
payload design is also integrated with a conceptual level design of the space segment of a mission that incorporates the
payload. The flow of the concurrent design process is described, and design outputs are provided.
Root causes of mission critical failures and major cost and schedule overruns in complex systems and programs are
studied through the post-mortem analyses compiled for several examples, including the Hubble Space Telescope, the
Challenger and Columbia Shuttle accidents, and the Three Mile Island nuclear power plant accident. The roles of
organizational complexity, cognitive biases in decision making, the display of quantitative data, and cost and schedule
pressure are all considered. Recommendations for mitigating the risk of similar failures in future programs are also
provided.
Complex products are best developed in a collaborative design environment where engineering data and CAD/CAE
results can be shared across engineering discipline boundaries within a common software interface. A new software tool
that allows Electro-Optical (EO) sensors to be developed in this manner has been used to conduct an integrated
Structural/Thermal/Optical (STOP) analysis of a critical lens subassembly in a flight payload. This paper provides a
description of the software environment and a summary of the technical results that were produced with it.
We present a design and tolerancing approach that permits the achievement of a high degree of spatial and spectral uniformity of response from a pushbroom imaging spectrometer. Such uniformity of response is crucial for the extraction of accurate spectroscopic information from remotely sensed data. The spectrometer system example comprises two independent spectrometer modules covering the 400 - 2500 nm range, separated through a dichroic mirror. The relative merits of alternative approaches are briefly reviewed before concentrating on the problem of building a flight-worthy system that can approximate its design performance. The tolerancing approach requires simultaneous monitoring of many parameters, and specifically: overall image quality, spectral distortion, spectral MTF variation with field, spatial distortion, spatial MTF variation with wavelength, and slit magnification to within a small fraction of a pixel. It is shown that the wavefront error alone or even supplemented by distortion figures is insufficient for characterizing a system with high response uniformity. Tolerance values on the components and their positioning are primarily guided by the need to achieve the same magnification between the two spectrometer modules, as well as by the interferometric alignment method.
We describe a pushbroom imaging spectrometer having a number of attractive features for remote sensing applications, including compact and simple form, good image quality, high efficiency, and very low levels of distortion. These properties are made possible by the unique characteristics of convex gratings manufactured by electron-beam lithography. A laboratory prototype has been built and is under evaluation. If has an f-number of 2.8, covers a spectral band from 400 to 1000 nm with 3 nm spectral resolution and has 750 spatial elements across the entrance slit. Experimental results are shown that demonstrate very low distortion, on the level of 2 percent of a pixel.
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