Research Motivation

The Next Generation Space Telescope (NGST) represents a challenging problem from the point of view of integrated modeling of structural dynamics, controls and optics. This is due to the fact that NGST will make extensive use of deployable (deployment movie) , inflatable and lightweight components, while taking into account launch weight and fairing dimensional constraints. In order to meet the scientific objectives, NGST will have to be diffraction limited at a wavelength of l=2.2mm and be able to point the Optical Telescope Assembly (OTA) with a precision of 4.8 milli-arcseconds (1s). The two key metrics, which relate to these science requirements during observations are the root-mean-square wavefront error (RMS WFE) and the line-of-sight jitter metric (RMS LOS), which is representative of the motion of the image centroid on the focal plane. It is important to assess the impact of the expected micro-vibration environment on the scientific performance before design, construction and launch. Another important mode for NGST is slewing, which is required for time-optimal acquisition of new science targets within settling time and torque authority constraints.

All current concepts for the NGST are innovative designs, which present unique systems-level challenges. Standard practices for developing systems error budgets, such as the "root-sum-of-squares" error tree, are insufficient for designs of this complexity. Simulation and optimization are the tools needed for this project; in particular tools that integrate disturbances, controls, optics, structural analysis, and design optimization. A set of tools is being developed, which will allow the NGST design team to perform disturbance, sensitivity and uncertainty analyses during the conceptual design phase. These tools provide a realistic prediction of the expected system end-to-end performance while accounting for parametric uncertainties. The research includes studying the fine pointing and slew modes and will provide the ability to trade different architectures with respect to each other. A fundamental motivation for this research is that it will not be possible to fully test the observatory in 1g environment prior to launch.