KEYWORDS: Systems modeling, James Webb Space Telescope, Observatories, Thermal modeling, Data modeling, Mathematical modeling, Solid modeling, Space telescopes, Performance modeling, Distortion
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014.
The imaging performance of the telescope will be diffraction limited at 2μm, defined as having a Strehl ratio >0.8.
System-level verification of critical performance requirements will rely on integrated observatory models that predict the
wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms)
through to the wave-front sensor focal plane is met. Furthermore, responses in several key disciplines are strongly crosscoupled.
The size of the lightweight observatory structure, coupled with the need to test at cryogenic temperatures,
effectively precludes validation of the models and verification of optical performance with a single test in 1-g. Rather, a
complex series of incremental tests and measurements are used to anchor components of the end-to-end models at
various levels of subassembly, with the ultimate verification of optical performance is by analysis using the assembled
models. The assembled models themselves are complex and require the insight of technical experts to assess their ability
to meet their objectives. This paper describes the modeling approach used on the JWST through the detailed design
phase.
Michael Menzel, Marie Bussman, Michael Davis, Gary Golnik, Sandra Irish, Jon Lawrence, Richard Lynch, Peiman Maghami, Landis Markley, Kimberly Mehalick, Gary Mosier, Danniella Muheim, Keith Parrish, Shaun Thomson, Paul Geithner, Joseph Pitman, James Wehner, Jonathan Arenberg, Brian Costanza, Satya Anandakrishnan, William Burt, Reem Hejal
KEYWORDS: Observatories, James Webb Space Telescope, Thermal modeling, Space telescopes, Cryogenics, Solid modeling, Systems engineering, Systems modeling, Integrated modeling, Space operations
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014.
System-level verification of critical performance requirements will rely on integrated observatory models that predict the
wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms)
through to the wave-front sensor focal plane is met. This paper describes the systems engineering approach used on the
JWST through the detailed design phase.
The Laser Interferometer Space Antenna mission is a planned gravitational wave detector consisting of three spacecraft
in heliocentric orbit. Laser interferometry is used to measure distance fluctuations between test masses aboard each
spacecraft to the picometer level over a 5 million kilometer separation. Laser frequency fluctuations must be suppressed
in order to meet the measurement requirements. Arm-locking, a technique that uses the constellation of spacecraft as a
frequency reference, is a proposed method for stabilizing the laser frequency. We consider the problem of arm-locking
using classical optimal control theory and find that our designs satisfy the LISA requirements.
KEYWORDS: Space operations, Control systems, Sensors, Sun, Solar radiation models, Motion measurement, Systems modeling, Signal attenuation, Aerospace engineering, Stars
The Space Technology 7 (ST7) experiment will perform an on-orbit system-level validation of two specific Disturbance Reduction System technologies: a gravitational reference sensor employing a free-floating test mass and a set of micronewton colloidal thrusters. The ST7 Disturbance Reduction System (DRS) is designed to maintain the spacecraft's position with respect to a free-floating test mass to less than 10 nm/√Hz over the frequency range of 1 to 30 mHz. This paper presents the overall design and analysis of the spacecraft drag-free and attitude controllers. These controllers close the loop between the gravitational sensors and the micronewton colloidal thrusters. There are five control modes in the operation of the ST7 DRS, starting with the attitude-only mode and leading to the science mode. The design and analysis of each of the control modes as well as the mode transition strategy are presented.
William Folkner, Sasha Buchman, Robert Byer, Daniel DeBra, C. Dennehy, Manuel Gamero-Castano, J. Hanson, Vlad Hruby, George Keiser, Andy Kuhnert, F. Landis Markley, M. Houghton, P. Maghami, David Miller, S. Prakash, Robert Spero
KEYWORDS: Space operations, Control systems, Electrodes, Interferometers, Magnetism, Sensors, Aerospace engineering, Control systems design, Prototyping, Microfluidics
The Disturbance Reduction System (DRS) is a space technology demonstration within NASAs New Millennium Program. DRS is designed to validate system-level technology required for future gravity missions, including the planned LISA gravitational-wave observatory, and for formation-flying interferometers. DRS is based on a freely-floating test mass contained within a spacecraft that shields the test mass from external forces. The spacecraft position will be continuously adjusted to stay centered about the test mass, essentially flying in formation with the test mass. Colloidal microthrusters will be used to control the spacecraft position within a few nanometers, over time scales of tens to thousands of seconds. For testing the level of acceleration noise on the test mass, a second test mass will be used as a reference. The second test mass will also be used as a reference for spacecraft attitude. The spacecraft attitude will be controlled to an accuracy of a few milliarcseconds using the colloidal microthrusters. DRS will consist of an instrument package and a set of microthrusters, which will be attached to the European Space Agencys SMART2 spacecraft with launch scheduled for August 2006.
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