Research Summaries

Back Large Aperture Lightweight Space-Based Optics - Phase III

Fiscal Year 2008
Division Graduate School of Engineering & Applied Science
Department Mechanical & Aerospace Engineering
Investigator(s) Agrawal, Jr., Brij N.
Sponsor Secretary of the Air Force/FMBMB-AFOY (Air Force)
Summary For an imaging spacecraft to provide truly persistent surveillance capability, the satellite should be in a higher orbit, requiring large aperture lightweight deployable mirrors, in the range of 10-20 meters in diameter. The objective of this research program is to improve adaptive optics control techniques for flexible deployable space mirror surface and beam control and to minimize image aberrations. This is a continuing project. During Phase I, the major emphasis was to develop an adaptive optics test bed and demonstrate the ability to correct image aberrations by using adaptive optics. The test bed has two adaptive optics systems and one jitter control system. During Phase II, the emphasis was on three tasks; development of a six segment 16 inch diameter CFRP segmented mirror, improved adaptive optics control techniques, and development of phase diversity sensor. A parabolic segmented mirror with a 48 inch focal length was procured. Based on the experimental results on control methods, the modal method with combined integral and gradient feedback control was best to minimize image aberrations. Flexible dynamics were simulated by injecting a sinusoidal disturbance into the input signal. A phase diversity sensor was developed to correct piston and tip/tilt error of the segments for phase III. During Phase III, the segmented mirror and phase diversity sensor will be implemented on the adaptive test bed. Three actuators on the back of each segment will be added. Algorithms will be developed to determine piston and tip/tilt error from the phase diversity sensor. A Redundant Spacing Calibration technique will be also developed to calculate piston and tip tilt error. We will evaluate the application of Multi-Input Multi-Output (MIMO) with robust control for the surface control problem. Various multivariable robust control techniques, such as loop-shaping method, weighted mixed-sensitivity controller synthesis, and-synthesis, etc., will be investigated. For beam jitter control, jitter created by rotating devices such as CMGs and low frequency transients during slew maneuvers will be considered.
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Publications Publications, theses (not shown) and data repositories will be added to the portal record when information is available in FAIRS and brought back to the portal
Data Publications, theses (not shown) and data repositories will be added to the portal record when information is available in FAIRS and brought back to the portal