Automated rendezvous and docking (AR&D) is an activity that is vital to NASA's future endeavors. A team of NASA engineers has created a test bed that allows sensor systems to be tested but also incorporates operator interfaces in order to evaluate the information required by an operator to oversee automated systems. Several sensors have been run through the test bed and more are scheduled in the future. The test bed will be described along with the operator interfaces and results of sensor testing.
KEYWORDS: Sensors, Motion models, Particle filters, Systems modeling, Computer simulations, Data modeling, Control systems, Monte Carlo methods, Human-machine interfaces, Analytical research
The Contact Dynamics Simulation Laboratory (CDSL) of the Marshall Space Flight Center provides for refined hardware-in-the-loop real-time simulation of docking and berthing mechanisms and associated control systems. This facility is employed to verify the performance of docking/berthing mechanisms during Earth-orbit operations, determine the capture envelope of docking/berthing devices, measure contact loads at vehicle interfaces, and evaluate visual cues for man-in-the-loop operations. The CDSL has developed test verified analytical models of such systems as the International Space Station (ISS) Common Berthing Mechanism (CBM) and the Hubble Space Telescope (HST) Three Point Docking Mechanism. This paper will describe the modeling and test techniques employed at the CDSL and present results from recent programs.
A system which estimates the global radius of curvature (GRoC) and corrects for changes in GRoC on a segmented primary mirror has been developed for and verified on McDonald Observatory's Hobby Eberly Telescope (HET). The GRoC estimation and control system utilizes HET's primary mirror control (PMC) system and the Segment Alignment Maintenance System (SAMS), an inductive edge sensor system. A special set of boundary conditions is applied to the derivation of the optimal edge-match control. The special boundary conditions allow the further derivation of an observer, which enables estimation and control of the GRoC mode to within HET's specification. The magnitude of the GRoC mode can then be controlled despite the inability of the SAMS edge sensor system, by itself, to observe or control the GRoC mode. The observer can be extended to any segmented mirror telescope. It will be shown that the observer improves with accuracy as the number of segments increases. This paper presents the mathematical theory of the observer. Performance verification data from the HET will be presented.
The Segment Alignment Maintenance System (SAMS) was installed on McDonald Observatory's Hobby-Eberly Telescope (HET) in August 2001. The SAMS became fully operational in October 2001. The SAMS uses a system of 480 inductive edge sensors to correct misalignments of the HET's 91 primary mirror segments when the segments are perturbed from their aligned reference positions. A special observer estimates and corrects for the global radius of curvature (GRoC) mode, a mode unobservable by the edge sensors. The SAMS edge sensor system and GRoC estimator are able to maintain HET's primary figure for longer durations than previously had been observed. This paper gives a functional description of the SAMS control system and presents performance verification data.
The software development for an upgrade to the Hobby-Eberly Telescope (HET) was done in LabVIEW. In order to improve the performance of the HET at the McDonald Observatory, a closed-loop system had to be implemented to keep the mirror segments aligned during periods of observation. The control system, called the Segment Alignment Maintenance System (SAMS), utilized inductive sensors to measure the relative motions of the mirror segments. Software was developed in LabVIEW to tie the sensors, operator interface, and mirror-control motors together. Developing the software in LabVIEW allowed the system to be flexible, understandable, and able to be modified by the end users. Since LabVIEW is built using block diagrams, the software naturally followed the designed control system's block and flow diagrams, and individual software blocks could be easily verified. LabVIEW's many built-in display routines allowed easy visualization of diagnostic and health-monitoring data during testing. Also, since LabVIEW is a multi-platform software package, different programmers could develop the code remotely on various types of machines. LabVIEW's ease of use facilitated rapid prototyping and field-testing. There were some unanticipated difficulties in the software development, but the use of LabVIEW as the software "language" for the development of SAMS contributed to the overall success of the project.
KEYWORDS: Sensors, Mirrors, Telescopes, Space telescopes, Control systems, Image segmentation, Process control, Signal processing, Simulation of CCA and DLA aggregates, Image quality
NASA's Marshall Space Flight Center, in collaboration with Blue Line Engineering of Colorado Springs, Colorado, is developing a Segment Alignment Maintenance System (SAMS) for McDonald Observatory's Hobby-Eberly Telescope (HET). The SAMS shall sense motions of the 91 primary mirror segments and send corrections to HET's primary mirror controller as the mirror segments misalign due to thermo-elastic deformations of the mirror support structure. The SAMS consists of inductive edge sensors. All measurements are sent to the SAMS computer where mirror motion corrections are calculated. In October 2000, a prototype SAMS was installed on a seven-segment cluster of the HET. Subsequent testing has shown that the SAMS concept and architecture are a viable practical approach to maintaining HET's primary mirror figure, or the figure of any large segmented telescope. This paper gives a functional description of the SAMS sub-array components and presents test data to characterize the performance of the sub-array SAMS.
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