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Boussalis, D.

Publications and source records attributed to Boussalis, D..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

An Integrated Optimal Estimation Approach to Spitzer Space Telescope Focal Plane Survey

This paper discusses an accurate and efficient method for focal plane survey that was used for the Spitzer Space Telescope. The approach is based on using a high-order 37-state Instrument Pointing Frame (IPF) Kalman filter that combines both engineering parameters and science parameters into a single filter formulation. In this approach, engineering parameters such as pointing alignments, thermomechanical drift and gyro drifts are estimated along with science parameters such as plate scales and optical distortions. This integrated approach has many advantages compared to estimating the engineering and science parameters separately. The resulting focal plane survey approach is applicable to a diverse range of science instruments such as imaging cameras, spectroscopy slits, and scanning-type arrays alike. The paper will summarize results from applying the IPF Kalman Filter to calibrating the Spitzer Space Telescope focal plane, containing the MIPS, IRAC, and the IRS science Instrument arrays.

optimal estimations↗
NASA NTRS1991

Experimental study of adaptive pointing and tracking for large flexible space structures

This paper describes an experimental study of adaptive pointing and tracking control for flexible spacecraft conducted on a complex ground experiment facility. The algorithm used in this study is based on a multivariable direct model reference adaptive control law. Several experimental validation studies were performed earlier using this algorithm for vibration damping and robust regulation, with excellent results. The current work extends previous studies by addressing the pointing and tracking problem. As is consistent with an adaptive control framework, the plant is assumed to be poorly known to the extent that only system level knowledge of its dynamics is available. Explicit bounds on the steady-state pointing error are derived as functions of the adaptive controller design parameters. It is shown that good tracking performance can be achieved in an experimental setting by adjusting adaptive controller design weightings according to the guidelines indicated by the analytical expressions for the error.

Boussalis, D.↗
NASA NTRS1989

Figure control concepts for segmented reflector telescopes

Control analysis activities related to the development of figure control technologies for large space telescopes with precision segmented actively controlled primary reflectors are reviewed. The Precision Segmented Reflector (PSR) configuration is described along with the development and use of the PSR models. Geometric and dynamic models, characterization of figure estimation errors and optimal sensor placement, and the development of quasi-static and dynamic control concepts are outlined. The structure of a quasi-static controller is presented, that utilizes edge sensor measurements to estimate displacement errors at the actuator level and generates figure correction commands. The second approach considers decentralization of the reflector system at the panel level, while the third considers decentralization at the actuator level.

Boussalis, D.↗
NASA NTRS1985

Vector Lyapunov Functions for Stochastic Interconnected Systems

Theoretical paper presents set of sufficient conditions for asymptotic and exponential stability with probability 1 for class of stochastic interconnected systems. Theory applicable to complicated, large-scale mechanical or electrical systems, and, for several design problems, it reduces computational difficulty by relating stability criteria to fundamental structural features of system.

Boussalis, D.↗
NASA NTRS1983

Dynamic isolation via momentum compensation for precision instrument pointing

The concept of a momentum-compensated inertially stabilized platform (IPPADS) for carrying scientific instruments is presented, the platform's function as a mechanical diode is explained, and the implications of momentum compensation for platform pointing and cost are discussed. The equations of motion for momentum compensation in the IPPADS five-body system are derived, and the results are used to computer simulate the system under consideration with two examples.

Boussalis, D.↗
NASA NTRS1983

Dynamic isolation of a spacecraft science platform via momentum compensation

The dynamic isolation of a two degree of freedom inertially stabilized science platform from the spacecrft basebody is examined. The important implications of a momentum compensated platform for pointing performance and cost are discussed, and the concept of a new system called the Integrated Platform Pointing and Attitude Control Subsystem utilizing the above property is presented. The results established in this paper are demonstrated by a computer simulation.

Boussalis, D.↗
NASA NTRS1982

Velocity estimation on a dual-spin spacecraft

The problem of estimating the changes in velocity during the various dV maneuvers of a dual-spin spacecrft is examined. A concise estimator suitable for on-board computer implementation is then developed to provide dV estimates based on the measurements obtained from two asymmetrically mounted accelerometers.

Boussalis, D.↗
NASA NTRS1981

Pointing system modeling for performance prediction

The paper considers the modeling and analysis of the JPL Precision Pointing and Tracking System, a gyro stabilized platform pointing system using optical target tracking. Sensor and actuator models are described which realistically represent actual hardware, and a practical controller and state estimator is developed through modern control techniques. The effect of the actuator nonlinearities on the system performance evaluation is discussed along with the modeling of the noise sources in the gyro. Finally, the limitations of implementing the control algorithms on the spacecraft computer, and the resulting tradeoffs are presented.

Boussalis, D.↗