Spacecraft formation-keeping using a closed-form orbit propagator and optimization technique

This thesis examines the use of thrusters and solar sails for spacecraft formation keeping control at the Earth-Moon L4 point. Particular emphasis was placed on the study of underactuated control, in which fewer control inputs than the system's degrees of freedom are available. A linear LQR control scheme, an integral augmented sliding mode controller and a bang-bang controller were applied to the dynamic spacecraft system. The nonlinear controllers produced errors falling with tighter tolerances than the linear controllers in the perturbed environment. Performing similarly well as the underactuated thrusters system was the solar-sails-controlled spacecraft formation using a bang-bang controller. This shows that solar sails could be a viable propellantless technique for relative control. A linear control technique was able to bound errors to within a couple of hundred metres, using a hybrid propulsion system. Of the cases studied, only the fully-actuated thrusters-based system was able to explicitly track a circular trajectory, but had [Delta]V requirement of more than 100 times greater than that needed for tracking the natural, elliptical trajectory.

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Heuristic Optimization of Ribbed Cooling Channels With Variable Length and Roughness

Journal of Heat Transfer ◽

10.1115/1.4047835 ◽

2020 ◽

Vol 142 (11) ◽

Author(s):

Faizan Ejaz ◽

Leslie K. Hwang ◽

Beomjin Kwon

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Closed Form ◽

Optimization Technique ◽

Absolute Error ◽

Optimization Method ◽

Channel Length ◽

Heuristic Optimization ◽

Fully Developed Flow ◽

Cooling Channels

Abstract This paper presents a heuristic optimization method for cooling channels with internal repeated-rib roughness. The method rapidly explores a design space to simultaneously optimize two geometric parameters, channel length, and rib roughness ratio. For a rapid and accurate optimization, the method combines a heuristic optimization technique, simulated annealing (SA), and numerically derived closed-form models of heat transfer and pressure drop. It is shown that approximately 1 million designs are evaluated within 6 s, resulting in optimal designs having minimal thermal resistance for given pressure thresholds. Closed-form correlations for developing and fully developed flow are derived by evaluating discrete design points using a finite volume model (FVM). The derived correlations predict the channel properties with acceptable ranges of mean absolute error (<5% for Nusselt number and < 15% for pressure drop) against the FVM. Optimal channel designs exhibit up to about 12 times greater performance factor compared to smooth channels, supporting the efficacy of optimization. The introduced method demonstrates the potential of rapid numerical optimization method in designing heat transfer devices with complex geometries.

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Formation-Keeping Strategies At The Earth-Moon L4 Triangular Libration Point

10.32920/ryerson.14665923 ◽

2021 ◽

Author(s):

Frank Y. W. Wong

Keyword(s):

Degrees Of Freedom ◽

Sliding Mode ◽

Libration Point ◽

Control Technique ◽

Solar Sails ◽

Hybrid Propulsion ◽

Triangular Libration Point ◽

Spacecraft Formation ◽

The Earth ◽

Formation Keeping

This thesis examines the use of thrusters and solar sails for spacecraft formation keeping control at the Earth-Moon L4 point. Particular emphasis was placed on the study of underactuated control, in which fewer control inputs than the system's degrees of freedom are available. A linear LQR control scheme, an integral augmented sliding mode controller and a bang-bang controller were applied to the dynamic spacecraft system. The nonlinear controllers produced errors falling with tighter tolerances than the linear controllers in the perturbed environment. Performing similarly well as the underactuated thrusters system was the solar-sails-controlled spacecraft formation using a bang-bang controller. This shows that solar sails could be a viable propellantless technique for relative control. A linear control technique was able to bound errors to within a couple of hundred metres, using a hybrid propulsion system. Of the cases studied, only the fully-actuated thrusters-based system was able to explicitly track a circular trajectory, but had [Delta]V requirement of more than 100 times greater than that needed for tracking the natural, elliptical trajectory.

Download Full-text