Deployment/retrieval optimization for flexible tethered satellite systems

Abstract

A methodology for deployment/retrieval optimization of tethered satellite systems is presented. Previous research has focused on the case where the tether is modeled as an inelastic, straight rod for the determination of optimal system trajectories. However, the tether shape and string vibrations can often be very important, particularly when the deployment/retrieval speed changes rapidly, or when external forces such as aerodynamic drag or electrodynamic forces are present. An efficient mathematical model for flexible tethered systems is first derived, which treats the tether as composed of a system of lumped masses connected via inelastic links. A tension control law is presented based on a discretization of the tether length dynamics via Chebyshev polynomials. A scheme that minimizes the second derivative of length over the trajectory based on physically meaningful coefficients is presented. This is utilized in conjunction with evolutionary optimization methods to minimize the rigid body and flexible modes of the system during deployment/retrieval. It is shown that only a very small number of parameters are required to generate accurate trajectories. The results are compared to the case where the tether is modeled as a straight rod. P. Williams ( ) 1/4 Maylands

Advances in dynamics and control of tethered satellite systems

“…The modal functions used for approximation are usually taken as the functions in time because of the time dependence of the tether length during the tether deployment and retrieval. In the second kind of approaches, the tether is discretized physically into a collection of interconnected elements, either based on the finite element method (FEM) [64] or in the form of a series of beads (point masses) connected by massless rigid rods [65], springs [66,67], or combinations of springs and dashpots [46,68]. An interesting problem is how to use the discrete models for the simulation of the tether deployment and retrieval.…”

“…Mantri et al [91] conducted a detailed study on the deployment dynamics of a TSS with five dimensional and two dimensionless parameters taken into account. Recently, Williams [65] presented a novel methodology for deployment and retrieval optimization of a multibody model of two-body TSS, where the tether was modeled as an inelastic but flexible element.…”

Mission-function control of tethered satellite/climber system

“…Thus, many studies have considered deployment, station-keeping and retrieval of subsatellites [2][3][4][5][6][7][8].…”

Anti-sway control of tethered satellite systems using attitude control of the main satellite

“…There is a broad literature in controlling the motion of TSS in these phases [2,[10][11][12][13][14][15][16]. Deployment phase is the first and indispensable phase of the mission which is inherently stable provided that certain deployment speeds are not exceeded.…”