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Dynamics and Control of a Tethered Enhanced Gravity Tractor Performing Asteroid DeflectionThe dynamics and control of an Enhanced Gravity Tractor (EGT) augmented with a tether for deflecting an asteroid are studied. A conventional EGT consists of collected asteroidal mass collocated with the spacecraft. Because of the presence of a tether, the collected mass is placed where the EGT would have been without a tether, and the spacecraft is placed farther away from the asteroid. Doing so improves the fuel efficiency and safety margin of the EGT operation without significantly sacrificing the gravitational attraction between the asteroid and the EGT. The tether is modeled as a series of particles connected by spring-dashpot systems. Physical properties of the tether are selected to be similar to those of the SPECTRA-1000, Kevlar-29, and Kevlar-49 fibers. It is assumed that control is applied only to the spacecraft, and there is no active control associated with the collected mass. A Proportional-Derivative (PD) controller is employed to maintain the spacecraft and the collected mass at desired positions relative to the asteroid. Numerical simulations of tethered EGT operations at 2008 EV5, Itokawa, Apophis, and a fictitious ellipsoidal asteroid are performed. It is demonstrated that a PD controller is capable of accomplishing the control objectives. The gravity gradient and the control force keep the tether stretched throughout a normal tethered EGT operation, and the load on the tether is well within the design limit of the tether material. While including multiple particles in the tether model is essential in capturing details of tether vibration, the number of particles does not significantly affect the motions of the collected mass and the spacecraft. In addition, the distance from the asteroid mass center to the collected mass should be chosen judiciously in the case of a rotating slender asteroid; some distance ranges should be avoided as excessive lateral oscillations can be excited by resonance between the asteroid rotation and tether pendular motion.
Document ID
20180006288
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Shen, Haijun
(Analytical Mechanics Associates, Inc. Hampton, VA, United States)
Roithmayr, Carlos M.
(NASA Langley Research Center Hampton, VA, United States)
Li, Yingyong
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
October 16, 2018
Publication Date
February 2, 2018
Subject Category
Astrodynamics
Report/Patent Number
AAS 18-061
NF1676L-28096
Report Number: AAS 18-061
Report Number: NF1676L-28096
Meeting Information
Meeting: AAS Guidance and Control Conference
Location: Breckenridge, CO
Country: United States
Start Date: February 2, 2018
End Date: February 7, 2018
Sponsors: American Astronomical Society
Funding Number(s)
WBS: WBS 432938.11.01.07.54.05.01
Distribution Limits
Public
Copyright
Public Use Permitted.
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