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Geometric Control of Tethered Satellite Formations by Controlling the Tether Length

Makarem, Hadi | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43419 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Alasty, Aria
  7. Abstract:
  8. Satelites formation which is a specic spatial conguration of satellites, is of great importance in design and control of satellite systems. Reducing the required power to maintain that conguration, while imposing complicated dynamics on the system, connecting satelites through tethers has recently attracted researchers' attention. Developing a new model based on which the motion of the satellite formation will be expressed through simple equations, followed by the study of how the tether length control participates in the orientation control of the system, are the principal aims of current research. First, a new model is proposed for a group of tethered satellite for- mations, and based on this model, the attitude kinematic and dynamic equations are developed. Next, supposing no external forces or moments, control laws are designed to reshape and re-orient the formation to the desired conguration. For better under- standing the eect of the tether length control on the attitude control of formations, this thesis mainly concentrates on triangular and tetrahedral formations. Using geo- metrical methods and control theorems on Lie groups, Lyapanuv based methods, and sliding modes open-loop and closed-loop control laws are designed for these two special systems. Moreover, the orbital motion of satellite formations is studied in this research, and in the presence of gravity gradient moments, relative equilibruim congurations, and tightness conditions for the tethers are obtained based on the proposed model. Results show that the attitude kinematic and dynamic equations, gravity gradient moment, and tightness conditions for the tethers, are all reduced to simple mathe- matical relations based on the model. Furthermore, according to the designed control laws, length control has a great role in the attitude control of the formation, without considering tethers' tightness conditions. Considering the mentioned conditions, one may introduce some facts which are unavoidable and were discussed beforethe control problem will face some facts , which are also addressed before
  9. Keywords:
  10. Geometric Control ; Attitude Control ; Nonholonomic System ; Tethered Satellite Formation

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