STRUCTURAL CONTROL INTERACTION FOR A LSS ATTITUDE CONTROL SYSTEM USING THRUSTERS AND REACTION WHEELS

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STRUCTURAL CONTROL INTERACTION FOR A LSS ATTITUDE
CONTROL SYSTEM USING THRUSTERS AND REACTION WHEELS
1. INTRODUCTION

• Problems related to LSS
• Most of the current research in the field of
  structural control for mitigation of responses
  due to environmental loads neglects the effects
  of control-structure interaction (CSI) in the
  analysis and design of protective systems.
• The CSI are associated with structural
  flexibility and/or any kind of fluid or mobile
  part as component of the LSS system.
• The space environment may excite the elastic
  vibration to such a level that the control system
  loses efficiency.
• Conversely the control system actuation may
  create forces which excite the flexible structure

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• Taking into account that most of spacecraft
  structure includes some level of flexibility, it
  is mandatory to access the structural interaction
  with control systems or, conversely to assess the
  interaction of the control systems with the
  structure.
• If the structure control interaction, CSI, is
  improperly assessed, the spacecraft performance
  can be jeopardized, structure components can
  fail, or, in the worse case, the vehicle may be
  destroyed.
• The CSI for a specific design can be anticipated
  and the potential problems avoided through space
  vehicle modeling simulations and tests execution.
  
• Such task requires a cooperative effort between
  the structural and control designers. To make
  those designers work as a team is a difficult
  mission. The need to overcome this typical
  problem gives birth to the integrated structural
  control discipline.
• The problem still persists and is very difficult
  to reach a structural configuration that in the
  first design satisfies both control and structure
  requirements.

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One form of assessing the control structure
interaction is to develop space structure
mathematical models followed by a dynamics
analysis, including the space vehicle dynamics
computer simulations.
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Some examples - CSI problems
Space Vehicle Problem Cause
Explorer I Directional instability Internal energy dissipation and bending of whip antennas
ATS-5 Dynamics instability Internal energy dissipation due to fluid motion inside heat pipes attached to cylindrical solar arrays
Alouette I Despin Thermal bending of satellite booms.
RAE Undesirable oscillations Very long booms vulnerable to large deflections
OGO III Limit-cycle oscillations Control system interaction with boom flexibility.
M2-F2 Limit-cycle oscillations and Structural resonance vibrations Lightweight control system gyro mount allowed vibration from control surface motion to be sensed.
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Problem Formulation - LSS Mathematical Model
The problem consists of the computer simulation
of a large space structure mathematical model to
analyze the control structure interaction
phenomenon.
dm
LSS Physical Model
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Mathematical Model
Zs
Ys
z
y
rs
ra
rp
rd
x
Xs ?
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Kinetic Energy
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Discretization Procedure Assumed Mode Method
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Potential Elastic Energy
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Then the equations were linearized about the
gravity-gradient stabilized orientation and
integrated via computer
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Results
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