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Space Station




                                           Complex Systems Control
                                     ...
Introduction

With many years spaceflight experience, Draper has developed unique
    -   work processes, technologies, to...
Spaceflight Experience – Space Shuttle (1980’s – Present)

 Design agent for on-orbit Flight Control System (FCS) for 20+ ...
Spaceflight Experience – Other Spacecraft
 Space Station (1998 - Present)
  -   Perform CSI Flight Readiness Certification...
Expand Capability – Shuttle Control Of Very Large Payload

  Developed new attitude control system capabilities within exi...
Expand Capability – Shuttle Control Of Very Large Payload




 Flexure at Docking
      Interface
Can Cause Instability
 W...
Expand Capability – Space Station Control Of Very Large Payload

  Developed new attitude control system capabilities with...
Expand Capability – Space Station Control Of Very Large Payload

                   Reposition Orbiter Using Robotic Arm

...
Expand Capability – Space Station Large Angle Rotation w/ CMGs

Developed new CMG attitude control system capability withi...
Expand Capability – Space Station Large Angle Rotation w/ CMGs
                 90o ZPM - Flight Telemetry Animation




 ...
Recover From Failure – Catch Tumbling Station With CMGs

  Applied ZPM guidance to command CMGs and recover attitude contr...
Recover From Failure – Catch Tumbling Station With CMGs
              0.1deg/sec Initial Rate Simulation Animation




   ...
Unique Technologies To Reduce Cost/Schedule/Risk

  Nonlinear Control
   -   Phase Plane for thruster actuated systems
  F...
Unique Tools To Reduce Cost/Schedule/Risk

  Modular, dynamically scalable, and automated tools using COTS SW
   -   Exten...
Capabilities

  Modeling
   -   Multi-Body Rigid + Flex Dynamics
  Analysis
   -   Frequency Response
   -   Robust Stabil...
Backup Material




                  16 - 05/09/08
Expand Capability – Space Station Control Of Very Large Payload
                                  Orbiter Position wrt Sta...
Unique Work Processes – Draper Control Framework

  Key Design Criteria
   -   Controllability, Stability, Loads, Performa...
Space Station GN&C Systems Certification
  Integrated platform for design and verification of aerospace systems
    Develo...
Unique Work Processes – Flight Readiness Certification I

   Quantify achievable performance and risk exposure for availab...
Unique Work Processes – Flight Readiness Certification II
         Confidence in System Performance is Exponentially Faste...
Shuttle – Flexible SRMS – Space Station Simulation




                                                     22 - 05/09/08
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Spacecraft Control Design Verification

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Complex Systems Control

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Spacecraft Control Design Verification

  1. 1. Space Station Complex Systems Control Naz Bedrossian The Charles Stark Draper Laboratory Hubble Space Telescope Space Shuttle 42Klb RS Functional Cargo Block Berthing 1 - 05/09/08
  2. 2. Introduction With many years spaceflight experience, Draper has developed unique - work processes, technologies, tools for reliable and high confidence control of complex space systems which - meet and exceed performance requirements while - reducing overall cost and risk with demonstrated capability to - extend lifetime, expand capability, recover from failure System Life-Cycle Phases Where Draper Can Contribute LIFE EXTENSION EXPAND CAPABILITY FAILURE RECOVERY 2 - 05/09/08
  3. 3. Spaceflight Experience – Space Shuttle (1980’s – Present) Design agent for on-orbit Flight Control System (FCS) for 20+ years - For unique Shuttle payload flights and Space Station assembly - Payloads: Space Station, MIR, Hubble Space Telescope, Space Radar Topography Mission Perform FCS Flight Readiness Certification for all payloads - Formal process by which spacecraft performance is assured to meet mission objectives despite uncertainties and failure contingencies Perform Controller-Structure-Interaction (CSI) Certification - To preclude dynamic interaction between control systems and spacecraft structure Provide mission support - Perform real-time development of contingency responses to in-flight anomalies Develop FCS Updates - To meet changing program objectives and reduce operational cost - Thruster pulse-train solutions have been designed and certified to minimize structural loads Provide simulation and modeling expertise - Develop flight validated simulations for Orbiter & Shuttle Remote Manipulator System (SRMS) - Draper SRMS is NASA’s highest fidelity simulation 3 - 05/09/08
  4. 4. Spaceflight Experience – Other Spacecraft Space Station (1998 - Present) - Perform CSI Flight Readiness Certification for each assembly stage ⋅ For both US CMG and Russian Thruster control systems - Designed attitude control system for Orbiter Repair Maneuver contingency ⋅ 250Klb Orbiter maneuvered by flexible SRMS while attached to flexible 400Klb Station flexible - Implemented in flight software load minimizing thruster pulsetrain - Provide Russian control systems modeling expertise Large Space Structures (Classified) - Derive mission requirements and develop control systems for flex control Hughes Satellites - Developed independent vehicle dynamics and control simulations ⋅ Draper derived and implemented the equations of motion for the 5 body flexible dynamics model - Designed qualification tests 4 - 05/09/08
  5. 5. Expand Capability – Shuttle Control Of Very Large Payload Developed new attitude control system capabilities within existing flight software in order to control very large payloads - MIR space station, International Space Station, Hubble Space Telescope Challenge - Low frequency flex can cause instability Solution: Modify Attitude Control System - Developed notch flex filters to attenuate flex and thruster command shaping to not excite flex Notch Filtering - Attenuate low frequency and large amplitude flex for stable control without adversely affecting rigid-body performance Thruster Command Shaping - Used to reduce structural excitation due to control action - Break-up command into a pulsetrain and introduce time delay between pulses 5 - 05/09/08
  6. 6. Expand Capability – Shuttle Control Of Very Large Payload Flexure at Docking Interface Can Cause Instability When Orbiter Is In Control amp *1, freq *0.7, no notches amp *2 freq *1: notches enabled Without Notch With Notch 0.080 0.20 0.040 0.10 0.000 0.00 Tekplot Tekplot WERRY WERRY hall hall -.040 -0.10 Thu Oct 12 16:20:26 2000 Fri Oct 13 14:18:28 2000 -.080 -12.0 Unstable -8.0 -4.0 ATTERY 0.0 4.0 -0.20 -15.0 -10.0 Stable -5.0 ATTERY 0.0 5.0 10.0 6 - 05/09/08
  7. 7. Expand Capability – Space Station Control Of Very Large Payload Developed new attitude control system capabilities within existing flight software in order to control Shuttle attached to robotic arm - Required capability after Columbia accident to repair Shuttle Tile Protective Services Tile Challenge - Damp large rate errors (up to 0.2deg/sec) while avoiding large Orbiter motion or contact with Station Orbiter - Low frequency (in 0.01Hz range) and 10X larger amplitude flex than any other robotic operation than - Controller rigid body BW and flex close to each other - Achieve adequate stability margins while maintaining vehicle control control - Design controller not requiring updates even though mass properties and flex different at each waypoint properties - Russian thruster controller could not be used as it could not limit thruster on times resulting in large loads limit Solution: Modify CMG Attitude Controller For Thruster Control - Developed new Pulse-Width-Modulation mode for US CMG attitude hold PID controller with new flex filters Pulse- Width- to command thrusters instead of CMGs (CMG-RCS in figure) (CMG- - This US Thruster Only (USTO) mode has been in use since 2005 for nominal operations Flex Filters - Active control of very low frequency flex modes, < 0.04Hz - Attenuate higher frequency flex modes, > 0.04Hz - Designed using novel Computational Optimization approach 7 - 05/09/08
  8. 8. Expand Capability – Space Station Control Of Very Large Payload Reposition Orbiter Using Robotic Arm 8 - 05/09/08
  9. 9. Expand Capability – Space Station Large Angle Rotation w/ CMGs Developed new CMG attitude control system capability within existing flight software to perform large angle rotations without saturating CMGs - Does not use any thrusters/propellant Challenge - Avoid CMG momentum and torque saturation during large angle rotation - Do not impose restrictions on Station operation, e.g. array articulation Solution: Develop New ZPM Guidance Method To Command CMG Controller - Exploit knowledge about environmental dynamics to optimally plan commanded attitude trajectory in order to extract angular momentum from environment - Solved using Computational Optimization without any modifications to flight software Flight Demonstration - Commanded CMGs to rotate Space Station 90deg (11/5/2006), and 180deg (3/3/2007) without need to desaturate CMGs with thrusters or change flight software - On 1/2/2007 identical 180deg rotation with thrusters used ~110lbs of propellant @ ~$1,100,000 9 - 05/09/08
  10. 10. Expand Capability – Space Station Large Angle Rotation w/ CMGs 90o ZPM - Flight Telemetry Animation 10 - 05/09/08
  11. 11. Recover From Failure – Catch Tumbling Station With CMGs Applied ZPM guidance to command CMGs and recover attitude control of Space Station from a tumbling state without saturating momentum Challenge - Russian computers failed on June 11, 2007 during STS-117 Shuttle mission - Closed-loop Station attitude control capability with thrusters was lost - Station would tumble out-of-control after Shuttle undocking - Astronauts would have to abandon Station Solution: Recover Station Attitude Control With ZPM Guidance - First rate damp without controlling attitude - Then rotate Station to desired long-term attitude hold orientation 11 - 05/09/08
  12. 12. Recover From Failure – Catch Tumbling Station With CMGs 0.1deg/sec Initial Rate Simulation Animation 12 - 05/09/08
  13. 13. Unique Technologies To Reduce Cost/Schedule/Risk Nonlinear Control - Phase Plane for thruster actuated systems Forcing Functions - Used to rapidly evaluate Controller-Structure-Interaction and Loads Computational Optimization - Used to design linear and nonlinear control systems for ⋅ Space Station Orbiter Repair PWM thruster control PID gains and flex filters ⋅ Space Station Momentum Manager with peak momentum constraint - Used for nonlinear trajectory generation ⋅ Space Station ZPM guidance for CMG large angle propellant-free rotations Command Shaping - Used to reduce structural excitation due to control action ⋅ Break-up command into a pulsetrain and introduce time delay between pulses Active Structure Control 13 - 05/09/08
  14. 14. Unique Tools To Reduce Cost/Schedule/Risk Modular, dynamically scalable, and automated tools using COTS SW - Extensively used to support Shuttle & Space Station Flight Readiness Certification SiVAT - Singular Value Analysis Tool - Provides Shuttle stability margins for nonlinear reaction control systems NoFDAP - Notch Filter Design Analysis Package - Design Shuttle notch filters to ensure flex stability, stability envelope for robotic motion, and worst case structural loading DRS - Draper RMS Simulation - Flight validated super hi-fi Shuttle arm model DSS - Draper Space Station Simulation - Family of modular, hi-fi flex on-orbit simulations including ⋅ Russian Service Module, US CMG, Interim Control Module (NRL) flight control systems, Solar and flight Radiator Array Controllers, Robotic Systems DSAT - Draper Station Analysis Tool - Automated simulation configuration/analysis process/analysis documentation ⋅ Stability, CSI and robust performance evaluation 14 - 05/09/08
  15. 15. Capabilities Modeling - Multi-Body Rigid + Flex Dynamics Analysis - Frequency Response - Robust Stability - Monte Carlo Control - Vibration Isolation - Active Structure Control - Command Pre-Shaping - Controller-Structure-Interaction - Precision Pointing & Tracking 15 - 05/09/08
  16. 16. Backup Material 16 - 05/09/08
  17. 17. Expand Capability – Space Station Control Of Very Large Payload Orbiter Position wrt Station Space Station Attitude wrt LVLH Existing CMG controller design Orbiter CM Rotation [deg] CMG controller interacts with SRMS dynamics Orbiter CM Translation [in] ! iter y Orb Space Station Holding Attitude! na wa Ru Large Orbiter motion with respect to Station A really bad day at the office! 17 - 05/09/08
  18. 18. Unique Work Processes – Draper Control Framework Key Design Criteria - Controllability, Stability, Loads, Performance Key System Functions - Dynamics, Control, Filtering, Command Shaping 18 - 05/09/08
  19. 19. Space Station GN&C Systems Certification Integrated platform for design and verification of aerospace systems Developed by Draper and in use since 1998 for flight readiness certification of integrated performance of ISS flexible structure with Russian and US control systems 19 - 05/09/08
  20. 20. Unique Work Processes – Flight Readiness Certification I Quantify achievable performance and risk exposure for available resources Quantify achievable performance and risk exposure for available resources Start with simple system models and gradually add fidelity - Capture most significant dynamics first ⋅ Nonlinear time-invariant rigid dynamics, linear modal form time-invariant flex dynamics time- time- ⋅ Provides qualitative understanding and confidence to proceed - Allows low cost and rapid turnaround - Risk reduced due to rapid evaluation capability for wide range of conditions and parameters Reduce analysis scope where possible - All steps for all flights/operations => enormous scope, large $! - Use analytic and frequency domain methods to rule-out and identify worst-cases ⋅ Classify and prioritize analysis - Reduces cost and schedule while identifying high risk conditions High-fidelity complex dynamic models are expensive and time consuming to develop and do not provide insight and qualitative understanding - Only gives the illusion of understanding and confidence 20 - 05/09/08
  21. 21. Unique Work Processes – Flight Readiness Certification II Confidence in System Performance is Exponentially Faster & Cheaper To Confidence in System Performance is Exponentially Faster & Cheaper To Achieve with Simpler Models Than Accuracy with Complex Models Achieve with Simpler Models Than Accuracy with Complex Models Draper uses a two-stage process - Screening & High-Fidelity Simulation Analysis Screening Analysis: ~90% of resources - Wide scope evaluation with high speed tools to ID high risk conditions - More important to assess performance for a large number of system parameters/conditions than perform detailed analysis of a few operating points High-Fidelity Simulation Analysis: ~10% of resources - For spot-checks and detailed narrow scope evaluation - Using nonlinear time-varying articulating multi-body rigid/flex dynamics ⋅ Insures time varying effects do not adversely impact performance Risk vs Cost vs Schedule Tradeoffs 21 - 05/09/08
  22. 22. Shuttle – Flexible SRMS – Space Station Simulation 22 - 05/09/08

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