Testbed for nanosatellite formation flying control systems verification

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Testbed for nano-satellite formation flying
control systems verification

• University of Southampton, UK
• Sandor M Veres, Steve B Gabriel and Nick Lincoln

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Summary of features

• Precision level table with toughened glass cover.
  
• Space-curtains complete darkness constant
  light sources
• Custom rotating satellite frames
• Base unit with vertical movement mechanism if
  required (? 6DOF)
• Metrology frame with 10-20 cameras, stereo vision
  system with self-calibration
• Computing infrastructure for command centre
• On board devices available on demand solid
  state gyros, embedded computers mini, micro,
  nano-ITX boards with ultra-slim HD or flash
  memory, batteries, remote safety switches, PCBs
  for actuators, etc.

University of Southampton, UK
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Two modes of operation

• A two phase approach is taken to test a
  autonomous docking system
• Testing of the processors and communication
  electronics with a limited number of sensors and
  actuators (gyros, reaction wheels, CMGs, cameras,
  etc.) This is called ground-based satellite
  frames testing (GSFT).
• Testing of the actual control algorithms, with
  real devices but simulated dynamics and sensor
  signals. This is called hardware in the loop
  testing (HILT).

University of Southampton, UK
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GSF Testing

• 1 Processor systems suitability on board to
  handle the payloads as well as realtime
  mechanical controls.
• 2 Reliability of the agent based software
  architecture.
• 3 Communications devices as they would be used in
  space, so that the system integrity and
  reliability can be assessed.
• 4 Control devices, nearly as they would be used
  in space. Gyroscopes, reaction wheels and
  air-jets are to be tested with real dynamics and
  not only based on manufacturer's descriptions.
• On board camera systems can be similar or
  identical to that to be used in space.

University of Southampton, UK
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GSF Testing

• Features of surrounds
• Precision-level table rests on a reinforced
  concrete slab supported by a passive vibration
  isolation system to remove ground vibrations.
• Surrounding curtain rails have been tailored
  for the facility to exclude light interference
  from the outside. Internal lightening provides
  homogenous light conditions when used.
• Ready made frames are provided that can be used
  to mount custom electronics brought by satellite
  companies or academics. Custom frames can be
  manufactured on site in the EDMC facility of the
  School of Engineering Sciences.

University of Southampton, UK
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GSF Testing

• GSFT (ground-based satellite frames testing )
  allows testing of systems software and hardware
  in operation with real components
• solid state gyros (actual)
• accelerometers (actual)
• reaction wheels (actual)
• on board computers (actual)
• communication electronics (actual)
• propulsion substitutes (similar in dynamics)

University of Southampton, UK
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Some video clips
5DOF movements demo

• 5DOF very low friction satellite models
• Steady movements across (gyro and camera
  feedback)
• Stabilisation after disturbance (gyro and
  camera feedback)
• Docking experiments

University of Southampton, UK
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Available GSFT frames

• 3 with model aircraft propeller actuation (8
  bidirectional actuators in each frame)
• 3 frames are being built that have air-jet
  actuators (16 unidirectional actuators on each
  frame)
• Custom frames we can produce as required

University of Southampton, UK
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Gas (air) thrusters system in preparation
16 thrusters with electronic valve control
electronic thrusters
Pressurised air tank (30-90 minutes operation)
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Hardware in the loop (HIL) Testing
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HILT

• The HIL Testing facility can be characterized as
  follows
• It can use exactly the same control algorithm as
  those intended for use in space.
• It can use the same software. Hence the
  sampling devices and filters can be the same as
  in space.
• It substitutes the dynamics between issued
  actuator signals (inputs) and sensors signals
  (outputs) with very realistic, simulated realtime
  dynamic ones that mimic signal characteristics as
  they would occur in space. Note that actual
  sensor voltages are generated using D/A
  converters and the actuator voltages sampled by
  A/D converters only the translational and
  rotational dynamics of an individual satellite is
  simulated.

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Metrology infrastructure
University of Southampton, UK
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Metrology features
A calibrated camera based observation system
(version I is shown here) is possible to install
Self-calibrating camera system that estimates
camera parameters automatically and is able to
provide the 3D coordinates of any marked point
after calibration
University of Southampton, UK
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12 camera spatial metrology system
1-2cm precision in 3D space at any point in the
experimental space
University of Southampton, UK
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Possible use Testing of nano-satellite autonomy
and cooperation
Frames in preparation for testing
University of Southampton, UK
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Anticipated use testing of multi-agent systems
on nano-satellite hardware

University of Southampton, UK
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Testing of nano-satellite autonomous maneuver and
docking controls
ThrustersCMGs reaction wheels
Mechanical actuators of payload
ThrustersCMGs reaction wheels
Mechanical actuators of payload
Control system
Control system
cameras
IMU, gyroscope
cameras
IMU, gyroscope
Apart from thrusters substitutes and
star/Sun/Earth sensors, the functionality of the
space system can be tested on ground
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Future extension potentials

• Precision positioning using laser range finders
• Formal system verification software can be added
• Ready made modules top be supplied with hardware
  standards
• Other types of mechanical solutions for real
  nano-satellite testing

University of Southampton, UK
University of Southampton, UK
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Conclusions

• Facility almost ready for industrial use
• GSFT and HILT are complementary and can be done
  at the same time at our facility
• Low cost of testing

THANK YOU !
University of Southampton, UK
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Various movements clips
5DOF movements demo

• 5DOF very low friction satellite models
• Steady movements across (gyro and camera
  feedback)
• Stabilisation after disturbance (gyro and camera
  feedback)
• Docking experiments

University of Southampton, UK
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Current experimental setup

• An 800 MHz mini ITX embedded computer with WLAN,
  2USB, parallel and serial ports. 2GByte flash
  memory or 30GByte hard drives are options. The
  Computer is powered by a rechargeable
  lithium-polymer battery.
• 18 channels of 16bit A/D, 4 channels of D/A and
  16 PWM outputs controllable from the embedded
  computer.
• A MEMS solid state gyrocube provides onboard
  inertial information acceleration vector and
  rotational rates about the satellite frame axes.
• PCBs for data channelling and actuator driving.
• Reconfigurable LiPo battery setup for the two
  control variants, depending on the use of
  propellers or air jets 3 1 batteries for the
  motors and the computer 21 for valve actuators
  and the computer, respectively.
• Reaction wheels fitted internally provide
  additional attitude control possibility in all 3
  satellite axes.