Formation
Control Testbed
Task Objective
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FCT Robot
Concept |
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FCT Robot
Engineering Layout |
The Formation Control Testbed (FCT) is a system-level ground
hardware testbed with multiple 6DOF robots on air-bearings
with on-board guidance and control (G&C) capability for development
and validation of Formation Flying control architectures
and algorithms. The FCT will:
- Demonstrate end-to-end formation flying system in a realistic
hardware testbed with a large range of displacements and
articulations.
- Validate formation flying control architecture and algorithms
in a realistic test environment with distributed sensing,
communication, and computing.
- Demonstrate key Terrestrial Planet Finder (TPF) Formation
Flying mission scenarios, including:,
- Formation Acquisition
- Observation-on-the-fly maneuver
- Collision Avoidance.
Task Products
- Three, 6DOF robots with on-board avionics (H/W and S/W)
capable of full 6DOF control capability.
- Facility and the ground support equipment to support
the operations of the FCT.
- Functional and performance demonstration and validation
of formation flying control algorithms and architecture.
Task Description
The FCT will be a ground-based laboratory consisting of
three robots emulating TPF formation. FCT will demonstrate
formation acquisition, TPF-like formation maneuvering, and
operations using the formation algorithms. To emulate the
real spacecraft dynamics, the testbed design will have realistic
spacecraft-like dynamical behavior within the given 1-g ground
test environment. With such dynamical and functional similarity
to the TPF spacecraft, the FCT will provide direct emulation
of spacecraft behavior with thruster and reaction-wheel based
actuation and onboard attitude and inter-robot range/bearing
knowledge of the resulting 6DOF motion. These architectural,
functional and dynamical similarities between the FCT robots
and multiple spacecrafts in a FF flight mission, like TPF
mission, will provide a direct migration path of the FCT
demonstrated integrated formation system to the flight system.
Goals and Challenges
Perform end-to-end system level formation flying functional
demonstration and performance validation in a realistic dynamical
testbed to cm and arcmin level.
FCT Robot Testbed
The high-level FCT objectives will be achieved by accomplishing the following goals:
- Develop a multi-robot hardware dynamical testbed with
large angle articulations and spatial displacements capabilities
in 6 degrees-of-freedom (6DOF)
- Develop robot on-board avionics with spacecraft-like
communication, sensing, and control capability using thrusters,
reactions wheels, gyros and other sensors.
- Use software architecture portable to flight mission,
with capability to support flight commanding, and telemetry.
- Integrate formation control algorithms portable to FF
flight missions.
- Develop and deploy a Formation Flying Technology Laboratory
(FFTL) facility and the required ground support equipment
to house the multi-robot FCT.
- Demonstrate and validate end-to-end precision FF control
architecture and algorithms in a realistic end-to-end system
level hardware testbed.
Additional multi-robot and simulation testbeds are discussed on the Facilities page. Watch: FFTL_FAST_movie
Celestial Sensor
Task Objective
Provide the FCT robots with an attitude determination system and relative position measurements.
Task Description
The Celestial Sensor was developed to provide the FCT robots with measurements of their pose. The pose information, consisting of both attitude and position, is given relative to a coordinate frame defined in the room in which they operate. The Celestial Sensor consists of an analog camera that is used to image IR beacons placed on the ceiling and walls of the test facility. Due to the close proximity of these beacons, the camera direction measurements are coupled to both translation and attitude of the robot. This allows unique determination of each quantity, provided enough beacons are in the camera FOV.
The beacons are turned on in a sequential manner. This sequence is repeated at a 5 Hz rate. Identification of a given beacon is done based on its location within a given cycle of the strobe. An Extended Kalman Filter is executed on a peripheral DSP that takes the set of beacon bearing measurements and solves for the robot’s pose. This algorithm uses a catalog of beacon positions in much the same way as a flight star tracker would use a star catalog.
The attitude portion of the pose measurement is then mixed with gyro measurements using a traditional attitude estimator. This mixing provided a 3X reduction in the standard deviation of the attitude estimates. One sigma estimation errors, after mixing, were on the order of 1.0 arcminute for each axis. Accuracy of the raw attitude, prior to mixing, was 15.0 arcminutes.
The accuracy of the raw position was determined through testing to be less than 3.0 cm.
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