Tethered Formation Flying
Encyclopedia
Tethered Formation Flying is one of many applications for space tether
s. This sub-set represents an entire area of research using a non-conductive tether to connect multiple spacecraft.
Spacecraft formation flight is becoming a key research area, where distributed computation and decentralized control schemes, as well as information flows between elements, are explored. One such example includes stellar interferometers in which multiple apertures in controlled formation collect light for coherent interferometric beam combination, thereby achieving a fine angular resolution
comparable to a large monolithic aperture telescope. The possible architectures of spaceborne interferometers include a structurally connected interferometer (SCI) Space Interferometry Mission
, which allows for very limited baseline changes, and a separated spacecraft interferometer (SSI) Terrestrial Planet Finder
where the usage of propellant can be prohibitively expensive. A tethered formation flight interferometer represents a balance between SCI and SSI. Such a system is currently being considered for NASA’s Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) mission. The dynamics of SSI are coupled by the definition of relative attitude whereas tethered formation spacecraft exhibit inherently coupled nonlinear dynamics.
The MIT
Space Systems Laboratory conducted ground experiments that tested a fully decentralized nonlinear control law, which eliminates the need for inter-satellite communications.
Contraction theory
was used to prove that a nonlinear control law stabilizing a single-tethered spacecraft can also stabilize arbitrarily large circular arrays of tethered spacecraft, as well as a three-spacecraft inline configuration. In order to validate the effectiveness of the decentralized control and estimation framework, a new suite of hardware has been designed and added to the SPHERES
(Synchronize Position Hold Engage and Reorient Experimental Satellite) testbed. A 2007 PhD thesis introduced a novel relative attitude estimator, in which a series of Kalman filters incorporate the gyro, force-torque sensor, and relative distance measurements.
The closed-loop control experiments can be viewed at.
The MIT team also reported the first propellant-free underactuated control results for tethered formation flight. This is motivated by a controllability analysis that indicates that both array resizing and spin-up are fully controllable by the reaction wheels and the tether motor.
Space tether
Space tethers are cables, usually long and very strong, which can be used for propulsion, stabilization, or maintaining the formation of space systems by determining the trajectory of spacecraft and payloads...
s. This sub-set represents an entire area of research using a non-conductive tether to connect multiple spacecraft.
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Spacecraft formation flight is becoming a key research area, where distributed computation and decentralized control schemes, as well as information flows between elements, are explored. One such example includes stellar interferometers in which multiple apertures in controlled formation collect light for coherent interferometric beam combination, thereby achieving a fine angular resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
comparable to a large monolithic aperture telescope. The possible architectures of spaceborne interferometers include a structurally connected interferometer (SCI) Space Interferometry Mission
Space Interferometry Mission
The Space Interferometry Mission, or SIM, also known as SIM Lite , was a planned space telescope developed by the U.S. National Aeronautics and Space Administration , in conjunction with contractor Northrop Grumman...
, which allows for very limited baseline changes, and a separated spacecraft interferometer (SSI) Terrestrial Planet Finder
Terrestrial Planet Finder
The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...
where the usage of propellant can be prohibitively expensive. A tethered formation flight interferometer represents a balance between SCI and SSI. Such a system is currently being considered for NASA’s Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) mission. The dynamics of SSI are coupled by the definition of relative attitude whereas tethered formation spacecraft exhibit inherently coupled nonlinear dynamics.
The MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
Space Systems Laboratory conducted ground experiments that tested a fully decentralized nonlinear control law, which eliminates the need for inter-satellite communications.
Contraction theory
was used to prove that a nonlinear control law stabilizing a single-tethered spacecraft can also stabilize arbitrarily large circular arrays of tethered spacecraft, as well as a three-spacecraft inline configuration. In order to validate the effectiveness of the decentralized control and estimation framework, a new suite of hardware has been designed and added to the SPHERES
SPHERES
The Synchronized Position Hold, Engage, Reorient Experimental Satellites experiment is a testbed consisting of three miniaturized satellites that can operate in a variety of environments, including inside the International Space Station...
(Synchronize Position Hold Engage and Reorient Experimental Satellite) testbed. A 2007 PhD thesis introduced a novel relative attitude estimator, in which a series of Kalman filters incorporate the gyro, force-torque sensor, and relative distance measurements.
The closed-loop control experiments can be viewed at.
The MIT team also reported the first propellant-free underactuated control results for tethered formation flight. This is motivated by a controllability analysis that indicates that both array resizing and spin-up are fully controllable by the reaction wheels and the tether motor.