KEYWORDS: Space operations, Magnetism, Electromagnetism, Superconductors, Solid state lighting, Control systems, Resistance, Interferometry, Space telescopes, Ferromagnetics
The ultimate limiter of mission lifetime for current space systems is onboard propellant supply. In the past, propellant usage once on-orbit was primarily for station keeping, requiring only a modest amount of mass. However, the increased interest in flying spacecraft in formations that evolve in some prescribed way over time has greatly increased the potential amount of propellant needed over a mission lifetime. For cluster missions that are insensitive to their center of mass location this constraint can be lifted by using internally generated electromagnetic forces between vehicles as an alternative method of formation control. Such missions include rendezvous and docking applications and sparsely distributed apertures for interferometry. The dipole nature of the electromagnetic force allows for full control of the relative degrees of freedom, position and orientation, provided reaction wheels are used for angular momentum storage and control. This paper briefly presents the current research in this area at the MIT Space Systems Laboratory (SSL), and develops the theory behind electromagnetic formation flight under the far field approximation, specifically addressing the operation of clusters within the Earth's magnetic field. Discussion of the hardware technology associated with Electromagnetic Formation Flight (EMFF) and the testbed currently under development at the SSL is also provided.
KEYWORDS: Space operations, Signal to noise ratio, Imaging systems, Image processing, Interferometry, Space telescopes, Image resolution, Spatial frequencies, Hubble Space Telescope, Fourier transforms
The Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) is a proposed mission being considered by NASA to take high resolution sky images at the submillimeter wavelengths. At these wavelengths, we can observe highly red-shifted light that has been traveling towards the Earth over a great deal of time, allowing observation of the developing universe in the distant past. To achieve Hubble class resolution, the system must synthesize an aperture that is 1000 meters in diameter, making interferometry the only currently reasonable approach to design. This paper addresses a high level system trade of a general class of rotating tethered architectures that reel apertures in and out radially to fill the u-v plane. A metric of cost per image is used to identify how aperture area and number of apertures should be selected, and considerations of how spectral information is acquired is used to generate design ideas for reducing the overall system mass.
KEYWORDS: Satellites, Space operations, Electromagnetism, Electromagnetic coupling, Magnetism, Interferometry, Space telescopes, Signal to noise ratio, Imaging systems, Nickel
Sparse aperture arrays use rotation as a method of filling the u-v plane for interferometric image construction. Tethers and electromagnetic coupling are two methods that have been proposed to hold these arrays of spacecraft in formation without the use of on-board propellant. Tethers and electromagnetic coupling can also be used to tailor the aperture velocity profile and re-target the array without any propellant usage. In the case of the electromagnetic coupling, complete control of all relative degrees of freedom within an array can be achieved. This paper will describe these two methods and demonstrate how they can be used to control the angular momentum of the arrays while deployed. The dynamics of each method are explained with examples to demonstrate performance.
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