Cryogenic heat pipe for cooling high temperature superconductors with application to Electromagnetic Formation Flight Satellites

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 195-200).An emerging method of propellant-less formation flight propulsion is the use of electromagnets coupled with reaction wheels. This technique is called Electromagnetic Formation Flight (EMFF). In order to create a large magnetic field necessary for actuating formation flying spacecraft, EMFF uses high temperature superconducting (HTS) wire since it is able to carry a large current at low power. To achieve superconductivity, the HTS wire needs a cryogenic thermal control system to maintain the wire temperature below the critical temperature and this temperature must be maintained over the entire EMFF coil, which could be as large as two meters in diameter. For commercially available HTS wire, this critical temperature is 110 K. Since EMFF obviates the need for consumables for formation flying maneuvers, the thermal system must also be consumable-free. The research in this thesis investigates a consumable-free method of maintaining isothermalization for a large scale HTS coil. The HTS coil resides inside a thermally conductive jacket which is used for isothermalization. A cryocooler is attached to the thermally conductive jacket and is used for heat extraction. Wrapped around the thermally conductive jacket is multilayer insulation which is used to reduce the heat load into the HTS coil. This thermal system has the ability to maintain constant temperature in the presence of a rapidly changing thermal environment, such as low Earth orbit. Both a solid conductor and a heat pipe were investigated for use as the thermally conductive jacket. Finite difference models were developed to model a single coil in space and a coil inside a vacuum chamber. In addition, the research in this thesis investigates the design, operation, and testing of a cryogenic heat pipe. The heat pipe uses nitrogen as a working fluid and a stainless steel mesh as the wicking structure. As a proof of concept, an 86 cm long heat pipe was constructed as the thermally conductive jacket enclosing the HTS wire. The working fluid, at saturation condition, maintains a constant temperature below the HTS wire critical temperature. Testing of the heat pipe in a vacuum chamber was conducted to verify the power capacity of the heat pipe. Verifying the proof of concept cryogenic heat pipe led to construction of a full scale circular heat pipe for testing in a two meter diameter toroidal vacuum chamber. This system also achieved saturation condition and showed the potential for HTS cooling. The experiments in this thesis demonstrate the feasibility of operating large HTS coils for future formation flying missions.by Daniel W. Kwon.Ph.D

Electromagnetic formation flight of satellite arrays

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.Includes bibliographical references (p. 167-169).Proposed methods of actuating spacecraft in sparse aperture arrays use propellant as a reaction mass. For formation flying systems, propellant becomes a critical consumable which can be quickly exhausted while maintaining relative orientation. Furthermore, the total required propellant mass is highly dependant on [delta]V, which requires propellant mass to increase exponentially. Additional problems posed by propellant include optical contamination, plume impingement, thermal emission, and vibration excitation. For those missions where control of relative degrees of freedom is important, we consider using a system of electromagnets, in concert with reaction wheels, to replace the consumables. A system of electromagnets, powered by solar energy, does not rely on consumables such as propellant mass. To fully understand the benefits of using formation flown architectures, we first investigate how the science returns are affected, using NASA's Terrestrial Planet Finder (TPF) as an example. Electromagnets are then implemented on simple multi-spacecraft arrays to understand how the design impacts overall system performance. This model is expanded to include subsystems critical for operation using electromagnets. TPF is then used to benchmark its performance against various micropropulsion systems. Finally the use of electromagnets for multiple roles in space systems is discussed.by Daniel W. Kwon.S.M