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UT PR 85 - PR 85 Weldon Publications

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ELECTROMAGNETIC LAUNCHERS FOR SPACEAPPLICATIONSBy:W. F. WeldonCenter for ElectromechanicsThe University of Texas at AustinPRC, Mail Code R7000Austin, TX 78712(512) 471-4496PR 85 Fourth Symposium on Electromagnetic Launch Technology, Austin, TX, April 12-14, 1988 IEEE Transacitons on Magnetics, vol. 25, no. 1, January 1989, pp. 591-592©1989 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.504 IEEE TRANSACTIONS ON MAGNETICS, VOL. 25, NO. 1, JANUARY 1989 ELECTROMAGNETIC LAUNCHERS FOR SPACE APPLICATIONS J. M. Schroeder, J. H. Gully, and M. D. Driga Center for Electromechanics The University of Texas at Austin Austin, TX 78758-4497 Abstract: An electromagnetic launcher (EML) was designed for NASA-Langley to boost large models to hypervelocity for flight evaluation. Two different concepts were developed using railgun and coilgun principles. A coilgun was designed to accelerate a 14-kg mass to 6 km/s and, by adding additional equip- ment, to accelerate a 10-kg mass to 11 km/s. The railgun system was designed to accelerate only 14 kg to 6 km/s. Of significance with this develppment is the opportunity to use the launcher for aeroballistic research of the upper atmosphere, eventually placing packages in low earth orbit with the application of a small rocket. The 11 km/s velocity is interesting because it is exactly the escape velocity from Earth. The earth's atmosphere, however, is the nemesis, slowing an earth launched projectile. This paper will describe railgun and coilgun launch designs and suggest a reconfig- uration for ,placement of 150-kg parcels into a low earth orbit for aeroballistic studies and possible space lab support. Each design is detailed along with the performance adjustments which would be required for circular orbit payload placement. Introduction __l..l The Center for Electromechanics at The University of Texas at Austin (CEM-UT) performed a feasibility study of an EML system for a hypersonic model test facility for NASA-Langley Research Center [l]. The work resulted in a high-energy EML design to acce- lerate large, complex 18 in. winged aircraft models up to 11 km/s (25,000 mph) at less than 33,000 gees. Two different designs evolved which are based on railgun and coilgun concepts. Both designs make use of low current density, very long, low acceleration electromagnetic (EM) motors. Coaxial System Description The induction launcher system (fig. 1) is com- prised of modular coaxial accelerator sections, each module being energized by its own electrical pulse machine. The payload is accelerated at an average 32,800 gees, to an exit velocity of 11 km/s by a tra- veling magnetic wave produced by 1.72 MA currents in each three-phase stator coil. SPECIFICATIONS VELOCITY: 6 kmlsrc MASS: 10 kg CONSTRUCTION TIME: 30 moa. COST: 547 M Figure 1. Induction accelerator 0018-9464/89/0100-0504$01.0001989 IEEE ©1989 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.The launcher itself consists of a system of sta- tor coils. These coils, when connected to a multi- phased power source, produce a traveling field which accelerates an armature carrying current induced by a starter coil as in figure 2. The fact that the arma- ture has no electrical contact with the stator and rides on the traveling magnetic wave makes this induc- tion accelerator very attractive for a space launch faci 1 i ty . rARMATURE 'OIL w- SOURCE ( c, Figure 2. Principle of coaxial accelerator The major components of this system are: launcher, power supplies, and projectile. The launcher has a total length of 200 m, including the starter coil. Each induction module is made up of helical coils with only the pitch or lengths differing in size. The multiple power supply concept divides the barrel in several segments, each being fed by its independent power supply. Each section of the acce- lerator is electrically independent, although the tra- veling magnetic wave continuously sweeps the entire length of the stator. The four different compensated pulsed alternators (compulsators) are operated at dif- ferent frequencies initially, each frequency being slightly higher than the frequency required in that portion of the accelerator, storing a total of 3 GJ in spinning rotors. Figure 3 describes the frequency and voltage variations for each compulsator with respect to discharge time and energy stored by each module. During rapid discharge of each compulsator, the kinetic energy stored in the rotors is transformed into a train of high energy sinusoidal pulses pro- ducing the traveling magnetic wave required for launch.[2] The generators must be synchronized and switched on at definite moments in time during the launch; however, this requirement is the result of a trade for energy savings achieved by energizing only the part of the launcher containing the accelerating projectile. As the projectile passes through launch segments powered by individual compulsators, roughly half of the stored energy is released, driving the magnetic wave in the launcher. The frequency and voltage of each power supply drops 30% from prelaunch values. The projectile is handed-off to the next accelerator section, powered by compulsators with increasing fre- quency, with each section's wave timed to embrace the armature in a slightly retarded magnetic trough. This allows additional armature slippage into the driving wave and simultaneous build-up of armature current while traveling through the sections. The


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