Induction Launchers

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IEEE TRANSACTIONS ON MAGNETICS, VOL. 25 , NO. 1, JANUAR Y 1989ELECTROMAGNETIC LAUNCH TECHNOLOGY:

THE PROMISE AND THE PROBLEMS

I n t r o d u c t i o n

H a n s M a r kC h a n c e l l o r

T h e Un ive rs i t y of T e x a s S y s t e m

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current switching systems are needed that can controlheavy flows of electric current. Finally, some kind of guidesystem, be it an electromagnetic railgun or a set of sol-enoid magnets, is required to launch the projectile. Withthese devices, a system can be built that would make itpossible to launch projectiles having velocities that are farin excess o f what is poss ib le wi th chemica l h igh

It is a great pleasure for me to welcome this group toTh e University of Texas at Austin. In addition to beingyour host, I have to confess to another major reason whythis field is of strong perso nal interest to me. My latebrother. Professor Peter Mark of Princeton Universitv, was~one of the people, along with Dr. Harry Fair, Dr. Henry explosives or rocke t techniques.Kolm (who are both here today) and, of course, ProfessorWilliam F. Weldon of The University of Texas at Austinwho really revived modern interest in electromagneticlaunch technology. In a certain sense then, I have aprofessional interest in what you are doing.

The applications of this technology are obvious, andthe one that I believe is most important is to militaryweapons. Th e declin ing relevance of nuclear arms ascurrent trend which is to search for "conventional" meansto enhance ou r combat capabil i ty. This is necessary

strong family reason for being here in addit ion to a control more popular accentuates the

What I would like to do for the next few minutes is totalk a little bit about the state of electromagnetic launchertechnology an d to mix in some promising applications in amore or less stochastic manner. Hopefully, this procedurewill then permit us to define some areas of basic scientificresearch that are critical to achieving the objectives thatwe have in mind for electromagnetic launch technology.After all, the universities are the c enters of basic research

because the l ikely opponents we have in foreseeablewars will continue to vastly outnumber any armies that theUnited States and its a l l ies can f ie ld. Therefore, thesearch for technologies that wil l provide a decis iveadvantage will always have a very high priority. With theconclusion of the Intermediate Nuclear Forces (INF)Treaty , the s i tua t ion in Europe demands immedia teattention.

vation for the development of e lectromagnetic launchtechnology. As the technical objectives are achieved, wewil l , in the next decade, come much closer to testingvehicles both on land and at sea that u se electromagnetic

The essentia l objective of electromagnetic launch means for accelerating large projectiles. These will dotechnology is to overcome the limits that are inherent in damage at closeange du e to the high kinetic energy ofthe parameters characterist ic of chemically-driven pro- motionhe y possess, A projecti le moving in ofjectiles. BY parameters here, I mean the muzzle velocities, 5 m/s as much kinetic energy as the equivalentthe ultimate kinetic energies of projectiles fired from guns, mass of high explosive that the projectile could carry as aand the termina l velocities of vehicles drive n by rocket conventional shell. ~ h ~ ~ ~ f ~ ~or the militarypropulsio n. The Promise O f electromagnetic launch application, it is important to understand damage mech-technology is, Of course, to Overcome the thermodynam ic anism as well. It is, in fact, high kinetic energy that offe rslimits that gove rn chem ical PrOpUlSiOn. In order to achieve the promise to overcome some of the new protectivethis objective, it is necessary to develop electromagnetic armor concepts that ha ve been incorporated in the lateststorage devices with energy densities that are comparable armored vehicles. The development of m eans to test highto those of high explosives or chemical rocket fuels. This velocity projectiles and to assess damage mechanisms isrequirement is absolutely basic to anything else that might a most importa nt face t of e lectroma gnetic la unchbe done. In add i t ion to energy storage devices, h igh technology,

T h e P r o m i s e of E l e c t r o m a a n e t i cL a u n c h T e c h n o oa y

0018-9464/89/0100-0017$01.0001989 IEEE

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The other important area in which electromagneticlaunch technology is likely to see important applications isin space transportation. Electromagnetic launchers arenot really good for getting things from the surface of theearth to earth orbit. The p roblem is that the velocity profileis wrong. The virtue of an electromagnetic launcher is thatit achieves high velocities very quickly, but in the case oftransportation to e arth orbit, that is actually a drawbac k. Itis not desirable to move rapidly close to the ground wherethe atmosphere is dense; rather the velocity profile of arocket which starts slowly and achieves high velocit iesonly at high alti tudes is what is required. Howev er,electromagnetic launch technology is excellent for spacetransportation once one reaches earth orbit. For trans-portation from one orbit to another, or from orbit to thesurface of the m oon and b ack, electromagnetic launchertechnology ha s important advantages. This point was, ofcourse, recognized long ago by a number of people,including Henry Kolm and Gerry O'Nei l l , who haveadvocated the use of electromagnetic launchers for spacetransportation for many years.

There is good reason to bel ieve that space launchtechnology wil l also be an important motivation for newdevelopm ents in electromagnetic launchers. PresidentReagan recently issued a new space policy for the UnitedStates. One of the importa nt points of the six that con-stitute the policy is to expand human presence beyond theearth and into the solar system. This implies the eventualconstruction of a base on the moon. My own feeling is thatthe next administration is very likely to announce the goalof placing a permanent base on the moon with humanoccupants by the year 2000. There are very goodtechnical rea sons for bel ieving that electromagnet iclaunch technology wil l play a most important part inachieving this particular objective. In addition, and this isprobably more important, once a base on the moon isestablished, then lunar materials will be used to constructvarious things in orbit around the earth and around themoon. It is in this effort where the use of electromagneticlaunch technology will really come into its own. Since themoon has no atmosphere, the electromagnet ic accel-eration of materials off the surface of the moon is a verypromising m ethod for moving large quantit ies of matterfrom the surface of the moon into earth orbit. It turns outthat it is much more economical to move things from themoon to earth orbit than from the surface of the earth toearth orbit. And this is, of course, the insight that is due toGerry O'Neill and his collaborators.

Technical ProblemsAchieving the objectives that I have just outl ined

requires the solution of a number of technical problems.Let me try to l ist these in a more or less systematicmanner.

Enerav Storaae DevicesThe most commonly used energy storage devices for

electromagnet ic launchers are homopolar generators(HPGs) or capacitors. The energy density that can bestored in a rotating machine depends on the strength ofthe material of which the rotor is made, since the energystored depends on the rotational kinetic energy of therotor. In the case of capacitors, the energy stored de-pends on the dielectric constant of the material betweenthe capacitor plates. In recent years, there has been sig-nif icant progress in the deve lopment of strong materialsfrom which rotors can be m anufactured and in the creationof dielectric materials with very high polarizabilities. Bothof these technologies n eed to be vigorously pursued.Switchina Devices

The ability to control high density and high currentflows of electrons is critical to the development of electro-magnetic launch technology. A wide variety of switchingdevices ranging f rom brushes on HPGs, to crowbarswitches for the d ischarge of capa citors, to the contactsthat the projecti le has to make with the railgun arenecessary for success. Construct ing such switchesdepends on a knowledge of material properties as well asan unde rstanding of electric arcs and plasma dynamics forthose devices that depend on gases to carry the electriccurrents.

Rails and Solenoid AcceleratorsThe projectiles for electromagnetic launch devices are

usually accelerated by a railgun which forms the armatureof a linear electric motor or by a solenoidal magnet whosefields are energized in sequence as the projecti le accel-erates. In the case of railguns, the crit ical technicalproblem has to do with the contacts between the railgunand the projecti le. Success ful contacts depend on theproper materials and the proper understanding of theerosion processes that occur as the projectile accelerates.In the case of solenoidal accelerators, the important issue

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19is how to develop materials that ca n take the stresses a ndstrains imposed by very large magnetic fields which are inturn created by the large current pulses through thesolenoids. An interesting aspect of solenoidal launchersis to determine whether the new high temperature super-conductors that are now being developed have a role top lay in e lect romagnet ic launch technology us ingsolenoids.Effects of Hiah Acceleration on Proiectilesand ImDact Phvsics

These two areas are important in understanding theapplications of electromagnetic launch technology. Forexample, if "smart" projecti les launched with electro-magnetic guns are to have mil itary value, then meansmust be found to create sensors and electronic equipmentin the projectile that can stand levels of acceleration verymuch higher than those found in conventional artillery. Atthe sam e time, it is necessary to study the effects that veryhigh velocity projectiles have on probable targets. In thiscase, it is necessa ry to und erstand the behavior of ma-terials in pressure regimes that are somewhere betweenthose in the multimegabar region expe rienced in nuclearexplosives an d those that exist in conventional artillery.

In examining this list, it is interesting to see that all ofthese problems have in common a requirement that weneed to know more about the behavior of materials underunusual conditions. This is the primary challenge that Isee in front of us. What is the state of basic research in thearea of matter under unusual conditions? This, I believe,is the important question that must be dealt with beforeany real progress can b e made.

State of Materials TechnoloayOur understanding of the p roperties of matter depends

on quantum mechanics. Concep tually, we know a greatdeal about what it is that makes materials behave the waythey do. The problem tends not to be a conceptual onebut rather one which requires the performance of detailedcalculations based on fair ly well understood concepts.This by itself is an important area of basic research thatrequires a great deal of attention. The development ofmeans for predicting the prope rties of materials from basicprinciples is sti l l something beyond the range of currentscientific knowledge. To be able to perform such calcu-lations that have real predictive value could be enor-mously important to electromagnetic launch technology.The proper approximat ions to use for looking at the

equation of state of materials that are in pressure rangesof 100 kbar to 1 Mbar is also something that requiresfurther research. Finally, there is the question of theapplications of som e of the new work in f luid m echanicsparticularly in the area of chaos theory and turbulence tosome of the problems inherent in electromagnetic launchdevices.

If I were to list these things sy stematically, I would askfor support in ba sic research in the following areas.a. Comp utational physics. This has to do with the

appl icat ions of high-sp eed computers to make cal-culat ions having high predict ive values on var iousmaterial properties. Compu tational physics also will haveapplications in the fluid mechanics inherent in the pre-diction of the effects the high velocity projectiles have ontheir targets.

b. Development of more accurate equations of statefor materials under unu sual conditions. In this field, bothatomic physics and solid-state physics have a place. Inthe case of atomic physics, it is important to understandthe properties of multi-ionized atoms and the properties ofatoms under high pressures. The approximations thatwork under normal conditions and under very high pres-sures and temperatures are simply not applicable in theregion of interest here.

c. Fluid mechanics. This is a very broad field whichhas other applications that may be much more relevant tobasic developme nts. Nevertheless, the combination ofmechanics, electromagnetic phenomena, and fluid phe-nomena that exist in electromagnetic guns may be unique.It is therefore poss ible that much can be learne d from abasic study of fluid mechanics as related to the other twothings that are important in electromagnet ic launchtechnology.

I would make a plea with this group that in the de-velopment of this new technology attention be paid tobasic research in the areas I have just outlined. If this isnot done, then I believe we wil l not be able to commandthe arsenal of "tricks" that will be needed to make electro-magnetic arti l lery and electromagnetic launchers thathave genuinely important practical applications.

Let me repeat once again that I am most pleased to behere and to have the opportunity to open this importantconference. It is always excit ing to be with people whoare on the edge of doing something new.

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