Glenn E. Rolader

Thermodynamic and electrical properties of railgun plasma armatures

A model including the nonideal effects is presented that describes the plasma composition, equation of state, internal energy, and electrical conductivity for a very dense and relatively cool plasma like that which exists in a railgun plasma armature. Results are presented for four elements of specific interest for plasma armatures-hydrogen, lithium, aluminum, and copper-for pressures ranging from 1 to 1000 atm and temperatures ranging from 10000 to 50000 K. The results are presented in a graphical format which should prove useful to modelers and experimentalists investigating plasma armatures. >

Effect of in-bore gas on railgun performance

Acceleration of a projectile in a nonevacuated railgun bore produces a series of shock waves traveling through the gas in front of the projectile which retards the projectiles motion. A model is presented which describes the three components of this retarding force-the force required to accelerate the gas to the projectile velocity as it is entrained by the shock front, the force required to continue to accelerate previously shocked gas as the projectile accelerates, and the force required to overcome the viscous drag which arises from the interaction of the shocked gas and the gun tube. The authors address the relative contributions of the three components of the force and the significance of the retarding force when compared to the net accelerating force. The validity of the strong shock approximation for computing the retarding force is discussed. >

A time‐dependent model for railgun plasma armatures

In this paper a one‐dimensional, time‐dependent model is described for the analysis of railgun plasma armatures. The model assumes that the armature is isothermal, and that the electrical conductivity and degree of ionization in the plasma are uniform and constant in time. The model is applied to the analysis of three problems—armature initiation, armature response to a change in current, and armature response to a change in mass. In each case, the perturbation induces damped oscillations in the armature length and projectile acceleration about the corresponding steady‐state values. The period of the oscillations is, for early times, approximately equal to 3leq/a0, where leq is the equilibrium armature length corresponding to the steady‐state solution and a0 is the acoustic propagation velocity in the plasma. The exponential decay time for the cases studied ranges from 140 to 200 μsec. Although most calculations are completely numerical, a partly analytic, limiting‐case perturbation solution of the govern...

Earth-to-orbit railgun launcher

An overview of a comprehensive study of the feasibility of launching relatively small payloads into orbit using electromagnetic launcher technology is provided. The specific question addressed was whether serious consideration should be given to hypervelocity gun launch to space as an alternative to conventional rocket powered launch vehicles. An overview of the concept developed is provided along with a discussion of the major subsystems. The above question is answered in the affirmative, because the mission can readily be accomplished using state-of-the-art technology; a considerable cost savings is offered with respect to conventional rocket launch systems; and a revolutionary launch frequency, comfortably placing six payloads in orbit each day, is possible, which greatly increases operation flexibility. >

Transient modelling of railgun plasma armatures

Simulations are performed with a one-dimensional, time-dependent model to investigate the dynamic behavior of railgun plasma armatures. Specifically, the model is applied to the analysis of three problems: (1) the simulation of the release of a projectile; (2) the simulation of the latter stages of the initiation of an armature, with the initial arc length 50% of its final equilibrium length; and (3) a second initiation simulation where the initial arc length is 10% of its final equilibrium length. For all three simulations, the armature length and projectile acceleration exhibit damped oscillations. After the first armature expansion, the period of oscillation of the armature length can be approximated by 3l/sub eq//a/sub 0/ where l/sub eq/ and a/sub 0/ are the armature length and acoustic propagation velocity, respectively, calculated for an equilibrium, isothermal plasma whose thermodynamic characteristics are obtained from a mass average of the properties in the nonisothermal simulation. This characteristic period of oscillation is consistent with the period observed in isothermal armature simulations. >

Effect of a transient current profile on the dynamics of railgun arcs

A one-dimensional, time-dependent model for describing transient behavior in railgun plasma armatures is used to investigate the effects produced by a time-varying current profile. Ablation from the rail surface is also accounted for. The governing equations are solved numerically to produce as a function of time and space the electrodynamic and thermodynamic properties of the arc. These quantities are shown to be considerably different from those predicted by commonly used quasi-static models. The importance of these transient effects and how they can affect the design of projectiles and the analysis of diagnostic data are discussed. >

Self-healing minefield

The Self Healing Minefield (SHM) is comprised of a networked system of mobile anti-tank landmines. When the mines detect a breach, each calculates an appropriate response, and some fire small rockets to “hop” into the breach path, healing the breach. The purpose of the SHM is to expand the capabilities of traditional obstacles and provide an effective anti-tank obstacle that does not require Anti-Personnel (AP) submunitions. The DARPA/ATO sponsored program started in June 2000 and culminated in a full 100-unit demonstration at Fort Leonard Wood, MO in April 2003. That program went from “a concept” to a prototype system demonstration in approximately 21 months and to a full tactically significant demonstration in approximately 33 months. Significant accomplishments included the following: (1) Demonstration of a working, scalable (order of a hundred nodes), ad hoc, self-healing RF network. (2) Demonstration of an innovative distributed time synchronization scheme that does not rely on GPS. (3) Demonstration of a non-GPS based, self-mapping, relative geolocation system. (4) Development of an innovative distributed safe, arm, and fire system that allows for independent firing of eight rockets within a single node. (5) Development of a small rocket design with a novel geometry that meets the propulsion requirements.

Barrier Discharge Optimization for Nitric Oxide Destruction

Abstract Concern over smog and acid rain has created a need for innovative technologies that destroy or remove nitric oxide (NO) from many gas streams. One promising technology is the Non-Thermal Plasma Discharge (NTPD). Although NTPDs have been used to oxidize and reduce NO, previous studies found that these devices required a non-competitive amount of electrical energy input, preventing their wide-spread application. In this paper, we report on our experimental investigation into techniques to increase the efficiency of NTPDs. Specifically, two approaches were investigated. The first approach considered was the upstream injection of chemical additives. It is known that certain additives increase the chemical efficiency of desired reactions, thus reducing the required electrical energy. Several additives were tested, and their effect is summarized in this paper. It was found that upstream injection of ethanol in a diesel exhaust stream reduced the energy requirement from more than 150 electron volts (eV) per NO molecule oxidized to less than 20 eV per NO molecule oxidized. In addition, ethanol was found to produce no precipitate on the dielectrics that can lead to electrode failure. The second approach investigated was varying the dielectric material on a Double Dielectric Barrier Discharge (DDBD), a type of NTPD. Several dielectrics were tested and their effect is reported. It was found that, with the ethanol injection, using Teflon PFA instead of glass dielectrics reduces the energy requirement from approximately 22 eV per NO molecule oxidized to 17 eV per NO molecule oxidized. In addition, the Teflon PFA coated electrodes were more durable than typical glass electrodes. Techniques, experiments, and conclusions are presented in this paper.

Performance calculations for battery power supplies as laboratory research tools

The design and construction of a battery power supply (BPS) capable of providing several megaamperes of current for several seconds are described. This system consists of six modules (each containing 2288 automotive batteries) which may be connected in two different series-parallel arrangements. The electrical characteristics of the BPS are defined at the component level. The characterization is done theoretically and through the examination of experimental results. A mathematical model of the BPS is developed which contains a variety of potential upgrade options. The BPS model is then coupled to an existing railgun simulation code. This combined model is used to investigate a variety of topics as they relate to electromagnetic launcher laboratory power supplies. Potential railgun performance versus candidate BPS upgrade options are studied. >

Comparison of partition function calculations for metal plasmas

Three methods are commonly used to handle the unobserved energy levels in calculating the properties of plasmas. The contribution of the levels may be simply ignored, or the energies of the levels may be estimated by either the hydrogenic or the Rydberg–Ritz approximation. In this paper we compare the predictions of plasma properties obtained with each of these methods for Cu and Al plasmas for temperatures of 10 000–50 000 K and pressures from 0.1 to 600 atm. The validity of simplifying assumptions used to handle the unobserved levels has been documented, and regimes where each method is most appropriate have been identified.