Derek A. Tidman’s research while affiliated with Army Research Laboratory and other places

The dynamics of projectile acceleration in a slingatron ring that gyrates with a constant frequency is analyzed, assuming that projectile sliding friction forces are negligible. It is found that projectiles injected into the ring can accelerate for several turns around the ring to very high velocity, but must then exit before they start to decelerate. The interaction can be formulated as a "soft elastic collision" between the projectile and the track displacement wave that travels at high speed around the orbiting ring. Projectiles execute a swing in phase relative to the traveling wave as they accelerate and are thrown forward. The diameter of the slingatron in this case is smaller than for a slingatron designed for phase-locked acceleration to the same velocity. This same phase swing approach could be used to reduce the size of both ring and spiral slingatron mass accelerators. A multiturn spiral machine with close turns approximates a ring and appears capable of launching a stream of projectiles to high velocity. Scaling arguments indicate that both the friction coefficient and the fraction of projectile mass lost in sliding to a given velocity become smaller for larger projectiles.

The phase-lock phenomenon of a mass sled sliding along in a circular slingatron is studied both numerically and analytically. Parameters that describe a slingatron, in which the phase angle of the swing arms increases quadratically in time, are found to be simply related to the sled's speed during phase lock. The time required for phase lock to occur is related to a simple exponential function of the gyration speed and the coefficient of friction between the sled and track. Accurate time histories describing the motion of the accelerating sled are expressed in terms of confluent hypergeometrie functions 1F1. These results are then used to obtain physical insight into why the phase-lock phenomenon takes place and to describe the important role that friction plays by damping the oscillatory motion of the sled.

A slingatron is the name given to a propellantless mechanical means of launching a projectile. To date, slingatrons are only conceptual in nature, but their potential use as a ground-to-space launch mechanism for unmanned payloads is under investigation. Slingatrons can be configured in a variety of geometries; one form consists of a spiral track (or launch tube) that gyrates at a constant frequency about a set radius. Under proper conditions (design parameters), a projectile entering the spiral at its small radius end will undergo nearly constant tangential acceleration before exiting. The differential equations governing the motion of the projectile within the spiral are highly nonlinear, making the optimum design solution nonintuitive. This paper briefly describes how the slingatron works, then uses the numerical integration procedures within the computer software environment of Simulink(R) and MATLAB(R) to search for the minimum-sized slingatron needed to launch a 1000-kg projectile into space.

The slingatron mass accelerator is described for several track configurations (shapes), and numerical simulations of this accelerating mass traversing a given track configuration are presented. The sled is modeled as a point mass that interacts with the slingatron track using both a conventional and a new empirical velocity dependent friction law. The closed loop circular slingatron was found to produce high maximum sled velocities provided the gyration angular speed is always increasing. In contrast several spiral shaped slingatron tracks reveal that high maximum sled velocities are obtainable with the gyration speed held constant. In fact, a slingatron constructed out of semi-circles is shown capable of generating high velocity sleds in such a way that no initial sled injection is necessary. Choosing the proper initial gyration phase with an empirically determined friction model allows the mass sled to gain ever-increasing velocities when placed in a semi-circle slingatron. The sled bearing pressure and its total acceleration are examined and presented.

The dynamics and engineering of a spiral slingatron mass accelerator are described together with the status of experiments. The potential utility of this mechanical device for space launch applications is discussed.

The mechanics of a spiral slingatron mass accelerator is discussed, together with some experiments to measure the sliding friction and mass loss of projectiles in such a machine. The potential utility of this machine for defense applications is also discussed, including examples of 1 kg and 50 kg projectiles launched at 3 km/sec. The device appears capable of high launch velocity with repetitive fire without over-heating the steel guide tube, since hot high-pressure gas is not used. It could derive power from a turbine that burns kerosene and it fires projectiles without propellant cartridges. Angular dispersion of emerging projectiles can be minimized, but would be larger than for conventional guns. However, projectiles that are smart enough to reduce dispersion of the projectile stream would suffice for many applications. Smart projectiles would also be needed for any gun capable of the long-range missions available due to high launch speed.

A circular mass-accelerator concept is described in which a projectile of large mass could be accelerated to high velocity using a relatively low-power input (compared to a hypervelocity gun). The machine, called a slingatron, is dynamically similar to the ancient sling, and has a phase stability similar to a modern synchrotron. The projectile slides in a low-friction manner around the accelerator ring using a gas bearing, and work is done on the mass by a phased small-amplitude gyration of the entire accelerator ring. A spiral version of the accelerator (that gyrates with a constant frequency) is also discussed that is phase stable and analogous to a cyclotron. The radius of the ring (or outer ring for the spiral) could range from meters to kilometers, and potential applications include hypervelocity impact research, ground-to-space launch of rocket projectiles, and propulsion.