Advances in Baffled and Railed Tube Ram Accelerator Operation and Modeling

Abstract

The ram accelerator is a novel chemical propulsion device capable of accelerating projectiles up to orbital velocities. It utilizes a ramjet-like propulsive cycle, where a projectile travels through a stationary tube filled with a gaseous propellant, experiencing high levels of thrust throughout the tube. The projectile carries no onboard propellant and has no moving parts. This makes the ram accelerator a relatively simple, more efficient, and high-performance alternative to guns and rockets for a first stage launch system. While originally developed to utilize finned-projectiles in a smooth bored tube, additional ram accelerator configurations have been developed to accommodate axisymmetric projectiles in baffled and railed tubes (the BTRA and RTRA). These newer configurations allow for a more practical implementation of ram accelerator technology in numerous applications and have been found to expand the capabilities of ram accelerator systems. This dissertation includes a comprehensive experimental study of the BTRA, RTRA, and two newly invented ram accelerator configurations, as well as the development of a new computational model for BTRA and RTRA operation. The experimental effort focused on the testing of newly developed BTRA and RTRA hardware, a survey of viable BTRA propellants, and the development of two new ram accelerator configurations: the RTRA with sweeper baffles and the baffled start stage (BSS). The BTRA testing discovered that smaller diameter baffle chambers are capable of producing higher thrust with higher efficiency, while larger diameter baffle chambers allow for operation at lower Mach numbers. The BTRA has now been demonstrated to operate at as low as Mach 1.85. The RTRA was found to achieve significantly higher thrust and efficiency than the BTRA, while requiring higher Mach numbers for operation. The new RTRA with sweeper baffles concept was shown to be a viable ram configuration for improving the performance and expanding the operational envelope of an RTRA. The newly developed BSS was shown to be a good technology for producing ram starts without the typical use of an obturator. The new computational model, called the ram accelerator plug flow reactor (PFR) model, proved to be a significant advancement in the modeling of ram accelerator operation. The ram PFR model is a quasi-1D model that resolves the entire ram flowpath. It includes a model for the effects of baffles on the ram flowfield, accommodates real projectile geometries as used in experiments, and includes corrections for the non-inertial projectile reference frame. The new ram PFR model is able to predict the operational envelopes of the BTRA with remarkable accuracy and will now serve as a valuable tool in the development of future ram accelerator configurations.