Trajectory Simulations , Qualitative Analyses and Parametric Studies of A Laser - Launched Micro - Satellite Using OTIS ( Preprint

This paper will discuss Air Force Research Laboratory (AFRL) Propulsion Directorate’s theoretical and computational results regarding trajectory simulations, qualitative analyses and parametric studies of a 25-cm focal diameter Laser Ramjet (X-25LR) using Optimal Trajectories by Implicit Simulation (OTIS). OTIS has been used to produce an optimized trajectory simulation of a laser ramjet’s flight to Low Earth Orbit (LEO). The baseline case that has been simulated is a flight vehicle powered by a 1 MW, 10.6 μm, CO2, ground-based laser (GBL) with an initial power capture of 82%. The fuel that is used during rocket flight is Delrin doped with energetic additives to increase the coupling coefficient and thrust by a factor of five. Additionally, a nozzle extension was considered which increased performance by 40%. The flight trajectory was separated into three phases: 1) Airbreathing ramjet flight to a specified altitude of ~30 km and Mach number of ~10; 2) Rocket powered flight into a trajectory with a final Mach number ~27; and 3) Un-powered coasting flight to the final altitude of 185 km. Additional sounding rocket trajectory flights with 10-kilowatt class CO2 lasers have been assessed for a variety of laser powers. Also to be discussed in this paper are the parametric trade studies of the rocket phase comparing high thrust vs. low thrust and the effects of different-size vehicles. LASER RAMJET/ROCKET CONSIDERATIONS Chemically-Augmented Laser Ramjet/Rocket The laser ramjet/rocket in the context of this study is a small (~25 cm diameter) vehicle that “rides” the beam of a ground-based laser (GBL) to LEO. Within the useable atmosphere (up to ~30 km), the LR acted as an air-breathing ramjet, using it’s conical fore-body as an external compression surface before the air passed through the inlets of the annular shroud which acted as a combustion chamber. There the air was subjected to an intense laser pulse which had been reflected and concentrated into the shroud’s focus by the parabolic after-body of the LR which acted as a mirror and an external expansion surface. This laser pulse resulted in a detonation wave which expanded along the after-body of the LR producing thrust through pressure effects on the vehicle. During the air-breathing phase, the LR was augmented with solid or liquid chemical fuel to increase the available thrust by a factor of three to five. The geometry and physical specifications of the chemical system were not treated in this report. Above the atmosphere, the LR operated as a conventional rocket, through conservation of momentum as the laser pulses ablated the propellant, which was Delrin that could be doped with energetic chemicals to increase the coupling coefficient by a factor of five. The total initial vehicle mass consisted of structural