Maximum-payload trajectories for a laser-propelled launch vehicle

Abstract

The feasible trajectories of a laser-propelled launch vehicle are restricted by the laser power available, the power lost to atmospheric absorption and beam spreading, and the thruster design. These constraints result in optimal trajectories that are significantly different from those for conventional launch vehicles. The problem formulation and constraints for a launch vehicle using a pulsed-laser thruster with two laser power transmission models are presented. A maximum payload problem for launch to various circular orbits is solved for both transmission models using sequential quadratic programming. An unusual backs wing trajectory feature is obtained for most of the optimal trajectories presented. The optimal trajectories for various circular orbit altitudes are discussed, and the effects of altering the power transmission efficiency are shown. ASER-PROPELLED launch vehicles were first proposed in the early 1970s.1 Advances in laser and optics technology since then have increased the feasibility of very high power, ground-based, laser launch systems.2'3 Such systems offer the potential of thousands of launches to low Earth orbit (LEO) per year at greatly reduced costs over current launch vehicles.4 Kantrowitz5 has proposed an extremely simple (and hence cheap) design for a laser-propelled launch vehicle. The vehicle is essentially a right circular cone of some solid propellant with a payload in the apex as shown in Fig. 1. The conical shape allows the vehicle to turn relative to the laser beam without exposing the payload to the laser. When struck by a double-pulsed laser beam, the entire base of the vehicle acts as a double-pulse planar thruster (DPPT) as described by Kare. 4 A low-power pulse evaporates a desired amount of propellant from the thruster surface to form a thin layer of gas. The gaseous propellant is then heated by a laser-supported detonation (LSD) wave initiated and sustained by a second, highpower laser pulse. The hot gas then expands one dimensionally producing thrust.