Tech Briefs

The cost per unit payload might be reduced by orders of magnitude.

A study of lightcraft propulsion systems in general has led to the conception and analysis of such a system for launching a small (having a mass no more than a few kilograms) satellite into a low orbit around the Earth. This study built on theoretical and experimental investigations of the feasibility of lightcraft, performed by a number of researchers during the past two decades. The word “lightcraft” signifies an aircraft or spacecraft that derives its propulsive energy from a laser beam aimed toward it from an external platform that, for the purpose of the present study, would be a ground station.

The conceptual lightcraft would operate in two different propulsion modes during successive phases of flight: Immediately after launch and during flight through the lower atmosphere, it would operate in an air-breathing (detonation- wave) mode, in which the laser beam would be used to heat ingested air to make the air expand in a rearfacing nozzle and thereby generate thrust. Once it exceeded a speed of about Mach 5 and an altitude of about 30 km, the lightcraft would operate in a rocket mode, in which the laser beam would be used to generate thrust through heating of a propellant material stored on board.

This Conceptual Lightcraft would be a single-stage launch vehicle thatwould derive its propulsive energy from a laser beam incident from therear. It would operate in an air-breathing mode in the altitude range up toabout 30 km, then in a rocket mode at higher altitude.
Viewed from the side, the conceptual lightcraft would resemble an acorn (see figure). The forebody would have an approximately conical shape designed to effect compression of incident air during operation in the air-breathing mode. An annular cowl surrounding the wide end of the forebody would constitute the outer wall of a ring-shaped air inlet and laser-energy-absorption/ propulsion chamber. The aft body would have a paraboloidal mirror outer surface that would serve as the primary optic for reception of the laser beam and as an external plug nozzle expansion surface. The aft-body mirror would focus the laser beam into the ringshaped chamber. In the airbreathing mode, the laser beam would heat the compressed air, and the resulting rearward expansion of the air would generate thrust. In the rocket mode, the air inlet would be closed.