Concept studies for a laser powered orbital transfer vehicle

Abstract

The concept of beamed energy propulsion, where power from a remote source is transmitted to a space vehicle and then converted into useful thrust, is an attempt to decouple the energy source from the rocket vehicle. It is hoped that in this way high thrust levels and high exhaust velocities can be produced while eliminating the need for a heavy on-board source. Instead of using energy from chemical reactions to heat a propellant, a powerful beam of energy is employed. The efficiency of microwave power generation, transmission, collection and rectification is much higher than for laser beams. However, rectennae dimensions of about 1 km radius are required for propagation over a few thousand kilometres, and a geostationary orbit system would need a radius of about 10 km. While such large systems are feasible, they are well beyond current technical capabilities, and hence the use of microwaves for powering space vehicles must be ruled out in favour of the use of laser powered systems, at least for the present. This paper describes concept studies carried out on a continuous laser power system. The studies suggested that the possibilities for the use of lasers in such a role were optimistic, with the vehicle involving nothing that was outside current technology. A round trip mission with a velocity increment of 10 km/s was considered. A vehicle with an initial mass of about 18 tonnes could propel a 7 tonnes payload on a round trip from low Earth orbit to geostationary altitude and back. The time taken for the mission would be of the same order as chemical systems, with transfer times measured in hours rather than days.