Bae named the laser thruster based on the photon recycling in an active optical cavity Photonic Laser Thruster (PLT). Such optical cavities are used for gravitational wave detection as in LIGO, for their extreme sensitivity to the movement of mirror. Bae originally proposed to use photon recycling for use in a nanometer accuracy formation flight of satellites for this reason. Bae, however, discovered that in an active optical cavity formed by two high-reflectance mirrors and a laser gain medium in between, similar to the typical laser cavity, photon recycling becomes less sensitive to the movement of mirrors. An optical cavity can be made with two high-reflectance mirrors, forming a Fabry–Pérot optical resonance cavity in which any small movement of mirrors would destroy the resonance condition and null photonic thrust.

The laser light is reflected back and forth many times improving the force transmitted but importantly allows the large lens to remain in a more stable position as it is not greatly influenced by the laser lights momentum.Īn optical cavity allows greater re-use of photons, but keeping the beam in the cavity becomes much more challenging. In this configuration the laser shines light on a probe sail accelerating it outwards which is then reflected back through the Fresnel lens to be reflected off a larger more massive reflector probe going in the other direction. There is also a multi-bounce photonic sail configuration which uses a large Fresnel lens around a laser generating system. Metzgar and Landis proposed a variant on the laser-pushed sail, in which the photons reflected from the sail are re-used by re-reflecting them back to the sail by a stationary mirror a 'multi-bounce laser-based sail.' This amplifies the force produced by recycling the photons, resulting in considerably higher force produced from the same laser power. An extension of the idea is to have nuclear materials on the mini sails that undergo fission or fusion to provide a much more powerful force but the collision velocities would have to be much higher. The ionising collisions could then be used to interact with a powerful magnetic field on the spacecraft to provide a force to power and move it. Each alternative mini sail is slowed down by a laser from the home system so that they collide at ionising velocities. The laser-pushed sail is proposed as a method of propelling a small interstellar probe by the Breakthrough Starshot project.Īnother method of moving a much larger spacecraft to high velocities is by using a laser system to propel a stream of much smaller sails. The laser may alternatively be a large phased array of small devices, which get their energy directly from solar radiation. This gets more important when going from interplanetary travel to interstellar travel, and when going from a fly-by mission, to a landing mission, to a return mission. The beam has to have a large diameter so that only a small portion of the beam misses the sail due to diffraction and the laser or microwave antenna has to have a good pointing stability so that the craft can tilt its sails fast enough to follow the center of the beam. Further analysis of the concept was done by Landis, Mallove and Matloff, Andrews and others. Use of a laser-pushed lightsail was proposed initially by Marx in 1966, as a method of interstellar travel that would avoid extremely high mass ratios by not carrying fuel, and analyzed in detail by physicist Robert L. The advantage of lightsail propulsion is that the vehicle does not carry either the energy source or the reaction mass for propulsion, and hence the limitations of the Tsiolkovsky rocket equation to achieving high velocities are avoided.

Laser-pushed sails are examples of beam-powered propulsion.Ī laser-pushed lightsail is a thin reflective sail similar to a solar sail, in which the sail is being pushed by a laser, rather than the sun. Thus, the second is fundamentally limited in final spacecraft velocities by the rocket equation. Thus, the first uses the laser for both energy and reaction mass, while the second uses the laser for energy, but carries reaction mass. The second method uses the laser to help expel mass from the spacecraft as in a conventional rocket. The first way uses photon radiation pressure to drive momentum transfer and is the principle behind solar sails and laser sails. Laser propulsion systems may transfer momentum to a spacecraft in two different ways. An exposition of Kantrowitz's laser propulsion ideas was published in 1988.

Propulsion concepts using laser-energized rockets were developed in the 1970s by Arthur Kantrowitz and Wolfgang Moekel, with a variant using laser ablation pioneered by Leik Myrabo. The basic concepts underlying a photon-propelled 'sail' propulsion system were developed by Eugene Sanger and the Hungarian physicist György Marx.

Laser jump speed