Laser propulsion is any method of propelling a spacecraft that uses the energy of laser beams. All such methods remain conceptual or in the early stages of experimentation. There are two main types of laser propulsion, depending on whether the laser is onboard or off-board the spacecraft. Onboard methods involve the use of lasers as part of a nuclear propulsion system. Off-board laser propulsion is part of a larger class of propulsive methods known as beamed-energy propulsion. Its great advantage is that it removes the need for the spacecraft to carry its own source of energy and onboard propulsion system. The propulsive energy comes instead from a fixed, high-power laser beam that is directed onto the spacecraft by a tracking and focusing system. Off-board techniques have been proposed to boost lightweight vehicles either from the ground to orbit, or on interplanetary or interstellar missions. These techniques include laser-powered launching to orbit and laser light sails.
Powerful lasers developed as part of the United States SDI (Strategic Defense Initiative) program have the potential to launch lightweight spacecraft into low Earth orbit. Tests have already been conducted, by Leik Myrabo of the Rensselaer Polytechnic Institute and other scientists from the United States Air Force and NASA, using a 10-kW infrared pulsing laser at the White Sands Missile Range and an acorn-shaped craft with a diameter of 12.2 cm and a mass of 50 g. The base of the craft is sculpted to focus the beam from the laser on to a propellant. In tests so far, this propellant has been air, which is heated by the beam to a temperature of 10,000–30,000°C, expands violently, and pushes the craft upwards. A height of 71 m was achieved in an October 2000 trial. To orbit a 1-kg spacecraft will demand a much more powerful, one-megawatt laser and a supply of onboard propellant, such as hydrogen, to take over at altitudes where the air gets too thin.1
Laser lightsails would be interplanetary or interstellar spacecraft powered by one or more extremely powerful, orbiting lasers. For details, see space sail.
1. Kantrowitz, A. "Propulsion to Orbit by Ground Based Lasers," Aeronautics
and Astronautics, 9(3), 34-35 (1972).
2. Pakhomov, A. V., and D. A. Gregory. "Ablative laser propulsion: an old concept revisited," AIAA Journal, 38, 725-727 (2000).