Beam-powered propulsion
|
|
Beam-powered propulsion is a class of spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant.
Many proposed spacecraft propulsion mechanisms use power in the form of electricity. Usually these schemes assume either photoelectric power, or an on-board reactor. However, both power sources are heavy. Alternatively, one could leave the power-source stationary, and directly heat the propellent on the spacecraft with a maser or a laser beam from a fixed installation. This permits the spacecraft to leave its power-source at home, saving significant amounts of mass.
Since the laser can heat the propellent to extremely high temperatures, this potentially greatly improves the efficiency of the rocket, as exhaust velocity is proportional to the square root of the temperature. Normal chemical rockets have an exhaust speed limited by the fixed amount of energy in the propellents, but beamed propulsion systems have no particular theoretical limit.
Microwave broadcast power has been practically demonstrated several times. The first time was at Goldstone California, in 1974.
The power beam can also be used to provide impulse directly, for example using a solar sail to reflect a laser beam or using a magnetic sail or MMPP sail to divert a beam of charged particles from a particle accelerator.
A "laser broom" intended to sweep space debris from Earth orbit is another proposed use of beam-powered propulsion. In this case the laser is used on objects that were not designed to be propelled by it, even small pieces of scrap knocked off of larger satellites.
Ablative Laser Propulsion is another form of laser propulsion that uses a laser to create a plasma plume from a metal propellant, thus producing thrust.
Testing
Recent tests by Leik Myrabo, with the US Army, have demonstrated the feasibility of using ground-based lasers to propel objects into orbit; possibly reducing orbit-flight costs by a factor of 1000. The test succeeded in reaching over 100 feet, which compares to Robert Goddard's first test flight of his rocket design.
Myrabo's "lightcraft" design is a reflective funnel-shaped craft that channels heat from the laser, towards the center, causing it to literally explode the air underneath it, generating lift. This method, however is dependent entirely on the laser's power, and even the most powerful models currently can only serve for modest test purposes.
Non-spacecraft applications
In 2002 a Japanese group propelled a tiny aluminium airplane by using a laser to vaporize a water droplet clinging to it, and in 2003 NASA researchers flew an 11 ounce (312 g) model airplane with a propeller powered with solar panels illuminated by an infrared laser. It is possible that such beam-powered propulsion could be useful for long-duration high altitude unmanned aircraft or balloons, perhaps designed to serve as communication relays or surveillance platforms.
See also: spacecraft propulsion