Introduction to Optical Propulsion Technology

More than 20 years ago, the United States began to develop a missile defense system code-named "Star Wars". The system is designed to track missiles fired by other countries and use lasers to shoot them down. While the system was designed for warfare, the researchers found that these high-power lasers have numerous other uses. In fact, lasers could one day be used to propel spacecraft into orbit and other planets.
Humans currently use the space shuttle to fly into space, and to launch the space shuttle, in addition to loading several tons of fuel, two huge rocket boosters must be tied. Lasers could allow engineers to create lightweight spacecraft that don't need to be loaded with energy. The bareboat itself acts as an engine, and the fuel is light, the most abundant energy source in the universe.
 
The basic principle of optical thrusters is to heat the air with a ground-based laser, causing it to explode and propel the spacecraft. If it works, not only would optical thrusters be thousands of times lighter and thousands of times more efficient than chemical rocket engines, they wouldn't cause any pollution. In this blog post, we'll learn about two versions of this advanced propulsion system, one that takes us from Earth to the moon in just five and a half hours, and the other that takes us along the "path of light" "Go on a trip to the solar system.
Light-propelled rockets sound like spaceships out of science fiction -- riding a laser beam into space with little or no propellant and pollution-free. This seems inconceivable, since humans have yet to develop anything close to that for routine ground or air travel on Earth. Although it may take 15-30 years to achieve this goal, the principles of building a bareboat have been successfully experimented with many times. A company called Lightcraft Technologies continues to refine research that began at Rensselaer Polytechnic Institute in Troy, New York.
The basic principle of a bareboat is very simple - an acorn-shaped vehicle uses a mirror to receive and focus an incoming laser beam to heat the air and explode it, thereby propelling the vehicle. The essential components of this revolutionary propulsion system are listed below:
CO2 Lasers - Lightcraft Technologies uses the Pulsed Laser Damage Testing System (PLVTS), a product of the Star Wars Defense Program. The experimental lightship currently uses a 10-kilowatt pulsed laser, one of the most powerful in the world.
Parabolic Mirror - The bottom of the spacecraft is a mirror that focuses the laser beam onto the engine intake or the onboard propellant. There is also a telescope-like mirror that acts as a secondary ground-based transmitter for directing the laser beam onto the light boat.
Absorption Chamber - The intake air is introduced into the absorption chamber and heated and expanded by the laser beam, thereby propelling the light boat.
Airborne Hydrogen - When the atmosphere is too thin to provide enough air, a small amount of hydrogen propellant is needed to provide rocket thrust.
The bareboat fires with a jet of compressed air that spins it at about 10,000 revolutions per minute (rpm). This rotation is necessary for gyro-stabilized aircraft. Take American football, for example: in order to pass the ball more accurately, the quarterback spins the ball as he kicks it. Applying rotation to this extremely light vehicle makes it more stable through the air.
Once the lightship is spinning at optimal speed, the lasers turn on, propelling the lightship into the air. A 10 kW laser emits pulses at a frequency of 25-28 pulses per second. By firing pulses, the laser continues to propel the vehicle upward. The beam is focused by a parabolic mirror at the base of the craft and heats the air to 9982-29982°C, several times hotter than the surface of the sun. At high temperatures, the air transforms into a plasma state, which then explodes and propels the vehicle upward.
Lightcraft Technologies, sponsored by FINDS (early flights funded by NASA and the U.S. Air Force), conducted several tests of a small bareboat prototype at the White Sands Missile Test Range in New Mexico. In October 2000, a small bareboat with a diameter of 12.2 cm and a weight of only 50 grams reached a height of 71 meters. Lightcraft Technologies hopes to send the prototype bareboat to an altitude of more than 150 meters in 2001. Putting a kilogram of a satellite into low-Earth orbit requires a 1-megawatt laser. Although the model is made of aircraft aluminum, the final standard bareboat will likely be made of silicon carbide.
This laser lightship can also use mirrors, which are mounted inside the lightship to project beam energy in front of the ship. The heat from the laser beam creates air spikes that deflect the air around the craft, reducing drag and the amount of heat absorbed by the light craft.
Another propulsion system is currently under consideration for bareboats, involving microwaves. Microwave energy is cheaper and easier to upgrade to higher power than laser energy, but requires a larger diameter spacecraft. Bareboats designed for such thrusters look more like flying saucers (in fact we are gradually turning science fiction into reality). It will take longer to develop this technology than a laser-propelled lightship, but it could take us to exoplanets. Developers also envision building thousands of these bareboats, powered by a fleet of orbital power stations, and replacing conventional aircraft.
Microwave-powered bareboats would also utilize energy sources other than those of the spacecraft. When using a laser powered propulsion system, the energy source is on the ground. The microwave propulsion system is the opposite. Microwave propulsion spacecraft will rely on the power sent down by an orbiting solar farm. The energy doesn't push the bareboat away, it pulls it closer.
To fly a microwave lightship, scientists must first place a 1-kilometer-diameter solar farm in orbit. Leik Myrabo, who led the bareboat research, believes that such a power station could generate up to 20 gigawatts of power. The power station orbits 500 kilometers above Earth and sends microwave energy to a 20-meter-diameter bareboat that can carry 12 people. The top of the craft is covered with millions of small antennas that convert microwaves into electricity. With just two orbits, the power station can gather 1,800 gigajoules of energy and send 4.3 gigawatts of power to the bareboat for it to be driven into orbit.
The microwave lightship will be equipped with two powerful magnets and three propulsion engines. When the bareboat takes off, it uses solar cells that cover the top to generate electricity. The electrical current ionizes the air, which then propels the craft. Once launched, the microwave lightship uses internal reflectors to heat the surrounding air and travel through the sound barrier.
Immediately after rising to a certain height, the bareboat leans to one side to achieve supersonic speed. Half of the microwave power is then reflected in front of the bareboat, heating the air and forming air pegs that propel the spacecraft through the air at 25 times the speed of sound and into orbit. The aircraft's top speed is about 50 times the speed of sound. The other half of the microwave power is converted into electrical current by the aircraft's receiving antenna, which is used to power the two electromagnetic engines. The two engines then accelerate the slipstream, the air that flows around the aircraft. By accelerating the slipstream, the craft cancels out any acoustic shocks, allowing the lightship to fly silently at supersonic speeds.