Photo courtesy NASA
Another propulsion system being considered for a different class of lightcraft involves the use of microwaves. Microwave energy is cheaper than laser energy, and easier to scale to higher powers, but it would require a ship that has a larger diameter. Lightcrafts being designed for this propulsion would look more like flying saucers (now we're really heading into the realm of science fiction). This technology will take more years to develop than the laser-propelled lightcraft, but it could take us to the outer planets. Developers also envision thousands of these lightcraft, powered by a fleet of orbiting power stations, that will replace conventional airline travel.
A microwave-powered lightcraft will also utilize a power source that is not integrated into the ship. With the laser-powered propulsion system, the power source is ground-based. The microwave propulsion system will flip that around. The microwave-propelled spacecraft will rely on power beamed down from orbiting, solar power stations. Instead of being propelled away from its energy source, the energy source will draw the lightcraft in.
Before this microwave lightcraft can fly, scientists will have to put into orbit a solar power station with a diameter of 1 kilometer (0.62 miles). Leik Myrabo, who leads the lightcraft research, believes that such a power station could generate up to 20 gigawatts of power. Orbiting 310 miles (500 km) above Earth, this power station would beam down microwave energy to a 66-foot (20-meter), disk-shaped lightcraft that would be capable of carrying 12 people. Millions of tiny antennae covering the top of the craft would convert the microwaves into electricity. In just two orbits, the power station would be able to collect 1,800 gigajoules of energy and beam down 4.3 gigawatts of power to the lightcraft for the ride to orbit.
The microwave lightcraft would be equipped with two powerful magnets and three types of propulsion engines. Solar cells, covering the top of the ship, would be used by the lightcraft at launch to produce electricity. The electricity would then ionize the air and propel the craft for picking up passengers. Once it's launched, the microwave lightcraft used its internal reflector to heat the air around it and push through the sound barrier.
Once in a high altitude, it would tilt sideways for hypersonic speeds. Half of the microwave power could then be reflected in front of the ship to heat the air and create an air spike, allowing the ship to cut through the air at up to 25 times the speed of sound and fly into orbit. The craft's top speed peaks at around 50 times the speed of sound. The other half of the microwave power is converted into electricity by the craft's receiving antennae, and used to energize its two electromagnetic engines. These engines then accelerate the slip stream, or the air flowing around the craft. By accelerating the slip stream the craft is able to cancel out any sonic boom, which makes the lightcraft completely silent at supersonic speeds.