Microwaves can do amazing things. For example, for many people, it's hard to imagine life without a microwave oven. Every day, millions of Americans use microwaves to make their meal preparation much simpler and quicker. But, NASA researchers believe that microwaves still have much untapped potential. They believe that the same waves of energy that cook frozen food in mere minutes could one day be used to propel spacecraft through the solar system.
Microwave-based propulsion systems could be used to create more lightweight spacecraft by greatly reducing, or eliminating, the amount of fuel they would need to carry. Rather than using its own propellant as a source of energy, a microwave-powered spacecraft would instead use energy received from an outside source to power its propulsion system and to give its propellant the momentum to push the craft forward.
While possibly not as mature as other propulsion technologies proposed for future generations of launch vehicles, microwave-based propulsion is not as far fetched as it may sound. In fact, the first use of microwave propulsion for a spacecraft may well come before the end of the year. The Planetary Society and Cosmos Studios are working with NASA's Jet Propulsion Laboratory (JPL) to test microwave propulsion on their planned Cosmos 1 spacecraft. Cosmos 1 will be the first solar sail spacecraft, and will rely primarily on the pressure of sunlight for propulsion. However, a test will also be conducted in which microwave energy will be beamed from JPL to Cosmos 1 to study this method of propulsion. Rather than using beamed energy to power a propulsion system, Cosmos 1 will actually use the microwaves hitting the sail to push the craft forward. While this system does not require an additional fuel source, it is not practical for generating the same levels of thrust as a system relying on an additional propellant.
NASA researchers are working to develop a system that relies on microwaves beamed either from the ground or from satellites for propulsion to launch payloads into orbit. The goal is to be able to deliver people and medium-sized payloads into low-Earth orbit for about $100 per pound, or roughly 1 percent of the cost of launching the same payload using the Space Shuttle. The researchers hope to develop the technology to do this within the next 20 years. Microwaves beamed to such a craft would be converted to electricity by special antennas inside the vehicle, or refocused by those antennas to points outside the vehicle, to power its propulsion system and energy storage system. NASA is currently performing tests on "rectennas" (or rectifying antennas) designed in Canada that could be used to convert beamed energy. For such a system to be able to launch from Earth into orbit would require the development of a lightweight air-breathing electric propulsion system. Such an air-breathing system would use the microwave energy to convert the air in the atmosphere into fuel for the craft.
Some researchers even believe that microwave-based propulsion could be used for air travel on Earth, as well. Orbiting power stations would convert solar energy into microwaves that would be beamed down to special lightweight aircraft. For optimum performance, these craft might be disc-shaped, making them resemble flying saucers.
If NASA's scientists are successful in developing a microwave-based launch vehicle, it could drastically reduce the cost of sending humans and equipment into orbit, and could someday make space more accessible to people wishing to travel beyond the atmosphere. And given the number of different possible applications for microwaves in propulsion, someday they may be as ubiquitous in high-tech transportation as they are in food preparation today. And when that happens, when people say they’re going to use the microwave, they may not be doing some fast cooking -- they may be going somewhere fast.