Using parts from a 1,000-watt kitchen microwave oven, an engineer has built a prototype propulsion system that he thinks shows promise as a cheaper, safer thruster for positioning and maneuvering satellites in space.
"Existing chemical positioning and maneuvering systems for communications satellites account, with their fuel, for a very large fraction of the total launch mass," Michael M. Micci, associate professor of aerospace engineering, said. "Though less commonly acknowledged, these existing systems are also responsible for the majority of satellite failures."
The microwave-powered thruster has the potential to reduce the amount of propellant needed by up to 50 percent. The fuel savings can be used to install more payload on the satellite or can be taken in launch cost savings.
"In addition, since many commercial communication satellites in orbit today were still operational when they ran out of maneuvering fuel, the increased capacity could extend satellite life by a number of years," he said.
Micci says the idea for a microwave thruster has been around for more than a decade. However, his is the only prototype currently undergoing active ground testing. His ambition is to see the system tested in space.
The thruster concept is based on the fact that microwaves can be used to create and maintain a free-floating plasma or superheated, electrically-charged gas within a cavity, Micci said. If a cold "fuel" gas is passed through or around the plasma in the cavity, the cold gas will become heated and create thrust when allowed to flow out through a nozzle and heat energy is converted to kinetic energy, the energy of movement.
Since the plasma creates temperatures higher than those possible by chemical combustion, the plasma creates more thrust from the same amount of cold "fuel" gas than chemical combustion, Micci said.
In addition to being more fuel-efficient than chemical systems, the microwave-powered thruster is inherently safer as well, he said. The thruster operates only when the magnetron, or microwave source, is generating microwaves. If the magnetron is turned off, so is the plasma that heats the fuel.
In Micci's prototype the electrical hardware and magnetron came from a conventional 1,000-watt kitchen microwave oven. The system has been operated using hydrogen, nitrogen and ammonia fuel gases. To date, the research has shown that the device can be successfully operated with a number of propellants and can easily create and maintain plasmas from them.
The engineer said the thruster can potentially be operated with water as fuel. Water is heavier than ammonia but lighter than nitrogen. Micci has achieved his best performance with hydrogen, the lightest gas. However, hydrogen is difficult to store in space. Ammonia was closest in performance to hydrogen. Nitrogen's performance came in third.
Micci and his commercial partner, Research Support Instruments Inc., have applied for patents on the prototype device. He has also detailed the device and research results in a paper, "Current Status of the Microwave Arcjet Thruster."