Imagine sending rockets into orbit with larger payloads using laser beams or microwave beams aimed at the rocket from the ground. That image could become reality with today’s technology according to scientists at NASA.
According to an article in Astrobiology Magazine, using lasers or microwaves to power space launches would achieve a number of desirable goals. First, instead of multi-stage one use rockets, you would have reusable one stage rockets saving time and money. It would also allow more rocket launches per year.
Second, payloads on rockets could be bigger than the three percent fraction overall that limits payload size. Instead, payloads could be five to fifteen percent fraction of overall weight. Larger payloads mean more equipment and experiments can be launched more often and more cheaply than current payloads.
“Usually in a conventional rocket you have to have three stages with a payload fraction of three percent overall,” says Kevin Parkin, leader of the Microwave Thermal Rocket project at the NASA Ames Research Center. “This propulsion system will be single stage with a payload fraction of five to fifteen percent.”
The new launch process is called beamed thermal propulsion. By focusing laser or microwave beams on a heat exchanger on the rocket it converts the rockets liquid fuel into a gas. The gas coming out of the bottom of the rocket propels it upward. Since the beams are adding energy externally, less fuel is needed.
“The basic idea is to build rockets that leave their energy source on the ground,” says Jordin Kare, president of Kare Technical Consulting, who developed the laser thermal launch system concept in 1991. “You transmit the energy from the ground to the vehicle.”
In order for that to happen, it would take a few hundred commercially available lasers that would provide between 25 to 100 megawatts of energy. Laser systems would take about eight to ten minutes to put a spacecraft into orbit.
If microwaves were used instead of lasers, it would take an array of 100 to 200 megawatts of commercially available microwave sources called gyrotrons. Even though more energy is required in the microwave system, rockets would only take three to four minutes to make it into orbit. Of course the cost for the microwave system is higher than the laser system.
The size of either array would be equivalent to a golf course. The space between the the array and the rocket would need to be kept free of airplanes and satellites. The technology for a beamed thermal propulsion system currently exists. NASA is expected to finish a study on the use of such a system by March of this year.
Regardless of which beamed thermal propulsion system is used, it would still be cheaper than the current system. It would be safer because you would have fewer pieces falling back to earth, and it would enable more launches and bigger payloads.
Let’s see what NASA has to say about the idea in March. So far it sounds like a better mouse trap.
Graphic:A conceptual microwave-propelled lightcraft receives microwave beams from an array of microwave sources on the ground. Credit: Kevin Parkin