Can rockets ride on a microwave beam? A radical launch idea is moving beyond the lab
The concept of using microwave beams to power rockets is an intriguing one, and it's gaining traction in the scientific community. While it's not a new idea, recent advancements have brought it closer to reality, with researchers making significant strides in various aspects of microwave-powered propulsion.
One of the most notable experiments was conducted by a team of Japanese scientists, who successfully sent power to a free-flying drone using a 28-gigahertz microwave beam. This drone, weighing only 0.4 kilograms, hovered for 30 seconds at a height of 0.8 meters above the transmitter, demonstrating the potential of microwave-powered flight.
However, the experiment also revealed the challenges of this technology. Only about 4% of the transmitted power made it through the beam, and the overall transmission efficiency was a mere 0.43%. This highlights the need for further improvements in beam tracking, plasma management, and energy conversion.
The key to microwave-powered rockets lies in the ability to create plasma and pressure inside a thruster using the microwave beam. This is achieved by focusing a high-power millimeter-wave pulse into the vehicle, where it breaks down the surrounding gas, creating hot, electrically charged plasma. This plasma then heats nearby neutral gas, producing a shock wave that pushes against the thruster's internal surfaces, generating thrust.
A critical aspect of this technology is the need for precise alignment. The beam must remain centered within the thruster to ensure efficient energy transfer. A study published in the Journal of Propulsion and Power in 2024 demonstrated the impact of misalignment on propulsion efficiency. The researchers found that even slight deviations from the ideal position can significantly affect how energy enters the thruster and where plasma forms.
To address this issue, a novel approach called 'tractor millimeter-wave beam propulsion' was introduced in 2025. This design separates the beam entrance from the exhaust, allowing microwave energy to enter from the front and pass through a lens that focuses it near the rear of the vehicle. This arrangement creates plasma and a shock wave, pushing the vehicle toward the microwave source while heated gas escapes in the opposite direction.
The tractor-beam design has shown promising results, with researchers observing dense plasma and measuring a positive net impulse. However, the system is still far from being used in orbit. The infrastructure required for an orbital launch would be immense, with estimates suggesting an 80-megawatt beam and a transmitting antenna 90 to 175 meters across.
Another fascinating development is the use of a vortex phase plate to reshape the microwave beam into a doughnut-shaped pattern. This innovation, published in 2025, allows for better control over where gas breaks down and where the force is applied. By altering the beam's phase and energy distribution, operators can adjust the plasma formation inside the vehicle, making the beam both a power source and an adjustable engine component.
Monitoring the plasma's behavior is also crucial. Researchers have developed a compact sensor called a rectenna that can measure changes in standing waves reflected by the moving plasma front. This technology could enable real-time adjustments to pulse length, beam shape, or aim, ensuring the rocket's safe and efficient flight.
Despite the progress, microwave-powered rockets face significant challenges. The energy losses during transmission and conversion, as well as the need for precise tracking and control, make it difficult to achieve the efficiency required for orbital launches. Additionally, safety concerns arise due to the potential for plasma and shock waves to affect nearby aircraft, wildlife, and communities.
Environmental impacts are another consideration. While microwave propulsion may reduce the need for solid rocket motors and some chemical exhaust, the electricity powering the beam must come from a sustainable source. The overall benefit depends on the energy source, launch rate, atmospheric effects, and the propulsion system used after leaving the atmosphere.
In conclusion, the idea of rockets riding on microwave beams is no longer a distant dream. Researchers have made significant progress in various aspects of this technology, from beam tracking to plasma management and beam shaping. However, there are still substantial engineering, economic, and safety challenges to overcome before microwave-powered rockets can become a reality. The question now is whether these challenges can be addressed to make the beam powerful, precise, and reliable enough to lift something larger than a laboratory model.
