'Metajets' could allow future spaceships to be propelled by nothing but light

If an alien in the Alpha Centauri star system were craving pizza, it would take tens of thousands of years to deliver it using today’s rocket technology. According to a press release, researchers at Texas A&M University have developed a technology that could one day reduce delivery to a mere 20 years using nothing but light for propulsion.

In their research, published in Newton, the team successfully lifted and steered tiny devices in multiple directions using nothing but light – no fuel, motors, or physical contact. While the immediate experiment involved microscopic structures rather than spacecraft, the researchers argue that the same underlying physics may one day contribute to advanced propulsion systems that could dramatically reduce travel times across space.

Now, the concept of light propulsion is not new. Scientists have understood for more than a century that light exerts pressure, a phenomenon often called radiation pressure. That principle has already been demonstrated in several forms. In one of many examples, NASA and JAXA have both flown solar sail spacecraft that use sunlight for gentle but continuous thrust.

However, one of the major challenges in light propulsion has been controlling the generated motion. Pushing an object forward is one thing; keeping it stable, steering it accurately, and allowing it to maneuver in multiple directions is another. This becomes especially important for future light sails traveling at extreme speeds, where even tiny instabilities could send a craft, originally on its way to Mercury, straight to Jupiter.

At the center of the concept are tiny devices called metajets, made from metasurfaces: ultrathin materials patterned with nanoscale structures that can precisely redirect incoming light. When a laser beam hits the surface, the patterned features bend or scatter the light in specific directions. Because light carries momentum, changing its direction creates an equal and opposite reaction force on the object itself. In simple terms, the light pushes the device as it is redirected.

What makes the system notable is that the movement is built into the material design rather than the laser beam alone. By carefully arranging the nanoscale patterns across the metasurface, researchers can generate forces in multiple directions simultaneously. This allows the metajets to move sideways, rise upward, or travel forward, giving them full three-dimensional maneuverability.

In tests, laser illumination caused the prototypes to levitate and propel laterally simultaneously. This demonstrates a level of optical control beyond traditional light-manipulation systems, which often only trap or push objects in one direction.

The significance of the experiment is less about immediate applications and more about proving the principle that carefully engineered surfaces can convert laser energy into directed, programmable force. If that principle scales as expected, it could open the door to systems ranging from microscopic robots to much larger light-driven vehicles.

That is where the discussion turns to travel time. The nearest star system, Alpha Centauri, lies about 4.37 light-years away. Conventional rocket-powered spacecraft travel far too slowly for such journeys to be practical. At the speeds of today’s deep-space probes, a trip would take tens of thousands of years. Laser propulsion concepts aim to change that by accelerating extremely lightweight craft to a significant fraction of the speed of light. If a probe could reach around 20% the speed of light, the journey could theoretically be reduced to roughly two decades instead of many millennia.

Before we get too excited, the current prototypes are microscopic, smaller than the width of a human hair. The gap between this laboratory demonstration and a real interstellar vehicle remains enormous. Scaling the concept would require immensely powerful laser systems, advanced materials capable of surviving intense illumination, precise beam control over vast distances, and navigation systems for craft traveling at unprecedented speed. None of those challenges is close to solved.

Still, the force produced in the experiments scales with the power of the incoming light rather than being fundamentally limited by the device’s size. This means that the same principles could eventually be applied far beyond microscale systems.

Source: Texas A&M University