Researchers Explore Photophoresis to Lift Metal Sheets into Atmosphere

A team of researchers has proposed an innovative approach to leverage the photophoresis effect to elevate metal sheets into the upper atmosphere. This concept, which builds on the principles demonstrated by the Crookes radiometer, could enable the development of probes that operate in the mesosphere, a region too high for balloons and too low for satellites.

The Crookes radiometer, often misrepresented in explanations, operates not through radiation pressure but via photophoresis. This phenomenon occurs when there is a temperature difference between the dark and light sides of the radiometer’s blades. The dark side, absorbing more heat from light sources, causes gas molecules to gain thermal energy and escape faster, resulting in a pressure difference that drives the blades to spin.

In an effort to harness this effect for practical applications, researchers have designed a configuration termed “nanocardboard,” consisting of two thin metal sheets—one dark and one light—arranged parallel to each other. These sheets are perforated to reduce weight, and some include connecting pipes that enhance thermal insulation and airflow, thereby optimizing lift.

The research team created a model to evaluate various configurations and maximize the lift generated by the system. Key parameters included the geometry of the sheets, the density of perforations, and ambient gas conditions. The study found that the ideal conditions for lift are similar to those inside a Crookes radiometer, which operates at significantly lower atmospheric pressures than those at sea level.

The findings revealed that a square millimeter of nanocardboard could produce over ten times more lift per unit area than larger pieces. The optimal lift occurs in the mesosphere, situated between 50 and 100 kilometers above Earth, where conditions favor the effectiveness of the photophoretic effect.

In practical trials, the researchers fabricated lightweight sheets from materials such as chromium and aluminum oxide. When exposed to a laser or bright light, these sheets successfully generated measurable lift in a controlled, low-density atmosphere, demonstrating the potential of this technology.

Despite the promising results, achieving practical applications poses significant challenges. The mesosphere is difficult to explore, as it lacks the density required for balloons yet has enough gas to hinder satellites. The team envisions transforming these devices into instrument-carrying aircraft, which would necessitate adding structural components for stability and payload capacity.

Launching these devices into the upper atmosphere remains a hurdle, as they cannot generate sufficient lift at lower altitudes. They would need to be transported to the stratosphere using another vehicle and released gently to avoid structural damage. Additionally, any deployment during nighttime could result in the devices descending rapidly back to the surface.

While the path to practical implementation is fraught with challenges, the research offers exciting possibilities. The principles of photophoresis might not only provide new insights into atmospheric science on Earth but also potentially extend to exploration efforts on other planets, such as Mars. This research underscores the fascinating interplay between light and physical phenomena, paving the way for future advancements in atmospheric technology.