Lighter Than Air

In mid-March of 2020, physicist Miles Beaux and chemist Chris Hamilton were in hot pursuit of a harebrained idea, when the coronavirus pandemic forced them to a grinding halt. Their project—to build a solid object that is lighter than air—needed the scientists to fly to Boston to see about having a piece custom built. But then Boston called and said, “Don’t come,” and then Los Alamos said, “Go work from home,” so they went home and started thinking of workarounds.

Beaux doesn’t dispute the characterization of “harebrained” for his idea of a solid material that is lighter than air. But that’s no reason not to do it. He’s encountered naysayers at every turn, and he’s kept going, and around each corner, so far, he’s found success. 

It started with an offhand comment to Hamilton, an aerogel expert, about how aerogels could be the way to build a helium-free air-buoyant balloon. Hamilton suggested a particular aerogel—polyimide, commonly used in the production of electronics and medical supplies—and with that the air-buoyant-solid project was off the ground.

Aerogels only start as gels—they are ultralight liquids that solidify into ultralight solids with high porosity and low density. The first challenge was to make a hollow polyimide sphere and see if it would hold vacuum. Because the aerogel material itself is heavier than air, the inside of the sphere must be evacuated of air in order for the object’s overall density to be light enough.

Beaux explains, “It’s like a ship on the ocean surface with pockets full of air, compared to a sunken ship whose pockets have filled with water. Only in our case, with pockets full of air the object sinks—we need pockets full of nothing.”

The team produced two three-inch polyimide hemispherical shells, put them together, and evacuated the center chamber, fully expecting one of two things to happen: either air would pass freely through the material, making vacuum impossible, or the vacuum would cause the material to collapse or shatter. But neither happened. The two halves held together with no glue, only the ambient air pressure pushing against the vacuum interior, for nearly a minute. Buoyed by this success, the team doubled down, incrementally decreasing the thickness and optimizing the density of the material until eventually a test sample held vacuum—again without glue—for over 12 hours.

Initially the team used a combination of heat, pressure, and vacuum to solidify the polyimide from liquid to solid, but that method only allowed for up to three-inch diameter prototypes. To build a larger sphere, they had to move to a freeze-drying method which similarly facilitated the state transition, but still maxed out at 11.5 inches. This is the largest the team has achieved so far, but even if it holds vacuum—they are preparing for those tests now—it won’t float. That’s because it is still not big enough. According to Beaux’s calculations they need a sphere of at least 1.4 meters in diameter for the ratio of material to vacuum to be sufficient for liftoff.

Beaux and Hamilton were going to Boston to have the 1.4-meter version made by a private aerogel company. When their trip was canceled because of the pandemic, they started working on in-house ways to make the full-size prototype. Their meantime efforts paid off, and they now have a 1.4-meter hemispheric mold. But it’s too big for either the heat-plus-pressure method or the freeze-drying method, so they are presently working on developing a new method.

With large diameters and thin walls, Beaux expects the full-size prototype may need reinforcing. But he’s got a plan for that. Beaux’s background is in nanomaterials, and he’s already demonstrated that the inclusion of helical nanofibers within the polyimide, like microscopic ropes made from silica, can increase the material’s strength several hundred times over without weighing it down too much. Like the other hurdles he’s cleared so far, Beaux is confident he will clear this one.

Why is Beaux pursuing this? Well, one reason is that helium is a non-renewable resource, and the world is running out. So scientific balloons, party balloons, anything that relies on helium to stay aloft, will need a new way. Another application would be to provide floating, distributed internet to rural locations that presently lack adequate infrastructure. Besides, pursuing harebrained ideas and making them work in the face of doubt has a certain satisfaction all its own. LDRD