How Blowing Massive Polymer Bubbles Could Help Us Build Structures in Space

One of the most significant impediments to humans becoming a truly spacefaring species is the astronomical cost of going orbital: at the moment, you can expect to pay about $10,000 per pound of junk you launch above the Karman line, which makes building the large scale structures that our space civilizations will need prohibitively expensive.

One of the proposed solutions to this dilemma is to just manufacture these structures in space, rather than sending them in pieces over several launches. While this is certainly a good workaround in theory, manufacturing in microgravity presents a host of its own technical challenges, such as extreme temperatures and working in a vacuum.

Fortunately, researchers at the US research and development company Physical Sciences, Inc. recently found a way to make the microgravity environment and its discontents work in their favor, developing a novel method for manufacturing which involves blowing giant polymer bubbles in space.

Funded in part by the Defense Advanced Research Projects Agency and Missile Defense Agency, PSI's patented bubble blowing method works by coating a spacecraft's "injector port" with a polymer film and proceeding to pressurize the film with a gas such as nitrogen, argon or xenon, forming bubbles that can be as little as one micron thick and up to hundreds of meters in diameter.

The purpose of the bubble is ultimately to create large, extremely thin metallic surfaces to use as a building material in space.

"We are talking about specific applications here: large structures involving curvatures, such as microwave reflectors, solar sails, drag devices to induce orbital decay and so forth," said Prakash Joshi, the manager of Advanced Systems Technologies at PSI, in an email. "In this context, to make structures on the scale of tens of meters in linear dimension, it becomes difficult to fabricate them here on earth and then transport them to orbit. Therefore, wouldn't it be better to fabricate very large, lighter weight structures in space?"

Several methods for space manufacture have been proposed over the decades, ranging from the highly exotic (see: Wake Shield Facility) to the relatively banal (see: 3D printing), but so far all methods have struggled with producing anything even remotely near the size envisioned by the architects of this bubble blowing method.

The team's success largely lies in the fact that they put a number of environmental conditions found in space to work in the manufacturing process, such as ultraviolet radiation. The polymer film used to blow the bubble includes a curing agent called benzophenone which makes the bubbles harden when exposed to the sun's UV rays. Once the bubble is rigid, vaporized metal is sprayed inside, coating the bubble with iron, copper, aluminum, or whatever is needed for the manufacturing process at hand, a dispersal method which is aided by microgravity.

After the first bubble is formed like this, a second bubble is made using the same technique but is not coated with a vaporized metal. Next the polymeric and metallic bubbles are made to intersect. This will form either a flat or spherically curved plane, depending on whether the bubbles are of similar or dissimilar sizes, respectively.

The connected bubbles are then passed through two adjacent rings which are charged with an electric current. This current serves to lop off the unwanted portion of the bubbles, which is everything except for their plane of intersection. The result is a massive, ultra thin flat or curved polymer surface with one side coated in metal, which the patent imagines being used in everything from solar sails to satellite calibration systems.

"The next step would be demonstrate the deployment of a spherical bubble in space. This could be done at reasonably low cost from a small spacecraft, such as a Cubesat, for a limited duration mission in low earth orbit," said Joshi. "The obstacles for the demonstration are not technological or engineering, it is a matter of finding the needed funding."

Although it may be a while before we see the technique deployed in orbit, the proof of concept alone may very well have ushered in the era of large-scale manufacturing in space.