Humanity's oldest flight technology, ballooning, proved instrumental at the beginning of the space age, helping loft the world's first communications satellite, Echo 1, 50 years ago.
Now inflatable structures are seeing a resurgence in space ? they are, for instance, the foundation of a new effort from Bigelow Aerospace to build the first private space station.
"We're trying to take the next step from where Echo was," said Mike Gold, Bigelow Aerospace's director of Washington, D.C. operations and business growth. "We're going to go to low Earth orbit and beyond with expandable technology."
Echo-1 and beyond
The world's first communications satellite was also the world's first inflatable satellite ? a silvery plastic Mylar balloon 100 feet (30 meters) wide.
Soaring roughly 1,000 miles above the Earth (1,600 km), the giant "satelloon" served as a mirror scientists bounced radio signals off, relaying the first voice communication via satellite, the first coast-to-coast telephone call via satellite and the first image transmitted via satellite.
Although satelloons that passively reflected signals quickly fell out of favor to make way for satellites that actively transmitted signals, NASA pursued the idea of inflatable space stations.
"People have been talking about inflatable structures for a long, long time ? they're interesting concepts," said Roger Launius, space history curator at the Smithsonian's National Air and Space Museum. "People were talking about them in the '50s, and a lot of studies were done in the '60s."
The challenge with putting stations in space is that they are potentially both large and heavy. Inflatable structures help address both problems with relatively lightweight components that can reduce their size inside the limited space aboard rockets and then expand once in orbit.
"The fundamental advantages of inflatable structures ? or, as we prefer, expandable systems ? still remain true," Gold said. "You can get a large amount of volume into a slim rocket fairing, and save on mass and cost."
NASA even commissioned tire-maker Goodyear to construct prototypes for an inflatable space station, which resembled nothing less than a big rubber inner tube. Still, "the main concern was that micrometeorites would hit and deflate them," Launius said. "They were abandoned in the late 1960s."
Rise of the balloons
The resurgence that inflatable structures saw beginning in the 1990s owes thanks to advances in synthetic fabrics. "Kevlar and other composites are much more rugged, hardy materials, can withstand much more than a Mylar balloon," Launius said.
Currently, Bigelow Aerospace has two fully inflated space station module prototypes already in orbit. In 2014, the company plans to launch real modules to assemble them into the first private space station. Two years after that, a second station is scheduled to follow.
Space entrepreneur Robert Bigelow, founder of Bigelow Aerospace, has ambitions beyond inflatable stations in orbit ? he envisions inflatable moon bases as well.
NASA has already tested an inflatable moon base prototype at the South Pole, and this year launched a contest for students to design the best inflatable house for life in space or on another world. NASA scientists even have said that inflatable modules could be part of future missions to asteroids and to Mars.
"We've pretty much overcome complaints when it comes to inflatable structures about potential hazards in terms of both deflation from micrometeorites and orbital debris, and of inflation ? of them inflating too fast and exploding," Launius said.
"Any depictions of development of space beyond low-Earth orbit, at a Lagrange point or the moon or Mars always involved expandable space habitats," Gold said. ?Lagrange points are positions in space where the gravitation tug of objects balance out, allowing spacecraft to take up station-keeping positions. There are five Lagrange points around Earth.
"Expandable structures are the next logical step in the evolution of habitats. There were a lot of questions about the technology, and a lot of detractors, and a lot of them didn't think our structures could survive the launch environment, much less in space. Our work so far has lived up to the promise we all hoped for them."
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