Anatoly Zak

RKK Energia, the manufacturer of the Soyuz spacecraft

and the prime contractor on the Russian part of the International Space Station, quietly published in its annual report last week details on an innovative inflatable space habitat.

Wrapped into multilayered synthetic skin instead of metal, the expandable module could be attached to the Russian part of the International Space Station and inflated like a beach ball, providing greater comfort for the crew and extra room for yet-to-be-disclosed experiments, RKK Energia's report said. Thanks to its compact size during the launch (the most expensive phase of any space mission), inflatable structures promise to deliver much more habitable volume per unit of mass than the one available inside the traditional spacecraft. According to Russian researchers, inflatable modules will provide three times more volume and 1.5 more surface area per unit of mass than traditional metal structures. Also, inflatable modules promise lighter and better micrometeoroid and radiation shielding than would metal spacecraft.

The Russian company began work on this exotic technology in 2011 using its own funds and is currently working on a scaled-down prototype. Eventually, RKK Energia hopes to get a contract from the Russian space agency, Roscosmos, to build the full-scale inflatable habitat. RKK Energia did not disclose any details about the composition or properties of the skin comprising its flexible structure beyond saying it would use domestically produced materials.

An official representative of RKK Energia, Anatoly Khabarov said in an email to PopMech that "… unfortunately, at present, our developers can not provide anything for publication." However documents we obtained show that the company had initially considered fitting the inflatable structure into its 7-ton Progress cargo ship, which has been routinely used to deliver supplies and propellant to the ISS. In the past, the Progress was also successfully employed to deliver new modules to the orbiting outpost.

A Short History of Space Inflatables

Although inflatable structures had never been widely used in space, they have attracted the attention of space architects since the dawn of the space era, as the most effective and economical way of creating a large pressurized habitat.

The USSR pioneered inflatable structures in space with a flexible air lock that was launched aboard the Voskhod-2 spacecraft in 1965. During that historic mission, the inflatable design enabled the world's first space walk, by Soviet cosmonaut Alexei Leonov. Soviet engineers also used inflatable airbags to soften landings of its early lunar probes. More recently, a Russian firm tried (with mixed results) to return cargo from orbit using an inflatable heat shield. (One small experimental cargo did return to Earth successfully in 2000, but a larger inflatable device was lost during the reentry, and several further reentry attempts were aborted due to launch failures.)

It was NASA's Johnson Space Center, though, that has come closest to launching a manned inflatable module, to be called Transhab. Conceived as living quarters of a Mars-bound spacecraft, Transhab was intended to ride on the shuttle to the ISS to demonstrate the feasibility of inflatable technology. But because of financial and political problems, Congress killed the maverick project in 2000.

Since then, Nevada-based firm Bigelow Aerospace had acquired NASA's engineering heritage in the hope of building an orbital hotel for space tourists and commercial researchers. Bigelow's near-Earth facility would be comprised of several inflatable structures whose scaled prototypes had been successfully boosted in orbit in 2006 and 2007—ironically, aboard converted Russian ballistic missiles. Bigelow is also working with NASA to add a small inflatable structure to the American segment of the ISS that would stay in place for at least two years. The module is currently scheduled to ride to the station aboard a SpaceX Dragon spacecraft in the summer of 2015.

The Hurdles

When we asked a Bigelow Aerospace representative about the news of these Russian plans, the reaction was a combination of surprise, excitement, and competitive spirit.

"It is a first time I've heard of this, I am very surprised … wow!" Michael Gold, director of D.C. operations and business growth at Bigelow, told PopMech. "That would be outstanding [if Russia succeeds in the development of such a vehicle] … it is a great technology and I am glad to see that if the world adapts it, it will really help space exploration and lower its cost, which, obviously, is really important in this fiscally constrained environment."

Gerard Valle, a specialist in inflatable structures at Johnson Space Center and veteran of the Transhab project, agreed that inflatable technology provides favorable volume-to-mass ratio when compared to traditional metal spacecraft. At the same time, he warned, developers still face major technical risks and high costs.

The biggest hurdle for inflatable habitats, Valle says, particularly those that would house humans in space, is overcoming "creep"—the slow deformation of a structure under stress. "We have a whole program with Langley (space center) to show that those materials are good (on creep issues)," Valle said, "(This problem) is common for all materials and you have the same concern with metal structures, but it is definitely a concern with inflatables and you have to understand it and you have to prove it." NASA scientists made special effort to come up with innovative methods of testing which could simulate decades of stress in just a few years or even months, Valle says.

Extreme temperatures in space would present additional hurdles. "If you are at the cold temperatures for the very long time, the module's flexible bladder will crack," he says. "Therefore you have to make sure that it either has heaters or you have a really good bladder."

Valle says only deep-space missions, such as an expedition to Mars, would ultimately justify the technical risks and expenses associated with inflatable spacecraft': "If you're just going to low Earth orbit, you can probably get by with a metal can."

Up to Speed

After a nearly decade-long hiatus caused by years of economic problems in the country after the collapse of the Soviet Union, numerous Russian space projects have been revived. RKK Energia's engineers are currently putting finishing touches on the 20-ton multipurpose laboratory that is scheduled to join the ISS before the middle of the next year. It would be followed within a year or two by an innovative Node Module, equipped with six docking ports for multiple "plug-in" spacecraft. RKK Energia recently released images of the flight version of the globular-shaped spacecraft being assembled at the company's workshops. With the Node Module's projected life span of several decades, Russian engineers would have practically unlimited opportunities and plenty of ports to expand their part of the space settlement with additional laboratories and habitats, including some inflatable.

Given the late start in the assembly of the Russian segment, the nation's space officials hinted that they had been considering separating the newest Russian modules of the outpost and leaving it in orbit after the deorbiting of the main portion of the ISS currently expected at the beginning of the 2020s.

Anatoly Zak is an editor of RussianSpaceWeb.com and the author of Russia in Space: The Past Explained, The Future Explored, to be released by Apogee Books later this month.

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