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Russia jumps on the inflatable bandwagon
Almost half a century after Aleksei Leonov floated into open space through an inflatable airlock, the company that built his spacecraft started work on future expandable structures, which one day can become space station modules or even serve as shelters on the surface of the Moon and Mars. This work mirrored the US effort, which culminated with the successful launch and deployment of an experimental inflatable module on the International Space Station, ISS, in the spring of 2016.
A concept of the Russian inflatable module for the International Space Station, ISS.
Why inflatable structures?
In its annual report for 2012, Russia's premier human space flight contractor, RKK Energia, said that inflatable structures could pave the way for a new generation of space station modules, interplanetary spacecraft and planetary bases. According to the company, inflatable modules will provide three times more volume and 1.5 more surface area per unit of mass than traditional metal structures. Also, the new technology promised lighter micrometeoroid and radiation shielding than would metal spacecraft.
On the Russian segment of the ISS, an inflatable module could dramatically expand available room as well as increase comfort for the crew. The new architecture could also provide extra volume for complex scientific and technological experiments, RKK Energia's engineers said. They likely referred to equipment, such as a centrifuge designed to create artificial gravity in space. In order to accommodate larger experimental subjects, such as humans, the centrifuge would have to be enlarged dramatically, putting serious technical hurdles on its way into space. An inflatable structure would be an ideal, if not the only solution for accommodating a really large experimental centrifuge inside the pressurized space station module.
RKK Energia began development of an inflatable module in 2011 using its own funding, in the hope of getting a future contract for such a structure from the Russian space agency, Roskosmos.
During 2012, RKK Energia evaluated two basic sizes of the inflatable module, which could be launched either on the Soyuz-2-1b rocket or on the Proton-M and Angara-A5 rockets. Images available at the time depicted the inflatable module built around the Progress cargo ship. Later incarnations of the design showed a larger structure based on what appeared to be the descent module of the next-generation spacecraft, PTK NP.
In the course of the project, RKK Energia procured domestic materials suitable for an inflatable module and developed a structural design and composition of the module's flexible skin. Engineers then worked out a plan to test samples of the new materials as well as to build an experimental scaled model of the expandable structure. RKK Energia also assembled a team of subcontractors for the project and began procurement of materials for the construction of experimental prototypes.
Experimental testing of material samples and fragments of the inflatable structure started at RKK Energia at the end of 2012.
The status of the inflatable module development as of the end of 2012:
One of the key challenges facing any structure in space, especially one designed to function for many years, and even more so soft inflatable structures, is meteoroid protection. Fortunately, spacesuit designers have dealt with the problem for decades. In cooperation with the TsNIIMash research institute (the main research center at Roskosmos), RKK Energia successfully tested proposed meteoroid protection for the inflatable space structures. A new protective material was tried alongside the traditional AMG-6 aluminum alloy used in aerospace industry. According to the company, the new material provided 95 percent of the required level of protection. The remaining five percent of the issues were not described at the time.
Besides their ability to withstand meteor strikes, the program of experiments with structure segments also sought to test the following properties of expandable materials:
Initial studies resulted in the selection of two designs of four-layer flexible and expandable anti-meteoroid structures made of domestically produced materials. Moreover, in cooperation with its subcontractors, RKK Energia developed a new composite material impregnated with heavy metal powder, which showed the best test results. According to RKK Energia, the system showed good flexibility and could be applied to surfaces with complex geometry.
Known specifications of the flexible anti-meteoroid protection system for the Russian transformable module:
Meteoroid penetration tests
Naturally, it was most critical for the engineers to prove the ability of flexible structures to withstand meteor strikes. By shooting aluminum projectiles into the material, developers established key resistance properties of the new material:
During the final high-speed tests, fragments of the 11.5-millimeter particle were caught in the final protective screen, but failed to penetrate it. According to RKK Energia, the anti-micrometeoroid protective layers with composite shielding exceeded necessary requirements for penetration resistance.
To fix the compromised flexible shielding, engineers planned to use the polyurethane glue designated ADV-5. (784)
Read much more about the history of the Russian space program in a richly illustrated, large-format glossy edition:
An animation of an inflatable module concept for the Russian segment of the International Space Station. Copyright © 2013 Anatoly Zak
The design of the inflatable module likely based on the crew module of the next-generation spacecraft, PTK NP. Credit: RKK Energia
A 400 by 400-millimeter unpressurized sample of an inflatable structure. Credit: RKK Energia
A 400 by 400-millimeter test segment of an expandable structure. Credit: RKK Energia
A 400-millimeter assembly of an expandable structure sample with pressurized internal layers. Credit: RKK Energia
Leading specialist at RKK Energia Nikolai Bryukhanov demonstrates a segment of inflatable module to Deputy Prime Minister Dmitry Rogozin on June 14, 2016. Credit: RKK Energia
A skin segment used for impact tests by a 11.5-millimeter aluminum projectile at a speed of 6,510 meters per second. Credit: RKK Energia
Damage to the outer layer of the expandable module skin after an impact. Credit: RKK Energia