More details emerge on NASA's plan for inflatable ISS module
By Brian Dodson
January 20, 2013
NASA announced last week that it has contracted Bigelow Aerospace to construct an inflatable module to test on the International Space Station. Following the release of more information and imagery, here's a closer look at what the plan entails.
The Bigelow Expandable Activity Module (BEAM) is an expandable space station module currently being developed by Bigelow Aerospace, under contract to NASA, for use as a module on the International Space Station (ISS) during 2015 to 2017.
Bigelow Aerospace licensed the technology developed by NASA for multi-layer expandable space modules after Congress cancelled the SpaceHab unit being developed as part of the International Space Station (ISS) in 1999. Bigelow has now spent a decade and nearly US$200 million on the technology and practice of inflatable space habitats, including launching two test modules, Genesis I and II, into orbit in the mid-2000s.
The BEAM module being developed for the ISS is quite small, and will only add about two percent to the overall pressurized volume of the ISS. Four meters (13 ft) in length and 3.2 m (10.5 ft.) in diameter, the BEAM is roughly cylindrical in shape. (A doughnut-shape was considered initially, but in the end a cylinder seemed more likely to meet NASA's testing requirements.)
The BEAM module will be launched in folded form in the unpressurized cargo compartment on the eighth SpaceX Dragon cargo resupply mission, currently scheduled for 2015. Following on-orbit arrival at the ISS, a robotic arm will be used to install the BEAM on the aft port of the Tranquility node (see NASA video below). Afterwards, the station crew will activate a pressurization system to expand the structure to its full size using air stored within the packed module.
The fabric walls consist of several sets of layers. On the outside there is a layer made up of sheets of aluminum foil separated from one another by a small space. This serves two functions. The separation makes the outer layer act as an extremely efficient and lightweight thermal insulation, similar in concept to that being constructed for the James Webb Space Telescope. The second function is that of a Whipple shield, which serves to vaporize the smallest micrometeoroids, thereby allowing inner layers to avoid penetration.
Next is a set of several layers of more substantial Whipple shields. These consist of a thin metal sheet positioned over and separated from a thicker sheet. They work the same as the thermal insulation layer, but protect the contents of the BEAM module from larger micrometeoroids.
The inner layers of the walls comprise several sheets of Vectran, a super-strength polymer having about double the strength of Kevlar. These protect against both external and internal penetration, and are strong enough to survive, say, pieces of equipment accidentally propelled into the inner walls. Despite their intricate structure, the walls weigh only about 25 kg/sq m (5.5 lb/sq ft), compared to about 110 kg/sq m (25 lb/sq ft) for a similar sized ISS compartment built using conventional construction.
Testing indicates that the BEAM walls will be at least as resistant to both radiation and micrometeoroids as is the rest of the ISS. An advantage of the inflatable modules for deep-space applications is that, unlike metal, high-energy cosmic rays just pass through without forming a shower of secondary high energy x-rays.
During the two-year test period, station crew members and ground-based engineers will gather performance data on the module, including its structural integrity and leak rate. An assortment of instruments embedded within module also will provide important insights on its response to the space environment. This includes radiation and temperature changes compared with traditional aluminum modules.
Astronauts will occasionally enter the module to gather performance data and perform inspections. “The plan is to have the hatch closed most of the time, with the crew going in and out a few times a year to collect data," says NASA Deputy Administrator Lori Garver.
Following the test period, the module will be jettisoned from the station, burning up on re-entry.
Bigelow also plans to build a second BEAM module for use as an airlock on its Bigelow Commercial Space Station. The module's inflatable nature would provide room for up to three crew or tourists to spacewalk simultaneously, compared with a maximum of two that can operate outside the ISS.
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