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ISS-TransHab attached to ISS during assembly operations

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Partially dissected view through layers of the TransHab shell

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Vertical cutaway showing all three levels.

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CAD diagram of core structural components

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TransHAB Shell Development Unit (SDU)

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Level Three: Exercise Area and Stowage

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Semi-transparent cutaway of Level Two core area

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Isometric view of wardroom and galley areas of Level One

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Two studies for woven pattern of TransHab shell's inner "scuff barrier"

To Metropolis article...

TransHab (short for “Transit Habitat”) is the first space inflatable module ever to be designed by NASA.  It was first thought of as a technology which is capable of supporting a crew of six on an extended space journey such as the six-month trip to Mars.  During its development in 1997-2001 at NASA’s Johnson Space Center in Houston, Texas, TransHab was considered for use on International Space Station “Alpha” as a Habitation module for two reasons: first, because of its superior ability to support crew needs, and second, so that its technologies might be tested and proven effective for a human mission to Mars.

 

Why TransHab?… on Alpha

TransHab is better for the crew because it was the first spacecraft to be carefully designed from the beginning around human requirements, not just engineering solutions to the challenges of spaceflight.  Because of that, it is roomier, it offers space for enough stowage to take care of a crew for over six months, and it houses all the crew activities from sleeping to exercise.  This would reduce clutter and activity elsewhere on the ISS, and allow other modules on Alpha to be a better environment for the scientific experiments that are the station’s primary purpose.

 

…and for Mars

For all of these reasons and more, TransHab is also an important part of the human exploration of Mars or other bodies in our Solar System.  Without a vehicle as large and as usable as TransHab, the cost of getting a crew safely to a remote destination like Mars would be much higher, and the crew would be much more likely to experience stress and low efficiency before the most challenging part of their mission even begins.  This makes TransHab a vital part of NASA’s Mars Design Reference Mission, as the crew habitat for the journey between planets.   At the beginning of the “DRM”, TransHab is launched in a Space Shuttle bay, deflated and packaged tight; once on orbit it can be unfolded, inflated and deployed.  At that time, elements which served structural functions during launch are reconfigured to serve as walls, partitions and furnishings. 

All of this is possible because it is specifically designed for use in a microgravity** environment, so its pieces are lighter than other modules.  Once ready to go, TransHab would be attached to the propulsion and guidance systems that take it and its crew on the six-month trip to the Red Planet.  When they reach Mars, the crew would “park” TransHab in orbit and take a transfer ship to the surface, where their surface habitat is already in place and waiting for them.  At the end of their 425-day scientific expedition on Mars, the crew would then launch back up to orbit and reboard TransHab for the journey home.

 

Significance
Although people have tried to build space inflatable vehicles since the 1960s, the previous attempts had no hard structure to keep the shape and attach equipment, and the inflatable shells themselves were not robust enough.  TransHab represents a major breakthrough in that it solved the “problem” of inflatables and at the same time invented a whole new way of building for space and earth.

All spacecraft flown up until now have been of an exoskeletal** type—i.e., its hard outer shell acts both as a pressure container and as its main channel for structural loading.  This includes the rest of Alpha, which is currently under construction in Low Earth Orbit  (LOE) at about 250 miles above the Earth. 

By contrast, TransHab is the first endoskeletal** space habitat, consisting of a dual system: a light, reconfigurable central structure and a deployable pressure shell.

The shell is so resilient because it is made of several layers, each with its own specific purpose.
Principal among these is the restraint layer, which is interwoven to distribute tremendous loads evenly and efficiently around its torus**, much in the same way as the reeds in a round basket are woven to spread weight and give the basket strength.  Each strap is made of an aramid-fiber** material which has a very high strength-to-weight ratio and great impact resistance, and is often used today in the making of bullet-proof vests.  Woven together into the vehicle’s main shell, these straps when inflated form a system which is capable of withstanding up to 4 atmospheres of pressure differential (over 54psi) between interior and exterior. 

Inside the restraint layer, multiple bladders of heavy, flexible plastic are mounted to hold in the air.  Although only one bladder is necessary to do the job, the requirements for safety in spacecraft design are so high that TransHab’s designers put three bladder layers to protect the vehicle in case one of them failed.  On the outside of the restraint layer, a  shield of impact-resistant layers separated by open-cell foam is mounted to defend TransHab against tiny meteor-like particles which are often encountered in space, traveling at  velocities up to seven kilometers per second.  The outermost layer of the shell is made of a glass fiber cloth which resists abrasion by charged particles in the Earth’s ionosphere**

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