Inflatable Habitats

Although inflatable Habitats have been mentioned in studies and press releases, precious little detailed data have been provided.

A published article in 1998 briefly described JSC efforts in inflatable Habitats:77

"The design is compiled of a metallic central core with a flexible composite outer shell that is cylindrical and has toroidal ends. The inflatable structure is packaged around the central core to decrease its volume for launch, then inflated, on-orbit, to its approximate 7.6m diameter by 9.1m length (Figure 4.15).

... The inflatable structure is a series of material layers that perform numerous functions including: gas retention, structural restraint, micrometeoroid/orbital debris impact protection, thermal protection, and radiation protection. Gas retention is achieved by a doubly redundant bladder assembly. Structural

74 SICSA selected a crew of eight rather than six because of the diversity of roles and skills that they conjectured would be required.

75 It is noteworthy that in their reports on ECLSS, NASA does not provide the total amount of resources used, but, rather, only the estimated mass of the ECLSS system. The SICSA report was the only place in the literature where this figure was cited.

76 Use of a figure of 90% recycling for water is very conservative, as various DRMs have typically used estimates of —98%.

77 Inflatable Composite Habitat Structures for Lunar and Mars Exploration, D. Cadogan, J. Stein, and M. Grahne, IAA-98-IAA.13.2.04.

Figure 4.15. 30-foot diameter TransHab Test Unit. [Inflatable Composite Habitat Structures for Lunar and Mars Exploration, D. Cadogan, J. Stein, and M. Grahne, IAA-98-IAA.13.2.04, 1998.]

restraint is achieved by a series of Kevlar webbings that are interwoven and indexed to one another to form a shell. The webbings are terminated to pins that are mounted to the ends of the metallic core structure. The webbings are sized to withstand 101 kPa internal pressure loads with a factor of safety of 4 over ultimate. This yields a structure that must withstand approximately 2,232 kg/cm maximum stress in the hoop direction and 893 kg/cm stress in the longitudinal direction. Other materials, such as Vectran, are also being considered for the webbings in the later configurations. Micrometeoroid and orbital debris (MMOD) impact protection is accomplished by a series of woven 1.5 mm thick Nextel layers separated by foam spacers to create a multi-hull structure. This structure was tested for hypervelocity particle impact by JSC and found to provide greater protection than the current Space Station design. Testing revealed that 1.8 cm particles traveling at 7 km/sec would not penetrate the structure. This provided an improvement over the current limit of 1.3 cm particles at 7 km/sec for the Space Station in a roughly equivalent mass system. The Nextel layers were coated with polyethylene to enhance their stability. The polyethylene also provides a significant amount of radiation protection. Thermal protection is accomplished by a series of metallized films on the exterior of the assembly that reflect radiation."

An Internet article on the JSC inflatable TransHab appeared in 2000 based on an interview with George Parma of JSC. It said:

"TransHab provides greater protection against space debris than metal ... The skin is over a foot thick and made of almost 24 layers. Starting from the outside, tightly woven white Beta cloth protects TransHab from erosion from the 'sandblast' effect of atomic oxygen. Insulation is provided by blankets and Mylar. Next comes debris protection, consisting of multiple layers of Nextel, between layers of open cell foam. Any particle aimed at the walls would 'shatter' as it hits, causing it to lose energy as it penetrates deeper into the layers. The shell also contains a 'restraint layer' of Kevlar, that holds the shape of the module, with air held in pressure bladders made of an air-tight material layered with Kevlar. The inside wall is made of fireproof Nomex cloth, that protects the bladders from scuffs or scratches. Even if space debris did manage to penetrate the TransHab wall, it's interesting to note that the module would not 'burst' like a balloon. It would leak, but not pop. The reason for this is that the pressure difference between the interior of TransHab and space is only about 10 lbs per square inch.

A number of tests have been run on TransHab to investigate its durability. In 1998, a test module with a diameter of 23 feet was inflated in the huge pool used by astronauts for EVA training at the Neutral Buoyancy Laboratory at JSC. The shell was found to hold pressure four times as great as the Earth's atmosphere at sea level. Later that year, the full-scale module, with a diameter of 27 feet, was inflated in JSC's vacuum chamber, to simulate the vacuum of space.

The amount of air required to inflate TransHab is 3 times that required for an existing Space Station module. Sufficient supplies will therefore need to be taken up along with the deflated module.

TransHab might serve as a prototype habitation for a Mars mission or the establishment of a lunar base. The only adaptation required for these types of environments would be the addition of some lightweight floors, as both Mars and the Moon are subject to gravity. He feels TransHab could be ideal for taking on a long-duration mission, due to the fact that it can be transported in a compressed state and inflated when it reaches its intended location.''

Details on these tests do not seem to be available to the public. Since year 2000, almost no data or information have been released. Inflatable Habitats may provide great benefits to Mars missions, but the technology does not seem to have evolved past the ''gee whiz'' press release phase.

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