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Currently there seem to be two efforts under way:

The latter source (an article in the Popular Mechanics by Anatoly Zak) intimates that structural creep is a major engineering hurdle.

However, I'm not convinced it's the only one.

What are the engineering problems that we have to watch out for while building and deploying inflatable structures in LEO and beyond?

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Problem 1: Material Strength

Strong and Flexible generally means heavy. The material has to be strong enough to handle the stresses of both the internal pressure when inflated, but also the localized pressures during inflation.

Problem 2: Inflation Sequencing

As the Russians discovered, inflation sequencing can go awry. This can result in a variety of issues, from wrapping around the launching craft, to binding against itself into the wrong shape.

Problem 2.1: Vacuum effects on materials

Many projects tested in pressure react differently in the lack of pressure. It must be accounted for. It affects lubricants, expanding pressure-driven components, and a variety of other factors.

Problem 2.2: Microgravity effects on containers

Microgravity can allow some aspects to deform in ways that can be anticipated, but in gravity tend to be overlooked.

Problem 3: Utilization Based Requirements

At present, all such proposals are either for fuel depots or for habitat modules. The fuel depot proposals are for planetary use, either on Luna or Mars, and so have related considerations, but are not "inflatable space modules", and thus beyond the question

Which leaves habitation modules.

Problem 3.1: Radiation Resistance

Modules must provide protection for occupants from 2 forms of radiation, both high energy particles (solar wind) and electromagnetic radiation (especially US, Gamma, and X). Spacecraft at present do not provide adequate protection from Gamma, X, and particulate radiation, so lifetime space travel limits are imposed by NASA. The particulates are supposedly better stopped by liquids rather than solids, but shipping that much liquid up isn't cheap. It is, however, a 1-time deal for a long-term module.

Problem 3.2: Puncture Resistance

The resistance to microbody interactions, specifically, being hit by mirco-asteroidal bodies and space-junk, requires a specific set of engineering challenges. Note that space-suits share this requirement, and extensive NASA documentation is available for them.

Problem 3.3: Internal Fittings

An inflatable structure still may require additional fittings inside. A habitation module will, at a minimum, require air circulation fittings, while a science lab will require workspaces. How to attach and configure these is a significant issue.

Problem 3.4: Human Psychological Needs

Humans are not well adapted to enclosed spaces. This is part of the reason for inflatable modules; more open spaces are expected to be helpful in long duration spaceflight. Also, view-ports, privacy enclosures, designated work spaces, and similar considerations require engineering consideration.

Problem 4: Overall Launch Weight

The proposed inflatable modules are intended to reduce the launch weight per unit volume of habitation modules. Still, the limit on size is a function of weight lofted, and individual launchers still have relatively limited payloads.

Problem 5: Overall Cost

While not strictly an engineering consideration, no engineer can work on a project without considering the costs. All projects have budgets, and Engineers who can't keep designs within them don't see their work built.

Problem 6: Inflation & Assembly Crew Requirements

Spaceflights have very limited crews. If the inflation and assembly require 5 men, then it's going to be impractical for a soyuz launch to inflate, but the ISS could do so at a changeover.

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  • $\begingroup$ Would using foam to inflate be helpful (and sufficiently beneficial to compensate for greater mass)? $\endgroup$ – Paul A. Clayton Aug 10 '13 at 3:04
  • $\begingroup$ @PaulA.Clayton I honestly don't know. $\endgroup$ – aramis Aug 10 '13 at 3:14
  • $\begingroup$ @PaulA.Clayton - not really, what you are planning to do with foam next is pretty unclear. $\endgroup$ – Deer Hunter Aug 10 '13 at 9:41
  • $\begingroup$ @DeerHunter The thought was that the foam would solidify (a bit like the foam insulation that is sprayed on for houses) and be part of the structure. (It was just a wild thought. If I could generate a million, a thousand might be useful but obvious to one skilled in the art and one might be useful and not entirely obvious.) $\endgroup$ – Paul A. Clayton Aug 10 '13 at 12:01
  • $\begingroup$ Thinking about most of the insulfoam applications, stuff's curing process vents fumes that are semi-toxic. (If you watch, the shuttle's ET's foam layer is applied by guys in respirators.) And application in vacuum would probably be unpredictable, adding to the inflation and assembly issues to consider... but use of foam would fall into the above considerations. $\endgroup$ – aramis Aug 10 '13 at 17:13
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It can burst as did one of the earlier, 1991 attempts to produce a large inflatable object. That has happened because the envelope hitched an antenna. during deployment.

enter image description here enter image description here enter image description here

Or as did the IRT -- an even earlier attempt (1984). Because "the lanyards pulled loose from the orbiter instead of pulling out of the canister. The nitrogen inflation cartridge did fire as scheduled, and the balloon burst as it began to inflate inside its canister."

enter image description here

Also it can wrap around your spacecraft during inflation phase. See the picture number three there. Note the Progress space craft completely covered by the thin envelope.

enter image description here

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