NASA Confusion About What "Inflatable" Means
Keith’s update: NASA held a press conference on CRS-8 SpaceX cargo flight. Jason Crusan was talking about the Bigelow Module that is being flown up to the ISS. Don’t call it “inflatable”. Call it “expandable”. This strange insistence by Crusan et al at NASA with regard to BEAM not being an “inflatable” module but rather being an “expandable” module instead is weird since it can only “expand” if it is “inflated” and it is a module that is capable of being inflated ergo it is an “inflatable” module. Then again “NASA” = “Never A Straight Answer”.
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We’re launching an expandable habitat to @Space_Station on @SpaceX #Dragon Friday. See why: https://t.co/OwFFoEx19w pic.twitter.com/A9xRCk96xE
— NASA (@NASA) April 5, 2016
I feel left in the dark about what’s going on. Usually you you also post other people’s twitter posts or link to an article.
At least they did not call it an “inflatable bounce house for the international space station” like our local Fox morning news guy did. Worst thing about that statement was that he’s the meteorologist. Usually they know a little about science and technology.
It is what it is. Not strictly “inflatable” like a balloon since it has rigid internal strucure, but the external pressure hull is flexible and does expand when pressurized with air.
the internal structure supports it during launch but has no function after deployment
WRONG. That internal structure is rigidly attached to the end bulkhead structures, which in turn attach to the docking port and the whole structure holds the module to the ISS. The outer shell which is expanded/inflated (take your pick) does not react forces from the ISS (nor could it, it would come apart). The internal structure also gives equipment a mounting location and gives astronauts handholds to move about in the module.
This does not sound right at all. Take the case of an aluminum soda can. When it’s full of soda (pressurized with carbonated beverage) it’s quite strong. A 200 pound person can easily balance on top of a sealed can of soda. Now open that same can and it becomes far less strong since the walls of the can are very easy to buckle.
In fact, an inflatable/expandable structure like BEAM is *very* resistant to buckling when pressurized at 14.7 psi (sea level air pressure).
The expandable outer layers of a Transhab-design-based module are not designed to react on-orbit loads from the ISS or anything to which they are docked. That is reality. The outer layers may be able to react some of them just due to coincidence (but they won’t, because the module reacts all external forces from the docking connection through the internal truss). IMHO, it would be unknown at what load the outer layers would fail, because that was never an intended design feature; and would be incredibly hard to model I would imagine(familiar with trying to model elastic structures…it’s HARD). Of course, you’re being a good engineer to want to see numbers; but I don’t believe they exist. You might pore through publicly available Transhab design documents and find something.
Of course it wasn’t “designed” to handle those loads, but the fact remains that a (roughly) spherical shape that large which is pressurized to 14.7 psi *could* take quite a bit of force before failing. Just how much would depend on how much of a factor of safety was designed into the original structure and how much of that you’re comfortable “dipping into”.
BEAM is a far smaller module than a BA-330, but I’m guessing that it was built using materials and techniques planned to be used for the BA-330. If this is the case, there may be a huge factor of safety to play with.
TransHab burst at twice the operational load.
I was just going off of what Bigellow guys have on their website
It’s a silly and completely arbitrary distinction made by Bigelow (and apparently NASA is trying to not offend them by using the wrong term. Same as they do with Musk’s
bargeship.)“Inflatable” or “expandable” could both describe a stretching skin, which is the ambiguity that Bigelow is so weird about, neither is more or less than the other. Balloons inflate and in doing so, they expand. There’s simply no word in English that differentiates between inflating a stretchy-skin balloon and inflating a non-stretchy football or airbed.
(My personal pedantry wants me to say that “expandable” is more ambiguous, because the Bigelow module is definitely being inflated with air. Therefore the latter makes “inflatable” a more complete description of the act. After all, the entire ISS is “expandable”, since it’s being expanded with a new module, BEAM. While BEAM can’t be further expanded after being inflated, since it has no docking or attachment points. But again, this is a completely arbitrary emphasis on a specific interpretation of the meaning of the two words.)
It is unfortunately necessary to form the discussion around the technology since people with no tech knowledge (like Munkie below) can’t understand the tech, and thus it is SMART to head off misunderstandings about the tech by describing it in a way that emphasizes the strengths of the tech. Because the end user will probably never understand that the Transhab tech is safer than normal AL can modules with the very high-tech protective layers that stop micrometeorites.
The reason why they want to avoid the word ‘inflatable’ has previously explained – it has the wrong connotation about being easy to burst or break, even due to small puncture.
They are paranoid about the word so nobody reading a popular science article would take it for a space balloon.
NASA’s paranoia is couched in a not-too far fetched belief that most taxpayers are non-tech savvy and/or have a lower-than-genius-level IQ, who (thanks to the media) think this is a Giga-$ space-balloon ready to “pop”… to be followed by much wailing and gnashing of teeth by a just as un-savvy Congress.
NASA could give a simple and really dumbed down clarification that the shell of the module is extremely thick (a BEAM cutaway looks to be ~6″, and I’ve heard BA330 may be 1.5′) and it’s made out of layers & layers of bullet-proof Kevlar. I realize that’s not uber-accurate to make engineers and techno-geeks happy but the purpose is to win over Joey Janitor and his tax-paying/voting buddies… the true audience of NASA’s paranoia.
That is an overly simplistic explanation of who is concerned about this design. They actually found a large number of people had this initial reaction when they heard the word inflatable. It isn’t a big deal or inaccurate to call it expandable, and honestly that word fits the technology better when giving the benefits of folding a small package that can expand to give a crew a large amount of space once it is in place.
If you know people are going to react unfavorably to a word why make things harder. Especially if you have to sell that word to a large number of people who are going to have a negative reaction.
What causes the structure to expand? Is it a mechanical mechanism or is it the air pressure being pumped in. It the air pressure is causing it to expand, than inflatable is probably the best description. If it is expanding through some other mechanism and the air is just filling the new space, than expandable is probably better.
This seems like an appropriate place to give credit to the REAL designers of the BEAM tech. Gary Spexarth and Jason Raboin and the Transhab team at NASA. Their original design is finally coming to fruition and as much as BA would like to take credit for their work (I’ve seen RB actually put his name down as ‘inventor’ and that must have bent some people the wrong way); it is still the basic tech developed in the 90s. Also credit is due to Thin Red Line who developed much of the expandable outer shell tech.