At present the space station is very vague as to its purpose. Nobody seems to be sure why it is there. The orientation of NASA is to explore the possibilities of space exploration both by robots and by humans. A severe limitation of this purpose is the expense of getting the vehicles into Earth orbit before they are sent onto their longer journeys and the amount of energy expended to get the structures free of the gravity well on the Earth's surface. If there were a larger pressurized "hanger" constructed as a complement to the nucleus of the now constructed space station within which space vehicles could be assembled under zero gravity, more elaborate exploration vehicles could be slowly constructed and tested under actual space conditions. The "hanger" itself could be,in effect, a huge balloon which would be cheap ánd easy to put together with lightweight materials. If it happens to be pierced by space rubble or meteors, the leakage would be slow enough for patches to be quickly placed to remedy the damage and repressurization to take place. The environment would also provide an experimental volume for significant progress in actual space habitats to be placed at L5 point for further space advances.
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This hanger would significantly increase the drag of the station and thus would require the station to be boosting its orbit much more frequently than now (which I think is twice a year). It would also require a significant increase in the amount of air and water shipped up to the station.
How are you going to get your vehicles in and out of this balloon hanger? Why do you even need a hanger to build spacecraft when it can be done by astronauts in space suits?
Drag? In the vacuum of space?Yes, it would increase the necessity for air and water and probably other materials as well. But the experience of creating a working environment in space would be well worth it. Working in space suits is very difficult business and can be done in only short and uncomfortable spurts.When the assembled vehicles are completed, the balloon can be collapsed and removed or an air-lock system can be easily devised for smaller units. Whatever supplementary boosting might be required would be well worth the advantage of assembling large mechanisms in orbit.
One further thought on the logistics of space efforts. It is, currently, extremely expensive and insecure to send anything into space. Although the rocket systems have been improved over the years, there are still frequent failures where horrendously expensive satellites and probes are lost on the initial launch. Also the space machines must be designed to open up into their workable configurations from the shapes necessary to conform to the aerodynamic shape of the launch rocket. All of this requires sophisticated mechanisms such as joints and motors and power supplies which add weight and uncertainty and expense to the machines which would be eliminated in space assembly wherein parts could be shipped up and the entire effort would not be subject to the failure of a single component.And the completed unit could be much lighter in construction as it would not have to endure the rigors of an Earth launch. Beyond this, the entire unit could be thoroughly tested in space before it is sent on its way. And the space rocket to carry it to its destination could be an ion engine which can bestow gentler acceleration and higher ultimate velocities.
Low Earth Orbit is not quite the vacuum of space. The atmosphere doesn't exactly stop, but fades out. In LEO there is actually quite a lot of atmosphere and I think that I remember reading that without a boost the station would re-enter in something like 8 months (not sure on that - I'll look it up) a la Skylab. This bubble would probably triple the drag profile and and require a boost every two months instead of every six.
I agree that there are many merits of construction in space and that this is how we should build the next set of moon/Mars vehicles. I just don't think the Space Hanger's advantage in assembly time will make up for the disadvantages I've noted. I haven't done the math, and I doubt you have either so really we're just arguing that the cost of x (building/maintaining the hanger) is or isn't more than y (added construction costs of building in suits as opposed to in a hanger) and unless we come up with some #s, we're just talking out of our respective a$$s.
Whether a balloon hanger with a shirtsleeve environment would be advantageous enough to offset the expense of maintainance is, on my part, as you surmised, a matter of personal conjecture. But the important thought revision of the nature of a space station's basic use seems to be a point of agreement on both our parts. It seems to me that a space station is essentially a gateway to and from deeper space and instead of the latest proposed Moon base (which, in the very long run may be useful in other ways) for Mars launch it might be more economical to construct a duplicate space station that would permit long habitation and move it at an easy pace into Mars orbit uninhabited and then dispatch humans to it once it was in place to more comfortably initiate Mars exploration with a nearby haven in case of trouble.
1 big problem: the station is already vulnerable to the myriad bits of space debris (scrap bits, spanners, waste) whizzing around in orbit. 1 word: POP!
I read about proposals of this same idea back in the late 80's or early 90's and I've always thought it was a great idea. The beauty is that you could build a spacestation on the ground that could be collapsed to fit inside a launch vehicle (like the Space Shuttle) that, when deployed, is larger than the vehicle it came out of!
The bag material would be similar to a spacesuit. It would be made of multiple layers of advanced modern materials, including kevlar and carbon fiber. It would be at least as resistant to punctures as a ridged spacecraft, maybe more. It would be able to flex to absorb the energy of impacts in a similar fashion to soft body-armor. If it was punctured, it certainly wouldn't "pop" like a rubber balloon, as it would be extremely tear resistant. The layers of material might even provide a degree of self-sealing.
The interior would provide a shirt-sleeve working environment that would enable the workers to work many times faster than in spacesuits. It would also be safer and it would eliminate the problem of tools or hardware drifting off into space.
To remove the completed project, you could remove the air and literally unzip the bag. Unzipping could also be used to bring large items into the bag. It could use a heavy-duty version of a regular zipper. When closed, a strip of plastic adhesive tape could be applied over the zipper on the inside of the bag to prevent any leakage. The same tape could be used to patch any holes created by impacts.
When people first envisioned space stations (Clarke, for instance), the purpose was clearly to build spaceships in orbit to go farther out. Watch Sagan's Cosmos.
So I think this hanger idea is great, but I don't need it to be a bubble--I'd rather see something more permanent. A door, not a zipper. And a fully stocked machine shop, sheet metal fab/welding facility and equipment to autoclave or build composites too.
Also, the cost of getting materials to space would seem to indicate that anything metal already floating around without a use would be very lucrative for 'trash collecting.' We could even melt-down and re-alloy scrap in orbit. I expect you could build trash-collecting ships that operate remotely and magnetically, too. These have been a staple of Sci-Fi writing--this is not a new idea, are these ideas not being looked at?
This would decrease the danger from 'space junk' and turn it into useful stuff. I think each ship should have radar that will see incoming space-junk and if it's slow enough, intercept it--use it, not be damaged by it. Even meteors have metal in them.
Also, I think we should be keeping any more metal from falling back to earth--it's such a waste to boost it, then let if fall. Skylab, the Shuttle-center tanks, etc. Keep them up there for the materials.
Hrench, what difference would it really make using an inflatable soft structure verses a rigid structure? A "bubble" could be just as permanent as a rigid structure. It could do all of the things you listed. It can be made heat resistant if necessary. There is no advantage of a "door" verses a zipper, which acts as a door anyway. The zipper could run in a horseshoe shaped curve which would effectively form a door. You could even put a motor on the zipper to open and close it automatically if desired.
If you really need a rigid structure, you can use the soft structure as a place to build it.