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I have read about an ISS module that is under development (called TransHab) that is inflatable. It is claimed that the new module will have much more volume than a conventional module, better protection against radiation, and better protection against micrometeoroids, all while being smaller and lighter to launch. I have read about plans that use inflatable habitats on mars, but has anyone ever considered making the interplanetary spacecraft itself inflatable? If it is an interplanetary craft (not used in atmospheric flight), and it uses a low thrust but high ISP propulsion, I do not see anything that would prevent an inflatable spacecraft from working. All of the advantages of inflatable spacecraft would be even more useful for an interplanetary craft than for a space station, so it would seem that inflatable is the way to go. The only disadvantage I have been able to find about inflatable spacecraft is that they are more expensive to produce. However, I think much of the expense comes from one-time development costs, so they should become cheaper as more experience is gained with inflatable technology.
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Euler: Nice image the inflatable habitat idea conjures up. A large-volume chamber in it might enclose a suspended centrifudge for sleeping. Of course, if it ever "got away" the image rapidly deteriorates, literally!. "Flying" sports would be possible for recreation, and room available for microgravity hydroponics to produce good sized plants. Privacy cubicals could be changed in size according to pairing-up needs, and saunas, washrooms, etc. would become feasible. It might even be the place, once established in LMO, that the New Martians will launch-up to, for a little rest and recreation, between working stints down there in the dust and red dirt on the surface. Of course, it would have to be crewed in rotation, for maintenance and housekeeping (like the ISS is currently) and orbital surveillance to back-up those on the surface.
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Inflatables do have a lot of advantages. ILS Dover developed TransHAB for NASA, and they would like to use it for Mars. I also suggested an inflatable. The only disadvantage (other than development cost) is that it can't endure the heat of atmospheric entry. This is why I suggested leaving the interplanetary spacecraft in Mars orbit, then dropping a separate surface habitat on Mars. The surface habitat would enter Mars atmosphere deflated with just a capsule large enough for a seat for each astronaut. The surface habitat itself would be inflated once it is on the surface. That eliminates the need for a micrometeor shield for the surface habitat; Mars has an atmosphere so micrometeors can't reach the surface. The surface has to deal with dust storms, and heating/cooling are different than space. I would then replace the Earth Return Vehicle with a Mars Ascent Vehicle that would just have a seat for each astronaut and place to store sample containers. The cabin of the MAV would not even have to be pressurized, the astronauts could ride in their spacesuits. The MAV would dock with the orbiting interplanetary habitat, then the MAV would push the habitat into trans-Earth trajectory. This permits the in-situ propellant production for the return trip without wasting fuel to lift the habitat off the Mars surface. You also don't need a redundant food supply: if an abort is necessary on arrival at Mars the interplanetary habitat would loop around Mars to come back to Earth. So that habitat requires food for the trip to Mars and back. A normal mission would use the same habitat for the return from Mars orbit, so the same food and life support is used for the return trip.
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Inflatables are definitely the way to go, especially if we are stuck with small launch vehicles that can only put up items 4-5 meters in diameter. The only problem to remember is that once the inflatable is set up, you can't shrink it back down to the original smaller diameter.
Heat shields will be needed for aerobraking, but an umbrella-like device could fit in a small diameter and open up after deployment, so there is probably a way to get a heat shield onto a large inflatable. If nothing else, the heat shield could consist of bolt-on panels attached in orbit.
The one problem with leaving the earth-return hab in Mars orbit is the danger of something going wrong in 18 months when no one is there to fix it. It could result in an Apollo-13 style disaster. Zubrin's plan has the elegance of putting the return vehicle on the Martian surface where it can be inspected, fixed, and where it can serve as a backup against a disaster on the surface. I suspect it's the better way to go, especially since it has to be accompanied by only 1/18th of the fuel needed for the return flight (the hydrogen). I understand there were several problems with the Russian Salyut when it was umanned that nearly were a disaster. On the other hand, techology will be better by then, and the biggest possible disaster comes from the rocket engines, which will be on the surface anyway. If the return hab could be placed on Phobos, it would not need gyroscopes, just functioning solar panels (or perhaps a small RTG to produce a small amount of continuous radioactive-based power for communication and computers). Of course, getting anything to Phobos and then back to an orbit for flying to Earth takes a delta-vee of at least 0.5 km/sec, more if a plane change is needed.
-- RobS
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