Larger modules are also not always more mass efficient, despite them naturally having the advantage (for not needing docking/berthing/assembly provisions).
Unless you plan to commit to on-orbit construction, with "superlifts" as the individual segments. There are projects that would require even multiple launches of superheavy launchers.
Though I would be more concerned about complexity
increase than mass increase, a stronger structure in a larger module (for example) is not as expensive as a set of thrusters, batteries/solar panels, an automated docking system, and the actual docking mechanisms and hatches themselves. Now that might be more than offset by the economic advantages of multiple smaller launches, but it still makes me uneasy, especially considering that after construction, it is just parasitic.
The first three could be made redundant by either a space tug (i.e. parom) or some sort of orbital manuvering collar, that is attached to the payload on the launch vehicle, guides it to the construction site, and then deorbits after it's use is complete. I like the first more because it makes more economic sense, but I like the second more because it allows faster delivery and less chance for accidents. But I suppose the automatic docking system would be better at handling gravity-gradient torque induced rotation than an inexperienced orbinaut.
and if a module breaks a smaller one is easier repaired or replaced (by better interface definitions) than a large one.
I would imagine that it would depend on the circumstance. It wouldn't do much good to try and replace Unity or Harmony, or Destiny, because too much of the station structure surrounds them. Whereas replacing Columbus or Pirs would be (relatively) easy.
Smaller modules allow you to better ride out failure in general anyway, if you have a loss of pressure. With three Skylabs you basically have the same pressurised volume as the ISS, but if one loses pressure, you loose a whole lot more volume. The only way to prevent that is to have internal pressure bulkheads, which adds mass and would increase the internal volume/mass ratio, negating any potential mass saving from a group of smaller modules.
The problem is just: If you can assemble an ISS in three launches,you have a launcher that is only needed three times for such a project and then just consumes a lot of money for idling around. A medium lift vehicle, or even a heavy medium lift vehicle, can be sold to other customers or better used in other programs.
Unless you have a market that is better suited to such a large vehicle. Of course we don't have that now, and we won't have it for quite some time, but I see no reason why it is impossible.
I actually did some research into launch economics a few days ago. By looking at the number of launches in 2010 of the Proton (11 launches), Delta IV heavy (1 launch), Ariane 5 (6 launches) and STS (3 launches), I came up with a figure of 21 launches in total, and 450 tons launched into orbit (created by adding together the maximum payloads of every vehicle). This is an average of 21.4 tons per vehicle.
To launch Saturn V 21 times a year would require a yearly up-mass of 2500 tons, to launch Ares V 21 times a year would require a yearly up-mass of 3950 tons, and to launch Sea Dragon 21 times a year would require a yearly up-mass of 11 550 tons. Whatever on Earth (or in this case, in space) those payloads would be, I have no clue.
Now, this is a very simplistic calculation, and it assumes a lot, because I never got bothered actually researching the real payload masses and figuring out what the real
mass launched into space last year was, and I'm also discounting the fact that more up-mass on more launches is more economically attractive.
I also noticed how many payloads were destined for GEO, or other high orbits (such as for GPS satellites). The fact is that our current launch market doesn't really resemble that for a large manned spaceflight program at all. Hopefully that'll change over the coming years, with more commercial interest in space and the eventual- and much fabled- return to BEO operations.
Many people are just, in their expectations, stuck in the 1950s, when big was beautiful and EVA maintenance and assembly appeared unrealistic.
B...but... big is always beautiful, what a real space program needs is a big manly rocket, that can get the masses inspired and that every 8 year old boy can own a model of. Preferably something like Sea Dragon, so they can launch even the largest payloads at ease, and also kill thousands of hapless fish. :shifty:
In all seriousness though, early science fiction
had plenty of examples of space construction... Von Braun's vision had the pointless hamster wheel space station, and the absurdly gigantic moon ships, and 2001 had both an under-construction space station as well as moon landers and interplanetary spacecraft that were undoubtedly constructed- at least in part- in space.
A warp drive would be much better. To mars in a few seconds. Just think about the possibilities and how much money we could save if we would have a warp drive ready.
Fat chance. You'll save months of travel time, but all that negative matter comes with a hefty price tag.
Let's just say that the mass of the warp bubble will not be the only number in the negative... :lol: