bad_astra - 13/9/2007 9:10 AM
Unless you're building an Oneal colony from Earth Materials (exactly the opposite of how it should be built, anyway), there is no reason, ever, for a Sea Dragon.
How many launches of this kind of vehicle could be needed by one country in one year? One? Maybe one every 2? You still need standing army to maintain it, it's prep facilities, etc during the off time so you really get no savings from having such a monster. And if you LOSE a Sea Dragon, how many years are you unable to go to space at all because you bet the farm on one LV and killed off the rest of the competition?
What is far more reasonable and robust is a diverse lv's with high flight rates.
I agree. Keep in mind in every mode of transportation, we've seen progressions to larger and larger vehicles just as is occuring in launch vehicles now. Sometimes as in the case of ships, this process has repeated itself many times as new technologies are developed. But there's always a point past which growing larger becomes uneconomical. For example, rather than build larger train engines, multiple smaller engines are used to pull the larger loads. Planes and ships could technically get a lot bigger, but the infrastructure isn't able to handle them.
As I see it, the Sea Dragon is too big for us now. There's no mission that requires it nor can we guarantee a high enough flight rate (a high flight rate being the most important way to lower launch costs) to justify its existence. And as bad astra notes, there are other disadvantages from the lack of diversity.
An area of squandered opportunity is devising techniques that exploit the relatively cheap launch vehicles with smaller payloads but high launch rates and good cost per kilogram. That means orbital assembly and construction techniques, refueling, perhaps even finer grained manufacture techniques. It may be impractical or too unreliable to launch everything via the restricted spaces of these small rockets and later assemble them into larger structures.
But I dislike the impulse to assume that one can make a heavy launch vehicle and then design the mission around that. There are many examples of specialized transportation systems (for example, city subways; airport walkways, shuttles, and light rail; ore conveyance systems in mines, military transportation), but these invaribly are intended to have a lot of traffic. In current heavy LV plans, there's no high volume need.