This item has been deliberately left for last, because, in the opinion of the author (who has several engineering degrees, was a project manager at a major space firm, and considers himself first and foremost a technologist), it is of the least importance. While the conventional wisdom is that technology is the show stopper for low-cost routine space transportation and a viable space tourism business (as exemplified by NASAs ongoing promotion of such technology demonstration programs as X-33, X34, et. al.), a serious analysis of the situation reveals that the current technology level is the least of the problems confronting space tourism entrepreneurs.
Accordingly, specific technologies needed to reduce the costs will not be addressed here, except to note that all of them have second or third order effects on cost, relative to the much more fundamental driver of economies of scale. Even a poorly-designed, low-technology vehicle, if flown at high enough rates, will be less costly to operate than any space transportation system operating today. Conversely, the best-designed space transportation system will still have astronomical costs if only flown a few times a year, e.g., (not to imply that its design couldnt have been improved) the Space Shuttle.
There are many ways of building high-flight-rate vehicles, and many technical solutions to solving the design requirements, but the most difficult problem remains not in design and implementation, but in raising needed investment funds. It is hoped that this paper, and similar ones, will help in reducing this more fundamental barrier.