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My driving goals are these: Payload delievery, landing on a runway, turn around. We need to be able to come as close to commercial aircraft parameters as is humanly possible. The day we can take off, deliver to space, return, reload, take off and deliver to space again, using the same craft in less than twelve hours will be the day space becomes commonplace. At that point, you won't be able to close the door ever again. Within eighteen months we will have hundreds of people in space. Within five years we'll have thousands. Within a decade we'll have tens of thousands in space.

A cheap way, relatively cheap, is piggyback launch. An ordinary jetliner for first stage, the second stage the orbiter and return vehicle that lands on the same runway the jetliner took off from. The jetliner can also launch dumb cargo orbiters when it isn't necessary to have staff accompany the tonnage.

The manned orbiter needn't be huge like the Space Shuttle. It would carry just personnel. Their luggage would be on the freighters, probably launched first.

The Shuttle system lifts 250,000 lb into orbit -- it's just that 200,000 lb of it is Shuttle.

An SSTO won't alter that equation very much -- you still have to launch and then land an aircraft. If anything, an SSTO carrying capacity will be far less than a Shuttle due to mass fraction limitations.

The real issue is getting stuff into space cheaply and easily. The Shuttle is expensive primarily because of how much manpower is required to prepare it for launch. Expendable boosters tend to cost far less per launch, but they're also far less flexible.

The main question for an SSTO is whether it can reliably turn around in 12 hours to perform the same mission. As with the Shuttle, the major issues affecting rapid turnaround are maintenance and durability of the vehicle structure and thermal protection systems; and the reliability of the propulsion systems.

If one or both of these turn out to be finicky -- as they likely will be due to their extreme performance requirements -- then an SSTO will not provide rapid turnaround.

In addition, integration of payloads with the vehicle tends also to be time-consuming.