Multiple-Vehicles Scenario
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Economics and Efficiency of SSTO to the Moon

The idea of sending an SSTO to the moon is reduce the program cost. Two vehicles would be far more efficient from an engineering standpoint. Three would be even better. Five, with space stations in Earth orbit and lunar orbit, would almost be the epitome of engineering efficiency, but we could do even better with multi-stage rockets at each end with fly-back boosters; perhaps 10 vehicles total.

Now think about the development and operating costs. That leads us to the SSTO, which from an engineering standpoint is horrendously inefficient. The same approach leads us to landing an atmospheric vehicle on the moon, complete with wings and heat shields and ghu knows what else we don't need on the moon.

The most energy-efficient intercontinental passenger transport aircraft would be a superduper 747 that never lands, maintained and refueled in flight. Launching a Boeing 747 isn't quite as inefficient as launching a rocket, but it's close; we'd be far better off accelerating and lifting all that mass only one time. We could even leave off the landing gear and all those heavy flaps, too. We'd get passengers there by flying them up in smaller aircraft that shuttle between the big airplane and the airport. Conceivably, this could be done; but imagine the cost those vehicles and their supporting systems. Imagine the problems of transferring passengers and baggage from one airplane to the other.

Back to technical thoughts. We can worry about the weight of the heat shield when we have some real numbers to deal with. A large team of Japanese companies are working on a vehicle very similar to the one envisioned, and we can assume they've done their homework. Before we abandon the initial concept, let's crank some numbers and find out out where we are. Once that is done, we can worry about refining the concept.

But always, always, always close the loop on cost. It doesn't matter if we burn 1,000 times as much oxygen as we could with the best engineering approach. Liquid oxygen is cheap; incredibly cheap to buy today (less than half the cost of gasoline, certified for hospital use), and mind-bogglingly cheap if make and store it ourselves. The only problem with Earth's oxygen is that it's inconveniently located at the bottom of a gravity well. Tanks and sheet metal are cheap, too. So the size of the vehicle does not drive cost nearly as much as you'd think. The number of vehicles and the number of unique parts is by far the biggest factor.

The size of vehicle, however, is why we picked a nice, relatively isolated place like Groote Eylandt, Australia, as a launch site. A floating dry-dock launch facility sounds to me like the least expensive way to get these things into orbit. After the flight they land back in the water and we move the dry-dock under them for the next launch.

Having put a few years of thought into this one, we still haven't found a less costly way of getting lots of passengers to the moon and back, and by putting it all in one vehicle, we can do it in comfort and style.

Why don't we do something like this for the reference mission?

The mission objectives and the basic assumptions are different. For the initial flights, we want to land a heavy exploration base, as heavy as we can get it, on the moon and leave it there. Each subsequent development flight will be different, so at first we can't take advantage of the economies of scale in producing our spacecraft. We'll get way ahead using off-the-shelf modular components like the SPACEHAB module, but there will be some new design work for each mission.

With the commercial SSTO, we want to carry as many passengers to the moon and bring them back, do it repeatedly, and offer each passenger the same level of comfort. Most important, we assume we've developed the infrastructure on the moon so we can refuel the SSTO in Earth orbit without having to make 25 more flights from Earth just to fill the tanks. That lunar oxygen business is the leveraging factor that makes the cost-effective transportation system work.

Once the lunar community is ready to get into heavy manufacturing, then we can start thinking about spacecraft that stay on orbit and huge Earth-orbiting hotels.

We've heard the argument many times before that we should first develop the Earth-orbit facilities, and then worry about going on the moon. But that's doing it backwards! We need to go to the mines and dig out the metal first, and the least expensive way to get that material to Earth orbit is to start on the moon.

Multiple-Vehicles Scenario

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