The argument is straightforward and tempting. In terms of energy and complexity, getting into low earth orbit (LEO) should cost on the order of, perhaps, ten times as much as transcontinental jet travel. At present, though, the cost ratio is nearer to a thousand. The Shuttle, billed in the 1970s as a way to dramatically reduce the cost of spaceflight, has turned out instead to cost more per pound of payload than the expendable rockets it was meant to replace.

To call this frustrating is an understatement. The cost of getting into LEO is the great barrier to further space development, whether it be orbital industries, interplanetary missions ... or the ultimate El Dorado of colonization. So long as it costs ten million dollars to put a one-ton payload in orbit, little or none of that is going to happen.

Within what may be called the space movement it is nearly an article of faith that the blame rests immediately on NASA, and more broadly on government. The movement is strongly tinged with libertarianism. Part of the reason is frontier nostalgia, but part is also due to the maddening lack of progress over the last quarter-century in getting launch costs down. To many in the space movement, it is as if space launch were run by the Postal Service.

The analogy is pretty unfair: the post office will deliver your letter, with about a 99 percent success rate, at half the cost of a Snickers bar. I am also more than a bit skeptical of claims that an orbital launcher can be developed at a low cost, by some equivalent of the Wright Brothers (or, in or times, of Steve Jobs) working in a garage. Such claims are commonly justified by arguing that private enterprise can do the job for less than government programs. This is doubtless true much of the time -- for projects that private enterprise will undertake at all -- but seems most unlikely that the development cost could be reduced by orders of magnitude, no matter who was in charge.

It's easy to imagine that if a century ago a government agency, a Gilded Age NASA, had contracted with the railroads to build an airplane, the result would have cost millions of dollars -- the equivalent of billions now -- and had the flight performance of, well, a steam engine. The Wright Brothers' bicycle shop, which seems so quaint today, was in fact a perfect place to invent the airplane: At the turn of the last century, bicycles were the cutting-edge technology for high strength-to-weight vehicles.

Unfortunately, there is at the moment no sign of some equivalent new technology, having the same relationship to conventional space boosters that bicycles did to locomotives. Radical new technologies abound, but not for getting into orbit: All current proposals are at bottom some kind of rocket or rocket-aircraft combination. Some ingenious amateur may yet come up with something entirely new, or at least with a garage-built vehicle capable of putting a small payload into orbit. But for serious space access we need vehicles capable of orbiting payloads on the order of tons -- and the techniques and technology for doing it will almost surely be broadly similar to existing aerospace technology.

If this changes, I'll dine on some virtual crow here, preferably con mole.   But until then we'd best deal with the aerospace industry as it is. And after all, though some amazing high-performance kitplanes are available for well-heeled enthusiasts, no one has yet managed to turn out jetliners at one-tenth of Boeing's costs.

Today it costs the aerospace industry several billion dollars to develop a new jetliner, often having a good deal of new technology, but with performance characteristics broadly similar to existing ones. Even developing a new model of an existing plane costs upwards of a billion dollars. Viewed in that light, development to service of a reusable single-stage-to-orbit (SSTO) space launcher is likely to cost on the order of $10-25 billion -- the higher figure being more likely.

This has a startling and important implication for the cost of getting to orbit. Even if the operating cost (fuel, servicing, etc) were zero, the up-front costs of the program would still have to be paid off -- and this would impose a very considerable cost-to-orbit.

Suppose that a fleet of ten SSTO's were built, each capable of making a flight a week, and with a service life of 20 years. Thus the fleet would have a total capability of some 10,000 flights (10 x 50 x 20). Assuming the $10-25 billion development cost suggested above, the pro-rated cost per flight -- simply to pay off the front end -- comes to $1-2.5 million per flight. This doesn't count profit or interest charges ... and the capital markets won't shell out the money, up front, without expecting a payoff beyond the whoosh of rockets.

Then another tricky factor comes into play. That cost per flight, of $1-2.5 million, depends on enough customers stepping forward to pay for all 10,000 flights. If the system only made, say, 5,000 flights in its service life, the full development cost still has to be charged against them, doubling the pro-rated cost per flight. In commercial space flight, payload is a very literal term.

If each SSTO can carry about four to ten tons into orbit, the cost per ton under these assumptions comes to somewhere between $100,000 and $1 million. Is there enough demand for this many flights, at this cost level? Possibly, maybe even probably, but not certainly. Something could always come along to reduce demand -- for example, fiber optic technology might cut into the market for communications satellites.

(A note for tourists. Given that current airliners carry about four passengers per ton of freight capacity, the passenger cost to orbit by this reckoning could be about $25,000-250,000. However, a passenger-carrying spacecraft would be a good deal more expensive than an unmanned vehicle: the life support system adds costs, as does the higher safety requirement of a commercial passenger carrier. Have your credit cards ready.)

After all these cautions, time for a bit of good news. (You were hoping for some, weren't you?) A modified version of the SSTO could have profitable non-space uses. An SSTO that doesn't quite reach orbit becomes a very fast intercontinental transport -- anywhere to anywhere in about 45 minutes. The cost should be somewhat less than the cost to orbit: more cargo can be carried instead of some fuel, and the vehicle only has to operate in space for a short time.

Apart from possible passenger demand, there may well be a market in ultra-fast express delivery. The cost for a one-pound package might be as low as $50, including the delivery truck at each end. (Though a few hundred dollars is more likely.) Is there a demand for, say, one-hour package express service from London to Los Angeles at these rates? Undoubtedly! Enough demand to support the service? (You can't fly the ship -- at least, not economically -- without something close to a full load) We won't know till someone offers it.

But, oh yes, a small niggling point. All of the above guesstimates dealt only with development cost -- not the operating cost of running the thing: maintaining and servicing the fleet, ground and tracking facilities, hiring and training astronauts and ground crews, and so forth. This won't come free, and could involve a very pretty penny. Today it actually costs more to launch an expendable rocket than it costs to build it. The cost per flight of an SSTO fleet is likely to be comparable to the pro-rated development cost.

All in all, then, building a commercial space system involves uncertainty -- risk -- at both the front end and the back end. At the front end, the development program might cost more and deliver less than anticipated. The first law of development: Everything costs more and takes longer. At the back end, no one can be quite sure what the market will be. Ten billion dollars, or maybe much more, is a tidy sum to hit up the capital markets for, given these kinds of risks.

Transportation has almost always been oddly resistant to purely private initiative: from Roman roads to the transcontinental railroads to the present-day airline industry, transportation has almost always been shot through with overt or hidden public subsidies. It shouldn't be a surprise if space transportation proves no different. The potential is as uncertain as it is enormous; the prospective cost is also enormous, even by the standards of the capital markets. Put most bluntly, if enough people with enough money thought there was more money to be made by developing a private SSTO space booster, they would have done it.

Yet looking back over all the above figures -- I worked them out more or less on the fly -- they are oddly tantalizing. If the costs were much lower, it would be clearly doable. If they were much higher, all we could do is sigh upon a star. But as they are, the thing seems just on the edge of the plausible.

Anyone have, say, $10 billion handy, and want to talk? Email me here.