Patrick Collins worked as a consultant to the European Space Agency from 1979 through 1981, while earning his doctorate on the economics of satellite solar power stations. Since 1983, he has taught managerial economics in London University's Imperial College of Science, Technology, and Medicine and has continued his research on the commercial prospects for the space industry.

The idea of tourism in space plays a part in several well-known science fiction stories: Roben Heinlein's 1957 story The Menace from Earth is about a rich tourist learning to fly in a large canyon on the Moon which has been covered over and filled with air for recreational flying - a realistic possibility for the 21st century. Arthur Clarke's 1961 novel A Fall of Moondust concerns the misadventure of a party of lunar tourists, while Joanna Russ's 1968 novel Picnic on Paradise, set much further into the future when interstellar travel is common, concerns a party of tourists who get caught up in a civil war while visiting a distant planet. More recently, Galactic Tours, by David Hardy and Bob Shaw, illustrates a whole range of tourist possibilities, from skiing on Europa (one of the moons of Jupiter) in our solar system, to weird and exotic possibilities in other star systems. And one day humans will go skiing on Europa - at least a few early explorers will within the 21st century. Most recently, Ben Bova devoted several pages of his "Moonbase Orientation Manual" (Part II, July 1987 Analog) to tourism on the moon 50 years from now. With continuing world economic growth, the longer-term prospects for space tourism are clearly limitless.

However, the beginnings of space tourism will be very much nearer home, quite literally, for the first destination will be a mere 200 miles away - in low Earth orbit. And although less exotic than the longer-term prospects, visits to nearby space will be hardly less attractive. Despite the seriousness of their training, and their tight work schedules when in orbit, everyone who has experienced it agrees that space travel is fun. Sally Ride, the first English-speaking woman astronaut, summed it up when she said of her first flight in the Space Shuttle: "It was great fun . . . and I guess it will be the greatest fun I ever have". U.S. Senator Jake Garn even wangled himself a flight. Irrespective of any scientific or political value that their flights may have had, none of the astronauts would have missed them for anything.

More than being fun, a visit to low Earth orbit is also fascinating. The absence of gravity introduces novelties into every activity, making the experience endlessly interesting. Washing, dressing, eating meals, and other ordinary activities are all transformed in zero gravity. Even just moving around is so different that the Skylab astronauts reported that they could never resist making acrobatic movements, somersaults, spins and so on, when they had to move some distance. In addition to this, the view of Earth from low orbit is literally breathtaking, both by night when the globe flickers with lightning storms and polar aurorae, and by day when the ever-changing terrain below is dazzlingly clear. Photographs and films of the view are beautiful, but to experience it for real is apparently stunning. Astronauts in Skylab spent hours on end watching the Earth through the porthole whenever possible. The absence of air also, of course, provides perfect conditions for observing the Moon, Sun, planets, stars and nebulae.

Even more than this, however, and perhaps most important for anyone (including many science fiction readers) with some feeling for the immense future stretching ahead of the human race, as we explore in turn the solar system, the nearby stars, the whole milky way galaxy (and eventually of course, even other galaxies), these first tiny steps above the Earth's surface have extraordinary evolutionary significance. To visit low Earth orbit at this point in history is to feel yourself as part of our species just peeping out into space, as the first protoamphibians must have peeped out of the prehistoric seas at the land covered in primitive plants. As such, the experience of seeing the sky darken into the blackness of space as you climb above the Earth's atmosphere carries such emotions of excitement, awe, and inspiration that for many people a trip to orbit will be an absolute must, an almost magical event, a once-in-a-lifetime, modern-day pilgrimage.

Even for those not lucky enough to have this perspective, a visit to low Earth orbit will nevertheless be uniquely entertaining - and the public already understands this. Astronauts have been children's heroes for decades (despite their limited activities since the Apollo program), while a recent survey carried out for the American Express Company in the UK found that more than 50% of those under 45 years old and more than 60% of those under 25 would like a holiday in space if it was available. Even the most experienced traveler who has "been everywhere", from the Caspian Sea to Jamaica, from the Taj Mahal to Alaska, has never done anything remotely like taking a holiday in space.

However, although these early space tourist services will clearly become available long before more exotic services such as trips to the Moon, many of you may feel that even trips to low Earth orbit are not going to be available on a commercial basis within your lifetimes. This, I claim, is wrong, and much of the rest of this article will argue the case that it is feasible for space tourism to begin this century (yes, during the 1990s), and that once it starts it will grow rapidly and the price will fall so that within 20 years, although still expensive, orbital trips will become widely available for people prepared to save their holiday budget for a few years.

The key, of course, is to bring the costs down within customers' reach, and unfortunately the U.S. Space Shuttle is a step in the wrong direction: Due to the conflicting political requirements placed on its design, it costs more to launch a ton of payload than the expendable Saturn V of the 1960s! However, there are two design approaches for reusable launch vehicles using existing technology which could bring down the cost of a short trip into space low enough to establish a profitable industry (see below). Nevertheless, in order to reduce costs sufficiently, the turnover of passengers must be high enough to gain the maximum economies of scale - which will depend both on the price and on the popularity of what is being offered. And I believe that when it becomes commercially available, the possibility of paying a short visit to a "hotel" in low Earth orbit will be extremely popular, even at a price of thousands of dollars, because of the unique range and variety of entertainments that will be available.

In addition to the extraordinary views to be had from an assortment of portholes, panoramic windows, viewing domes, and observatories, holidays in orbiting "hotels" will provide zero gravity. Among other activities, this provides the opportunity for human-powered flight in large gymnasiums, using fabric wings attached to the arms and tails attached to the ankles. Just learning to fly will be fascinating in itself, but flying will also provide further scope for many new leisure and sports activities-racing, aerobatics, chase games, dancing. For those interested in the details, flying in zero gravity will not be the same as flying on Earth since there will be no need to generate lift: objects continue moving in a straight line unless they experience an external force. However, wings and tail will be needed for propulsion, steering, and stopping-so having accelerated to the speed you want by flapping your wings, turning, swooping, and coming to a stop will be much like that of a bird. For instance, altering the angle of attack of one or both wings will allow you to roll, climb and dive at will, while raising your tail segments (attached to your ankles) will tip your body "down" perpendicular to your flight direction, and flapping your wings from back to front (while keeping your balance!) will bring you to a halt. There's clearly plenty to learn!

Zero gravity water sports in a large, gymnasium-sized room will also offer many new experiences. The behavior of water in zero gravity is dominated by surface tension, and a swimming-pool sized "piece" of water could be broken up into dozens of different sized "pieces" offering different attractions: it would be possible to dive right through large pieces and emerge from the other side, while swimming would have the novelty that bodies at the surface would float very high, whereas "underwater" you would not rise to the surface spontaneously. (For safety, people may wear small bottles of compressed air with a mouthpiece to allow them to breathe when underwater.) Armfuls of water could also be thrown as a means of propelling yourself around the room, while smaller pieces the size of tennis balls would be as handy as snowballs! A room containing many "pieces" of water would provide an interesting environment for hiding and chasing games. A large, slowly rotating, cylindrical swimming chamber would also enable people to swim around the inside curve in low pseudo-gravity for exercise, as well as to dive out and float in the central air space.

Zero gravity also provides extraordinary scope for completely new ball games, chase games, and games of skill. Acrobatics would become a different, more leisurely, high precision art form. The use of simple air thruster packs would allow people to maneuver in three dimensions without effort, or to "dog-fight" with each other. Just learning to make gentle, controlled movements while preserving your balance will be interesting, and sleeping with a partner will have its novelty, for instance in "rendezvous and docking," as well as its advantage-no more arms going to sleep! The list of enjoyable uses of zero-g is as long as your imagination.

For those wanting less energetic pursuits (or those temporarily exhausted) zero gravity also offers fascinating possibilities for demonstrating physical phenomena not possible on Earth. Water and other liquids behave quite differently; they can be formed into "ropes" or rotating donuts, or expanded with bubbles that don't rise to the surface and burst. This would make it possible to bake "ultralight" cakes or to make objects out of metal "foam", while the unconstrained behavior of magnetic materials and spinning objects can also be shown in zero-g. Again, the possibilities are endless.

On a different note, orbiting botanical gardens would hold enormous interest as they revealed the exotic ways in which different plants adapted to a zero gravity environment. Many will grow much larger than they do in the 1 g gravity field on Earth, and they will grow in much weirder ways without the gravity vector to guide them. A 3-D ramble through a zero-g hanging jungle, complete with "waterfalls" and pools, will be a possibility at a later stage! It is easy to get carried away musing on the delightful possibilities that are going to be available one day, but we must come back to Earth if we are to seriously consider how soon these ideas may be feasible.

There are several reasons for being optimistic about the feasibility of a commercial space tourism industry starting this century. The first reason is that technically the project lies well within what is possible today. In most respects the technical requirements of both the necessary launch vehicles and the orbital accommodation units lie within the limits of technology that either exists or is currently being developed. For instance, accommodation modules required for an orbiting hotel are much less technically demanding than Spacelab modules: There is no requirement for state-of-the-art laboratory hardware, computing equipment, or telecommunications facilities. Nor are large amounts of power required; nor are accurately controlled attitude or gravitational fields required in a hotel. Much of the astronomical cost of the planned U.S. space station is to be incurred in developing new technology in all these areas.

Tourism merely requires comfortable accommodations and leisure facilities, which require only standard structural modules with lightweight interior partitioning and suitable furnishings. Environmental control and life support, power, thermal control, attitude control, communications, and other systems would need little adaptation from systems that already exist. The only significant new developments are the need for plenty of windows in every module and semi-autonomous environmental control systems with multiple redundancy throughout the facility-and even for these the technologies are already fully developed. The single respect in which space tourism operations would need to be innovative is in achieving standards of safety of both launch vehicles and accommodation facilities similar to civil aviation standards. This is impossible to achieve with current launch vehicles, which are expendable or partly expendable, but the use of fully reusable launch vehicles will enable reliability to reach the level of civil airline operations through step-by-step development.

A second reason for optimism about the prospects for space tourism is the fact that there is enormous scope within the space industry for reducing costs. Space projects today typically involve politically determined developments financed exclusively by governments, followed by production of small numbers of the end product. This is quite unlike normal commercial industries, and among other consequences costs remain extremely high. As an example, while U.S. industry was developing the Space Shuttle during the late 1970s and 1980s, Europe and Japan broadly repeated U.S. work of the 1960s with their development of the HM7 and LES cryogenic rocket engines (more or less duplicating the Pratt & Whitney RLIO engine), and they are currently developing the HM60 and LE7 engines (which roughly duplicate Rocketdyne's J2 engine). The resulting low utilization of all these engines ensures that their costs remain extremely high, despite the fact that they are inherently simpler than jet engines.

There have also been some spectacular examples of cost reductions: A company in the U.S. auto industry was recently invited to manufacture some nickel-hydrogen batteries used in NASA satellites. By applying their commercial expertise in cost reduction, they reduced the production cost from $25,000 to less than $1,000, and they expect it to fall eventually below $400! Likewise the cost of food on the Space Shuttle is a fraction of the Apollo astronauts' food bill. Much of it is now bought from supermarkets, instead of being developed from scratch.

In recent years the intensity of competition between manufacturing industries worldwide has rocketed - particularly in the speed of new product and model development, increased product quality and reliability, and speed of reaching mass production. These features have become particular hallmarks of Japanese manufacturing industry, and American and European companies are having to rapidly learn new forms of organization and engineering professionalism in order to catch up. The diffusion of these qualities throughout manufacturing industry is, of course, exactly what is required to reduce costs in the space industry-in which the Japanese are also making rapid advances.

A third reason for optimism is the very large scale of the potential demand for space tourism services. As already mentioned, opinion polls have found that more than 50% of the population would take a trip into space if given the opportunity, but the significance of this figure is greatly increased by the fact that it is based only on curiosity on the part of the public. When better informed about the range of interesting possibilities described above, an even higher proportion of the population would be likely to favor a short "holiday" in space. Perhaps most important, however, once space tourism starts, a "word of mouth" effect is likely to accelerate its spread. Hearing how much fun it is from a personal friend who's been into orbit will probably be one of the strongest inducements to try it!

Although the high level of spontaneous interest in visiting space is very encouraging, we need to know how many people per year would pay a given price. A "demand curve" is the name of the graph used to illustrate this information (Figure 1). So, for instance, if 10 million people per year were prepared to pay $10,000 for a trip to space, there would be no problem: $100 billion of revenues per year would pay for enormous development expenses. On the other hand, if only 1,000 people per year were prepared to pay $10,000, it would clearly not be feasible:

$10 million of annual revenues would be nowhere near enough. So what do we know about the demand curve for space tourism?

Market surveys in the U.S.A. suggest that, initially, a few thousand people per year would be prepared to pay between $50,000 and $100,000 for a short trip into low earth orbit, as proposed by the U.S. travel company Space Expeditions. (Their " Project Space Voyage" comprises a seven-day residential stay in a hotelcum-training-facility on Earth, followed by a twelve-hour orbital flight.) Such a level of demand should be enough to justify initial production of the " Phoenix" passenger launch vehicle designed by Pacific American Launch Systems Inc. Given the likelihood of sales of the " Phoenix" to other customers, some hundreds of millions of dollars of annual tourism revenues should, after deducting operating costs, be able to pay off approximately $1,000 million of initial investment. The project would be a cinch if given even a fraction of the billions of dollars of government subsidies provided to the Space Shuttle or Europe's Ariane launcher.

It is not known how many people might pay between $20,000 and $100,000, and obtaining reliable estimates will require well-prepared market research. However, reasonably convincing arguments can be made that as many as one million passengers per year would pay $10,000 for a short stay at an orbital "hotel". This level of traffic (several hundred times current launch rates) would provide major economies of scale: One million passengers, each spending, say, three days at an orbital hotel, would need launch vehicles to transport 20,000 passengers to and from orbit each week, as well as simultaneous accommodation for 10,000 people in orbit, or perhaps 40 hotels for 250 guests each. Such hotels might initially comprise some 30 Spacelab-like modules (50' long by 14' in diameter), plus perhaps six much larger modules made from converted Space Shuttle external tanks (150' by 28' in diameter). The required production runs of 1,200 smaller modules and 240 larger ones, plus perhaps 100 fully reusable launch vehicles, are far larger than have been achieved with space hardware hitherto, and would make a major contribution towards achieving the target of $10,000 per guest.

A fourth factor suggesting that commercial space tourism can be expected to develop rapidly (given that these other conditions make it profitable), is the large scale, the rapid growth, and the competitive vigor of the foreign travel industry today. With approximately one million tourists flying abroad every day, and a turnover of more than $100,000 million per year, the industry has an annual growth rate of around 5% in real terms (so it will double again by the end of the century). In seeking to generate the large increase in launch traffic that is potentially available from space tourism, intense competitive pressure will be exerted on launch costs, bringing about major cost reductions.

Although the popular image of tourism is of a rather "lightweight" business, comprising mainly simple services such as restaurants and beaches, it has a long track record as a major driver of new technological developments - particularly in transportation, telecommunications, and computers. The continuing technological improvements in commercial passenger shipping over the past two centuries, and in commercial aviation this century, have been driven primarily by the requirements of the public as customers, while the need for global booking, ticketing, and foreign exchange systems required by airlines have put continual pressure on computer and telecommunications systems manufacturers to innovate. Thus it would be no more than a continuation of its past history for tourism to play the leading role in knocking another industry into shape, and bringing the technology of space transportation to commercial maturity.

These facts are very encouraging, and provide good grounds for optimism. The space industry is only just beginning to consider space tourism seriously, but all that is needed is a few of the world's real entrepreneurs to take an interest - that is, people who can take serious risks with serious amounts of money, on the order of hundreds of millions! If the initial, higher-priced phase begins before the end of the century, with the vigorous growth in demand that could be expected for such a high-profile service, the turnover could reach one million passengers per year within twenty years.

At $10,000 per head, a holiday in space is clearly still not going to be an everyday affair. After all, who has $10,000 to spare? In other words, until the price falls even further to just a few thousand dollars, it will remain a once-in-a-lifetime experience for most people. However, with continuing economic growth, in 20 years' time most middle-income earners will be able to afford one trip in their lifetime. With tax efficient savings plans, if you earned 10% compound interest for 20 years, you would need to put away only $1,500 today, or less than $175 per year. Even at 7% it would be only $250 per year, or $160 per year over 25 years. If a space holiday was sure to be available in 20 years' time, many people would be prepared to make this sacrifice, while older people would set up plans on their children's and grandchildren's behalf. Lotteries with tickets as prizes are also likely to become popular, and to be widely used by business as promotional schemes. There are thus many reasons why even a relatively high price (in absolute terms) should not prevent the service reaching a wide public - you and me!

The costs of all operations in space depend critically on the cost of space transportation, and space tourism is no exception. The design of passenger launch vehicles for low cost; "airline" operations is therefore vital, and work is progressing in two main directions. A major constraint in designing a launch vehicle is the need to carry sufficient propellant. The cost of propellant tanks increases with their surface area, and so, since a sphere has the lowest surface area per unit of volume, a nearly spherical shape is attractive in having the lowest mass for a given quantity of propellant. Using something approaching such a shape, it is possible to design a single-stage-to-orbit vehicle that takes off and lands vertically. Several designs were made of such vehicles in the 1960s and 19705, and more recently by Pacific American Launch Systems, all of which are fairly close to spherical, being roughly conical, blunt-nosed, simple cylindrical structures. Expeditions' cost target for PacAm's " Phoenix" is $50,000 per passenger, which should be feasible once operations have shaken down, around the end of the century.

The second main route in designing a launch vehicle is to take off horizontally using wings to generate lift in the early stages of the flight. This has the advantage that the initial thrust required is only about 25% of the vehicle mass (instead of about 140% in the case of vertical takeoff), but it is possible only for vehicles with a gross liftoff weight of no more than about 500 tons. (The Space Shuttle's weight of around 2,000 tons makes horizontal takeoff impossible). Two-stage winged vehicles, in which only a small upper stage reaches orbit, are much easier to design than single-stage vehicles, and a particularly promising low-cost approach is the "Spacebus" design of David Ashford in the UK. This is somewhat similar to the West German " Sanger" vehicle, except that it would be cheaper to develop since it would require less new technology. In such vehicles the propellant cost per passenger will be around $3,000, and the other components of cost will fall progressively as the number of passengers handled grows, given full reusability and long vehicle life.

It therefore seems likely that there will be a choice for space tourists between the more exotic vertical takeoff vehicles, in which they will experience up to 3 g acceleration, and a more conventional airline-like launch in 2-stage winged vehicles. At a later date, when the technology has matured, the development and operation of single-stage winged launch vehicles may be commercially justifiable.

As mentioned above, the requirements for orbiting hotels could be satisfied easily using equipment developed for the U.S. Space Shuttle and space station. The earliest facilities will comprise simply a few cylindrical Spacelab-type modules, and/or refurbished Space Shuttle, external tanks, as proposed, for instance, by the US External Tanks Corporation. It isn't necessary to be able to predict future developments in detail to foresee that as traffic builds up and prices fall there will be continuing demand for more elaborate facilities. As a result, progressively more advanced hotels will be constructed, starting with larger assemblies of different modules, and later including much larger modules launched in component form and assembled in orbit. Subsequently, there will be tethered extensions providing fractional gravity several kilometers above or below the main section. Rotating sections will also be used to provide pseudo-gravity in the style of the classical rotating space stations. Later hotels will also be put in polar orbits, giving wider views of the Earth, as well as scope for interesting transfer trips between facilities. Ultimately, orbital hotels will include "buildings" with dimensions in kilometers, which will provide almost limitless scope for novel environments and entertainments.

There is one proviso to all the foregoing-namely that the demand for space holidays will depend critically on their both being, and seeming to be, safe. This will require assurance on three different matters: First, the vehicles and facilities will have to be mechanically safe, requiring the performance of flight test programs to civil aviation standards, as well as the availability, once in operation, of safety devices and rescue vehicles. Second, health risks must be no greater than for other tourist activities. Short-term exposure to zero gravity has been shown to have no damaging effects, but there will be a need for sheltered areas within orbital hotels to provide protection from solar flare particles (for which there are, conveniently, a few minutes' warning). Third, there must be no significant risks from collisions in orbit (primarily with debris). Achieving this will almost certainly require international agreements to reduce debris in orbit, and eventually orbital traffic regulations.

If space tourism develops as I suggest, it will have a number of important implications for the rest of the world. First, if one million tourists per year are paying $10,000 for an orbital trip in 20 years time, commercial investment is likely to be rapid, leading to a market of perhaps 20 million passengers per year within a further 20 years. In addition, the reduction in launch costs that the growth of space tourism will bring about will make other activities in space commercially viable. For example, the construction of satellite solar power stations (orbiting solar energy collectors with areas of many square kilometers, to be used to transmit gigawatts of electric power to Earth as microwave or laser energy) will be a profitable investment at such launch costs. The demand for energy in the next century from an increasingly industrialized world, given that the use of both nuclear and fossil fuels are likely to face serious constraints, will drive electricity supply industries to exploit such opportunities. This will lead to further progress in space industrialization, including in particular the extraction and processing of metals, ceramics, and other materials from the Moon and asteroids.

Second, of the changes taking place in the world, one of the most important for humanity is economic growth in the developing countries, where living standards are generally very low. This requires the continuation of the well-established pattern of global economic development whereby countries industrialize by progressing from simpler to more complex manufacturing industries. This depends, in turn, on the richer countrjes continually developing new and more advanced products to balance the developing countries' progressive takeover of more basic industries. Unfortunately, in recent decades there has been insufficient new employment in the richer countries, and growing political pressure to protect their older industries against the more competitive manufactured goods of the developing countries. In this situation, the development of a rapidly growing commercial space industry will create a dynamic new focus for industrial growth and investment in the advanced countries. This will reduce the pressure for protectionism, encourage increased imports from developing countries, and so remove one of the major obstacles to their economic growth.

A further benefit will be to provide commercial demand for many of the most advanced technologies which have been developed primarily for military purposes. By providing an alternative outlet for many of these technological skills, the expansion of a commercial space tourism industry will reduce the need for governments to encourage exports of military equipment which currently aggravate regional conflicts. Thus the development of a proper, commercial, profit-making space industry in the rich countries, initially driven by the currently unsatisfied demand for space tourism, will help to get them off the backs of the developing countries in more ways than one.

A different, but perhaps equally important, benefit of the development of space tourism will be to motivate young people to study technical subjects at school, by creating enthusiasm for engineering and science. This was very noticeable in the U.S.A. during the Apollo Program of the 1960s, and is now urgently needed to redress the drift away from sciences seen in the U.S.A. and Western Europe in recent years.

Many science fiction stories, such as Poul Anderson's "Tales of the Flying Mountains" are set in a future in which industrial society has spread through the solar system-and this is surely inevitable provided that we do not destroy ourselves or the environment of our planet. However, no stories provide a convincing description of how this is going to come about. The technological potential for the development of a commercial space industry has existed for nearly twenty years-essentially since the maturing of liquid hydrogen rocket technology in the U.S.A. during the 1960s. However, although the industry has seen further technological advances in electronics and materials since then, it has barely advanced commercially, and its revenues still come almost exclusively from taxpayers. And since the space industry isn't profitable today, it is a burden on the taxpayer, and suffers all the ills of being a political football.

The space establishment is currently proposing to spend some $80,000 million of taxpayers' money to send some scientists back to the moon, and maybe twice this to send a manned vehicle to Mars. This is like a government of the l920s proposing to spend several times the turnover of the aircraft industry of the day on, say, building a "national aeroplane" to carry 500 people around the world: it would have been an inappropriate project at that stage of the industry's development, and would have diverted resources away from commercial purposes. What actually happened was much more valuable: the government subsidized the establishment of a competitive commercial aviation industry (both manufacturers and airlines) by offering guaranteed mail contracts. The objective of flying round the world was, of course, achieved spontaneously in due course, without further taxpayers' funds.

A similar step today, subsidizing the development of true passenger launch vehicles, would cost only a small fraction of $80,000 million, would be much more popular with the public, and would be far more economically beneficial, not least by establishing a commercially self-sustaining space industry. And once the space industry is independently profitable, its destiny will be in its own hands, with no foreseeable limits to growth. As taxpayers, we pay for government-funded space programs. It is therefore up to us to tell politicians how to spend these funds. If we want space tourism (which appears to be the case), we have only to start pressing for it. Governments could do a lot worse than take a page out of the history books, and guarantee to purchase a minimum number of passenger seats into orbit each year. The idea that the door into the Space Age will be opened by the "human" route of popular curiosity - people taking holidays in space to see what it's like, rather than elitist activities of central government - is an attractive one.

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