As another sign of the growing acceptance of the idea, in July 1998 the American Institute of Astronautics and Aeronautics ( AIAA, the largest organisation of aerospace professionals) published the report of a working group that also endorsed the subject, concluding:

"In light of its great potential, public space travel should be viewed as the next large, new area of commercial space activity. It will be international by its nature and should be given high priority and visibility by space agencies, space manufacturing and service industries, terrestrial travel and tourism industries, and the financial and insurance communities" (2).

The first space tourism services that are expected to be offered will be short "sub-orbital" flights to space lasting just a few minutes. These will be followed by orbital flights lasting a few hours. However, market research has shown that most potential customers would prefer to spend a few days in orbit (3). Consequently, if the market potential of space tourism is to be developed fully, orbiting accommodation facilities, or "space hotels" will certainly be required.

The main pre-requisite of a space tourism business is low-cost access to space, and this is becoming increasingly feasible in the foreseeable future as several privately-financed piloted launch vehicles are currently being developed, such as Bristol Spaceplanes' "Ascender" (4), Rotary Rocket's " Roton" (5), Vela Technology's "Space Cruiser" (6) and others.

From a technical point of view the development and operation of orbiting accommodation facilities are easier targets than developing vehicles capable of carrying passengers to and from orbit at low cost. Nevertheless a range of technical, economic and legal issues associated with Earth-orbiting "space hotels" need to be resolved, and these are beginning to be addressed (7, 8).

A number of science-fiction writers, notably Arthur C. Clarke, have drawn the parallel between cruise ships and space ships carrying passengers on long-distance journeys between planets lasting one year or more, as can be expected to occur sometime in the future. By contrast, the present paper examines possible similarities in the design and operation of cruise ships and "space hotels" operating in low Earth orbit just a few hundred kilometres above the Earth's surface, which are expected to be in operation within two decades or less. Haltermann has discussed some aspects of this analogy (9), and this paper continues and extends that discussion.

Cruise ships are seen as a better analogy for space hotels than Earth-based hotels since they are self-sufficient in food, water, staff and entertainment while they are at sea. Similarly, as in a cruise ship while it is at sea, in a space hotel it will not be possible for passengers to go out for a meal or to seek entertainment "outside" - at least not in the early days of the industry, before there are multiple tourism facilities sharing the same orbit (thereby enabling guests to make visits between them).

Over the past decade the cruise industry has grown steadily, and has extended beyond its past "exclusive" image into the mass market. In 1998 4.6 million passengers took cruises, representing a turnover of some $10 billion (10). Due to ever-increasing demand, ships are being stretched and new designs are grower ever larger. In 1990 the average new ship carried 775 passengers, in 1995 1173 passengers, and in 1998 1900 passengers (10). Large new cruise ships now cost as much as $500 million - similar to the cost of a large hotel.

In view of the similarities between cruise ships and space hotels discussed below, it is foreseeable that some of the companies currently operating cruise ships may become investors in space hotels, due to the relevance of their experience.

In 1986, Collins and Ashford outlined four possible stages in the development of space tourism (11), which are listed below (with the price-ranges slightly updated):

Phase 1 Pioneer phase
Price per trip: $1,000,000 - $250,000

Phase 2 Exclusive phase
Price per trip: $250,000 - $50,000

Phase 3 Mature phase
Price per trip: $50,000 - $10,000

Phase 4 Mass market phase
Price per trip: $10,000 -

From recent developments, it would seem likely that the "pioneer phase" will start within the first few years of the 21st century. Several companies are currently developing vehicles capable of sub-orbital passenger flights to 100 km altitude. The travel company Zegrahm Space Voyages Inc is currently taking bookings for such flights at $98,000, nominally from 2001 (6). Space Adventures Ltd is offering similar flights at $90,000 starting in late 2002 / early 2003 (12).

Building on the experience of operating sub-orbital flights, the industry will move on to provide regular orbital trips in the pioneer and exclusive phases, when orbiting space hotels will play a key role in stimulating market growth. Once this phase begins, hotels are likely to be developed rapidly in order to exploit the growing demand as prices of orbital trips decline. Space hotel development is likely to follow three stages as the industry matures:

Stage 1: "Outposts" or small space stations

This stage will correspond to the pioneer phase of orbital tourism, and the orbital vehicles used will be similar to Mir or cylindrical modules of the International Space Station ( ISS), catering for perhaps 10 - 20 passengers. (It is notable in this context that "Almaz" space stations (which have extensive operating experience from the past) are commercially available from the former Soviet Union, and NASA has discussed the possibility that space on the ISS may be made available for early tourism ventures.) As a technical point, these early outposts will offer guests only "zero-gravity" accommodation, since this is the easiest environment to provide; providing partial gravity involves creating a rotating structure, which adds to the complexity of the design and operation.

The closest analogy to this stage would be research ships which have minimal leisure facilities but carry passengers on ecological, and/or action-type holidays, such as visits to the wreck of the Titanic. On such trips passengers are often expected to carry out some work functions, and this experience is regarded as an integral part of the vacation.

Stage 2: Small hotels, accommodating up to 100 passengers.

This will correspond to the "exclusive" phase of the industry. The analogy with shipping here would be the type of ships used for Antarctic holidays which carry between 50 and 150 passengers on exclusive trips and have a reasonable standard of luxury, but certainly not all the facilities of larger cruise ships. Typically they are converted Russian ice breakers or research ships, such as those operated by Quark Expeditions (13).

Stage 3: Large hotels accommodating several hundred passengers or more.

This will correspond to the "mature" phase, leading on to the "mass market" phase. The cruise ship analogy to this phase is the large specialised cruise ships carrying between 500 and 2,000 passengers with a high degree of luxury and many facilities - including swimming pools, gymnasiums, entertainment, restaurants, bars, shops, casinos and others.

This section examines the facilities and activities found aboard large, purpose-built cruise ships today, and looks at analogous facilities that should be provided in space hotels, particularly in the "mature" phase of development when the industry will grow to a substantial scale commercially. Descriptions of space hotel facilities have to date concentrated on early phases, and have considered mainly the activities of Earth-watching and enjoyment of the "zero-G" environment. These activities will undoubtedly both remain popular pastimes, but during a stay of a week or so most guests are likely to be interested in other activities as well. Consequently a range of more conventional activities will also be needed. The following is a list of some possibilities.

A well-designed observatory lounge is obviously a "must" for a space hotel. All astronauts report that Earth-watching is one of the most fascinating pastimes in space, and it is likely to be one of the major selling features of any orbital vacation (along with "zero-gravity" or "zero-G"). Any space hotel design must feature as much window area as technically possible, as well as telescopes and binoculars for enhancing the view. As on board Earth-bound ships, viewing sunrises and sunsets, as well as the star field, are also likely to be major attractions. Viewing domes which give as far as possible the impression of being outside are also desirable features - however much the structural engineers may complain! Cabins should also have windows wherever possible, and as in cruise ships the price for an inside cabin with no window will surely be lower than that of an outside cabin.

Obviously walking outside is not possible in a space hotel (except for "Space-Walking", as discussed below) but a perimeter walk of some kind may be attractive to prevent feelings of being enclosed and to facilitate exercise. Ultimately a zone of artificial gravity created by rotation - something like in the space station in "2001: A Space Odyssey" - would be attractive, for increased variety. The proportions of zero gravity and partial gravity volumes are likely to vary between hotels, although all hotels are likely to have large volumes of zero-G as this is one of the two most important selling features of an orbital vacation (along with Earth watching).

Cruise ships usually offer a range of cabins with a range of features. Usually lower-priced cabins are on the inside with no window while the most expensive are "Owners' suites" or penthouses with separate living rooms and large external windows. All cabins have en-suite facilities. A typical ordinary grade cabin in a cruise ship measures approximately 4 metres by 3.5 metres by 2.5 metres high, and this could be a baseline figure for a space hotel. Zero-G conditions may make smaller volumes tolerable, but this is not yet clear. In view of some of the problems encountered with the toilet on the US Space Shuttle, much effort clearly needs to be devoted to the design and reliability of waste disposal systems dealing with human waste from many cabins.

Salons offering a wide range of treatments including sauna/massage, some unique to the zero-G environment, are likely to be popular. Even in the new world of space, guests are surely going to want to look and feel good. This need may be enhanced by the small changes in bodily proportions that people undergo while living in zero G, including swelling of the face.

Keeping fit in space is an important activity and many guests at a space hotel are likely to be regular exercisers. A range of machines, adapted to zero-gee, will be necessary. Many of these have been used on previous space missions, such as the treadmill on Mir (14), and the stationary bicycle on Skylab (15). The zero-G environment also allows many new sports that involve moving in three dimensions and flying. For a discussion of some of the possibilities as well as the structures needed see Collins et al (16).

These will be of particular interest to children and teenagers. "Shoot 'em up" games involving invaders from space may be particularly popular.

These may specialise in showing the latest movies, as well as science-fiction space classics such as "2001", "Star Wars" etc. Clarke (18) describes the most popular film on a journey from Saturn to Earth as being "'If This is Tuesday, This Must be Mars', a selection from the countless space-travel movies made in the days before space-flight was actually achieved." To continue the quotation: "This invariably reduced the audience to helpless hysterics, and it was hard to believe that it had once been banned for in-flight screening because some unimaginative bureaucrat feared that its disasters - such as accidentally arriving at the wrong planet - might alarm nervous passengers. In fact, it had just the opposite effect: they laughed too much to worry." Of course some scary space movies may be banned (e.g. the Alien series?) in the same way that cruise lines don't generally show "Titanic".

This will be essential, especially news channels, sports channels and movie channels, as well as an on-board information service. Many guests will not wish to be "out of touch" even when holidaying.

Full telephone fax and e-mail facilities should be available (charged to the customer) - and also video-phones permitting "leading-edge" communication services.

One traditionally popular aspect of cruising on Earth-bound ships is formal dinners and meeting the Captain. Although dinner-jackets may perhaps be considered out of place in a future space hotel, some equivalent new "tradition" may well develop to mark this new form of human travel. Meeting the Captain and senior crew-members is also likely to be a tradition worth continuing, adding value to guests' stay aboard the hotel.

Eating is a universally popular leisure activity, and most cruise ships have a range of restaurants, ranging from formal to informal. The provision of restaurants will represent a major franchise opportunity for operators of space hotels. Some high-profile restaurant chains such as "Hard Rock Café" and "Planet Hollywood" would probably pay a high sum for the franchise on a restaurant in a space hotel. The merchandising opportunity for "Hard Rock Cafe: Low Earth Orbit" T-shirts and other things is exciting!

Sales of alcohol represent a significant extra revenue source for cruise ships, all meals normally being included in the price of the cruise. Although there are some arguments against serving alcohol on safety grounds, it seems likely that guests' demands will be catered to. Many people like to drink alcoholic drinks while on vacation, and prohibition would be likely to lead to smuggling. In addition there is great commercial potential for development of new drinks such as branded "space cocktails". In view of the fact that some branded alcoholic drinks are vehicles for major advertising budgets, the possibilities of developing new brands for this application represent major business opportunities. Thus, on balance it is the authors' guess that space hotels which serve alcohol will outnumber those that do not.

Hotel facilities will have to have a high degree of inherent safety. This will require intelligent security systems like those seen in modern hotels, in addition to inherently secure physical systems preventing actions such as both accidental and deliberate opening of external doors - like systems used in airliners, and elsewhere.

There will be a need for storm shelters for use in the event of solar flares. Consideration of these and other emergency issues raises the question of what safety systems and procedures will be needed in a large space hotel to cope with possible worst-case accidents such as large-scale depressurisation through collision with another vehicle or other space object. Among other systems, air-tight doors and quickly reconfigurable air-supply systems enabling damaged areas to be isolated will be required, as on ships and submarines, as well as widely distributed temporary breathing kits.

International regulations require that all cruise ships have a lifeboat drill for all passengers. Although in the early days the space hotel business may not be heavily regulated, regulation is bound to follow the development of a growing industry responsible for the safety of thousands of passengers. It seems unlikely that space hotels will be permanently attended by lifeboats sufficient to carry all passengers and crew, except perhaps in the early stages of small facilities. However, it may be required at some stage - hopefully without the jolt of some Titanic-like disaster. Alternatively, secure areas capable of providing autonomous life-support for all guests for a specified minimum length of time may be a more appropriate requirement. In either case, some safety drill will have to be practised, even if it follows the somewhat jaded, although serious, in-aircraft demonstration of what to do in the event of a cabin depressurisation, fire or crash-landing.

Large cruise ships typically have a theatre used for entertainment in the evening, as well as for other large gatherings such as briefings and lectures. Space hotels will surely have a similar feature. As well as conventional entertainment (singers, comedians, musical shows) special shows designed to utilise the unique movements and gymnastics possible in zero-G will surely be devised and produced.

Swimming pools in space stations have long been discussed in science fiction and speculative works. Clarke, who is a rich source of similarities between ships and space hotels, no doubt inspired by his experience of long journeys on ocean liners of the 1950s and 1960s, discusses a space hotel having a spherical swimming pool as an attraction, possibly even with an air space in the centre (18). As Clarke acknowledges, there are many technical problems such as anchoring such a pool and preventing it being dispersed by splashing (presumably this could be handled by some collection and recycling system). Collins et al have started to consider the engineering of zero-G and artificial gravity swimming pools (19). In the case of artificial gravity pools, the authors discuss various possible designs based on a torus, either open at both ends or closed at one end, and possibly of varying depth. This would be a much smaller version of the cylindrical sea in Clarke's "Rendezvous with Rama" (20).

These are surely a desirable feature for guests' relaxation. The feasibility of designing baths for use in zero G involves some of the same issues that apply to swimming pools. For example, with suitable enclosure, a roughly hemi-spherical hot tub ("ofuro" in Japanese) may be possible.

Souvenir sales represent another significant source of income for cruise ships, and will undoubtedly do so for space hotels. Some items may have to be ordered while in-orbit but delivered from Earth-based depots. There will, however, certainly be a demand for items that have actually "been there". Therefore space and mass allowance will need to be made for small, and more importantly low-mass items similar to those sold on board aircraft.

Another additional source of revenue on cruise ship is art auctions. Similar auctions concentrating on space art and space memorabilia could be held on-board space hotels. Given a) the proven interest in space of the guests, b) their above average income (at least until the mass market phase of the industry), and c) the euphoria created by actually being in space, the potential for gaining high prices at auctions would appear to be good. On cruise ships, art auctions are run by a separate company as a franchise operation, and the same method could apply in space hotels. Most items would be stored on Earth and shipped to the purchaser's address, although certain, selected items could be flown on the hotel to add value and that magical feature of auction items, "provenance". Earth-bound space art and memorabilia auctions have already achieved considerable success, which shows the potential for this activity and its operator (21).

Gambling is a major source of revenue for cruise ship operators and could be for future space hotel operators. No international regulations exist to regulate gambling in space, and recent developments on Indian reservations and US river-boats show the potential for novelty venues other than Las Vegas or Atlantic City. The development of new major hotels in Las Vegas such as the Las Vegas Stratosphere Tower, which blur the distinction between hotels and theme parks, show the need for gambling and entertainment or spectacle in combination (22). Space "purists" may dislike gambling, but viewed realistically it may become a popular reason for some guests to visit a space hotel. What more impressive spectacle for a guest who tires of playing roulette (suitably modified for zero-gee) than to watch the Earth floating below them?

Cruise ships usually have an on-board photographer taking pictures of guests, which are then for sale as souvenirs. This is an obvious activity for a space hotel and could include video. In addition, as suggested in the Zegrahm brochure, passengers could wear head mounted mini-video cameras to record their own personalised video of their experience (6). Alternatively they could purchase a standard souvenir video with footage of themselves edited in, as is done today at some bungee-jumping venues. In a similar vein, another merchandising opportunity would be to sell photographs taken from the space hotel of the guest's home town or city at various resolutions. (The range of locations would be limited by the hotel's orbital inclination and altitude, but photos from other satellites could also be used.) Photography and video is another activity that would lend itself to a franchise operation and sponsorship, e.g. from one of the film companies, as there are official partner film companies in Disney World and at the Olympics.

On Caribbean cruises, SCUBA diving is often offered as an extra activity in which passengers can receive some basic training and undertake a short dive. An obvious parallel in a space hotel is Space-walking, or "EVA" (Extra Vehicular Activity). Not all guests may want to space-walk, and facilities may not exist to allow everyone to do so, even if demand did exist, so this might be an extra service at an additional cost. By all accounts being outside a spacecraft in a space-suit is a thrilling experience, and many space enthusiasts would consider it the highlight of a stay in a space hotel (15). Obviously safety and logistical issues would need to be addressed. A system similar to SCUBA diving in which one experienced instructor leads 5 to 10 trainees for a short (1 to 2 hours) undemanding dive after half a day's training could be a realistic model. A system using non-autonomous life-support based on air-hoses connected to the hotel might be sufficient for a basic service. The need to allow many people to enter and leave quickly for such a service has implications for the size of external airlocks. For passenger transfer between launch vehicles and hotels there will clearly be a need for an international standard wide airlock - probably of the order of 2 metres in diameter.

As in all spacecraft in science fiction movies there will surely have to be a control room or "bridge" giving a comprehensive view of the hotel, its various sub-systems and other vehicles in the vicinity. Tours of the bridge (as well as other behind-the-scenes areas) will be available for interested guests.

On most cruise ships the "galley" or kitchens take up a significant amount of the total floor area. Obviously issues such as food delivery, storage and preparation in a space hotel need to be considered and designed for. Zero-G adds a new dimension to this function, and will make unique new cookery possible.

Most cruise ships have resident lecturers. In a space hotel, lectures might be given on the following subjects, inter alia: history of space flight, future space projects, the technologies of the space hotel, careers in space, Earth watching (meteorology, oceanography, geology, geography), the search for extra-terrestrial life, archaeology, history, and other subjects such as the great empires or the great animal migrations that could be illustrated by looking down at Earth. On certain cruises celebrity guest lecturers, for example astronauts and cosmonauts from the early days of space exploration, would be invited to lecture.

Space tourism is expected to grow rapidly as launch prices fall below $1000/kg and thereby allowing passenger prices to fall below $100,000/person. At such launch-prices an orbital hotel weighing 100 tons will cost of the order of $100 million to launch. The profitability of assets costing $100 million or more, such as a cruise ship, hotel or airliner depends critically on achieving high utilisation. Being in the same cost bracket as cruise ships, hotels and airliners, the same need to achieve high utilisation will apply to space hotels.

Cruise ships typically have a home-port which they visit periodically. In order to minimise their time out of revenue-earning operation, cruise ships generally disembark all their passengers and embark new passengers on the same day. This requires considerable planning and organisation - of passengers, of staff and of supplies. However, unlike cruise ships, orbital hotels will not return to a "home-port" on Earth, but will instead remain permanently in orbit where they will be visited by passenger-carrying launch vehicles arriving from many different sites on Earth. The equivalent for a cruise ship would be for passengers to be ferried to and from it by smaller boats when it is within a short distance of any of several different ports.

Also unlike a cruise-ship, a space hotel will not have a particular itinerary, but will simply orbit the Earth continuously. Consequently it will not generally be necessary to disembark and embark all the guests of a space hotel in a single day. The preferred schedule will be likely to depend on the size of the hotel relative to the size of the passenger ferries. In some cases they may be similar - for example proposals have been published for passenger launch vehicles carrying 20, 50, 100 and more passengers, such as the Phoenix (23), Kankoh-maru (24), BETA (25), and the unnamed vehicle analysed in (26). At different stages of development, orbital hotels of each of these sizes may be constructed and operated.

Which launch vehicles could best cope with high levels of demand remains to be seen: there is a complex trade-off between the economies of scale in manufacturing and operating many relatively smaller vehicles versus the economies of carrying more passengers simultaneously in (fewer) larger vehicles. Additional factors that must be included in the estimation is the load-factor achieved on each flight, and the initial investment required. Koelle argues strongly for vehicles capable of carrying at least 100 passengers (25), whereas Bekey argues that the need to minimise the amount of investment required for development of the first vehicle favours a size of as few as 20 passengers (27).

In the 1960s, the "Pegasus" Single Stage to Orbit ( SSTO) VTOL vehicle was proposed with a 1500 ton gross weight, and capacity to carry 170 passengers to an orbiting hotel (28). Much larger vehicles were also proposed, such as the "Ithacus Senior", with a 6400 ton gross weight, which could deliver as much as 360 tons of payload to low orbit (28). However, since it is not generally economical for manufacturers to develop a vehicle unless they can sell at least 50-100 (and preferably many more) units, such large vehicles are likely to become available only if launch demand grows to a scale of millions of tons per year - that is clearly at a "mass market" phase of activity.

(Note that it is not necessary that such demand be only for tourism - delivery of large-scale supplies of microwave power from space to Earth could also become a profitable business at low launch costs.) Both SSTO VTOL and two-stage spaceplane launch vehicles are believed to be feasible using existing technology, but they have yet to be proven; the potentially large market for space tourism provides the opportunity to develop the vehicles required on a commercial basis.

Whatever sizes of launchers are employed, if it was required to transport as many as 1000 people to and from a space hotel in a single day, this would have implications for the operation pattern of the launch vehicles being used. Once orbital hotels reach the scale of 1000 guests or more, the business of embarking and disembarking them will create considerable traffic around the hotel, with vehicles arriving from several different launch sites and departing to several different landing sites (29).

One possible mode of operation is for launchers to combine passengers and cargo, like "combi" airliners today. This would allow them to deliver supplies to the space hotel, return with a full load of disembarking passengers, then make another trip carrying embarking passengers, and so on. Optimisation of the launch vehicle utilisation will involve taking into account the need to deliver consumables, disembark and embark guests, and remove waste.

Space hotels will require a range of standard "house-keeping" systems common to all space stations: closed environment life support (CELSS), attitude control, station-keeping, propulsion for orbit boosting, communications. They will also require a range of systems more familiar in hotels and cruise-ships, suitably adapted for orbital accommodation.

Preserving safety of passengers and third parties will require a range of additional systems, including fire alarms and fire suppression, public address (PA) for both routine and emergency announcements, Closed Circuit Television (CCTV), and some form of "people movers". All of these are used today both in cruise ships and in large buildings. In modern, large "intelligent buildings" these systems are typically integrated: they communicate with each other over an Information Technology (IT) network, and use PCs typically running MS Windows. The benefits of system integration include reduced capital costs due to reduced cabling and number of monitors, ease of upgrading, standard man-machine interface for all systems, and reduced need for specialised operators (30). There is no reason why this practice should not be closely copied in space hotels. In some respects space hotels can be considered as simply intelligent buildings.

Another system which will need to be much more advanced than on space stations to date is waste management. Even more than in the seas, dumping anything into space is rapidly becoming unacceptable on both safety and environmental grounds. Therefore the waste management system will need to be at least partially closed, and the recycling ratio should be gradually increased as far as economical, based on the condition that any waste products that cannot be recycled will need to be returned to Earth for disposal. It will be important to avoid any failure of a plumbing system servicing hundreds of guests!

Most cruise ships are owned by off-shore companies operating out of countries with beneficial tax and regulatory regimes such as the Bahamas. Space hotel operators will also try to minimise the taxes they pay, and so will probably use the same approach - acknowledging the fact that legal regimes in space are still a new area with very few details decided. Some orbital facilities are expected to create their own jurisdiction, while others will choose from existing jurisdictions on Earth. As in shipping, some countries may be expected to establish lax regulatory frameworks in order to make themselves more attractive to operators of space hotels. The extent to which this may reduce safety is limited by passengers' requirement for safety, and the need for insurance companies to cover the facilities.

Within the cruising industry there are different niches such as exclusive, luxury ships with small numbers of passengers and a high ratio of staff to passengers (often resembling large private yachts); mass-market ships with the emphasis on entertainment and gambling; ships owned by theme park operators such as Disney; and smaller ships aimed more at the ecological/adventure holiday tourism market. In the development of the space hotel industry, similar niche markets seem likely to be developed, some utilising themes from popular science fiction stories.

From the wide range of topics listed above, it is clear that the analogy between orbital hotels and cruise ships is a fruitful one: many facilities and services provided today aboard modern cruise ships are likely to be offered in space hotels at different stages in the future. However, it is interesting also to compare space hotels with airliners and terrestrial hotels, with which they will also have a number of similarities. For brevity a comparison of several aspects is summarised in Table 1. Noteworthy points according to which space hotels and cruise ships are notably different include their construction: while ships are built in a shipyard, a space hotel will be assembled on site from components, more like a terrestrial hotel than a cruise-ship or airliner. Also unlike a ship, it will be built out of light-weight materials such as aluminum and composites in order to reduce the cost of launch. It will also be closer to a terrestrial hotel in length of continuous operation, since passenger rotation will be continuous rather than in batches. And although it is not yet decided, it is likely that space hotels will be regulated by aviation authorities, though some of the practices will be more like shipping than aviation. In particular, the captain will presumably have far-reaching legal powers, including summary execution in emergencies, like the captain of an airliner or ship, but unlike a hotel manager. Another difference from a cruise ship is that guests will be carried to and from a space hotel, rather than the hotel visiting a port or airport to embark passengers, which is more like a terrestrial hotel than a cruise ship.

Finally, whereas the time zone in an airliner or cruise ship changes to match its current longitude, a space hotel will be in a unique situation, since the day-length in low Earth orbit is only some 90 minutes. And while the time zone of the headquarters of the management company on Earth may have some priority, guests will arrive from departure points around the globe, and they will not wish to waste time waiting for restaurants or other facilities to open. Thus it seems likely that the natural mode for a space hotel will be a genuinely seamless 24 hour operation.

Similar to both hotels and cruise ships, we can expect orbital hotels to grow larger and offer an ever wider range of entertainents. The relative ease of building large structures in zero gravity will encourage the planning of facilities such as large as sports stadia and eventually even theme parks. In the same way some of the largest new hotels on Earth are beginning to blur the distinction between hotels and theme parks. The different stakeholders in a space hotel - manufacturers, owners, operators, customers, staff, suppliers, insurers, regulators - will all have different interests, and the analogy with cruise ships is more or less close according to the different viewpoints.

The cruise industry has grown progressively over recent years to reach an annual turnover of some $10 billion (10). Once launch costs are reduced through the development of reusable passenger- carrying space vehicles, the commercial market for passenger travel to low Earth orbit will develop following a similar growth pattern as it moves out of the exclusive phase and into the mature market phase.

In considering the future design of space hotels the analogy with cruise ships is useful for defining necessary features and systems, as many of the facilities offered on cruise ships will also be required on space hotels. The analogy can be used to sketch out a number of likely design-features of space hotels, and patterns of operation and resupply in more detail than has been done to date.

The analogy suggests that owners and operators of cruise ships should consider orbital hotels as a possible future direction for diversification. These companies seem well-suited to develop and operate the type of facilities needed for space hotels, as many of the managerial, operational and financial skills needed will be directly transferable - at least more so than either aerospace manufacturers' or airlines' experience. However recent progress by the FAA in starting to apply the aviation regulatory process to reusable launch vehicles show that marine analogy is not exhaustive. Orbital hotels represent a unique new field which will draw on several existing fields of business and law. It is thus genuinely open to major contributions and roles by successful innovators and entrepreneurs from many different fields today.

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26. J Penn and C Lindley, 1997, "RLV Design Optimization for Human Presence in Space", Aerospace Corporation; also downloadable from: www.spacefuture.com
27. I Bekey, 1998, "Economically Viable Public Space Travel", Proceedings 49th IAF Congress; also downloadable from: www.spacefuture.com
28. P Bono and K Gatland, 1969, " Frontiers of Space", Blandford Press Ltd.
29. T Williams and P Collins, 1997, Orbital Considerations in Kankoh-Maru Rendezvous Operations", Proc. 7th ISCOPS, AAS Vol 96, pp 693-707; also downloadable from: www.spacefuture.com
30. CdC Systems Limited brochure and web site: www.cdc.uk.com. See also: R Haltermann, 1998, " Cruising to the Moon", Space News, Vol 9, No 414, p 27.