The current commercialization of expendable rockets and satellite communication services depends on space technology developed by governments which monopolized space activities since the sputnik era. Remembering that planned economy is being replaced by free economy, we can expect a new context of space commercialization demanded by other fields than the current space business. One of such a business will be space tourism supported by a true space transportation system which will be operated like commercial airlines.

The key issue that makes the true transportation system uncertain is the future of reusable space vehicles which can be operated like aircraft. The Space Shuttle, which was proposed as the National Transportation System has failed in demonstration of low cost transportation by reusable vehicles. Experiences of Space Shuttle indicate that the low cost operation of airline systems cannot be achieved by winged vehicles without improvement of complex launch operation and expendable hardware. The recent demonstration of DC-X and development of related technology seem to make SSTO feasible.

The current airline systems make a global infrastructure for transportation. The true space transportation system will be designed on the base of this infrastructure. In this respect, air-traffic control systems, airport service for passengers and cargo and ground facilities for maintenance and operation are expected to support more or less the space transportation systems. An only exception will be propellant supply facilities which will handle a large amount of liquid hydrogen. This paper is intended to clarify the characteristics of the propellant industry to prepare for the new space transportation system.

Space tourism will be defined as spaceflight for the general public. Since it is necessary for tourism that passengers can pay the fee for each and the service should be conveniently provided by travel agents, the spaceflight for space tourism will be significantly different from the past spaceflight which have been made exclusively by qualified astronauts selected under a strict standard. The key issue to make the difference is the vehicles to be used. The vehicles that serve for space tourism will be featured as follows.

1. Vehicle manufacturers will participate in the economic activities of space tourism. The vehicles will be built on a production line and avail-able to commercial transportation operators.
2. The procedures for operation and maintenance of vehicles will be standardized and the qualified operators are responsible for implementation of transportation safety.
3. Airports will provide space transportation systems with common services for airlines at reasonable cost.

Before discussing features of the liquid hydrogen industry, we will explain about general features predicted for the space tourism. Table 1 (ref. 1) is a representative cost targets for space tourism to show an example of requirements imposed on transportation systems to be used for space tourism. In Table 1, such a space vehicle is compared with typical wide body aircraft. We will examine individual figures in this table from the standpoint of their application for a preliminary demand analysis of liquid hydrogen. The number of 50 vehicles is assumed to be the minimum of this kind of production model, so that the general figures shown by this table will be considered moderate. The price of each vehicle assumed here will be highest and should be lower than 100 billion Yen when more experiences are accumulated in this field.

The number of flights per year, 300 are required for each vehicle. Considering 20% of off-service days in a year for maintenance, this figure assumes each vehicle makes one flight every service day, less frequently than a Wide-bodied Jet that makes two flights everyday through a year.

Total cost required for each flight is divided into three categories; amortization, fuel and miscellaneous. The sum of these costs is 79 million Yen. From an economic point of view, the number of passengers and the fee have to be determined to cover this cost. An example shown here is for 50 passengers to pay 1.6 million Yen for each. It should be noted that the price and life of a vehicle which affect the amortization, depending on the engineering efforts. So far, no serious study was not made for development of such a vehicle.

In Table 1, most of the vehicle characteristics were given as a statistical data of a transportation system, except for the numbers of passengers and the cost of fuel per flight. To estimate quantitative demand of liquid hydrogen, based on these figures, design data of some vehicles will be used. Actually, there are few choices of vehicles which have potential capability to carry fifty human passengers by propellants worth 16 million Yen.

Table 2 shows selected mass properties of three vehicles of SSTO which were designed conceptually (ref.2, 3 and 4). Payload mass of the JRS study vehicle includes fifty passengers and the crew members and necessary accommodations. If the same mass proportion is applied for payload mass of Phoenix, its passengers will be calculated to be thirty two. Then, propellants mass per passenger is larger for Phoenix than JRS study. However, Phoenix reserves additional mass for the pilot module which seems to give a conservative mass estimation. The BETA is a well-known vehicle, although its mass breakdown for passenger accommodation is not available.

Table 2 Comparison of SSTO Mass Properties

Vehicle	BETA	Phoenix C	JRS Study
Payload (ton)	4	4.77	7.51
Passengers (persons)	-	32	50
Lift-off mass (ton)	131.5	206	550
Propellants mass (ton)	117.5	183.8	494.9
Mixture ratio (Lox/ LH2)	5.5-8.0	7-13	6

Because of the convenience of communicating with the concept developers for technical detail, we have chosen the JRS study model as a reference vehicle to estimate the operation cost required for the passenger vehicle in Table 1, and summarize the propellants consumption data in Table 3 for further study.

According to the cost requirement shown in Table 1, the cost of 424.2 ton of liquid oxygen and 70.7 ton of liquid hydrogen of this model should be 16 million Yen. Since the current prices of both liquids are almost same if measured per volume, the target prices of both liquids will be ten Yen per litre for each, which is nearly half of the current price of these liquids in the U.S.

The consumers of liquid hydrogen and oxygen are space transportation operators at launch sites of major airports, as described later. Fueling operation for rockets used to be more time-critical than for aircraft in order to avoid loss of cryogenic propellants due to incomplete thermal insulation of the vehicle tank system. For the advanced space vehicle for space tourism, maintenance procedures will be simplified and overall procedures will be so designed to be repeated on a daily base. However, at the last moment of launch operation starting for chilldown and filling propellants, the situation will not be improved so much from that of Space Shuttle whose procedure of filling propellants takes about two hours including ten minutes for chilldown. The advanced passenger vehicles will be designed to make the required time for fueling procedure shorter than one hour, which means the transfer speeds of liquid hydrogen and oxygen should be increased a little faster than those for Space Shuttle.

Figure 1 shows an image of a spaceport provided with three vehicle spots where passenger boarding and ground support operation will be performed. A vehicle will return to one of the spots exactly in the same way as it is placed for lift-off. Ground operation will be started for the next flight as soon as it lands on the spot. Probably fueling pipelines will be connected soon after de-planed.

Different from traditional thinking, a preliminary study (ref.4) suggests that the launch sites for space tourism should not be remote from populated cities but attached to or a part of major airports, since vehicles for space tourism to be designed to assure passenger safety by more strict safety standard than existing safety standards used for ammunition and traditional space rockets.

When fifty vehicles are to enter operation, about ten spaceports will be required to provide services to their flights. The fifty vehicles will be owned by more than ten operating companies. As far as the propellant supply is concerned, in the early phase of space tourism, four to five flights will take place at each spaceport everyday. In this case, each spaceport will be required to handle 4000 kl (280 ton) of liquid hydrogen and 1500 kl (1600 ton) of liquid oxygen for net loading in vehicles everyday.

In this paper, liquid hydrogen supply will be mainly discussed, since the present level of production of the hydrogen industry is too low to satisfy the predicted future demand while the oxygen industry is already a well established industry. In Japan, for example, annual production of hydrogen is equivalent to 7000 kl (500 ton) of liquid hydrogen, and the one third of which is used for rocket propellant. The full capacity of production facilities is equivalent to 22000 kl of liquid hydrogen which correspond to 60 kl (4.2 ton) per day, only 6 % of demand for a single vehicle operation previously discussed. As for the cost, the present cost of liquid hydrogen in Japan is 40 times higher than the target cost in Table 1. (Data as of 1993).

Although being considered to contribute and benefit from development of space tourism, the liquid hydrogen industry stresses evolutionary growth of production, being concerned about the risk of investment in the future of the great but unknown market.

An example of a supplier's plan of progress of liquid hydrogen supply for the space tourism industry is shown by eight phases defined as follows;

1. Development of vehicles.
2. Test flight.
3. Three flight per year.
4. Ten flights per year
5. Twenty flights per year
6. Thirty six flights per year.
7. Seventy flights per year.
8. Daily flights through year.

In case that one flight requires 70.7 ton of liquid hydrogen, the total quantity of liquid hydrogen to be loaded on vehicles in a year of each phase has been calculated, as shown by Table 4.

Net loading quantity of liquid hydrogen**

If the vehicles are assumed to be produced in line like commercial aircraft, engineering works such as design, subsystem tests, assembly and flight tests will be necessary before certification of a production model is accomplished. Considering the quantity of liquid hydrogen for each phase, the scenario described above can be applied for vehicle development activities. This development period is especially important for both vehicle industry and liquid hydrogen industry to establish a reliable relation of supply and demand of liquid hydrogen. Experience during this period will be useful for planning a large scale operational hydrogen supply systems, and vehicle development activities through certification of the vehicle will assure the successful flight operation that will require large scale hydrogen facilities.

Although length of each phase is not specified for the liquid hydrogen scenario, a constant step-up of production capacity will be desirable. On the other hand, there will be another requirement for time schedule of vehicle development which determine the demand of liquid hydrogen. It is the most desirable that the demand increases keeping a good balance with the growing hydrogen supply shown by the scenario. Figure 2 is a diagram to show liquid hydrogen supply in a scale of net loading capacity of liquid hydrogen vs. vehicle development time schedule. The liquid hydrogen supply shown by the bars is based on a hypothetical time schedule of a vehicle development prepared to show an example of relation between increases of demand and supply of liquid hydrogen. In this case, the increase rate is logarithmically uniform. In an actual case, however it will depend on largely on the certification flight requirements that is to be determined.

Once mass production started, the demand of liquid hydrogen will rapidly increase in proportion to vehicle and flight numbers. Table 5 shows a result of a case study of operational vehicle production. According to the study, the fifty vehicles are assumed to be produced in seven years, that is, 0.6 vehicle is delivered every month to globally deployed operators who are based on each home spaceport. By the end of seven years of production, the global liquid hydrogen supply capacity will be increased to 3535 ton/day.

The present air transportation system will be a basic model for deployment of spaceports for space tourism on a global base in three regional zones; the eastern Asia and Oceania, the north and south America and the Europe and Africa. Table 5 also shows a scenario of opening spaceports in these regions.

In spite of the forecast shown by the case study, the U.S. and Canada are considered to be the best for the first operational base for vehicle operators, since even now the price of liquid hydrogen is much lower than in Japan and Europe and very close to the target cost. The high price and low production featuring the Japanese liquid hydrogen industry are due to high electricity cost and unnecessarily strict regulation for transportation and storage. If liquid hydrogen is transported by large vessels specialized to the purpose, like LNG carriers, even now the suggested quantity of liquid hydrogen propellant will be supplied on a global base by commercial suppliers.

The main field of a large scale hydrogen use under study is clean energy to substitute carbon fuel for terrestrial use in large scale. However, demand for hydrogen as clean energy is a matter of the future of humankind which is too general to be a driving force to motivate technology development for large scale liquid hydrogen supply systems. On the other hand, demand of rocket propulsion for space tourism is definite, especially in the requirements of cost and quantity. The customers for space tourism do not need to stick to usage of hydrogen produced from non-carbon materials for clean energy. The space vehicle operators deployed on a global base. This will be a good opportunity for liquid hydrogen industry to consider global supply network. Once technology has been established for large scale use of hydrogen, the space tourism will also contribute to development of clean energy hydrogen material, such as application of dedicated hydroelectric power stations for electrolytic production of hydrogen.

Liquid hydrogen is the key issue for space transportation to be used for space tourism. Considering the early phase operation of public space transportation and the present technology of liquid hydrogen production and transportation, space tourism featured by low price and mass transportation will be technically feasible. The future of liquid hydrogen business will be opened by this customers and will be followed by new energy for mankind.

1. P Collins, 1993, "Towards Commercial Space Travel", JSTS Vol.9 No.1, pp. 8-12
2. D E Koelle, 1971, "BETA, A single-stage Re-usable Ballistic Space Shuttle Concept", Proc. of the 21st IAF Congress, North-Holland
3. G C Hudson, 1985, " PHOENIX: A Commercial, Reusable Single-stage Launch Vehicle", Pacific American Launch Systems, Inc
4. K Isozaki, A Taniuchi, K Yonemoto, H Kikukawa, T Maruyama, T Asai and T Murakami, "Vehicle Design for Space Tourism", presented at the 19th ISTS, Yokohama (preprint: ISTS-94-g-22p) and revised to be included in JSTS Vol. 10, No. 2, pp .22-34
5. JRS Space Tourism Study, 1993, 'Customers Requirement for Passenger Rocket Vehicles', JRS, Preliminary Draft
6. This figure was based on a concept developed for Committee for SPS Study, March 1994