The "Golden Age" of space travel , the 1960s, which brought us the Manned Moon Landing and many more highlights of human achievement in space, also saw the beginning of space tourism research. In 1967, the late Krafft Ehricke laid the foundation for later studies in this field and released his paper "Space Tourism" 1. Back then, many people thought that current achievements in manned space travel would lead to short term utilization of newly developed launcher technology for commercial purposes. Unfortunately, the evolution of manned space travel took a different path due to economic and political reasons.

Today, space travel is still the privilege of some "Happy Few"; with the tax payer as uninvolved bystander. NASA, for instance, ruled out the Space Shuttle for Space Tourism in 1985, even before the Challenger accident 2. Private persons who want to fulfill the dream of their life still have no opportunity to book a commercial space trip. One exception however, was the Japanese Toyohiro Akiyama, who had been booked as passenger on a Soyuz TM spacecraft in December 1990 3. Akiyama's employer, a Japanese TV station, had to pay about $18 million for the trip. Since the Soviet Union does no longer exist and the now-Russian space program is in big trouble, the future for commercial flights aboard Russian spacecraft is bleak. Otherwise, privately initiated ventures, like the ill fated "Project Space Voyage" 4,5 by Society Expeditions and Pacific American (day trips to orbit for $50,000 per ticket, starting in 1992), haven't yet turned out to be successful.

The present specific transportation cost per passenger to orbit is far too high to allow any sustainable development of space tourism. The Space Shuttle, for instance, while being the only operational (partially) reuseable launch system worldwide, costs at least $30 million per flight and person, depending on annual launch rate and crew size. A proposed 74 passenger module for the Shuttle 6 would have caused cost reductions to about $4 million per ticket. If NASA had not ruled out the Shuttle for space tourism in 1985, these cost figures alone would have been prohibitive for broad market development.

The message for potential space travel agencies is clear: the availability of inexpensive space transportation systems is a prerequisite for space tourism. Unfortunately, the process which may lead to developing a new generation of launch vehicles is caught in a kind of vicious circle: as long as present launch systems are so expensive, the transportation demand will remain low. In the same way, as long as transportation demand remains low, the motivation for developing new cost efficient vehicles will remain low as well (see Fig. 1).

High transportation demand can either result from space tourism itself or from some big extraterrestrial project (i.e. a Space Solar Power System (SSPS)) as catalyst.

Four different market scenarios of future passenger transportation to LEO have been worked out as input for computer simulation. Time horizon for all scenarios is 50 years (2001 to 2050). Future transportation demand results from a combination of space tourism and "business traffic".

Even if space tourism never happens, manned spaceflight is here to stay. Potential trends in space commercialization associated with "man in space" include various projects in the sectors of energy conversion (SSPS), production (space manufacturing facilities), orbital services and transportation. These activities will more or less lead to a particular passenger transportation demand. One can therefore assume demand for a future launch system to handle these "business flights".

In addition to this baseline demand, space tourism could be a driving force for increasing the Earth to orbit transportation amount.

Diverse assumptions on future business and tourism development lead to the definition of four different scenarios:

Reference scenario:

National space agencies will offer spare passenger transportation capacities on a Shuttle successor vehicle (2 stage VTOHL) for being marketed by a commercial company. Demand is low. Business flights begin in 2008, tourism starts in 2010.

Scenario A:

Same as reference scenario, but the vehicle is more advanced (2 stage HTOHL). Demand is moderate. Business flights begin 2010, tourism in 2012.

Scenario B:

Companies which build up very large space infrastructures (SSPS) offer capacities on HLLVs (2 stage VTOVL) for being assigned to commercial passenger transport, including space tourism missions. Demand is high. Business flights begin 2003, tourism in 2010.

Scenario C:

Advanced space vehicles (1 stage VTOVL, 1 stage HTOHL), which are spin offs of aerospace R&D efforts are utilized exclusively for space tourism. Demand is high. Operations (tourism only) begin 2001. Transportation system replacement takes place after 20 years, when the ballistic vehicle is replaced by an ultra modern winged SSTO.

The demand trends assumed for the four scenarios are illustrated in Fig. 2 and 3.

The knowledge which has been accumulated in over three decades of operating manned launch systems indicates that manned space flight is still more like a R&D enterprise than a routine affair. Specific transportation costs are far too high while operational safety still offers much room for improvement. Optimal vehicle layout for commercial utilization requires a "design for operations". This means that top priority is given to reduction of recurring costs and to vehicle safety. The design objectives of advanced launch vehicles are shown in Fig. 4.

Present trends in space technology which correspond to these objectives are:

• LOX/LH2 propulsion for main engines, orbital maneuvering and attitude control
• Advanced low maintenance rocket engines
• Advanced airbreathing engine concepts (for HTOHLs)
• Fly by wire systems with electric actuators replace hydraulic systems
• Advanced avionics/astrionics
• Modular, fault tolerant electronics
• Health monitoring
• Advanced lightweight structures
• Full reusability (including reusable tanks for cryogenic propellants and reusable all-weather thermal protection systems)

Recent discussions concerning the development strategy for future space transportation show that five vehicle designs are most favorable for passenger transport:

1. A fully reusable Space Shuttle successor (reference design: Shuttle II/AMLS 7) of relatively conservative, low risk design.

2. An advanced two stage vehicle with airbreathing hypersonic first stage (reference design: SÄNGER 8). This design is currently very popular in Europe, but requires development of some advanced technologies.

3. A heavy lift launch vehicle, primarily designed for heavy cargo transports; payload shroud can be replaced by very large passenger capsule (reference design: NEPTUN 9). Design is conservative and relies on many off the shelf components, including the propulsion system.

4. An advanced ballistic single stage to orbit vehicle (SSTO). This design is currently very popular in the U.S. ("Delta Clipper", by McDonnell Douglas 10) and involves some new technologies. The "PHOENIX E" ballistic SSTO by Pacific American was once suggested for space tourism operations, but could not be financed. Nevertheless, PHOENIX served as reference design 11.

5. A NASP-derived vehicle (NDV 12), a kind of "Super Concorde", which can operate like an airliner from conventional airfields. This design comprises revolutionary technologies like airbreathing transatmospheric engines and advanced lightweight structures.

The relevant technical data of the five different launch vehicle designs are shown in Tab. 1.

The operations model was developed according to the assumptions made during scenario writing. Based on the different demand functions for business transportation and tourism, model application delivers the main operations parameters vs. time for the different transportation systems as they are used in the four scenarios. The most important parameters are depicted in Fig. 5 and Fig. 6.

The simulation's results are used as input for the subsequent computation of cost trends.

The estimation of cost parameters vs. time applied a statistical-analytical method which is based on the "Transcost" model 13 by D.E. Koelle. Many of the original Transcost equations were adapted, while some Cost Estimation Relationships (CERs) were either "customized" or newly developed to handle a couple of special cases which were not taken into account by the original model.

The philosophy behind the cost model and its computer implementation is laid out in Fig. 7. Financing costs have been left out due to their dependence on pricing policy, but will be discussed afterwards.

The prime objective of cost analysis within this study has been the specific transport cost ($ per passenger per flight) of the different transportation systems. The specific cost equals total cost (gross operations cost) divided by numbers of passengers. The gross operations costs split into five cost elements. These comprise direct operations cost, indirect operations cost, vehicle amortization cost, launch site/range cost and cost for maintenance and refurbishment.

In order to avoid cost peaks due to acquisition of new vehicles, the acquisition costs are amortized via the launch rate. This means that the vehicles are either leased from the manufacturer or financed by bank loans. In both cases interest rates are set to 5 percent.

The accuracy of cost figures is naturally limited by the accuracy of Cost Estimation Relationships (CERs). "Transcost" which delivered most of the CERs utilized in this model, estimates accuracy to be +/- 15 to 20 percent.

Keeping ticket prices as low as possible is imperative for sparking development of a passenger transportation market.

As the cost trends in Fig. 9 show, the achievable degression per seat is limited. Computer simulations with transportation numbers of up to 100 million passengers per year suggest that a figure of $30,000 ($1990) per passenger is the absolute minimum within reach of an advanced NDV. This contrasts sharply with other studies 14, where specific costs of as little as $1000 per seat (for 100 million passengers per year) are given.

Pricing is the most important issue in the context of commercial space ventures. The strong interdependence between ticket price and space transportation demand as mentioned before (see Fig. 1) makes this clear. So a high value was set on price policy.

Pricing strategy has to take into account the negative effect high profitability leading to rising prices could have on demand. Here the premise is to initiate a new market for manned space transportation systems in conjunction with public access to space. Therefore a high profit margin is not the focus of interest.

The following has to be considered developing a price policy:

• A positive cash flow will have to appear after no longer than 10 years of operations in order to pay off creditors.

• At begin of operations, specific transport cost will be too high to pursue low pricing. So, ticket prices should at least cover expenses to minimize the financial burden on life cycle profit. During this phase a ticket price of about $500,000 ($1990) seems to be obtainable.

• With the cash flow becoming positive, a price reduction will have to be carried out to stimulate demand.

• Later on, ticket pricing is continually optimized to achieve lowest fares and avoid negative cash flow in one. A maximum profit must not be the focus of interest.

According to these considerations the so called "skimming pricing" seems to be very suitable to initiate a commercial manned Space Transportation System (STS). Starting with high fares, these are reduced later on according to market exploitation. The objective of skimming pricing is to amortize a high startup cost within a relatively short period.

Ticket price trends resulting from this policy are depicted in Fig. 10.

As one can see, the lowest ticket price can be achieved in Scenario C. By using a very advanced NASP derived vehicle (NDV) for the transport of over 40,000 passengers a year, the time from the year 2040 on may bring ticket prices as low as $60,000 ($1990). Compared to the present situation, this would be a significant improvement, but the transport system operators would have to do without much profit.

Three out of four scenarios presented in this paper rely on transportation systems of which development is either financed by government (Scenario Ref, A) or by large commercial space ventures which are primarily non tourism (Scenario B). The master question is: Can space tourism finance itself?

The first stumbling block for setting up a commercial passenger transportation service is the availability of a sufficient transportation system, because R&D of the latter has to be financed. Initiating space tourism as a venture which first requires development of a specially assigned passenger transportation system appears to be highly unfeasible. R&D cost of an advanced STS, which are in the range of tens of billions, are far too high to be amortized via ticket sales. Any price margin which allowed R&D payoff within an adequate timespan, would be high enough to strangle ticket demand. For instance, in scenario C, R&D amortization would almost double ticket prices.

Therefore R&D costs have to be raised by an organization not exclusively engaged in space tourism. If access to governmental funds were impossible, potential financiers could come from following branches:

• Aerospace engineering
• Airlines
• Tourism and travel

If an adequate launcher is made available, the second stumbling block will be the need to sacrifice high profits in order to stimulate ticket demand: Profit margins of as low as 10 percent may require some risk sharing among different partners. Therefore, operations of a regular passenger transportation service could be organized in the way of a joint venture between the three interest groups named above. All these branches would benefit from a high passenger transportation rate to orbit. The aerospace industry would be able to customize transportation systems, which are originally destined for non tourism purposes, in order to open up new markets for space systems namely passenger transportation and to gain product improvement as well as spin offs for other aerospace products. For airlines, the operation of an Earth to orbit vehicle would be a very effective means for advertising their ability to manage any kind of high tech transportation vehicle and to stress corporate excellence. Tourism industry, especially adventure travel companies (after all, the first one to offer commercial space trips has been Society Expeditions of Seattle, WA, a world famous specialist for extreme adventure travel) will be able to exploit an attractive new segment of high end adventure tourism.

In a joint venture the aerospace industry could contribute transportation systems, airlines their know how in operations and the tourism branch could provide capital and marketing measures. In view of world tourism revenues reaching $3,500 billion in 1992 15, a market share of, say, 0.1 percent would by far be sufficient for sustaining growth of an extraterrestrial travel business.

The authors of this paper are convinced that space tourism, or better "public access to orbit", is a prime objective for future development of space activities. With its relatively high passenger transportation demand, space tourism is an excellent reason for justifying development of new cost efficient launch vehicles. Besides, an existing option for every enthusiast to go into orbit may bring back some of the public support for manned space activities as it had been in the 1960s. Space tourism may appear to be out of time, but this is not so. Passenger trips to LEO can promote public awareness of our home planet's vulnerability and, above all, it is hard to imagine any form of travel which is more fascinating than a space trip.

The technical problems which are to be overcome before introducing a commercial passenger vehicle do not appear to be insoluble; after all, it took only ten years to send humans to the Moon. Aerospace literature gives enough examples for advanced space vehicles adequate for passenger transportation. Unfortunately, in this case utilization of high technology means high cost. Even if one avoids R&D costs being amortized via ticket prices, space trips will be the absolute high end of the tourism market. With ticket prices of at least $60,000 ($1990), as given in this paper, a single day trip to orbit will be more expensive than, say, the most luxurious 60 day first class sea cruise. It is therefore doubtful, whether space tourism will ever reach the development stage of a mass market with millions of passengers per year; at least not with the technology yet in sight. Otherwise, if one wants to fulfill a lifetime's dream and fly into space, he or she should be given a means to do so at a reasonable price. Opening up space for the public is an imperative.

AMLS	Advanced Manned Launch System
CER	Cost Estimation Relationship
HLLV	Heavy Lift Launch Vehicle
HTOHL	Horizontal Take Off, Horizontal Landing
IOC	Initial Operating Capability
LEO	Low Earth Orbit
NASP	National Aerospace Plane
NDV	NASP Derived Vehicle
R&D	Research and Development
SSPS	Solar Space Power System
SSTO	Single Stage To Orbit
STS	Space Transportation System
VTOHL	Vertical Take-Off, Horizontal Landing
VTOVL	Vertical Take Off, Vertical Landing

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