Abstract - This paper describes a qualitative business plan for starting a space tourism business. The first step is the development of the Ascender small sub-orbital spaceplane - a sort of "re-invented X-15" - designed for quick turnaround, and capable of carrying two pilots and either experiments or two passengers. Ascender uses no new technology and could be flying in three years. There is a large enough market for such an aeroplane, without depending on carrying passengeres, for a good return on investment. After a few years in service as a general purpose research aeroplane it would be certified for carrying passengers on brief space experience flights. The resulting sub-orbital passenger flights should provide the credibility needed for the development of full scale orbital tourism.

This paper considers how to fund the first phase of a space tourism business. The strategy is to start with a project small enough to be funded privately but which nonetheless should generate the credibility needed for funding the development of orbital space tourism.

Orbital space tourism is defined for present purposes as fare-paying members of the general public visiting space hotels, i.e. space stations in low Earth orbit equipped for leisure, entertainment and education. Sub-orbital tourism involves short zoom-climb flights to space height.

From the experiences of some 350 astronauts to date we know that trips to space are fascinating experiences. The main attractions are the views of the Earth, views of the various heavenly bodies, and playing around in microgravity. Thus it seems likely that large numbers of people will want to go as soon as it is sufficiently safe and economical.

From work done so far on space tourism, the following statements are suggested as representing a consensus:

1. The main development required is safe and economical transport to orbit. For the pioneering phase of space tourism, safety will have to approach that of adventure holidays on Earth, and the cost around $100,000 to attract significant revenues. To enable a large scale business, safety will have to approach that of airliner transport, and the cost around $10,000 so that middle income people prepared to save can afford at least one trip in a lifetime.

2. Costs of this order can be achieved with reusable launch vehicles that have matured to airliner standards of turn-around time, maintenance costs, airframe life, etc.

3. There has been sufficient experience of manned spaceflight over the past thirty five years to be confident that there are no insoluble safety problems. Clearly however, the risks due to space debris, radiation, de-pressurisation and reentry will need careful management.

4. Once space tourism starts, it is likely soon thereafter to become the largest commercial use of space, and to provide the operating experience and commercial incentive to drive costs down towards their mature level. Such a development will transform traditional space activities by greatly reducing cost and improving reliability.

There is less agreement on the type of transport spaceplane that will be required. Arguments still have to be resolved between single stage to orbit versus two stage to orbit; vertical take off and landing versus horizontal take off and landing; pilotless versus piloted; subsonic versus supersonic versus hypersonic separation speed; and air-breathing versus rocket engines.

Bristol Spaceplanes Limited has suggested that these basic design features should be chosen with the aim of reaching maturity as soon as possible, and that the first spaceplanes should therefore be piloted, have two stages separating at supersonic speed, jet and rocket engines on the lower stage, and take off and land horizontally. The arguments behind these conclusions are given in [1] to [3], and are discussed later.

There is even less agreement on how the development of space tourism should be funded. The problem is that the traditional source of funding for developing launch vehicles has been government space agencies, who have neither the inclination to pursue tourism vigorously, nor the ability in the present political climate to raise the funding. Thus the private sector will have to take the lead. This leads to a circular argument. Industry traditionally looks to government for space infrastructure funding and advice and support for commercial developments. Governments will not take space tourism seriously until there is a strong consensus in industry.

NASA has indeed started a process by which space tourism should eventually happen. They are part-funding two demonstrators for reusable launch vehicle technology, the X-33 and X-34. These should lead to operational reusable launchers which in the fullness of time should achieve adequate maturity to start a space tourism business. But these vehicles were not designed with early maturity in mind, and if space tourism is to start soon a new approach is needed.

Such an approach is described in this paper.

In order to attract private investors to space tourism, it is essential to minimise the risk capital involved, because of the uncertainties involved. What is wanted is a pilot scheme that does not cost much to develop, that has an early market that does not depend on tourism, but yet can be used for early demonstrations of the feasibility of space tourism.

The Ascender small sub-orbital spaceplane meets these requirements. A prototype could be developed at low cost, it would have a market as a general purpose high speed/high altitude research aeroplane, and after a few years in service could be certified for carrying passengers on sub-orbital flights. Ascender is described in the next section, and follow-on developments in subsequent sections.

3 ASCENDER

Figure 1. Ascender.

Ascender, fig. 1, is designed to be able to carry four people to and from the edge of space. It is a sort of "re-invented X-15", designed to be able to make several flights per day. (The X-15, fig. 2, needed typically two weeks between flights. The DC-X has demonstrated the feasibility of reusable launch vehicles with short turn around time.) Ascender has evolved from the Shuttle Sounding Rocket and Spacecab Demonstrator projects, [2] and [4], and was first published in [5].

Ascender has a cabin equipped for a crew of two and a payload bay. The payload can either be experiments or two passengers. The engines provisionally selected are two Williams-Rolls FJ44 turbofans and one Pratt & Whitney RL10 rocket.

Figure 3. Ascender Flight Path.

A typical trajectory is shown in fig. 3. Ascender takes off from a conventional runway and climbs on jet power at subsonic speed to an altitude of 8 km. The rocket motor is then started and the pilot pulls up into a near vertical climb. When the rocket fuel is used up, Ascender is climbing close to the vertical at a height of 64 km and a speed of Mach 2.8. It then coasts on an unpowered ballistic trajectory (i.e. zoom climb) to a maximum height of 100 km and then enters a steep dive. On reaching the effective atmosphere the pilot pulls out of the dive and flies back to the airfield from which he took off some 30 minutes previously. It would offer about two minutes of microgravity, and would fly high enough for superb views of the Earth and for the sky to turn black with bright stars even in daytime.

The key point about Ascender is that a prototype can be built with entirely existing technology. The aerodynamic shape is scaled down from that of the Space Shuttle Orbiter. The heat loads are far less than those of the Shuttle, and a simplified and updated thermal protection system can be used, in turn permitting the use of a conventional aluminium alloy structure. (The X-15 had an advanced nickel alloy "hot" structure.) The engines are in service, although the safety and reliability of the rocket motor for manned aeroplane flight will need careful consideration.

The feasibility of an aeroplane like Ascender is not in doubt. The X-15 flew somewhat higher and faster more than thirty years ago. By using higher performance engines now available, Ascender avoids the need for air-launch and is smaller. Systems for life support, reaction controls, communication and navigation are all well within the state of the art.

In aerospace history, the timescale from a record-breaking experimental aeroplane to operational deployment of the new capability has usually been less than ten years. Sub-orbital aeroplanes have been neglected since the X-15, and a rapid catching up is possible.

Ascender would be designed for fast turnaround and low maintenance cost. The aeroplane closest to Ascender in terms of potential operating cost is probably the Saunders-Roe SR.53 jet plus rocket fighter, which first flew in 1957, fig. 4. The two aeroplanes are of broadly comparable size and weight, and both have a jet engine and a rocket motor. Only two prototypes of the SR.53 were built, and it did not enter service. Had it done so its cost per flight would probably not have been very different from modern jet fighters, which is typically around $10,000. This provides a preliminary target for the cost per flight of Ascender when mature.

In order to achieve costs that low, the life and maintenance cost of the rocket motor and of the thermal protection system will need considerable improvement. The timescale to reach such maturity is discussed later.

The SR.53 had a theoretical ballistic height of 40 km. A simple estimate shows that if fitted with a modern rocket (with higher specific impulse) it could reach some 80 km, which is the usual definition of space. Such a development would need reaction controls, enhanced life support, and probably some thermal protection. All these additional systems are well within the state of the art, which provides added evidence that Ascender does not need new technology.

Ascender would be used initially as a reusable sounding rocket for space research and as a spaceplane technology test-bed. It would be suitable for: carrying microgravity experiments, high altitude photography, astronaut training, upper atmosphere measurements, testing satellite instruments; and as a spaceplane technology test bed. In particular, it would be useful for testing advanced thermal protection systems, life support systems, and long-life rocket components.

A conservative estimate is that five Ascenders would be sold over a five year period, for research purposes.

After a few years in service Ascender would be certified for passenger carrying passengers. The fare per passenger should be around $5000. It is difficult to assess the early market for sub-orbital tourism at this price. From recent market research, [6] and [7], it seems conservative to assume that one million people per year would pay $10,000 for a trip of a few days to a space hotel. This would require a fleet of some 50 spaceplanes, which is a larger credible demand than for any other projected use of spaceplanes in the near or medium term future.

A sub-orbital flight offers far less, but has the attraction of a pioneering novelty. If we assume, probably conservatively, an annual demand of 100,000 passengers per year worldwide, that Ascender is stretched to carry four passengers, and that each aeroplane makes on average two flights per day, then a fleet of some 30 Ascenders would be required.

Ascender could thereby start an embryonic space tourism business.

The development programme for Ascender (and for the follow-on Spacecab, described later) is shown in fig. 5 Ascender is a far less advanced project than the X-33, which is planned to fly some three years from go-ahead. Ascender has a maximum speed of Mach 4.4, an all up weight of 8800 lb, and a propellant mass fraction of 54%. The corresponding X-33 values are Mach 15, 273,000 lb and 77%. Thus Ascender could also be flying in three years, given the required funding.

Figure 5. Ascender and Spacecab Development Programmes.

A new airliner requires typically 1000 test flights to obtain its type certificate. If we assume that Ascender requires 2000 flights and that five aeroplanes each make two research flights per week, then certification would take four years.

Thus sub-orbital space tourism could start in about seven years.

To estimate the time to reach maturity there is a useful analogy with jet engine development. The first jet aeroplane to fly was the Heinkel He 178 in 1939. The first operational jet fighters (Gloster Meteor and Messerschmitt Me 262) entered service in 1944. The first jet airliner to enter service was the de Havilland Comet, in 1952. Thus it took just thirteen years from first jet flight to first commercial jet airliner service.

The total number of flying hours to date of rocket motors (in missiles, launchers and rocket powered aeroplanes) is comparable to that of jet engines at a very early stage of development, probably around 1944. The reliability and life of jet engines have improved by three orders of magnitude since then (the time between overhauls of the Junkers Jumo 004 worked up to about eight hours), and it does not seem unreasonable to assume that rocket motors could follow broadly comparable learning curves. By mature aeroplane standards, rocket motors are at an experimental stage of development. Much the same applies to thermal protection systems. Thus it seems probable that mature Ascender operations could be approached within about 15 years.

The reason for the slow maturing of rocket motors to date has been the lack of a strong demand for long life. Their use in aeroplanes has been limited, and there has not yet been a reusable launch vehicle. The longest life high-performance rocket motor to date was the 8000 lb thrust Bristol Siddeley BS 605, used as a take-off booster by the Blackburn Buccaneer bombers of the SAAF. A life of 60 firings between overhauls was claimed.

The development cost of Ascender to the prototype stage useful for research should be comparable with those of the X-34 and DC-X, i.e. in the region of $50 million to $100 million, assuming an experimental workshop approach to development. At such a cost, the estimated market of five Ascenders would be sufficient for a healthy return on investment.

4.1 Spacecab

Ascender would pave the way for the Spacecab piloted two stage spaceplane. It is designed for launching satellites in the one tonne class, and for ferrying six crew to and from space stations. Spacecab, fig. 6, is described in [1] to [3]

Figure 6. Spacecab.

Spacecab is essentially an updated version of the 1960s European Aerospace Transporter projects modified to use technology developed since then.

The carrier aeroplane lower stage looks not unlike Concorde, but has a simpler aerodynamic shape and structure. This is acceptable because Spacecab has only to accelerate to maximum speed, release the upper stage, and fly back. There is no long range cruise requirement, and hence no need for the last percentage point of aerodynamic or structural efficiency.

(It was primarily the range shortfall of the Concorde prototypes that necessitated the subsequent stretch to the so-called pre-production standard, and yet another stretch to the production standard. Even the first two "production" aeroplanes did not enter commercial service. It was this extended evolution that was mainly responsible for the development cost and time overrun.)

The lower stage of Spacecab has conventional jet engines for acceleration to Mach 2. Rocket engines then take over for acceleration to Mach 4 and climb to the fringe of the atmosphere. Separation takes place where the air is thin and dynamic pressure low. Air loads during separation should therefore be a manageable design problem.

The upper stage has six engines in the RL-10 or HM7 class. It is essentially a refined and enlarged Ascender. It has a lightweight wing/tank which is partially pressure stabilised.

Spacecab would be used initially for launching small satellites, for ferrying crew and supplies to and from space stations, and for transporting mechanics plus spare parts to service satellites in low orbit. These missions are those in greatest need of a new launcher. After a few years in service Spacecab would be certified for carrying passengers, and would then start an orbital tourism business.

The basic design features of Spacecab were chosen in order to reach short turnaround time and low maintenance cost as soon as possible. A useful measure of maturity is type certification for passenger carrying, i.e. meeting FAR 25 or similar requirements as adapted for spaceplanes. It seems likely that the design capable of reaching this milestone the soonest will also mature the soonest. (Type certification is but one of several regulatory issues that will need to be addressed [8], but is probably the most critical for an early tourism business.)

The following discussion considers how the requirement for early civil certification affects the required fundamental design features. The arguments are summarised from those in " A Preliminary Feasibility Study of the Spacecab Low-Cost Spaceplane and of the Spacecab Demonstrator", [3].

Civil certification means higher safety factors and system redundancy than those of present or planned launchers. It would also be prudent to assume that pilots will be required, since there are no plans for pilotless airliners in the foreseeable future.

These requirements in turn mean higher weight, which for an early design favours two stages. The need for the X-33 demonstrator indicates that the engines and materials do not exist today for a reusable SSTO satellite launcher, let alone for a passenger carrying one.

Horizontal take off and landing is inherently safer than vertical take off and landing, and is therefore desirable for an early design.

For early certification the use of advanced technology should be minimised. This means that stage separation should be at supersonic speed, probably around Mach 4. Subsonic separation eases the upper stage design task compared with taking off unaided, but not enough to avoid the need for an advanced structure or advanced engine. (True SSTOs need both.) Hypersonic separation requires an advanced lower stage, and involves a difficult flyback problem. At around Mach 4 a design can be derived such that both stages can use existing technology.

Jet engines on the lower stage are desirable for ferry flights, flyback, aborted landings, and cruise to the required orbit plane. Off-the-shelf jet engines suitable for rapid development to airliner maturity are limited to about Mach 2. Additional rockets are therefore required to reach Mach 4.

Thus an early tourist carrier would be piloted, have two stages, supersonic separation, jet and rocket propulsion during the boost phase, and would take off and land horizontally. In the 1960s there were many projected piloted two stage spaceplane projects, and the consensus at the time was that they were feasible, but needed a programme of enabling technology development. Several of these projects were inspired by the X-15 and XB-70, fig 2. Many thought at the time that an orbital successor to the X-15, hydrogen-fuelled, delta winged, and air-launched from a re-designed B-70, would be the quickest way to achieve an orbital aeroplane.

For reasons having perhaps more to do with politics than with engineering or commercial arguments this approach has never been followed.

Spacecab was the subject of a feasibility study for ESA [3], that showed that Spacecab could use existing engines and conventional structural materials. A subsequent independent review for the UK Minister for Space "has not identified any fundamental flaws in Mr Ashford's concept"[9].

The development cost of a Spacecab prototype should be in the region of one to two billion dollars to the point of revenue service [1] and [2]. As a check on this estimate, it can be compared with that of the X-33, at around $1.2 billion [10]. The Spacecab upper stage is not unlike an X-33 of one third the gross weight but using existing engines and proven materials. It should therefore cost less to develop, say half as much at $600 million.

A preliminary estimate for the lower stage prototype can be obtained by scaling the development cost of Concorde, which is about $12 billion at present prices. This can be multiplied by 50% because Spacecab uses existing engines whereas half the Concorde development cost went on the propulsion system. It can be multiplied by a further 10% because prototype aeroplanes cost typically 10% of the total cost to certification. Spacecab can earn revenue even as a prototype by launching satellites as soon as the flight test programme reaches orbit, which might take around 20 flights. Concorde needed some 2000 flights involving six non-deliverable aeroplanes to achieve its type certificate.

Multiplying these factors indicates a development cost for the lower stage prototype of around $600 million, and a total for both stages of $1.2 billion. Allowing for the preliminary nature of this estimate, it seems that the development cost of Spacecab would be recovered by substituting it for four or fewer Shuttle flights at some $500 million each. Since 28 Shuttle flights are planned for the International Space Station alone, it is probable that many more than four Shuttle flights would be saved.

Thus NASA, for example, could bring about a rapid reduction in launch cost and save money by sponsoring the development of a piloted two-stage launcher. (A preliminary business plan on these lines is given in [11].) This is an important conclusion.

Spacecab would be followed by the 50 seat Spacebus, which when mature has a direct operating cost per person to orbit of some $5000 [2].

We have seen that sub-orbital space tourism could start in about seven years in a re-invented X-15, given the required funding, and that orbital tourism could follow a few years later. We have also seen that tourism is then likely to become the largest commercial use of space, and will thereby provide the commercial incentive to drive costs down to their mature level, which will in turn lead to a mature orbital infrastructure of benefit to all space users. The cost per person to orbit will be more than 1000 times less than it is today.

The result will be a paradigm shift in astronautics, with launchers based on aeroplane technology replacing those based on ballistic missiles. There is perhaps an analogy with the way that aeroplanes largely supplanted balloons early this century, causing a paradigm shift in aeronautics.

These results may seem surprising to many: perhaps less so to those who have studied space tourism. We have become so used to the high risk and cost of human spaceflight, because of the use of launchers relying on ballistic missile technology, that the concept of a mature spaceplane takes some getting used to. When thinking about a new airliner, the maturity standard is taken for granted. When thinking about new launchers, whether reusable or not, the tendency is to assume that its maturity will be that of an expendable vehicle like a ballistic missile, or of an experimental high performance aeroplane like the X-15.

The new factor is a potential market - space tourism - large enough to require a large fleet size and to provide the operating experience and the commercial incentive for the continuous product improvement needed to approach airliner maturity.

It is interesting to note that thirty years ago the concept of a piloted two-stage spaceplane was widely considered to be the logical next step in space transportation. At that time it would have required a major development programme. Surprisingly, now that the technology exists and it would involve a development programme costing about as much as a small airliner, such a project is not even on the mainstream agenda!

1. A qualitative business plan has been described for starting space tourism. The first step is the development of the Ascender sub-orbital spaceplane. This would be used initially as a research aeroplane, and later for carrying passengers on brief space experience flights.
2. Ascender should have a good return on investment in its own right when developed to the prototype stage only. Revenues from subsequent passenger carrying production versions would be a bonus.
3. By analogy with jet engine development, Ascender should approach a mature cost per flight of some $10,000 within fifteen years from now.
4. Ascender would provide the credibility needed to gain the funding for a piloted two-stage spaceplane, Spacecab. The development cost of this project would be recovered by substituting for just four Shuttle flights. Spacecab would be used initially for carrying crews and supplies to and from space stations, and for launching small satellites.
5. An enlarged and mature development of Spacecab, called Spacebus, would have a direct cost per person to orbit of some $5,000 when mature, which is about 1000 times lower than the present cost.
6. The sooner that space tourism gets on to the mainstream space agenda, the sooner this transformation of our space activities is likely to be achieved.

1. D M Ashford and P Q Collins, Jan/Feb/March 1989, " The Prospects for European Aerospace Transporters", Aeronautical Journal
2. D M Ashford, June/July 1995, " The Spacecab Demonstrator Project", Aeronautical Journal of the R.Ae.Soc.
3. Bristol Spaceplanes Limited, February 1994, " A Preliminary Feasibility Study of the Spacecab Low-Cost Spaceplane and of the Spacecab Demonstrator". Bristol Spaceplanes Limited Report Number TR6. Prepared for the European Space Agency under Contract No 10411/93/F/TB. (Volume 1 subsequently published as " The Potential of Spaceplanes" in the Journal of Practical Applications in Space, Spring 1995.)
4. D M Ashford, June 1983, " The Aeroplane Approach to Launch Vehicle Design", JBIS April 1984. Presented at the 18th European Space Symposium, London
5. D M Ashford, Feb 1-8 1997, "Space Tourism - How Soon Will It Happen?", Presented at 1997 IEEE Aerospace Conference, Snowmass, Colorado
6. Patrick Collins, Yoichi Iwasaki, Hideki Hanayama and Misuzu Ohnuki, "Commercial Implications of Market Research on Space Tourism", Journal of Space Technology and Science Vol.10 No.2 pp 3-11
7. P Collins, R Stockmans and M Maita, December 1995, "Demand for Space Tourism in America and Japan, and its Implications for Future Space Activities", Presented at Sixth International Space Conference of Pacific-Basin Societies, Marina del Rey, California
8. Dr William A Gaubatz, April 1996, "Comments on Certification Standards for New Reusable Launch Vehicles", Presented at FAA Office of Commercial Space Transportation Public Meeting to Address Issues Related to Commercial Space Transportation
9. Letter from Ian Taylor MBE MP, Parliamentary Under-Secretary of State for Trade and Industry, to The Rt Hon Sir John Cope MP, 23 March 1995
10. "Follow-on Plan Key to X-33 Win", Aviation Week, July 8, 1996
11. D M Ashford, October 1995, " A Development Strategy for Space Tourism", JBIS February 1997. Presented at 46th International Astronautical Congress, Oslo.

David Ashford is director of Bristol Spaceplanes Limited, a spaceplane and space tourism consultancy. He graduated from Imperial College, University of London, in aeronautical engineering and spent one year at Princeton doing post graduate research on rocket motor combustion instability. His first job, starting in 1961, was with the Hawker Siddeley Aviation spaceplane design team. He has worked as an aerodynamicist, project engineer or project manager on various aerospace projects, including DC-8, DC-10, Concorde, the Skylark sounding rocket, and various naval missile systems. He co-authored the first serious book on space tourism "Your Spaceflight Manual - How You Could be a Tourist in Space Within Twenty Years", by David Ashford and Patrick Collins, Headline 1990.