Spaceflight Revolution / David Ashford / 20 May 2003

Post:	3 Forest Hills, Almondsbury, Bristol BS32 4DN
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Email:	david.ashford@bristolspaceplanes.com
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A transformation of spaceflight is poised on the edge of lift-off. Within perhaps fifteen years, the cost of sending people to orbit may decrease a thousand-fold. This would, in turn, greatly reduce the cost of space science and exploration. Space tourism would become a major industry. This spaceflight revolution is being led by small companies and would cost far less than present government space plans.

These opening statements may seem too good to be true, but are based on the robust and straightforward plans of two private companies. The background analysis is described in more detail in [1].

Scaled Composites has recently unveiled its ‘Tier One’ programme, shown in Figure 1. The vehicle that flies to space, ‘SpaceShipOne’, is in the foreground and its carrier aeroplane, ‘White Knight’ at the rear. The idea is for White Knight to carry SpaceShipOne to a height of 50,000 ft (15 km) and then release it. SpaceShipOne then uses its rocket motor to pull into a steep climb and to zoom up to the lower edge of space. Carrying a pilot and two passengers, it reaches a maximum height of some 100 km, which is about ten times higher than the cruising height of a jet airliner. Gravity then pulls SpaceShipOne down towards Earth and it lands back at the airfield that it took off from, some thirty minutes after being released from White Knight.

Passengers will feel weightless for about two minutes, will see an area several hundred kilometres across at one time, and will see the sky turn dark with bright stars even in daytime. Burt Rutan, the President of Scaled Composites, says that the first flight to space could be this year or early next [2]. He estimates the cost per flight at under $80,000.

Rutan has not said so but, with further development towards a mature system capable of several flights per day, the cost per flight could approach that of two business jets of comparable size. The passenger fare would then be less than $5000. Achieving such maturity would take time and money, but is clearly possible.

Preliminary estimates indicate that the cost of development up to the stage of early flights to space should be in the region of $20-30 million, and that the cost of certification for commercial passenger carrying would be approximately $100-300 million.

SpaceShipOne is sub-orbital in that it will achieve enough height to reach space but not enough speed to remain in orbit. Satellite speed is some six times greater than the maximum speed of SpaceShipOne, and an orbital spaceplane will cost of the order of ten times more to develop than a sub-orbital one with comparable payload.

The second example from the private sector is Bristol Spaceplanes Limited founded in 1991 by the author. Spacecab, a fully reusable orbital spaceplane (Figure 2) designed to provide safe transportation to and from space stations, was the subject of an ESA feasibility study in 1993/4 [3]. The study concluded that it did not need major new technology, that development cost would be around $2 billion, and that the cost per flight would be some $10 million on early flights. And when the system had matured, with long-life rocket motors and other equipment, the cost would be reduced to less than $1 million. This study was broadly endorsed by an independent review carried out by the British National Space Centre at the request of the then Minister, Ian Taylor [4].

Ascender, shown in Figure 3, has a performance comparable to that of SpaceShipOne, but is a more conventional design. The sub-orbital Ascender is intended to pave the way for the orbital Spacecab by developing the market, demonstrating the feasibility of aeroplanes capable of several flights per day to space, and providing a focus for maturing the technology. Ascender is derived from the Spacecab Demonstrator project described in [5].

In contrast with these fully reusable designs, NASA is proposing an Orbital Space Plane (OSP), which is a manned spacecraft launched by expendable vehicle. The launcher is likely to be based on the latest version of Atlas or Delta, both of which derive from ballistic missiles. OSP is designed to carry crews to and from the International Space Station. One contending design is shown in Figure 4.

The table below compares some of the leading data of Spacecab and OSP. Spacecab would cost some five times less to develop; in addition, it would cost about ten times less to fly on early flights. When mature, the cost plummets to 100 times less. Not only would it be far less expensive, but it would also be far safer. (The arrows indicate progress from prototype to mature system.)

	Orbital Space Plane	Spacecab
Development cost, $bn	10+	» 2
Cost per flight, $m	100+	10 Þ 1
Flights per fatal accident	» 100	10,000 Þ 1,000,000

The explanation for this apparent paradox is that spaceplanes can cost less to develop than spacecraft launched by expendable vehicles precisely because they are so much safer and less expensive to fly. Expendable launchers are inherently unsafe for several reasons. The high cost per flight, which is more than the cost of a new vehicle, precludes a progressive flight test programme like that of an aeroplane. Pre-delivery test flights are not possible, and the economics of expendability lead to lower design margins and less system redundancy. As a result, it is simply not practicable to make a large and complex single-shot vehicle anything like as safe as a fully reusable one. Manned spaceflight has a poor safety record to date: one fatal accident per (approximately) 100 flights, compared with one per 10,000 during the flight-testing of new airliners and one per 1,000,000 for passenger-carrying flights.

With a spaceplane, an operational prototype can be built in an experimental workshop, which costs about ten times less than developing a fully certificated design. White Knight and SpaceShipOne were so built, which helps to explain their very low development cost. Such cost saving is not possible with projects like OSP that use expendable launchers, because of the inherently high risk.

The Space Shuttle, Figure 5, uses large throwaway components (the External Tank) and recyclable components (the Solid Rocket Boosters) and is much more like a manned spacecraft launched by an enlarged ballistic missile than it is like an aeroplane.

After a mere five low-speed gliding flights, the first powered flight of the Shuttle went all the way to orbit. Such a leap into the unknown would be unthinkable with a new aeroplane. Concorde, for example, made 69 flights before reaching even supersonic speed, and made more than 2000 test flights before being allowed to carry passengers. The Shuttle made some 100 flights in its first twenty years of service, an average of just five per year.

As explained earlier, it may take $300 million to certify SpaceShipOne for passenger carrying. But this is still less than the cost of a single Space Shuttle flight and is approximately equal to NASA’s budget for one week. This point is worth repeating: A certificated passenger-carrying spaceplane, albeit sub-orbital, can be developed for less than the cost of a single Shuttle flight.

The X-34, Figure 6, is perhaps more relevant than SpaceShipOne to a fully orbital vehicle, and was also built in an experimental workshop. This project was funded largely by NASA as a test-bed for the technologies required for a reusable launch vehicle. It was cancelled in 2001, for largely political reasons, when almost complete but before it could fly. Its development cost would have been some $250 million.

The X-34 was designed to reach about one third satellite speed on a sub-orbital flight. A simple thought experiment shows how a fully reusable orbital vehicle based on X-34 technology could be developed at low cost. Imagine an X-34 scaled up to have about ten times the original weight, and designed for use as a high-speed carrier aeroplane. Imagine the X-34 itself with a more advanced engine and larger propellant tanks, and air launched from the new carrier aeroplane. The resulting vehicle would be similar to some of the more promising 1960s projects mentioned later, and the new upper stage would be able to reach orbit.

Development cost tends to increase somewhat less than directly proportionally to vehicle weight, and the cost of an operational prototype of this orbital spaceplane would be in the region of $2 billion (eight times that of the X-34 itself), which is comparable to that estimated for Spacecab (and about five times less than that of the proposed OSP).

Prototypes of either this ‘Orbital X-34’ or Spacecab could be built in about five years, given priority. They would be used for launching small satellites, servicing large satellites, and supplying space stations. Their most important use in the near term would be providing safe and economical transport to and from the beleaguered International Space Station.

Given the obvious benefits of full reusability and the potential for low development cost, why is NASA insisting on an expendable launcher for OSP? A related question is why, if spaceplanes are so straightforward to develop, were they not developed years ago?

The answers to both these questions can be found in the history of US launch vehicle development. The modern US space programme started after World War II with captured German V-2 ballistic missiles. These were developed into progressively bigger and better ballistic missiles, further developments of which are still used to launch satellites. Due to the intense pressures of the Cold War, modified ballistic missiles sent the first men to space and enlarged developments were used for the race to the moon.

By the time of the first lunar landing in 1969, the technology was well in place for a fully reusable launcher. The X-15 research aeroplane had demonstrated much of the required engineering by flying to space height on sub-orbital trajectories. (SpaceShipOne and Ascender capability is close to that of the X-15.) During the 1960s, most large aircraft companies had design teams studying spaceplanes, leading to a consensus that they were the obvious next major development and that they were just about feasible using the technology of that period.

The original design of the Space Shuttle, intended to replace the mighty Saturn and other expendable launchers, was indeed for it to be fully reusable. However, it was far larger than most of the 1960s projects and therefore had a very high development cost. President Nixon then imposed a budget cut and the large reusable design could no longer be afforded. NASA then sacrificed full reusability to maintain the same payload capacity. There was a lobby in favour of a smaller but fully reusable design, but this was swamped by the politics of megaprojects.

The X-15 last flew in 1968 and remains the only fully reusable vehicle to have flown to space. This failure to follow up the X-15 with a fully reusable orbital spaceplane is a prime example of a large monopolistic organisation ignoring a promising but radical idea for as long as it can.

The International Space Station continues this saga of high cost almost for its own sake. Its through-life cost will be some $100 billion, while it can readily be shown that better science could be achieved for about 10% of this money by building several small space stations and a spaceplane to transport crew, spare parts, and consumables. Unless strong external pressure is brought to bear, it seems likely that this spendthrift tradition will be well maintained by OSP.

What, then, will it take to persuade governments to change tack and back the development of low-cost spaceplanes? It will probably take the successful flight to space of a sub-orbital spaceplane to persuade a critical mass of people that the spaceflight revolution can and should begin soon.

Progress thereafter is likely to be rapid. After test flights demonstrate adequate safety, production developments of sub-orbital spaceplanes would be used for carrying passengers on brief space experience flights, which is probably the biggest market for such vehicles. This would create a virtuous spiral of lower cost, higher traffic levels, maturing technology, and even lower costs. This growing maturity would transfer naturally to fully orbital spaceplanes. Within perhaps ten years after the prototype first flight, a mature orbital spaceplane could achieve a cost per seat to orbit around $20,000, which is about 1000 times less than the present cost of sending people to space. Many middle-income people would be prepared to pay this for the trip of a lifetime.

All this industry needs is a good kick-start. This ‘trigger project’ could be SpaceShipOne, or a military vehicle such as the RASCAL funded by the US Defense Advanced Projects Research Agency, or another private sector project. In fact, more than twenty organisations have registered for the X-Prize, an award of $10 million for the first to fly a fully reusable vehicle to a height of 100 km (62 miles). One such company is Bristol Spaceplanes Limited, with Ascender.

The major challenge facing these would-be spaceplane entrepreneurs is credibility. The idea that a small company can lead the way in slashing the cost of access to space seems too good to be true. By revealing SpaceShipOne to the world, Burt Rutan has rendered us all a great service by showing that it is indeed very likely to be true. And what is true is very good indeed.