In this controversial opinion piece, guest blogger David Ashford argues strongly that spaceplanes, not rockets should be the way forward for low-cost space access and, given enough will and resources, could be in service sooner than we think. [caption id="attachment_3473" align="alignnone" width="300" caption="Bristol Spaceplanes Ascender - one vision of the future (Bristol Spaceplanes)"][/caption] Spaceflight could soon be transformed into a routine and widely affordable activity. The biggest obstacle is the entrenched thinking of large government space agencies and major space corporations. The race is on to see which one of these will be the first to overcome its prejudices. Within about fifteen years of this change in mind-set, there will be a new golden age of space science and exploration. Most of you who want to will be able to spend a few days in orbit round the Earth in a space hotel. The impending spaceflight revolution involves abandoning the expendable launchers that have been used exclusively to date. These can fly once only. Imagine air travel if you had to parachute out over your destination and your airliner went on to crash into the ocean! Throwaway launchers will be replaced by aeroplanes capable of flying to and from orbit—spaceplanes. The technology, funding streams, and markets have all existed for several decades. All that is needed is for a critical mass of people to change the way they think. This is a rare example of something that seems too good to be true actually being true beyond reasonable doubt.

How spaceplanes can transform spaceflight

So, how will spaceplanes transform spaceflight? A spaceplane is defined here as an aeroplane that can fly to and from space. It may take off unaided or be launched from a carrier aeroplane. Either way, the spaceplane itself and any vehicle used to launch it are fully reusable. There are two categories of spaceplane—suborbital and orbital. Suborbital spaceplanes can fly fast enough to climb steeply up to space for just a few minutes before gravity pulls them back towards the Earth. Orbital spaceplanes can accelerate and climb to orbital speed and height. They can stay in orbit indefinitely like a satellite. Orbital spaceplanes need about eight times the speed and twice the height of suborbital ones. They will cost about ten times more to develop. Most space science and all exploration and applications such as communications, satnav, and global weather observation need orbital flight. Suborbital spaceflight is at present used only for some niche science experiments, although carrying passengers on brief space experience flights is likely to start within a few years. [caption id="attachment_3474" align="alignnone" width="300" caption="Figure 1. A typical expendable launch vehicle and airliner. (ESA, Airbus)"][/caption] Now let us compare two existing types of flying machine–expendable launchers and airliners, Fig. 1. Neither of these is a spaceplane, but the comparison nonetheless illustrates some useful points. The cost per seat to orbit in present-day expendable launchers is some ten million pounds; that of a long-distance flight in an airliner is more than ten thousand times less at, say, four hundred pounds. Why this big difference? A factor of about ten is due to launchers being able to carry fewer passengers than an airliner of comparable take-off weight. The remaining factor of 1,000 is due to two main reasons. First, a launcher can fly only once whereas an airliner can make tens of thousands of flights in its useful life. Second, the total number of satellite launches per year is usually somewhat fewer than one hundred, whereas the total number of airliner flights is of the order of ten million, say ten thousand airliners making one thousand flights per year each. There are of course other major technical differences, but these have a relatively small impact on cost. If airliners could fly to and from orbit with a full passenger load, the cost per seat would be reduced some ten thousand times. The problem of course is that present designs can’t. Let us therefore consider what changes are needed for an airliner that can indeed fly to orbit. First, the shape has to be changed so that it is stable and controllable over a wide speed range. The Shuttle Orbiter (see Fig. 4 later) is a good example of how this can be done. Changing shape by itself need not greatly affect cost. Second, it needs rocket engines. Jets can be used for only the early part of an ascent to space because they need oxygen from the atmosphere, whereas rockets carry their own supply of oxidant—often liquid oxygen. Present-day rocket engines have useful lives of just a few tens of flights whereas airliner jet engines last for thousands. Thus early spaceliners will have a high engine maintenance cost. However, this should approach airliner levels after a long production run and a programme of continuous product improvement. Third, it needs to carry much more propellant (fuel in the case of jet engines, fuel plus oxidant in the case of rocket engines). The propellant needed to accelerate and climb to orbit is very roughly comparable to that needed for an aeroplane to fly round the world one and a half times non-stop. Modern long-range airliners can fly just about half way round. The present record is once around, and the Virgin Atlantic Global Flyer that holds it was a marginal one-off design carrying just a pilot. Fourth, it will need two stages if more or less existing technology is to be used. A carrier aeroplane will fly to supersonic speed and then release an orbiter stage. If there were a requirement for a useful aeroplane built using more or less existing technology to fly round the world one and a half times non-stop, it too would need two stages—a large aeroplane that carried a smaller long-range aeroplane part of the way before releasing it and then flying back to base. Having two stages will clearly increase the cost. [caption id="attachment_3487" align="alignnone" width="300" caption="EADS Astrium has proposed this concept for a sub-orbital spaceplane for space tourist flights. (EADS)"][/caption] Fifth, it will probably use some liquid hydrogen as this has the highest performance of any practicable rocket fuel. Hydrogen fuel is more expensive than kerosene, which is the most widely used fuel for airliners. Sixth, it will need additional systems for operating in space and for re-entry. These include reaction controls and a layer of surface insulation to protect the structure from the heat of re-entry (or advanced materials that can withstand the heat). These systems will increase cost but not by a lot. Taking all this into account, the cost per flight of a fully developed spaceplane will be about three times more than that of an airliner of similar take-off weight on a long-distance flight. This low cost assumes a technology level such that prototypes are built using more or less existing technology and the design is then matured over a long production run with a programme of continuous product improvement to reduce operating costs. It also assumes that this low cost leads to a greatly increased number of space flights per year to provide economies of scale and to justify airline-like operations. Early prototypes will cost perhaps ten times more per flight. Such a spaceplane will carry about eight times fewer passengers than an airliner of comparable take-off weight because it has to carry much more propellant. The cost per seat will therefore be approximately twenty-four times greater (three times the cost per flight multiplied by eight times fewer seats) at around ten thousand pounds compared with four hundred. The cost per seat to orbit today in the Shuttle or Soyuz is very roughly ten million pounds. Thus spaceplanes have a cost per seat potentially a thousand times less than the cost today. One thousand times! Costs that low would revolutionise spaceflight. The cost of science in space would become comparable to that in Antarctica. Public access to space for business and leisure would become routinely affordable. Very large space telescopes and other astronomical instruments would become affordable. We could afford to send large robotic probes to all bodies of interest in the Solar System. We would have a new space age.

Spaceplane history

The first machine capable of reaching space height was the German V-2 ballistic missile of World War 2, Fig. 2.   As you can see, it had the now-classic ‘rocket’ shape—tall and slim, a rocket engine at the base, a body filled mostly with propellant, and a payload bay at the top.   In the case of the V-2, the ‘payload’ was a high-explosive warhead, so the vehicle was in effect a long-range artillery shell. There was therefore no need for it to be reusable! [caption id="attachment_3475" align="alignnone" width="300" caption="Figure 2. The V-2 ballistic missile and winged developments. (Deutches Museum)"][/caption] The V-2 was the progenitor of all ballistic missiles and orbital launch vehicles used since then. In 1945, the Germans flew two V-2s fitted experimentally with wings. The idea of the wings was to extend the range so that they could be launched out of reach of Allied bombers. The Germans designed a piloted version of the winged V-2, Fig. 2, but the war ended before it could be built. The idea was for a very brave pilot to fly to space, carry out a gliding re-entry, drop a bomb, and fly back using a jet engine. The piloted V-2 would have been a true suborbital spaceplane. It would have been fully reusable and used wings for landing. Now imagine that the piloted V-2 had gone into service in significant numbers and that it was in production for several years. Its cost per flight would then have been about 1000 times less than that of the V-2 itself. The marginal cost per flight of the piloted version would have been that of crew, fuel, and maintenance.  That of the V-2 was a new vehicle. (Roughly speaking, the marginal cost per flight of an airliner on a long-distance flight is one thousand times less than its purchase price.) So, as far back as 1945, the technology was in place for a true spaceplane with the potential to reduce the cost of suborbital spaceflight by about 1,000 times. An orbital development would have taken a further ten years or so to bring to fruition. How then can it be possible that fifty-five years later we are still using throwaway launchers for transport to space? The answer lies in the pressures created by the Cold War. Following the WW2, the US and the Soviet Union engaged in a deadly race to develop ballistic missiles with nuclear warheads. As ballistic missiles can fly to space, it was natural enough to use them to launch early satellites, the first of these being the Soviet Sputnik in 1957. This was followed by a race to put the first man in space and then on the Moon. Because national prestige was at stake and time was of the essence, expendable launchers continued to be used. Thus the mighty Saturn V launcher, Fig. 3, used for the brilliantly successful US Moon landings of 1969 to 1972, had the size and cost of a small warship but was destroyed each time it was used. [caption id="attachment_3476" align="alignnone" width="300" caption="The mighty Saturn V launcher of the late 1960s. It had a length of 110m and a launch weight of 3,000 tonnes but could be used once only. (NASA)."][/caption] The next major project was the Space Shuttle, Fig. 4. When its design was started in the early 1970s, the benefits of reusability were well understood and early proposals indeed had two spaceplane stages. However, President Nixon imposed a budget cut and NASA could no longer afford their large reusable design. They had a choice between a much smaller fully reusable design, which would have introduced the aviation approach, or largely giving up on reusability. The habit of expendability was by then strong enough for NASA to make the disastrous mistake of choosing the latter course. This decision has put back low-cost access to space by thirty years and counting. The Orbiter has wings for landing and is reusable but is in effect a manned spacecraft launched by expendable ballistic missile technology. Its cost per seat and fatal accident rate are about ten thousand times worse than those of a large airliner. Every time the Shuttle flies, a crew of seven is in effect flight-testing a ballistic missile. [caption id="attachment_3477" align="alignnone" width="277" caption="The Space Shuttle. The winged Orbiter is the only fully reusable component. (NASA)."][/caption] This history has created institutions and habits of thought that persistently reinforce the throwaway launcher habit. Even today, NASA, ESA, and other major space agencies are promoting expendable launchers.

Spaceflight revolution

Before considering the way ahead for the impending revolution in spaceflight, let us consider two previous revolutions in transportation, triggered respectively by the invention of the steam locomotive and the aeroplane, Fig. 5.  Before the steam locomotive, the maximum speed and size of land vehicles was limited by the power of the horse. Travel between cities was slow and expensive, and most people hardly moved beyond the next village. The steam locomotive and iron track allowed speed to be greatly increased and the cost reduced. This led to an explosive growth in land transport. Stephenson’s Rocket of 1829 is generally credited as being the progenitor of the ‘modern’ steam locomotive. [caption id="attachment_3478" align="alignnone" width="300" caption="Figure 5. Stephenson’s Rocket of 1829 and the Wright Flyer of 1903."][/caption] Before the Wright Brothers flew the first practical aeroplane, just over one hundred years ago, the only way to fly was in a balloon. These were used for several niche purposes such as passenger experience flights, artillery spotting, and atmospheric research. However, balloons cannot fly into wind, so cannot be used for an airline service. The Wright Brothers showed that flight into wind at reasonable speed was a practical proposition, and this led to an explosive growth in aeronautics. In a similar way, expendable launchers are far too expensive and unsafe for an airline service to orbit. However, as we have seen, spaceplanes can provide the low costs needed for large-scale access to space. They can also provide greatly improved safety because aeroplanes are inherently far safer for passengers than ballistic missiles are for astronauts and the same goes for spacefaring developments. [caption id="attachment_3482" align="alignnone" width="300" caption="Spaceplanes have been tried in the US - however NASA's X-30 National Aerospace Plane (NASP) project was abandoned. (NASA)."][/caption] Thus the first orbital spaceplane is likely to trigger a revolution in spaceflight comparable to the revolutions in land and air transport brought about by Stephenson’s Rocket and the Wright Flyer. As soon as the first successful orbital spaceplane enters service, it will be able to undercut any expendable launcher of comparable payload. Low costs and improved safety will increase traffic levels, which in turn will release funding to enlarge and mature the design. This will further reduce costs and increase traffic levels, thereby releasing even more funding. The result will be a virtuous downwards cost spiral until the lower limit of spaceplanes using mature developments of more or less existing technology is approached. As discussed earlier, this works out at about ten thousand pounds per seat to orbit. The total cost of a few days in a space hotel will be about twice this amount, which is affordable by middle-income people prepared to save for the holiday of a lifetime. This rapid improvement will be comparable to that of steam locomotives and aeroplanes following the pioneering work of Stephenson and the Wright Brothers. Within a few decades of these developments, land and air transport had changed beyond recognition. The big difference of course is that Stephenson and the Wright Brothers were working right at the limits of the technology of the day, whereas spaceplane development has been held up for several decades by no more than, and no less than, lack of vision and political will. Another difference is that Stephenson and the Wright Brothers had access to sufficient funds to carry out their pioneering developments whereas an orbital spaceplane is at present beyond the means of individual entrepreneurs. A third difference is that space policy has been dominated by large government agencies whereas rail transport and early aeroplane development was led mainly by the private sector. So, the private sector does not yet have the resources to develop the first orbital spaceplane and government space agencies ‘don’t want to know’. How is this deadlock going to be broken? Probably, through suborbital spaceplanes. These cost about ten times less to develop than orbital spaceplanes and several designs are being built by the private sector. Virgin Galactic plan to start suborbital passenger flights within about three years. It is only a matter of time before suborbital science and passenger space experience flights are a commercial success. This will show incontrovertibly the advantages of aeroplanes over expendable vehicles. (Present day suborbital research is carried out using expendable sounding rockets.) Suborbital spaceplanes will also pave the way technically for orbital ones. [caption id="attachment_3480" align="alignnone" width="300" caption="Virgin Galactic have already hinted that orbital flight may follow sub-orbital space tourism with SpaceShipTwo. (Virgin Galactic)"][/caption] The growing ‘new space’ lobby will then have the ammunition needed to persuade space agencies and/or the private sector to fund orbital spaceplane development. It can readily be shown that pioneering missions like the first lunar base would cost about ten times less using spaceplanes than using expendable launchers, including the cost of developing the spaceplanes themselves. All that is needed is for space agencies to take this prospect seriously. Developing the first orbital spaceplane might take seven years and improving the design to the point of enabling orbital travel that is widely affordable would take a further eight or so years, given a high level of funding to mature the design. [caption id="attachment_3481" align="alignnone" width="300" caption="Another British spaceplane concept is Reaction Engines' Skylon. (Reaction Engines) "][/caption] So, you could be taking your first flight to orbit in about fifteen years time. To this has to be added the time for a critical mass of minds to be changed. A way ahead on the lines discussed here is reasonably obvious from first principles but is counter to current space agency culture. This mind changing could be speeded up if more pressure were put on space agencies to overcome their prejudices.  The first country to adopt the aviation approach to spaceflight will make large economic and political gains from pioneering the new space age. So, if you want your flight to space soon, or would like to see far more space science and exploration, or would like to see your country’s industry prosper, start asking questions now.

Royal Aeronautical Society
17 December 2010