Into Thin Air

Following the appearance of the article "More Aircraft Blow In" , Paul Kidder of Los Angeles has been in touch again with more pictures of his wind tunnel and presentational models, this time of vehicles designed to fly into thin air at altitude and then into the vacuum of space. He says:Following the appearance of the article “More Aircraft Blow In” , Paul Kidder of Los Angeles has been in touch again with more pictures of his wind tunnel and presentational models, this time of vehicles designed to fly into thin air at altitude and then into the vacuum of space.  He says:

“Here are the pictures of the machined aluminium XB-70 wind tunnel model fuselage (note there is no canard). The model measures 36.75 inches long. Unfortunately, there were no other parts that came with the model.  Too bad I don’t have drawings, it would be a nice model to restore.  I have also included an  artist rendition of an early XB-70 with no canard or enclosure around the six engines.  Is this my model? I don’t know.  I need to more research”

The curving cylindrical fuselage North American XB-70 Valkyrie - as built and flown - is described in more depth in the article Bristol and the Bomber Gap on this website while Paul was also able to expand on the subject of winged re-usable spacecraft following his coverage of the ramjet powered National Aero Space Plane.The curving cylindrical fuselage North American XB-70 Valkyrie – as built and flown – is described in more depth in the article Bristol and the Bomber Gap on this website while Paul was also able to expand on the subject of winged re-usable spacecraft following his coverage of the ramjet powered National Aero Space Plane.

Explaining that both the XB-70 and Y shaped wind tunnel models pictured were indirectly acquired from a North American engineer who worked on both projects, Paul commented that the latter was referred to as a "Mach 20" and was a high speed manned (note the canopy) re-entry vehicle. The 40.75" model is made of a mixture of machined stainless steel and aluminium and a sting would attach to the rear fuselage. It could be that North American was working on some kind of re-usable space plane based directly on the experience of operating its air launched X-15 rocket vehicle - pictured below - in the early 1960s.Explaining that both the XB-70 and Y shaped wind tunnel models pictured were indirectly acquired from a North American engineer who worked on both projects, Paul commented that the latter was referred to as a “Mach 20″ and was a high speed manned (note the canopy) re-entry vehicle.  The 40.75” model is made of a mixture of machined stainless steel and aluminium and a sting would attach to the rear fuselage.

However, the X-15 had to do more than merely fly very fast and high. Above Mach 2, aircraft encounter the so-called Heat Barrier - a phenomenon caused by friction between the aircraft itself and the particles of air it passes through. Even the leading edges of the wings and tailplane of the nickel-alloy steel built X-15 glowed red at maximum velocity despite operating at the most rarefied edge of the Earth's atmosphere.It could be that North American was working on some kind of re-usable space plane based directly on the experience of operating its air launched X-15 rocket vehicle – pictured left –  in the early 1960s.

Certainly at this time it was realised that despite the success of rival Vostock and Mercury programs both were wasteful and inefficient ways of putting a man in space – a ballistic multi-stage rocket being thrown away to orbit a spacecraft that could only fly once.

In the case of both Soviet and American projects, no rocket booster was powerful or efficient enough to form a single stage to orbit (SSTO) vehicle, let alone one which could then make a controlled de-orbit manoeuvre and land vertically using its engine - as depicted in such science fiction films as 1950's Destination Moon. Even the Grumman LEM eventually used to land Apollo astronauts on the Moon would comprise separate Descent and Ascent stages.In the case of both Soviet and American projects, no rocket booster was powerful or efficient enough to form a single stage to orbit (SSTO) vehicle, let alone one which could then make a controlled de-orbit manoeuvre and land vertically using its engine – as depicted in such science fiction films as 1950’s Destination Moon.  Even the Grumman LEM eventually used to land Apollo astronauts on the Moon would comprise separate Descent and Ascent stages.

Thinking outside the box for a moment, the only possible way for an SSTO launch vehicle based on known rocket technology to work would be to avoid a static vertical launch from the surface of the Earth.  Air dropping from a “mother” plane will be discussed in more detail towards the end of this feature but has the disadvantage of limiting the size and weight of the SSTO vehicle.

Similarly, vehicle size and weight would limit the possibilities of a rocket or electromagnetically powered launch ramp as envisaged by the German rocket scientists of the 1940s - and dramatically portrayed in the Gerry Anderson TV science fiction show "Fireball XL5".  Even if an SSTO could be catapulted aircraft carrier style off a three mile long ramp at 600 mph it would still be flying at a shallow angle through thick air before its rocket engines could take it higher at a steeper rate of climb.Similarly, vehicle size and weight would limit the possibilities of a rocket or electromagnetically powered launch ramp as envisaged by the German rocket scientists of the 1940s – and dramatically portrayed in the Gerry Anderson TV science fiction show “Fireball XL5”.  Even if an SSTO could be catapulted aircraft carrier style off a three mile long ramp at 600 mph it would still be flying at a shallow angle through thick air before its rocket engines could take it higher at a steeper rate of climb.

An improvement on this situation would be to build the launch ramp with an upward - or even vertical - ski jump style end and locate it on a mountain as portrayed in George Pal's 1951 Paramount film "When Worlds Collide".  However, although saving as much as five miles from the vertical journey of a spacebound rocket ship, building and operating such a mountainside ramp in remote and hostile conditions would be highly problematic, as would its negative environmental impact.An improvement on this situation would be to build the launch ramp with an upward – or even vertical – inclined ski jump style end and locate it on a mountain as portrayed in George Pal’s 1951 Paramount film “When Worlds Collide”.  However, although saving as much as five miles from the vertical journey of a spacebound rocket ship, building and operating such a mountainside ramp in remote and hostile conditions would be highly problematic, as would its negative environmental impact.

However, another approach to space infrastructure building would ultimately only need just an SSTO or perhaps no rocket booster at all!  As has been described in The Telstar Story on this website, modern communications satellites are placed in geosynchronous orbit 22 000 miles above the Earth.  This means that they constantly keep pace with the rotation of the planet over a fixed spot on the Equator and, in effect as viewed from the ground, stand still in the sky.  If only a cable could link the fixed spot on the Equator with the geosynchronous satellite, payloads and people could be winched into orbit by solar power.  This concept was first popularised by Arthur C. Clarke - who also invented the idea of communications satellites - in his 1979 novel "The Fountains of Paradise" and although no currently available material is both strong and light enough to form the necessary cable, research into carbon fibre nanotubes for the purpose is continuing.However, another approach to space infrastructure building would ultimately only need just an SSTO or perhaps no rocket booster at all!  As has been described in The Telstar Story on this website, modern communications satellites are placed in geosynchronous orbit 22 000 miles above the Earth.  This means that they constantly keep pace with the rotation of the planet over a fixed spot on the Equator and, in effect as viewed from the ground, stand still in the sky.  If only a cable could link the fixed spot on the Equator with the geosynchronous satellite, payloads and people could be winched into orbit by solar power.  This concept was first popularised by Arthur C. Clarke – who also invented the idea of communications satellites – in his 1979 novel “The Fountains of Paradise” and although no currently available material is both strong and light enough to form the necessary cable, research into carbon fibre nanotubes for the purpose is continuing.

A slightly less ambitious plan advanced in August 2015 when Ontario based Thoth Technology was granted a patent for a 12.4 mile (20 km)  high freestanding tower made of inflatable segments and using a complex array of flywheels to keep the structure upright.  The inventor of the Canadian Thoth X tower, Dr Brendan Quine, was quoted in the Daily Mail of 18 August 2015 as saying “Astronauts would ascend to 12 miles by electrical elevator.  From the top of the tower, space planes will launch in a single stage to orbit, returning to the top of the tower to refuel.” The article also mentioned the potential of the tower – 20 times higher than Dubai’s Burj Khalifa – for tourism, communication and wind energy generation and that a shorter prototype could be built by 2023.

Just twenty days after the successful sub-orbital flight of Alan Shepherd in Freedom 7, US President John F. Kennedy made the following Special Address to Congress On The Importance of Space on 25 May 1961.More immediate in the 1960s, though, was the problem of shielding a returning space vehicle from the heat caused by friction when re-entering the Earth’s atmosphere.  In the case of Mercury or Vostock vehicles, blunt conical or spherical shapes hit the ever-thickening atmosphere first, thus creating drag which did not permit the air beneath to get out of the way fast enough and so creating an air cushion below the vehicle. 

The round hole in the coned Vostock fairing allowed the cosmonaut to eject to safety from his ball-like re-entry capsule if the R-7 failed on launch. By 1967, this had been replaced by an Apollo- style rocket escape tower on the three man Soyuz spacecraft which also featured a larger service module below the re-entry vehicle and an extra R-7 launching stage.However, this compressed air cushion under the vehicle became increasingly hot while the air heated by friction formed a shock cone above.  In addition, the downward sides of both Soviet and American manned spacecraft were given a coat of ablative material that further dissipated heat into the upward shock cone but was itself destroyed in the process and could not be replaced afterward.  A further disadvantage of using this kind of ablative heat shield was the weight of the material needed.  In the case of the Apollo Command Module, the heat shield comprised one third of the vehicle weight.  Once at a lower altitude and slower speed, both Vostock and Mercury spacecraft deployed parachutes for landing.  Although steerable parachutes were suggested for the later Apollo missions, conventional round parachutes made the precise sites of space vehicle landings unpredictable, whether at sea in the case of Mercury capsules or on land for Vostock.  In addition, both crew and re-entry vehicles had to be recovered from remote and sometimes problematic environments.

Given these problems, the ideal solution would be a vehicle which could somehow survive re-entry into the Earth's atmosphere more than once, land under control in a given location (ideally near to the next launch site) and then be launched again either by itself or with a minimal number of other booster modules, ideally themselves re-usable. From 1981 to 2011, NASA's Space Transportation System - pictured above - addressed a number of these issues with varying degrees of success. It did allow the same aerodynamic winged orbiter vehicles to be used more than once, although each of these had to be heavily repaired if not virtually rebuilt after each mission, making them only slightly cheaper than the single use multi-stage rockets they were intended to replace.Given these problems, the ideal solution would be a vehicle which could somehow survive re-entry into the Earth’s atmosphere more than once, land under control in a given location (ideally near to the next launch site) and then be launched again either by itself or with a minimal number of other booster modules, ideally themselves re-usable.  From 1981 to 2011, NASA’s Space Transportation System – pictured above –  addressed a number of these issues with varying degrees of success.  It did allow the same aerodynamic winged orbiter vehicles to be used more than once, although each of these had to be heavily repaired if not virtually rebuilt after each mission, making them only slightly cheaper than the single use multi-stage rockets they were intended to replace.

Among the high-maintenance aspects of these orbiters was the Thermal Protection System which involved a number of different materials applied to different parts of the aluminium Shuttle orbiter vehicle for its 40 degree nose up re-entry into the Earth’s atmosphere.  Among these were relatively heavy Reinforced Carbon Carbon – applied to the nose cap, area around the nose landing gear doors and wing leading edges where re-entry temperature exceeded  1 260 degrees Celsius – and felt and blanket like materials for the coolest parts not expected to exceed 371 degrees Celsius, a temperature still almost twice as hot as a steak pie cooking in a domestic oven.

Had the Space Shuttle Orbiter been as small as the North American X-15 it might have been possible to built it from high temperature metal alloys that – although heavy – could have been capable of withstanding re-entry heat by simply getting hot and re-radiating the absorbed heat – a phenomenon known as “heat sink” thermal protection. 

However, given that each Orbiter was designed to carry seven astronauts and a large payload, much of the thermal protection had to come from light weight tiles made from LI-900 silica, a very pure quartz sand.  These tiles were such poor conductors of heat that it was possible to pick up a red hot one by the corners with bare hands but at the same time the low density that gave them this lack of heat conductivity made each tile brittle, easy to crush and liable to damage from any kind of flying debris.

In addition, each of the 24 300 shaped tiles was glued to the Orbiter via pads which would allow for expansion and contraction of the underlying metal and this adhesion process was found to take forty man hours per tile – thus pushing back the anticipated launch of the first Space Shuttle from 1979 to 1981.  Similarly, some engineers were concerned that the loss of just one tile before de-orbit would create a “zipper effect” during re-entry in which other tiles around the hole would start to detach.  This in turn prompted investigations into ways of repairing the smooth, fragile tiled heat shield while in orbit and resulted in the development of the Martin Marietta Manned Manoeuvring Unit first tested in space by Bruce McCandless in 1984. 

Following the loss of the Space Shuttle Columbia on 1 February 2003 – after foam insulation from the disposable fuel tank punctured the Reinforced Carbon Carbon on the leading edge of the port wing during launch – even stricter inspection of the LI-900 tiles and other parts of the Thermal Protection System further increased the cost of Space Transportation System launches although by this time it was possible to use the robot arm on the International Space Station to help inspect and repair any visiting Shuttles.

Once safely within the lower reaches of the Earth’s atmosphere, the Space Shuttle did have an excellent record of landing on designated runways, usually at Cape Canaveral close to its maintenance and launch facilities.  However, as by this stage in its mission the Orbiter was essentially a delta winged glider, it had no capacity to “go around” if a landing was aborted and could not “stack” with other aircraft above a conventional airport.

In contrast, the Soviet equivalent of the Space Shuttle - the RKK Energia Buran - landed at Baikonur Cosmodrome on 15 November 1988 for the first and only time on its second attempt: sensors aboard the automated spaceplane having detected dangerous crosswinds and throttled up the jet engines in the tail to go round a rectangular traffic pattern.In contrast, the Soviet equivalent of the Space Shuttle – the RKK Energia Buran – landed at Baikonur Cosmodrome on 15 November 1988 for the first and only time on its second attempt: sensors aboard the automated spaceplane having detected dangerous crosswinds and throttled up the jet engines in the tail to go round a rectangular traffic pattern. 

In fact the Buran – Russian for snowstorm, seen above – makes an interesting comparison with the Rockwell built STS.  Both spaceplanes were designed with the intention of placing military cargoes into orbit, both were launched vertically but landed horizontally and both had similar thermal protection systems, Buran losing five of its 38 000 silica tiles on its sole robotic test flight. 

However, Buran employed a simpler launch system in which the orbiter was attached to a single-use three section liquid fuelled Energia rocket which took it beyond the Earth.  The winged vehicle was then able to detach from the spent Energia booster and use its own rocket motors purely to manoeuvre in space – such as moving to a higher orbit as was achieved in 1988 – and then re-enter the atmosphere using gas turbines when needed.

The Shuttle Orbiter, meanwhile, used its own rocket motors to blast off from the launch pad, supplied with liquid fuel from the large brown tank seen in the picture above.  This tank was expendable within the context of STS, and ultimately covered in a layer of solid foam to insulate the volatile fuels from boiling off in the Florida sunshine of Cape Canaveral.  It was some of this foam breaking off from the top of the tank which punctured the port wing of the Shuttle Columbia in 2003, dooming it to destruction during descent due to hot gases entering the wing.

Indeed, it was another combination of flawed design and extreme weather that caused the other lethal Shuttle malfunction when Challenger exploded shortly after launch on 28 January 1986, again killing all seven astronauts.  The launch had been postponed due to issues with potential Transoceanic Abort Landing sites in North Africa (with RAF Fairford in Gloucestershire also being on standby had an early return to Earth been necessary) and during this postponement the prepared Orbiter, fuel tank and Solid Rocket Boosters had been subjected to unseasonable freezing temperatures.  This compromised the integrity of the rubber O-Rings used to connect sections of the Morton-Thiokol built Solid Rocket Boosters, one of which then failed causing hot gases to effectively destroy the right hand SRB, the fuel tank and with it the Orbiter.

The O-Rings were needed to seal sections of the SRB which were manufactured in Utah and had to be transported to Cape Canaveral by rail before final assembly.  However, even if the SRBs had been built in one piece in Florida before attachment to the Orbiter and fuel tank, they would still have represented an extra risk to the Space Transportation System just by the fact that solid fuelled rockets are uncontrollable once lit.  Although these boosters could be recovered from the sea by parachute and re-used once they had fulfilled their function and detached from the Orbiter and fuel tank – making the whole STS theoretically more economical than Buran – the Challenger disaster made the US Air Force use conventional Titan rockets rather than the STS to launch its classified military satellites from Vandenburg AFB in California.

Meanwhile in France, the Challenger disaster also forced the European Space Agency to reconsider plans for its own re-usable Hermes space plane, serious studies for which were approved in November 1987.Meanwhile in France, the Challenger disaster also forced the European Space Agency to reconsider plans for its own re-usable Hermes space plane, serious studies for which were approved in November 1987. 

Rather than six astronauts and 4 550 kg of cargo as outlined as far back as 1975, Hermes was later based on the concept of three astronauts on ejector seats and 3 000 kg of cargo which could realistically be placed in orbit by an Ariane V booster.  Unlike the American STS and Soviet Buran, there would also be no dorsal cargo bay doors opening to place objects in space and Hermes would also orbit the earth with a conical Resources Module – seen here with solar panel wings – attached until being jettisoned for re-entry.

As such, only the Hermes spaceplane itself would have been re-usable but at least it was designed to be on top of the Ariane V rather than attached to the side, giving the spaceplane the option of using its own rockets to escape if the Ariane booster malfunctioned at launch as well as making an ejector seat based egress more likely to succeed.

Due to financial pressures, technical issues and the possibility of ESA working with American and Russian space agencies after the end of the Cold War in 1989, Hermes was cancelled in 1992 before any hardware had been built.

Three decades earlier, the United States had found itself in a very similar position with the Boeing X-20 Dyna-Soar ordered by the Air Force being cancelled - although in this case choice of launch vehicle was an issue as well as cost and value for money.Three decades earlier, the United States had found itself in a very similar position with the Boeing X-20 Dyna-Soar ordered by the Air Force being cancelled – although in this case choice of launch vehicle was an issue as well as cost and value for money.

The concept of a winged vehicle which would be boosted into space on a liquid fuelled rocket before gliding vast distances back to Earth was first proposed by Eugene Sanger and Irene Bredt in Nazi Germany as a way of bombing New York – with the “Silbervogel” manned craft then being recovered somewhere in the Japanese held Pacific. 

Assisted by a horizontal launch on a railed rocket sled, the “Silver Bird” would, according to Sanger and Bredt,  re-enter the Earth’s atmosphere in a series of “bounces” rather than making one steep de-orbit dive and so gradually dissipate speed and height.  A post War review of their calculations however revealed that even these shallow atmospheric excursions would generate enough heat to make a heavy ablative or tile-type shield or heat soak construction essential for the flat underside, making the Silver Bird’s already small payload even smaller.

However, Silver Bird would still have the advantage of intercontinental ballistic missile speed into space, a potential gliding range to take photographs of or bomb any target on Earth and present a very small target when approaching a runway to land.

The Silverbird concept was taken to America and promoted by Dr Walter Dornberger, formerly head of Germany’s rocket programme who later worked for the Bell aircraft company.  After considering many boost-glide concepts from various manufacturers – including North American – the USAF Air Research and Development Command issued a proposal for a “Hypersonic Glide Rocket Weapons System” on 24 October 1957.  Also known as Weapons System 464L, this envisaged a glide test of a research “Dynamic Soarer” – hence the term “Dyna-Soar” – in 1963 followed by a reconnaissance and then a bomber Dyna-Soar.

The contract to build this spaceplane was awarded to Boeing on 9 November 1959

The overall design of the Dyna-Soar - given the X-20 designation on 19 June 1962 - was outlined in March 1960. It had a low-wing delta shape, with winglets for control rather than a more conventional tail. The framework of the craft was to be made from the nickel-based super alloy René 41, previously used to make aircraft and missile components that had to survive extreme heat. The underside of the Dyna-Soar was to be made from molybdenum sheets placed over insulated René 41, while the nose-cone was to be made from graphite with zirconia rods.The overall design of the Dyna-Soar – given the X-20 designation on 19 June 1962 – was outlined in March 1960. It had a low-wing delta shape, with winglets for control rather than a more conventional tail. The framework of the craft was to be made from the nickel-based super alloy René 41, previously used to make aircraft and missile components that had to survive extreme heat.  The underside of the Dyna-Soar was to be made from molybdenum sheets placed over insulated René 41, while the nose-cone was to be made from graphite with zirconia rods.

Due to the changing requirements, various forms of the five ton Dyna-Soar were designed. All variants shared the same basic shape and layout. A single pilot sat at the front, with an equipment bay situated behind. This bay contained data-collection or reconnaissance equipment, weapons or- in the X-20X “shuttle space vehicle” – a four-man mid-deck.

A transition-stage rocket engine, located behind the equipment bay, would steer the craft in orbit or fire during launch as part of an abort sequence. This trans-stage would then be jettisoned before descent into the atmosphere, during which time an opaque heat shield would protect the window at the front of the craft. This heat shield would then be jettisoned after aerobraking so the pilot could see to safely land.  As it was feared that the heat of atmospheric re-entry would burn rubber, the Dyna Soar would have been equipped with Goodyear-built wire brush skids made of René 41 rather than conventional tyres, as used on NASA’s STS.

Like Sanger and Bredt’s Silver Bird, the Dyna-Soar was also envisaged as having the capability of bouncing off the top of the Earth’s atmosphere – and then firing its rocket motors to change orbital inclination for a fraction of the physical force usually needed by a spacecraft to achieve this.  As such, the Dyna-Soar could have had a military capacity of being launched into one orbit and then rendezvousing with a satellite in another, even if the target were to expend all its propellant in evasively changing its orbit. However, acceleration forces on the pilot would be severe in such a manoeuvre.

Although a procession of finned Titan rockets - as illustrated above - eventually led to the triple-core Titan IIC being chosen as the definitive Dyna-Soar launch vehicle, the US Air Force also considered various combinations of Atlas-Centaur and Saturn 1 - all causing confusion and delay to the project. Also, from 1961, astronauts were going into space in cone-shaped single use craft under the direction of the National Aeronautical and Space Agency and many questioned whether the USAF should have a its own manned space programme. Similarly, unmanned military spy satellites had taken over the Dyna-Soar's reconnaissance role and the Partial Nuclear Test Ban Treaty in October 1963 forbade the testing of nuclear weapons in space. By this point too, the Dyna-Soar was unlikely to fly before 1965.Although a procession of finned Titan rockets – as illustrated above – eventually led to the triple-core Titan IIC being chosen as the definitive Dyna-Soar launch vehicle, the US Air Force also considered various combinations of Atlas-Centaur and Saturn 1 – all causing confusion and delay to the project.  Also, from 1961, astronauts were going into space in cone-shaped single use craft under the direction of the National Aeronautical and Space Agency  and many questioned whether the USAF should have a its own manned space programme.  Similarly, unmanned military spy satellites had taken over the Dyna-Soar’s reconnaissance role and the Partial Nuclear Test Ban Treaty in October 1963 forbade the testing of nuclear weapons in space.  By this point too,  the Dyna-Soar was unlikely to fly before 1965.

As such, Dyna-Soar was cancelled by Secretary of Defense Robert S. MacNamara on 10 December 1963 despite a mock up having been built and millions of dollars having been spent on machine tools for production and astronaut training. On the same day, it was announced that the Dyna-Soar budget had been re-allocated by Congress to a US Air Force Manned Orbiting Laboratory to be served by Gemini spacecraft - only for this plan to be later cancelled too.As such, Dyna-Soar was cancelled by Secretary of Defense Robert S. MacNamara on 10 December 1963 despite a mock up having been built and millions of dollars having been spent on machine tools for production and astronaut training.  On the same day, it was announced that the Dyna-Soar budget had been re-allocated by Congress to a US Air Force Manned Orbiting Laboratory to be served by Gemini spacecraft – only for this plan to be later cancelled too.

Of his own low-speed wind tunnel model of the X-20 Boeing Dyna-Soar with the trans-stage attached, Paul says:

“The model is around 52 inches long with a 24 inch wing span.  It is made up of a combination of fiberglass, metal and wood.  The trans-stage is made out of aircraft grade aluminium. The model was used for low speed wind tunnel testing and later coated with silver and used for testing radar reflection. Surprisingly enough, this model was found at the Martin Marietta (Denver, Colorado) surplus store back in the 1960’s after the program was cancelled.   There is speculation that even though the X-20 program was cancelled, it may have been actually built and flown. Funding may have come from other another government source that funds secret projects. There are I am sure many secretly funded programs that we may never hear about”

Indeed, following the X-20 being cancelled as a project of its own, the Central Intelligence Agency did look at using a very small piloted Dyna-Soar type vehicle launched from a Boeing B-52 bomber over the Atlantic to spy on the Soviet Union before landing in Nevada. However, this concept was found to be massively expensive - and the rocket plane too easily mistaken by the Soviets for an incoming nuclear missile - and abandoned..Indeed, following the X-20 being cancelled as a project of its own, the Central Intelligence Agency did look at using a very small piloted Dyna-Soar type vehicle launched from a Boeing B-52 bomber over the Atlantic to spy on the Soviet Union before landing in Nevada.  However, this concept was found to be massively expensive  – and the rocket plane too easily mistaken by the Soviets for an incoming nuclear missile – and abandoned..

Later during the 1960s additional practical research into winged space vehicles was carried out in America, both in terms of lofting man-sized models on top of expendable rockets and also by operating experimental air-dropped manned "lifting bodies" - aircraft with wings and tails blended into the fuselage - from 1963 to 1975. These were part of the joint USAF-NASA Project PILOT and included the Martin Marietta X-24, pictured above and first flown in 1969, and the 1966 vintage Northrop M2-F2, seen below.Later during the 1960s additional practical research into winged space vehicles was carried out in America, both in terms of lofting man-sized models on top of expendable rockets and also by operating experimental air-dropped manned “lifting bodies” – aircraft with wings and tails blended into the fuselage – from 1963 to 1975.  These were part of the joint USAF-NASA Project PILOT and included the Martin Marietta X-24, pictured above and first flown in 1969, and the 1966 vintage Northrop M2-F2, seen below.

The sixteenth and last glide flight of the M2-F2 on 10 May 1967 ended in disaster when it crashed into the dry lake bed at Edwards Air Force Base in California, rolling over six times and coming to rest upside down. The pilot, Bruce Peterson, survived the accident but sadly later lost an eye due to an infection contracted during the trauma. However, film of the crash - along with footage of the later Northrop HL-10 lifting body - was later used in the opening sequence of the 1973 TV show "The Six Million Dollar Man" with the premise that the fictional pilot Steve Austin - "A man barely alive" - could be rebuilt as a cyborg. In the real world however, it was realised as soon as 1970 that although lifting bodies had the potential to successfully re-enter the Earth's atmosphere using heat soak or tiled thermal protection they had unreliable low-speed aerodynamics and their shapes would not lend themselves to worthwhile payloads.The sixteenth and last glide flight of the M2-F2 on 10 May 1967 ended in disaster when it crashed into the dry lake bed at Edwards Air Force Base in California, rolling over six times and coming to rest upside down.  The pilot, Bruce Peterson, survived the accident but sadly later lost an eye due to an infection contracted during the trauma.  However, film of the crash – along with footage of the later Northrop HL-10 lifting body – was later used in the opening sequence of the 1973 TV show “The Six Million Dollar Man” with the premise that the fictional pilot Steve Austin – “A man barely alive” – could be rebuilt as a cyborg.  In the real world however, it was realised as soon as 1970 that although lifting bodies had the potential to successfully re-enter the Earth’s atmosphere using heat soak or tiled thermal protection they had unreliable low-speed aerodynamics and their shapes would not lend themselves to worthwhile payloads.

Less well known however is a British proposal for a reusable winged orbiter dating from the early 1960s. The idea of the Multi-Unit Space Transport And Recovery Device - given the acronym MUSTARD, grew from an Air Ministry contract for the British Aircraft Corporation (BAC) to make a study of an aircraft which could travel at over Mach 5.Less well known however is a British proposal for a reusable winged orbiter dating from the early 1960s.  The idea of the Multi-Unit Space Transport And Recovery Device –  given the acronym MUSTARD, grew from an Air Ministry contract for the British Aircraft Corporation (BAC) to make a study of an aircraft which could travel at over Mach 5. 

A team to do this assembled at the former English Electric works at Warton, near Preston in Lancashire, under the leadership of Thomas William Smith who had first worked for the Gloster Aircraft Company after graduating from London University in 1948 before moving to English Electric in 1949.

At Warton Tom Smith had been one of a team of four, under Freddie Page, working on the early development of the Canberra bomber. He was subsequently heavily involved in the development of the Lightning fighter aircraft and he took a flight in one of the two-seater trainers to become one of the few people who, at that time, had flown faster than the speed of sound. He was also among the leaders of the team which developed the TSR-2, the strike and reconnaissance aircraft which was cancelled by the Labour government in 1965.

“We started by looking at things which were Concorde-ish in nature,” Smith recalled before his death aged 85 in 2012, “and went on from there to high speed aircraft which would travel at Mach 12. We gradually realised that we could go from air-breathers, which would stay in the earth’s atmosphere, into space.”

The design work for MUSTARD was completed in 1964 and 1965, and the following year, in a lecture to the Royal Aeronautical Society, Lord Caldecote, BAC’s Deputy Managing Director and Chairman of its Guided Weapons Division, described a fully recoverable multi-stage aerospace vehicle which could put Western Europe into the space age within 10 to 15 years.

The design was a three-stage reusable aircraft, consisting of three similar crewed, delta-winged vehicles which could be stacked together and launched as a single unit. Two of the units would act as boosters to launch the third into orbit, feeding any excess fuel to the unit which was to become the spacecraft, before separating at 200 000 feet and returning to earth as normal aircraft. After placing a payload weighing as much as 5 000lb into a 1 000 mile high orbit, the third unit would return to Earth in a similar fashion.The design was a three-stage reusable aircraft, consisting of three similar crewed, delta-winged vehicles which could be stacked together and launched as a single unit. Two of the units would act as boosters to launch the third into orbit, feeding any excess fuel to the unit which was to become the spacecraft, before separating at 200 000 feet and returning to earth as normal aircraft. After placing a payload weighing as much as 5 000lb into a 1 000 mile high orbit, the third unit would return to Earth in a similar fashion.

MUSTARD was regarded as a suitable project for joint development by European aerospace companies, with a cost estimated to be around “20 to 30 times cheaper” than that of the expendable rocket launch systems of the time. Unfortunately, as with so many other British inventions, the government of the day decided not to proceed. About three years after MUSTARD was cancelled, the Americans became interested in a reusable aircraft.

In a later interview Smith – later involved inthe development of the SEPECAT Jaguar and Panavia Tornado – said that he felt MUSTARD’s problem was that it was “so far ahead of its time” and there had been no political will to push it forward. “There is nothing worse than being right at the wrong time,” he reflected.

However, for one year collaborative work was done at Edwards Air Force Base, not long before the first American lifting body aircraft appeared.

An apparently more elegant two - rather than three- stage to orbit vertical launch solution was put forward by Maxime Faget, the designer of NASA's Mercury spacecraft who by 1969 was working for NASA's Manned Spacecraft Center (MSC). In June that year North American Aviation was contracted to investigate the practicality of both this and a range of modular space stations and bases.An apparently more elegant  two – rather than three- stage to orbit vertical launch solution was put forward by Maxime Faget, the designer of NASA’s Mercury spacecraft who by 1969 was working for NASA’s Manned Spacecraft Center (MSC).  In June that year North American Aviation was contracted to investigate the practicality of both this and a range of modular space stations and bases.

Faget realised that although the blended lifting body design philosophy of the Silbervogel, Dyna-Soar and MUSTARD offered the strongest shape for initial atmospheric re-entry, these had poor low-speed handling and relied on a constant centre of gravity during design, construction and operation. 

In contrast, a more traditional aircraft layout of separate wings, fuselage and tail would allow the wings and tailplane to be swept backward and forward as and when the centre of gravity needed to be changed due to engine, fuel and payload developments.  However, such a craft would be inherently heavier and protecting the leading edges of relatively unswept wings from the heat of re-entry would be a problem. 

Faget’s solution on what would become known as the North American DC-3 was for the orbiter to re-enter the atmosphere at a 60 degree high angle of attack – the same way that North American’s X-15 rocket plane had descended from high altitude.  This would only have exposed the flat underside of the vehicle, as most of the thermal energy would have gone into the shock wave forming in front of the vehicle and the high drag would also have shortened the duration of the heat pulse.

The DC-3 wing – optimized for subsonic flight and landing – would have greatly reduced development cost and time but the low lift-to-drag ratio reentry profile advocated by Faget would also have limited the DC-3’s crossrange during re-entry.  That is to say that the orbiter would have been unable to fly larger distances than about 300 miles to the left and right of an initial direction of flight, making it less easy for the DC-3 to return to its base after one orbit.

When launched in near-perfect conditions from a base on the Equator, such as Kourou in French Guiana, an orbital spacecraft will first rise to the east to take advantage of the direction of the rotating Earth.   However, once it has orbited the Earth to the point where it started its journey, the spacecraft will then have to continue travelling to reach its launch base which will have turned with the Earth during that orbit.

In addition, despite being at the south eastern extremity of the USA, the Kennedy Space Centre at Cape Canaveral is thirty degrees north of the Equator, making spacecraft launched east from it adopt an inclined orbit.  Any spacecraft wishing to return to its base in Florida would thus have to be able to sufficiently manoeuvre away from its orbital path after-re-entry.

To maximise orbiter performance, the winged booster vehicle would also have had to do a similar job to an expendable multi-stage rocket and release the orbiter at Mach 10 at 45 miles altitude, making it necessary for the booster to have its own thermal protection system for atmospheric descent as well as jet engines (potentially chosen from Rolls Royce)  for safe recovery and ferry flights back to base.  Indeed, Faget envisioned a DC-3 booster landing automatically at Fairford, Rabat or somewhere further east before being refuelled and flown back to Cape Canaveral on its jet engines by a human crew.

All of this would in turn add to the weight of the booster, whereas in MUSTARD the booster function would have been shared between two vehicles – at least one of which would have disconnected further down the atmosphere. 

By 1970 however, with American astronauts having beaten the Soviet Union to the Moon, US President Richard Nixon was keen to cut NASA’s extremely large budget and limit further projects to a space station served by expendable rockets OR a re-usable space shuttle.  To help the cause of such a winged orbiter – which eventually did help build the International Space Station – NASA Director James Fletcher joined forces with the US Air Force to develop a space plane which could launch a 60′ long 40 000 lb spy satellite into either Equatorial or a more challenging Polar orbit and which would require a crossrange of 1 500 miles.  In the case of a south-rising polar launch from Vandenburg Air Force Base, California would have moved from its launching position even more by the time that the orbiting spacecraft caught up with it than in the case of Kourou in an eastward Equatorial launch. 

As a result, Faget’s DC-3 was abandoned in favour of the delta winged Space Shuttle that flew from 1981 to 2011.  Had the X-20 Dyna Soar not been cancelled in 1963 perhaps the US Air Force might have developed it as an astronaut’s taxi to its own expanding Manned Orbital Laboratory and even produced a robot version to take cargo into space, leaving NASA to send the DC-3 orbiter to its own space stations.  We can only guess. 

What can be revealed though, more than 50 years after the cancellation of the Boeing X-20, is the vertically launched, unmanned but re-usable Boeing X-37B Orbital Test Vehicle (OTV) which in 2013 gained the World record for being - at just over 29' long and a quarter the size of NASA's Space Shuttle - the smallest robotic horizontal-landing spaceplane.What can be revealed though, more than 50 years after the cancellation of the Boeing X-20, is the vertically launched, unmanned but re-usable Boeing X-37B Orbital Test Vehicle (OTV) which in 2013 gained the World record for being – at just over 29′ long and a quarter the size of NASA’s Space Shuttle –  the smallest robotic horizontal-landing spaceplane.

The X-37 began as a NASA project in 1999 and was originally to be launched from the Space Shuttle until expendable rockets were found to be cheaper.  The project – initially to refuel and repair satellites – was then transferred to the United States Air Force in 2004. An engineless X-37A was first drop tested from Virgin Galactic’s Scaled Composites White Knight Two high altitude carrier plane on 7 April 2006 before the first X-37B orbital mission on 22 April 2010 using an Atlas V rocket with a Centaur second stage to loft OTV-1. 

This successfully flew back to Vandenberg Air Force Base on 3 December 2010 – its silica tile thermal protection system having survived a Mach 25 re-entry to make only the second automatic landing of a winged spaceplane.  It was followed by a second vehicle – OTV 2- launched on 5 March 2011 and recovered on 16 June 2012.  The third mission,  which re-used vehicle OTV-1, launched on 11 December 2012, and – having set a new automated spaceplane orbital record of 470 days in March 2014 – landed at Vandenberg AFB, California, on 17 October 2014.  A fourth X-37 mission launched on 20 May 2015 and is still in progress at the time of writing.

In 2011, Boeing announced plans for a scaled-up variant of the X-37B, referring to the spacecraft as the X-37C. The X-37C would be between 165% and 180% larger than the X-37B, allowing it to transport up to six astronauts inside a pressurized compartment housed in the cargo bay.  Using an advanced version of the Atlas V rocket, this could reach the International Space Station and provide an alternative to Boeing’s Crew Space Transportation -100: designed along the lines of the Apollo Command Module but with a lightweight yet replaceable ablative shield.

Having mentioned Virgin Galactic's Scaled Composites White Knight Two, this twin fuselage jet carrier plane - capable of reaching an altitude of 70 000 feet - was designed to carry and air-launch Virgin Galactic's rocket powered SpaceShipTwo, seen above attached to the underside of the central section of White Knight Two's wing.Having mentioned Virgin Galactic’s Scaled Composites White Knight Two, this twin fuselage jet carrier plane – capable of reaching an altitude of 70 000 feet – was designed to carry and air-launch Virgin Galactic’s rocket powered SpaceShipTwo, seen above attached to the underside of the central section of White Knight Two’s wing. 

Although looking similar in shape to the Boeing Dyna-Soar, the six-passenger SpaceShipTwo is only designed to reach a sub-orbital height of 68 miles and so does not require heat shielding for re-entry, instead feathering its tailplanes to maximise drag until air thick enough for conventional gliding is reached.

For the purposes of this article however, a more interesting development is Virgin Galactic’s unmanned LauncherOne, carried and dropped in the same way as SpaceShipTwo but then using a more powerful rocket motor to take a small satellite into orbit.  Air launching has been part of experimental rocket aviation in America since the 1940s and has the advantage of more conventional horizontal take off, needing only a suitable airport for the mother ship rather than the launch gantries and other equipment needed for rocket booster launches from the ground.  Although the payloads involved are inevitably more limited, air launching in this manner also has the advantage of the mother ship being deployable to any given advantageous spot over the Earth for both Polar and Equatorial launches. 

British free newspaper Metro of Friday 4 December 2015 reported:

Virgin are adapting one of their Boeing 747 passenger jets to act as a launchpad for their Virgin Galactic satellite.

Nicknamed ‘Cosmic Girl’ when it flew for Virgin Atlantic – the plane will be used to carry the firm’s Launcher One satellite to high altitude before the craft will blast into space.  The Boeing 747-400 will be modified so the Launcher One can be mounted underneath its left wing, meaning the launcher has an increased maximum payload capacity to 400kg.  Virgin Galactic founder Sir Richard Branson said: ‘The Boeing 747 has a very special place in my heart: we began service on my first airline, Virgin Atlantic, with just one leased 747.Nicknamed ‘Cosmic Girl’ when it flew for Virgin Atlantic – the plane will be used to carry the firm’s Launcher One satellite to high altitude before the craft will blast into space.  The Boeing 747-400 will be modified so the Launcher One can be mounted underneath its left wing, meaning the launcher has an increased maximum payload capacity to 400kg.  Virgin Galactic founder Sir Richard Branson said: ‘The Boeing 747 has a very special place in my heart: we began service on my first airline, Virgin Atlantic, with just one leased 747.

‘I never imagined that today one of our 747s would get a second chance and help open access to space.  ‘I’m absolutely thrilled that Cosmic Girl can stay in the Virgin family – and truly live up to her name.’

Launcher One is described by the company as ‘an affordable dedicated ride to orbit for small satellites’ aimed at commercial and government customers, costing under £6.6 million.

Virgin Galactic CEO George Whitesides added: ‘Air launch enables us to provide rapid, responsive service to our satellite customers on a schedule set by their business and operational needs, rather than the constraints of national launch ranges.  ‘Selecting the 747 airframe provides a dedicated platform that gives us the capacity to substantially increase our payload to orbit without increasing our prices.’  The plane will not be used to launch passenger flights on Space Ship Two, which has its own dedicated carrier called White Knight Two.

Virgin Galactic are also looking at the possibility of air launching manned orbital vehicles in the future, but to conclude here is an article from the SEN website from 14 January 2014:Virgin Galactic are also looking at the possibility of air launching manned orbital vehicles in the future, but to conclude here is an article from the SEN website from 14 January 2014:

Two very different spaceplanes being developed in Europe and the United States have each won the interest of parties on the opposite sides of the Atlantic

The UK’s design for Skylon – and in particular its revolutionary SABRE hybrid engine – is to be studied and assessed by the US Air Force to see if the technology has potential to power its hypersonic vehicles And the European Space Agency (ESA) has agreed to work with Sierra Nevada Corporation (SNC) to find areas where they can work together to develop the American company’s Dream Chaser spacecraft.

Yesterday Reaction Engines Ltd (REL) in the UK announced its first formal link-up with the US government. The company, based at Abingdon, near Oxford, has entered into a Cooperative Research and Development Agreement (CRADA) with the Air Force Research Laboratory’s Aerospace Systems Directorate. The US interest is the latest major success for REL. Last year the British government pledged £60 million investment to continue development of the Skylon project. And that came after experts from ESA concluded a study by agreeing that the technology behind SABRE – it stands for Synergistic Air-Breathing Rocket Engine – had proved itself

Validation of this technology clearly caught the eye of the Americans too. They will have been impressed at how SABRE will switch in flight from air-breathing mode which takes it to Mach 5.5 – twice as fast as a jet – to that of a rocket engine, reaching Mach 25, or 7.5 km per second. The engine’s hybrid nature will allow a spacecraft to take off from a runway and fly directly into orbit

Its secret is heat exchanger technology that can can cool air entering the engine from 1,000°C to minus 150°C in just one hundredth of a second whilst preventing ice from forming within the unit. And it is all done using equipment that weighs less than a standard car to transfer as much heat – 450MW – as generated by an electricity power station.

The engines will be able to power Skylon to become a reusable replacement for the Space Shuttle, carrying cargo and crews to space stations from any airport with a long enough and strong enough runway, and with a speedy turnaround time between missions.

But the SABRE engine also has the potential to power other vehicles, and could fly passengers at hypersonic speed from one side of the Earth to the other – e.g. London to Sydney – in less than four hours

REL’s managing director Alan Bond, the inventor behind Skylon and SABRE, said: “The signing of this agreement with AFRL builds on an extraordinary period for Reaction Engines Ltd which has seen the successful demonstration of SABRE’s ultra-lightweight high performance heat exchanger technology and a UK Government commitment of £60 million ($100m) towards the next phase of development of the SABRE engine

Barry Hellman, for AFRL, said: “This CRADA opens the door for joint development and testing to help AFRL understand the SABRE engine’s technical details, and whether it may offer unique performance and vehicle integration advantages when compared to traditional hypersonic vehicle concepts. We look forward to exploring the engine and its lightweight heat exchangers which have the potential to enable hypersonic air-breathing rocket propulsion.

In early November 2015,  20 per cent of Reaction Engines Limited shares were purchased by BAe Systems.  Full details of this news, along with some impressive animated graphics, can be found at

 http://uk.businessinsider.com/bae-systems-investment-in-reaction-engines-2015-11

The Daily Telegraph report of 2 November 2015 concluded with the paragraph:

“BAE’s backing means the project, which is in the final stages of winning a £60 million government investment, should have a complete engine ready for ground testing by the end of the decade, with flight tests starting in the early 2020s.”

Meanwhile, Sierra Nevada’s new deal with ESA could be seen as a bid to broaden the potential market for their mini-shuttle Dream Chaser. This reusable vehicle is still undergoing early flight tests while rival commercial companies have flown successful missions to the International Space Station

SNC believe the strength of their vehicle is that, once hoisted by a conventional rocket, it will be able to return to a runway landing just as the Shuttles did. In their view, it could therefore lift astronauts and cargo into low-Earth orbit but also serve as a platform for technology demonstrations, construction and repair in space, as well as crewed and un-crewed scientific missions

ESA will work with Sierra Nevada Corporation to identify how European hardware, software and expertise can be used to further develop the Dream Chaser with a view to it being used to fly European missions. A passenger vehicle is missing from Europe’s own range of spacecraft. Its Automated Transfer Vehicle (ATV) has proved itself as a vey capable cargo-carrier but, sadly, it was not designed for crews and ends its missions by being destroyed in the atmosphere

A new and advanced docking system for the ISS will also be explored. After an initial evaluation and planning phase by ESA and SNC this year, the organisations expect to continue the relationship through a long-term agreement leading to actual flights by Dream Chaser into orbit.

Meanwhile, on 8 August 2015 the Daily Telegraph reported:

Airbus's plans for a Mach 4 passenger jet have been left in the slow lane by US researchers’ hopes of building a spaceplane capable of flying at more than 10 times the speed of sound.Airbus’s plans for a Mach 4 passenger jet have been left in the slow lane by US researchers’ hopes of building a spaceplane capable of flying at more than 10 times the speed of sound.  America’s Defence Advanced Research Projects Agency -DARPA – aims to build a reusable vehicle that it hopes will provide “quick, affordable and routine” access to space, which it says is “increasingly critical for both national and economic security”.

Darpa has now awarded three contracts to Boeing, Masten Space Systems and Northrop Grumman, which will subcontract Virgin Galactic to develop a demonstration vehicle, identify and reduce risks to the technologies on board, and come up with a plan to build and flight-test the spaceplane.

It hopes its unmanned XS-1 spaceplane – which will fly at more than 6,500mph, or Mach 10 and above – will slash the cost of putting large satellites in space and reduce the time it takes to schedule and execute launches.

The XS-1 demo vehicle would be able to fly at hypersonic speeds – defined as five times the speed of sound or more – at least once. It would also be capable of being launched 10 times in 10 days and should be able to launch into orbit a dummy payload simulating a satellite.

It also aims to take the price of getting small payloads – ranging from 3,000lb to 5,000lb – into space down to less than $5m (£3.2m). According to NASA, the current cost of putting just 1 lb into space is $ 10 000.

The XS-1 is intended to operate like an aircraft, taking off from a runway rather than relying on a traditional “stack” of rockets beneath a payload module, and flying into a low orbit. It would then use an expendable upper stage to boost the payload into the desired orbit, while the main spaceplane returns to earth and lands on a conventional runway, where it could be quickly turned around and used again.

Jess Sponable, Darpa programme manager, said: “We chose performers who could prudently integrate existing and up-and-coming technologies and operations, while making XS-1 as reliable, easy to use and cost-effective as possible.

“We’re eager to see how their initial designs envision making spaceflight commonplace – with all the potential military, civilian and commercial benefits that capability would provide.”

Darpa said that the companies awarded the contracts for the XS-1 would be expected to look at how the vehicle could be used by military, civil and commercial operators.

As well as launching payloads into space, they will investigate how the spaceplane could support testing of future ultra-high speed aircraft and new spacecraft.

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