phase1_bAn artist's impression of an early X-30 NASP design in flight [IMG: NASA]On February 4th 1986, mere days after the United States had been shocked by the Challenger disaster, President Reagan rose before Congress to give his State of the Union Address. "We're going forward with our shuttle flights. We're going forward to build our space station. And we are going forward with research on a new Orient Express that could, by the end of the next decade, take off from Dulles Airport, accelerate up to 25 times the speed of sound, attaining low Earth orbit or flying to Tokyo within 2 hours." 

Reagan's 'Orient Express' was not a new idea, but his announcement allowed a project from the Black world of classified budgets to step into the light. The name had been carefully chosen to  emphasise the potential for a new era of rapid transit for the general public but in reality the National Aerospace Plane (NASP) as the project was officially christened, was being designed with a very different role in mind and promised the fulfilment of a dream that stretched all the way back to the late 1950's.

The NASP represented just the latest attempt to attain one of the holy grails of aviation, the Single Stage to Orbit (SSTO) vehicle. SSTO has been a hugely seductive concept for aerospace designers since the 1950's. The idea of being able to access space with a vehicle that is completely re-usable and therefore promises massive economic benefits, holds a clear attraction. Couple this with thoughts of a steady evolution from high speed and high altitude aviation, leading to a true aerospace plane that can take off and fly into orbit before landing horizontally on a runway and it's easy to see why the idea receives periodic revisits.

But for all of the apparent elegance and simplicity that SSTOs seem to offer there are good reasons why none have yet flown. The problems of creating such a vehicle are daunting, requiring huge leaps in the state of the art regarding propulsion, materials and design and testing techniques. There is also the major stumbling block for an SSTO - by it's very nature it must carry its entire vehicle weight into orbit and back again, meaning such designs are extremely sensitive to increases in weight or reductions in performance that may occur in the detailed planning stages.

To understand why Reagan's advisors though the concept was workable in the mid 1980's we first need to go back to a little known Air Force initiative to provide routine, affordable orbital access.

The Air Force Aerospaceplane
Even as the space age was in its earliest stages in 1957, some within the United States Air Force were beginning to turn their thoughts to how the existing expendable boosters could be recovered and reused as a way of lowering the costs involved in placing payloads in orbit. Initially these ideas revolved around adding wings to existing designs such as the Convair Atlas, but as new technologies and requirements developed, more ambitious plans began to take shape. Initiated by Weldon Worth, Director at the Air Force's Aero Propulsion Laboratory (APL), the Aerospaceplane project (initially just called Spaceplane) sought to bring together emerging ideas around high speed propulsion and lifting airframes to create an SSTO to deliver Department of Defence (DoD) payloads to orbit with aircraft-like operations.

AerospaceplaneAn artist's impression of an Aerospaceplane design in flight [IMG: Wikipedia under CC license]Related studies were already underway into a number of promising propulsion technologies including the Liquid Air Cycle Engine (LACE) and Air Collection Engine System (ACES). These systems aimed to take the air entering a vehicle's inlets and remove and condense the oxygen for use as an oxidiser at higher speeds and altitudes. Such a system would remove the need for an SSTO to carry all of its fuel and oxidiser at take-off as rockets did. LACE and ACES were to be used as part of a combined cycle propulsion system where turbojets could be employed for the initial low-speed stages of the flight before switching to ramjets and then eventually rocket propulsion using the stored oxidiser.

Under the Aerospaceplane project Convair, Martin, Boeing, Lockheed, North American and Goodyear all worked on initial feasibility studies before creating a wide variety of design solutions for what seemed a workable SSTO. Initial projections were for an operational system within the 1966-68 timeframe, but unsurprisingly there were huge technical hurdles between paper designs and a practical vehicle. While LACE and ACES seemed to offer practical approaches under test conditions, a full-size system was never constructed and ramjet research was stagnating due to the growing realisation that speed and height was no longer a defence for bombers and interceptors. The cancellation of projects such as the Republic XF-103 combined cycle interceptor had a knock on effect for SSTOs.

Beyond the technical issues, more practical problems dogged the Aerospaceplane. The Air Force was unable to provide a clear operational need for the project at a time when they had Atlas and Titan ICBMs capable of providing orbital access. Coupled with this they were also pursuing a winged Boost/Glide vehicle, the Dyna-Soar which would have overlapped with many of the proposed roles for an Aerospaceplane. (To see more about the X-20 Dyna Soar CLICK HERE)

Given the hugely ambitious nature of the project, it was unsurprising that 1963 saw the official cancellation of Aerospaceplane, but some activities did carry on beyond this point in the hope that an air launched sub-scale demonstrator could still fly. But one key technology considered for the Aerospaceplane did survive to become a focus for the projects that followed - the supersonic combustion ramjet or Scramjet.

Scramjet Developments
As the demands for propulsive performance increased during the 1950's with designers seeing speed and altitude as the ultimate for winged vehicles, so new ways were sought to provide air-breathing alternatives to limited duration rocket propulsion. The ramjet had held much early promise, but rapidly the capabilities of turbojets coupled with efficient inlets provided Mach 3+ performance negating much of the need for ramjets. The problems for air breathing propulsion came above these speeds and this is where the scramjet came in.

Designed to work in the range between Mach 3 and, theoretically at least, orbital velocities of Mach 25, the scramjet takes advantage of the speed of the airflow to compress the air prior to combustion but whereas a ramjet must decelerate this air to subsonic speeds prior to combustion, a scramjet allows supersonic flow throughout the process.

Most early scramjet designs were axisymmetric - essentially they were podded engines with a circular inlet channeling airflow around a centre body. During the 1960's various experimental scramjet programmes were run by the US Navy and Air Force (under the APL) but early results were not encouraging. Small models were able to achieve ignition and thrust, but the drag the axisymmetric configuration produced cancelled this out meaning they were unable to produce net thrust - clearly an issue for an effective propulsion system.

As work moved forward to improve scramjet configurations, plans were made for flight test vehicles. By this time, the United States already had a Hypersonic capable research craft, the North American X-15, and plans were submitted to modify one of the three flight articles into a more advanced scramjet testbed. Opportunity to action these ideas came as a result of a serious crash involving the number 2 aircraft during an emergency landing in November 1962. Although badly damaged, the decision was made to rebuild and modify this craft to a new configuration, the X-15A-2. This more advanced vehicle allowed for additional propellants to be carried for both the main XLR-99 engine and an additional scramjet test article to be carried on the lower ventral fin. This engine was known as the Hypersonic Research Engine (HRE) and was to be built by Garret AiResearch under the direction of Tony DuPont. DuPont was a member of the famous chemical manufacturing family and had impressed Garret and NASA with his proactive and innovative approach to requests for an HRE design.

X-15A2X-15A-2 leaves the B-52. The dummy HRE is attached to the lower ventral fin stub [IMG: NASA]Before an actual working HRE was ready for testing, NASA and the Air Force decided to test a dummy object in place on X-15A-2 to investigate the aerodynamic configuration in flight. Unfortunately these attempts almost led to disaster during the programme's maximum speed flight as Pete Knight took the vehicle to Mach 6.7 in October 1967. During the flight, shockwaves caused by the dummy HRE caused a loss of structural integrity due to excessive heating in the X-15's lower ventral area. Had the influx of hot gases reached further into the vehicle this could easily have led to the loss of the craft. Knight was able to recover the flight but it marked the end of X-15A-2's flying career and consequently the end of the HRE programme.

While the HRE was foundering, studies at NASA's Langley Centre were investigating a very different scramjet configuration. A podded axisymmetric scramjet would never be able to take advantage of the majority of the air flowing past a vehicle's body making the design inefficient. The new research examined placing scramjets with simpler rectangular inlets across the lower section of the vehicles body, meaning the shape of the vehicle would form part of the propulsive system by compressing the incoming air ahead of the inlet, then shaping the exhaust aft of the scramjet's nozzle. Struts within the inlets could act as fuel injectors as well as structural elements, making a far simpler design which would become the characteristic configuration for all scramjet powered vehicle proposals that would follow.

ScramjetDiagramThe airframe integrated scramjet design, originated by NASA Langley and adopted for NASP [IMG: NASA]Problems with this approach remained, but it was decided given the integrated nature of the airframe and the propulsion system and the lack of high Mach test facilities, the best way to solve many of these issues was during flight test. NASA and the Air Force hoped to generate enough interest in the concept to create a new hypersonic research vehicle, the X-24C, during the mid-late 1970's to pick up where the X-15A-2 had left off. Unfortunately, funding could not be obtained and after detailed design work by Martin Marietta and Lockheed's famed Skunk Works the project went no further. The early promise of the scramjet looked likely to fade away, after all with the new Space Transportation System (the Space Shuttle) approaching operation and various expendable launchers still available it appeared America's launch requirements could be amply catered for during the coming years.

Following Ronald Reagan's election victory in 1980, the new administration began to look at potential responses to the Soviet Nuclear arsenal. Although new weapons building programmes were initiated to allow an equivalent nuclear response to any attack, other strategies were also under consideration. The concept of a new space based system for missile defence, capable of nullifying the Soviet threat, became popular within the National Security Council and over the coming years this concept developed into the Strategic Defence Initiative (SDI) announced by Reagan in 1983 and more commonly known as Star Wars.

Clearly any such system would require regular and reliable orbital access. Initial estimates suggested at least 100 new items vehicles would be placed in orbit although this was seen as a highly conservative estimate with some commentators claiming over 2000 new satellites may be required. Concurrently, some within the DoD were beginning to question the Air Force's commitment to the Shuttle. While Air Force payloads and involvement had been vital in making the case to develop the Shuttle, by 1982 it was becoming clear that it was not going to provide the routine easily maintainable transportation system that had originally been pitched. There were also concerns about the safety of the system with a damaging 1982 study by the RAND corporation predicting that up to 3 of the Shuttle fleet may be lost during the operational life of the programme. (For more on the Air Force's role in the design of the Shuttle CLICK HERE)

Against this backdrop the DoD began to cast around for potential alternatives including a spaceplane of their own. The Air Force Aeronautical Systems Division (ASD) started work on an initiative for a Shuttle replacement that became known as the Trans Atmospheric Vehicle (TAV) programme but elsewhere the Defence Advanced Research Projects Agency (DARPA) was also showing an interest.

DARPA had originated during the Eisenhower administration in 1958 as the Advanced Research Projects Agency (ARPA) to provide a means for promoting scientific and technological research in the wake of Sputnik. Having been heavily involved in the initial American responses to Soviet space successes, the agency later broadened its remit to cover all areas of technology including the initial development of what would become the Internet.

During the early 1980's DARPA Director Robert Cooper remained interested in Aerospace projects and through his encouragement of the advanced propulsion field came into contact with Tony DuPont. Since his involvement with the HRE, DuPont had continued his work on advanced propulsion systems and by 1982 felt he had found a way through many of the problems that had previously dogged scramjet developments. Finding a receptive audience in Cooper, DuPont was put in contact with leading DARPA aerodynamicist Robert Williams. Between them DuPont and Williams began working on a series of investigations into an SSTO vehicle featuring a combined cycle propulsion system utilising scramjets. By 1984, these initial steps appeared to show great promise and subsequently grew into a classified project named COPPER CANYON - an attempt to show how routine reliable access to space could be developed to support the needs of the SDI.

The key goals for COPPER CANYON were to provide a vehicle capable of taking off and landing horizontally on a standard runway and able to reach orbit as and when required, delivering or retrieving payloads. To do this it would need not only an advanced combined-cycle propulsion system, but also a means to deal with the extreme aerodynamic heating created by speeds up to Mach 25. DuPont proposed that this could be achieved by using the Hydrogen fuel carried to power the scramjets. By passing this around the structure of the vehicle, much of the heat could be carried away from the surfaces. Other predicted advances in heat resistant materials and Computational Fluid Dynamics (CFD) would allow the creation of a vehicle that was both robust yet light enough to endure these extreme velocities and return intact and ready to fly again with a minimum of post-flight processing.

COPPER CANYON represented Phase 1 of the programme, concluding with the production of a baseline design an air-breathing SSTO vehicle. The next stage was to invite manufacturers onboard to propose how they would develop the key technologies required to make it a reality and to do this COPPER CANYON needed to shed it's classified status, take on a new identity and go public.

Selling the dream

X-30_futuristic_nasaThe "Orient Express" takes flight in an artist's impression of an early NASP design [IMG: NASA]As Reagan introduced America to the new National Aerospaceplane as "...a new Orient Express" in 1986, he was really introducing them to a continuation of COPPER CANYON. The NASP project would represent Phase II and III of development, leading to a full SSTO flight test vehicle named the X-30, proving the viability of the technologies across the full operational regime and allowing for the development of operational follow-on vehicles. The Air Force had by now suspended any further work on their TAV initiatives and were fully on board with the new programme.

In using the term "Orient Express" and highlighting the benefits of such a vehicle as a rapid intercontinental transport, the administration were being slightly economical with the truth. Early concept art showed a dart shaped craft in colourful airliner style livery to help sell this idea, but in reality aviation analysts were quick to recognise NASP's primary role - as an SSTO to support SDI and related initiatives. Certainly, the same technologies could be used to produce the next generation of air travel but attempts to interest airlines in lending their to NASP produced very little in the way of commitment from this sector.

Moving the programme out of the Black and into the public realm allowed NASA to become fully involved. They became one of the project partners alongside the Air Force, Navy, Strategic Defence Initiative Organisation (SDIO) and DARPA. Overall control of the program would continue to rest with DARPA with an estimated 80% of funding coming from DoD budgets. What NASA were able to bring was a huge amount of knowledge in, as well as facilities to test, many of the key areas highlighted under Phase II, namely:

  • Advanced Airbreathing Propulsion
  • Advanced Materials
  • Computational Fluid Dynamics
  • Actively Cooled Structures

Initial estimates for the project using the baseline design developed under COPPER CANYON were extremely optimistic with Tony DuPont suggesting a 50,000 pound vehicle within 5 years for $5bn. Following Reagan's announcement, slightly more conservative timescales were developed with a heavier vehicle aiming for flight tests in the late 1990's. Initial research contracts for Phase II were divided between airframe and propulsion contractors were let during 1986. Rockwell International, McDonnell Douglas, General Dynamics, Boeing and Lockheed received airframe contracts and General Electric (with Aerojet TechSystems) and Pratt & Whitney received the propulsion contracts. Rocketdyne also elected to enter the propulsion contest using their own funds.

conical_acceleratorAn early 'Conical Accelerator' design undergoes testing [IMG: NASA]Phase II was envisioned to last until 1993 at which point decisions would be made on final airframe and propulsion contractors and the programme would move into Phase III - the design and construction of the X-30 vehicle. From the outset a wide variety of airframe configurations were examined to ascertain their relative strengths and weaknesses. Very quickly it became apparent that the original government baseline design had been extremely optimistic in most areas. DuPont's configuration devised under COPPER CANYON had included no landing gear, orbital manoeuvring system or fuel reserves. While the government baseline design presented at the outset of Phase II had sought to rectify some of these issues, it still presented best case scenarios in all of the key technical areas and now the airframe and propulsion contractors struggled to produce workable solutions that could produce anything like the baseline performance.

configurationsAirframe configurations examined during Phase II of the NASP Programme [IMG: NASA]By 1987 initial airframe designs were reviewed with the lightest configuration coming from Rockwell International, but this still weighed 175,000 pounds - some three times DuPont's original estimate. Two manufacturers (Lockheed and Boeing) were eliminated at this stage as their designs were the heaviest. To compound the problems with weight growth in the airframe, the propulsion system also looked like producing less thrust than had originally been anticipated. The complicated combined-cycle system would use scramjet and rocket propulsion with a complex and untried ejector system to maximise thrust across the flight regime. A LACE system would be used to extract oxidiser from the atmosphere during flight and high density Hydrogen Slush would be used as the main fuel. Methane was also to be used to provide rocket propulsion for the low-speed end of the flight envelope.

As Phase II development continued, the design gradually evolved from the sleek delta-winged circular cross-section wing/body model proposed by DuPont into a far larger rectangular cross section blended lifting body. As the size increased and performance remained marginal, so some of the potential missions began to fall away. High inclination or Polar orbits no longer appeared achievable - taking with them a key factor in the NASP's usefulness to the DoD.

phase2A revised design from later in Phase II [IMG: NASA]As President Bush took office in 1989 it was against a backdrop of changing political realities. The old adversary, the Soviet Union, was beginning to lose it's grip over much of its territory leading to its eventual breakup. With the Cold War over, the need for SDI and the increased re-armament of the Reagan years quickly subsided and with these changing priorities NASP fell under the spotlight of Defence Chiefs. By 1990 the baseline design now weighed in at 400,000 pounds and it was clear that the programme was still years away from solving many of the fundamental issues associated with air-breathing hypersonic flight. Secretary of Defence Dick Cheney accepted a recommendation to terminate the programme, but it was saved by interventions from the National Space Council, reactivated by Vice-President Dan Quayle.

By 1992, although development continued, the project was still some distance away from a set of workable solutions to take into Phase III - the design and construction of the X-30 Flight article. An additional phase (II-E) lasting three years was suggested to construct scale models for flight test. The early confidence that CFD could accurately model flight conditions between the Mach 8 attainable in test facilities and the Mach 25 required for orbital flight appeared less well founded now and it seemed prudent to test in flight prior to a commitment to build a full size X-30.

Dates for a first flight of the full-sized vehicle began to push into the next century and the Air Force, recognising the NASP programme was a huge drain on their shrinking resources and an asset they no longer required, decided to withdraw support leading to the eventual termination of the programme.

At the time of the NASP's cancellation in 1995 an estimated $5.5 billion had already been spent (although given that much of this came from DoD sources this may well not be accurate). Moving to Phase III could well have tripled this spend and there was no consensus that all of the problems could have been solved. At the end of the programme many advances had been made in terms of materials and CFD techniques but there was still no workable SSTO design.

It's difficult to look at NASP and not conclude that some sort of collective wishful thinking settled upon the decision makers at DARPA and the DoD. The concept seemed so logical and to offer so many advantages over the Shuttle or existing expendable launchers that it's understandable it could gain support, but as Ivan Bekey, formerly a Senior Engineer with NASA's Office of Exploration and a seasoned SSTO advocate observed "Being airplane-like the NASP concept attracted powerful backing because it was intuitively easy to grasp. The nation fooled itself into believing that because the NASP image was what was desired, the reality itself was therefore attainable."

Former head of the Lockheed Skunk Works Ben Rich was somewhat more forthright in his assessment of NASP. "Reagan called [NASP] the 'Orient Express' because it would fly from New Your to Tokyo in only two hours. Reagan wanted to build it in four to eight years. He'd be lucky to do it in fifty" adding "...whoever dreamed up that Presidential address ought to be canned."

Both COPPER CANYON and NASP could certainly have done with a severe dose of realism and far greater due diligence of the challenges involved and project risks they posed prior to moving forward. It's unrealistic to base any engineering project, especially one as revolutionary as an SSTO spaceplane, so firmly on best case scenarios. The techniques and materials required were far beyond 'state-of-the-art' even a decade after the project's genesis and the conventional wisdom in aerospace design - that weight will always increase as a design develops - seems to have been disregarded.

cfdA Computational Fluid Dynamics (CFD) model from the NASP programme [IMG: NASA]The reliance on CFD techniques to answer so many of the aerodynamic and thermal questions was exposed as the project moved forward with many unanswered questions regarding thermal stresses across the flight regime. The project did push forward CFD techniques and subsequent projects have benefitted as a result, but again placing too much faith in an what at the time was an incomplete science cost NASP dearly.

The high profile of NASP and repeated assertions that the technology was within the reach led many to speculate that the whole project had been a front for a classified vehicle. The shadow of the mythical Aurora looms large over many aerospace projects and given NASP's stated goals it seemed like a good fit for many secret plane watchers. In reality, there is little in the NASP project documentation to suggest that a hypersonic spy plane could have been produced much quicker than the X-30. A scramjet powered craft of the projected size of the X-30 would certainly be a fairly conspicuous presence in the skies!

In the wake of the NASP failure the SSTO dream still persisted as a way to replace the Shuttle in the longer term. The DoD moved to a very different approach with the McDonnell DC-X, a vertical takeoff and landing rocket demonstrator that produced impressive results during the early 1990's. NASA also looked to a different approach with the X-33, a vertical takeoff horizontal landing lifting body which started development in the mid 1990's. (For more on the story of the X-33 CLICK HERE)

x-43A rendering of the NASA X-43A in flight [IMG: NASA]The dream of air-breathing hypersonic also underwent a renaissance via NASA's Hyper X programme leading to the X-43 technology demonstrator. In many ways a true extension of the Phase IIE NASP proposal, the small uncrewed X-43 shared a broadly similar configuration to the eventual NASP baseline design. With a hydrogen fuelled scramjet engine, the X-43 was air launched from a B-52 and boosted to a speed in excess of Mach 4 by a Pegasus rocket. These velocities were needed for scramjet ignition, but eventually in November 2004 a speed of Mach 9.6 was reached.

More recently, the X-51 was able to achieve longer duration hypersonic cruise using it's scramjet engine and although the proposed follow on vehicle, Blackswift, was cancelled a new generation of hypersonic weapons look set to benefit from the lessons learned from these projects.

As for an air-breathing SSTO, current attention has shifted to the British Reaction Engines Ltd SKYLON project with it's revolutionary SABRE propulsion system, but where this promising project goes remains to be seen.

Hopefully the costly lessons of NASP will be heeded.

The X-Planes: X-1 to X-45 - Jay Miller
Facing the Heat Barrier: A History of Hypersonics - T.A. Heppenheimer
Critical Issues in the History of Spaceflight: Chapter 9 "A failure of National Leadership" Why no replacement for the Space Shuttle - John M. Logsdon
Space Shuttle: The History of the National Space Transportation System - Dennis R. Jenkins
Secret Projects: Military Space Technology - Bill Rose
Aerospace Projects Review: Volume 2, Number 5
Report of the Defence Science Board on National Aerospace Plane Program - November 1992
Skunk Works - Ben R. Rich & Leo Janos

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