With hindsight, it is now popular to view the Space Shuttle as a flawed concept, born out of political compromise and budget constraints. Never able to maintain anything like the original projected flight rates, hugely expensive and time consuming to maintain, the shuttle can seem like something of a developmental dead end or, as some have claimed, proof that reusability can never be economically viable.
As we enter an era where both SpaceX and Blue Origin aim to prove that Vertical Takeoff/Vertical Landing rockets can offer a sustainable route to Earth orbit and beyond, it’s interesting to look back at a reusable spaceplane concept that predated NASA’s shuttle studies and could, had things been different, have ended up being America’s national launch system from the 1970s onwards. But this is also the story of the man behind the concept, Max Hunter, a visionary who – along with contemporaries such as Philip Bono (see more on Bono’s SSTO designs) – helped define the desirability of reusable launch vehicles at a time when the world was still focused on the short-term spectaculars of Apollo’s race to the Moon.
When the USAF’s Dyna-Soar spaceplane programme was cancelled on December 10th 1963 (see Death of the Dyna-Soar for more on this), outwardly at least it looked like the Air Force’s long held ambition for a winged space vehicle had come to an end for the foreseeable future. At around the same time as Dyna-Soar’s demise, the even more ambitious Aerospaceplane project, an attempt to create a scramjet powered Single Stage to Orbit (SSTO) vehicle, had also foundered judging correctly that the technologies and materials required to achieve this still lay decades into the future (click for more on Aerospaceplane as a precursor to NASP).
Secretary for Defence Robert McNamara had pointed the Air Force in the direction of NASA’s capable Gemini capsule as their likely route into space. Initially Air Force astronauts would share flights with NASA crew members before pursuing a separate ‘Blue Gemini’ programme. Gemini was also to be a component of the Manned Orbiting Laboratory (MOL), announced alongside Dyna-Soar’s cancellation. But Gemini wasn’t a perfect solution to the Air Force’s perceived requirements. Firstly it didn’t offer the mission flexibility or cross range they saw as essential in a rapid-response spacecraft, and secondly unless they could perfect the Rogallo wing recovery method shelved by NASA, any blue-suited astronauts would find themselves dependent on the Navy to fish them out of the ocean at mission’s end – a far from ideal arrangement for the junior service.
So while the race to the Moon consumed the public’s attention and MOL continued its lengthy development, the Air Force quietly went on with examining new directions for space access more suited to their needs.
Hunter’s big idea
During the early years of human spaceflight, competition with the Soviet Union had driven the United States towards ballistic capsules as a way to expedite getting an American into space. Kennedy’s 1961 declaration of his intention to place a man on the moon ensured that this approach would remain pre-eminent until the end of the decade, but already within NASA and the aerospace industry some were beginning to think beyond Apollo to what might come next. One such visionary was Maxwell W. Hunter.
Having worked on the Thor IRBM and the Saturn S-IV stage whilst still at Douglas aircraft, Hunter was now at the centre of the burgeoning space industry, but unlike many of his contemporaries he also brought with him valuable insights from his time in the aviation industry, most notably an understanding of the Air Transport Association’s operating-cost-calculation-formula (a mathematical model developed to help airlines and manufacturers ensure economical everyday operations in aviation services). Hunter intuitively grasped that until the issue of expendable launch vehicles was addressed, the exploitation of space could never become truly economical and payloads would have to remain relatively small and extremely expensive to orbit. He recognised a correlation between the ATA formula and his thoughts on orbital access, later stating “I am presumably not the only person who made most of his life in rocketry after first having a strong involvement with the economics of air transportation, but subsequent events have convinced me that it is a pretty rare combination.”
His experiences at Douglas suggested that if a way could be found to design a space vehicle that could be at least partly reusable and at the same time apply the maintenance and automated checkout models adopted by commercial aviation, then spaceflight could move beyond its initial government led expendable phase and truly become affordable commercial pursuit. In 1965, Max Hunter joined Lockheed Missile & Space Company (LMSC) based in Sunnyvale, California and set about outlining an enduring vision for reducing launch costs while bringing these aircraft-like operations to spaceflight. What emerged was a design for a delta bodied semi-reusable spaceplane that became known as STAR Clipper (the STAR standing for Space Transport And Recovery).
Unveiled in 1968, the original STAR Clipper was an elegant delta shaped lifting body, sharply swept with upturned fins and powered by five main engines. At launch the bulk of STAR Clipper’s propellants would be contained in a large V-shaped tank arrangement that flanked the front of the spaceplane. Taking off vertically, the vehicle would accelerate like a normal rocket before jettisoning the external tank when its propellant supplies were exhausted. The STAR Clipper would then continue into orbit using a smaller internal supply of propellants. This approach was characterised as One and a Half Stage to Orbit (1.5 STO).
The vehicle had a large 9ft by 40ft internal bay in which it could carry around a 20,000 pounds of payload. With the mission complete the vehicle would use the main engines to de-orbit then carry out a long lifting reentry with its shape allowing for cross-range manoeuvres to bring it in for a controlled landing on a conventional runway. STAR Clipper would use standard materials such as aluminium and titanium covered by a thermal protection system of ceramic tiles and quartz-felt blankets with reinforced carbon being used for the areas subjected to the highest thermal load.
The vehicle’s shape was derived from a long line of investigation by the Air Force’s Flight Dynamics Laboratory (FDL) which had been working on lifting body shapes since the early ‘60s. Their FDL-8 shape formed the basis for work on the initial STAR Clipper configuration, designated LSC-8AX. LMSC expended a great deal of time and effort evaluating their design and by 1968 had a high degree of confidence that the concept would work given sufficient investment. A variety of configurations and baseline missions were developed and presented to the FDL as part of their Integral Launch and Reentry Vehicle (ILRV) programme, but unfortunately the Air Force chose to pass on STAR Clipper at the time. Fortunately for LMSC though, a new potential customer had entered the market for a reusable space transportation system…
Enter the shuttle
Even while Apollo was undergoing its initial test flights and the final push for the moon began, some NASA centres, their development work on the lunar programme complete, began to look at what may come next. At their Marshall (MSFC) and Manned Spacecraft Centre (MSC) plans were being developed for a significant expansion of America’s operations in LEO and beyond. With much of the Apollo Applications Programme having been shelved the new Integrated Program Plan (IPP) centred around the construction of large orbital stations and refuelling depots. From here nuclear powered craft would move between orbits and eventually support the construction of facilities in lunar orbit and on the surface of the moon. Large ships would be constructed on orbit for America’s next great step – an expedition to Mars during the 1980s. It was expected that the Saturn V would still play a part in these plans, providing a heavy lift capability to support the construction of the considerable orbital infrastructure, but beyond this a need was recognised for a smaller, more economical means for reaching orbit on a regular basis.
By 1968 NASA were beginning to seek proposals for what was, somewhat confusingly, also initially termed the Integral Launch and Reentry Vehicle (ILRV) like the Air Force’s similar programme, but which soon became known as the Space Transportation System or, more commonly, the Space Shuttle. George Mueller was an early advocate of such a system, speaking publicly about the advance it would represent in affordable, regular orbital access. LMSC were quick to grasp the opportunity to take Hunter’s STAR Clipper concept and adapt it to NASA’s ILRV requirements. On September 30th 1968 LMSC submitted their 1.5 STO design and in February they were awarded a Phase A study contract along with General Dynamics/Convair, North American and McDonnell Douglas (Martin-Marietta also chose to participate using their own funds). At this stage NASA were open to a wide variety of approaches for the Shuttle ranging from the use of existing expendable boosters to fully reusable winged vehicles.
In December 1969, LMSC released their proposal for the LS-112 – an enlarged 3-engined delta-bodied orbiter based on STAR Clipper that could either be used as part of a fully reusable system with the addition of a large flyable booster stage, or even two winged boosters as part of a ‘triamese’ arrangement. The orbiter would also now include pop-out wings, extensively researched by the FDL, and additional jet engines to aid reentry and landing characteristics as well as to give the vehicle a ferry-flight capability. The payload capacity had increased to 32,000 pounds – considerably more than in the original LSC-8AX version.
Given the high flight rates predicted by NASA at this stage LMSC were informed that the 1.5 STO drop-tank approach would probably prove less desirable than the fully reusable system, but LMSC elected to continue work on this direction in parallel to their NASA funded efforts – a decision that would prove prescient.
Political pressure mounts
Whilst the Phase A Shuttle concepts were being created by NASA and their chosen contractors, the politics of spaceflight in America were undergoing significant upheaval. The ready access to funding that had characterised the Apollo years could no longer be relied upon and even as acting NASA Administrator Thomas O. Paine presented his ambitious IPP for to Vice President Spiro Agnew’s Space Task Group, it quickly became obvious that there was no appetite within Nixon’s administration for more grand space adventures on the scale of Apollo. The war in Vietnam, economic concerns and the increasing need to sort out problems on the ground before reaching for Mars all combined to create a difficult funding situation for NASA.
As the 1970s dawned it looked for a time as if, rather than spaceflight and orbital operations becoming an everyday occurrence, the very existence of an American human space programme itself may be under threat. Against this background, plans were rapidly reorganised. Out went the grand visions of large space stations and nuclear space tugs. Where the Shuttle had been seen as one link in the IPP chain, it now became the sole survivor. To add to the programme’s woes, NASA’s flight rates were called into question and increasingly the Department of Defence (DoD) became the key customer for the system as only the addition of their flight manifest seemed to make the Shuttle economically viable. In return for moving to the Shuttle and abandoning their own expendable launch vehicles, the DoD gained a far stronger influence on the vehicle’s configuration and this was to lead to considerable differences of opinion between NASA and the Air Force over the coming years.
A battle of ideas
Max Faget was a design legend within America’s manned spaceflight community. He had been one of the original engineers at Langley who had pushed for blunt-bodied capsule configuration on America’s initial spacecraft, Mercury. His opinion held great sway within NASA and as a result of the design competition for the Apollo spacecraft many aerospace contractors began to suggest that ‘what Max Faget wants, Max Faget gets’. Having been converted to the idea of a winged shuttle vehicle in the late 60’s, Faget had originated a design which became known as the MSC-002 or, more commonly, DC-3. With sort, straight wings and a blunt body, the DC-3 was really an extension of Faget’s earlier capsule work. Rather than ‘flying’ back into the atmosphere and creating lift and therefore controllability at hypersonic speeds, the high-drag DC-3 would enter relatively steeply with a high angle of attack. This would allow the blunt body shape to generate a shockwave, just as contemporary capsules did, keeping the worst of the heat away from the Orbiter and its wings. Once back inside the atmosphere the DC-3 would then fall forward from its nose-high attitude to allow aerodynamic flight for the approach and landing.
Faget was far less enamoured with lifting body concepts, citing their high sink rates and landing speeds as undesirable in a returning spacecraft. While his DC-3 had many supporters within NASA it certainly wasn’t popular with the Air Force, particularly with the FDL who saw the transition from high-angle-of-attack to regular flight as dangerously close to a stall – they argued a delta planform would give a far better transition in the vehicles centre of gravity during reentry, but they also had another key reason for pushing for delta wings – cross-range. Faget’s DC-3 would offer very low cross-range, that is the ability to deviate laterally from the ballistic path. Perhaps surprisingly his design actually offered less cross-range than the Apollo Command Module. While Faget felt this was acceptable offering the Orbiter a return a prescribed landing site once a day, the Air Force needed far more flexibility.
Many of the missions they wished to fly would be launching from Vandenberg AFB in California and entering high inclination or polar orbits. Should the shuttle encounter an abort situation during ascent, the Orbiter would need high cross-range to make it back to a landing site. The Air Force also wished to have the ability to fly single orbit missions, meaning they needed at least enough cross-range to compensate for the distance the Earth had moved under the spacecraft’s orbital track during the single revolution. A high cross-range ability would also add to the general safety of the system they argued offering safe return from a range of abort scenarios that the DC-3 never could.
Wishing to defer a final decision on the configuration NASA proposed that for Phase B of the Shuttle process the bidders should submit 2 configurations – one following Faget’s straight-winged DC-3 concept and a second delta-wing design to meet the high cross-range requirement. A number of other key requirements were brought in at this stage most notably the need for a fully reusable system with both components being able to undertake ferry flights between landing and launch sites. What this meant in practical terms was an end to any concepts with expendable elements, such as the Lockheed disposable fuel tanks. NASA were also keen to bring aerospace companies together on joint bids at this stage of the process, figuring this would help by spreading the massive demands in the development of a large Two Stage To Orbit (TSTO) system.
LMSC partnered with Boeing for a Phase B bid consisting of a STAR Clipper derived Orbiter from Lockheed, while Boeing concentrated on the large winged booster stage. The designs that emerged were more refined than the earlier LMSC TSTO proposals, with the Orbiter and booster being mated base-to-base. As with all of the Phase B winged boosters, the Boeing model would have been huge and, considering that the American aerospace community’s main experience of hypersonic flight at the time came from the short flights of the X-15, incredibly ambitious. As part of their Phase B submission a design for a straight winged Orbiter was included to meet the low cross-range requirement.
An alternative option
Unfortunately for the LMSC/Boeing team they weren’t selected for Phase B of the process with McDonnell Douglas/Martin Marietta and North American/Convair being the two teams to gain development contracts. While this could have spelled the end for LMSC’s delta-bodied designs, another route now opened up for them.
While NASA’s Phase B requirements had stipulated a fully reusable TSTO system, some within NASA and the Air Force were well aware of the high technical risk involved in such a revolutionary approach. It was decided that while the fully reusable system should remain the key focus, partially expendable 1.5 STO concepts should also receive further examination as a fall-back plan should the TSTO approach prove too challenging and costly. Consequently, LMSC received a contract from MSFC under the Alternate Space Shuttle Concepts (ASSC) study in July 1970. What this meant in practical terms was that Lockheed could now return to something very similar to Max Hunter’s original STAR Clipper design with it’s expendable V-shaped propellant tanks and over 3,700 hours of wind tunnel testing and five years of design studies behind it.
What emerged from the ASSC study were a variety of configurations under the LS-200 designation – a larger, deep bodied design offering higher internal volume and blunter edges to reduce local heating problems. Configurations studied included a 1.5 STO with expendable tanks, Fully reusable TSTO with a winged booster and a ‘convertible’ version which could begin its operational life using the expendable drop tanks, but then at a later date be converted for launch from a winged booster. In its TSTO form the LS-200 would require fewer engines, so would have a lower weight and offer enlarged payload capacity. LMSC pointed to many advantages in their approach; it would avoid the need to develop two revolutionary vehicles simultaneously making the whole system more affordable over a longer period, it removed the need for two flight test programmes and avoided, or at least deferred, many of the uncertainties around the separation of two large vehicles during hypersonic flight.
Other approaches were also examined as part of the ASSC study including launching the LS-200 using existing expendable boosters, but by the end of the contract NASA concluded that a fully reusable two-stage system was still preferable even with the massive initial financial outlay and technical uncertainties. The shuttle would not be a Lockheed delta-body, but rather would come from one of the two contractor teams working under Phase B.
The end of the road?
NASA’s 1971 decision not to pursue Lockheed’s ASSC concepts further marked the end of the line for the delta-body shape as far as the Space Shuttle went, but the concept has re-emerged periodically over the years and there were certainly echoes of the STAR Clipper in Lockheed’s Venture Star vehicle, proposed as a commercially run SSTO launcher during the 1990’s. A sub-orbital demonstrator for this vehicle was under construction by Lockheed Martin’s Skunk Works under the NASA X-33 programme (Click here for more on the X-33), but due to a variety of technical issues and huge budget overruns was cancelled shortly before completion. One of the huge ironies of the Lockheed Martin X-33 design is that, while it promised to see Max Hunter’s original vision for the STAR Clipper take flight at last, in doing so it beat out McDonnell Douglas’s proposal, based largely on experience gained from the DC-X vehicle – the end result of Hunter’s most notable post LMSC effort, the Space Ship Experimental (SSX) SSTO (Click here for more on the SSX and DC-X) .
In conclusion, there seems little inherently wrong with the Lockheed delta-bodies designs of the late 60’s and early 70’s when viewed alongside many of the other proposed space shuttle designs. They were based on a huge amount of work by the Air Force FDL and no small commitment of time and resources by Lockheed themselves. Almost certainly STAR Clipper, or any vehicle derived from it, would have faced major technical challenges, especially in terms of thermal protection. As Faget’s team also pointed out during the Phase A shuttle studies, lifting body shapes are also more vulnerable to the increases in weight which are almost inevitable during project development – a fact that would come back to haunt Lockheed with the X-33 and quite possibly would have affected the earlier vehicle had it progressed to production. But given the many difficulties encountered by the Shuttle both during development and through its operational life and the fact NASA did end up having to return to a semi-expendable system, it’s interesting to speculate whether Hunter’s original 1.5 STO STAR Clipper concept could have proved at least as successful in the long-run. Maybe in the future the design will undergo another of its periodic renaissances and we may yet see the a delta-bodied vehicle in orbit.