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In the early 1980s, several aerospace contractors studied concepts for a small space shuttle vehicle. This vehicle would have been carried atop a 747 and then launched into space. (credit: Boeing)<\/p>\n
by Dwayne A. Day
Monday, November 10, 2025<\/p>\n
\nRecently, NASA and Sierra Space announced that the Dream Chaser spacecraft would not be used to resupply the International Space Station but would instead fly on a standalone mission, blurring its path to commercial viability. Small winged spacecraft do not have a storied record\u2014the European Space Agency\u2019s Hermes spaceplane and the US Air Force\u2019s Dyna-Soar were both canceled during development. Some small experimental spaceplanes such as the Soviet Bor and the Air Force\u2019s PRIME had limited test flights.\n<\/p>\n
Hydrogen would also be pumped into afterburners on the 747\u2019s large turbofan engines, providing up to 400 percent thrust augmentation. As jumbo jets go, it would have been a real hot rod.<\/p>\n
\nThe concept still lives. China has flown a small spaceplane three times. More recently, Dassault Aviation has unveiled the sexy VORTEX spaceplane, short for V\u00e9hicule Orbital R\u00e9utilisable de Transport et d\u2019Exploration (Reusable Orbital Transport and Exploration Vehicle). But after three quarters of a century of spaceflight, the only real success for small spaceplanes has been the US Space Force\u2019s secretive Boeing X-37, which has flown eight times in 15 years.\n<\/p>\n
\nBesides the Dyna-Soar and the X-37, the Air Force has considered other winged space vehicles, most seriously in the 1980s. Early in that decade, the United States Air Force sponsored studies of what was initially designated a Space Sortie Vehicle, then renamed the Air Launched Sortie Vehicle, or ALSV. The ALSV would have launched into space off the back of a 747. In one early concept, the 747 would have been equipped with multiple rocket engines in its tail to boost it to launch altitude. Boeing conducted several studies of \u201cTrans-Atmospheric Vehicles\u201d in 1983, including a revised variant of the ALSV. This Sortie Vehicle would have fired its own rocket engines while on top of the 747 and pushed both vehicles higher before separating the spacecraft to head into orbit.\n<\/p>\n
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The Air Launched Sortie Vehicle (ALSV), later also known as the Transatmospheric Vehicle (TAV), was a proposal for carrying a small space shuttle and its disposable fuel tank, atop a modified 747. Early studies included 747s equipped with afterburners as well as a rocket engine, or multiple rocket engines, in the tail. These were to boost the aircraft to high altitude for deployment of the space vehicle. (credit: Boeing)<\/p>\n
Early Origins of the ALSV<\/p>\n
\nIn late 1980, Don Hart, the head of the Air Force Rocket Propulsion Laboratory, outlined what was described as \u201can Air Force Sortie Space System\u201d in a seven-page overview document. According to Dana Andrews, who later worked on the concept, Hart was concerned about the Air Force\u2019s lack of responsive launch capability. The Space Sortie System had three major parts: a launch platform, drop tanks, and a space vehicle. General Dynamics performed a basic assessment of the concept for the Air Force.\n<\/p>\n
\nThe launch platform was defined as a 747 that not only carried the space vehicle and drop tanks on its back, but also had liquid oxygen and liquid hydrogen storage tanks inside its fuselage. The tanks would be low boil-off dewars and the propellants would be pumped into the drop tanks just before separation of the vehicle and drop tanks.\n<\/p>\n
\nThis would be no ordinary 747. Not only would it have the internal tanks, but the hydrogen would also be pumped into afterburners on the 747\u2019s large turbofan engines, providing up to 400 percent thrust augmentation. The 747 would fly a zoom parabola, with vehicle separation at 15,200\u201316,800 meters (50,000\u201355,000 feet) altitude. As jumbo jets go, it would have been a real hot rod.\n<\/p>\n
\nThe space vehicle would have two attached drop tanks based upon design, materials, tooling, and fabrication techniques for the Atlas launch vehicle. The tanks would be covered with the Space Shuttle\u2019s spray-on insulation if necessary. The tanks would form an aerodynamically-shaped nose for a lifting ascent trajectory and be released from the space vehicle shortly before it reached orbit, to burn up on reentry. If necessary, they would be explosively blown into pieces. Unlike more traditional launch vehicles, like the Space Shuttle, each tank would have three inner tanks, with hydrogen in the front, oxygen in the middle, and hydrogen at the rear to control the center of gravity for a lifting ascent. Overall, the vehicle would be approximately 10.7 meters (35 feet) wide and 15.2 meters (50 feet) long.\n<\/p>\n
\nThe space vehicle would be reusable, making a runway landing after return from orbit. The vehicle\u2019s shape would be derived from several flown or heavily studied lifting body type vehicles such as the FDL-5, FDL-8, or X-24C. The vehicle would be powered by ten modified RL10 engines arranged in a 2 x 5 array. The turbomachinery and injector would be the same as the standard RL10, but the thrust chamber would be slightly longer, the expansion ratio slightly less, and there would be upper and lower expansion plates for better performance in vacuum. The backside of the expansion plates would also provide vehicle pitch control. During reentry, the plates would close completely, forming a boattail over the rear of the vehicle.\n<\/p>\n
\nThe vehicle itself would have a large crossrange, the ability to come down a significant distance from its orbital track. It could be piloted, but could probably carry no more than one person. The 747\u2019s payload capability dictated the gross weight of the space vehicle and its drop tanks of no more than 100,000 kilograms (220,000 pounds).\n<\/p>\n
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The first concept for the ALSV dated from around 1980, and was primarily a proposal to develop a rapid launch capability that benefited from technology advances made with the Space Shuttle. (credit: USAF)<\/p>\n
\nAs Don Hart explained it, the spacecraft could fly several kinds of missions. The basic mission would be to fly to low Earth orbit, stay there for the mission, possibly leaving a small payload in orbit, and then return to a runway landing. Another mission could involve delivering a medium weight payload to low Earth orbit by releasing the payload at vehicle apogee and immediately returning to Earth. A mission described as \u201clow altitude penetration of target area\u201d would involve flying a shallow trajectory, skipping into the target area, and then reigniting the engines to power out and land. Finally, there was a maximum weight payload to low Earth orbit mission. This would not involve the space vehicle itself, only a cargo carrier and the ten RL10 rocket engines, which would fly into orbit and would not be returned, although they could be retrieved by a Space Shuttle at a later date.\n<\/p>\n
\nHart also noted that another option would involve a very different vehicle sized to fit inside the Space Shuttle payload bay. Three shuttle flights would bring up the vehicle and separate fueled drop tanks. The vehicle would be assembled in orbit and could fly up to geosynchronous or another high energy orbit. After the mission it would return directly to a runway landing.\n<\/p>\n
\nAccording to Hart, a major goal for the Space Sortie System was rapid response. The aircraft and spacecraft could be supported from any Air Force base as long as there was an available supply of liquid hydrogen and oxygen. The vehicle could stand at \u201calert status,\u201d with propellants inside the launch aircraft. It could take off on warning and fly to any azimuth because it would not produce debris that could fall on a populated area. The goal would be to enable flyover of any point on Earth within 75 minutes, including 747 taxi, takeoff, and climbout. It could fly by any low Earth orbit satellite or space station within 75 minutes and rendezvous with any satellite or station within five hours. As Dana Andrews later explained in his book Chasing the Dream, one of the benefits of the ability to store hydrogen and oxygen inside the aircraft for long periods was that the plane could be deployed to remote airfields.\n<\/p>\n
\nThe vehicle would not only be reusable, but would have rapid turnaround of hours, not days. \u201cAll phases of sortie are under Air Force control. All ground operations by Air Force crews at Air Force bases,\u201d Hart wrote. Nobody would have to worry about working with NASA.\n<\/p>\n
\nAccording to Hart, there were few technological risks and he outlined various aspects of the technology that already existed. The ability of a 747 to carry a piggyback payload had already been demonstrated by the shuttle program. An afterburner modification for the 747\u2019s engines was already available and would not require changes to the fan, compressor, burners, or turbine. The drop tanks would be based on the Atlas tooling and fabrication techniques. The RL10 rocket engine had a long history and there was data on how it operated in multiple engine configurations. The \u201clifting ascent trajectory\u201d had already been \u201cexamined in other programs,\u201d according to Hart. The one unknown that he identified was whether or not the drop tanks would burn up entirely. That would require further study.\n<\/p>\n
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Pratt & Whitney\u2019s venerable RL10 rocket engine was at the core of the ALSV proposal. The initial proposals included 9-10 of the engines in the vehicle\u2019s tail. As Boeing revised the spaceplane design, they reduced the number of RL10s. The RL10 is still in use today and is seen here on the second stage of a Delta IV rocket. It is now made by Aerojet Rocketdyne. (credit: Aerojet Rocketdyne)<\/p>\n
\nHowever, despite the optimistic assessment of the technology maturity, Hart\u2019s document overlooked several important related issues. What kind of thermal protection would the vehicle use? Although the Space Shuttle had pioneered a new thermal protection system, would it be applicable to a differently-shaped vehicle? What kind of structure would the spacecraft use? Would separating a large vehicle from a 747 at high altitude pose any problems? And finally, would pumping large amounts of liquid oxygen and liquid hydrogen from one vehicle to another while in flight be problematic?\n<\/p>\n
\nThe system would be a near-term solution whose existence \u201cwould certainly challenge USSR strategic defense structure,\u201d Hart wrote. It was \u201cnot a traditional launch vehicle, nor a traditional satellite, nor a traditional aircraft,\u201d and therefore \u201cnon-traditional thinking\u201d was needed to determine what it could accomplish.\n<\/p>\n
\nIt is unclear what prompted the Air Force Rocket Propulsion Laboratory to propose such a vehicle or what kinds of missions it could fly. The small payload and at most single crewman limited what it could do. The Space Sortie System apparently was more of a concept for a rapid response launch vehicle than the potential answer to a clear\u2014or even vague\u2014military requirement. In some ways it resembled earlier Air Force concepts of piloted space vehicles such as the late 1950s BOMI (\u201cbomber missile\u201d) and the early 1960s X-20 Dyna-Soar. Those concepts never found clear justifications for their costs and were not developed to flight vehicles.\n<\/p>\n
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This illustration depicts the second phase of the ALSV concept. The first phase envisioned two rows of five RL10 engines mounted in a rectangular pattern. This was replaced by a design involving seven engines in a circular configuration and two outboard engines. The RL10 was attractive because it could be throttled during ascent. A later phase reduced the number of RL10 engines. (credit: Boeing)<\/p>\n
Evolving the ALSV<\/p>\n
\nAfter December 1980, several contractors began considering such a spacecraft, including Space Shuttle contractor Rockwell International, engine manufacturer Pratt & Whitney, and Boeing.\n<\/p>\n
It is unclear what prompted the Air Force Rocket Propulsion Laboratory to propose such a vehicle or what kinds of missions it could fly. The small payload and at most single crewman limited what it could do.<\/p>\n
\nIn November 1981, AFRPL awarded a contract to rocket engine manufacturer Pratt & Whitney, who completed a study by August of 1982 and went public with it soon after. A story about the concept appeared in Aviation Week & Space Technology, and other articles appeared in other publications. Dramatic artwork produced by Boeing showing the spacecraft separating from its 747 mothership appeared in numerous publications, even as obscure as the Buffalo Evening News. The artwork was usually accompanied by captions referring to this as \u201cthe Air Force\u2019s new spaceship.\u201d\n<\/p>\n
\nAccording to two Pratt & Whitney engineers, Jerry Cuffe and Charles \u201cChuck\u201d Limerick, who wrote about their study in 1983, normally the Air Force would hire a prime contractor to perform a study, and that prime contractor would then hire subcontractors, like rocket engine companies, to perform specific portions of the work. It was unusual for Pratt & Whitney to be hired as the prime, with Boeing as a subcontractor. But the Air Force took this path because the engine was the primary driver in the design\u2014and also presumably because the Air Force Rocket Propulsion Laboratory was used to dealing with rocket companies.\n<\/p>\n
\nBoeing was hired as a subcontractor because the study dictated use of a 747 and \u201cit was also essential that the propulsion system performance sensitivities and requirements imposed by the 747 aircraft capability, vehicle weight, and mission trajectory were realistic,\u201d Cuffe and Limerick wrote. Vince Caluori was the Boeing program manager, and Dana Andrews was Boeing\u2019s technical leader for the project. Other Boeing engineers who worked on it were Jim Jenkins, who served as systems engineer; Bob Conrad, who was the weights engineer; and Harrison Whippo, the propulsion specialist. In addition to determining if a 747 could carry the weight and how it would be modified, part of Boeing\u2019s task included evaluating if a 747 could be flown in the manner required for deploying the spacecraft.\n<\/p>\n
\nCuffe and Limerick explained that normally, to maximize performance, they would have designed a new engine from scratch. However, one of the primary Air Force requirements was to field the Space Sortie System within the decade. With limited time, \u201ca modified, existing engine was therefore essential,\u201d they explained. Other modified and existing systems would also be used when possible.\n<\/p>\n
\nCuffe and Limerick added that because the delta-v requirement for reaching orbit was so high, the only viable propellant combination for the mission was liquid hydrogen and liquid oxygen. The United States at that time had only two LOX\/LH2 rocket engines, the powerful Space Shuttle Main Engine (SSME) and the RL10. The SSME was too large to provide a multi-engine capability in event of an engine shutdown. It also lacked the ability to throttle down its thrust substantially. The ability to throttle down is important because as a rocket burns up fuel, it gets lighter and therefore it accelerates more. If the engine thrust is not reduced, this can overstress the structure and it will break, at high speed.\n<\/p>\n
\nAt the time of their study, the standard engine in production was the RL10A-3-3A, but this engine was not suitable for the mission. With several upgrades, such as increasing the throat diameter of the engine and changing the contour of the nozzle, the RL10 engine\u2019s thrust could be more than doubled from 73,400 newtons (16,500 pounds) in vacuum to 153,500 (34,500 pounds) of thrust. It would only operate at this high level for a short period of time after launch before throttling back to 133,000 newtons (30,000 pounds) of thrust. In contrast, a version of the RL10 used three decades later generated 110,000 newtons (24,750 pounds) of thrust.\n<\/p>\n
\nThe basic Sortie Vehicle would use nine of these \u201c34.5K\u201d RL10 engines in its tail for power. The Sortie Vehicle engines would operate for approximately 160 seconds after launch at full power, then throttle down to their 30K cruise thrust setting. They would stay at this setting until a further throttle down was required to limit the acceleration loads on the vehicle. Eventually, the vehicle would start shutting down engines, jettison its external tank, and finally only three engines would be used to push it the last little bit into orbit.\n<\/p>\n
Spacecraft configuration<\/p>\n
\nPratt & Whitney\u2019s study originally started off with a cluster of 30K engines consisting of two rows of five RL10s, contained in a rectangular shroud that was intended to improve their performance at high altitude. As a rocket gets higher, there is less air pressure, which allows the exhaust plume to spread out. This lowers performance, so rocket designers try to contain the plume as much as possible as the air pressure decreases.\n<\/p>\n
The 747 is a big and powerful aircraft, but not when it has another massive aircraft sitting on its back.<\/p>\n
\nBut the engineers quickly realized that as engines were turned off to prevent exceeding the acceleration limits, this rectangular shroud would be inefficient; as an engine shut down, the other engines would be farther away from the edge of the shroud and so their exhaust would spread out. The shroud at the back of the vehicle would not be fully filled when less than four engines were still firing. Another problem was that with the engines all packed in closely next to each other, they could not be gimbaled to provide vehicle control capability during ascent. This also produced a longer and wider vehicle than desirable because the spacecraft had to be triangular for reentry and landing.\n<\/p>\n
\nOnce the engineers determined that they could uprate the RL10 engine power to 34.5K, they could eliminate one of the ten engines and change the way they were mounted at the rear of the vehicle. Rather than putting the engines in two flat rows, they produced a configuration of seven engines mounted in a circle, with two engines outboard on either side. This made for a taller, shorter vehicle. It also meant that the engines in the circle could be shrouded, increasing their performance, and the two outboard engines could be gimbaled for attitude control.\n<\/p>\n
\nIn this new configuration, the engineers initially looked at the possibility of a cylindrical shroud surrounding the engines in a circle. The shroud would extend as the vehicle gained altitude, operating at two positions during the flight before being jettisoned. But the shroud had poor performance at low altitude, and as a next step the engineers looked at a reusable four-position extendible\/retractable shroud. Both the disposable and reusable shrouds would allow for the two outboard engines to be pressure-fed with a low thrust capability.\n<\/p>\n
\nThe reusable shroud design improved performance, but not by much. At best it provided a net payload increase of 135 kilograms (300 pounds). But this came at the cost of added complexity, operational and maintenance problems, and increased difficulty of system testing during development. The engineers determined that it was a better idea to simply leave the shroud off and accept slightly lower performance. This also allowed the outboard engines to delete the pressure-fed configuration and use the same design as the other seven engines.\n<\/p>\n
The hot rod 747<\/p>\n
\nThe 747 is a big and powerful aircraft, but not when it has another massive aircraft sitting on its back. With the Sortie Vehicle attached it could only reach a maximum altitude of 7,600 meters (25,000 feet). But the amount of mass that the space vehicle could inject into orbit depended heavily upon the altitude at which it separated from the 747 and the flight path angle. Also, separating the two vehicles at less than 9,100 meters (30,000 feet) would result in the Sortie Vehicle slowing down due to air drag, which would push propellants in their tanks away from the rocket engine inlets, making it hard to start them.\n<\/p>\n
\nAccording to Limerick and Cuffe, although hydrogen afterburners for the 747 were possible, they did not already exist, and this would require a lengthy development program. Instead, they decided to select an existing rocket engine to mount to the 747.\n<\/p>\n
\nAs Dana Andrews remembered it, Boeing\u2019s engineers first proposed using the Space Shuttle Main Engine \u201cas a major performance improvement\u201d to the 747. The SSME has over 2.18 million newtons (490,000 pounds) of thrust in vacuum. It\u2019s a powerful thoroughbred of an engine.\n<\/p>\n
\nBut Pratt & Whitney\u2019s engineers countered that the SSME was not ideal for the job. Instead, they opted in favor of a cluster of seven RL10s at the rear of the fuselage. They would be identical to the ones used in the Sortie Vehicle but would have different nozzles. The RL10 required less than a minute of preconditioning prior to start, compared to approximately 40 minutes for the SSME. The RL10 cluster provided engine-out capability, reduced initial and operating costs, and \u201cripple start capability\u201d that reduced the tank pressure requirements for starting compared to the SSME. Pratt & Whitney even posed the possibility of using the RL10s during aircraft takeoff to get off the ground, just like the \u201cJet-Assisted Take-Off,\u201d or \u201cJATO\u201d rockets used to launch heavy aircraft in the 1940s and 1950s.\n<\/p>\n
\nThe aft end of the fuselage proved to be a good location for the rocket engines. The rear of the 747\u2019s passenger cabin contains the end of the pressurized compartment of the plane. The pressure in the tank pushes against the back of the tank, and the rocket engines could be mounted on the other side of the tank and would push forward against the air pressure inside the tank pushing back. It was a structurally sound design.\n<\/p>\n
\nThe launch aircraft would be a modified 747-200F, the freighter version of the jumbo jet. A single large cylindrical 19,500-kilogram (43,000-pound) liquid hydrogen dewar would fill most of the aircraft interior. Two smaller cylindrical dewars carrying 114,000 kilograms (250,000 pounds) of liquid oxygen would be mounted over the wing base of the aircraft. The entire craft was supposed to be capable of standing alert on a runway, ready to take off on short notice.\n<\/p>\n
\nTotal weight of the 747 and its Sortie Vehicle and tank at takeoff would be 390,000 kilograms (860,000 pounds), including 128,000 kilograms (283,000 pounds) of cryogenic propellants and 72,500 kilograms (160,000 pounds) of fuel for the 747\u2019s turbofan engines. The system could place 10,500 kilograms (23,150 pounds) into a nominal 185-kilometer (100-nautical-mile) polar orbit, enabling approximately 1,360 kilograms (3,000 pounds) of \u201cdiscretionary mission equipment\u201d to be carried \u201con a round-trip mission.\u201d\n<\/p>\n
One option was to use a \u201clifting ascent\u201d whereby the vehicle generated lift as it flew forward so that the engines did not do all of the work.<\/p>\n
\nThe Sortie Vehicle\u2019s single drop tank would have a diameter of 4.32 meters (170 inches) and a length of 24.4 meters (80 feet). It would require some thermal protection due to heating caused during ascent. Because the tank would be so lightweight, it would also require support by a cradle that fully distributed the load. The tank would be jettisoned as the vehicle reached 109,000 meters (357,000 feet).\n<\/p>\n
\nLimerick and Cuffe acknowledged that they had not evaluated all of the possible options for the craft. For instance, one option, which was mentioned in the original December 1980 document that outlined the Space Sortie System, was to use a \u201clifting ascent\u201d whereby the vehicle generated lift as it flew forward so that the engines did not do all of the work. Such a design would not have the large bulbous tank that they projected, but presumably a more wedge-shaped design capable of generating some lift of its own.\n<\/p>\n
\nPratt & Whitney\u2014an engine company, not a spacecraft company\u2014did not devote much attention to the actual design of the Sortie Vehicle and determined the best shape primarily by what would best support the engines. Rockwell, which was conducting its own study, investigated both a wedge-shaped FDL-5-derived lifting-body shape as well as something that looked more like a stunted Space Shuttle design. In comparison, the Pratt & Whitney design was a wedge-shaped pyramid, approximately 15.8 meters (52 feet) long and 9.1 meters (30 feet) wide and weighing about 9,100 kilograms (20,000 pounds). It had tall, angled sides, and small winglets and a single tail. The \u201cdiscretionary equipment bay\u201d would be approximately 2.5 meters (100 inches) long and increase from approximately 1.3 meters (53 inches) in diameter at the front to 1.6 meters (64 inches) in diameter at the rear. This was big enough to carry an astronaut. (By comparison, the X-37\u2019s payload bay is 2.1 by 1.2 meters.)\n<\/p>\n
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Boeing studied three “transatmospheric” or TAV concepts in 1983. These included the 747-launched ALSV, a two-stage, fully-reusable concept using both an all-new carrier aircraft and wedge-shaped space vehicle, and a reusable aerodynamic space vehicle that would have been launched on a rocket-powered sled. The ALSV would have required the least new development work, but would have had the smallest payload. (credit: Boeing)<\/p>\n
Boeing\u2019s Refined ALSV\/Trans-Atmospheric Vehicle<\/p>\n
\nBy 1983, the Air Force had initiated a \u201cTrans-Atmospheric Vehicles\u201d (TAV) initiative that further refined the ALSV. This period is confusing because the Air Force was engaged in several overlapping studies including the Advanced Manned Spaceflight Capability (AMSC) Study that started in 1981, and several contractors, including Rockwell and Boeing, were apparently studying similar vehicle concepts both for the AMSC and TAV work, possibly using some of their own internal research and development funding to keep the studies alive between Air Force contracts.\n<\/p>\n
\nBoeing conducted three TAV studies by May 1983, which the company labeled concepts B-1, B-2, and B-3 for ease of reference. Boeing\u2019s concepts involved vehicles that could place 2,268 to 13,608 kilograms (5,000 to 30,000 pounds) of payload into low Earth orbit using horizontal takeoff vehicles. The B-1 concept was a \u201cTwo-Stage Horizontal Take-Off Launch System\u201d that used a large, V-shaped mothership equipped with eight jet engines and a single SSME to drop a SSME-powered orbital vehicle at very high altitude to ascend to orbit with a substantial payload. Boeing\u2019s B-2 concept was derived from the Air Launched Sortie System originally studied by Pratt & Whitney with Boeing as the subcontractor. The B-3 concept was designated the \u201cReusable Aerodynamic Space Vehicle System\u201d and equipped with SSMEs and launched on a rocket-powered wheeled sled that was also equipped with two SSMEs.\n<\/p>\n
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By 1983, Boeing’s revised concept envisioned a flatter (less pyramidal) spacecraft. It would have one pilot and a small cargo bay. (credit: Boeing)<\/p>\n
\nThe Air Force required Boeing to submit the three TAV concepts to Batelle Columbus Laboratories for evaluation. Battelle\u2019s evaluation took place between May and December 1983, when Batelle issued its final report to the Air Force. Rockwell also studied a rocket-sled launch concept, its own version of the ALSV, and another concept that involved dropping a Sortie Vehicle design attached to a rocket out of the rear of a C-5 Galaxy and igniting the rocket during freefall.\n<\/p>\n
\nBoeing\u2019s three concepts were crewed, and \u201cwere conceived with military operational readiness as a prime overall requirement,\u201d according to the Batelle report. \u201cEach concept achieves survivability by rapid dispersion airfield to airfield.\u201d\n<\/p>\n
\nIn the Batelle report, \u201cALSV,\u201d \u201cTAV,\u201d and \u201cB-2 Orbiter\u201d were used interchangeably, but Boeing had further refined the partially-reusable vehicle, and it differed from the earlier Pratt & Whitney-led ALSV in several respects, notably the inclusion of a crew cabin, fewer engines, and a refined, more rounded and less angular vehicle shape. Boeing had also greatly simplified the launcher aircraft, eliminating any need for hydrogen-augmented jet engines, or the earlier concept\u2019s most striking feature: the SSME in the 747\u2019s tail. Instead, the orbiting vehicle would fire its two outboard rocket engines while still attached to the 747 to provide a last bit of acceleration required before vehicle separation.\n<\/p>\n
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Boeing’s revised concept would have been equipped with one Space Shuttle Main Engine and two RL10 engines. It would have used shuttle-derived technology. (credit: Boeing)<\/p>\n
\nCompared to the B-1 and B-3 concepts, the ALSV\/TAV approach was intended to require the least new development, particularly by using a 747 as a launch aircraft compared to the Two-Stage Horizontal Take-Off Launch System (i.e. concept B-1), which required an all-new rocket-powered mothership aircraft. The rocket-sled launched RASV (concept B-3) required not only the rocket sled, but also heavily modified SSMEs with deployable exhaust shrouds to deal with the different atmospheric pressures as the vehicle went from the ground to outer space.\n<\/p>\n
\nThe revised ALSV\/TAV would use existing engines, the SSME and RL10. Although the 747 had been simplified compared to the previous concept, it would not have been a stock 747, but a \u201cgrowth derivative\u201d 747 with a larger, 650-square-meter (7,000-square foot) wing. Such a wing had already been studied by the company for an upgraded 747, but to carry the ALSV\/TAV, it would also require additional strengthening. Boeing claimed that design and tooling costs for the new wing could be offset by freighter or commercial production, although that required commercial customers in addition to the Air Force.\n<\/p>\n
\n\u201cThe Air Launched Sortie approach trades early low-cost, low-risk development against higher operating costs,\u201d the report stated. But according to the Batelle evaluation, the key question was the breakeven flights per vehicle.\n<\/p>\n
\nThe 747 would contain large dewars in its fuselage for long-term storage of liquid hydrogen and liquid oxygen. The ALSV\/TAV\u2019s fuel tank would be empty upon liftoff, but once at its cruising altitude, the 747 could pump the hydrogen and oxygen into the external tank and the orbiter\u2019s internal tanks in preparation for launch.\n<\/p>\n
\nThe orbital vehicle would only operate for one or two orbits, minimizing losses of cryogenic propellant. The internal propellant could be used for the de-orbit burn or other propulsive maneuvers.\n<\/p>\n
\nThe ALSV\/TAV orbiter eliminated the nine heavily-modified RL10 engines of the earlier studies in favor of a single SSME and a pair of \u201cstandard\u201d RL10s. Increased thrust-weight eliminated need for rocket augmentation of the 747.\n<\/p>\n
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Boeing’s 1983 concept eliminated the advanced propulsion requirements for the 747 carrier aircraft. (credit: Boeing)<\/p>\n
\nThe operational plan was to have the vehicle on the ground in \u201cready alert\u201d condition with fuel in dewars, remaining in readiness condition for up to 30 days. It could be off the ground in five minutes, \u201ctherefore meeting the Strategic Air Command bomber alert\u201d requirement. It would climb to cruising altitude in 30 minutes. If the launch was approved, the 747 could then transfer propellant into the external tank and into the Sortie Vehicle. \u201cThe mated vehicles perform a pull-up maneuver using the 747 engines and the outboard engines on the Sortie vehicle,\u201d the report stated. After about one minute the 747 would go through a pushover maneuver to generate negative g\u2019s and the vehicles would separate. After separation, the Sortie Vehicle would go up to full thrust and ascend into orbit.\n<\/p>\n
\nThe original ALSV concept was for an optionally manned spacecraft. Boeing\u2019s revised vehicle was sized for two crew members, but would normally carry only one. The vehicle could also be flown autonomously, with no crew aboard. The payload bay would be 2.1 by 4.6 meters (7 by 15 feet). It could carry 2,268 kilograms (5,000 pounds) into near-orbit in a once-around polar capability, meaning that the vehicle landed after a single orbit, or 3,629 kilograms (8,000 pounds) in a 296-kilometer (160-nautical-mile) orbit when launched into a 28.5 degree inclination.\n<\/p>\n
\nThe 747 would be equipped with a V-tail to enable use of orbiter thrust to obtain a higher flight path angle and altitude\u2014the engines would burn a conventional tail. According to Boeing, the 747 could fly up to two missions per day. But an impediment to achieving fast turnarounds was integrating the payload into the orbiter. Experience with the Space Shuttle had demonstrated that this required a lot of time unless both payload and orbiter were equipped with standard mounting interfaces that tended to be bulky and heavy. Boeing\u2019s recommendation was to purchase more orbiters and integrate the payloads and drop tanks in advance.\n<\/p>\n
![\"ASLV\"\/](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/11\/5100k.jpg\")
![\"ASLV\"\/](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/11\/5100l.jpg\")
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To satisfy its Air Force customer, Boeing proposed that the vehicle could be kept fueled on ground alert, ready to launch at moment’s notice. This was more in keeping with existing concepts of bomber and fighter operations than space vehicles. Satellites at the time required extensive pre-launch preparation and integration into their launch vehicles. (credit: Boeing)<\/p>\n
\nThe vehicle would cost more than fully reusable concepts because the tank would be discarded. But the proposers suggested that with high enough flight rates, the ALSV could be more cost effective.\n<\/p>\n
\nThe development time was estimated at seven and a half years from the start of concept definition to hardware delivery, with an estimated $4.2 billion development cost. The study suggested that ten carrier aircraft and 50 orbiter vehicles and support equipment at ten airbases would cost $11.4 billion. In comparison, the B-1 and B-3 concepts had significantly higher development costs and longer times to becoming operational\u2014the two-stage concept would take nearly 12 years to become operational, for example. However, the other two vehicles did offer significantly larger payloads, up to six times the mass of the ALSV\/TAV payload.\n<\/p>\n
\nBoeing\u2019s ALSV\/TAV team considered several possible growth versions of their design, but none offered significant performance increases. The baseline design was therefore the best option.\n<\/p>\n
\nThe study also indicated that the Air Force could develop its own Space Transportation System based on the ALSV concept. This could include a ground launch using shuttle-derived hardware such as the external tank and solid rocket boosters along with an ALSV, and an unmanned launch vehicle that would also launch off the back of a 747.\n<\/p>\n
\nBatelle did not recommend any of Boeing\u2019s three TAV vehicles\u2014that was not the purpose of their evaluation\u2014but the company did provide a set of criteria the Air Force could use to evaluate their performance. Batelle also made recommendations about a future Phase II trans-atmospheric vehicle program and options for future rocket-powered aircraft based upon the two-stage (B-1) concept that clearly required the most new development.\n<\/p>\n
![\"ASLV\"\/](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/11\/5100j.jpg\")
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Boeing proposed that the ALSV could also be adapted for ground launch atop a rocket, and could also be adapted to an expendable cargo-only vehicle. (credit: Boeing)<\/p>\n
Air launch, grounded<\/p>\n
\nAlthough both the 747 and the spacecraft were reusable, like the Space Shuttle the ALSV was only partially reusable. According to Dana Andrews, although the studies showed that the vehicle could be built, the Air Force was thwarted by the cost of the external tank. Andrews said that the tank alone was estimated to cost $15 million, although in Chasing the Dream he noted that they used a NASA cost-estimation tool that probably over-inflated the cost. It was more than the Air Force was willing to pay for the ability to place only 2,268 kilograms of cargo into polar orbit. Furthermore, at that time the Space Shuttle was subsidized by NASA, and Andrews remembered that the price for putting a payload on the more-capable shuttle was less than the cost of an ALSV tank.\n<\/p>\n
The moral of the ALSV story is one that has existed throughout the history of spaceflight: just because an idea seems cool doesn\u2019t mean that it makes any sense.<\/p>\n
\nThe ALSV also had another inherent limitation, its reliance upon air-launch. Numerous air-launch rockets have been proposed and tested over the decades, but their track record is unimpressive. Virgin Orbit\u2019s LauncherOne achieved technical success, reaching orbit on four out of six attempts, but failed commercially. Stratolaunch produced the largest aircraft in the world, Roc, but proved to be a poor approach to launching satellites. In the 2000s, AirLaunch LLC had a dubious concept to launch a rocket by dropping it from the back of a C-17 transport aircraft, but did not succeed commercially. The only successful air-launched rocket, Pegasus, had a very low flight rate.\n<\/p>\n
\nFor air-launched rockets, the primary limitation is the payload capacity of the launch aircraft, which not only limits the size of the rocket, but prevents it from being substantially upgraded. Many rockets have been upgraded with new engines and longer tanks during their lifetime, but an air-launched rocket is usually designed as large as possible for the carrier aircraft and there is no margin left for improvement. Jumbo jets like the 747 require expensive maintenance even when not being used to launch spacecraft, costing money. Launch pads also require maintenance, but not to the same extent as an aircraft.\n<\/p>\n
![\"ASLV\"\/](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/11\/5100n.jpg\")
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There have been numerous proposals over the years for both small spaceplanes and air-launching rockets. These include (clockwise from top left) Dassault\u2019s proposed VORTEX, Stratolaunch and its large Roc carrier aircraft, the late 1980s Soviet MAKS proposal, Boeing\u2019s X-37, and Virgin Orbit’s 747 and its fuselage-mounted rocket. Only the X-37 is operational. (credit: Dassault, Stratolaunch, Buran.ru, USAF, Virgin Orbit)<\/p>\n
There\u2019s no there, there<\/p>\n
\nProbably the biggest obstacle to this concept was like the story about the dogfood company that couldn\u2019t sell its flashy new product for the simple reason that the dogs did not like it. It was never clear what the ALSV could do that was vital to national security. In the early 1980s, it was still official Air Force policy to retire its fleet of expendable launch vehicles like the Atlas and Delta and switch all remaining national security payloads to the Space Shuttle. It would not make sense to launch really small payloads aboard the shuttle, and so the ALSV could have provided that service. But there were no stated requirements for such a vehicle from the senior levels of the Air Force or the Pentagon.\n<\/p>\n
\nThe single-orbit requirement was also unusual\u2014the stated requirement was for the vehicle to fly once around the Earth at \u201c500,000 feet,\u201d or 152 kilometers. It is not possible for a spacecraft to orbit at such a low altitude, and any payload it deployed would either have to boost itself into orbit or would fall back to Earth. It is possible that the idea was to carry a quick-response reconnaissance payload. But the requirement was more akin to flying a bombing profile than operating a launch vehicle, and to an adversary the ALSV would have looked like a potential first-strike weapon.\n<\/p>\n
\nThat requirement and others, such as the ability to stand ready alert on an airfield, were more appropriate to air-breathing bombers such as B-52s. The ALSV and other TAV concepts appear to have been defined more by the airplane part of the Air Force than the space operations part of the Air Force, with a poor understanding of what satellites do and are used for.\n<\/p>\n
\nThe actual payloads that needed or could use the capabilities established in the requirements were never defined. Early warning, communications, reconnaissance, meteorology, and other satellite missions are not mentioned in the report, leaving the impression that those who established the requirements didn\u2019t understand those missions and also assumed that satellites are not much different than munitions in terms of their ruggedness and ability to hang underneath an aircraft (or inside a bomb bay) unattended for long periods of time.\n<\/p>\n
\nALSV\u2019s other attributes, such as its ability to launch from virtually anywhere in the world to any orbit, were not sufficiently attractive to keep the program going. Over the next several years, the Air Force continued general studies into the possibility of a quick-reaction craft that could operate either at extremely high altitudes or possibly even in low orbit. But these did not proceed to development. In 1988, the Soviet Union evaluated a \u201cmultipurpose aerospace system\u201d known as MAKS that was clearly inspired by the ALSV concept. It would have launched off the top of a giant Antonov An-225 Mriya aircraft that had been developed to carry the Soviet Union\u2019s Buran space shuttle.\n<\/p>\n
\nThe moral of the ALSV story is one that has existed throughout the history of spaceflight: just because an idea seems cool doesn\u2019t mean that it makes any sense.\n<\/p>\n