AKA: SR-3;XOV. Status: Study 1990. Gross mass: 30,000 kg (66,000 lb). Height: 30.00 m (98.00 ft). Diameter: 13.00 m (42.00 ft).
In March 2006 Aviation Week and Space Technology made the astounding claim that the United States had developed a reusable two-stage-two-orbit manned spacecraft in the 1990's, dubbed Blackstar, and flown it on numerous orbital and suborbital missions. The system was said to be out of service by 2005. If this system actually existed and was flown, the history of manned spaceflight would have to be revised.
The first stage of the Blackstar system consisted of a Mach 3+ winged air-breathing first stage evidently developed from North American's XB-70 bomber; and an XOV manned eXperimental Orbital Vehicle lifting body second stage. The system was developed by a consortium of US aerospace companies at the behest of an unspecified US government agency. The system was so classified that it remained unknown to the nation's top military and civilian space planners, while they labored to design, but never developed, an equivalent white-world system. Blackstar was designed to handle numerous missions: strategic reconnaissance; anti-satellite; quick-reaction small satellite launch; and delivery of small conventional warheads.
The existence of Blackstar could explain several puzzling aspects of the arms and space race during the Cold War and thereafter. These included the Department of Defense's cancellation and later lack of enthusiasm in resurrecting the SR-71 Mach 3 reconnaissance aircraft and various anti-satellite systems; and the Soviet Union's continued fear of such systems in the late1980's despite the absence of a visible American threat. In Aviation Week's scenario, the decision by the military to field such a system came after the Challenger disaster in 1986 and the realization that the US had no assured quick-reaction access to space. Evidently building on plans of the 1960's for air-launch of the X-15-3 or X-20 spaceplane by a modified XB-70 bomber, the final design consisted of an XOV that would be dropped from the SR-3 at Mach 3.3 and 31.6 km altitude. The XOV's linear aerospike rocket engines would carry the spaceplane to an orbital or suborbital trajectory depending on the mission.
The SR-3 had the same basic layout and dimensions as the XB-70. It was a completely different aircraft in detail, having variable geometry rather than fixed canards; a blended double-delta wing rather than a straight delta; fixed-upward swept combined wingtips/vertical stabilizers rather than deployable-downward swept wingtips and fixed twin vertical stabilizers; four engines in two nacelles rather than six in a single nacelle. The use of two nacelles had been proven in the North American B-1 design, and would have provided the necessary space for the carriage of the XOV on the belly. The X-15/B-70 concepts had envisioned launch from the back of the B-70, but the loss of an A-12 on 30 July 1966 while launching a Mach 4 D-21 drone had shown this to be dangerous.
The XOV was reportedly preceded by an unmanned predecessor 20 m long. The later manned version was 30 m long. Both had a double-delta planform like the space shuttle, but a complex blended lifting-body shape more akin to NASA Ames hypersonic designs of the late 1950's and early 1960's. The vehicle was said to have a spade-shaped forebody and downward-canted outer wing-body sections, augmented by a thick, stubby vertical stabilizer that fitted into the SR-3's lower fuselage. Payload bays on the upper surface of the XOV allowed carriage of reconnaissance sensors or payloads/weapons to be dropped in space. Propulsion was by aerospike rocket action, possibly air-augmented and fed by ribbed or straked channels in the lower surface of the vehicle. The engines used a high-density gelatinous fuel doped with a boron additive to increase specific impulse. The type of oxidizer used was not mentioned. The spaceplane's outer structure was made of lightweight heat-resistant composite materials.
Funds for development of the Blackstar were said to be buried in X-30/National Aerospaceplane and A-12 naval strike aircraft budgets. Both of these projects ran up huge bills before being 'cancelled' due to 'technical problems'. The X-30 was a good candidate for hiding such programs, but the A-12 was the subject of humungous post-cancellation litigation and lawsuits. Some have said that it was unlikely that the funds could have been buried there (unless the contractor's were cynical enough to use the government's desire to keep the program secret as leverage in reaching the final settlement). Development of the Blackstar stalled in the late 1980's until the fuel for the spaceplane was perfected in 1991.
An XOV said to have been spotted at Holloman AFB in New Mexico in 1994. What may have been an XOV on an aborted mission may have made an emergency landing at Kadena AFB in Okinawa during the same year. A sighting was reported in 1998 of the XOV mounted on the belly of the SR-3 The SR-3 itself was seen as early as 1990 and as late as 2000.
There were several curious aspects to the Aviation Week account, many of them brought up in web chatter and very critical commentary after the announcement (see articles cited at the end of this article). One was the known lack of advantage of using a supersonic launch aircraft. This had been studied many times over the years, and nearly always found not to be worth it. The total delta-V required to reach an any-inclination orbit is around 9500 m/s, including air drag and gravity losses during ascent. Air launch of an orbit-bound vehicle from a subsonic aircraft contributes the equivalent of 270 m/s to the delta-V required to reach orbit, while launch from a Mach 3 aircraft contributes only the equivalent of 950 m/s. There are operational advantages to air launch, but the minimal additional delta-V savings were usually seen as not worth the extra cost and complexity of developing a supersonic drop aircraft. However if the XOV design was so marginal that every amount of additional delta-V was crucial, then the decision could have been made to proceed with this solution.
It was said that the SR-3 used surplus J-93 engines from the XB-70 program, and that only four of these were used in the SR-3 (as opposed to six in the XB-70). This would imply a vehicle of 2/3 the GLOW of the XB-70 (e.g. 180 metric tons). The lower takeoff mass would suggest a range of only 2600 km compared to the 7870 km of the XB-70 (the B-70 design range was 12,000 km; however 10% was lost when the boron-doped zip fuel was abandoned in 1959, and flight test showed the aircraft another 25% deficient in range due to higher-than-expected transonic drag and lower than-expected supersonic lift-to-drag). This would basically allow the aircraft barely enough time to accelerate to launch velocity and speed, immediately drop the XOV, then return to base. However the SR-3 was intended as a launch aircraft, not a supersonic bomber, so this limitation was perhaps considered acceptable. It would also be likely that the SR-3, like the SR-71, was topped off by aerial refueling immediately after takeoff.
The connection of the XB-70 to the SR-3 seems tenuous at best. The detailed differences are so great that they represent an entirely new aircraft. The use of engines, stored for twenty years, with no existing logistics chain, seems very unlikely. Only if the SR-3 was an existing aircraft, which had evolved from the XB-70 in a long black development process beginning in the mid-1960's, making it available for use when the Blackstar was conceived in the 1980's, can some kind of direct connection be considered possible.
The description of the XOV propulsion system harkens back to various Aerojet studies of the 1960's for the Aerojet Ares rocket engine, designed to power a single stage ICBM to replace the Titan 2. Use of aerospike technology, air-augmentation, high-pressure combustion, and storable N2O4 and Aerozine-50 propellants were expected to result in a specific impulse as high as 360 seconds. Russian tests with N2O4 and Pentaborane propellant indicated an additional 22 seconds of specific impulse could be achieved with this combination. Finally, tests of gelled hydrazine fuel doped with aluminum showed higher combustion chamber temperatures (but dangerous instability - and borane would be even worse). So it can be estimated that the described rocket system would have a specific impulse of 390 seconds at the very best. Given a delta-V to orbit of 8500 m/s after the 950 m/s assist from the SR-3, this would imply a mass ratio of 10, or a dry mass fraction of 10%. Commentators noted that this was well outside the scope of any known lifting body, which typically have dry mass fractions of 22%.
However mention was also made of very lightweight materials for the external aeroskin and very dense propellants, perhaps loaded in disposable cartridges. This combination of jettisonable fuel casings and a lightweight aeroshell could - barely - be a solution to the mass fraction problem. But either extremely formidable technical problems were overcome, or the XOV was a suborbital vehicle, capable only of releasing a third stage that would be required to take payloads to orbit (as in the X-43).
Some commentators took these issues, together with Aviation Week's alleged lack of reliability in similar earlier cases, as evidence that the whole story had the same credibility as Roswell saucer crash accounts. However, the earlier false stories cited were related to Soviet systems (the nuclear bomber of the 1950's, the beam weapon of the 1970's). These represented analysis failures on the part of US intelligence rather than reporting failures by Aviation Week. It was also noted that some earlier black aircraft revealed by the magazine had never surfaced. But this could represent continued classification of these programs rather than reporting failures.
So it seems still possible that the Blackstar actually existed and was tested. What was not clear was how often the system was actually flown and whether it ever achieved orbit or even reached altitudes over 100 km. If it did, the history and logs of manned spaceflight will have to be rewritten. Only when - if ever - the US government decides to declassify the aircraft, if it existed, can this be known.
Crew Size: 1.