The constant development of new aviation capabilities has been a theme ever since the Wright brothers first flew a rickety contraption called the Wright Flyer in 1903. In the years and decades following this historic first flight, aircraft have gained in both size and performance and can perform a staggering variety of roles in both military and civilian use.
The new millennium continues this trend, and exciting experimental applications for aircraft are proposed, tested and often adopted into general use on a regular basis.
However, sometimes a good idea can come to nought despite having been proven to function safely and efficiently, and a good example of this is an ambitious scheme to launch rockets into orbit from a high-flying aircraft.
The aircraft which was designed and manufactured to achieve this formidable technical feat was the Scaled Composites Stratolaunch, which by the very nature of its intended purpose is one of the largest aircraft ever constructed.
The Stratolaunch was constructed to carry and launch the Pegasus II, a multi-stage rocket designed to carry payloads of varying weights into Low-Earth Orbit (LEO) or Geosynchronous Transfer Orbit (GTO).
To carry such a large rocket obviously demands a massive carrier aircraft, and the Stratolaunch is exactly that: boasting dimensions that include the widest wingspan of any aircraft ever constructed.
Design and Manufacture
Stratolauch Systems was launched by one of the founders of Microsoft and the owner of the Scaled Composited aerospace company, to provide Air-Launched-To-Orbit (ALTO) services for getting commercial and scientific payloads off the planet.
ALTO is one of the many options examined over the years to try to reduce the high cost of inserting satellites and other cargo into orbit and to try and break the monopoly of only using expensive single-use heavy orbital rockets to get cargo into space.
From Gerald Bull’s High Altitude Research Project (HARP) using heavy gun barrels to ‘shoot’ objects into space and SpaceX’s new reusable launch boosters, the quest to lower costs for space exploration and transport is ongoing and will continue.
ALTO is an ingenious principle; the first stage of any orbital rocket has to do the most work and be correspondingly powerful, large and expensive to lift the entire assembly off the ground. But what if you could launch a rocket from nearly ten or so kilometres off the ground?
The savings would be twofold: a smaller and cheaper rocket still able to carry a payload into orbit, and a re-usable launch aircraft ready to be prepared to carry another rocket for launch at short notice.
But, like all ambitious projects, a proof-of-concept test vehicle/system must be manufactured to test the entire concept, and work commenced on prototyping both the cargo rocket and the launch aircraft.
Design and computer testing commenced in 2010, but was only formally announced to the aerospace community in 2011. With the general dimensions of the proposed rocket as a guide, the Scaled Composites aerospace company began to manufacture the Stratolauncher at its facility at Mojave Air and Space Port at Mojave, California.
The aircraft was mostly completed by late 2016 and was revealed to the public in 2017. A comprehensive series of ground and taxi tests commenced from this time.
Stratolaunch Systems originally contracted to SpaceX to supply the proposed cargo rocket, which was originally intended to be a specialised adaption of the company’s Falcon 9 orbital booster.
The design parameters of the Stratolaunch were formulated to carry and launch this booster, and the dimensions of the aircraft were adjusted to accommodate this rocket, but differences of opinion and squabbles over priorities between the two companies led to SpaceX withdrawing from the project in 2012.
Stratolaunch Systems turned to a company called Orbital Sciences Corporation to provide an orbital booster, and it responded with a multi-stage design called the Pegasus II, which was developed between 2012 and 2015. Originally with the lower two stages being solid fuelled and the third stage being liquid fuelled by cryogenic chemicals, it was later decided that all three stages would utilise solid fuel engines.
The Pegasus II was envisaged to be fitted with wings and a V-tail with moveable control surfaces for atmospheric manoeuvring, as well as a thrust-vectoring nozzle being used in both the first two stages of the launch to help with attitude control in the thin upper atmosphere.
The basic design had the same diameter as one of the Space Shuttle’s two solid boosters but was constructed out of modern composites and polymers to save weight. Despite some early promise the economic modelling of the rocket project began to look less promising, and the Pegasus II was abandoned in 2015 with Stratolaunch System evaluating many new rocket models until the ALTO concept was initially abandoned in 2019.
The Stratolaunch had its first test flight on April 2019, which lasted 2 hours and was mostly successful. Ironically, the troubled collaboration with Orbital Sciences Corporation took its toll on the company’s financial health. Stratolaunch Systems folded as a concern in May 2019, with the company’s assets, including the Stratolaunch aircraft, transferred to Cerberus Capital Management in June of that year.
This company continued to evaluate rocket systems for ALTO employment but mainly employed the Stratolaunch aircraft for high-speed flight-test services.
Scaled Composites Stratolaunch
As befitting an aviation giant envisaged to carry and launch a massive space rocket into orbit from a very high altitude, the Stratolaunch is a gigantic aircraft and one of the biggest aerial vehicles ever constructed. It is of a twin-fuselage design, as the cargo rocket would need to be safely suspended between the two main airframe components, which are joined by a large horizontal tailplane at the rear, and by the massive main wing.
All pilot seating and controls are in the nose of the right fuselage, and the left cockpit area is unpressurised and used to house avionics equipment.
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The nickname of the Stratolaunch is the ‘Roc’; referencing the mythical giant bird from the Sinbad stories, which was said to be big enough to carry off an elephant. The aircraft is gigantic indeed, with a height of 50 feet (15 metres), a length of 238 feet (73 metres) and a wingspan of 385 feet (117 metres), which exceeds that of the previous record holder, the ‘Spruce Goose’ built by Howard Hughes.
Empty, the airframe has a mass of 500,000 lbs (226,790 kg) and a gross weight (without payload) of 750,000 lbs (340,190 kg). The Mass Take-Off Weight (MTOW) of the Stratolaunch is a staggering 1,300,000 lbs or 589,670 kilograms.
The Stratolaunch is powered by six Pratt & Whitney PW 4056 turbofans, which each produce 56,000 pounds of thrust. This gives the aircraft a maximum speed of 530 mph (850 km/h), and a service ceiling of 35,000 feet or 11,000 metres. The operational range of the Stratolaunch is 1,200 miles (1,900 kilometres), and the ferry range is 2,900 miles or 4,600 kilometres.
The aircraft is able to carry a payload of 550,000 lbs (250,000 kg) which approximates the weight of the Pegasus II orbital rocket, and it was intended to launch this from a height of 35,000 feet or 11 kilometres into orbit.
When fully loaded with a Pegasus II rocket with orbital payload the Stratolaunch requires a take-off run of more than 12,000 feet (3,700 metres). The long range of the aircraft is required as a steady climb to launch altitude at moderate speeds. It is flown so as not to subject the cargo rocket to any high-G stresses before launch.
The future of Stratolaunch Systems was on shaky ground after the 2018 death of Paul Allen of Microsoft fame, who helped launch the company in 2011. Despite the first successful test flight of the Stratolaunch aircraft less than three months later, the original reason for being of Stratolaunch Systems was severely compromised by the repeated failures of the company to secure a viable rocket system to launch payloads into orbit.
Without this crucial element of the combined system, the aircraft became a specialised and very expensive white elephant, and this confluence of factors meant that the original company structure folded, and the company assets were acquired by a new owner.
The new owners of the Stratolaunch have utilised the aircraft for high-speed aerial testing work, and until recently it seemed that any chance of using the aircraft to again launch rockets into space was non-existent. But lately, this set of circumstances looks to be changing. A new series of rockets are being evaluated, and the Stratolaunch has carried and deployed hypersonic aerial vehicles for testing purposes.
The aircraft has made 9 flights up to October 2022, and more are contemplated now that a renewed effort is being made to again use the Stratolaunch for its original intended purpose.
The concept of Air-Launched-To-Orbit (ALTO) technology is innovative, and daring and has great potential for technical and commercial success, but the developmental road is steep and rocky for projects like these. While other companies have proposed similar projects for ALTO launch systems, the Stratolaunch appears to be the most advanced of these programs to date.
If the new rocket systems are successfully integrated into the project, we may one day see this magnificent and gigantic aircraft launching rockets into space on a regular basis.
- Length: 238 ft (73 m)
- Wingspan: 385 ft (117 m)
- Height: 50 ft (15 m)
- Empty weight: 500,000 lb (226,796 kg)
- Gross weight: 750,000 lb (340,194 kg) with no external payload
- Max takeoff weight: 1,300,000 lb (589,670 kg)
- External payload: 550,000 lb (250,000 kg)
- Powerplant: 6 × Pratt & Whitney PW4056 turbofan, 56,750 lbf (252.4 kN) thrust each
- Maximum speed: 460 kn (530 mph, 850 km/h)
- Range: 1,000 nmi (1,200 mi, 1,900 km) radius
- Ferry range: 2,500 nmi (2,900 mi, 4,600 km)
- Service ceiling: 35,000 ft (11,000 m) with payload