SpaceShipOne is an experimental air-launched rocket-powered aircraft with sub-orbital spaceflight capability at speeds of up to 3,000 ft/s (2,000 mph) / 910 m/s (3,300 km/h)
using a hybrid rocket motor. The design features a unique "feathering" atmospheric reentry system where the rear half of the wing and the twin tail booms folds 70 degrees upward along a hinge running the length of the wing; this increases drag while retaining stability. SpaceShipOne completed the first crewed private spaceflight in 2004. That same year, it won the US$10 million Ansari X Prize and was immediately retired from active service. Its mother ship was named "White Knight". Both craft were developed and flown by Mojave Aerospace Ventures, which was a joint venture between Paul Allen and Scaled Composites, Burt Rutan's aviation company. Allen provided the funding of approximately US$25 million.
Rutan has indicated that ideas about the project began as early as 1994 and the full-time development cycle time to the 2004 accomplishments was about three years. The vehicle first achieved supersonic flight on December 17, 2003, which was also the one-hundredth anniversary of the Wright Brothers' historic first powered flight. SpaceShipOne's first official spaceflight, known as flight 15P, was piloted by Mike Melvill. A few days before that flight, the Mojave Air and Space Port was the first commercial spaceport licensed in the United States. A few hours after that flight, Melvill became the first licensed U.S. commercial astronaut. The overall project name was "Tier One" which has evolved into Tier 1b with a goal of taking a successor ship's first passengers into space.
The achievements of SpaceShipOne are more comparable to those of the X-15 than to those of orbiting spacecraft like the Space Shuttle. Accelerating a spacecraft to orbital speed requires more than 60 times as much energy as accelerating it to Mach 3. It would also require an elaborate heat shield to safely dissipate that energy during re-entry.
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Reference material for this entry is drawn from the open encyclopedic record, including Wikipedia , available under the CC BY-SA 4.0 license. Images are credited individually beside each photo.
SpaceShipOne's official model designation is Scaled Composites Model 316.
Design
Design goal
The Scaled Composites Model 316, known as SpaceShipOne, was a spaceplane designed to:
The fuselage is cigar-shaped, with an overall diameter of about 1.52 m (5 ft 0 in). The main structure is of a graphite/epoxy composite material. From front to back, it contains the crew cabin, oxidizer tank, fuel casing, and rocket nozzle. The craft has short, wide wings, with a span of 5 m (16 ft) and a chord of 3 m (9.8 ft). Large vertical tailbooms are mounted on the end of each wing, with horizontal stabilizers protruding from the tailbooms. It has gear for horizontal landings.
The overall mass of the fully fueled craft is 3,600 kg (7,900 lb), of which 2,700 kg (6,000 lb) is taken by the fully loaded rocket motor. Empty mass of the spacecraft is 1,200 kg (2,600 lb), including the 300 kg (660 lb) empty motor casing.
Originally the nozzle protruded from the back, but this turned out to be aerodynamically disadvantageous. In June 2004, between flights 14P and 15P, a fairing was added, smoothly extending the fuselage shape to meet the flared end of the nozzle. On flight 15P the new fairing overheated, due to being black on the inside and facing a hot, black nozzle. The fairing softened, and the lower part crumpled inwards during boost. Following that flight the interior of the fairing was painted white, and some small stiffening ribs were added.
The craft has a single unsteerable and unthrottleable hybrid rocket motor, a cold gas reaction control system, and aerodynamic control surfaces. All can be controlled manually. See the separate section below concerning the rocket engine.
The reaction control system is the only way to control spacecraft attitude outside the atmosphere. It consists of three sets of thrusters: thrusters at each wingtip control roll, at the top and bottom of the nose control pitch, and at the sides of the fuselage control yaw. All thrusters have redundant backups, so comprising twelve thrusters in all.
The aerodynamic control surfaces of SpaceShipOne are designed to operate in two distinct flight regimes, subsonic and supersonic. The supersonic flight regime is of primary interest during the boost phase of a flight, and the subsonic mode when gliding. The craft has separate upper and lower rudders, and elevons. These are controlled using aviation-style stick and pedals. In supersonic mode the trim tabs are controlled electrically, whereas the subsonic mode uses mechanical cable-and-rod linkage.
The wings of SpaceShipOne can be pneumatically tilted forwards into an aerodynamically stable high-drag "feathered" shape. This removes most of the need to control attitude actively during the early part of reentry: Scaled Composites refer to this as "care-free reentry". One of the early test flights actually performed re-entry inverted, demonstrating the flexibility and inherent stability of Burt Rutan's "shuttlecock" design. This feathered reentry mode is claimed to be inherently safer than the behavior at similar speeds of the Space Shuttle. The Shuttle undergoes enormous aerodynamic stresses and must be precisely steered in order to remain in a stable glide. (Although this is an interesting comparison of behavior, it is not an entirely fair comparison of design concepts: the Shuttle starts reentry at much higher speed than SpaceShipOne, and so has some very different requirements. SpaceShipOne is more similar to the X-15 vehicle.)
An early design called for a permanently shuttlecock-like shape, with a ring of feather-like stabilising fins. This would have made the spacecraft incapable of landing independently, requiring mid-air retrieval. This was deemed too risky, and the hybrid final design manages to incorporate the feathering capability into a craft that can land in a conventional manner. The tiltable rear sections of the wings and the tailbooms are collectively referred to as "the feather".
The landing gear consists of two widely separated main wheels and a nose skid. These are deployed using springs, assisted by gravity. Once deployed, they cannot be retracted inflight.
The spacecraft is incapable of independent takeoff from the ground. It requires a launch aircraft to carry it to launch altitude for an air launch.
The parts of the craft that experience the greatest heating, such as the leading edges of the wings, have about 6.5 kg (14 lb) of ablative thermal protection material applied. The main ingredient of this material was accidentally leaked to Air and Space. If it flew with no thermal protection, the spacecraft would survive reentry but would be damaged.
The spacecraft's aerodynamic design has an acknowledged "known deficiency" that makes it susceptible to roll excursions. This has been seen on SpaceShipOne flight 15P where wind shear caused a large roll immediately after ignition, and SpaceShipOne flight 16P where circumstances not yet fully understood caused multiple rapid rolls. This flaw is not considered dangerous, but in both of these flights led to the achievement of a much lower altitude than expected. The details of the flaw are not public.
Cabin
The spacecraft cabin, designed to hold three humans, is shaped as a short cylinder, diameter 1.52 m (5 ft 0 in), with a pointed forward end. The pilot sits towards the front, and two passengers can be seated behind.
The cabin is pressurized, maintaining a sea level breathable atmosphere. Oxygen is introduced to the cabin from a bottle, and carbon dioxide and water vapor are removed by absorbers. The occupants do not wear spacesuits or breathing masks, because the cabin has been designed to maintain pressure in the face of faults: all windows and seals are doubled.
The cabin has sixteen round double-pane windows, positioned to provide a view of the horizon at all stages of flight. The windows are small compared to the gaps between them, but there are sufficiently many for human occupants to patch together a moderately good view.
The nose section can be removed, and there is also a hatch below the rear windows on the left side. Crew ingress and egress is possible by either route.
Spaceplane navigation
The core of the spacecraft avionics is the System Navigation Unit (SNU). Together with the Flight Director Display (FDD), it comprises the Flight Navigation Unit. The unit was developed jointly by Fundamental Technology Systems and Scaled Composites.
The SNU is a GPS-based inertial navigation system, which processes spacecraft sensor data and subsystem health data. It downlinks telemetry data by radio to mission control.
The FDD displays data from the SNU on a color LCD. It has several distinct display modes for different phases of flight, including the boost phase, coast, reentry, and gliding. The FDD is particularly important to the pilot during the boost and coast phase in order to "turn the corner" and null rates caused by asymmetric thrust. A mix of commercial and bespoke software is used in the FDD.
Hybrid rocket engine
Tier One uses a hybrid rocket engine supplied by SpaceDev, with solid hydroxyl-terminated polybutadiene (HTPB, or rubber) fuel and liquid nitrous oxide oxidizer. It generates 88 kN (20,000 lbf) of thrust, and can burn for about 87 s (1.45 min).
The physical layout of the engine is novel. The oxidizer tank is a primary structural component, and is the only part of the engine that is structurally connected to the spacecraft: the tank is in fact an integral part of the spacecraft fuselage. The tank is a short cylinder of diameter approximately 1.52 m (5 ft 0 in), with domed ends, and is the forwardmost part of the engine. The fuel casing is a narrow cylinder cantilevered to the tank, pointing backwards. The cantilevered design means that a variety of motor sizes can be accommodated without changing the interface or other components. The nozzle is a simple extension of the fuel casing; the casing and nozzle are actually a single component, referred to as the CTN (case, throat, and nozzle). Burt Rutan has applied for a patent on this engine configuration.
There is considerable use of composite materials in the engine design. The oxidizer tank consists of a composite liner with graphite/epoxy over-wrap and titanium interface flanges. The CTN uses a high-temperature composite insulator with a graphite/epoxy structure. Incorporating the solid fuel (and hence the main part of the engine) and the ablative nozzle into this single bonded component minimizes the possible leak paths.
The oxidizer tank and CTN are bolted together at the main valve bulkhead, which is integrated into the tank. There are O-rings at the interface to prevent leakage; this is the main potential leak path in the engine. The ignition system, main control valve, and injector are mounted on the valve bulkhead, inside the tank. Slosh baffles are also mounted on this bulkhead. Because the oxidizer is stored under pressure, no pump is required.
The tank liner and the fuel casing are built in-house by Scaled Composites. The tank over-wrap is supplied by Thiokol. The ablative nozzle is supplied by AAE Aerospace. The oxidizer fill, vent, and dump system is supplied by Environmental Aeroscience Corporation. The remaining components—the ignition system, main control valve, injector, tank bulkheads, electronic controls, and solid fuel casting—are supplied by SpaceDev.
The CTN must be replaced between firings. This is the only part of the craft, other than the fuel and oxidizer themselves, that must be replaced.
The solid fuel is cast with four holes. This has the disadvantage that it is possible for chunks of fuel between the holes to become detached during a burn and obstruct the flow of oxidizer and exhaust. Such situations tend to rapidly self-correct.
The oxidizer tank is filled and vented through its forward bulkhead, on the opposite side of the tank from the fuel and the rest of the engine. This improves safety. It is filled to a pressure of 4.8 MPa (700 psi) at room temperature.
The nozzle has an expansion ratio of 25:1, which is optimized for the upper part of the atmosphere. A different nozzle, with an expansion ratio of 10:1, is used for test firing on the ground. The nozzles are black on the outside, but for aerodynamic testing, red dummy nozzles are used instead.
The rocket is not throttleable. Once lit, the burn can be aborted, but the power output cannot otherwise be controlled. The thrust in fact varies, for two reasons. Firstly, as the pressure in the oxidizer tank decreases, the flow rate reduces, reducing thrust. Secondly, in the late stages of a burn the oxidizer tank contains a mixture of liquid and gaseous oxidizer, and the power output of the engine varies greatly depending on whether it is using liquid or gaseous oxidizer at a particular moment. (The liquid, being far denser, allows a greater burn rate.)
Both the fuel and oxidizer can be stored without special precautions, and they do not burn when brought together without a significant source of heat. This makes the rocket far safer than conventional liquid or solid rockets. The combustion products are water vapour, carbon dioxide, hydrogen, nitrogen, nitrogen oxides and carbon monoxide.
The engine was upgraded in September 2004, between flights 15P and 16P. The upgrade increased the oxidizer tank size, to provide greater thrust in the early part of the burn, allow a longer burn, and delay the onset of the variable thrust phase at the end of the burn. Prior to the upgrade the engine generated 76 kN (17,000 lbf) of thrust and could burn for 76 s (1.27 min). After the upgrade it was capable of 88 kN (20,000 lbf) thrust and an 87 s (1.45 min) burn.
Launch aircraft
Tier One's launch aircraft, Scaled Composites Model 318, known as White Knight, is designed to take off and land horizontally and attain an altitude of about 15 km (9.3 mi), all while carrying the Tier One spacecraft in a parasite aircraft configuration. Its propulsion is by twin turbojets: afterburning J-85-GE-5 engines, rated at 15.6 kN (3,500 lbf) of thrust each.
It has the same cabin, avionics, and trim system as SpaceShipOne. This means it can flight-qualify almost all components of SpaceShipOne. It also has a high thrust-to-weight ratio and large speed brakes. These features combined allow it to be used as a high-fidelity moving platform flight simulator for SpaceShipOne. White Knight is also equipped with a trim system which (when activated) causes it to have the same glide profile as SpaceShipOne; this allows the pilots to practice for landing SpaceShipOne. The same pilots fly White Knight as fly SpaceShipOne.
The aircraft's distinctive shape features long, thin wings, in a flattened "W" shape, with a wingspan of 25 m (82 ft), dual tailplanes, and four wheels (front and rear at each side). The rear wheels retract, but the front ones, which are steerable, are permanently deployed, with small fairings, referred to as "spats", in front. Another way to look at the overall shape is as two conventional planes, with very thin fuselages, side by side and joined at their wingtips, with the cockpit and engines mounted at the point of joining.
Although White Knight was developed for certain roles in the Tier One program, it is a very capable aircraft in its own right. Scaled Composites describe it as a "high-altitude research aircraft".
Flight profile
SpaceShipOne takes off from the ground, attached to White Knight in a parasite configuration, and under White Knight's power. The combination of SpaceShipOne and White Knight can take off, land, and fly under jet power to high altitude. A captive carry flight is one where the two craft land together without launching SpaceShipOne; this is one of the main abort modes available.
For launch, the combined craft flies to an altitude of around 14 km (8.7 mi), which takes about an hour. SpaceShipOne is then drop-released, and briefly glides unpowered. Rocket ignition may take place immediately, or may be delayed. If the rocket is never lit then SpaceShipOne can glide down to the ground. This is another major abort mode, in addition to being flown deliberately in glide tests.
The rocket engine is ignited while the spacecraft is gliding. Once under power, it is raised into a 65° climb, which is further steepened in the higher part of the trajectory. The maximum acceleration during ascent was recorded at 1.70G.
By the end of the burn the craft is flying upwards at some multiple of the speed of sound, up to about 900 m/s (3,000 ft/s) and Mach 3.5, and it continues to coast upwards unpowered (i.e. ballistically). If the burn was long enough then it will exceed an altitude of 100 km (62 mi), at which height the atmosphere presents no appreciable resistance, and the craft experiences free fall for a few minutes.
While at apogee the wings are reconfigured into high-drag mode. As the craft falls back it achieves high speeds comparable to those achieved on the way up; when it subsequently reenters the atmosphere it decelerates violently, up to 5.75G. At some altitude between 10 km (6.2 mi) and 20 km (12 mi) it reconfigures into low-drag glider mode, and glides down to a landing in about 20 minutes.
White Knight takes longer to descend, and typically lands a few minutes after SpaceShipOne.
