SpaceShipOne is an experimental air-launched rocket-powered aircraft with sub-orbital spaceflight capability at speeds of up to / 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.
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: Carry three humans (one of them a pilot) in a sea-level pressurized cabin. Be propelled by rocket from an altitude of to in excess of . Reenter atmosphere and shed kinetic energy in an aerodynamically stable configuration. Glide transonically and subsonically. Land horizontally on a standard runway.
Vehicle description The fuselage is cigar-shaped, with an overall diameter of about . 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 and a chord of . 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 , of which is taken by the fully loaded rocket motor. Empty mass of the spacecraft is , including the 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 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 , 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 of thrust, and can burn for about .
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 , 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.