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==Design== {{more citations needed|section|date=June 2017}} ===Design goal=== The '''Scaled Composites Model 316''',<ref name="SpaceNewsPreludeToHistory">{{cite news|last1=Foust|first1=Jeff|author-link1=Jeff Foust|title=Prelude to history?|url=http://www.thespacereview.com/article/166/1|access-date=21 December 2015|work=[[The Space Review]]|publisher=[[SpaceNews]]|date=21 June 2004}}</ref> known as '''SpaceShipOne''', was a [[spaceplane]] designed to: * Carry three humans (one of them a [[pilot (spaceflight)|pilot]]) in a sea-level pressurized cabin. * Be propelled by [[rocket]] from an altitude of {{convert|15|km|abbr=on}} to in excess of {{convert|100|km|abbr=on}}. * Reenter atmosphere and shed kinetic energy in an [[aerodynamic]]ally 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 {{convert|1.52|m|abbr=on}}. 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 {{convert|5|m|abbr=on}} and a [[Chord (aircraft)|chord]] of {{convert|3|m|abbr=on}}. 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 {{convert|3600|kg|abbr=on|lk=in}}, of which {{convert|2700|kg|abbr=on}} is taken by the fully loaded rocket motor. Empty mass of the spacecraft is {{convert|1200|kg|abbr=on}}, including the {{convert|300|kg|abbr=on|adj=on}} empty motor casing.<ref name="ssone">{{cite web|url=http://www.astronautix.com/s/spaceshipone.html|archive-url=https://web.archive.org/web/20161228034631/http://astronautix.com/s/spaceshipone.html|url-status=dead|archive-date=December 28, 2016|title=SpaceShip One|website=www.astronautix.com}}</ref><ref name="sdhyb">{{cite web|url=http://www.astronautix.com/s/spacedevhybrid.html|archive-url=https://web.archive.org/web/20161228044350/http://astronautix.com/s/spacedevhybrid.html|url-status=dead|archive-date=December 28, 2016|title=SpaceDev Hybrid|website=www.astronautix.com}}</ref> Originally the nozzle protruded from the back, but this turned out to be aerodynamically disadvantageous. In June 2004, between flights [[SpaceShipOne flight 14P|14P]] and [[SpaceShipOne flight 15P|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 [[Flight control surfaces|control surface]]s. 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 [[elevon]]s. 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 (physics)|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 {{convert|6.5|kg|abbr=on}} of ablative thermal protection material applied. The main ingredient of this material was accidentally leaked to ''Air and Space''{{Clarify|date=February 2010}}. 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 [[flight dynamics|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 {{convert|1.52|m|abbr=on}}, with a pointed forward end. The [[pilot (spaceflight)|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 [[spacesuit]]s 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 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]] [[Rocket engine|engine]] supplied by [[SpaceDev]], with solid [[hydroxyl-terminated polybutadiene]] (HTPB, or [[rubber]]) [[fuel]] and liquid [[nitrous oxide]] [[oxidizer]]. It generates {{convert|88|kN|abbr=on}} of thrust, and can burn for about {{convert|87|s|abbr=on}}. 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 (geometry)|cylinder]] of diameter approximately {{convert|1.52|m|abbr=on}}, with domed ends, and is the forwardmost part of the engine. The fuel casing is a narrow cylinder [[cantilever]]ed 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''' ('''c'''ase, '''t'''hroat, and '''n'''ozzle). [[Burt Rutan]] has applied for a [[patent]] on this engine configuration. There is considerable use of [[composite material]]s 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 [[ablation|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-ring]]s 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 (partition)|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 {{convert|4.8|MPa|abbr=on|lk=in}} 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 [[SpaceShipOne flight 15P|15P]] and [[SpaceShipOne flight 16P|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 {{convert|76|kN|abbr=on}} of thrust and could burn for {{convert|76|s|abbr=on}}. After the upgrade it was capable of {{convert|88|kN|abbr=on}} thrust and an {{convert|87|s|abbr=on}} burn. ===Launch aircraft=== {{About|section=yes|design|information on flights made by White Knight|Scaled Composites White Knight}} [[File:White Knight One by Don Ramey Logan.jpg|thumb|White Knight One 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 {{convert|15|km|abbr=on}}, all while carrying the Tier One spacecraft in a [[parasite aircraft]] configuration. Its propulsion is by twin [[turbojet]]s: afterburning J-85-GE-5 engines, rated at {{convert|15.6|kN|abbr=on|lk=in}} 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 {{convert|25|m|abbr=on}}, 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 aircraft|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<ref>{{Cite journal|last1=Munro|first1=Cameron|last2=Krus|first2=Peter|last3=Llewellyn|first3=Edward|date=2002|title=Captive Carry Testing as a Means for Rapid Evaluation of UAV Handling Qualities|url=http://www.icas.org/ICAS_ARCHIVE/ICAS2002/PAPERS/832.PDF|journal=ICAS|publisher=International Council of Aeronautical Sciences}}</ref> 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 {{convert|14|km|abbr=on}}, 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.<ref>{{Cite web|url=http://www.aerorocket.com/SS1/SS1.html|title=SpaceShipOne|last=Cipolla|first=John|date=4 October 2004|website=AeroDRAG & Flight Simulation 7.0 Validation|access-date=16 March 2020|archive-date=16 February 2020|archive-url=https://web.archive.org/web/20200216072147/http://www.aerorocket.com/SS1/SS1.html|url-status=dead}}</ref> By the end of the burn the craft is flying upwards at some multiple of the speed of sound, up to about {{convert|900|m/s|abbr=on}} and [[Mach number|Mach]] 3.5, and it continues to coast upwards unpowered (i.e. [[ballistics|ballistically]]). If the burn was long enough then it will exceed an altitude of {{convert|100|km|abbr=on}}, at which height the atmosphere presents no appreciable resistance, and the craft experiences [[weightlessness|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 {{convert|10|km|abbr=on}} and {{convert|20|km|abbr=on}} 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.
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