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Tier One

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SpaceShipOne

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Status: Retired 2004. Payload: 400 kg (880 lb). Gross mass: 7,700 kg (16,900 lb). Height: 5.00 m (16.40 ft). Diameter: 1.52 m (4.98 ft). Span: 15.00 m (49.00 ft). Location: Mojave, California. Apogee: 110 km (60 mi).

Burt Rutan of Scaled Composites, Mojave, California, started conceptual design of the Tier One space launch system in 1997. Some of the concepts for the Tier One launch aircraft were worked out in Rutan's Proteus high-altitude, multi-mission aircraft which first flew on 26 July 1998. Microsoft billionaire Paul Allen signed a contract, estimated at $20 to $30 million, for full development of the Tier One in April 2001. Aerodynamic design was done entirely using CFD (computational fluid dynamics) software - no wind tunnel testing was conducted. Development included thermal tests of the ablative re-entry coating, heat-resistant portholes, and subscale drop tests of re-entry configurations.

The immediate objective of Tier One was to win the $10 million X-Prize, by being the first to fly a privately-developed, reusable spacecraft over 100 km. While Rutan estimated that the cost per flight of Tier One would be about $80,000, there were no plans to develop a commercial, paying-passenger version of the experimental aircraft. Rutan was unwilling to deal with the government red tape for that. The main concern was to show that the X-Prize objective of private spaceflight could be achieved, safely and economically, using innovative aerodynamic and propulsion concepts.

Tier One vehicle consisted of two stages: the White Knight carrier-launch aircraft, and the SpaceShipOne (SS1) spaceplane. In the vehicle's baseline mission, the White Knight would carry SpaceShipOne suspended beneath to a point 65 km from Rutan's Mojave Airport base, then release it at 15 km altitude at 215 kph. SpaceShipOne would fire its rocket engine and go into an 84 degree climb. After a 65 to 80 second burn, the engine would shut down, and the spacecraft continue on a ballistic ascent to 110 km altitude. This would be followed by re-entry into the atmosphere, and a glide landing back at Mojave Airport.

The White Knight was a manned, twin-turbojet research aircraft intended for high-altitude missions. The White Knight's cockpit, avionics, electronic control system, pneumatics, trim servos, data system, and electrical system components were identical to those installed on SpaceShipOne. Therefore test flights of the White Knight served to flight-qualify all of the spacecraft's systems, except rocket propulsion. The White Knight's high thrust-to-weight ratio and enormous speedbrakes allowed the pilots to simulate realistically SpaceShipOne flight maneuvers of boost, approach and landing. The aircraft therefore served both as a launch aircraft and a high-fidelity trainer for SpaceShipOne pilots.

SpaceShipOne was a three-place, high-altitude research rocketplane, designed for sub-orbital flights to 100 km altitude. The tail number N328KF (328 kilofeet) was selected after it was discovered N100KM was already taken. The unique configuration allowed aircraft-like qualities for boost, glide, and landing. Rutan wanted to avoid the use of fly-by-wire stability augmentation systems normally required to handle the instability inherent in transonic aircraft. He originally planned to use petal-like drag brakes, to be followed by a vertical parachute recovery. But finally he decided to use pneumatic actuators to pop-up the wing and tail boom in a 'shuttlecock' configuration. This provided for a stable high-drag re-entry, which required no control inputs from the pilot. After the aircraft had slowed to 160 kph, the wings and tail would return to their normal position, and the pilot would fly the aircraft in a 185 kph glide in descending circles to the airfield.

Roll and pitch were controlled by elevons on the twin tail booms. Linked upper rudders moved outward only for drag, and electrically powered lower rudders provided trim. All controls were manual. The rocketplane's fuselage was a monocoque structure with the skin made of carbon/epoxy composite with a Nomex core. Aft of the horizontal stabilizer, where the heating was less, fiberglass was used as a radio-transparent skin material. The wings were also used carbon/epoxy skins, built up over structural ribs. High-temperature areas added phenolic resin to the mix. The leading edge of the wings and the belly of the rocketplane used a red ablative material, which would be reapplied before each mission.

Designed for a 'shirt- sleeve' environment, the 1.52 m diameter cabin was outfitted with nine twin-pane viewports for outstanding visibility. The crew was not equipped with spacesuits; gas bottles served to keep the cabin pressure at 1800 m equivalent regardless of loss of hull integrity. The aircraft was naturally stable, and used all manual controls. These included aerodynamic controls in the atmosphere and a cold-gas reaction control system in space. The same gas bottles provided for cabin pressurization, the reaction control system, and pneumatic operation of the actuators that feathered the empennage for re-entry and released the landing gear for landing.

Propulsion was by a SpaceDev hybrid rocket engine, selected after competitive testing against an eEC design. The enormous liquid nitrous oxide tank dominated the fuselage interior. The HTPB fuel burned in the presence of the nitrous oxide to produce a chamber pressure of 37 atm, expanded through a 25:1 nozzle. Thrust loads were transmitted from the fuel casing, through the nitrous oxide tank, and then to the spacecraft through rubber that bonded the tank to the fuselage.

Liquid nitrous oxide (N2O / dinitrogen monoxide / 'laughing gas') was the oxidizer of choice for the Tier One application because it was storable, and self-pressurizing to 48 atmospheres at 17 deg C. The combination of HTPB solid fuel and N2O was totally benign and non-toxic. It was difficult to find a rocket motor safer than one using rubber/plastic and laughing gas. It was non-explosive. The fuel had to be vaporized in the presence of an atomized oxidizer with a high temperature igniter in order for it to burn. Even in failure mode, it was safe. Flow oxidizer without vaporized fuel and nothing would happen. Vaporize fuel without oxidizer and nothing would happen. Ignition only occurred when fuel was vaporized in the presence of an atomized oxidizer with a high temperature igniter. The engine could be shut down at any time by cutting off the flow of oxidizer.

All technical data were considered confidential and the data presented here are estimated.

Crew Size: 3. Spacecraft delta v: 1,700 m/s (5,500 ft/sec). Payload: 400 kg (880 lb) to a 110 km altitude. Development Cost $: 30.000 million. Launch Price $: 0.080 million in 2004 dollars in 2004 dollars. Boost Propulsion: Lox/Kerosene. Cruise Thrust: 73.500 kN (16,523 lbf). Cruise Thrust: 7,500 kgf. Cruise engine: SpaceDev Hybrid. Maximum speed: 5,300 kph (3,200 mph). Minimum range: 65 km (40 mi). Initial Operational Capability: 2004. Total Number Built: 1.

Stage Data - Tier One

• Stage 0. 1 x White Knight. Gross Mass: 4,100 kg (9,000 lb). Empty Mass: 1,200 kg (2,600 lb). Thrust (vac): 34.300 kN (7,711 lbf). Isp: 2,000 sec. Diameter: 1.52 m (4.98 ft). Propellants: Air/Kerosene. No Engines: 2. Engine: J85-GE-5. Status: In production. Comments: Carries SpaceShipOne to release point 65 km from Mohave Airport base, then releases it at 15 km altitude at 215 kph. Wing area 43.5 sq m.

• Stage 1. 1 x SpaceShipOne. Gross Mass: 3,600 kg (7,900 lb). Empty Mass: 1,200 kg (2,600 lb). Thrust (vac): 73.500 kN (16,523 lbf). Isp: 250 sec. Burn time: 80 sec. Diameter: 1.52 m (4.98 ft). Span: 5.00 m (16.40 ft). Propellants: N2O/Solid. No Engines: 1. Engine: SpaceDev Hybrid. Status: In production. Comments: Wing area 15 sq m.