TYPE: High-altitude platform.

PROGRAMME: Design conception started 1996, but existence unknown until shortly before first flight (N318SL) on 1 August 2002; officially unveiled 18 April 2003 as launch platform for suborbital SpaceShipOne and, possibly, other payloads. First captive-carry flight with SpaceShipOne attached, 20 May 2003; 29 sorties (43.1 hours) flown by 29 July 2003.

DESIGN FEATURES: Designed to provide high-altitude airborne launch of company's SpaceShipOne manned, suborbital spacecraft, and equipped to flight-qualify all of latter's systems except rocket propulsion. Objective is to demonstrate possibility of relatively inexpensive spaceflight. Cockpit avionics, ECS, pneumatics, trim servos, data system and electrical system components are identical to those in SpaceShipOne. High thrust/weight ratio and large speed brakes allow trainee astronauts to practise such spaceflight manoeuvres as boost, approach and landing in a realistic environment, thus effectively serving as a flying simulator for SpaceShipOne pilot training.
Twin-boom configuration with separate T tails and short fuselage pod. High-aspect ratio wings have marked anhedral inboard of booms and approximately equal dihedral outboard, raising fuselage high above ground. Podded jet engine pylon-mounted to fuselage above each wingroot. Tailbooms sharply tapered to narrow point at front. Forward section of fuselage pod bulged, in similar fashion to Proteus but with 16 circular windows and forward-opening circular crew door.
Although intended primarily for high-altitude missions such as launch of SpaceShipOne, other roles could include reconnaissance, surveillance, atmospheric research, data relay, telecommunications, imaging, and booster-launch for microsatellites.

FLYING CONTROLS: Manual, with three-axis electric trim; ailerons outboard of tailbooms, rudders and elevators on T tails. Pneumatic speed brakes inboard of tailbooms can be operated separately as inboard and outboard pairs to allow steep descent with lift/drag ratio of less than 4.5:1.

STRUCTURE: All carbon fibre epoxy materials, primarily using sandwich construction with honeycomb and PVC foam cores.

LANDING GEAR: Wide-track, four-wheel type. Pneumatically retracting (rearward) mainwheel with compressed rubber shock absorption in each tailboom, in line with wing anhedral/dihedral junction. Small, non-retractable, 'spatted' nosewheel at front of each boom; starboard one is steerable.

POWER PLANT: Two General Electric J85-GE-5 turbojets (each 17.13 kN; 3,850 lb st with afterburning). Fuel tanks (see under Weights and Loadings for capacity) in wing leading-edges and forward part of tailbooms.

ACCOMMODATION: Three-place cabin, qualified for unlimited altitude. Two crew doors (one on port side, one in nosecone), with dual-pane windows. Cockpit allows single-pilot operation (VMC day conditions only).

SYSTEMS: Pneumatic system for main landing gear extension/retraction. Hydraulic system for wheel brakes and nose gear steering. Dual-bus electrical system.

AVIONICS: Flight: Include INS-GPS nav, flight director, flight test data (recording and telemetry), air data, vehicle health monitoring and video systems.
Instrumentation: Back-up flight instruments.