Space Access: SKYLON - Technical

The SKYLON vehicle consists of a slender fuselage containing propellant tankage and payload bay, with delta wings attached midway along the fuselage carrying the SABRE engines in axisymmetric nacelles on the wingtips. The vehicle takes off and lands horizontally on its own undercarriage.

The information presented here is for the SKYLON C1 vehicle configuration designed with a target payload of 12 tonnes to Low Earth Orbit. In order to incorporate the technology advances and updated market analysis since the C1 configuration was finalised, a redesign exercise has been conducted to revise the SKYLON system to the D1 configuration with a payload of 15 tonnes to Low Earth Orbit.

SKYLON in orbit.

SABRE Engines

SKYLON uses SABRE engines in air-breathing mode to accelerate from take-off to Mach 5.5 which allows 1,250 tonnes of atmospheric air to be captured and used in the engines, of which 250 tonnes is oxygen which therefore does not have to be carried in propellant tanks. At Mach 5.5 and 25 kilometres altitude the SABRE engine transitions to its rocket engine mode, using liquid oxygen stored on board SKYLON, to complete its ascent to orbit at a speed of Mach 25. In this space access application, SABRE engines need an operational life of only 55 hours to achieve 200 flights, significantly less than the 10,000s of hours needed for conventional jet engines.

Control and Manoeuvrability

During atmospheric flight, control is provided by aerodynamic surfaces:

  • An all moving tail fin provides yaw control.
  • A delta foreplane (canards) provide pitch control.
  • Ailerons extending along the entire wing trailing edge provide roll control.

During the rocket powered ascent the combustion chambers are gimballed to provide pitch, yaw and roll control. Once in space, reaction control thrusters take over from these control surfaces.

SKYLON Cutaway

Material Construction

SKYLON's fuselage and wing load bearing structure is made from carbon fibre reinforced plastic and consists of stringers, frames, ribs and spars built as warren girder structures. The aluminium propellant tankage is suspended within this, free to move under thermal and pressurisation displacements.

The external shell (the aeroshell) is made from a fibre reinforced ceramic and carries only aerodynamic pressure loads which are transmitted to the fuselage structure through flexible suspension points. This shell is thin (0.5mm) and corrugated for stiffness. It is free to move under thermal expansion especially during the latter stages of the aerodynamic ascent and re-entry.

Take-off and Landing

The vehicle takes off and lands using a relatively conventional retractable undercarriage. By special attention to the brake system it has proved possible to achieve an acceptably low undercarriage mass. A heavily reinforced runway will be needed to tolerate the high equivalent single wheel load.

At the start of the take-off roll the vehicle weighs 275 tonnes, whilst maximum landing weight is 55 tonnes. At take-off the vehicle carries approximately 66 tonnes of liquid hydrogen and approximately 150 tonnes of liquid oxygen for the ascent.

The ground handling operations will be carried out using a standard aircraft tractor and a bonded goods cargo building permitting overhead loading and protection from the elements. For safety and operational simplicity the cryogenic propellants are loaded subcooled without venting of vapour. Cryogen loading is automatic through services connecting in the undercarriage wells whilst the vehicle is stood on the fuelling apron.

Payload Capabilities

In the SKYLON configuration presented here, the SKYLON payload bay is 4.6m diameter and 12.3m long. It has been designed to be compatible with expendable launcher payloads but in addition to accept standard aero transport containers which are 8 foot square in cross section and 10, 20, 30 or 40 feet long. It is anticipated that cargo containerisation will be an important step forward in space transport operations, enabling the "clean" payload bay to be dispensed with.

The design target for the SKYLON C1 vehicle was 12 tonnes to a 300km equatorial orbit, 10.5 tonnes to a 460km equatorial spacestation or 9.5 tonnes to a 460km x 28.5 deg spacestation when operating from an equatorial site. The updated SKYLON D1 configuration has a payload of 15 tonnes to a 300km equatorial orbit.

Although essentially a cargo carrier the payload bay can accommodate tankage for propellant supply to orbit based operations, upper stages for orbit transfer operations and, once endurance certification is achieved, a cabin module for 30 passengers.

SKYLON provides no payload support being purely a transport system.

Propellants

SKYLON employs two SABRE hybrid air-breathing/rocket engines. These engines employ liquid hydrogen fuel with atmospheric air up to Mach 5.5 and on-board liquid oxygen beyond that to orbital velocities.

Whilst in orbit the main propellant tanks are vented and allowed to warm to ambient conditions. Propulsion and attitude control are provided by the Orbital Manoeuvering System (OMS) or Reaction Control System (RCS). This uses a common LH2/LO2 propellant storage which is heavily insulated and cryogenically cooled. This system can remain operational on orbit up to 7 days. The RCS employs gaseous propellants supplied by the Gaseous Propellant Supply System (GPSS). The GPSS also supplies reactants to the fuel cells and the auxiliary power turbines.

Re-entry

During re-entry, which occurs at an altitude between 90 to 60km the heat is radiated away from the hot aeroshell. Heat is prevented from entering the vehicle by layers of reflecting foil and the low conductivity shell support posts. Liquid hydrogen is evaporated in the main tanks, passed through thermal screens to intercept the small residual heat leak and then vented overboard.

SKYLON C1 Statistics

Length

82m

Fuselage diameter:

6.25m

Wingspan:

25m

Unladen Mass

41,000kg

Fuel Mass

220,000kg

Maximum Payload Mass

12,000kg

Maximum Take-Off Mass

275,000kg

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