Certainly one of the sleekest designs of all is the Skylon advanced spaceplane concept of Reaction Engines Limited, based in Oxfordshire, England. It is also one of the largest. The greater part of the volume of Skylon is taken up by propellant tankage, precisely what is required to achieve single-stage to orbit capability in a reusable spaceplane. Skylon is capable of flying without a crew, which increases available room for propellants. Its advanced combined cycle turborockets enable the craft to deliver 12 metric tons of cargo directly to low Earth orbit without wasting spent stages. It makes full use of the atmosphere, using both its wings and its advanced engines to enter orbit (Fig. 12.4).

Skylon's slender fuselage contains huge propellant tanks for the liquid hydrogen and liquid oxygen, as well as a sizable payload bay designed to accept standard launch packages. Delta wings support twin dual-mode Sabre turborocket engines in axisymmetric nacelles mounted on the wingtips. Foreward of the main wings are canards for pitch control in the atmosphere. An all-movable vertical stabilizer and conventional ailerons provide yaw and roll control. In space, a reaction control system draws from the main propellant supply. The vehicle operates from reinforced

Fig. 12.4 Skylon spaceplane in low Earth orbit. It requires no external tanks, drop-off boosters, stages, or carrier aircraft. It is the epitome of the advanced spaceplane (courtesy Reaction Engines Limited)

Table 12.1 Skylon specifications


82 m

270 ft


6.25 m

20% ft


25 m

82 ft

Empty weight

41,000 kg

90,000 lb

LH2 fuel

66,000 kg

145,000 lb

LO2 oxidizer

150,000 kg

330,000 lb

Maximum payload

12,000 kg

26,000 lb

Max. takeoff weight

275,000 kg

600,000 lb

Landing weight

55,000 kg

120,000 lb

runways without auxiliary aircraft or boosters. It is a completely self-contained vehicle, landing and taking off like any airplane.

The Sabre engine, also designed by Reaction Engines Limited, can operate either in an air-breathing or in a rocket mode. From takeoff to about Mach 5, it draws in atmospheric air, to be used as oxidizer and propellant, by means of a two-shock axisymmetric intake. The air is precooled via a closed helium loop just before entering the combustion chamber. The helium loop is itself cooled by the cryogenic liquid hydrogen fuel. Therefore the helium is never used up while performing useful work. In rocket mode, the engines use the onboard liquid oxygen and liquid hydrogen (see also Fig. 12.5).

There is additional information on Skylon and Sabre at http://www.reactionengines.

Fig. 12.5 General three-view arrangement of the Skylon advanced spaceplane concept (courtesy Reaction Engines Limited)

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