Skylon Guide, Meaning , Facts, Information and Description
Skylon is a plausible design by top British rocket scientist Alan Bond for an aeroplane that would be able to fly into low earth orbit, and return, completely intact.Historically, getting into space has required something called 'staging'. Staging is when parts of a rocket are dropped during the flight to reduce weight- where otherwise the rocket and payload would be too heavy to make orbit.
This staging causes a number of problems, it is difficult, expensive and often even impossible to recover and reuse and reassemble the parts.
The Skylon design promises to takeoff, from a specially strengthened runway, fly into space, and then reenter, and land back on the runway like a conventional aeroplane, without staging. This is known as single stage to orbit (SSTO).
The main features of the design are the engines, called SABRE. The engines are designed to operate like a jet engine at up to around mach 5, and then close off the air inlet and operate as a highly efficient rocket to orbital speed.
Operating a jet engine at up to mach 5.0 is difficult, previous engines proposed by other designers have been good jet engines but poor rockets; this engine is a good rocket engine, as well as being an excellent jet engine at all speeds. The problem with operating at mach 5.0 has been that the air coming into the engine heats up as it is compressed into the engine, and the engine ends up melting.
The SABRE engine avoids this by using some of the liquid hydrogen fuel to cool the air, the air is then burnt much like a conventional jet. At high speed, beyond mach 5, the air would still end up unusably hot- so the air inlet closes and the engine instead turns to burning the hydrogen with onboard liquid oxygen as a rocket.
Because the engine uses the atmosphere as reaction mass at low altitude, it burns about 5x less propellent there; and so takes off with much less. This, in turn, means that it doesn't need as much thrust or lift, and it allows using conventional wings at takeoff. The wings, in turn, hold much of the weight of the vehicle, and this also reduces the fuel needed- conventional rockets burn a considerable amount of propellent just holding the rocket up on a column of fire until reaching orbit (these are called "gravity losses").
And these differences make all the difference- the Skylon design can make orbit, and back, in a single stage.
The vehicle design is physically big- 82 m long and 6.3 m in diameter- mainly because it uses the low density fuel liquid hydrogen. The relatively large tanks are kept very light by running them at low pressure. In some ways, this size is actually an advantage as it means that the vehicle has a much easier time during reentry, than say, the Space Shuttle. The vehicle ends up slowing down at higher altitude where the air is thinner- it turns out that this in turn means that the vehicle doesn't get nearly as hot- the skin of the vehicle only goes up to 1500 °C or so, the extremely fragile tiles that the Space Shuttle employs are not required. This makes it safer and more practical (the Shuttle's tiles get shredded even flying through rain- the proposed Skylons skin material is reinforced ceramic and should be much more durable).
Indeed, the proportion of the takeoff weight that is payload is more than twice that of normal rockets and it should be fully reusable- that means that each flight makes twice as much money; and the vehicle is cheaper to run because the vehicle doesn't get thrown away or reassembled after each flight- further increasing the profit margin.
Skylon was based upon a previous project, HOTOL that failed when the funding was cut by the UK government.
One difference is the undercarriage. HOTOL was to use sled launch. Skylon uses relatively conventional-looking retractable undercarriage. This is achieved by using high pressure tires on a specially strengthened runway, and using water cooled brakes. Upon successful takeoff, the water is jettisoned. This reduces the weight of the undercarriage by many tonnes- weight that directly contributes to payload.
Skylon also uses a different engine design- HOTOL condensed the air and separated out the oxygen, whereas Skylon merely precools it. This is partly due to patent and Official Secrets Act issues, but it turns out that the SABRE engine has higher performance anyway.
Another issue that Skylon has circumvented is that the aerodynamic stability of the HOTOL vehicle was intrinsically poor. The center of mass of the rear-engined vehicle was near the rear. Since the center of drag was more central; this tends to make the vehicle 'want' to fly backwards. Attempts to fix this problem ended up costing most of the payload the HOTOL vehicle could supply, and contributed to the failure of the project. Skylon solves this by putting the engines on the end of the wings nearer the center of the vehicle and thus moving the center of mass forward.
Skylon Statistics:
* Length: 82 m * Fuselage Diameter: 6.25 m * Wingspan: 25 m * Unladen Mass: 41,000 kg * Fuel Mass: 220,000 kg * Maximum Payload Mass: 12,000 kg * ISP: 2000 to 2800 lbf.s/lb (20 to 27 kNs/kg) atmospheric, 450 lbf.s/lb (4.41 kNs/kg) exoatmospheric * SABRE thrust:weight ratio >10The projected ticket price is around $250,000 to get to orbit and back.
Space Tourism may be a very popular activity if this vehicle works as designed.
The project has a projected R&D cost of $10 billion and an estimated program length of 7-10 years. Skylon research, mainly associated with the SABRE engine heat exchangers, is currently being carried out by Alan Bond's company Reaction Engines Limited.
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