Britain’s Spaceplane Skylon – hopefully nearer to taking off!
Britain has a long engineering history when it comes to developing advanced engines from F1 motor racing to jet fighters. Sadly some potential innovations never made it to full development and manufacturing because of the short sightedness of some UK governments. The UK had a viable rocket and satellite business in the 1960s, however the government of the day withdrew funding and so from being up there with the US and USSR, Britain’s space faring became moribund. Only since the 1990s has Brit technology been a major part of collaborative space missions. Since Sir Frank Whittle an ace RAF fighter pilot and enginer developed the first turbo jet engine in the 192os, Britain has continued to innovate jet engine technology. Rolls Royce (RR) PLC vies with US General Electric as the worlds biggest jet and turbo propulsion engine maker. RR’s adanced engines are famous and used by many airlines, air forces and navies throughout the world. It’s latest Trent Engines are regarded as the peak in precision engineering and will continue to be researched & developed. Rolls Royce has worked with British Aerospace and with government funding to develop more advanced and faster engines.
Their most famous development was HOTOL(Horizontal Take-Off and Landing), which was an all British air-breathing rocket hybrid space shuttle.
HOTOL was designed to be a single-stage-to orbit (SSTO) reusable winged vehicle launched from a rocket sledge . It was to be fitted with a unique air-breathing engine, the RB545 called the ‘Swallow’, developed by Rolls Royce. The engine was technically a liquid hydrogen/liquid oxygen design, but dramatically reduces the amount of oxidizer needed to be carried on board by utilising atmospheric oxygen through jet engine action as the spacecraft climbed through the lower atmosphere before rocket propellant would kick in when the air was too thin at high altitude. when the rocket propuslion was engaged on the edge of space, it could reach between mach 5-7 ( 5328 mph/8574 kph). A journey from London to Australia would take between two & three hours! With the potential amazing speeds there was much excitement generated.
However during development, it was found that the comparatively heavy rear-mounted engine moved the center of mass of the vehicle rearwards. This meant that the vehicle had to be designed to push the center of drag as far rearward as possible to ensure stability over the entire flight regime. Redesign of the vehicle to do this cost a significant proportion of the payload, and made the economics unclear. In particular, some of the analysis seemed to indicate that similar technology applied to a pure rocket approach would give at least as good performance at lower cost. With these problems in 1988 the UK government withdrew further funding, the project was approaching the end of its design phase but the plans were still speculative and dogged with aerodynamic problems and operational disadvantages. It is moot whether these technical problems would have been overcome in short order thus leading to distance shrinking travel, however the best was to come…
In 1989 the HOTOL co-creator Alan Bond formed a company called Reaction Engines Limited (REL). Learning from previous development, REL began developing a successor to HOTOL with the previous technical issues eventually being solved and more innovative development introduced.
The result decades later is the Skylon space plane, which if it continues with the succesful development so far, will achieve what HOTOL was suppose to do and even more. It would be a space plane more advanced than the Space Shuttle, not needing to be attached to a large expensive rocket as the Shuttle had to be. Skylon would take off and land on a normal runway using its own inbuilt dual propulsion system consisting of an advanced jet engine and rocket propulsion in order to achieve a speed of Mach 5 (3691 mph/5 940 kph). A journey from Britain and Europe to Australia would take about 4 hours.
Also when Skylon reached and altitude of 26 miles (42 kms) into the sky, the rocket propulsion would then be engaged to push the space plane into orbit where it could perform the functions of the Space Shuttle before retuning to earth. Unlike the unpowered Shuttle, Skylon woud have it’s own jet engine and be able to fly (and not have to glide like the Shuttle) to landing on a runway. The payloads it would carry could be delivered into space at a fraction of current costs. This would open up access to space on a much larger scale than having to use and rely on large costly rockets and remote launch sites.
Skylon could be prepared and reused in a two day turnaround and could be used at least 200 times in its operational lifetime. As with HOTOL, development and evolution of Skylon would continue.
The major problem dealing with the intense heat entering the jet engine at hypersonic speeds has been solved with innovative heat exchangers that rapidly cool super hot air allowing maximum thrust to be maintained by the Sabre engine.
In November 2012, REL based in Culham, Oxfordshire, ran a series of tests on key elements of the Sabre propulsion system under the independent eye of the European Space Agency (ESA), who afterwards confirmed that all the demonstration objectives were met. More investment is needed and will surely come even from the British Government! REL are confident other investors seeing the enormous potential would be also interested.
I would hope that if Skylon flies commercially, it’s air fares for passengers would eventually be cheaper than the innovative British -French Supersonic (SST) Concorde. While being the first commercial plane to travel at twice the speed of sound (Mach 2) carrying 300 passengers, it was not truly a commercial success due to running costs, high fares only the wealthy could afford. A bad crash in 2000 added to falling passenger numbers. Main airline companies wanted bigger aircraft to expand First and Business Class for subsonic travel, so concorde was retired in 2003 after 27 years service.
If Skylon development reaches maturity and it becomes a viable mode of hypersonic travel, an incredible and exciting future for both space and terrestrial travel appears to be getting nearer. It would be like the evolution from early propeller driven aircraft to the jet engine.
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.
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.
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.
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
|Maximum Payload Mass||12,000kg|
|Maximum Take-Off Mass||275,000kg|
Two decades of research work has resulted in technological leadership in the areas of:
- Ultra-lightweight heat exchangers
- Advanced rocket nozzles
- Combustion chamber design
- Contra–rotating turbines
- Lightweight airframe structures
- Robust lightweight thermal protection systems
- Engine and vehicles analysis software tools