Saturday, May 28, 2011

SKYLON Spaceplane, Heir To Space Shuttle, Gets ESA & UK Okay for Further Development

The UK Space Agency’s SKYLON technical assessment which was produced by the European Space Agency (ESA) has concluded that there are no significant barriers that would prevent successful continued development of the SKYLON Spaceplane.

Artist's impression of the SKYLON spaceplane taking off from a runway.
Artist's impression of the SKYLON spaceplane taking off from a runway. Credit: Reaction Engines Ltd
Credit: Reaction Engines Ltd

The report states that: Success on future engine test would mean "a major breakthrough in propulsion worldwide"

Artist's impression of SKYLON in orbit.
Artist's impression of SKYLON in orbit. Credit: Reaction Engines Ltd
Credit: Reaction Engines Ltd

The engine and vehicle can be developed with "today's current technology"

Reaction Engines will conduct an important demonstration of the engine's key pre-cooler technology later in the summer.

SKYLON is an unpiloted, reusable single stage to orbit (SSTO) spaceplane that will provide reliable access to space and be capable of delivering payloads of up to 15 tonnes into Low Earth Orbit (LEO, approx. 300km) at about 1/50 the of the cost of traditional expendable launch vehicles, such as rockets. SKYLON’s SABRE engines use liquid hydrogen combined with oxygen from the air at altitudes up to 26km and speeds of up to Mach 5 before switching over to on-board liquid oxygen for the final stage of ascent.

Artist's impression of SKYLON after landing.
Artist's impression of SKYLON after landing. Credit: Reaction Engines Ltd
Credit: Reaction Engines Ltd

The UK Space Agency’s commissioned report concluded that ‘no impediments or critical items have been identified for either the SKYLON vehicle or the SABRE engine that are a block to further developments’. 

Dr David Parker, Director of Technology, Science and Exploration at the UK Space Agency, said, "Both SABRE and SKYLON are exciting new technologies which could transform access to space. ESA's positive assessment should give everyone increased confidence that Reaction  Engines are on the right track. We are looking Engines are on the right track. We are looking forward to the upcoming technology tests with interest.”

The UK Space Agency’s technical assessment process was comprised of two parts. The first was a series of visits by technical experts from ESA to review Reaction Engines’ designs and witness critical tests of component performance.

The second part was the SKYLON System Requirement Review, held on the 20th and 21st September 2010, at which almost 100 international aerospace experts posed questions and made comments on SKYLON’s technical and economic feasibility. “The review ended with a consensus that no technical or economic impediments to the development of SKYLON or SABRE had been found.” 

Reaction Engines consider the review a success, and its spaceplane is attracting renewedintere st from the international aerospace community.

Alan Bond, inventor of the SABRE engine and Reaction Engines’ Managing Director, commented:  “Space has many things to offer humanity, but the sheer expense of rockets - which have served us well in the past - is inhibiting the growth of commercial activity in space.  To take one example, SKYLON promises to cut the cost of launching communication satellites, on which the digital revolution depends, by an order of magnitude. SKYLON will be fully commercial to operate and develop - generating jobs and investment for UK plc. We are delighted that this independent report from the UK Space Agency expresses confidence in SKYLON."

A Hybrid Air-breathing / Rocket Engine, SABRE Represents a Huge Advance over LACE Technology.

In the past, attempts to design single stage to orbit rockets have been unsuccessful largely due to the weight of oxidiser such as liquid oxygen. One possible solution to reduce the quantity of oxidizer that a vehicle is required to carry is being able to use atmospheric oxygen in the combustion process. The SABRE engine achieves this with its two modes of operation: its air-breathing and conventional rocket capabilities. This is made possible through a synthesis of elements from rocket and gas turbine technology.

Skylon vehicle detailed design for the passenger module, which could be swopped out for a payload module. Narrated by Brian Blessed.

Though the SKYLON has primarily been designed to launch satellites, consideration has been given to its passenger carrying capabilities. SKYLON is basically a hypersonic aircraft with hybrid engines, changing their mode of operation as the vehicle leaves the atmosphere. On return, because it is an aircraft, it has a cross range capability and ends its flights by landing conventionally on a runway.

The SKYLON payload bay is 12.7m long, 4.6m wide and 4.6m high. During normal satellite delivery operations, the bay would carry an interchangeable payload container. When used for passenger transport, an alternative pressurised, self-contained module could readily be fitted between flights. This module would provide a breathable atmosphere and additional life support for 30 or 40 passengers. Under the floor of the cabin, part of the space is needed for life support equipment, with the rest available for passenger baggage and cargo.

The central feature of the module is the transfer airlock, used for docking to a space station and for in-orbit transfer between vehicles. Normal ground access is by means of two side doors in the module, which line up with doors in the exterior of the SKYLON fuselage. Passengers would enter and exit using normal airport airbridges.

In case of a ground emergency, e.g. runway overshoot, passengers would exit the cabin through these doors and make their way to the ground by conventional inflatable chutes. The cabin also has two toilet cubicles, operating along the lines of those found on the Russian 'MIR' space station.

It would be possible to incorporate windows in the 'roof' of the module. During ascent and descent, the payload bay doors would be kept closed, but during the coasting ascent and while in orbit, the payload bay doors would be opened and SKYLON rolled 'upside down', providing views of the Earth. While not strictly necessary, windows would possibly reduce the symptoms of space sickness by providing a spatial reference, and of course, the views would far surpass anything that could be seen on a screen. These windows would need to be of a triple layer design, such as those found on the Space Shuttle.

Acceleration (G-Force) experienced by the passengers needs to be considered. It has been shown that it is possible to adjust the ascent profile in such a way that acceleration effects would be no more extreme than those felt on a modern fairground ride, and would not pose a problem for a typically healthy and fit person. Effects felt during the descent phase would be even less extreme.

The SABRE Engine
The design of SABRE evolved from liquid-air cycle engines (LACE) which have a single rocket combustion chamber with associated pumps, pre-burner and nozzle which are utilised in both modes. LACE engines employ the cooling capacity of the cryogenic liquid hydrogen fuel to liquefy incoming air prior to pumping. Unfortunately, this type of cycle necessitates very high fuel flow. 

Credit:  Reaction Engines Ltd.

These faults are avoided in the SABRE engine, which only cools down the air to the vapour boundary and avoids liquefaction. This allows the use of a relatively conventional turbo compressor and avoids the requirement for an air condenser.

The SABRE engine is essentially a closed cycle rocket engine with an additional pre-cooled turbo-compressor to provide a high pressure air supply to the combustion chamber. This allows operation from zero forward speed on the runway and up to Mach 5.5 in air-breathing mode during ascent. As the air density falls with altitude the engine eventually switches to a pure rocket propelling SKYLON to orbital velocity (around Mach 25).
Simplified SABRE Cycle

Air collection is via a simple conical two shock inlet with a translating centrebody to maintain shock-on-lip conditions. The centrebody moves forward to close the inlet for re-entry. A bypass system is used to match the variable captured air flow to the engine demand. This bypass flow is reheated in order to recover the momentum lost through the capture shock system.

The thrust during air-breathing ascent is variable but around 200 tonnes. During rocket ascent this rises to 300 tonnes but is then throttled down towards the end of the ascent to limit the longitudinal acceleration to 3.0g.

Credits: Reaction Engines Ltd.

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