Skylon space plane gets a thumbs-up (images)

A space plane that can take off and land from conventional runways is one step closer to reality.

Following a series of meetings in September 2010 at the International Space Innovation Center in Harwell, U.K., to look at the feasibility of a Reaction Engines design for a new generation of space-flight vehicle, the European Space Agency recently approved the Skylon vehicle and the SABRE (Synergistic Air-Breathing Rocket Engine) engine design for initial prototype development.

The meeting at which approval was given brought together nearly a hundred experts from Europe, Russia, the U.S., South Korea, and Japan to examine the technical and economic prospects for the new hybrid Air-Breathing-and-Rocket-Propulsion technology for future space planes.

The premise of the propulsion system is to develop a single-stage, fully reusable launch vehicle with short turnaround time and a flexible design capable of varied mission operations, including human transportation, cargo payload, and scientific missions.

According to Reaction Engines Limited, delivering payloads into orbit could drop from $15,000 per kilo to less than $1,000--vastly reducing the price of delivering payloads, such as telecommunications satellites, into orbit.

The single stage to orbit (SSTO) winged space plane's unique operation hinges on its reusability giving Skylon routine, low-cost access to space.

The vehicle has a gross take off weight of 275 tons, of which 220 tons are propellant, and is capable of placing 12 tons into an equatorial low Earth orbit. Additionally, the vehicle is capable of takeoff and landing on conventional runways, making it useable within existing flight infrastructures.

Challenges of the air and rocket hybrid design include the extremely high temperatures the vehicle would encounter at high speeds. The SABRE engine will have to operate with gases at temperatures of more than 1,000 degrees flowing through its intake.

The hot air will be cooled prior to being compressed and burnt with hydrogen by a unique system--a precooling heat-exchanger that will instantly cool the gases entering the intake to minus 130 Celsius.

The hydrogen-powered aircraft would take off from conventional runways and accelerate to Mach 5.4 at 26km using atmospheric air before switching the engines to use the internal liquid oxygen (LOX) supply to launch into orbit.
Reaction Engines Limited says the Skylon vehicle program is commercially viable, able to operate at profit and without subsidies while repaying development and production costs and with a lower price to orbit ratio than standard Expendable Launch Vehicle (ELV) launching systems.

Transition from air breathing to rocket mode occurs at about Mach 5 and at 26km, after which the vehicle climbs steeply out of the atmosphere to minimize drag loss.

The aspect of launch frequency and the ability for a quick turnaround before the next launch has important impacts on the design and is one of the factors that will heavily influence the economic model.

Skylon is being designed to achieve goals of more than 200 flights per vehicle over its lifetime and with a remarkable two day turnaround from landing to the next launch.

Because time spent in the hangar for maintenance and preflight launch preparations affects the frequency of flights and cuts into launch time, a short turnaround time means more flights and increased economic efficiency.

With a length of 90 meters, the fuselage of Skylon is expected to be a carbon fiber composite. It doesn't need to carry as much fuel as other designs, so it won't need disposable stages. Large and light, Skylon has the advantage of a reduced ballistic coefficient, thus reducing the heat stress on the vehicle on reentry.

The outer layer of the vehicle will reach only 1,100 Kelvin on reentry, in contrast to the space shuttle, which is heated to more than 2,000 Kelvin. This lower stress means the vehicle will not need a delicate silica thermal protection system and can instead use a thinner and more durable reinforced ceramic outer skin.

Following the review, the report released by the European Space Agency on May 6, 2011, backed continued development of the Skylon design for initial testing. The report stated that "the overall concept and structural design work undertaken by REL does not demonstrate any areas of implausibility, given the relatively benign environment of the flight trajectory. It is believed that concept maturity in this area can be achieved rapidly through sophisticated CAD and FEM analysis, CFD modelling, and subscale tunnel tests."

Many years of research and development are still needed in order to achieve flight, but with the backing of initial private investment, and the green light for continued development by regulatory commissions, Reaction Engines Limited is in a position to revolutionize commercial space flight.