Wednesday 25 January 2012

Reaction Engines Skylon and SABRE

Just been to a really interesting talk by Richard Varvill of Reaction Engines Ltd at the IMechE. It was really interesting and got me really excited.

Reaction Engines Ltd are a UK company who are developing a spaceplane called Skylon. Skylon is a Single Stage To Orbit (SSTO), unmanned, reusable and low-cost (comparable with today's expendable solutions) vehicle, with the intention of being a simple to use solution to putting hardware in low Earth orbit.

To achieve a SSTO vehicle (which has not been done to date) a special kind of engine is required, one that has not been made before or anything similar. Conventional vehicles achieving orbit today use rocket engines for the entire flight, as these work in both air and vacuum as they have their own supply of oxygen (oxidiser in the form of liquid oxygen carried in a tank with the vehicle). They also, importantly, provide thrust when the vehicle is not moving. The biggest problem trying to send a vehicle from stationary to orbit (0 - Mach 25) is the amount of fuel you need to start off with. Fuel for a rocket engine consists of a fuel, e.g. liquid Hydrogen and an oxidiser, e.g. liquid oxygen. These can burn together regardless of the atmosphere, or lack of, surrounding them. But, carrying enough fuel and oxidiser for the whole flight is both heavy and expensive.

So some way of making an engine that did not require carrying both the fuel and oxidiser with it for the entire powered flight was needed. Also, the propulsion would have to cope with the fact that it would be transitioning from ~1 bar atmospheric pressure (i.e. being in the air) to a vacuum when it left the atmosphere and approached orbit.

Founder of Reaction Engines, Alan Bond designed a Liquid Air Cycle Engine (LACE) engine which became the Rolls Royce RB545. This design has been taken by Reaction Engines and evolved to become the new SABRE engine for the Skylon.

I won't try and go into detail or replicate what can be said better on Reaction Engines' website, but basically, it is a combined air-breathing engine / rocket engine. From stationary to about mach 5.5 it is an air-breathing engine, using the oxygen in the atmosphere to burn with the hydrogen fuel. Then as altitude increases and the atmosphere starts getting too thin, it transitions into a conventional rocket engine, burning liquid oxygen and hydrogen from tanks on board.

The key stages are:
  1. Air is taken into the engine. At mach 5.5 the temperature of the air once it is taken in can be up to 1000°C
  2. The air is passed through a heat exchanger, called a pre-cooler, where it is cooled (using a closed loop helium system) down to -150°C
  3. Compressed to ~150 bar
  4. Fed into the rocket combustion chamber and mixed with the liquid hydrogen fuel to then burn and exit as hot gas out the nozzle.
  5. Air pressure drops as altitude increases and at about mach 5.5 the air-breathing part of the engine effectively deactivates and the on board liquid oxygen starts to be fed into th combustion chamber instead to complete the flight to orbit.
Benefits are that it is a single engine which can make use of the oxygen in the air whilst at low altitudes, therefore it does not need to carry the liquid oxygen that it would otherwise need for the first part of the flight. This reduces weight and cost. Cost would be more for extra liquid oxygen and the bigger tanks and therefore bigger vehicle to accommodate it.

I really love the fact that this is happening in the UK. I always dreamed of working in rocket science but would never get the chance to work for NASA. But here is something happening not far away from me, which is really exciting. I hope this project works and is successful and I will be following its progress and looking forward to seeing first flights (although I think these may be at least 15 years away unfortunately).

Here's a video of Richard Varvill talking about the SABRE engine.

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