Skylon ‘spaceplane economics stack up’

[EC]

It appears a feasible proposition, economically. That is the conclusion of a study that considered a European launch service based on a Skylon re-usable spaceplane.

The report, commissioned by the European Space Agency (Esa), was led by Reaction Engines Limited (REL) of Oxfordshire with help from a range of other contractors such as London Economics, QinetiQ and Thales Alenia Space (TAS).

It looked closely at how an operator of the UK-conceived vehicle might meet the demands of its market.

Those requirements would be primarily to loft big telecoms satellites high above the equator of the Earth, but also to put smaller, Earth-observing spacecraft in Sun-synchronous orbits (a type of orbit around the poles). These are the sorts of jobs the Ariane 5 rocket does today, and which Ariane 6, currently under discussion among European governments, may do from the early 2020s onwards.

Skylon is not in that discussion space at the moment - but it may get there at some point in the future if further technical studies prove positive and the financing can be found to push the concept forward.

The Skylon-based European Launch Service Operator (S-ELSO) study examined some of the hardware the vehicle would need to place satellites in orbit, and aspects of the economic model that would allow the operator to turn a profit. It even looked at how the vehicle could work out of Kourou in French Guiana - Europe's spaceport.

In all the areas the study considered, it found positive outcomes. The report was intended to provide Esa with the information it needs to help evaluate what would be a completely different way for Europe to go about its launcher business.
Skylon D1 To get telecoms satellites in position, Skylon would deploy a re-usable upper-stage propulsion unit

For starters, Skylon is nothing like the conventional rockets that Europe uses today. Skylon would operate like an aeroplane, taking off from, and returning to, a standard runway.
Ariane Traditional rockets dump exhausted boosters and propellant tanks as they ascend

Its technological trick would be its novel propulsion system - power units that work like jet engines at low altitudes and slow speeds, but then transition to full rocket mode at high altitudes and velocities in excess of five times the speed of sound.

This approach, if it can be made to work, would reduce that fraction of the vehicle's mass that must be carried as propellant, enabling the vehicle to take a practical payload to orbit in a single leap.

Although expensive to develop - think of a new Airbus design - it ought to be a good long-term investment because - again, like an Airbus - a Skylon is designed to be used over and over again. Today's rockets can be used just the once.

Indeed, the aviation model is a good one, because the idea as currently envisaged is that there would be a vehicle manufacturer (like an Airbus or a Boeing) that would sell Skylons to many operators (space equivalents of BA, Air France, Lufthansa, etc).

Via the BBC. More at link. http://www.bbc.co.uk/news/science-environment-27591432


Ram rocket engines are not exactly new technology. Rolls Royce developed a highly successful engine in the mid 70's. It tested out perfectly, but the UK space program got put on indefinite hold.

[massadvj]

Its technological trick would be its novel propulsion system - power units that work like jet engines at low altitudes and slow speeds, but then transition to full rocket mode at high altitudes and velocities in excess of five times the speed of sound.



https://www.youtube.com/watch?v=YUU2amJmtO4

[Oceander]

*  *  *

Ram rocket engines are not exactly new technology. Rolls Royce developed a highly successful engine in the mid 70's. It tested out perfectly, but the UK space program got put on indefinite hold.

It's not a ramjet (or a scramjet).  Initially it operates as a normal jet; as it reaches very high velocities - speeds at which regular jets fail because the incoming air gets too hot as it's compressed - it first compensates for that heat by using a "precooler" to keep the incoming air cool enough to be used, and finally once its speed becomes too great for even a precooled jet to work, it closes the external air intake and starts using its onboard liquid oxygen supplies.

The weak link, technologically, at this point appears to be the precooled stage because the necessary technology has just been developed and thus has a lot of room for surprises and failures to crop up until it becomes a more mature technology.

That being said, it sounds like a doable idea that's worth doing, or at least attempting.  And if the British can pull it off, then kudos to them!

[EC]

The only thing that really worries me about this design is the intakes. When you de-orbit you are coming in fast and hot, and the intake edges are going to be glowing like burning magnesium from the friction.

[Oceander]

The only thing that really worries me about this design is the intakes. When you de-orbit you are coming in fast and hot, and the intake edges are going to be glowing like burning magnesium from the friction.

True, which suggests that the engines would continue to operate with onboard lox until the velocity dropped to the point where outside air coming in through the intakes could be cooled sufficiently to let the engines perform adequately as jet engines.  On the other hand, given the altitude at that point, it might be possible to in effect use the engines as giant airbrakes by opening up the air intakes and allowing the turbines to work hard at compressing the hot air - the resulting combustion could be largely used to generate the force needed to turn the turbines rather than providing thrust to the aircraft (which is, after all, the effect that makes the jet engine inefficient when air intake temperature is that high) to slow the entire craft down to the point at which the engines can again begin to perform well enough to provide thrust to the aircraft rather than simply turning the turbines.  Basically something akin to the regenerative braking systems used in some hybrid autos, where the resistance caused by using the rotation of the wheels to generate an electric current slows the auto down just as a conventional braking system would.

[EC]

Ah - I see. Use the speed and air pressure to spin the turbines up to speed, without starting the fuel pumps. Introduce fuel at those sorts of temperatures and you are going to lose a wing or two.

Have to be one hell of a pilot to do that, but yes, it is doable. Fighter pilots have done the same before now in a flame out situation. Dived like hell to get the turbines up to speed and basically bump start the aircraft. Not exactly encouraging for any passengers though!

[Oceander]

Ah - I see. Use the speed and air pressure to spin the turbines up to speed, without starting the fuel pumps. Introduce fuel at those sorts of temperatures and you are going to lose a wing or two.

Have to be one hell of a pilot to do that, but yes, it is doable. Fighter pilots have done the same before now in a flame out situation. Dived like hell to get the turbines up to speed and basically bump start the aircraft. Not exactly encouraging for any passengers though!

Which is a good reason why this craft is unmanned.

I'm not really thinking of using speed to jump-start the engines, but more of using the engines to slow the aircraft down in much the same way that a jake brake slows a tractor-trailer down by causing the engine's compression to retard the vehicle's speed.  In this case, because a jet engine isn't a reciprocating engine, I don't think it would be wise to shut the engine down completely and let it free wheel because that would, I think, result in the turbine shaft being rotated in the opposite direction.  However, due to the work required to compress the extremely hot air in the intake, feeding in just enough fuel to keep the turbine shaft rotating in the correct direction would effectively result - I would think - in increased air resistance/drag not through friction of the skin against the air but through the increase in air pressure at the front of the engine without a corresponding increase at the back of the engine sufficient to overcome that forward pressure.  It's quite possible that this would be infeasible/dangerous if it generated too much turbulence, but I don't have the aerospace/fluid dynamics background or the maths needed to work that out.

[EC]

I got curious and asked Dad to have a look at the article and this thread - he spent 40 years designing engines for Rolls Royce. Turbines can only spin one way, it's the way they are built, and why thrust reversers are a clamshell design that forces the thrust though forward opening gates.

He did raise a couple of points I never thought of. Onboard power is going to be a huge issue. Most craft have a generator attached to the turbine shaft to keep the batteries topped off, and the voltage fluctuations are evened out by a regulator. It is doable because you have a limited and predictable range of shaft speed in the turbine itself. The current use of a slip clutch is going to have to be completely redesigned to take into account the wildly variable shaft speeds.

Engineering of the combustion chambers is going to be a complete bear. Obviously they have done it, since the engine is on test now, but he's puzzled as to how. The geometry for the two types of chamber (forced air and rocket) are completely different.

And one thing that really does concern him - it's basically a big drone. Are computers powerful and effective enough to handle de-orbit on their own? There is a stage in any re-entry where you simply lose radio contact for a bit.

He's having fun now though - Mom says he's got his pad and pen out and is busy designing, for the first time since he retired! 

[Oceander]

I got curious and asked Dad to have a look at the article and this thread - he spent 40 years designing engines for Rolls Royce. Turbines can only spin one way, it's the way they are built, and why thrust reversers are a clamshell design that forces the thrust though forward opening gates.

He did raise a couple of points I never thought of. Onboard power is going to be a huge issue. Most craft have a generator attached to the turbine shaft to keep the batteries topped off, and the voltage fluctuations are evened out by a regulator. It is doable because you have a limited and predictable range of shaft speed in the turbine itself. The current use of a slip clutch is going to have to be completely redesigned to take into account the wildly variable shaft speeds.

Engineering of the combustion chambers is going to be a complete bear. Obviously they have done it, since the engine is on test now, but he's puzzled as to how. The geometry for the two types of chamber (forced air and rocket) are completely different.

And one thing that really does concern him - it's basically a big drone. Are computers powerful and effective enough to handle de-orbit on their own? There is a stage in any re-entry where you simply lose radio contact for a bit.

He's having fun now though - Mom says he's got his pad and pen out and is busy designing, for the first time since he retired! 

glad he's having fun.  i'm keen to see what sort of results he comes up with.