Reusable in theory
but I suspect that the truth is that it will need significant overhaul after each flight - bit like a highly-tuned racecar engine.
Just refuelling and taxying back out sounds unlikely to me.
A British firm seeking to build a radical spaceplane – the Skylon – able to fly to orbit from a runway takeoff without any jettisoning of fuel tanks or boosters says that it will test its main technical special sauce this year. The announcement was made at a spaceplanes conference in California last week. Roger Longstaff, …
Haven't we been here before? The US decided to build a reusable space shuttle. They got it to work, but discovered that it needed a LOT of maintenance between flights - so a space shuttle launch costs a lot more than an expendable rocket. And saving money is the whole point of making a spacecraft reusable.
I bet the expendable SpaceX rockets will be cheaper than the "reusable" Skylon.
(And yes, I know the space shuttle is only mostly reusable - the shuttle and boosters are reusable but the external tank is replaced each time. My point still stands).
"The US decided to build a reusable space shuttle. "
NASA needed something to keep its research centres occupied. Shuttle was the only part of the programme Nixon permitted.
"but discovered that it needed a LOT of maintenance between flights"
Hardly The budget profile virtually *guaranteed* they'd sacrifice maintainability and operations costs over up front costs from day 1. The only "discovery" might have been that bonding a ceramic with 1/3 the thermal expansion coefficient of aluminium and then giving the sandwich a 1000c temperature gradient *might* cause a bit of a problem.
"And yes, I know the space shuttle is only mostly reusable "
No. The space transportation system is mostly *refurbishable" with lots of work.
Most of what you "know" is incorrect. What you don't know is also substantial.
You might find a bit more history would be useful.
"The problem with the Shuttle was that it was never really developed beyond it's original configuration."
" Not that it was actually a bad idea to start with"
The idea of a *reusable* (as in minimal maintenance, refuel, replenish and reload another payload then launch) is a good idea.
It's *implementation* was a *very* bad idea.
Early jet engines - and I'm talking about those in series production, not just prototypes - had lifetimes of the order of 10 or 20 hours before needing refurbishment. Given how few "refurbishable" space planes we've had so far (there have been two prototypes: the Shuttle and Buran) I don't think that we can discount the entire concept yet merely because of being refurbishable as opposed to reusable.
You have to start somewhere! I remember being rather disappointed when the Shuttle was rolled out and pointed into the sky attached to three huge rockets to get a supposedly reusable space plane aloft. But then that was a start as well, we now know how to fly from space to ground in a controlled manner. All we need to do now is to fly into space as well and we're done!
1. Initially it will be unmanned, so the checks required are reduced compared to say the shuttle.
2. It's much smaller and other than the engines, less complex than the shuttle. e.g. no life support.
3. No parts have to be recreated to make it ready for launch.
4. It shares more in common with an airplane than a typical rocket.
Reaction engines are claiming a 2 day turnaround.
You are almost certain to be correct (+1).
However, the harrier had the same problem - its was initially so weak it could barely VTOL/VSTOL itself on an empty tanks, never mind try it with full tanks, and full pylons (ie militarised).
Admittedly, even the last GR7 still can't VTOL with a full load, but it's way better than the initial prototypes...and few percent heavier than the prototypes (even after going with a carbon fibre wing).
They'll find a way, I'm sure. Glass half full an' all that.
You can't comment on a technology when you don't understand it.
Oxygen-Hydrogen rockets are not more powerful than Oxygen-Kerosene. In fact the latter are generally preferable for their larger "get you off the ground" thrust. The former are more efficient in terms of thrust per kg. of fuel burned, that quantity known as "specific impulse". This in turn is because the product molecules, water, are lighter than those from carbon-based rocket fuels, resulting in a higher mean gas velocity at a given exhaust temperature. Note that the Shuttle required (I guess the past tense is more appropriate now) high-thrust but low efficiency solid rocket boosters to get it to the point where the various boost factors meant that the oxy-hydrogen SSME could actually lift the assembly against gravity.
I hope the "chill out" technology doesn't slow down the incoming oxygen atoms to any great degree. There is definitely going to be some energy transfer to the cooling apparatus. How do they intend to counter the drag from doing what they do to the incoming air?
Discarding "pieces of technology" actually makes sense if the technology costs less than all the extra stuff needed to make the payload carrier re-usable.
And in the end, what is the point of "coming back in one piece"? Getting to orbit is hard, getting down is a lot easier, since the atmosphere is helping. You can do it in a capsule, which ought to be the preferred method.
How about some technology that gets a big load into orbit and leaves it there?
If you just want to send material into orbit then I would have thought something like a really big magnetic linear accelerator would do the trick right peachy. Build in in somewhere like Utah where it can easily be kilometers long and if you only shoot it at night then you can take advantage of all the surplus electricity generating capacity.
"You can't comment on a technology when you don't understand it."
Excellent advice. Rarely taken in practice.
"I hope the "chill out" technology doesn't slow down the incoming oxygen atoms to any great degree."
That's *exactly* it's objective.compressors work best at about 1/3 to 1/5 the speed of sound. Cooling the air "shrinks" it and allows the compressor to only need to operate well over a *relatively* narrow air speed, rather than the full M5+.
"There is definitely going to be some energy transfer to the cooling apparatus. "
Which is used to drive the compressor fan and the Hydrogen turbo pump in the first place.
"How do they intend to counter the drag from doing what they do to the incoming air?"
By doing it to as little air as possible at any stage of the flight. The inlets close as it speeds up and the rest is bypassed around the engine. Rather like the J58 installation on the SR71 in fact.
"Discarding "pieces of technology" actually makes sense if the technology costs less than all the extra stuff needed to make the payload carrier re-usable."
And you don't mind needing a massive firing range to deal with discarded parts falling out of the sky and/or you don't design *in* reusability from day 1.
"And in the end, what is the point of "coming back in one piece"? "
Eliminating the costs of recovery and re-integration. But that only counts if you're reuseable. Keeping the tanks (*especially* if they have LH2) makes for a large but "fluffy" vehicle with *very* low mass per unit area. This (in principle) give a slow relatively low temperature descent, it's also how some of the Shuttle's internal tanks survived to the ground in 1 piece during the last Shuttle breakup.
"Getting to orbit is hard, getting down is a lot easier, since the atmosphere is helping."
You've either got that backwards or severely underestimate the re-entry problem. consider how many countries have launch vehicles (up mass) versus how many have down mass capability in *routine* use.
You can do it in a capsule, which ought to be the preferred method.
You can do it in a capsule and historically it *has* been done in a capsule.
Except for the Shuttle, which wasn't.
Shuttle is the *only* data point of the winged landing type (Except for the sole Buran landing) to have flown repeatedly. With one data point you can extrapolate *any* curve you like.
http://en.wikipedia.org/wiki/Project_Daedalus and it's close relative Orion which showed that there IS a way to get lots of stuff to orbit - very efficiently in fact. You launch it with atomic bombs, and it's more efficient the more you launch, with talk of ships up to 8,000,000 tons.
Or of course what you really need is a space elevator:http://en.wikipedia.org/wiki/Space_elevator which is being developed by these guys: http://spaceelevatorconference.org/default.aspx amongst others.
Because it is. It disappeared because technical problems appeared with the engine design that needed to be fixed before it could be built.
Solutions to those were found a few years ago and also resulted in a redesign of the spaceplane too - hence Skylon.
Shame Tomorrow's world is now so dummed down that it is completely unwatchable!! - sigh.
Well keep in mind it's tail is at the front (twin canards) and I'm not sure if RE have ever said what the wing profile actually is, although the choice does seem limited.
Being a launch vehicle rather than a fighter compromises to improve maneuverability in a dog fight are not an issue.
They have said Skylon (unlike the Shuttle) is designed to be stable and not require active computer control
Note also that the C1 design (which this is) is being revised.
If they can't hit their weight targets, which is quite challenging for a single stage to orbit vehicle, the fallback is to go nearly to orbit with the Skylon, say 90%, and then eject the cargo with a small rocket attached. Pushing 10 tons of cargo through 800 m/s of velocity would require about 3 tons of fuel, so we are talking about a pretty small rocket. That is not as elegant as going all the way with one vehicle, but it gets the job done
If you don't have billions to spend on development, a Space Cannon can be demonstrated for about one thousandth the cost of the Skylon (15 million dollars). That would get a very small payload to orbit to demonstrate the idea works, after which you would build a larger bore gun to deliver useful size cargos. No, it is not useful for carrying people, but a lot of other things can stand 1000 g's just fine. For comparison, that is 1/6 of the acceleration of a modern artillery piece. Also a big f**king gun is just cool.
They've already done work on a cargo adaptor that they call a skylon upper stage. It's more of an inner stage really, but it ought to do the job in theory.
If they do find themselves in need of extra oomph, a better place to start would be to add disposable takeoff engines. Even with their funky pressure-adaptable expansion nozzles for efficient use at all altitudes, a runway takeoff with a rocket engine is inefficient.
A low altitude booster stage doesn't necessarily have to ruin their model, so long as it is extremely cheap and simple to install - preferably so cheap as to be trivial by airline standards and capable of being hauled around by forklift.
To achieve orbital velocity 17,500mph (LEO, Mach 25), launching from the surface of the earth it would need to go much faster due to aerodynamic drag, say Mach 30.
At Mach 25 or 30 no material would be able to withstand the temperatures induced due to the aerodynamic drag and would destroy the craft before it go anywhere near orbit.
"To achieve orbital velocity 17,500mph (LEO, Mach 25), launching from the surface of the earth it would need to go much faster due to aerodynamic drag, say Mach 30."
"At Mach 25 or 30 no material would be able to withstand the temperatures induced due to the aerodynamic drag and would destroy the craft before it go anywhere near orbit."
I was tempted to call troll on this but I think you misunderstood the animation.
First the fact Shuttle manages the process in *reverse* should tell you that with appropriate design and materials a vehicle can (and has repeatedly) survived this regime intact.
Skylon uses atmospheric Oxygen to accelerate to cM5. During that time it's climbing *continuously* and outside air pressure is dropping like a stone. Switchover to full rocket drive happens when it's *above* the bulk of the atmosphere.
It's not actually *flying* by aerodynamic lift. It continues to climb because it's kinetic energy is increasing and the equilibrium altitude where it is balanced by the Earth's gravity field is higher. Think Newton's analogy of a cannon on a mountain. A faster cannon ball is (on an airless planet) equivalent to a higher mountain. An *accelerating* cannon ball is like a cannon mounted on a continually rising platform.
"My reference was to the gun, i didn't emphasise this in the post."
My apologies for the suspected troll. *That* makes perfect sense.
That said IIRC the USAF at Holloman (home of the crash test dummy) did a rocket sled test that hit M5, but the last couple of M numbers were in a plastic tent filled with Helium to cut the drag. I think it was on a Discovery channel documentary. Impressive to watch but the tent was a write off afterward and I would not want to be *anywhere* near it once it started moving.
Adequate for getting a scram jet started but now you've got the *whole* atmosphere to get through without vaporizing the vehicle.
I like a big gun as much as anyone but the heating aspect is (I suspect) a bit under recognized as a problem by their supporters.
Railguns or other equivalent high G launcher's are great for very low atmospheric bodies, e.g. the Moon.
The other benefit on the moon, in addition to virtually no atmosphere and gravity is much weaker, so orbital velocity is lower.
But with the Earth it's just not practical for SSTO.
Now NASA has been looking at concepts that involve a rail launch first stage, to achieve say Mach 1 or 2, which is perfectly feasible.
If your idea of a big gun worked it would have been done by now. Remember as soon as the payload leaves the gun it will be subject to aerodynamic drag. IOW it will start to slow down as soon as it leaves the muzzle. So I invite you to calculate the muzzle velocity required for your capsule to be exceeding 17,500mph when it leaves the atmosphers.
Then you need to think about control, once the capsule gets out of the atmosphere it needs control to get it into the required orbit. You can't just shoot and hit the exactly the right orbit, the atmosphere is a bit unpredictable at times.
Finally there is the matter of safety control. The projectile needs to be controllable as soon as it's launched. How are you going to achieve that. We all know the space shuttle had emergency landing sites to cope should anything go wrong, so that it wouldn't just crash on Madrid if something went wrong in the first few minutes of flight. We also know about the remote detonation capability so that the whole shooting match could be blown up by some bloke near the launch site should something go seriously wrong after launch. How are you going to achieve that should your cannon turn out to be loose?
"If your idea of a big gun worked it would have been done by now. "
It hasn't been done before because explosive powered guns can't get the necessary speed. The hot gas produced by setting off chemical propellant does not expand smoothly at mach 20 - reaction product molecules are too large and so for any reasonable temperature range, they move too slowly, even if individual molecules are greatly exceeding the speed of sound.
There is a way to get around this, by heating pure hydrogen gas. It's a much lighter molecule, and so for a given energy and temperature range, the gas particles move a hell of a lot faster. All you need to do is heat up a reservoir of hydrogen to very high pressures and then release it behind your projectile - and this will get you the required speed.
The technology to do this without losing too much hydrogen to the outside world is still being developed, and is untested on a large scale, although it has been used for hypersonic engine tests to get very small scale models up to ignition speeds.
The way things work out, fuel costs are pretty minor, compared to the cost of building the vehicle.
Elon Musk is trying to reduce construction costs, essentially building hardware for mass production.
Skylon is aiming to reduce the per-flight hardware cost, by making the whole thing reusable.
Where Skylon might have an advantage is in how it might be able to land without reaching orbit. It's partly historical accident, launching from Florida, but the Shuttle had an awkward gap between being unable to return to KSC and being able to abort to a runway in (I think) Spain. Skylon isn't dropping bits off: it could launch from somewhere near Denver (that altitude is useful too) with abort runways across the USA.
There's a lot of details that could make a difference.
"It's partly historical accident, launching from Florida, but the Shuttle had an awkward gap between being unable to return to KSC and being able to abort to a runway in (I think) Spain. "
No. The Shuttle has various abort modes. They transition into each other. there is *no* gap. The most dangerous part of the flight are the roughly 2 minutes from launch to SRB separation. It's just assumed the stack stays together until they burn out. Note that most abort modes have *never* been actually tested (return to launch site or transatlantic abort for example).
BTW the integrated health management system NASA added to the Shuttle main engines allow throttle down, instead of just shutting the engine off. This down graded large portions of flight profiles from highly risky never been tried abort modes to to abort to orbit, which has and does work.
Not so, according to Elon:
-- -- Wikipedia Article: Falcon 9
-- -- -- -- http://en.wikipedia.org/wiki/Falcon_9
-- -- -- -- (1/4 of the way down)
-- -- Transterrestrial Musings: SpaceX Press Conference
-- -- -- -- http://www.transterrestrial.com/?p=27574
-- -- -- -- (near the bottom of the article, before the comments)
-- -- HobbySpace: Interview with Elon Musk
-- -- -- -- http://www.hobbyspace.com/AAdmin/archive/Interviews/Systems/ElonMusk.html
-- -- -- -- (near the top of the article)
Elon envisions the first stage of the Falcon 9 being fully reusable without a substantial impact on payload mass. He further indicates that the second stage could be also be reusable, but that making it reusable would most likely incur too steep a reduction in allowable payload mass.
However, since the bulk of a rocket's material launch cost (i.e., non-fuel/non-payload cost) is in the first (ground-launch) stage -- which is intended to be reusable -- the statement "must throw away huge amounts of expensive technology" would appear to be overkill, especially if it refers to the smaller and much less-expensive second stage.
More like an Avro 730, and the UK history makes this more likely.
The irony is that a one time Tory minister's claims about unmanned fighters/bombers look set to become true. Perhaps the Avro will come back to life.
We don't need no Steenkun Blackboid.
Max Faget's original DC3 design for the Shuttle orbiter which would have sat on top of an even larger winged booster. They'd have weighed nearly 2000 tonnes all up and taken off and landed horizontally. The DC3 would have had 11 SSMEs on the booster and another 2 on the orbiter.
It was canned once the USAF demanded a large cross-range ability and forced NASA to adopt a delta wing design. But in sheer Gerryandersonatiude it takes some beating - this might just be it.
But hold on - a 0.5mm shell on this beast - how robust would it be to bird strikes and the like?
The first is the light weight pre-cooler or "Fractal plumbing" heat exchanger, manufactured using specially developed production techniques (and possibly machinery).
The *very* special sauce is the frost control technology which stops the thing freezing the water vapor in the air into solid ice within a few seconds of it being switched on.
Frost control is *the* dirty little secret of all deeply pre cooled (SABRE) or liquid air cycle (LACE) systems like the one that Andrews Aerospace (Alchemist?) were developing which *must* be handled in order for them to function.
If this test is a full size pre-cooler *and* includes frost control it is a *major* milestone which (if the airflow is *anything* like realistic in terms of temp and pressure range) AFAIK this has *never* been done by any of previous attempts to do such a system.
I'll comment on Lewis's inaccuracies later.
"This has been "in development" longer than Duke Nukem Forever, and with less chance of success."
Probably on 1/10 of what DNF is spending on PR and lunches for journalists.
On a slightly more serious note it could be said that at this point they are *no* more successful than Lockmart with the X33.
IOW LM got $1.1Bn of US tax payers money to get there. Or rather to *fail* to get there.
RE have spent roughly 1/55 of that, mostly of private investment, to get here.
I have to give the effort a thumbs up.
If it works, great.
If not, then I hope that there are lessons learned and the concept continues.
As the author points out... the amount of start up costs are limited because they have to prove that key critical components must work prior to the rest of the aircraft being built.
The cool thing is that if these components work and others do not, its possible to redesign or to use these components in to other projects. Kelly Johnson was a freak of nature. Probably the first person to innovate the agile process too!
Good point. IIRC the design Skylon seems to derive from was developed post area rule.
However not that the area rule is most useful for vehicles that spend *most* of their time in the transonic (c0.9-1.1M ) range which is the worst for drag.
Note that if you're looking at how cross sectional area changes over length you need to take into the engine pods. You might also note that while *all* commercial airliners have to take this into account (since they all spend *most* of their time just below M1). You just don't see the distinctive "Wasp waisting" of earlier aircraft The rule can be met by quite subtle tweaks in detail design.
However Skylon *could* just ignore it and power through the sound barrier. It's a trade off. Launch vehicles *never* cruise. If area ruling the design lost them too much performance over more of the speed range (Orbital velocity is about M23) I'm sure they'd sacrifice it.
"The shape looks like its straight out of the 60's, and more than a little reminiscent of the SR-71."
Actually the planform looks like the AV Roe 730 M3 reconnaissance bomber of the 1950s (wing tip rather than mid wing engine pods and cannards rather than chines)
I'd guess the design team has better access to 730 design data than SR71.
Note they have stated they are planning a design review to "D" standard which might change things.
Out of the 60s yes, SR-71 no. Try the Avro 730 and look very carefully at the distinct similarity between them. The SR-71 has only a passing similarity.
Note; cancelled in 1957, and yes we could do these things if we wanted.
The Skylon should have an Apple logo on it, it just looks so much cooler than the other crap out there, just on this it deserves to be built.
I note the sabre engine also burns hydrogen and so is potentially emission free, not much being said about that but that does have an implication on conventional air travel which is a big polluter (does it not!)
Good on em for keeping trying, and taking a sensible staging approach to testing the technology personally after 30 years of this Reaction engines should work on the assumption there will be no help from UK PLC
What????!?!!!! Apple???? Never, not in trillion years. Apple is pretty yes, but that's about it! ;-)
On a more serious note, as far as developmental costs are concerned, this is subject to funding that increases as it jumps through the hoops. It is a very serious project and encouraged to be. I've been crossing my fingers about it for a few years now, and almost dread the interim reports and milestones, such as the one ahead.
This kit is very flexible and will dominate the skies for a while if successful. Imagine having instant rescue kit, or stuff that can flick up there to repair satellites, replace satellites, on demand. The future would begin there.
Those big red things at the start of the animation are the Hydrogen tanks. Its density relative to water is 7-7.7%, depending on how densified it is. It's big but *light*.
You might also check the *real* dimensions on this thing.
IIRC Takeoff and landing speeds are high. Part of their work has been designing a light weight braking system that borrows (of all things) from truck racing technology to use water cooled brake. Note the undercarriage weight is "light" relative to the *common* state of practice, not the state of the art. Landing gear weighing 1.5% of Gross landing mass (for airliners it's more like 4%) were flying in the 1950s and 1960s, specifically on the B58 Hustler.
As for "Barely manouvre" it depends how much you *need*. The tail fin + forward cannards should give aircraft like behavior but throttling the wing tip engines would give significant yaw capability. It might *look* a bit like an SR71 but conceptually its mission is *much* simpler. More or less in a straight line is fine.
Having designed a Freeze Drying Microscope taking samples down to -100C I can tell you from direct experience, the problem they face is ice. It is quite amazing just how much moisture there is in air. Moisture that will, instantly, turn into ice. Remember, when aircraft engines were first created, they had to fit heaters to their engine intakes to melt the ice as it formed..... or the engine would promptly fail.
They make no mention of what they are going to do about the ice that will, inevitably, coat the entire cooler system. Ice is their Achilles heel.
You're right and wrong, the secret to the machine's success is frost control.
It is mentioned on their website, but the technical details of this are deliberately kept secret, it is also the apparent breakthrough that they've made and will probably the main success condition of this test.
I've only commented on the bits I disagree with. The rest you can presume I go along with.
"Air is taken in at the front of the SABRE and almost instantly cooled down to the point at which it is almost liquid, using terrifically powerful freezer kit employing a liquid-helium loop."
And driven by a pair of oversize liquid Hydrogen tanks. A very cold thing makes a fairly warm thing substantially colder.
>>The supercold air takes the place of liquid oxygen in the combustion chamber, reacting with liquid-hydrogen fuel to produce thrust in much the same way as the space shuttle main engines. Heat sucked from the intake air is dumped into the fuel.<<
The amazing spaceplane is expected to be able to repay those big investment cheques, as it will be able to deliver payloads – admittedly, at first quite small ones of only 10 tonnes or so compared to its own substantial mass of 275+ tonnes – at low cost.
That's a payload which is c3.6% of GTOW. In the launch biz that's pretty good.
It's better than a Delta IV and on a par with an Atlas V. This counters the traditional whine that SSTO's can't deliver as much payload (as a portion of GTOW) as expendables.
The shuttle manages about 1.25% of GTOW. It has an SSTO payload fraction *without* the actual benefits of SSTO.
REL's engineers have been compelled to shave everything to the limit to produce a design which seems to show that SABREs and the fuel they need to reach orbit can fit into a re-entry-capable airframe along with some cargo.
In a word. No.
The ceramic aeroshell is to be just 0.5mm thick.
Slightly thinner than some part of the SR71 wing structure (which were *also* corrugated BTW).
Skylon's skin is only designed to carry the *thermal* load. Mechanical loads are carried by the geodesic truss framework. The technique was proposed for the X20 DynaSoar.
The undercarriage has had to be lightened too,
Below *common* state of practice, *not* state of the art as far back as the late 1958s (and not a CAD/CAM workstation in sight).
"so that a Skylon won't be able to land on just any runway"
Wrong. This thing might take off like Michelle McManus but it'll land like Britney Spears. Weather or not it'll be *allowed* to use ordinary airports, as it is technically a UAV, is something to be thrashed out.
" – it will need a special reinforced one able to cope with heavily loaded wheels moving rather fast."
On *takeoff* only.
If the craft itself should gain just a few per cent in fueled-up weight during the development process, this would wipe out its entire payload margin.
No. SSTO's are vulnerable to growth in the *dry* weight. In principle the wings make it *less* vulnerable in this area than vertical takeoff designs.
"There are those who would argue that operations using liquid hydrogen fuel will simply never be economical:"
Mostly they argue its a pig to handle. Liquid oxygen freezes out water on top of the insulation if it's not good enough. Hydrogen liquefies *Oxygen* out of the air.Insulation has to be *very* good. It's a PITA.
However *all* alt-space advocates agree the fuel cost is "In the noise".
The *real* cost is the manufacturing and "standing army" of managers, safety inspectors, managers of safety inspectors, document management team etc. Cost is strongly proportional to *complexity* and *weakly* proportional to size.
" the stuff takes up so much room that hydrogen aircraft – including the Skylon – are always made up mainly of fuel tanks."
*All* launch vehicles are mostly fuel tank.
" It is so troublesome, potentially dangerous and expensive to handle that it will infallibly destroy any business model based on it other than that of government-funded military or scientific projects."
Regarding RE's business model it's *strictly* for profit.
They build a vehicle. It's up to *other* people to operate it.
It's like building a taxi. Someone *else* operates it. If they don't make a profit *they* go out of business. Just like a *real* transport systems, not the insane 1 shot ticket-to-ride/govt cost++ system expendables foist on the users.
TBH there were a few moments when I was tempted to flag the article as Troll.
If this is Lewis on a subject I know something about what is he like on subject I don't know anything about?
<sigh> There goes my shot at the Reg spaceplane desk.
Due to the nature in which the engine works:
The second test that they have to endure is using the liquid oxygen to cool the engine.
Due to the inlet being cooled by the liquid hydrogen, the engine and nozzle assemblies need another source of coolant.
This is another reason for the need for cryogenic fuels and also why kerosene is not feasible as a fuel for this engine.
"Due to the inlet being cooled by the liquid hydrogen, the engine and nozzle assemblies need another source of coolant."
I'm not quite sure why they have mandated using air and Oxygen as the combustion chamber coolants and there is no reference on the simplified flow diagram for SABRE
However IIRC Oxygen cooled combustion chambers (might include using cooled air) were being investigated as part of the £6m from ESA. It was done by IIRC EADS Astrium in April 2010.
Or they could have asked NASA (unrestricted download) or Doug Jones of Xcor, both of whom have some experience of this. Xcor is probably the US aerospace company closest to RE in their approach to an orbital vehicle.
Sadly that would have enmeshed them with a US aerospace company (albeit not a *big* one) and ITAR. I'd love to know the legal position on designs that incorporate stuff you found out studying *freely* available NASA documents outside the US.
I'm quite sure RE know the best "simulator" when you're testing an engine component is a *working* engine. Build early, test early.
But that's what they can't afford. A test of full size precooler + frost control is presumably the last *core* component that has not been tested. I suspect a successful test will release substantially more funds. This would probably be the first *new* liquid rocket engine in the UK for 40 years.
BTW *most* common rocket engines use the fuel as a coolant *except* hypergolics (use NTO) and Hydrogen Peroxide (usual mass ratio is 6:1 so *plenty* available and it's got an SHC like water). This includes the Russian staged combustion engines like the RD180 powering the Atlas V 1st stage, which have *very* high chamber pressures.
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