Talk:Skylon (spacecraft)

Science fiction ?

So, there is still not a single working prototype, no technology developed and tested, - actually nothing, just some concept drawings + some speculations from REL about how they believe "it could possibly work", somewhere in the future. A proper material for a serious encyclopedia, indeed. But then again, when you have nothing to show well into half a century of the space age, you'll at least be glad you have some sketches. —Preceding unsigned comment added by 83.176.154.9 (talk) 19:57, 23 September 2010 (UTC)

You who? UK Black Arrow--Kitchen Knife (talk) 20:33, 23 September 2010 (UTC)

Why bother building real-world craft that really works? it's so old-school, when merely a pdf presentation is all you need these days —Preceding unsigned comment added by 83.176.153.214 (talk) 20:09, 24 September 2010 (UTC)

Is that a bit of bitterness from a German because the ELDO stage 3 which failed and but the European Space program back years, was designed by Germany.--Kitchen Knife (talk) 21:06, 24 September 2010 (UTC)

Dear Mr. Alan Bond, sir, please log in under your real name. Thank you. —Preceding unsigned comment added by 83.176.152.212 (talk) 08:53, 25 September 2010 (UTC)

Ah didums.--Kitchen Knife (talk) 12:44, 25 September 2010 (UTC)

This sounds like a highly national program—Go UK! So the theoretical HOTOL was proven to be unworkable… and was replaced by the theoretical Skylon, right? I’m guessing Skylon has little chance of seeing flight (why? oh, just a hunch ; ). What will replace Skylon? If you ask me, you're going to waste a perfectly good name. —Preceding unsigned comment added by 143.115.159.54 (talk) 17:25, 10 March 2011 (UTC)

They are working toward this goal with all the funding available.. which is not alot. Think that they got a grant from the ESA for the sabre engines which is the key to the whole design (using the atmosphere as reaction mass at low altitude). —Preceding unsigned comment added by 2.102.47.176 (talk) 02:18, 4 April 2011 (UTC)

March 2005 discussion on "burns 5x less propellent"

"burns about 5x less propellent there; and so can take off with less"

Has just been incorrectly replaced with for the second time.

"only needs 20% propellant there; and so takes off with much less"

I have several issues with this. I actually wrote the orginal text; so I actually know what it refers to. The 5x less propellent refers to the fuel efficiency i.e. [Specific Impulse], inside the atmosphere with the SABRE engine you burn fuel 5x slower than you would if this was a hydrogen/oxygen rocket. The ISP within the atmosphere ranges from 2000-2800 seconds, whereas the exatmospheric value is about 450 seconds. Hence the factor of about 5. A phrase such as "20% propellent" is meaningless. 20% of what? 20% of the takeoff mass? Nope, sorry, it ain't. The replacement sentence is meaningless. Please stop vandalising this page in this way. If you want to actually *clarify* it or add quantitative information go ahead. WolfKeeper

The changes are correct. You are the one who is confused. If you had been paying attention, you would also know that two different people have made this change; originally Bobblewik, then my reversion. It's your phraseology that's wrong.

It might take "5 times more" fuel in the atmosphere. That means it takes "0.8 times less" in the exoatmosphere. Or 80% less. Or 20% as much. The multiplier is applied to what you start with. And when it is less, it is never greater than one.

If you want to talk about "fuel efficiency" or "specific impulse", then do so. It doesn't matter if the fuel efficiency is 5 times as good; it still isn't "5 times less fuel". What do you multiply by five? So throw out some proposed rewordings here on the talk page if you'd like. Just realize that throwing it back in the way it was is likely to get reverted again by somebody. Gene Nygaard 03:13, 20 Mar 2005 (UTC)

Ok, fair enough. But your correction 'only needs 20% propellant there' wasn't grammatically or logically correct *either*.

It was not Gene that made that edit. It was me. My english and maths understanding does not extend to parsing phrases of the form 'x times less'. My best guess was that it meant '1/x'. If it did not, then I am at a loss as to what it meant. I am grateful that you have sufficient knowledge in this field to write the article and I was interested in what you had to say. I just didn't understand that bit. I might not be the only one that has difficulty with such phrases. Feel free to change my edits that I made. But rather than using that type of phrase, would you mind trying to explain it in another way? Thanks Bobblewik  (talk) 21:24, 20 Mar 2005 (UTC)

Thrust-to-weight ratio

Since Bobblewik has already started this discussion on Talk:SABRE I will continue it there. In my edit comment, I don't mean that nobody uses it as if it were dimensionless--but more on that page. Gene Nygaard 06:42, 21 Mar 2005 (UTC)

when?

The project has a projected R&D cost of under $10 billion and an estimated program length of 7-10 years.

But when did it begun?

It hasn't exactly, it's not funded yet. Alan Bond has a company that is working towards building an engine.WolfKeeper

Aren't brakes supposed to be for landing?

The article says Skylon uses water-cooled brakes, but the water is jettisoned on takeoff. So how will it land?

Frankie 16:59, 2005 August 11 (UTC)

The worse-case for the brakes are when the vehicle loses thrust *just* before takeoff. Then the vehicle is full of fuel, and has to stop before the end of the runway and needs to dissipate all the energy that represents.

Landing after reentry, the thing is light as a feather, and you don't need the extra cooling tricks (or atleast not nearly as much).WolfKeeper

I do not like the sound of this. If the flight has to be aborted near the start, say due to a bird strike, after the water has been dumped how does the aircraft land? Dumping liquid hydrogen is not safe. Andrew Swallow (talk) 20:24, 17 July 2008 (UTC)

FWIW dumping liquid hydrogen is perfectly safe. It will mix with the air and evapoarate and dissipate. Obviously you would really, really want there to not be an ignition source around, although Skylon's reentry-proof skin would probably handle this better than an awful lot of things if it did ignite.- (User) Wolfkeeper (Talk) 01:57, 24 February 2009 (UTC)

The hydrogen is near the ground it will land on people, animals, plants, machines and buildings. At liquid hydrogen temperatures it can produce cold burns.

Andrew Swallow (talk) 20:45, 9 November 2009 (UTC)

No, it wouldn't the aircraft flies quite fast even to take off so the hydrogen would have evaporated by the time it reaches the ground because it would be diluted down, and the aircraft wouldn't fly over anyone like that anyway. In any case talk pages are not places to discuss technical issues related to the article's topic.- Wolfkeeper 00:31, 10 November 2009 (UTC)

Takeoff Weight to Payload

In the article you said

...the proportion of takeoff weight to payload is more than twice that of normal rockets and it should be fully reusable. That means that each flight makes twice as much money...

From what I understand about rocketry, most of the takeoff weight is fuel. If maintenance costs can be controlled better than the US Shuttle, the cost of that fuel should consume most of the operational budget.

Um. No. Cost per kg of hydrogen based propellant is about $5. Even on Skylon it wouldn't be the highest cost, by a very long way.WolfKeeper

So if the ratio of takeoff weight to payload is twice that of normal rockets then the ratio of fuel to payload is twice that of normal rockets. This says that for a given payload it would be twice as expensive to use the Skylon as a normal rocket. Is the Skylon getting its savings from some economization other than takeoff weight to payload or was this improperly worded.

Actually, the most important metric is probably payload to unladen weight; and Skylon scores well on that too. The fact that you get the unladen back again after the mission is pretty important though.WolfKeeper

Then state that. The existing statement does not make sense and contradicts the claims in the SABRE article. This is an excerpt "the vehicle reaching orbit with more payload mass per take-off mass than just about any non-nuclear launch vehicle ever proposed." your article specificly states that the take off mass per unit payload is twice as high as any conventional rocket which is the opposite.Commdweeb

The next problem is "it should be fully reusable" implies that the entire take off weight including the fuel can be fully be reused. This doesn't make sense. Shouldn't this passage have been worded

I'm not sure if you're being serious, but strictly speaking, the fuel weight can be reused. Admittedly you have to wait for the water produced in the exhaust to rain out of the atmosphere, but 100% reuse is conceivable, since none of the exhaust reaches escape velocity.WolfKeeper

Hmmm, I am being serious.

You poor thingWolfKeeper

Are you??? The fuel is no more reusable than the external tank on the Shuttle. Both are burned and dispersed through the atmosphere on launch. Or am I missing something here. Are you arguing that the US Space Shuttle is a fully reusable launch system since none of it's componnents reach escape velocity? Commdweeb

...the proportion of takeoff weight to payload is less than half that of normal rockets and the vehicle should be fully reusable. That means that each flight costs less than half as much money...

or perhaps

...the proportion of payload to takeoff weight is more than twice that of normal rockets and the vehicle should be fully reusable. That means that each flight makes twice as much money...

I prefer the first version because, if you are running on a 10% profit margin and you reduce your costs by 50%, this increases the profit margin to 55% or more than five and a half times the original profit margin. On the other hand if you are running on a 60% profit margin halving your costs yields an 80% profit margin, or an increase in profit of only 30%. So I contend that the second proposed version and the original versions are ambiguous at best.

Center of mass

"The weight of the rear-mounted engine tended to make the HOTOL vehicle fly backwards"... shouldn't this be tip backwards?

Not exactly, it's sort of like a shuttlecock thrown feathers first; it tends to spin around in the air .WolfKeeper 14:07, 20 June 2006 (UTC)

couldn't they apply relaxed stabillity techneques using fly by wire to impose artifichial stability on the aircraft, or are there problems with control in a thin atmosphere at high altitude? also don't space planes have problems with getting the major axis of inertia in the right direction to avoid cartwhealing. i belive some erly space capsuals tended to tumbel in flight due to improper weight distribution with the craft rotating around the incorect axis, resulting in some very sick ocupents, also i think some space satalight recently had a simmilar problem where it was using too much power to keep it solar panels correctly orientated, resulting in the eventual loss of power, and loss of the satalite

don't mix up stability with equilibrium,(trim) all forces and moments in balance, regardless of how stable it is. it is likely that if the aircraft's CG is too far back it will be impossible to keep the aircraft in trim, let alone stable. its like trying to keep a pencil balanced at the tip but lying horizontally, never going to happen as its not in equilibrium. however a pencil balancing on its tip, vertically, is in equilibrium, but is not stable, this is what artificial stability on the aircraft is about. RichardMathieRichardMathie (talk) 22:33, 11 April 2008 (UTC)

Removed oringinal research

I rfemoved the following statement from the article, as it seemed to violate WP:OR:

The overall shape of the fuselage of Skylon bears a resemblance to the similarly named futuristic structure, the Skylon at the Festival of Britain.

Anxietycello (talk) 03:57, 22 December 2009 (UTC)

"standard payload container"

The article states, as of 26 March 2010, "The payload would be carried in a standard payload container." What is a "standard payload container" in this context? Is there some kind of "industry standard" payload container defined by some industry or government organization? Is that standard widely adopted? Is that the standard that is meant here? If so, let's specify what the standard is.

On the other hand, I suspect that, to date in the space industry, there have been few standards since government programs have been the major efforts in space programs and launch payload specifications have tended to be rather proprietary and launch-vehicle specific. In any case, I think we need to clarify the "standard payload container" claim in this article. Cheers. N2e (talk) 18:15, 26 March 2010 (UTC)

There aren't any standards for space vehicles at the moment, but Skylon would have a standard payload container, the linked reference talks about it somewhere or other.- Wolfkeeper 18:39, 26 March 2010 (UTC)

SERIOUS NEUTRALITY ISSUES HERE

Right, like I said, serious neutrality issues. YUK! 108.7.9.7 (talk) 21:07, 23 April 2010 (UTC)

Probably not. REL have published in reputable journals, and have delivered public lectures on the idea, there's no known howlers, although there is the odd tricky bit, and they've come from a background of conventional rocketry, and are well respected individuals. They've also been awarded funding from various government and non governmental organizations, those guys are not that easy to pull the wool over their eyes.- Wolfkeeper 21:41, 23 April 2010 (UTC)

I wasn't saying that the project itself was flakey, just that the article is not neutral. It is obviously written from the POV of the designers and promoters. Still YUK!!  :-)

108.7.9.106 (talk) 06:37, 12 July 2010 (UTC) (same guy)

Neutrality in the wikipedia is about trying to match the overall written analysis on the subject. There isn't that much criticism written about skylon that I'm aware of.- Wolfkeeper 15:40, 12 July 2010 (UTC)

I think Wolfkeeper is largely correct: there has not been much written analysis by other sources that would make for WP:V-compliant criticism. That being said, I think there is some copyediting we could do to make the article less WP:POV-ish. I made a first-pass attempt to do so with a few paragraphs in the lede: clarifying that this is a design concept/proposal/paper-studies-not-prototyped-fact/etc., and that most of the [{WP:V]] info on which the article comes from is from the development team, even if some of it is peer-reviewed-published. I think more of this sort of thing would probably be appropriate. And if this were done more thoroughly, I suspect it would partially ameliorate the sort of neutrality criticism by 108.7.9.106. N2e (talk) 19:26, 18 July 2010 (UTC)

The Sabre Engine

Is it possible to get consensus as to the nature of the SABRE engine, not just for this article but also for the engine itself? The current version of this article states;

"The proposed engine for the vehicle is not a scramjet, but a jet engine running combined cycles of a precooled jet engine, rocket engine and ramjet."

My first element of concern is the level one can describe that the ramjets are running in combined cycle with any of the other components. The air they use comes direct from the intake, it is air not cooled by the precooler or passed through any of the other components. Similarly the hydrogen drawn is only the heat sink for the helium based Brayton cycle. Secondly as they are simply a bypass system and not the driving principle of the engine is it not confusing to mention them except in the details of the engine's article?

Further, although a rocket engine is technically a form of jet engine is it not confusing to call this a jet engine + a rocket engine? Reaction Engines make clear that SABRE is a single rocket engine, in the "Skylon User Manual" it states, "SKYLON is powered by a combined cycle rocket engine which has two operational modes.". Furthermore, in the "A Comparison of Propulsion Concepts for SSTO Reusable Launchers" document engines of SABRE's type are referred to as, "Precooled Hybrid Airbreathing Rocket Engines". The SABRE article on their website also states, "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."

Calling it a (separate) jet engine + rocket engine, when a principle element of the design has been the creation of a high pressure system so that it can use as many rocket components as possible, seems unwieldy. The term that Reaction Engines themselves use seems more appropriate as a description of the system. It is also the least likely term to cause confusion. Frodz (talk) 22:20, 12 August 2010 (UTC)

I think that its whatever we agree it is here, using the information we have from the sources. I'm not entirely sure that they describe it very well, we need to use the words that will give the most accurate impression to the reader of how it works, and we have no requirement to use the same words as REL uses. We're trying to summarise it for our readers.- Wolfkeeper 22:58, 12 August 2010 (UTC)

Given that they are the experts on modern LACE-like engines I think it’s safer to defer to their opinion of what this engine is!

Yes I understand we need to summarise for the readers, but at the same time the terminology must be accurate. As I said I don’t think it is accurate to call it anything running in “combined cycles” with particular types of engines and in this case certainly not ramjets. “Combined cycles” refers to combinations of thermodynamic cycles, not to combinations of engines. The phrasing at present implies that this is more than one engine which isn't right.

It must also be clear as to the function, not to potentially imply things it clearly is not. The engine is closer to a turbo-compressor-fed rocket engine than to a pure jet engine, in fact the turbo-compressor is the only real component familiar from jet engines. At best it would be accurate to say the rocket engine works in a similar fashion to a conventional jet engine within the atmosphere, essentially it is an engine designed to mimic a conventional jet engine, but that doesn’t make it one.

This is why I think sticking to what the experts refer to this engine as is the safest for encyclopaedic use.

Is a football/soccer ball square because we say so on here? Frodz (talk) 23:35, 12 August 2010 (UTC)

No, never. But if they were playing some game with a square ball, and the professionals described it as other than that then we would still be at liberty to use the word 'square' if we agreed to do so based on a diagram of the shape of the balls or something.- Wolfkeeper 03:51, 13 August 2010 (UTC)

It's not a rocket in the atmosphere, it's an airbeathing jet engine. It might be combined cycle rocket/airbreathing jet engine if they're squirting in LOX as well from tanks.- Wolfkeeper 03:51, 13 August 2010 (UTC)

The rocket, turbocompressor and ramjetty burners do seem to be running different overlapping cycles. The ramjets don't have any compressors- just the inlet compression, the rockets use turbopumps and the turbocompressors use gas compressors.- Wolfkeeper 03:54, 13 August 2010 (UTC)

You are assuming that they are incorrect, but that requires evidence, and even then according to Wiki’s guidelines we would still have to include the expert’s opinion and provide a sourced counter-argument.

Reading the sources and providing a novel conclusion not presented in those or any other reliable sources is original research. I suggest that unless this assertion is backed by sources stating in so many words that the interpretation in the article is a correct one then it comes under WP:V and WP:OR, it’s sources that are important, not truth.

We cannot state any substantial ideas that are not referred to elsewhere by reliable sources, which would constitute original research, and especially not on issues within the article likely to be questioned which comes under verifiability. The nature of the SABRE engine is clearly a part of the article likely to be questioned.

Unless there is a source stating this interpretation of the facts as to what the SABRE engine is (which lets face it are more complex than a diagram of a ball), the only well-sourced description of the engine comes from Reaction Engines themselves.

This issue is notoriously confused, these articles until recently claimed without evidence that the engine is a turboramjet/turborocket/ramjet (take your pick!) which it categorically isn’t (and cannot be) and there’s now a reliable source on SABRE’s page explaining why. Frodz (talk) 11:28, 13 August 2010 (UTC)

For a start a turbopump is part of a Staged-combustion cycle! The turbo-compressers are run off the same Brayton cycle as the precooler is. This is the meaning of combined cycle as the engine combines the Brayton cycle with Staged combustion. It does not mean it is two (or more) different engines. The ramjets take their air direct, and the rejected hydrogen is a heat sink for the Brayton cycle, there is no combined cycle here. Again, even if there were given that the ramjets are just bypass burners and not designed to produce significant thrust, invoking them in the description on this page is clearly going to cause confusion with other engine concepts unnecessarily. But either way this is irrelevant as whatever is written must be backed by evidence the interpretation is correct. Frodz (talk) 11:29, 13 August 2010 (UTC)

Look, they describe it as:

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).

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 bit where it says 'a bypass system is used.... bypass flow is reheated' is clearly talking about a type of ramjet. That's what a ramjet is, it's a pipe with reheat (ironically reheat is a bit of a misnomer in this case since it's not heated in the first place...)- Wolfkeeper 18:16, 13 August 2010 (UTC)

I can summarise those two paragraphs as saying that the engine is a combined cycle airbreathing jet engine/ramjet/rocket without any concern whatsoever.- Wolfkeeper 18:16, 13 August 2010 (UTC)

As can be seen from my passages above I know there are ramjets in the system, I was the one that edited SABRE’s page expanding on that and supplying a video reference of a lecture Alan Bond gave where among other things he explains their function as bypass burners to increase efficiency. For example it explains that the Brayton cycle running the precooler currently requires much more hydrogen as a heat sink than the engine's combustion chambers can burn (the level of hydrogen drawn is well above stoich.) so the surplus is dumped into the burners before ever reaching the Staged Combustion cycle and that this is mixed with the air that bypasses the engine, I recommend watching it. But they do not exist for the purpose of providing significant thrust for the engine at any point. Quoting them as anything more than a detail in SABRE's article as if they are a significant part of the engines function is liable to cause confusion between this engine and actual ramjets/turboramjets, which rely on ramjets for primary propulsion, as has already happened! Indeed the function of the ramjets in this system is somewhat analogous to the fan in a Turbofan, they are both designed to control bypassed airflow to increase efficiency, one of the main differences is a lightweight fan wouldn’t be of much use at mach 3….You don’t refer to a Turbofan as a "jet engine + fan" do you? It’s simply a type of jet engine. In fact when SABRE was described as a turboramjet on here it was never at any point called a turbojet + ramjet despite it being far more sensible to say that if this were the case than in the case of what the engine actually is, an air breathing rocket. Why is it acceptable to call a turboramjet a single engine and not this one? Just because this engine has components familiar from other concepts does not make it sensible to call it multiple different engines and REL agree with that.

But that wasn’t the only issue with the line at present. That was that I believe describing it as a jet engine "running in combined cycles” with any other types of engine, and especially here with the ramjets, fundamentally does not make any sense. Combined cycle refers to combining thermodynamic cycles (Brayton, Staged Combustion etc), not combining “engines” like "jet engine + rocket engine". Please explain the combination of thermodynamic cycles that are present in the operation of the ramjets for example. The problem isn’t that ramjets are involved in the engine, it’s the description of them and the rest of the engine that is seemingly incorrect as well as liable to cause confusion, which is removed if you use REL's description of the system as a precooled hybrid air breathing rocket engine. REL explain it in the way they do because this is the way that makes most sense when you get what is going on, as opposed to just looking at individual components and assuming their function. Frodz (talk) 23:32, 13 August 2010 (UTC)

Sorry, but I'm certain that the term combined cycle in aeronautics doesn't only refer to combining thermodynamic cycles it can also be used to refer to combinations of engine types. For example combining ramjet/turbojet/scramjet is referred to as combined cycle. That's simply how it's used; but that's not what you'll get at combined cycle and the reason for that is that the Wikipedia isn't a dictionary, it only covers one meaning per article. In addition, the SABRE engine is actually running multiple cycles, there's cycles of the helium and hydrogen through the engine as well as those of the air and the rocket cycles.- Wolfkeeper 00:20, 14 August 2010 (UTC)

No, because none of that is supported by that passage. In fact the passage directly contradicts your summary. Everywhere in REL’s literature it is made clear that SABRE is a single air breathing rocket engine, albeit one with components familiar from other systems. To say anything else without a reference is original research and not encyclopaedic. Frodz (talk) 23:32, 13 August 2010 (UTC)

I'm sure that there's nothing I've written that is directly contradicted.- Wolfkeeper 00:20, 14 August 2010 (UTC)

Yes I’m aware of that, that’s because the standard “types” of engine tend to be based on a particular type of thermodynamic cycle, jets engines usually being versions of Brayton cycles for example. The problem however is that some engines do not run on a simple (or single) cycle so it’s not necessarily like for like. I wasn’t saying there wasn’t more than one cycle present, obviously there are in a combined cycle engine! The rocket engine and the precooler/turbo-compressor Brayton are working in combined cycle during air breathing for example. I am questioning how this is represented to be most accurate, to not cause confusion with other principles, and to stick as close as possible to references. For example a turboramjet is a combined cycle engine and yet we didn’t feel the need to break it down into component engine cycles and instead refer to it as a single engine.

Having said that, I’ve somewhat changed my mind re the ramjets. I overlooked the nature of the hydrogen in the rocket’s cycle. The problem would not be so much the ramjets as those could rather simply be described in combined cycle fashion, but can the precooler Brayton cycle be called a full jet engine cycle? It’s not a full cycle like the turbojet in a turboramjet for example. I'd be interested to know.

I still think referring to this engine by breaking it down into cycles is unnecessarily obfuscating. But given that the rocket cycle remains in both modes, if we must refer to all the cycles it would probably be better to use “combined cycle rocket engine” as the basis and then refer to cycles present in precooled turbojets and ramjets. Is something like this an acceptable compromise?

“The proposed engine for the vehicle is not a scramjet, but a rocket engine running combined cycles of a precooled jet engine and ramjets.”

Frodz (talk) 01:37, 14 August 2010 (UTC)

Well, we could just refer to it as simply as not being a scramjet, but being a precooled jet engine in the summary and then go into more details about the cycles further down.- Wolfkeeper 16:41, 14 August 2010 (UTC)

"“The proposed engine for the vehicle is not a scramjet, but a precooled jet engine.”- Wolfkeeper 16:41, 14 August 2010 (UTC)

And then just move the bit about combined cycles further down.- Wolfkeeper 16:41, 14 August 2010 (UTC)

Specially strengthened runway ?

So this aircraft needs a specially strengthened runway ?? It says so, twice. But if the aircraft has a takeoff mass only one tenth of a loaded Boeing 747, then why does it need a special runway ?Eregli bob (talk) 09:08, 21 September 2010 (UTC)

Simple...Momentum is the product of mass times velocity, and the runway has to deal with that momentum. Though this craft is far lighter than a 747, its takeoff speed will be massive (Half the speed of sound), and will subject the runway to a proportionate amount of stress.--Novus Orator 09:08, 26 September 2010 (UTC)

Well the 747 takes off at 290 km/hour. So "half the speed of sound" is double that. So if the skylon is one tenth of the mass, and double the speed, of the 747, then its momentum is only one fifth of that of the 747. So your rationale doesn't make sense at all.Eregli bob (talk) 13:16, 28 September 2010 (UTC)

747 442 tonnes Skylon 275 tonnes. Half speed of sound 615 km//hour. SO Skylon had 1.32 * the momentum, and 2.8 * the energy.--Kitchen Knife (talk) 14:34, 28 September 2010 (UTC)

I'm not convinced this explanation is sound. Momentum, like velocity, is a vector quantity, and its largest component by far is parallel to the runway. So increasing a plane's takeoff or landing speed (i.e. its groundspeed) doesn't seem relevant to me. As I see it, what's relevant re the necessary strength of the runway is only the momentum that's normal (perpendicular) to the runway, i.e. whether a plane makes a "hard landing" or a "soft" one, and how heavy it is. The vertical component of the velocity at which the plane touches down should be about the same as that of a 747. It would correspond to a vertical airspeed of just a few feet per second, one would hope: anything more and you have a crash landing, anything less and you overshoot and don't leave enough runway for braking after you touch down. The aircraft's groundspeed shouldn't matter at all except as it affects takeoff and landing/braking distance. It's been a long time since college physics, though, so perhaps I've neglected some factor that y'all are aware of?  – OhioStandard (talk) 02:36, 2 October 2010 (UTC)

Yes, you are correct, my explanation was not clear. As far as I understand it, velocity and acceleration are vector quantities, and the acceleration vector of the landing aircraft is diagonal to the runway, e.g. it has a x-component and a y-component. The Force of Kinetic Friction is equal to the Normal Force (Weight) and the mu k (frictional constant), which contribute the additional stress that I am referring to. The y-component is smaller than the x-component, but the Normal Force caused by the aircraft/(in this case spaceplane)'s mass is a part of the frictional force equation (which is the friction the runway exerts on the spaceplane's wheels). The combination of the y-component of the acceleration vector (working down) and the Fk (working horizontally against the wheels) together is what puts the stress on the runway.

To solve for the total linear force the runway must exert on the spaceplane (neglecting air resistance) is:

(in x) (1.0) Frictional Force in x-dimension=(mu k)×(Normal Force)

(in y) (1.1) Normal Force=mass × acceleration

If you wanted to find the Momentum of the Spaceplane once on the runway, you would then take the x-component of the resulting Force in the following equation:

(1.3) Momentum=[(Force of Thrust in x dimension)-(Frictional Force in x-dimension)]×(change in time)

Which you could then relate to the horizontal velocity in the Momentum equation:

(1.4) Momentum=mass×velocity

Though this is a very interesting topic, I am reminded of the policy WP:NOTAFORUM and therefore I must end this discussion. It's great knowing that there are editors out there who love Physics as much as I do.. --Novus Orator 03:12, 2 October 2010 (UTC)

I'm sorry, Terra Novus, but that won't do. I've reverted your deletion of the preceding, of this entire section, despite your having copy-pasted it to your talk page. This topic is germane to the improvement of the article, so wp:forum doesn't apply. I don't imagine you're bothered by your initial mistake, but if you are, please don't be. Every single editor here, myself included, has made many mistakes before, and we all will again. Heck, I've made some really remarkable ones, and then even continued to argue my point in the past when my mistake was pointed out to me because I didn't understand another editor's correction. Nothing to worry about in the least, it's a very normal part of the process, is all. Best,  – OhioStandard (talk) 05:37, 2 October 2010 (UTC)

The reason specially-strengthened runways would be desirable is explained on page 29 of The SKYLON Spaceplane, the Varvill & Bond article in JBIS, which is cited as a ref in our article. The designers wanted to keep the undercarriage and related components (i.e. the wheels, and all that support them) to no more than 1.5% of the plane's Gross Takeoff Weight. As I read page 29, they plan to do that by giving the plane a "highly loaded tightly spaced wheel assembly". They plan to give the plane less wheel surface to land on, in other words, to conserve both the weight and also the size of the wheels-up compartment inside the plane's hull or body. ( Remember it's really expensive to carry additional weight into orbit, so they want to minimize it. )

Think of it this way: fewer wheels (or, more exactly, less overall contact area between wheels and runway) means a higher load factor on the runway. It's just like the way a woman's spike heel shoe will put "dents" in a wood floor where the same woman in a more reasonable shoe won't. Her whole weight is concentrated over a much smaller area in the heels, and thus makes far greater demands re deformation on the floor. Same thing with decreasing tire-runway contact area for a plane of a given weight.

I don't have time right now to put this explanation into the article. But if we're going to mention the strengthened runways, we should explain why they need to be strengthened. So anyone who wants to, please go ahead and add the appropriate explanation to the article. Otherwise I'll try to get back to this within the next few days and do so myself. Best,  – OhioStandard (talk) 05:44, 2 October 2010 (UTC)(I had the time after all, see below. revised by Ohiostandard at 06:19, 2 October 2010 (UTC)

Thank you for pasting it back in. You are correct that it can be applied to improve the article...--Novus Orator 05:58, 2 October 2010 (UTC)

Thanks, Terra Novus. I did go ahead and change the article, too. See if you approve, or work it around any way you like. I have no particular attachment to my edits on this article, so feel free if you can phrase it better or want to expand on that at all. Best,  – OhioStandard (talk) 06:19, 2 October 2010 (UTC)

Citations and sources

Hi User:Terra Novus. Looks like you have made a lot of useful edits, and added a number of helpful inline citations to the article recently. I am happy to see that as this article needed that. I have a thought to offer on the use of refnames, especially as used for citing primary sources from the company website. My thought is that a refname is somewhat more useful—and importantly, a bit less likely to be misused in the future by other editors who may try to reuse the refname when looking at the source at a later date—if it contains an embedded date within the refname.

For example, if the article is a reliable secondary source, I generally embed the date of the source (e.g., for an Aviation Week article, something like <ref name=aw20100827>). However, for primary sources, my sense is that it is important to embed the date I looked at the source into the refname (e.g., if I looked at the Reaction Engines company website on 25 Jan 2011, I would do something like <ref name=re20110125>) which of course would then match the "accessdate=2011-01-25" in the citation metadata.

Many of your recent citations are to the company website, and have generic refnames such as <ref name=userskylon> or <ref name=skylonfaq>. While totally correct today (where you have noted the correct date accessed in the citation metadata), I would anticipate many future editors may look at those company websites, on future dates, and simply reuse the userskylon or skylonfaq cites, only now their new cites will be looking at a website that may be quite different from the website you looked at on 2011-01-25.

What do you think? Too much ado about nothing? Or useful input? If you are interested, I would be happy to help make some changes to existing refnames—but don't want to offend you recent good faith and diligent work. Cheers. N2e (talk) 18:33, 25 January 2011 (UTC)

That is an excellent idea. Go for it. I will be happy to help.--  Novus  Orator  04:10, 26 January 2011 (UTC)

I followed your suggestions on all the related references. Please feel free to help improve this article.--  Novus  Orator  04:48, 26 January 2011 (UTC)

Great work Novus! I think that will be helpful to the future quality of the article. And thanks very much for your kindness in taking the suggestion so well. N2e (talk) 14:14, 26 January 2011 (UTC)

Minor copyedit of the lede

I made what I hope is a fairly minor, and also accurate, copyedit of the part of the lede that summarizes funding on the project. My intent was to write at a lead-worthy level of abstraction (summary level) and ensure that the detail is adequately explicated in the body of the article.

On whether or not citations are required for each sentence or major assertion in the lede, I'm sort of agnostic. As long as the details are articulated, and fully sourced, in the body of the article, I'm okay with the citations not being repeated on the summary claims in the lede. I think this practice helps the lede stay at a high-level-summary level of abstraction. And it can oftentimes assist with the claims and cites not getting out of synch so quickly (when they are summarized differently but still redundantly cited in two parts of the article). Therefore, on the edits I just did, I did not duplicate the citations in the final lede paragraph (which is the only part of the lede I edited). Other editors preferences may vary. So if someone wants that paragraph sourced in the lede, as many other paras in the lede currently are, I'm okay if someone adds them back in. N2e (talk) 17:07, 27 January 2011 (UTC)

Yes the funding sourcing wasn't the best. I'm not so sure about some changes though, particularly that reference to the novelty of SABRE has been removed! This is the main feature of the spaceplane, the design of Skylon is built around its engines, they are fundamental to the subject. The only reason the Skylon proposal exists is because of the airbreathing engines, as such I think the lede now doesn't adequately get across what makes Skylon different to other concepts. ChiZeroOne (talk) 17:25, 27 January 2011 (UTC)

I have no problem with more about the engine uniqueness being in the lede. The lede should be about four paragraphs, which is currently is. So if more about the engine is to go in (which is, as you say, probably quite appropriate) it might be necessary to copyedit the several paras of the lede that I did not just copyedit with my recent edits. Cheers. N2e (talk) 17:39, 27 January 2011 (UTC)

GA pass

Congratulations to all the editors who contributed to getting this article to Good Article status.--  Novus  Orator  07:28, 9 March 2011 (UTC)

Sourcing

Quite a bit of the article is sourced with primary sources. While a lot of this is unavoidable—we must use Reaction Engines as a source for many claims where the information exists nowhere else—it is the case that we really ought to get more secondary sources supporting the major claims of the article. I will add below one recent source I just read, from CNN, in the mainstream press. Others please add secondary sources you run into as well. Cheers. N2e (talk) 17:01, 10 March 2011 (UTC)

• 'Skylon' space plane aims to fill void left by Discovery -- CNN -- 10 Mar 2011

This is a conclusion that I agree with; it would be helpeful to increase Secondary Sources, and it would look more professional to do so. I've brought in a good document from Parliament, now inserted in the Bibliography, which I recommend a good reading of for further referencing to. If wanted, I can fish around for more sources from good Secondaries as well. Kyteto (talk) 00:19, 11 March 2011 (UTC)

"...as it required a heat exchanger that was ten times lighter than the state of the art..."

I can't see that factoid quoted anywhere in the sources. —Preceding unsigned comment added by 213.208.114.181 (talk) 16:33, 24 May 2011 (UTC)

Rename?

As per this discussion there appears to be consensus that company names as disambiguators are not favoured for spacecraft. The actual name of the vehicle here is officially Skylon, not Reaction Engines Skylon. I suggest it would be consistent to rename the article "Skylon" or, given that there are other common uses, "Skylon (spacecraft)". This would be in line with the advice developed at the Spaceflight Wikiproject, WP:SPACENAME. ChiZeroOne (talk) 18:54, 23 April 2011 (UTC)

Support: Seems reasonable enough to me. --Xession (talk) 18:57, 23 April 2011 (UTC)

Support: Good. If this thing is successful it will most likely be referred to as just Skylon anyways...--  Novus  Orator  07:56, 25 April 2011 (UTC)

• Support - per nom. - BilCat (talk) 08:07, 25 April 2011 (UTC)
• Support - per nom also. Rememberway (talk) 02:20, 27 April 2011 (UTC)

Ok, support seems unanimous for the change, but the question is is this vehicle considered the primary topic? Although it does receive the most traffic i'm not sure it's necessarily enough to be considered the primary topic over Skylon (tower). If that's the case then it would make sense if "Skylon" redirected to the disambiguation page and this article be renamed "Skylon (spacecraft)". ChiZeroOne (talk) 19:08, 24 May 2011 (UTC)

I have gone ahead and made the changes. ChiZeroOne (talk) 17:14, 1 June 2011 (UTC)

Consistency

There appears to be a mismatch in a number of the figures given throughout this article because they are using values assigned to different iterations of the Skylon design. The figures given at the bottom of the page mostly use the latest C2 specification (which is effectively baselined with similar capabilities to the final D1 specification, which is part way through its design) given in an update of the manual. However the payload (12 tonne max, around 10 tonnes more likely though) comes from the "classic" C1 version, not C2's or D1's 15 tonnes.

The problem is because D1 isn't complete REL still often talk about Skylon based on the "current" C1 specs so mostly do not refer to the increased capablilities in media interviews, while their publicity does discuss these.

So what do we propose to do? The most detailed document, the user manual, is now written for C2/D1 but for the time being media reports for example will still report based on C1. ChiZeroOne (talk) 02:28, 24 April 2011 (UTC)

We follow WP:RS. We use the most reliable sources, which (in this case) would be the user manual, at least until more media coverage surfaces.--  Novus  Orator  07:53, 25 April 2011 (UTC)

WP:FA drive

Wikipedia:WikiProject Spaceflight would like to see more articles of Featured quality. Please post below if you are interested in helping raise this article to the next level.--  Novus  Orator  06:33, 25 May 2011 (UTC)

• Will do--  Novus  Orator  06:33, 25 May 2011 (UTC)

Rename to Skylon (spaceplane)

The title term spacecraft seems to imply that it's only a spacecraft, whereas actually it's a launch vehicle or spaceplane.

So I propose to rename it to Skylon (spaceplane). -Rememberway (talk) 11:46, 4 June 2011 (UTC)

• Support--  Novus  Orator  08:29, 5 June 2011 (UTC)