Quote from: 93143 on 07/10/2012 10:37 pmYour pessimistic assessment rests entirely on historical examples. It is thus manifestly invalid when dealing with an approach that specifically claims to solve the problems encountered in those examples.No, until it flies all they've shown is a potentially successful new approach. It might work, it might not. I didn't dispute the former, I merely pointed out the latter.
Your pessimistic assessment rests entirely on historical examples. It is thus manifestly invalid when dealing with an approach that specifically claims to solve the problems encountered in those examples.
Earlier approaches too have all had their own secret sauce, their own reasons to believe they would make it.
QuoteIt appears that you have no new information to add to the discussion, which means your pronouncements basically amount to a variant of "contempt prior to investigation".I feel no contempt of Skylon at all, I said I found the concept very interesting.
It appears that you have no new information to add to the discussion, which means your pronouncements basically amount to a variant of "contempt prior to investigation".
QuoteIt will be expensive. It's an airplane the size of an A-380, and it will probably cost a similar amount to develop, SSTO or not.It will cost a lot more, because it will include development of a new engine, and not just any old engine, an engine of a type that has never been flown before.
It will be expensive. It's an airplane the size of an A-380, and it will probably cost a similar amount to develop, SSTO or not.
That said, I'd love to see them succeed.
I'll try to rephrase: You've criticized Skylon for reasons that don't apply to it,
in an evident attempt to make general knowledge substitute for specific knowledge of the subject in question.
None of them had the kind of margin Skylon has. We're talking about a mass ratio of four and a half, with a payload fraction of 4.6% after structural and performance margins, on a vehicle in its fourth major design revision after two decades of engineering including lessons learned from other attempts.
And the only radical technological challenge is (was?) the precooler.
SABRE really is a game-changer if it works. And right now it looks like it will probably work, at least technically.
The 'acid test' (full-depth cryo) remains, but the precooler is not the big unknown it once was, and everything else about the engine is fairly well understood.
I said "a variant" of a commonly-referenced intellectual blunder. Basically the idea is that you seem to be more skeptical than is warranted by your level of knowledge, and your skepticism seems to be based not on the knowledge that you do have, but on general principle.
Most people here know it might not work. Most people here are at least passingly familiar with the history of attempts at rSSTO, and as you don't seem to have any special command of the thread topic
, I'm not sure your wet blanket approach (spiced up with the suggestion that you know how REL should be spending their money and effort better than they do) has added a whole lot to the discussion.
Do you have a good reason to flatly contradict REL on this point, or were you simply unaware of their estimate?
It's good to remember that we're all basically on the same side here.
Why don't they expect the first two prototypes to reach orbit? In what ways will those prototypes differ from the planned production variant?
Are you confident they will achieve the effective Isp and T/W for SABRE? If so, what do you base that on given that nothing has ever flown?
Looks like a deeply precooled air turborocket. I'm not convinced it will give them SSTO though and if you go with TSTO you could go with a less ambitious "undeeply" cooled hydrocarbon air turborocket, perhaps using LOX/methanol or methanol/peroxide.
It is fair to describe SABRE as an air turbo rocket. However it may be the bits you recognize are causing you to overlook the bits you don't.
SABRE's actual cycle has elements of both the RL10's expander cycle and the SSME's staged combustion.
It could also be said that the use of an inert fluid power transfer loop echos the Silverbird power plant of Eugene Sanger. REL's senior design staff have long memories.
Like the RL10 the “high temperature” drive turbine can be made of Aluminum because it only operates at a few 100 degrees.
By heating indirectly, rather than using the combustion products you avoid having to design turbines that can cope with 2x the chamber pressure while being bathed in superheated steam and hot GH2 moving at about Mach 0.5. A tough problem as SSME design engineers found.
If you have a model you'll need to factor those features in to see what difference that makes.
REL have stated that a successful test series will release c£200m in development funding. Judging by their press release this series has been successful. I'd strongly doubt that would happen if there were serious concerns over the tests validity.
If you have anything more than a hunch I'd be interested in hearing it, especially what assumptions you've made on the implementation.
It's risky but if you build another one of what you've always built (TSTO) you'll get pretty much what you've always got.
Spacex have gone with this path of conservatism. The VTO TSTO transitioning (hopefully) to VTOL TSTO. They believe there is substantial cost to be squeezed out of the process. Time will tell how much they can squeeze out. But it's still a TSTO and that 1st stage has to come down somewhere in between the launch pad and where ever the 2nd stage makes orbit.One of Skylons surprise (at least to me) selling has been it offers ELV payload fraction with SSTO re usability. All VTOL concepts seem to be *substantially* less than this (1% of GTOW seems to be the rule of thumb) which also seems to bother customers a lot.
IIUC Skylon will require multiple $billions to bring to fruition. If you amortise those development costs in a commercial fashion, how many launches do you need before Skylon surpasses SOTA cheap ELV (or rTSTO) in price?cheers, Martin
Quote from: MP99 on 07/12/2012 01:03 amIIUC Skylon will require multiple $billions to bring to fruition. If you amortise those development costs in a commercial fashion, how many launches do you need before Skylon surpasses SOTA cheap ELV (or rTSTO) in price?cheers, MartinThe flippant answer is REL don't care.They are manufacturers *not* operators.It's how many of them do they need to *sell* to make a profit. A rough guide on launch *price* is that the total propellant bill amounts to $10/Kg to LEO. What the servicing costs would be is another matter but there's a lot of scope to set pricing. It depends how much you'd have to charge to meet the interest payments you need to make to buy one in the first place.
They said in the interview linked here that their investors will recoup the investment if they sell 30 Skylons. How will the operators make money is the operator's own problem.
What's with the assumption I don't know what I'm talking about?
Yes. As well as an unusual counterrotating turbine and an unusual LOX cooled combustion chamber. I'm not aware of any production engine that uses LOX cooling, but there have been experimental ones and apparently it's not as risky as it might sound at first, even if there are leaks.
And they're also aware of patent issues.
Heating indirectly (or at least in a separate combustor that sees no air) is of course standard for a turborocket and is what sets it apart from turbojets and turbofans.
Well, I certainly don't have my own models, I wonder where people's confidence in models comes from and what models they've seen.
It seems to be the question is how much confidence we can have in the models presented by RE.
but I don't think it's fair to say TSTO is the same thing you've always got.
I like almost everything about the new website, but I'm not enjoying the music choice in their videos. They need something a little more grandiose. Ethereal sounding electronica or one or two carefully chosen classical pieces would do a better job of selling the technology.
Simply that you will not state exactly what your concerns are.
I'm suggesting you may have focused on the bits of the design you are familiar with while under rating other aspects that give it its edge.
SABRE is *like* an ATR as it is *like* a LACE.It is *neither* an ATR nor a LACE.
So they are uncommon but well within the state of the art.
That kind of sounds like a straw man argument to increase Fear Uncertainty & Doubt so far.
And they're also aware of patent issues. No doubt. They are not keen to discuss the frost control system for example.
And what sets SABRE apart from an ATR (apart from the fact that what is being heated is *not* the inlet air) is where that air is going.
Not to large combustion chamber which in a jet engine might be up to say 14atm above atmospheric, but to a rocket combustion chamber running 100-120Atm above atmospheric.
I was thinking more in terms of a set of configuration settings for one of the propulsion modelling codes professional engineers use in this field.
Well the UK Space Agency funded ESA to review the underlying technology and REL also hosted the 2 day "Requirements Review" on 20-21st of Sept 2010 where over a 100 guests had a chance to critique the design and the economics (perhaps you were there?) and both it and the ESA report were clear they saw no show stoppers, a process which AFAIK is also *unique* to REL, but I hope will be used by others in the future.
Every orbital launch vehicle I'm aware of has at least 2 stage to achieve orbit and is expendable.