Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 441979 times)

Offline ChrisWilson68

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1280 on: 03/05/2016 09:12 PM »
So the Air Force has found a concept that allows them to maximize system cost while minimizing the advantages? I mean... What should a two stag concept be good for? You replace a simple and scalable booster with an expensive SABRE design just to then add a second stage? Why???

Because a two stage system gives greater design margins.  A lot of experienced people believe Skylon has a lot of design risk because it's single-stage to orbit.  With two stages, there's more margin to work with, so the design doesn't have to push the edge of what's possible in so many ways, and there's more margin for making it more cost-effective.

Offline ChrisWilson68

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1281 on: 03/05/2016 09:14 PM »
So the Air Force has found a concept that allows them to maximize system cost while minimizing the advantages? I mean... What should a two stag concept be good for? You replace a simple and scalable booster with an expensive SABRE design just to then add a second stage? Why???

Because a two stage system gives greater design margins.  A lot of experienced people believe Skylon has a lot of design risk because it's single-stage to orbit.  With two stages, there's more margin to work with, so the design doesn't have to push the edge of what's possible in so many ways, and there's more margin for making it more cost-effective.

Plus, with two stages you can get the same payload to orbit with a smaller overall vehicle, or a larger payload to orbit with the same size vehicle.  Smaller size means lower cost, which can more than offset the additional complexity of having two stages.


Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1282 on: 03/07/2016 07:07 AM »
Anyone else building precoolers other than Reaction Engines?. Here hoping this isn't an attempt by the air force to replicate Reaction Engine technologies in the US without Reaction engine involvement.

That's debatable The programme mentioned in the space.com article is described here.

https://www.sbir.gov/sbirsearch/detail/870285

Note the bit upfront about ITAR and how access to USAFRL supecomputing facilities maybe by "qualified" staff only.

The joke is REL would be able to handle both phase I & II without breaking sweat given their prior experience.  :(

Time will tell if this is an effort by USAFRL to fund REL or if they are just trying to drain the tech from REL and inject it into an American company.  I'll note that AFAIK only REL have worked out what to build and how to build it. I sincerely hope REL take precautions to ensure that information remains with them.

IIRC an outfit called Andrews Aerospace has been pushing something called "Air Collection and Enrichment System" for decades, which is basically LACE. Somehow the words "Enthalpy of Vaporization" just don't seem to mean anything to them.

But SABRE is a launch engine, not a cruise engine.  It's designed to go Mach 0-23. If you want less, get a different design.  :(

Or (just throwing this idea out there) the USAF could pay REL to design a cruise engine, like normal customers do when they want something for a special purpose.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1283 on: 03/07/2016 07:29 AM »
Plus, with two stages you can get the same payload to orbit with a smaller overall vehicle, or a larger payload to orbit with the same size vehicle.  Smaller size means lower cost, which can more than offset the additional complexity of having two stages.
The current Skylon user manual gives a GTOW of 325 tones for a 15 tonne payload

That's a payload fraction of  4.6%

Which is better than a Delta IV, the nearest big LH2 LV around and probably better than an F9, given SX are remarkably secretive about such things.

Vertical Takeoff RLV's have always sacrificed payload fraction.  VTO SSTO's have sacrificed a lot of payload.

Skylon was designed to deliver a TSTO ELV payload fraction because its designers know there is no point in trying to raise funding for anything less.

Because a two stage system gives greater design margins. 
It's believed a TSTO design give greater margins.

So how come only 2 large designs in the 1930's were 2 stage aircraft? All commercial aircraft are "single stage."

Let's be clear the hidden message in this thinking is "we messed up the design of a stage, the other stage will compensate."

Why? Because the other stage will magically be better designed ? That might be true if the stages (like Saturn) were designed by different companies.

A single company is likely to end up with two underperforming stages instead of one.
Quote
A lot of experienced people believe Skylon has a lot of design risk because it's single-stage to orbit.  With two stages, there's more margin to work with, so the design doesn't have to push the edge of what's possible in so many ways, and there's more margin for making it more cost-effective.
AFAIK no one has experience of designing a successful SSTO of any kind, so who are these "experienced" people?

SABRE is designed to go the whole distance both in terms of speed and altitude. Skylon is designed to do the same. Splitting the task means..

(2 engine designs  + 2 vehicle designs + all their testing) x all the interactions between those stages.

Like the "Let's make a good TSTO ELV and then turn both stages into an RLV" meme it's one of those notions that sounds really sensible, and low risk but does in fact have an unquantifiable level of risk attached to it, to the point that one mfg has abandoned further efforts to do so with its existing architecture.

In contrast thousands of aircraft designs have gone from drawing board (and now CAD screen) to takeoff. Single stage winged vehicles have done sustained flight to M3.3+ and the X15 to M7+ for long enough to understand the issues. The Shuttle showed winged lift could handle M23 to M0 as well.

As the X30 programme showed the biggest risk of a HTOL SSTO is the engine and SABRE can be tested well enough on the ground that vehicle designers can be confident if their structural engineering is good enough it can get the job done.

If you're looking to get to LEO in a reusable system with minimum risk (and  you don't have some hobby horse to ride, like nuclear weapons delivery) you'd look at what flight regimes have the biggest knowledgebase you could leverage.

You'd also note that HTO means thrust can be 1/3 of GTOW rather than 1.1x (or more) of GTOW for VTOL systems.

But then you'd note there was no engine around that could the full range with adequate Isp and go back to rockets, which are also quite simple to model, relative to air breathing systems.

For pragmatic people who don't have a pet system to champion SABRE is a game changer.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline chipguy

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1284 on: 03/07/2016 04:38 PM »

The current Skylon user manual gives a GTOW of 325 tones for a 15 tonne payload

That's a payload fraction of  4.6%

Which is better than a Delta IV, the nearest big LH2 LV around and probably better than an F9, given SX are remarkably secretive about such things.


The key difference here is that DIV and F9 exist today and are launching payloads.

Skylon is a concept remarkably short of actual full scale technology demonstration of either propulsion or
vehicle structure and TPS. A slight shortfall in the performance of the former or underestimation of the
mass of the latter could reduce its SSTO performance from 15 tons to not reaching orbit at all with zero
payload.

Saying Skylon is *better* than a working system is nonsense. Maybe some day it might but I wouldn't
bet on it. The user manual for a non-existent system is science fiction.

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1285 on: 03/07/2016 05:44 PM »

Saying Skylon is *better* than a working system is nonsense. Maybe some day it might but I wouldn't
bet on it. The user manual for a non-existent system is science fiction.

Surely someone has to think "it is better" of a non-existent thing before they could be bothered to get out of bed and make it real?

Did the SpaceX founders think their non-existent clean sheet implementation would be better?

Offline chipguy

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1286 on: 03/07/2016 09:39 PM »

Surely someone has to think "it is better" of a non-existent thing before they could be bothered to get out of bed and make it real?

Did the SpaceX founders think their non-existent clean sheet implementation would be better?

Aspiring to do better than current solutions is what engineers like me do every day.

However, look at the tense of claim the previous poster made: " That's a payload fraction of  4.6%
Which is better than a Delta IV, the nearest big LH2 LV around and probably better than an F9"

You can't correctly claim that X is better than Y when Y exists and X doesn't. This especially true
when that claim about X is based on the development and perfection of technology that has never
been demonstrated before. X doesn't exist. A prototype of X or its engine doesn't exist. Performance
claims have to be taken with a freighter full of salt. History of this industry leads one to be sceptical.

A factually correct claim is "if X can be developed and if it performs up to the hopes of its proponents
then...". Anything stronger or more definite than that is intellectually dishonest.

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1287 on: 03/07/2016 11:54 PM »
To state the obvious: This thread is in Advanced Concepts. So off the bat we know that: 1] it doesn't exist yet, 2] people are interested in discussing the concept, and if/how it might come to exist.

So posts that point out it doesn't exist, and/or rush to conclude that it won't ever exist, or isn't worth discussing, really aren't moving the conversation forward very far...

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1288 on: 03/07/2016 11:59 PM »
A slight shortfall in the performance of the former or underestimation of the mass of the latter could reduce its SSTO performance from 15 tons to not reaching orbit at all with zero payload.

We've been over this before.  It's not a matter of a "slight shortfall"; this is not an all-rocket SSTO and is nowhere near as sensitive to either mass growth or engine underperformance.

According to my calculations, based on the numbers in the 2014 NISSIG presentation*, total payload loss would require one of:  A) an 11.6% Isp loss across both engine modes, B) a 12.2% rocket Isp loss with no airbreathing performance loss, C) a 72% loss of airbreathing Isp with no rocket performance loss, D) 30.5% dry mass growth, or E) some combination of the above.

But that's assuming no mass margin is being carried in the design, which is not accurate; they claim they're using mass growth margins "consistent with AIAA guidelines" for Skylon D1, which to me means at least 15% (IIRC their structural calculations for Skylon C1 back in the day used 15%).  Recalculating with dry mass divided by 1.15 results in the scenarios becoming:  A) a 16.8% Isp loss across both engine modes (for perspective, this would be like the SSME coming in at 379 s vac), B) a 17.5% rocket Isp loss with no airbreathing performance loss, C) an 80% loss of airbreathing Isp with no rocket performance loss, D) 50% dry mass growth, or E) some combination of the above.

* 325,000 kg at start of roll (from which I have subtracted 1,418 kg of brake water, under the assumption that not carrying it through the takeoff roll won't affect the numbers much), 299,819 kg at transition, 73,435 kg at MECO, 52,347 kg dry.  Payload to standard orbit is 15,000 kg with 986 kg performance margin.  For the purpose of these calculations, I have assumed that lost payload due to underperformance is subtracted from GTOW - ie: the vehicle is not being redesigned either to have lower dry mass or to carry more propellant in place of the lost payload.

intellectually dishonest.

It's shorthand, not intellectual dishonesty.  This thread would be way harder to read (and much more annoying to post to) if everyone had to rigorously finesse every single statement like you're demanding.
« Last Edit: 03/08/2016 05:41 AM by 93143 »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1289 on: 03/08/2016 09:57 AM »

Skylon is a concept remarkably short of actual full scale technology demonstration of either propulsion or
vehicle structure and TPS.
I see. So Skylon lacks a full scale demonstration because no one has built a Skylon yet. That alone makes you a doubter rather than a skeptic.

Your name suggests you deal with logic devices.

Do you understand the concept of a circular argument?
Quote
A slight shortfall in the performance of the former or underestimation of the
mass of the latter could reduce its SSTO performance from 15 tons to not reaching orbit at all with zero
payload.
You're thinking like it's a VTOL SSTO, where thrust must exceed GTOW just to lift off and you're structure mas can be no more than about 3% to give a payload of 1%, which is historically what Bono style VTOL have accepted.
Quote
Saying Skylon is *better* than a working system is nonsense. Maybe some day it might but I wouldn't
bet on it. The user manual for a non-existent system is science fiction.
Funny. I've seen plenty of semiconductor documentation marked "provisional."

In some cases I doubt they have even done the floor planning for the chip before telling the world it'll be available by next April, or whenever, yet they behave as if it will happen, and a lot of the time it does.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1290 on: 03/08/2016 09:58 AM »
To state the obvious: This thread is in Advanced Concepts. So off the bat we know that: 1] it doesn't exist yet, 2] people are interested in discussing the concept, and if/how it might come to exist.

So posts that point out it doesn't exist, and/or rush to conclude that it won't ever exist, or isn't worth discussing, really aren't moving the conversation forward very far...
Or indeed anywhere.   :(
« Last Edit: 03/08/2016 10:09 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Citizen Wolf

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1291 on: 03/08/2016 11:33 AM »
For the love of Thor. This is a discussion forum. On advanced concepts (stuff that hasn't been built yet).

We all know that. We don't need to repeat it and qualify our comments in very post.   smh
The only thing I can be sure of is that I can't be sure of anything.

Offline Hanelyp

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1292 on: 03/08/2016 04:38 PM »
According to my calculations, based on the numbers in the 2014 NISSIG presentation*, total payload loss would require one of:  A) an 11.6% Isp loss across both engine modes, B) a 12.2% rocket Isp loss with no airbreathing performance loss, C) a 72% loss of airbreathing Isp with no rocket performance loss, D) 30.5% dry mass growth, or E) some combination of the above.
...
LOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement.  Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload.  Allowing for the 15% margin looks even better.  Of course any payload loss reduces the economic margins of viability.

Taking the above as reliable, the biggest uncertainty may be maintenance requirements between flights.  Uncontained inspection and repair costs might render the whole system uneconomic even if full performance is delivered.

Offline chipguy

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1293 on: 03/08/2016 05:03 PM »
I see. So Skylon lacks a full scale demonstration because no one has built a Skylon yet. That alone makes you a doubter rather than a skeptic.

Your name suggests you deal with logic devices.

Do you understand the concept of a circular argument?

The DIV and F9 have existence proof of performance.

Skylon is a paper design relying on technologies yet to be demonstrated. I am all in favour of innovation
and progress and new ideas.

What I don't like is someone touting something hypothetical as if it was real and had proven performance.
An awful lot of things have to go very right for Skylon to live up to expectations. The history of attempting
to mix wings and/or air-breathing and/or hybrid propulsion systems with space flight suggests a healthy
scepticism is in order.

Quote
Funny. I've seen plenty of semiconductor documentation marked "provisional."

In some cases I doubt they have even done the floor planning for the chip before telling the world it'll be available by next April, or whenever, yet they behave as if it will happen, and a lot of the time it does.

I have never worked for such an organization. We disclose new products after we have thoroughly tested
them, have built thousands to assess manufacturability margins and ability to meet specifications with
good yield, and have performed extensive accelerated aging and stress tests to assure product operating
lifetimes.

OTOH you seem to be setting up a strawman to justify your touting Skylon so highly for an unbuilt system
relying on unproven technologies ("see, everybody does it"). The fact that you chose semiconductors as your
strawman category IMO hints at thinly veiled ad hominem attack.

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1294 on: 03/08/2016 07:46 PM »
I still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1295 on: 03/09/2016 07:13 AM »
LOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement.  Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload. 
The design of the SSME was off it's predicted Isp by about 3 secs. Note this was only the 2nd staged combustion engine built in the US and the first (and only) LH2 engine. That's 0.66% for a first of a kind (SC of LH2) design.  This suggests the rocket part at least is fairly well understood.
Quote
Taking the above as reliable, the biggest uncertainty may be maintenance requirements between flights.  Uncontained inspection and repair costs might render the whole system uneconomic even if full performance is delivered.
That's definitely one of the areas that the flight test programme will answer, to quantify damage between flights.

Note that while the Shuttle relied on a small army (several 100 staff IIRC) to inspect and repair the tiles & blankets a clean sheet design including the ConOps would incorporate embedded damage sensors in the airframe (NASA developed miniature remote reading data loggers to be dropped in the gaps between tiles to detect over temperature events. Multiple other options, including FO strain systems are possible) or an external scanning system as Carnegie Mellon proposed in the early 90's to move a sensor package over the whole skin and flag areas for attention.
« Last Edit: 03/09/2016 07:03 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1296 on: 03/10/2016 08:49 AM »
So posts that point out it doesn't exist, and/or rush to conclude that it won't ever exist, or isn't worth discussing, really aren't moving the conversation forward very far...

Except that's exactly what people did when they dismissed the USAF's TSTO proposal.

Yet the same people believe (and aggressively denounce anyone who questions that belief) that REL is so far beyond criticism, that we already know the non-existent Skylon's future payload accurate to one part in one thousand.

Your argument would be more believable if you had applied it in both cases.

Offline pippin

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The Reaction Engines Skylon Master Thread (5)
« Reply #1297 on: 03/10/2016 10:03 AM »
LOX-LH2 rocketry is a sufficiently mature tech that a large shortfall is ISP seems unlikely, even with the novel pump arrangement.  Which, presuming their engineers have done their jobs right, leaves substantial performance margins before complete loss of payload. 
The design of the SSME was off it's predicted Isp by about 3 secs. Note this was only the 2nd staged combustion engine built in the US and the first (and only) LH2 engine. That's 0.66% for a first of a kind (SC of LH2) design.  This suggests the rocket part at least is fairly well understood.
Not necessarily. Don't exactly know what you mean by "first LH2 engine", probably first LH2 staged combustion engine.
But if you look at the development effort you'll see that it had several years of delays and huge cost overruns in development.
As to hitting the ISP: they had to at all cost to make the whole thing viable, 10s less ISP and there goes your payload.

The general theory on how much ISP you can get out of a certain engine setup is pretty well understood, yes. But getting there can be very expensive and time consuming if you lack the experience and especially if it's a high ISP.
Look at Bezos' arguments as to why they are shooting for the mid range for BE4
« Last Edit: 03/10/2016 10:08 AM by pippin »

Offline Ravenger

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1298 on: 03/10/2016 12:25 PM »
There's a new article about Skylon and Sabre at The Verge website:

http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion

One bit of info was new to me:

Quote
"The company plans to test the engines this year"

This is exciting news if true.

Offline Hankelow8

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1299 on: 03/10/2016 12:36 PM »
There's a new article about Skylon and Sabre at The Verge website:

http://www.theverge.com/2016/3/8/11174670/rel-skylon-spaceplane-announced-jet-engine-rocket-propulsion

One bit of info was new to me:

Quote
"The company plans to test the engines this year"

This is exciting news if true.

Far too soon for engine testing, component testing  yes.
« Last Edit: 03/10/2016 12:42 PM by Hankelow8 »

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