The Reaction Engines Skylon/SABRE Master Thread (6)

[Stormbringer]

http://www.nextbigfuture.com/2016/12/reaction-engines-uk-progressing-to-full.html

Reaction Engines UK progressing to full demonstrator hypersonic engine in 2020 and fully reusable spaceplanes and hypersonic fighter jets around 2030

[oddbodd]

http://www.nextbigfuture.com/2016/12/reaction-engines-uk-progressing-to-full.html

Reaction Engines UK progressing to full demonstrator hypersonic engine in 2020 and fully reusable spaceplanes and hypersonic fighter jets around 2030

That "article" is just another example of atrocious quality blogger-level click-bait.

It's written using "we" and "our" by a guy who is in San-Fran, US. Obviously the guy has sweet F.A. to do with REL, so the pronouns used are very misleading, and the "article" is probably just cut-n-paste from elsewhere.

And for the love of God!!!! How many times do we need to read the completely factually incorrect "The oxygen in the chilled air will become liquid in the process." No, no, No, NO, NOOOOOOOOOOOO! SABRE is NOT LACE.

[momerathe]

yeah, no new info in the article AFAICT.

the community is particularly toxic on that site as well, to the extent that I directed my ad blocker to hide the whole comments section permanently.

[john smith 19]

I found several papers not by REL but about Skylon related issues.


A paper on the atmospheric response to large scale reusable launch vehicle use based on Skylon.
http://onlinelibrary.wiley.com/store/10.1002/2016EF000399/asset/eft2171.pdf;jsessionid=1B7858A9DD26B51D197FA5A6814938D8.f04t04?v=1&t=iwi25d7t&s=58b70fa89498d5126a7659f23187d3f15b1e29d7

You might want to check that URL, it comes up "forbidden" on my browser.

A paper about Skylon's approach to safety and certification.
http://www.saturnsms.com/wp-content/uploads/2016/06/Quinn_Varvill_SABRE_Enabling-Single-Stage-to-Orbit-Safely_final.pdf

Mentioned before but I think it gives a good description of how REL are dealing with the view that "It's a rocket it can't be regulated under aircraft rules" argument is being addressed.

An interesting paper on the economic value of reusability.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160013370.pdf

mentioned on the reusability costs thread and it's conclusion "It depends" is frankly not very helpful.

[AnalogMan]

I found several papers not by REL but about Skylon related issues.


A paper on the atmospheric response to large scale reusable launch vehicle use based on Skylon.
http://onlinelibrary.wiley.com/store/10.1002/2016EF000399/asset/eft2171.pdf;jsessionid=1B7858A9DD26B51D197FA5A6814938D8.f04t04?v=1&t=iwi25d7t&s=58b70fa89498d5126a7659f23187d3f15b1e29d7

You might want to check that URL, it comes up "forbidden" on my browser.

Try this link:

http://onlinelibrary.wiley.com/doi/10.1002/2016EF000399/abstract

or this one to go straight to a pdf download:

http://onlinelibrary.wiley.com/doi/10.1002/2016EF000399/pdf

[john smith 19]

or this one to go straight to a pdf download:

http://onlinelibrary.wiley.com/doi/10.1002/2016EF000399/pdf

Interesting article but it's assumptions should be taken with a substantial pinch of salt. On page 4, para 3 they explain how they got the figure for NOx production. They took the NOx profile calculated for the Shuttle in 1980 and scaled it by the (presumably) landing mass of Skylon. They also note that NOx is caused by air being heated to 1800K during entry, however IIRC the Skylon skin material is not expected to be used above 1400K. REL have also developed a combustion process they expect to deliver 1% of that of previous air/Hydrogen burners.

BTW REL's business goal is 30 Skylons sold over a period of at least a decade. That's 6000 flights in total. 

[john smith 19]

There would still be the difference that is, as near as I can tell, the whole point of the current dispute between you/JS19 and Ron/Chris.

I've not argued for any sort of government funding on the model of COTS or CCCP and in fact I understand the background of those projects well enough to know that the basis the UK govt would invest in Skylon is very different to the basis that the USG (through NASA) invested in COTS.

So please stop telling me what I'm arguing, especially when I'm not arguing about anything.

This is why many of us have suggested for years that REL was making a mistake in focusing so tightly on Skylon. (And got shouted down for our efforts.)
(What's interesting to me is that the main suggestions that were so authoritatively dismissed by you, JS19 and others is exactly what we're seeing evolve now. A D-21 type SABRE flight demonstrator. A TSTO as a stepping stone development. Etc.)

what you perceive as "shouting down" was being reminded that it was REL's plan to go with Skylon as their SABRE flight vehicle. It was REL's view that this would minimize overall budget and it was sized that big because there is a proven market for payloads of that size, something which is much more doubtful for smaller payloads.

My personal view (given the issues with scaling down LH2 turbopumps) would be to push for a a scaled down Skylon with 10-100Kg payload but full size SABRE engines. That would prove out the structures, materials, engines and aerodynamics in one go. I'm quite sure reducing the payload by 2-3 orders of magnitude would have a radical effect on reducing the overall vehicle size. However REL have a horror of scale effects and TBH any part on the sub scale Skylon would just have to be made again at full size. So do a thing once (at full size) or do a thing twice

I can see why REL have made certain choices. You confuse someone who can see why a choice has been made with agreeing with those choices and you don't seem to see that REL are acutely conscious of how much money they have had to work with at any given stage, hence their desire to do things once, rather than twice.

[Alpha_Centauri]

Found this recent presentation given to RAL Space;

https://www.ralspace.stfc.ac.uk/Pages/MarkThomas-SABRE.pdf

Not heavy on detail but some new imagery; particularly the full cut-down SABRE nacelle, a TSTO concept I hadn't seen before with a ventral payload bay, and the clearest CGI of Blue Boomerang.

But more importantly note the repeated references to TSTO...

[Katana]

Found this recent presentation given to RAL Space;

https://www.ralspace.stfc.ac.uk/Pages/MarkThomas-SABRE.pdf

Not heavy on detail but some new imagery; particularly the full cut-down SABRE nacelle, a TSTO concept I hadn't seen before with a ventral payload bay, and the clearest CGI of Blue Boomerang.

But more importantly note the repeated references to TSTO...

Is the simple cone inlet (instead of isentropic curved surface cone) efficient enough Up to M5?

[RanulfC]

http://www.nextbigfuture.com/2016/12/reaction-engines-uk-progressing-to-full.html

Reaction Engines UK progressing to full demonstrator hypersonic engine in 2020 and fully reusable spaceplanes and hypersonic fighter jets around 2030

That "article" is just another example of atrocious quality blogger-level click-bait.

It's written using "we" and "our" by a guy who is in San-Fran, US. Obviously the guy has sweet F.A. to do with REL, so the pronouns used are very misleading, and the "article" is probably just cut-n-paste from elsewhere.

And for the love of God!!!! How many times do we need to read the completely factually incorrect "The oxygen in the chilled air will become liquid in the process." No, no, No, NO, NOOOOOOOOOOOO! SABRE is NOT LACE.

The writing quality on NBF has really taken a nose dive, I'm surprised there wasn't a mention of the SABRE being a SCramjet along with everything else wrong with the article. (Though to be honest I suspect the "We're" part was supposed to be a quote from the way it was presented)

Randy

[Cinder]

The absence of any clue that NBF articles' content transitions to/from NBF/source - that has been a major issue and repeatedly brought up to the blogger/blog team.  It's been years and it seems is not about to change either.

[RanulfC]

The absence of any clue that NBF articles' content transitions to/from NBF/source - that has been a major issue and repeatedly brought up to the blogger/blog team.  It's been years and it seems is not about to change either.

Dating myself but I recall when that was an aberration rather than standard practice, I also remember concise and detailed articles with citations and links to various supporting works. This one is something I'd have expected as a fluff piece from a fashion writer assigned to cover a science announcement with all the mistakes and misinformation that would imply.

Randy

[RanulfC]

Having said the above I'm going to point out an article on a "Nuclear Thermal Turbo Ram Jet Engine" paper and Q&A that was posted there, (see specifically: http://www.nextbigfuture.com/2015/07/interview-with-john-bucknell-about-his.html, but also: http://www.nextbigfuture.com/2015/07/nuclear-thermal-turbo-rocket-with.html) finally found someone who actually 'gets' SCramjets, (though the author still believes the 'can' do better, 'eventually' at least he admits they have serious issue currently) in that with a heat source that does NOT depend on actual combustion dynamics they can in fact work and probably, (assuming you get the geometry right which is always possible to screw up) pretty well as long as you're willing to accept injecting super-heated hydrogen right out of a nuclear reactor into the air flow

The use of a MITEE cermetal reactor design and the ducting to the supersonic flow through fan blades is an interesting concept. but that's not REL/Skylon/SABRE I know but I'm pointing out this is why I still end up checking out NBF despite the "issues" in that it's the only place I can find some of this stuff. Which is why I wish they'd take their writing/research/etc more seriously.

Randy

[john smith 19]

The use of a MITEE cermetal reactor design and the ducting to the supersonic flow through fan blades is an interesting concept. but that's not REL/Skylon/SABRE I know but I'm pointing out this is why I still end up checking out NBF despite the "issues" in that it's the only place I can find some of this stuff. Which is why I wish they'd take their writing/research/etc more seriously.

That's some crazy tech.  . So basically a GH2 driven turbine operating up to M5 then (presumably) locking in place and running as a straight rocket?

[Katana]

SABRE runs very close to ramjet at M5.

Heat absorbing capability of LH2 is about 1/10 of combustion energy release. While at M5 the energy of air is near to combustion energy release. So the amount of cooled air is much lesser than hydrogen used in cooling, most part of hydrogen are burned in bypass channel.

[john smith 19]

SABRE runs very close to ramjet at M5.

Heat absorbing capability of LH2 is about 1/10 of combustion energy release. While at M5 the energy of air is near to combustion energy release. So the amount of cooled air is much lesser than hydrogen used in cooling, most part of hydrogen are burned in bypass channel.

I'm not clear what point you're trying to make. Could you be a little clearer?

[Katana]

SABRE runs very close to ramjet at M5.

Heat absorbing capability of LH2 is about 1/10 of combustion energy release. While at M5 the energy of air is near to combustion energy release. So the amount of cooled air is much lesser than hydrogen used in cooling, most part of hydrogen are burned in bypass channel.

I'm not clear what point you're trying to make. Could you be a little clearer?

At high Mach number the SABRE core could only cool and compress tiny amounts of extremely hot air. The operation cycle and hence the thrust performance converges to standard ramjet, and the core becomes dead weight.

The only benefit of SABRE over ramjet is start from zero speed to supersonic , which could also be done by conventional rocket engine, no heavier than the SABRE core and cost ~20% of total propellant.

The structure weight and fuel consumption of standard ramjet+rocket is not much worse than SABRE, but much easier to build.

[momerathe]

At high Mach number the SABRE core could only cool and compress tiny amounts of extremely hot air. The operation cycle and hence the thrust performance converges to standard ramjet, and the core becomes dead weight.

Which would explain why they transition to rocket mode at >M5.

The only benefit of SABRE over ramjet is start from zero speed to supersonic , which could also be done by conventional rocket engine, no heavier than the SABRE core and cost ~20% of total propellant.

I'm pretty sure the bolded statement is wrong. A conventional rocket has lower effective ISP, and therefore must use more fuel, almost by definition.

The structure weight and fuel consumption of standard ramjet+rocket is not much worse than SABRE, but much easier to build.

Are you talking about two separate engines, or something like an ejector rocket/air-augmented rocket? Because if it's the latter, there was NASA-GTX, but IIRC the design never closed. Certainly, it's been in the literature for a while, and nobody has seriously proposed building something similar, if it's so "easy".

Besides, whether a ram-rocket (or whatever) is feasible or not, isn't really relevant to this discussion..

[ChrisWilson68]

The only benefit of SABRE over ramjet is start from zero speed to supersonic , which could also be done by conventional rocket engine, no heavier than the SABRE core and cost ~20% of total propellant.

I'm pretty sure the bolded statement is wrong. A conventional rocket has lower effective ISP, and therefore must use more fuel, almost by definition.

You're misinterpreting what Katana is saying.  When Katana says "cost ~20% of total propellant" that means cost in addition to the prop that would be there for SABRE.  That's because Katana is agreeing with you that Isp is higher for SABRE so 20% more prop is needed for the non-SABRE alternative.

[john smith 19]

At high Mach number the SABRE core could only cool and compress tiny amounts of extremely hot air. The operation cycle and hence the thrust performance converges to standard ramjet, and the core becomes dead weight.

And you know this how?

The only benefit of SABRE over ramjet is start from zero speed to supersonic , which could also be done by conventional rocket engine, no heavier than the SABRE core and cost ~20% of total propellant.

The structure weight and fuel consumption of standard ramjet+rocket is not much worse than SABRE, but much easier to build.

On the basis you are not trolling I'll point out that SABRE's benefit is it is one engine that runs from M0-M23. You appear to be concentrating on one very  minor section of the whole trajectory when to make the system work you have to balance the whole task.

IIRC Hemsell (in a Space Show broadcast IIRC) said the improvement in Isp eliminates roughly 100 tonees (that's more like 30% of gross propellant) and it's associated structure.  I'd also caution anyone thinking that the mass saved is only the LOX equivalent. Air is 80% N2 so while it's not burnt it does give reaction mass that's thrown out the back. You could simulate this with your rocket but that would need a big water or LN2 tank to supply that mass. 

I'll also note SABRE's expected T/W is 14:1. You're hypothetical rocket and ramjet combination should be better than SABRE, not "not much worse" given your vehicle would be starting under rocket power and so the ramjet should not have to be sized to generate full takeoff thrust.

There is a spreadsheet from REL listing the SABRE 3 flows and loads in both air breathing and rocket modes. Have you used it?

BTW an early Skylon version looked at the idea of a "Zero length launch" using a brief rocket mode pulse. It's described in the 1989 Spaceflight article.

I suspect a fair bit of the criticism of the Skylon design is it's high structural fraction. However the traditional argument against reusable (VTOL) SSTO is you have to pack landing gear and TPS in a very small fraction of GTOW. Likewise it's known HTOL lets you need much less than 1.1x (or more) of GTOW as thrust.

But now you have to pack wings and a landing gear (and a TPS) into the (very small)  structural fraction that rocket systems allow you to have.

SABRE enables you to build a system that can take advantage of the reduced thrust an HTOL system needs without needing to pack wings and landing gear in a wafer thin (<10% GTOW) structural margin.