The Reaction Engines Skylon/SABRE Master Thread (6)

[edzieba]

Orientation doesn't really matter squat as long as Skylon can deploy it in microgravity and above the majority of the atmosphere, which as far as I am aware was always intended to be the case (think deployment like an STS IUS rather than like the D-21).

It does if the stage was originally designed to launch vertically. The weight distribution is very different. You may recall that SX pulled out of doing a horizontal rocket for Stratolaunch. AIUI the assumption has been "It'll just be a scaled down F9 on its side." It wasn't.

Stratolaunch want to launch a stage horizontally in atmosphere, and not in freefall. For Skylon, the stage will be launch in vacuum and in freefall.

[john smith 19]

It does if the stage was originally designed to launch vertically. The weight distribution is very different. You may recall that SX pulled out of doing a horizontal rocket for Stratolaunch. AIUI the assumption has been "It'll just be a scaled down F9 on its side." It wasn't.

Stratolaunch want to launch a stage horizontally in atmosphere, and not in freefall. For Skylon, the stage will be launch in vacuum and in freefall.

My comments were more in terms of the USAF design studies and the second stage they use.

For the full Skylon vehicle the US is needed for GTO payloads.

IIRC Skylon behavior up to 600Km been modeled, which I suspect would cover most of the range of what the USAFRL has been calling "Responsive space" or "responsive launch."

[edzieba]

OK, summary of questions (I'll get through as many as I can):

- Sub-cooled Methane in place of Hydrogen?

- Alternative uses for intercooler (e.g. GCNR)?

-Are there any plans to use the test bed engine (or a later version) in a flight vehicle? If so would it be 1, 2 or more engined and could it be orbit capable?

- Given the progress being made, all we are hearing about recently is SABRE. Is Skylon, or a similar SSTO craft, still the goal? (ref. AFRL/Spaceworks Enterprises Inc TSTO designs)

- After the precooler, what is the next most difficult item to get ready for flight?

::EDIT::
All answered and more, will write up in full later.

[edzieba]

First, a great presentation that actually answered most of the questions from here umprompted (were you watching here, Mark?  ), big thanks to Mark Wood.

Let's start with Methane: Yes, RE are actively looking at how performance would be changed by a switch to Methane, as well as confirming that it would simplify structure (prop density) and greatly simplify ground handling and safety particularly for manned flight and spaceflight. This also came with confirmation that while SSTO remains the 'holy grail' goal, RE are taking a much more pragmatic approach to development with TSTO being more viable. Which ties into...

Sklylon vs. other designs: RE are continuing with Skylon as the 'reference design'/use-case for SABRE, but are actively working with other companies to use Skylon both for spaceflight and for hypersonics. The SEI design got its own slide too, in place of Skylon as an example of a launch application, though not explicitly named.
Images of the SR-72 featured prominently (title slide and it's own dedicated slide), received a direct callout as a potential application, and a mention that Skylon's US location in Colorado was explicitly chosen for proximity to Lockheed Martin, and that the head of their US operations is the former head of Lockheed Martin's 'New Vehicles' division. So yeah, very much nudge-nudge-wink-wink-saynomore there.

And on the US note: The Hot Enthalpy Test (HET) of the HEX with hot intake air (current tests have been with ambient air) will involve the HEX and test stand being manufactured in the UK, then shipped to the US site for testing as a "black box". This is expected Q2/AQ3 this year.
ITAR is a definite concern, and RE are being careful to avoid any design or components that would be encumbered by ITAR. Keeping control of the IP is actually a condition of the government development grant.

The 'DEMO-A' testbed, which consists of the 'core' of the engine minus HEX (fed chilled air) a H2 turbopump from "an Ariane engine" (probably Vulcain), a COTS helium compressor, RE's Helium turbine, He/H2 HEX (flat planar with microchannels, modules wrapped around engine core just visible in public renders), combustion chamber, etc. Currently "70% company effort" into this demo unit and its test stand (as complex or mpre than the unit under test!). Internal wager between whether DEMO-A or the Wescott test site will be ready first. Wescott is expected to be structurally complete Sept 2019, to start test operations 2020.

Wescott site: site limitation of 5 tons Hydrogen on-site at a time, enough for "several seconds" of test operation. Will be UK's only H2 test site, expected to have "lots of Hydrogen tankers arriving" during operation.

Testbed designs: Slides showed a single-engine testbed looking a bit like a D-21 with a belly-mounted delta and no strakes. Mark confirmed this was the current concept for the test vehicle (though of course subject to change).

Testing timeline (admitted to be aggressive):
2019 - Expected to start seeing HEX spinout developments
2023 - Integrated engine test
2024 - Test vehicle flight
2025 - First 'application vehicle' flight ("Maybe!")

Speaking of the HEX (and the hot Helium turbomachinery) RE are indeed looking at applications in other industries, but have just set up a dedicated department to pursue these now they have demonstrated functioning operation of the HEX ("Very high confidence" in HEX functionality). Nuclear applications were acknowledged, though not something that are in active pursuit of, but also any heat exchange applications (e.g. high performance engines, supercritical CO2 applications). One interesting tidbit on the anti-icing (though still keeping schtum on how it works): it can be actively toggled on and off during operation, and activley rejects icing. HEX can be operated with anti-icing off and allow ice to (start to) build up, then turn it on and watch the ice melt.

Next biggest challenge after the HEX: Helium turbomachinery, followed by systems integration of all the parts into the complete engine, followed by engine sequencing (startup with preburner priming, transitions, etc). John's question on funding structures ties in here: the government grant in 2015 was structures such that RE self-funded development and, once milestones were reached, funds were released to RE. One of the milestones was for work on the Helium turbopump and He/H2 heat exchanger.

The Expansion/Divergent nozzle is in active development known as 'DEMO-R', but results are no longer going to be public (the old E/D pages from the RE website are long gone too) and will not be until very near end of development. Research is mostly underway at university partners at the moment, RE's focus is on DEMO-A.

The variable geometry intake was quickly touched on: intake movement not much to do with shock positioning within engine, much more to to with external drag.

The presentation included an utterly hilarious (standard Military Contractor Dodgy CGI) video from BAE with a not-a-Skylon (same planform, engine exhausts moved to the centrebody) being deployed as a military asset, comically outrunning some SAMs (they literally approach to within a few metres behind then drop away with humorous sound effects), dropping canisters backwards out of the wingtip pods (where the engines should be) while at hypersonic speeds that then decelerated and dropped to the target to... deploy some little reconnaissance drones. Mark was very careful not to cast any aspersions on BAE, and only expressed relief that the payload ("Did you see those pods where the engines normally go?") were not munitions (they got to see the video for the first time a day before BAE played it at a major airshow).

Bowie seems to be the 'in thing' for space at the moment, so the presentation ended with a quote from him to sum up RE "I don't know where I'm going from here, but I promise it won't be boring".

I think that about covers everything that was not already well known.

[e of pi]

Is video or audio available from the talk?

[CrewtaiL]

Testing timeline (admitted to be aggressive):
2019 - Expected to start seeing HEX spinout developments
2023 - Integrated engine test
2024 - Test vehicle flight
2025 - First 'application vehicle' flight ("Maybe!")

2020 - Start of core testing, a four phase programme over eighteen months.

The data collected from the 'black box' HX test in Colorado will be available to REL, iirc.

An in-house study has been done on the use of argon in place of helium. Indications (from body language) were that helium remains the preferred option for good reason(s). 

Lastly, the impression given was of a team - circa 160 strong now - that is not underestimating the challenges ahead; they're cognizant that a lot of the necessary technology has yet to be demonstrated.

[john smith 19]

Let's start with Methane: Yes, RE are actively looking at how performance would be changed by a switch to Methane, as well as confirming that it would simplify structure (prop density) and greatly simplify ground handling and safety particularly for manned flight and spaceflight. This also came with confirmation that while SSTO remains the 'holy grail' goal, RE are taking a much more pragmatic approach to development with TSTO being more viable. Which ties into...

Given how tightly LH2 has been woven into their plans this is a large shift in thinking within REL.
Any indications if this is a parallel plan or if they are considering switching away from LH2 entirely?

Sklylon vs. other designs: RE are continuing with Skylon as the 'reference design'/use-case for SABRE, but are actively working with other companies to use Skylon both for spaceflight and for hypersonics. The SEI design got its own slide too, in place of Skylon as an example of a launch application, though not explicitly named.
Images of the SR-72 featured prominently (title slide and it's own dedicated slide), received a direct callout as a potential application, and a mention that Skylon's US location in Colorado was explicitly chosen for proximity to Lockheed Martin, and that the head of their US operations is the former head of Lockheed Martin's 'New Vehicles' division. So yeah, very much nudge-nudge-wink-wink-saynomore there.

I think most people who saw the announcement for their test engine at about 44Klb would have been thinking "Hmm, just about right for slotting into that SR72 concept that LM have been talking about."
Except
LH2 killed Suntan in favor of the A12 (the original SR71). The USAF seems to have a horror of all cryogens, so IMHO even Methane wouldn't be enough to make them comfortable with this. But maybe performance trumps everything?
SR72 is very firmly in the "defense" usage category, putting REL in bed with the whole mess that is the US ITAR. 
LM seemed pretty clear that they already have an engine supplier in Orbital ATK with their "Dual mode ram/SCramjet."
Isn't the SR72 meant to be a near term thing? LM have made quite a play of the engine basically already been done, it's "just" a case of building the airframe,while the REL test engine is maybe 21 months away at least.

A question I would have asked also would be "On a scale of 1 to 10, where 1 is some powerpoints and 10 is a signed contract from some part of the USG, where would you put the SR72 programme?"

And on the US note: The Hot Enthalpy Test (HET) of the HEX with hot intake air (current tests have been with ambient air) will involve the HEX and test stand being manufactured in the UK, then shipped to the US site for testing as a "black box". This is expected Q2/AQ3 this year.

Interesting but not necessarily surprising. One of the SSME stands had to simulate the rest of the engine. It had 2000 fluid valves to do so. An obvious question would be will the US retain the test stand? I think that will be the newest hypersonic wind tunnel in quite some time.

ITAR is a definite concern, and RE are being careful to avoid any design or components that would be encumbered by ITAR. Keeping control of the IP is actually a condition of the government development grant.

Which one? The UK govt money or the DARPA funds to REL US?

The 'DEMO-A' testbed, which consists of the 'core' of the engine minus HEX (fed chilled air) a H2 turbopump from "an Ariane engine" (probably Vulcain), a COTS helium compressor, RE's Helium turbine, He/H2 HEX (flat planar with microchannels, modules wrapped around engine core just visible in public renders), combustion chamber, etc. Currently "70% company effort" into this demo unit and its test stand (as complex or mpre than the unit under test!). Internal wager between whether DEMO-A or the Wescott test site will be ready first. Wescott is expected to be structurally complete Sept 2019, to start test operations 2020.

I wouldn't bet on the Vulcain, it's about 6x too big for the test engine (and a bit small for the full SABRE).
The turbine on the Vinci is just a smidgen too small (about 40klb thrust Vs 44klb for test engine).
If so the Vinci turbine will be getting a very stiff workout. I suspect the result will help the Vinci developers.

Now that sounds like a 3 month "float" in the construction schedule. I do hope they also have plans in case things go right and they can get started sooner.  I know. But it could just happen.

Wescott site: site limitation of 5 tons Hydrogen on-site at a time, enough for "several seconds" of test operation. Will be UK's only H2 test site, expected to have "lots of Hydrogen tankers arriving" during operation.

And possibly other people as well? 5 tons may not be long for an engine this size but it's quite a bit for smaller engines.5 secs at 44 000lbs, double that for an RL10 class engines, minutes for something in the 1000lb class.

Testbed designs: Slides showed a single-engine testbed looking a bit like a D-21 with a belly-mounted delta and no strakes. Mark confirmed this was the current concept for the test vehicle (though of course subject to change).

Did he mention if the "application vehicle" is designed as an expendable or it will support an actual flight test programme?
Because if so I think that would make it the first reusable hypersonic test vehicle since the X15.
Which would make it quite valuable if designed with consideration for the sort of experiments potential customers might like to run.

Testing timeline (admitted to be aggressive):
2019 - Expected to start seeing HEX spinout developments
2023 - Integrated engine test
2024 - Test vehicle flight
2025 - First 'application vehicle' flight ("Maybe!")

Speaking of the HEX (and the hot Helium turbomachinery) RE are indeed looking at applications in other industries, but have just set up a dedicated department to pursue these now they have demonstrated functioning operation of the HEX ("Very high confidence" in HEX functionality). Nuclear applications were acknowledged, though not something that are in active pursuit of, but also any heat exchange applications (e.g. high performance engines, supercritical CO2 applications). One interesting tidbit on the anti-icing (though still keeping schtum on how it works): it can be actively toggled on and off during operation, and activley rejects icing. HEX can be operated with anti-icing off and allow ice to (start to) build up, then turn it on and watch the ice melt.

There is a patent. It talked about injecting Methanol at the front of the engine and collecting it at the back, then stripping out the water for disposal.

Next biggest challenge after the HEX: Helium turbomachinery, followed by systems integration of all the parts into the complete engine, followed by engine sequencing (startup with preburner priming, transitions, etc).

Yes I suspected as much. Helium is nearly as slippery to deal with as Hydrogen. Knowing how much trouble the development of the SSME start sequence caused I wouldn't be surprised if this is already receiving attention.

John's question on funding structures ties in here: the government grant in 2015 was structures such that RE self-funded development and, once milestones were reached, funds were released to RE. One of the milestones was for work on the Helium turbopump and He/H2 heat exchanger.

Interesting.

The Expansion/Divergent nozzle is in active development known as 'DEMO-R', but results are no longer going to be public (the old E/D pages from the RE website are long gone too) and will not be until very near end of development. Research is mostly underway at university partners at the moment, RE's focus is on DEMO-A.

Did he confirm that the engine is SABRE 4 and they are definitely going with the E/D nozzle?

The variable geometry intake was quickly touched on: intake movement not much to do with shock positioning within engine, much more to to with external drag.

That is a surprise.  Most of the writing on this subject talks about the importance of shock position relative to the internal geometry of the system, and how it changes with increasing speed, hence the moving spike.

The presentation included an utterly hilarious (standard Military Contractor Dodgy CGI) video from BAE with a not-a-Skylon (same planform, engine exhausts moved to the centrebody) being deployed as a military asset, comically outrunning some SAMs (they literally approach to within a few metres behind then drop away with humorous sound effects), dropping canisters backwards out of the wingtip pods (where the engines should be) while at hypersonic speeds that then decelerated and dropped to the target to... deploy some little reconnaissance drones. Mark was very careful not to cast any aspersions on BAE, and only expressed relief that the payload ("Did you see those pods where the engines normally go?") were not munitions (they got to see the video for the first time a day before BAE played it at a major airshow).

Bowie seems to be the 'in thing' for space at the moment, so the presentation ended with a quote from him to sum up RE "I don't know where I'm going from here, but I promise it won't be boring".

I think that about covers everything that was not already well known.

Thanks for covering it so thoroughly. It looks like things are really starting to move.

[john smith 19]

Testing timeline (admitted to be aggressive):
2019 - Expected to start seeing HEX spinout developments
2023 - Integrated engine test
2024 - Test vehicle flight
2025 - First 'application vehicle' flight ("Maybe!")

2020 - Start of core testing, a four phase programme over eighteen months.

The data collected from the 'black box' HX test in Colorado will be available to REL, iirc.

Were you there as well?

An in-house study has been done on the use of argon in place of helium. Indications (from body language) were that helium remains the preferred option for good reason(s). 

That is very surprising. IIRC they used Neon for their testing of a contra-rotating turbine test. Argon is AFAIK the cheapest of the inert gasses (it makes up the bulk of the inert gases in the atmosphere) but AFAIK it will freeze at LH2 or even LO2 temperatures.

Lastly, the impression given was of a team - circa 160 strong now - that is not underestimating the challenges ahead; they're cognizant that a lot of the necessary technology has yet to be demonstrated.

Which is way better than thinking everything will run like clockwork.

[JCRM]

And on the US note: The Hot Enthalpy Test (HET) of the HEX with hot intake air (current tests have been with ambient air) will involve the HEX and test stand being manufactured in the UK, then shipped to the US site for testing as a "black box". This is expected Q2/AQ3 this year.

Interesting but not necessarily surprising. One of the SSME stands had to simulate the rest of the engine. It had 2000 fluid valves to do so. An obvious question would be will the US retain the test stand? I think that will be the newest hypersonic wind tunnel in quite some time.

It's not a hypersonic wind tunnel. It simulates the post intake conditions - hot subsonic air.
We saw upthread that it was reusing some American equipment that uses a turbojet to heat and drive the air, and we've seem the designs and fabrication of the interface and enclosure for the heat exchanger. The plumbing for providing the cold helium, and handling/measuring the cooled air is certainly going to be interesting. I wonder if they'll be using the viper again to draw air from the cooler.

[Archibald]

Let's start with Methane: Yes, RE are actively looking at how performance would be changed by a switch to Methane, as well as confirming that it would simplify structure (prop density) and greatly simplify ground handling and safety particularly for manned flight and spaceflight.

Wow. Skylon switching to methane ? What's said above is pretty right. LH2 has well-known flaws that are becoming glaring (Musk endorsed methane, not only because ISRU and Zubrin, note that Falcon 9 still has no LH2 stage, too. Neither the Russians, by the way - Soyuz, Proton...)

Also 60 years of rocketry experience with LOX (hello, Sputnik R-7 launcher) can be applied to methane (same temperature and density).

Still I wonder what that switch will do to the carefully engineered SABRE cycle. Methane is "hotter" than LH2,       -180°C vs -270°C so atmospheric air heat "dumping" and "recycling" will be harder, although the helium loop might handle that.
More helium in the loop maybe ? or some kind of "open cycle" that drop more gaseous methane instead of fully recycling all the gaseous hydrogen as in SABRE ?

The difference between HOTOL and Skylon engines was that HOTOL literally bled itself of LH2 propellant just to cool the air, in the process it lost a crapload of LH2 that was dumped because it was now in a unusable gaseous state.
Skylon tried to solve that issue by using a closed helium loop to take the heat away, and also tried to make good use of the gaseous hydrogen in a turbine, instead of stupidly dumping it overboard.

Is video or audio available from the talk?

Seconded !

[edzieba]

They're investigating a switch to Methane, but it's far from a done deal. You save on structural mass, but you lose big on ISP and on engine thermal efficiency. It may work out as unviable for space launch, or unviable altogether.

The lunchtime lectures are supposedly recorded, but they're not in the IET video library or the London Community videos/files sections, so I have no clue where they're actually uploaded to (may just be for an offline archive).

[john smith 19]

Wow. Skylon switching to methane ? What's said above is pretty right.

They know. However to make the SABRE cycle work LH2 has very good properties (SHC 4x that of water is very hard to beat) and I doubt there has been sufficient incentive to look at anything else before.

Also 60 years of rocketry experience with LOX (hello, Sputnik R-7 launcher) can be applied to methane (same temperature and density).

TBH all the short chain hydrocarbons (Methane, Ethane, Propane, Butane and their Alkene homologues) are pretty similar.  Things only really improve when you get to the triple bonded HC's like Propyne.

Still I wonder what that switch will do to the carefully engineered SABRE cycle. Methane is "hotter" than LH2,       -180°C vs -270°C so atmospheric air heat "dumping" and "recycling" will be harder, although the helium loop might handle that.
More helium in the loop maybe ? or some kind of "open cycle" that drop more gaseous methane instead of fully recycling all the gaseous hydrogen as in SABRE ?

Well that's the question, isn't it?
In an earlier presentation REL said SABRE 4 can cope with hotter intake air (hotter is relative. "Does not need frost control" suggests > 0c after the precooler has done its work). So LH2s SHC is less important.

The difference between HOTOL and Skylon engines was that HOTOL literally bled itself of LH2 propellant just to cool the air, in the process it lost a crapload of LH2 that was dumped because it was now in a unusable gaseous state.

Are you sure you're not confusing HOTOL with the US "Aerospaceplane" programme of the early 60's? That insisted on a LACE engine to go to full liquid air. That phase change gulped LH2.
IIRC The HOTOL engine used 6x less LH2 than that unit.

Skylon tried to solve that issue by using a closed helium loop to take the heat away, and also tried to make good use of the gaseous hydrogen in a turbine, instead of stupidly dumping it overboard.

I'm not really sure what you're trying to say here.

Would it help to remind you that SABRE is the engine and Skylon is the vehicle?
Or that both designs have always used the heat removed from the incoming airstream to drive the turbo pump turbines?
Not "stupidly dumping it overboard" was part of the reason the LACE engines were so heavy that they spent a lot of mass finding clever uses for the excess H2, because they had so damm much of it.

If you cut excess H2 (over and above what you need to burn with the air) by 6x you don't need to work so hard to find another use for it. Burning it (in the spill ramjets) is good enough.

BTW the real issue of HOTOL (massive control moments, needing massive actuators, due to huge CoG shifts across a 0-M23-0 Mach range) will affect every large vehicle with engines in the tail and big tanks in the front. I suspect had Shuttle incorporated all the propellant in the ET inside the Orbiter it might well have been uncontrollable. 
It wasn't keeping the nose up in ascent, it was keeping the nose down in descent.
[EDIT Actually, now I come to think of it that's what makes upper stage reuse so hard as well. Protecting the engines and the structure while keeping it nose down without needing too much TPS, or any aerodynamic control surfaces.  ]
A fact anyone else planning a similar architecture today will discover for themselves.

[john smith 19]

It's not a hypersonic wind tunnel. It simulates the post intake conditions - hot subsonic air.
We saw upthread that it was reusing some American equipment that uses a turbojet to heat and drive the air, and we've seem the designs and fabrication of the interface and enclosure for the heat exchanger. The plumbing for providing the cold helium, and handling/measuring the cooled air is certainly going to be interesting. I wonder if they'll be using the viper again to draw air from the cooler.

Forgot about that.  I think the REL Viper will be staying in the UK. But doesn't the US system also use a small turbojet to get the flow? About the same size.

[Archibald]

What I did said was that RB-545 vs SABRE is that SABRE is more complex but makes better use (and far lower consumption) of LH2 than old RB-545. Sure, RB-545 might be better than aerospaceplane early LACE (20 years between the two) but SABRE beat the two hands down.

AFAIK both Aerospaceplane and HOTOL were pretty brute force and primitive in their approach to cool the air - dump large amount of LH2 on the air, and then the LH2 takes the heat away from the air, and become gaseous, and thus unuseful, and so it is dumped overboard.

SABRE by contrast a) cool the air more efficiently (helium loop) and thus b) waste far less LH2 in the process and c) that LH2 turned gaseous is not dumped but recovered and used in a secondary machinery or turbine (can't remember exactly).

[john smith 19]

What I did said was that RB-545 vs SABRE is that SABRE is more complex but makes better use (and far lower consumption) of LH2 than old RB-545. Sure, RB-545 might be better than aerospaceplane early LACE (20 years between the two) but SABRE beat the two hands down.

And the current SABRE 4 cycle does even better.
The key breakthrough that Bond made was decision not to liquefy the air. SABRE 4 uses 2 separate combustion chambers to allow the air breathing side to operate at chamber pressures more like those of conventional turbofans, cutting the energy needed to compress the flow and also the energy needed to be extracted from the flow to do so. 

AFAIK both Aerospaceplane and HOTOL were pretty brute force and primitive in their approach to cool the air - dump large amount of LH2 on the air, and then the LH2 takes the heat away from the air, and become gaseous, and thus unuseful, and so it is dumped overboard.

All of these systems  used heat exchangers. That is exactly what the pre cooler is as well. The difference is the Aerospace Plane ones used pipes cm in diameter, not millimetres. Some AP versions also tried to separate out the O2 by spinning the HX.
So you've got a multi tonne HX spinning at several 1000 RPM while exposed to an air flow of up to hypersonic speed, while running something 12x the LH2 needed to burn the air it was collecting.

[qquote author=Archibald]
SABRE by contrast a) cool the air more efficiently (helium loop) and thus b) waste far less LH2 in the process and c) that LH2 turned gaseous is not dumped but recovered and used in a secondary machinery or turbine (can't remember exactly).
[/quote]
All version of the Bond engine designs use the GH2 to drive the turbines that drive the turbopumps. Those turbopups bring the LH2 up to the pressue needed for whichever combustion chamber is running at the time but any excess is always dumped, by injecting it into the ramjet burners to "re-energize" the air flow slowed in the inlets. Above M5.5 this is no longer enough to overcome the nacelle drag so there's no real point in air breathing anymore. At which point it switches to full rocket rocket mode and internal Oxygen.

[JCRM]

The difference between HOTOL and Skylon engines was that HOTOL literally bled itself of LH2 propellant just to cool the air, in the process it lost a crapload of LH2 that was dumped because it was now in a unusable gaseous state.
Skylon tried to solve that issue by using a closed helium loop to take the heat away, and also tried to make good use of the gaseous hydrogen in a turbine, instead of stupidly dumping it overboard.

AFAIK both Aerospaceplane and HOTOL were pretty brute force and primitive in their approach to cool the air - dump large amount of LH2 on the air, and then the LH2 takes the heat away from the air, and become gaseous, and thus unuseful, and so it is dumped overboard.

SABRE by contrast a) cool the air more efficiently (helium loop) and thus b) waste far less LH2 in the process and c) that LH2 turned gaseous is not dumped but recovered and used in a secondary machinery or turbine (can't remember exactly).

You are mistaken.
The RB545 used the post-cooling gaseous hydrogen both to drive the air compressor and hydrogen pump and also to fuel both the main engine and the ramjet.
The helium loop doesn't increase the efficiency, nor does the helium in it contribute significantly to the cooling. At a minor loss of efficiency it reduces the amount of hydrogen plumbing, reducing the complications of hydrogen embrittlement. In particular it removes hot hydrogen from the turbomachinery.

The main differences between Swallow and SABRE were the helium loop frost control

[edzieba]

The data collected from the 'black box' HX test in Colorado will be available to REL, iirc.

The 'black box' is in regards to data available to the US side: REL gets full access to all data (after all, they built the thing!), while the US side gets only the final results, treating the test setup as a black box. REL have been bitten harshly by effectively the UK equivalent of ITAR before (essentially giving the kiss of death to using RB545 for any other project), so they are probably wary of letting out any details that could be declared as secret, particularly with their renewed focus on selling engines for use in other vehicles.

[t43562]

Reposting from FB, courtesy of Mark Perman:

At the upcoming Westcott Propulsion Conference on the 14th April Reaction Engines staff will be giving the following talk

Mike Hood – Test Facility, Lead Engineer & Russ Payne – Chief Design Engineer - Reaction Engines - SABRE TF1 – Development of the SABRE Demonstrator Test Facility

More information and tickets for the Conference are available from the British Interplanetary Society website here

https://www.bis-space.com/2018/01/14/20102/current-topics-in-rocket-propulsion-an-open-source-conference

[ChrisWilson68]

Let's start with Methane: Yes, RE are actively looking at how performance would be changed by a switch to Methane, as well as confirming that it would simplify structure (prop density) and greatly simplify ground handling and safety particularly for manned flight and spaceflight. This also came with confirmation that while SSTO remains the 'holy grail' goal, RE are taking a much more pragmatic approach to development with TSTO being more viable.

I'm really glad to hear that they're being pragmatic about considering both methane and two-stage launch vehicles.  If the engine technology is good but hydrogen and single-stage-to-orbit would make the overall program impractical, it would be a shame that the core technology wouldn't get a chance to prove itself.

And, if they can make a go of it with a methane, two-stage vehicle, then they would be in a position to try hydrogen and single-stage as next steps in the future.

[JCRM]

Let's start with Methane: Yes, RE are actively looking at how performance would be changed by a switch to Methane, as well as confirming that it would simplify structure (prop density) and greatly simplify ground handling and safety particularly for manned flight and spaceflight. This also came with confirmation that while SSTO remains the 'holy grail' goal, RE are taking a much more pragmatic approach to development with TSTO being more viable.

Is that they consider TSTO being more viable, or obtaining development funding for a TSTO is more viable?

I'm really glad to hear that they're being pragmatic about considering both methane and two-stage launch vehicles.  If the engine technology is good but hydrogen and single-stage-to-orbit would make the overall program impractical, it would be a shame that the core technology wouldn't get a chance to prove itself.

And, if they can make a go of it with a methane, two-stage vehicle, then they would be in a position to try hydrogen and single-stage as next steps in the future.

With SABRE 4's lower air breathing chamber pressure the deep cooling of hydrogen is no longer needed, and with the lower transistion speed identified for the TSTO optimisation (I assume due to higher T/W requirement) the peak amount of cooling required is lower. This opens the door on considering methane.
With a TSTO design the large hydrogen tankage (and consequential low ballistic coefficient) is no longer a strong virtue, so investigating it is no longer a pointless exercise, but significant work would need to be done to characterise such an engine's performance, and then then vehicles would have to be designed using those profiles. As it is no longer pointless, I'm sure REL would be prepared to accept paid research work to investigate the options for interested parties.

Having the potential of a fallback fuel option with shared engine components would reduce engine investor risk.

Application profiles with a cruise stage before higer speed air breathing and rocket transition would likely favour methane.

Having a customer and revenue stream would allow longer term development