The Reaction Engines Skylon/SABRE Master Thread (7)

[JCRM]

Now if they had gotten some cash under the ESA Future Launchers Preparatory Programme to pursue the E/D nozzle to allow higher expansion ratios at sea level without flow separation.....

The UK doesn't contribute to FLPP, so doesn't benefit from it.

[t43562]

The IAC2020 congress is online and registration and access is free. I think everyone should take a look at it - there are lots of interesting papers and talks and of course the most interesting to me are the 2 on SABRE.  I think they are both kind of exciting.

How to register:
https://iac2020.vfairs.com/en/registration

Video of the Development Status Update:
https://outin-6e4ede8fe1c911eaabb800163e1a65b6.oss-cn-shanghai.aliyuncs.com/0c26cc9e6b0044e4b5c3a73d9ab44b53/c3730d8cf88f4d4dbe5afe307918a0bc-2adb43c73bd1c7fbefa7c3c98c47ea53-ld.mp4


Video of Architecture and Ground Operations Concept talk:
https://outin-6e4ede8fe1c911eaabb800163e1a65b6.oss-cn-shanghai.aliyuncs.com/aa68f74abe384d459a12d9c5787ea008/2abad554242041bf93cfd942396e2441-eedb3e6f8ab36109f05f5ee1d735aeed-ld.mp4

[FutureSpaceTourist]

[FutureSpaceTourist]

[john smith 19]

Intriguing.

Especially the bit where they say the first stage still retains significant payload even in SSTO mode.

Obviously that only works if the skin is rated to full orbital reentry velocity.  But still....

[Asteroza]

the progress PDF had a throw away quote on page 3 mentioning they are also developing alternate heat exchanger formats, such as a design for a high pressure compact microchannel plate design. Which would suggest something PCHE-ish. Somebody finally decided welding all those tiny tubes, while now feasible, isn't preferable?

Instead of a pure monolithic PCHE setup, just have small stack PCHE plates, and curl them around the core the way the tube runs curl around towards the core right now.

Though making a monolithic PCHE using some sort of radial pressured diffusion bonding stack would be something.


Looks like they're back to the hammerhead forward fins and a single vertical rear rudder now as well? Though it was surprising they were even willing to entertain a TSTO concept with an all forward payload bay.

[edzieba]

the progress PDF had a throw away quote on page 3 mentioning they are also developing alternate heat exchanger formats, such as a design for a high pressure compact microchannel plate design. Which would suggest something PCHE-ish. Somebody finally decided welding all those tiny tubes, while now feasible, isn't preferable?

The microchannel heat exchangers are for HE-H2 fluid-fluid heat exchange as part of the HE loop. Microchannel heat exchangers do not work very well for gas-fluid heat exchange as they tend towards equal surface area between both flows, requiring much higher volumetric gas flow rates (or pressures, or both) for a given fluid flow rate for good efficiency (due to mass flow rate disparity). That's the whole reason the microtube heat exchanger exists: to allow for very high gas flow rates and matched low fluid flow rates without an oversized (and heavy) monolithic heat exchanger.

[JCRM]

Obviously that only works if the skin is rated to full orbital reentry velocity.  But still....

Are you mistaking the 5 tonnes to Sun Synchronous Orbit (SSO) for Single Stage to orbit (SSTO)?

I found it interesting that the TPS requirements are higher for suborbital reentry - AIUI, the lifting reentry needs the lateral speed to keep it higher as it loses speed.

the progress PDF had a throw away quote on page 3 mentioning they are also developing alternate heat exchanger formats, such as a design for a high pressure compact microchannel plate design. Which would suggest something PCHE-ish. Somebody finally decided welding all those tiny tubes, while now feasible, isn't preferable?

I think you misunderstood. There've been microchannel heat exchanger updates in all the progress reports I can recall - see attachment from IAC-13. As well as the Air intake heat exchangers, there are pre-burner to helium loop HX3 (mentioned in the next paragraph, previously described as using silicon carbide tubes) and helium loop to hydrogen feed HX4 (previously described as using micro-channel heat exchangers)

Looks like they're back to the hammerhead forward fins and a single vertical rear rudder now as well?

Skylon is Reaction Engines' reference design, and they've got a sophisticated computer model for it, which is why they used it. ISTR sub-orbital 30 tonnes upper-stage + payload was a mission they developed for the C1 (12 tonnes to LEO) but abandoned for the D1 due to re-entry difficulties.

Though it was surprising they were even willing to entertain a TSTO concept with an all forward payload bay.

They didn't, CNES did. Reaction Engines are developing the engine, customers can think about attaching it to whatever pays the bills.

[john smith 19]

Especially the bit where they say the first stage still retains significant payload even in SSTO mode.

Are you mistaking the 5 tonnes to Sun Synchronous Orbit (SSO) for Single Stage to orbit (SSTO)?

No. Check the chart at 5:00 in the first video. the audio at around 4:37 states

Positive mass margins at SSTO.

I suspect that the full paper puts actual numbers on that statement.

This simply means that although designed as a TSTO it could achieve orbit with at least 1Kg of mass that is not vehicle structure or propellant. 

If so that represents a very robust TSTO design that has a lot of margin for error mass growth or performance shortfall.

Personally I'd be astonished if that exceeded 100Kg of payload. OTOH it eliminates the whole cost of the one time use US, which has to be born by the payload operator.

The real  benefit of this would be the ability to incrementally stretch the design from TSTO into full SSTO. Something I had thought impossible until now. The second stage then only becomes necessary for GTO missions and could become reusable.

[JCRM]

No. Check the chart at 5:00 in the first video. the audio at around 4:37 states

Positive mass margins at SSTO.

I suspect that the full paper puts actual numbers on that statement.

Ah yes, you're right - it wasn't in the tables, but in the text it said

The 1st stage is capable of SSTO empty (with a 1^st
stage dry mass margin of 14%). This offers unique
operational capabilities over other launch vehicles (eg:
2nd stage recovery, down-mass etc).

-- assuming a similar mass:fuel ratio as Skylon, that gives 14 tonnes of the 56 tonne mass margin.  Presumably some of this would be needed for de-orbiting fuel and engines.

This simply means that although designed as a TSTO it could achieve orbit with at least 1Kg of mass that is not vehicle structure or propellant. 

Personally I'd be astonished if that exceeded 100Kg of payload. OTOH it eliminates the whole cost of the one time use US, which has to be born by the payload operator.

I'd quibble, and say that's at variance with "a significant payload" for a 400 tonne vehicle (given electron manages 150kg in 12.55 tonnes)

The real  benefit of this would be the ability to incrementally stretch the design from TSTO into full SSTO. Something I had thought impossible until now.

Given the design has been grown from 350 325 tonnes to 400, while reducing the payload from 13.5 tonnes to zero, I'm not sure stretching the design would be a good idea - unless removing the handicaps needed for TSTO operation is counted as stretching.

I think these two papers are brilliant for a number of reasons, especially politically, but lockdown anxiety is delaying my response.

[john smith 19]

First thoughts.

The critical enabling design choice that makes the recovery of the F9 booster possible was the decision to half the normal staging veloicty for the booster from about M12 to M6.

Once you realize that you also realize it's never going to be possible (with conventional booster materials) to go the other way and stretch the booster to an orbit capable vehicle.

Ever.

But with a SABRE powered HTOL vehicle you can do exactly that.

So that's a pretty remarkable result.

More later.

[john smith 19]

The 1st stage is capable of SSTO empty (with a 1^st
stage dry mass margin of 14%). This offers unique
operational capabilities over other launch vehicles (eg:
2nd stage recovery, down-mass etc).

-- assuming a similar mass:fuel ratio as Skylon, that gives 14 tonnes of the 56 tonne mass margin.  Presumably some of this would be needed for de-orbiting fuel and engines.

This simply means that although designed as a TSTO it could achieve orbit with at least 1Kg of mass that is not vehicle structure or propellant. 

Personally I'd be astonished if that exceeded 100Kg of payload. OTOH it eliminates the whole cost of the one time use US, which has to be born by the payload operator.

I'd quibble, and say that's at variance with "a significant payload" for a 400 tonne vehicle (given electron manages 150kg in 12.55 tonnes)

The real  benefit of this would be the ability to incrementally stretch the design from TSTO into full SSTO. Something I had thought impossible until now.

Given the design has been grown from 350 tonnes to 400, while reducing the payload from 13.5 tonnes to zero, I'm not sure stretching the design would be a good idea - unless removing the handicaps needed for TSTO operation is counted as stretching.

I think these two papers are brilliant for a number of reasons, especially politically, but lockdown anxiety is delaying my response.

Pulling up my copy of the Skylon Users Manual (Revision 2 May 2014) Dry mass is 53.4 t for a GTOM of 325t.
Scaling that to 400t gives a dry mass of 65.7.
A 14% margin of that would be 9.2t.
However these sorts of crude scalings are always risky because a big chunk of the 251t of propellant are now the US instead.

If I'm reading this correctly they are saying the CNES/REL 1st stage can reach orbit even if its dry mass increases 14% with zero payload. OTOH That still opens up the option for down mass, which Europe always lacked.
The flip side of that statement is that if the  booster meets it's dry mass target (and it's TPS was re entry capable) it could carry a payload equal to 14% of its dry mass to orbit.

This speculation should  be taken with caution.    the CNES/REL architecture is not Skylon and AFAIK no one mentions its actual dry mass. If it's half that of the scaled Skylon that 14% margin becomes more like a few tonnes, assuming the booster is more heavily constructed than Skylon (another pitfall in these simplistic scaling exercises)

But on that basis I may have been too conservative and a SABRE powered non optimized TSTO booster running in SSTO mode could hit 2000Kg+ to LEO.

I found the stuff on the Hypersonic Test Bed fascinating. The trouble is DEMO-A is at 44000lb. That's pretty big for a jet engine on a military aircraft (the only kind BAe know about).  I note their emphasize it's mainly to develop the nacelle structure but IMHO the air breathing to rocket transition is the critical element of SABRE that both separates it from all air breathing engines and which is difficult to test realistically on the ground.

REL have looked at this before and considered running it as a rocket powered aircraft but going with a gas turbine increases flight endurance. Ideally  they would like it scaled to DEMO-A size to minimize the re-design work and just drop the DEMO-A+ (flight weight and shape) straight in once the nacelle development work is complete.

This is probably not possible directly. 

Both are very interesting presentations and indicate a lot is going on inside REL and its partner organizations.

[john smith 19]

Skylon is Reaction Engines' reference design, and they've got a sophisticated computer model for it, which is why they used it. ISTR sub-orbital 30 tonnes upper-stage + payload was a mission they developed for the C1 (12 tonnes to LEO) but abandoned for the D1 due to re-entry difficulties.

Hempsell discussed this in an earlier thread.

IIRC he said Skylon could hit 30t of payload if the payload was released at a few 100m/s below orbital velocity.
The downside of this is a) The payload has to have significant propellant and a substantial engine on board and b)the time frame is quite tight if anything goes wrong.
So the question became how much of the payload you gained you lost on the propellant it has to carry?

I think Reaction remain in loose contact with a number of organizations who might become customers and the impression (again from Hempsell) was they were OK with 15tonnes. It was one of those interesting-but-not-really-necessary ideas.

[john smith 19]

I finally got round to viewing one of Alan Bond's older lectures on Skylon. I hadn't expected to find anything new but I did discover three things I didn't know before.

1) A key load case for landing gear is when the vehicle is turning. He noted they tried to keep those to a minimum while getting Skylon ready for takeoff, which I hadn't noticed.

2) They expected to load Helium at the time as they load LH2 and LO2.  It had not really occurred to me that was not just for the tank pressurization but also for the helium power loop. I had assumed this would be a sealed loop but people have pointed that helium is very difficult to seal in, especially over a very complex and long string of pipework.

3) Some people see SABRE and think it's a turbo-ramjet but Bond pointed out that the compressor is driven throughout the whole airbreathing stage. Turbo-ramjets like the J58 windmill at operating speed. He also stated the spill ramjet thrust peaks around M3+, not M5.

[Asteroza]

So a french Skylon variant is called Hyperstar?

https://twitter.com/RAeSTimR/status/1329038952041500673

https://twitter.com/RAeSTimR/status/1329040492584202243

[Steven Pietrobon]

Cropped image from the second tweet.

[john smith 19]

Cropped image from the second tweet.

Interesting. Like the CNES design in one of the joint papers with Reaction it has no canards but strakes or leading edge extensions.

It's difficult from the angle to decide if that's a V tail or just two sides of a conventional tail and fin arrangement.

[oddbodd]

It's difficult from the angle to decide if that's a V tail or just two sides of a conventional tail and fin arrangement.

I can only see a V tail. I can't even see a conventional arrangement if a squint through one eye while standing on my head. 

On the name... Ugh! Skylon was unique and had a sc-fi (i.e. Cylon) sound to it. Hyperstar? Really? It doesn't travel between stars, and doesn't have a hyperdrive. Did they throw a couple of darts at a wall of cheesy, cliched, space-related words?

[Arb]

...
On the name... Ugh! Skylon was unique and had a sc-fi (i.e. Cylon) sound to it.
...

Cool name, certainly. Unique, not quite:

The Skylon was a futuristic-looking, slender, vertical, cigar-shaped steel tensegrity structure located by the Thames in London, that gave the illusion of 'floating' above the ground, built in 1951 for the Festival of Britain.

The namers of the Reaction Engines ship are easily old enough to have visited the '51 festival in their youth.

^{Image courtesy Wikimedia Commons.}

[oddbodd]

...
On the name... Ugh! Skylon was unique and had a sc-fi (i.e. Cylon) sound to it.
...

Cool name, certainly. Unique, not quite:

The Skylon was a futuristic-looking, slender, vertical, cigar-shaped steel tensegrity structure located by the Thames in London, that gave the illusion of 'floating' above the ground, built in 1951 for the Festival of Britain.

The namers of the Reaction Engines ship are easily old enough to have visited the '51 festival in their youth.

^{Image courtesy Wikimedia Commons.}

There's always one pedant! Yes, I'm aware of the original Skylon, so unique was the wrong word. It is however not commonplace, and evokes some kind of emotional response. Bolting two common words together into a bland generic name does not. Facebook, OnePlus, and (dare I say it?) Starship are some prime examples.

[Edit] Seems there are a couple of restaurants in operation (or would be sans COVID) using the Skylon name. Still a better name than Hyperstar!