The Reaction Engines Skylon/SABRE Master Thread (6)

[RotoSequence]

*BFR and Skylon arguments*

BFR is the Booster and Spaceship. BFS is the spaceship component, which is the second stage for the launch architecture. It should still have enough Delta-V for insertion to orbit, and unless I've missed some sort of boat on SpaceX taking a big step backward on payload fairings vs cargo bay doors, this whole post seems enormously misleading.

[john smith 19]

*BFR and Skylon arguments*

BFR is the Booster and Spaceship. BFS is the spaceship component, which is the second stage for the launch architecture. It should still have enough Delta-V for insertion to orbit, and unless I've missed some sort of boat on SpaceX taking a big step backward on payload fairings vs cargo bay doors, this whole post seems enormously misleading.

Probably more my use of terminology. I tend to think of the BFR as the booster part only, rather than the the whole architecture. BFS can operated independently of BFR but BFR without BFS is not really much use for anything.  Other wise you have to distinguish when you're talking about the whole BFR or just the BFS part, as in "If BFS is the size of an A380 at around $10-15Bn then wouldn't that make the whole BFR nearer $20-30Bn" for example.
My apologies for misleading you. 

[Lampyridae]

There is no history for large CFRP structures with the range of cyclic stresses, over the range of temperatures, over the flight number. None. You're talking something the size of a wind turbine blade, accelerating up to M23, then back again, filled with LOX and liquid Methane.

Yup. There are always hidden surprises with these wündermaterials. (This is a carbon fibre fork failure, and of course there's SX COPV failures). It just takes time to work through them... which I don't think they account for on BFR/S - at least not publicly.

[chuck34]

Don't think mountain bikes when you think about carbon fiber, think more Formula 1.  Those cars at basically completely made of CF.  And carbon does amazing things on those cars.  The brakes are carbon, and handle crazy high heat, and stress.  The gear cases are carbon, and take high heat, and very high stress.  On and on.  That's the bleeding edge of this technology.  And it's no mistake that SpaceX has one of the largest (if not the largest) recruiting presences at Formula SAE (collegete racing competition) events every year, rivaling if not outpacing the recruiting efforts of the big 3 auto manufacturers in their own back yard.

Sorry to pull this further off topic

[envy887]

Skylon also needs fuel, engines, structures, and TPS that not only have never been flown, they haven't even gotten part component level ground testing. It requires much more advancement in SOA than BFR does, and somewhat more than BFS.

Except BFR is not a rocket, is it? It's a stage.
We think it will work but even then you're not even 1/2 way to orbit.

I'll repeat once again that SABRESkylon is a High risk/High cost/High reward programme.
Yet in fact BFR/BFS will be in the same cost range and comparable risk levels without similar rewards for anyone but SX.

Both will be flight proven on Falcon/Dragon.

Really? AFAIK Dragon  2 will also be PICAX. IIRC most (all?) development work on PICA X has been to make it cheaper to mfg, not to improve it's operating properties.

BFR will work reasonably well even if SpaceX grossly misses many of their performance targets.

Again, BFR is not a LV, it's a stage of a launch vehicle.  If LEO is "Halfway to anywhere" then BFR is "Not quite half way to being halfway to anywhere."

SABRE is high reward because it's pure research on technology that doesn't exist yet.

All the technology required to make a viable BFR/BFS system already exists and has flown. Such system with current technology wouldn't be as efficient, but it would still work. SpaceX is pushing the SOA to make it more efficient, but they have the option to falling back to proven technology if something doesn't work.

[Patchouli]

I think Skylon is a much better path to things like sub orbital P2P than BFR as I can see one being allowed to operate at large airport just outside of city limits but I don't see BFR/BFS being allowed fly over or near a large population center.
It can do rejected take offs ,stay aloft if thrust goes below 1 to 1 , even glide to a dead stick landing if needed and dump much of the propellant during an emergency like an airliner.
Plus lastly the gs are lower across the entire flight regime and lets face it nothing is going to compete with long haul subsonic airliners unless even your grandparents can ride it.
I'm not saying a HTOL like Skylon is better than BFR in every way it can't go to the Moon or Mars nor can it lift 100ton payloads I'm just saying it's probably a better solution to LEO and sub orbital passenger transport.
This is probably a good example why a one size fits all launch system is not realistic we don't have one size fits all airplanes,trucks,and ships?

[john smith 19]

Yup. There are always hidden surprises with these wündermaterials. (This is a carbon fibre fork failure, and of course there's SX COPV failures). It just takes time to work through them... which I don't think they account for on BFR/S - at least not publicly.

I'm not sure what's happening there but it looks pretty nasty. 

Don't think mountain bikes when you think about carbon fiber, think more Formula 1.  Those cars at basically completely made of CF.

True.

And carbon does amazing things on those cars.  The brakes are carbon, and handle crazy high heat, and stress. 

REinforced Carbon Carbon (which is what those brakes are made of) is not CFRP. It's essentially a ceramic with everything but Carbon selectively burnt off and it's thermal conductivity tuned to move heat away from the contact surface ASAP to keep it below about 500c. At that temperature, without a protective coat, RCC turns into what gas turbine people (who've been trying to introduce it into the hot sections of jet engines for decades) call "designer coal."

That's the bleeding edge of this technology.  And it's no mistake that SpaceX has one of the largest (if not the largest) recruiting presences at Formula SAE (collegete racing competition) events every year, rivaling if not outpacing the recruiting efforts of the big 3 auto manufacturers in their own back yard.

At room temperature CFRP's performance is impressive, even up to the skins on a M2 aircraft maybe.

Find out what happens when you stick it in a flask of liquid Nitrogen. Or stick it in a vacuum furnace, then pull it out when it's still glowing and see what happens.
Because (effectively) both of those will happen to the BFR's structure.

[john smith 19]

SABRE is high reward because it's pure research on technology that doesn't exist yet.

SABRE stopped being a research programme the day they solved the frost control issue.

All the technology required to make a viable BFR/BFS system already exists and has flown.

I'd say "sort of" exists, mostly. And in some cases (like the TPS) "Needs to be recreated from scratch."

No one has ever had to land an 85 tonne+ winged vehicle to a 1100tonne booster before. Nor have they every had to refuel in orbit using pressure based settling.

Such system with current technology wouldn't be as efficient, but it would still work. SpaceX is pushing the SOA to make it more efficient, but they have the option to falling back to proven technology if something doesn't work.

You can believe that if you want but if it was true they'd have been able to make F9 US reuse deliver an economically viable payload using LOX/RP1.
IOW the payload hit going reusable is massive. Putting wings on it won't help that mass issue.
So no "falling back" to Merlin and AlLi is not going to work.

BFR has been seen sold as a "safe" path to full reusability. In fact everything about it has to work. Weight. Isp. Thermal protection. 

The difference is rocket Isp's mean the margins for mass growth and material under performance are much  narrower.

Data point. The SSME Isp was too low by about 2 secs. The SRB's were low by about 3secs. This triggered a "Weight scrub" to cut orbiter mass by 15%, despite it being (effectively) a TSTO.

Rocket based VTO systems are very sensitive to Isp deficiencies. Keep in mind these were systems developed by experienced teams. It wasn't their first rodeo by a long way. The SRB in particular wasn't the biggest ever built by any means.

And rocket Isp, once you've set the propellant and chamber pressure has very limited options for increasing Isp, unless you slap a bigger nozzle on and risk flow separation.

[speedevil]

BFR has been seen sold as a "safe" path to full reusability. In fact everything about it has to work. Weight. Isp. Thermal protection. 

The difference is rocket Isp's mean the margins for mass growth and material under performance are much  narrower.

Data point. The SSME Isp was too low by about 2 secs. The SRB's were low by about 3secs. This triggered a "Weight scrub" to cut orbiter mass by 15%, despite it being (effectively) a TSTO.

Everything doesn't. Most things do.

Any one of heatshield only being good to 5km/s, Merlin class ISPs not Raptor, double the structural fraction on both stages pretty much gives you 50-70 tons to orbit, not 150.

Any one of these failing gives you a launcher that will utterly dominate the current launch market, and basically only impact things that are not currently possible. (Tripling passenger service and Mars/Moon cost).

The high effective ISP of an airbreathing stage does allow flexibility and allows weight growth in some ways that are otherwise problematic for a SSTO, but massive margins where achieving a third of the payload leads to overwhelming market success is a big plus for a rocket design.

[Lars-J]

I'm pretty sure that's not the case for any SSTO concept.

And it's the thinking that sort of verbal short hand engenders that means you need to spell out exactly your assumptions.
Because I think you mean any vertical take off rocket powered SSTO.

Where a) Thrust must exceed GTOW or no TO to begin with b)Rocket grade Isp's mean mass ratios are high and payload mass fractions low.

What people can't seem to grasp is that air breathing gives  you an Isp about 6x that of the best (useable) rocket propellant. That "buys" a lot of structure. So you can use wings, that give you benign failure modes. You don't need staging (eliminating separation failure modes) and you get a payload mass fraction equal to the same sized ELV. SSTO's historical inability to match TSTO payload fraction has been the killer to the concept.

That's what Skylon gives you. SSTO convenience with ELV payload fraction, on your launch schedule, not anyone else's.

What *you* can't seem to grasp is that we all grasp that.

What you don't seem to grasp, additionally, is that all those advantages end at the atmosphere and become drawbacks after that. So you trade a benefit in a small part of the flight regime for a drawbacks in the remainder (significant majority) of the flight.

So, please - no more "but that applies for VTOL SSTO only". It does not. Unless you have some flying HTOL SSTO examples out there that disproves this. All your HTOL mass fraction ideas are meaningless projections based on optimistic assumptions, which is why no HTOL SSTO has materialized after all these years.

[chuck34]

And carbon does amazing things on those cars.  The brakes are carbon, and handle crazy high heat, and stress. 

REinforced Carbon Carbon (which is what those brakes are made of) is not CFRP. It's essentially a ceramic with everything but Carbon selectively burnt off and it's thermal conductivity tuned to move heat away from the contact surface ASAP to keep it below about 500c. At that temperature, without a protective coat, RCC turns into what gas turbine people (who've been trying to introduce it into the hot sections of jet engines for decades) call "designer coal."

That's the bleeding edge of this technology.  And it's no mistake that SpaceX has one of the largest (if not the largest) recruiting presences at Formula SAE (collegete racing competition) events every year, rivaling if not outpacing the recruiting efforts of the big 3 auto manufacturers in their own back yard.

At room temperature CFRP's performance is impressive, even up to the skins on a M2 aircraft maybe.

Find out what happens when you stick it in a flask of liquid Nitrogen. Or stick it in a vacuum furnace, then pull it out when it's still glowing and see what happens.
Because (effectively) both of those will happen to the BFR's structure.

Carbon brakes operate up to 1000 degrees C, someone knows about heat management there.  RCC was also used on the shuttle as TPS, so maybe there's a use there.

There are plenty of other applications for carbon products in racing as well.  I will grant you not down to the extreme colds used for rocket fuel.  But....

Stick it in liquid nitrogen you say?  How about liquid oxygen with helium on the inside?  SpaceX had that one issue, but I bet you that their people are now the leading experts in the industry on the behavior of COPV in the industry because of it.

These are not show stoppers that you seem to imply (maybe I'm wrong about your point?)  SpaceX already has plenty of know how, they know how to get realavent information from NASA, and know that other industries and university have applicable knowledge and research that they can tap into.

[Robotbeat]

There is no history for large CFRP structures with the range of cyclic stresses, over the range of temperatures, over the flight number. None.

Wrong. The space shuttle payload bay doors were large CFRP structures, endured those cyclic stresses, and had fairly close to the same range of temperatures, and over a similar design flight number.

Write less and verify what you're saying more. And you're doing this as a concern trolling tactic, which is even worse.

[john smith 19]

Wrong. The space shuttle payload bay doors were large CFRP structures, endured those cyclic stresses, and had fairly close to the same range of temperatures, and over a similar design flight number.

Depends what you mean by "large" does it not?
Shuttle PLB doors.
18.3m longx 4.5m diameter.
But each door was made of 5 segments, A 4.5m dia gives a 1/4 circumferential  length of 3.53m. So a panel size of 3.66x3.53m.

Looking up the Shuttle reference manual for the midfusellage and PLB doors
https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/midfuselage.html
https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/baydoors.html

We find

In the upper portion of the midfuselage are the sill and door longerons. The machined sill longerons not only make up the primary body-bending elements, but also take the longitudinal loads from payloads in the payload bay.

Regarding the PLB doors themselves.

When the payload bay doors are closed, they are fixed at the aft fuselage bulkhead and allowed to move longitudinally at the forward fuselage. The doors also accommodate vehicle torsional loads (a force that causes a body, such as a shaft, to twist about its longitudinal axis), aerodynamic pressure loads and payload bay vent lag pressures. The payload bay is not a pressurized area.

So, torsional loads only. dynamic pressure (these are on the upper body) and near zero internal pressure (the bay vented on ascent and descent). Temperature limits were -112 to +57c.

Musk means 58m or 48m (for BFS) long and 9 in diameter, in 1 piece holding fluids of at least -161c and -183, but potentially sub cooled to to closer to  their respective melting points of -182 and -218c. It will carry all structural loads of the vehicle.

So no, not very close at all.

You'd have done better going with the B2 spirit. It has been flying since 1989 and is 52m wide by 22m long. So the size is about right.

Of course it's never been above Mach 1 and if it's ever hit it's service ceiling it's be at a chilly -56.5c and up to whatever the ground air temp is at its home airbase.

Look at the height of those BFR tanks, factor in the fluid density and work out what's the load on the aft bulkhead. Don't forget how much it will rise under acceleration.

Write less and verify what you're saying more. And you're doing this as a concern trolling tactic, which is even worse.

Words to live by. Along with "don't sound quite so much like an outraged amazing people"

[john smith 19]

Carbon brakes operate up to 1000 degrees C, someone knows about heat management there.  RCC was also used on the shuttle as TPS, so maybe there's a use there.

The reports I've seen say up to 1200c. However F1 is notorious for "single race" and life limited parts. IOW the teams may just let them burn, which is exactly what they will do without a protective coating. Such a coating would be a specialized area and proprietary to the different brake companies. Note such pads spread heat in the wrong direction for space use.

Stick it in liquid nitrogen you say?  How about liquid oxygen with helium on the inside?  SpaceX had that one issue, but I bet you that their people are now the leading experts in the industry on the behavior of COPV in the industry because of it.

Except the main tanks of BFR are not COPV's. Eliminating a liner (that's the thing that's being "overwrapped") is quite a big part of the design.

These are not show stoppers that you seem to imply (maybe I'm wrong about your point?)

You have it backwards.

WRT to this thread's title SX amazing people complain (loudly) that Skylon is untried technology.
My point was that on this scale, under this range of conditions BFR's materials and engine technology is no more a sure thing than REL's. It's doubtful if it will be cheaper either.

The only real "show stoppers" (for SX) are SX running out of money or Musk loosing control of the company.
Musk reckoned ITS was about $10Bn in development costs but BFR is smaller.

Unfortunately the "sub linear" cost rise curve, where doubling the size of something (not the # produced. That's the "learning" curve)  is less  than double the cost (provided it still fits all your existing machinery to make it so you don't have to buy new bigger stuff) works in reverse here.

So BFR may be cheaper (than ITS or MCT), but it won't be that much cheaper. If SX makes $10m a flight in net profit an $8Bn bill say (down from the ITS figure of $10Bn) is 800 F9 flights (or 126 if every cent of the price was profit, which would still be another 76 launches away).
People forget how generous the ISS transport contract is. 
This may be the best investment NASA has ever made in buying something.

As for Musk loosing control of SX or anything happening to him that seems unlikely. AFAIK He's the majority stockholder by a long way and is in pretty good health.

SpaceX already has plenty of know how, they know how to get relevant information from NASA, and know that other industries and university have applicable knowledge and research that they can tap into.

Not really sure what this means?
So do REL.
For that matter, so do I. 

Now can we return to discussion of what REL is doing, rather than SX?

[john smith 19]

What *you* can't seem to grasp is that we all grasp that.

What you don't seem to grasp, additionally, is that all those advantages end at the atmosphere and become drawbacks after that. So you trade a benefit in a small part of the flight regime for a drawbacks in the remainder (significant majority) of the flight.

Ahh the light dawns. 
Now I see the error in your logic.

So, please - no more "but that applies for VTOL SSTO only". It does not. Unless you have some flying HTOL SSTO examples out there that disproves this.

All what exactly?

All your HTOL mass fraction ideas are meaningless projections based on optimistic assumptions, which is why no HTOL SSTO has materialized after all these years.

I don't think I've ever met an optimistic British engineer.

They tend to start with the worst case outcome first. 

This may explain how they "Under promise, and over deliver," as opposed to others who "Over promise and under deliver"
NASP comes rather readily to mind. In fact any SCramjet project in the last 6 decades.

[Robotbeat]

Wrong. The space shuttle payload bay doors were large CFRP structures, endured those cyclic stresses, and had fairly close to the same range of temperatures, and over a similar design flight number.

Depends what you mean by "large" does it not?
Shuttle PLB doors.
18.3m longx 4.5m diameter.
But each door was made of 5 segments, A 4.5m dia gives a 1/4 circumferential  length of 3.53m. So a panel size of 3.66x3.53m.

Looking up the Shuttle reference manual for the midfusellage and PLB doors
https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/midfuselage.html
https://spaceflight.nasa.gov/shuttle/reference/shutref/structure/baydoors.html

We find

In the upper portion of the midfuselage are the sill and door longerons. The machined sill longerons not only make up the primary body-bending elements, but also take the longitudinal loads from payloads in the payload bay.

Regarding the PLB doors themselves.

When the payload bay doors are closed, they are fixed at the aft fuselage bulkhead and allowed to move longitudinally at the forward fuselage. The doors also accommodate vehicle torsional loads (a force that causes a body, such as a shaft, to twist about its longitudinal axis), aerodynamic pressure loads and payload bay vent lag pressures. The payload bay is not a pressurized area.

So, torsional loads only. dynamic pressure (these are on the upper body) and near zero internal pressure (the bay vented on ascent and descent). Temperature limits were -112 to +57c.

Musk means 58m or 48m (for BFS) long and 9 in diameter, in 1 piece holding fluids of at least -161c and -183, but potentially sub cooled to to closer to  their respective melting points of -182 and -218c. It will carry all structural loads of the vehicle.

So no, not very close at all.

You'd have done better going with the B2 spirit. It has been flying since 1989 and is 52m wide by 22m long. So the size is about right.

Of course it's never been above Mach 1 and if it's ever hit it's service ceiling it's be at a chilly -56.5c and up to whatever the ground air temp is at its home airbase.

Look at the height of those BFR tanks, factor in the fluid density and work out what's the load on the aft bulkhead. Don't forget how much it will rise under acceleration.

Write less and verify what you're saying more. And you're doing this as a concern trolling tactic, which is even worse.

Words to live by. Along with "don't sound quite so much like an outraged amazing people"

-112C is close to liquid methane temperatures, it is large, and it did have to withstand large cyclic stresses with a high flight cycle number.

Oh but it isn’t EXACTLY the same. Who cares? It was built using 40 year old tech, it’s actually okay for improvements to happen. You’re working so hard, writing a novel to basically contradict yourself. Enjoy your concern trolling, but keep the long winded ness to yourself.

[Avron]

Please do post an image or video of a rocket running off compressed air and fuel if there is any example, even a lab experiment - running means more than a second or two.

Never flown a bottle rocket? Squirt a little Butane into an empty plastic bottle, allow it to flash to vapour and mix with the air while you screw on the cap (with a hole for the nozzle), then poke in the igniter leads through said hole and provide a spark.
Gas/Gas Butane/Air autogenous pressure-fed cycle engine, possible one of the most test-flown engine cycles on the planet!

good luck flying that to orbit on compressed air

The STOIC Expansion-deflection nozzle tests ..

The 'rocket' part used LOX not compressed air

[Avron]

Please do post an image or video of a rocket running off compressed air and fuel if there is any example, even a lab experiment - running means more than a second or two.

Never flown a bottle rocket? Squirt a little Butane into an empty plastic bottle, allow it to flash to vapour and mix with the air while you screw on the cap (with a hole for the nozzle), then poke in the igniter leads through said hole and provide a spark.
Gas/Gas Butane/Air autogenous pressure-fed cycle engine, possible one of the most test-flown engine cycles on the planet!

if its that simple why don't we see that used for orbital vehicles ?

[john smith 19]

if its that simple why don't we see that used for orbital vehicles ?

good luck flying that to orbit on compressed air

The 'rocket' part used LOX not compressed air

-112C is close to liquid methane temperatures, it is large, and it did have to withstand large cyclic stresses with a high flight cycle number.

Oh but it isn’t EXACTLY the same. Who cares? It was built using 40 year old tech, it’s actually okay for improvements to happen. You’re working so hard, writing a novel to basically contradict yourself. Enjoy your concern trolling, but keep the long winded ness to yourself.

Shock news.

SX amazing people asks question.

SX amazing people gets answered.

SX amazing people moves goalposts.

And so it goes.

But by Dec 31st 2022 some will be proved right and some will be proved wrong.  That's 45 57 months from now.

I'd like to return to discussing SABRE and Skylon. If you don't mind of course.

[Lars-J]

So, please - no more "but that applies for VTOL SSTO only". It does not. Unless you have some flying HTOL SSTO examples out there that disproves this.

All what exactly?

You are fond of saying that mass fraction is a huge distinguishing element between HTOL and VTOL SSTO, but that is all conjecture. There is no data that supports that. And no, paper/powerpoint projects that have never flown do not count.

All your HTOL mass fraction ideas are meaningless projections based on optimistic assumptions, which is why no HTOL SSTO has materialized after all these years.

I don't think I've ever met an optimistic British engineer.

What part of HOTOL or REL have you missed?

Shock news.

SX amazing people asks question.

SX amazing people gets answered.

SX amazing people moves goalposts.

And so it goes.

But by Dec 31st 2022 some will be proved right and some will be proved wrong.  That's 45 months from now.

I'd like to return to discussing SABRE and Skylon. If you don't mind of course.

You are just as likely to have brought SpaceX into this thread as anyone else, JS19.

And talking about 'amazing people', that is like the the pot calling the kettle black ^ 2. You are the ultimate 'fanboi' - of Skylon. Your ability to believe anything that REL has ever presented, coupled with a skepticism for other approaches is legend.