Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 440961 times)

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1020 on: 12/07/2015 05:12 PM »
LH2 has a known boil off rate for a given tank and ambient conditions.  A factor to be engineered into the design, not a show stopper.  Consider that the tanks and heat shields will need to deal with a period of supersonic flight, with a hot skin.  This implies to me some insulation.  A limited amount of boil off should be part of the design.  For a moderately extended hold I don't expect too much trouble driving out a truck to top off the tanks.  Longer holds (hopefully very rare) imply return to the hanger.


LH2 doesn't do a "limited" amount of boil off.   It vigorously boils off.   The replenishment that other launch vehicle do is not just to replace the boil off but to keep the bulk temperature down.   It takes more than "some" insulation.  Not just ice but liquid air forms on inadequately insulated tanks.  Regardless of the hold time, Skylon will need insulation equivalent to the shuttle external tank.
« Last Edit: 12/07/2015 05:13 PM by Jim »

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1021 on: 12/07/2015 05:27 PM »
The propellants are loaded subcooled.

Also, the tankage is indeed insulated.  It's just that it's inside the spaceframe truss, which is inside the TPS, so you don't see the insulation.

What exactly is unrealistic about the payload integration facility?
« Last Edit: 12/07/2015 05:27 PM by 93143 »

Online pippin

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1022 on: 12/07/2015 05:48 PM »
How do you "subcool" LH2??

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1023 on: 12/07/2015 05:50 PM »
The propellants are loaded subcooled.

Also, the tankage is indeed insulated.  It's just that it's inside the spaceframe truss, which is inside the TPS, so you don't see the insulation.

What exactly is unrealistic about the payload integration facility?

No access platforms to the payload bay. 
It is a facility for hazardous operations, hence no offices much less a "passenger terminal" in it.
IOS 9 is not really a clean room. 
side by side vehicles for payload integration?  Means lifting payloads over other vehicles.  Not to mention that with the hilarious timelines, the payload installation is only 30 minutes and there will be need for 3 vehicles at a time?

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1024 on: 12/07/2015 08:52 PM »
Not really.  This is the first time I have seen it and it has some holes.  The first thing I saw that is wrong is the payload integration facility.  Totally unrealistic.
So you're quite a long way behind the curve. Perhaps you should do more background reading first?
Quote
And the timeline is just as funny as the two week shuttle turnaround.
"Payload integration" for aircraft is basically loading the cargo on the plane in a container or strapping it down to deck fittings.

REL staff did work on payload integration for the Shuttle. They are aware of the issues around Coupled Loads Analysis, which is why they don't plan to bolt the payloads to the airframe.

It uses LH2, which boils off quickly.   They have only talked about the flight vehicle and not the ground support equipment.

Indirectly they have.  It's in their references to the use of sub cooled propellants to avoid tank venting. Either the vehicle launches before the system starts to boil or the propellants recycle to long term storage.

How do you "subcool" LH2??
Sub cooling of LH2 was demonstrated as part of the X33 programe. It was one of the few parts that worked quite well.

Historically people have used LHe to cool the LH2 further. Simple in concept but expensive because He is very difficult to cool, keep cool and obtain in propellant tank sized quantities. IIRC the X33 programme use LH2 to cool LH2. 

The heat exchanger coils are in a tank of LH2.  By sucking out the vapor you can lower the BP of the coolant, despite both sides of the cooling loop having the same fluid. The down side is you need some pretty big fans to suck the vapour out fast enough.

The better the HX design the smaller the temperature difference the HX needs to function. IIRC X33 (with hardware from Barber Nicholls, who went on to supply the early SX turbo pumps) got it down to 1-2c. This is important. A small temperature difference across the HX means you don't need to suck out the vapour to such a low pressure, letting you use smaller fans. The fans took (IIRC) about 3x the energy as the system extracted from the LH2. 

And REL are very good good at building heat exchangers.
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Offline knowles2

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1025 on: 12/08/2015 01:00 PM »
I mean selling launches /before/ all orbital launches have been completed.

Just 2 years of flight testing for 400 flights is VERY optimistic, as we can see from SpaceShipTwo and other reusable test-bed vehicles.

And yes, I do think that such expensive vehicles will be a hard sell, especially with the significant ground support equipment that will be necessary.

There will be a lot of pressure by investors to get earlier income. That's why I think that if Skylon ever happens, Reaction Engines will be initially operating Skylon for customer launches (during the "test program," if you like). And at that point, it'd be really tempting to just continue operating, since they'll already have the infrastructure in place.

And of course, customers of Skylon would know this. That's part of why I am skeptical of the "just sell Skylons to people, and ignore the actual launch market." If Skylon ever happens, I really doubt that's how it will work.

I actually don't see the point of them doing 200-400 test flights and not at least using a few of them to place actual satellites in orbit.

Especially if the first few orbital flights are completed, especially if they are done without any major problems cropping.

These won't necessarily be big satellites, but things like cube satellites, small research satellites from universities and schools.

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1026 on: 12/08/2015 02:00 PM »

REL staff did work on payload integration for the Shuttle. They are aware of the issues around Coupled Loads Analysis, which is why they don't plan to bolt the payloads to the airframe.


Nonsense.  Don't know where to start since so much is wrong in that statement.
A.  The need for CLA's  is not determined by the method of attachment. 
b.  ELV's use clamp bands and still some have CLA issues
c.  It is more about the spacecraft structural stiffness
d..  A bolted interface was not the driver of shuttle CLA issues
d.  Skylon is using an interface that similar if not identical to the shuttle, the trunnion.
« Last Edit: 12/08/2015 04:34 PM by Jim »

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1027 on: 12/08/2015 02:01 PM »

Indirectly they have.  It's in their references to the use of sub cooled propellants to avoid tank venting. Either the vehicle launches before the system starts to boil or the propellants recycle to long term storage.


Subcooling doesn't prevent boil off
« Last Edit: 12/08/2015 02:12 PM by Jim »

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1028 on: 12/08/2015 02:14 PM »
I mean selling launches /before/ all orbital launches have been completed.

Just 2 years of flight testing for 400 flights is VERY optimistic, as we can see from SpaceShipTwo and other reusable test-bed vehicles.

And yes, I do think that such expensive vehicles will be a hard sell, especially with the significant ground support equipment that will be necessary.

There will be a lot of pressure by investors to get earlier income. That's why I think that if Skylon ever happens, Reaction Engines will be initially operating Skylon for customer launches (during the "test program," if you like). And at that point, it'd be really tempting to just continue operating, since they'll already have the infrastructure in place.

And of course, customers of Skylon would know this. That's part of why I am skeptical of the "just sell Skylons to people, and ignore the actual launch market." If Skylon ever happens, I really doubt that's how it will work.

I actually don't see the point of them doing 200-400 test flights and not at least using a few of them to place actual satellites in orbit.

Especially if the first few orbital flights are completed, especially if they are done without any major problems cropping.

These won't necessarily be big satellites, but things like cube satellites, small research satellites from universities and schools.
If you read the papers I posted you'll see that one off them was a paper outlining a plan to use the 20 test flights of the SUS to launch a series of space exploration missions using generic probes. Another paper outlines the purpose of the test programme, besides putting 204 flights on an airframe, of testing every mission scenario in the user manual which by definition means they will be putting satellites in orbit as part of the programme.

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1029 on: 12/08/2015 02:17 PM »

"Payload integration" for aircraft is basically loading the cargo on the plane in a container or strapping it down to deck fittings.


This isn't an aircraft nor is it carrying bulk cargo.

Offline Ravenger

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1030 on: 12/08/2015 04:10 PM »
This isn't an aircraft nor is it carrying bulk cargo.

It's got wings, takes off from a runway, and flies under its own power, which seems very much like an aircraft to me.

How do you define bulk cargo? The cargo bay is designed to take virtually anything up to the mass limit. That could include bulk items such as water, fuel and other consumables. It'd need specially designed cargo modules, but it'd be possible.

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1031 on: 12/08/2015 04:29 PM »

1.  It's got wings, takes off from a runway, and flies under its own power, which seems very much like an aircraft to me.

2.  How do you define bulk cargo? The cargo bay is designed to take virtually anything up to the mass limit. That could include bulk items such as water, fuel and other consumables. It'd need specially designed cargo modules, but it'd be possible.

1.  It goes into orbit, that negates the aircraft designation.  It is a launch vehicle.

2.  It isn't going to bulk cargo in the beginning.  It is going to deliver spacecraft

Offline Hanelyp

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1032 on: 12/08/2015 05:29 PM »
Presuming everything works to plan:
Vehicle comes in.
If in flight diagnostics, schedule, or a quick automated systems check say it needs maintenance, it goes to the maintenance bay.  Another vehicle from the fleet steps in to the rotation.
Otherwise, flush the lines, fill the tanks, charge the batteries, drop in a cargo palate, and head out for the next flight.

Rapid turn around keeping the vehicle flying is the essence of "aircraft like" operations we want to capture.  Runways and wings are artifacts that may or may not play a role when we finally get a working system.

Liftoff time may be more constrained by destination orbit, and maintenance likely more frequent than a mature tech airliner, but without cutting the time and effort needed to refit between flights cost won't go where we need it.
« Last Edit: 12/08/2015 09:43 PM by Chris Bergin »

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1033 on: 12/08/2015 06:02 PM »

1.  It's got wings, takes off from a runway, and flies under its own power, which seems very much like an aircraft to me.

2.  How do you define bulk cargo? The cargo bay is designed to take virtually anything up to the mass limit. That could include bulk items such as water, fuel and other consumables. It'd need specially designed cargo modules, but it'd be possible.

1.  It goes into orbit, that negates the aircraft designation.  It is a launch vehicle.

2.  It isn't going to bulk cargo in the beginning.  It is going to deliver spacecraft

So is it still not an aircraft when it's not going into orbit?
Is it not an aircraft when it's just flying from the factory to Kourou?
Or is it an aircraft then but it suddenly ceases to be one when the nose points up?
What if it aborts orbital launch at Mach 5 and turns round around and flies back to the runway, did the intention to perform orbital launch make it not an aircraft and the abort turn it into one?
Or would it have been an aircraft until the launch is completed and the abort just stopped it turning into not an aircraft?

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1034 on: 12/08/2015 09:43 PM »
Too many low quality posts. You're wasting your time because they will be deleted and you will be barred from posting on this thread again.

Trimmed. No more, and I mean no more crap like "It won't work. It's not what I like." etc. It's boring and embarrassing for a site like this.

And will someone for the love of God go round to Jim's house and show him have to respond to someone without making 15 posts. ;)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1035 on: 12/08/2015 10:11 PM »
Subcooling doesn't prevent boil off
But it will delay tank pressure rising to the point it becomes necessary, by which time either the Skylon will be on it's way to orbit and burning through the tank contents at a fair rate or it will have been recycled back to the hangar.

People think sub cooling is a nice to have bolt on but it's much better planned in from the start. With Skylon it is.

1.  It goes into orbit, that negates the aircraft designation.  It is a launch vehicle.
Skylon operates under the UK CAA rules.

It gets it's lift from wings while in UK airspace. That makes it an aircraft.

Nonsense.  Don't know where to start since so much is wrong in that statement.
At the beginning, then move to the middle and proceed to the end?  :)
Quote
A.  The need for CLA's  is not determined by the method of attachment. 
True. It's set by the wafer thin structural margins of most ELV's and the practice hard mounting to the LV, making for superb coupling between 2 major structures with opportunities to excite all kinds of failure modes.

Seriously LV's are the only transport systems that often require the cargo to be redesigned multiple times because it could be shaken to bits, or cause it's carrier can be shaken to bits by the resonance it can excite back into the carrier vehicle.

The reaction of the industry to this seems to have been "Oh well, that's just what you have to do to build a payload."

An attitude which in any other situation would have had the customers saying "No we don't. Get it fixed or we go elsewhere."
Quote
b.  ELV's use clamp bands and still some have CLA issues
I used CLA issues as an indication that REL are aware of all of the issue around payload integration between payloads and LV's.
Quote
c.  It is more about the spacecraft structural stiffness
I'd suggest the size and position of any spacecraft fluid tanks might be some effect on things as well. The point is it should have no effect. It should not require an FEA simulation to determine if there is or is not a problem.
Quote
d..  A bolted interface was not the driver of shuttle CLA issues
True. But I would ask if CLA was as big a problem with Shuttle as it is with ELV's?
Quote
d.  Skylon is using an interface that similar if not identical to the shuttle, the trunnion.
Which may or may not be a problem. OTOH the engines are not sitting directly behind the payload (as they were on Shuttle) to excite direct longitudinal vibrations.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Jim

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1036 on: 12/08/2015 11:15 PM »

1.  It gets it's lift from wings while in UK airspace. That makes it an aircraft.

2.  true. It's set by the wafer thin structural margins of most ELV's and the practice hard mounting to the LV, making for superb coupling between 2 major structures with opportunities to excite all kinds of failure modes.

3.  Seriously LV's are the only transport systems that often require the cargo to be redesigned multiple times because it could be shaken to bits, or cause it's carrier can be shaken to bits by the resonance it can excite back into the carrier vehicle.

4.  I'd suggest the size and position of any spacecraft fluid tanks might be some effect on things as well. The point is it should have no effect. It should not require an FEA simulation to determine if there is or is not a problem.

5.  True. But I would ask if CLA was as big a problem with Shuttle as it is with ELV's?


1.  Not talking about regulations but the approach from an operations and structural POV
2.  No, it about controllability of vehicle and not structural margins
3.  Seriously, its not.  More nonsense and exaggeration
4.  FEA is a basic aerospace tool.  It is not unique to spacecraft and launch vehicles.  Aircraft do it too.  But as far as CLA, Skylon isn't going to be any different from the shuttle, so they will be done.
5.  Neither were/are a big problem
6.  Engine location is not going to matter. Skylon has mass on both sides of the wing, it is going to have its own unique issues.
« Last Edit: 12/08/2015 11:17 PM by Jim »

Online pippin

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1037 on: 12/08/2015 11:38 PM »
Seriously LV's are the only transport systems that often require the cargo to be redesigned multiple times because it could be shaken to bits, or cause it's carrier can be shaken to bits by the resonance it can excite back into the carrier vehicle.

Umm... yes.
LVs are also the only transport systems I am aware of that expose their cargo to multiple g's of acceleration during most of the transport time and Skylon will be no exception to this, won't it?

Also, all other transport systems I'm aware of tend to require you to surround your sensitive cargo with extensive packaging which is usually there to mitigate the effects of even much more benign transport conditions and from which the cargo is then carefully being unwrapped after shipment.
Another aspectc Skylon doesn't really have in common with "other" transport systems.

So it occurs to me that Skylon will still look much more in common with traditional LVs than with traditional air transport if it comes to cargo interfaces.

Yes, shipping water, fuel and raw materials for whatever reason might result in simplified cargo interfaces but I suspect most of the cargo will still, like Jim said, be spacecraft.
« Last Edit: 12/08/2015 11:40 PM by pippin »

Offline ChrisWilson68

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1038 on: 12/09/2015 12:31 AM »

there is a difference in theory, and there is a difference for Skylon according with REL own plans. You might not like them, you might believe they are unrealistic and that "reality" today is different, but then again if anything that differs from how things are done today is unrealistic for the simple fact that they are not done today, why do you even bother about Skylon?

You are right.  I shouldn't bother since there is too much nonsense, unsupported conjecture and flat out just wrong statements on this thread.  Much of it should be in the scifi section because it isn't reality or come close to it.

Good, I'm glad we agree to disagree. Now it would be very kind of you if you could let us continuing our "nonsense conjectures" without further poisoning the discussion..

To me, having someone who disagrees isn't poisoning the discussion.

Poisoning the discussion is asking someone you disagree with to go away.

Offline ChrisWilson68

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1039 on: 12/09/2015 02:06 AM »
To me, having someone who disagrees isn't poisoning the discussion.
It depends on how they disagree. A great deal of insight can be gained from disagreements, provided they're presented in a more constructive form than "that's nonsense"

I agree, and sometimes Jim's posts are just that.  But I saw quite a few posts here where he posted more than just "that's nonsense".

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