Author Topic: The Reaction Engines Skylon Master Thread (1)  (Read 691205 times)

Offline grakenverb

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Re: Skylon
« Reply #220 on: 06/11/2011 05:44 pm »

When the Shuttle designers chose a vehicle with no early launch abort system, this was because all things considered, they didn't think one would be needed. Contrast this with SpaceShipTwo which automatically orientates itself to re-entry attitude. My guess is you could be tumbling with a full electrical failure on SS2 and still make it back OK.

Not so sure I'd want to be in SS2 in feathered mode when altimeter = 0 ;D

Offline adrianwyard

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Re: Skylon
« Reply #221 on: 06/11/2011 05:59 pm »
re Skylon TPS: No doubt, this is a key innovation, but the re-entry is very different to a Shuttle (10km higher due it's lower ballistic coefficient - more like an airship.)

Most recent info I can find says they are looking at something called
Pyrosic from Pyromeral Systems, with ten layers of Ti insulation below this:

http://www.reactionengines.co.uk//downloads/The%20SKYLON%20Spaceplane-Progress%20to%20Realisation,%20JBIS,%202008.pdf
« Last Edit: 06/11/2011 07:00 pm by adrianwyard »

Offline simonbp

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Re: Skylon
« Reply #222 on: 06/11/2011 10:32 pm »
The ESA evaluation had the TPS for the C1 as a carbon-silicon carbide (CSC) ceramic.

Offline Andrew_W

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Re: Skylon
« Reply #223 on: 06/12/2011 01:54 am »
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.

Can anyone tell me what the mass of the individual propellants is? For the lighter C1 version I've read that LH2 is 66 tonnes and LOX is 150 tonnes, do those ratios hold for the D1?
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

Offline Downix

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Re: Skylon
« Reply #224 on: 06/12/2011 03:02 am »
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.
The An-225 is 84 meters long.  As for weight, for the structure being discussed here, I see nothing which is a game breaker. I am curious how they got the weight down so much, personally.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Andrew_W

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Re: Skylon
« Reply #225 on: 06/12/2011 04:56 am »
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.

I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

Offline Lampyridae

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Re: Skylon
« Reply #226 on: 06/12/2011 09:46 am »
Doing a primitive all-rocket SSME comparison with Skylon C1 configuration:
Skylon 1100m tanks, 56 tonnes in orbit, of which ~19600kg for 2 Sabre engines.

http://www.spacefuture.com/archive/a_single_stage_to_orbit_thought_experiment.shtml
Using 3x 3200kg SSMEs would reduce vehicle mass by 10 tonnes - so 46tonnes to orbit.
Assuming 9200m/s deltaV and an ascent averaged Isp of 425s gives an initial mass of 418 tonnes needing 1040m of 358kg/m LOX+LH2.  3xSSME at 109% give lift off thrust to weight about 1.31.  Low drag and High L/D may enable the trajectory to be optimised for lower delta V.

That is 5% smaller fuel volume than Skylon.

There are probably also some additional weight savings to be had (reduced wing and landing gear loads, possibly smaller rudder and canard area requirements with all rockets close to axis in a boattail, and reduced dynamic pressures and pitching moments during ascent).

So if Sabre powered Skylon is feasible then does that also imply that VTHL SSTO is just as feasible?  It would almost certainly have less risk and far lower development costs.

A mountainside launch catapult giving a few hundred m/s might improve it to the point where it was greatly superior to Sabre Skylon.

BOTE calculations vs (cancelled) reality.



Also, Reaction Engines = UK company. Why do you think they're not bothering with the SSME?
« Last Edit: 06/12/2011 09:58 am by Lampyridae »

Offline lkm

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Re: Skylon
« Reply #227 on: 06/12/2011 01:55 pm »
Using Skylon mass estimating relations the dry mass of your BOTE calculation is closer to 62mt including 4 SSME's required for thrust to weight and engine out, this puts your payload at about 5mt.
This gives a payload mass fraction of 0.8% compared to to 4.3% for Skylon, a propellant fraction of about 90% versus 81%. About what you'd expect for all rocket versus Skylon.
 
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.



Offline Downix

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Re: Skylon
« Reply #228 on: 06/12/2011 04:28 pm »
The ESA evaluation had the TPS for the C1 as a carbon-silicon carbide (CSC) ceramic.
I heard carbon-silica carbide, which is lighter than carbon-silicon carbide by about 20gm^2.  But both would work.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Downix

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Re: Skylon
« Reply #229 on: 06/12/2011 04:38 pm »
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.

The numbers I have for Skylon are:
dry mass: 41,035 kg
Oxidizer: 150,235 kg
Fuel: 66,807 kg
RCS fuel: 2,357 kg

I see nothing breaking the model off paper in these numbers. If SABRE delivers even 90% of the promised performance, it will be able to fill a Delta II payload range.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Andrew_W

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Re: Skylon
« Reply #230 on: 06/12/2011 07:04 pm »
lkm:
Using Skylon mass estimating relations the dry mass of your BOTE calculation is closer to 62mt including 4 SSME's required for thrust to weight and engine out, this puts your payload at about 5mt.
This gives a payload mass fraction of 0.8% compared to to 4.3% for Skylon, a propellant fraction of about 90% versus 81%. About what you'd expect for all rocket versus Skylon.


I'm assuming HTHL, my T/W ratios are a little short of Skylon at lift-off, but with the higher fuel burn rate to Mach 5.5 are higher than Skylon at Mach 5. Modifications to C2 would be lengthening LOX tanks by a total of about 12 meters, increasing wing area by 60% and strengthening landing gear. 
(3.1MB pdf)
http://www.reactionengines.co.uk/downloads/SKYLON_User_Manual_rev1-1.pdf

Downix, those numbers are for the earlier C1 version of Skylon, payload for which was 12 tonnes to low equatorial orbit.
« Last Edit: 06/12/2011 07:36 pm by Andrew_W »
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
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Offline Hempsell

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Re: Skylon
« Reply #231 on: 06/13/2011 11:15 am »
What amazing TPS does this thing have that's cheaper, easier and better than the Shuttle?

As adrianwyard points out the black TPS is actually a reinforced high temperature glass (such Pyrosic from Pyromeral Systems) as except at peak temperature locations like the nose and leading edges where carbon - carbon is used, which is gray after a carbon-silicon carbide surface protection is added (just like the Shuttle).

The reason we can use the reinforced high temperature glass material and the Shuttle could not, is our surface temperatures are lower, because of a lower ballistic coefficient.  Although the downside is we have a longer high temperature soak leading to the use of liquid hydrogen as a heat sink as previously discussed.

Offline Hempsell

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Re: Skylon
« Reply #232 on: 06/13/2011 11:16 am »
OK, very primitive maths:
The combined propellant tank volume is by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% to allow for a heavier T/O weight making structural wt 40.8 tonnes, 2XSSME's (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a T"O weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

Call me a cynic, but I'm tempted to think that the weights work on paper because they have to work on paper, if they don't the Sabre's no longer have a function on a launch vehicle, and the entire enterprise is questionable.




With regards to Andrew_Ws pure rocket alternative.  The initial figures seem to leave out TPS, recovery system (wings parachutes or rocket relight) and landing gear all add many tonnes.  You also need all the OMS and RCS kit and their propellants and the power generation system.  Put all these in and past studies suggest you exceed a take off mass of 1000 tonnes for the class of payloads we are dealing with.  The dry mass then works out more than SKYLON which parametrics suggest will be more expensive.

Also you dont get 4500 m/s until you are in vacuum but then again 9907m/s is a bit high in this context 9500 m/s should do it.

Many in the Reaction Engines team have worked on pure rocket proposals (including myself on the Delta Clipper) and we are sure we are in a much better place.  But if someone wants to complete with a pure rocket system they are at liberty to do so.

Part of the passion in pure rocket SSTO debates is very small changes in assumed achievable mass ratio makes massive differences in performance if 12 % TOM gets you 9.5 km/s, then at then 11% things are brilliant nearly 10 km/s so what is the problem but at 13 % you are looking at 9 km/s still well short of orbit.  Thanks to the rocket equation such vehicle are incredibly sensitive, now as Alan point out (but the original observation was I think Bob Parkinson) if the world were 10% smaller it would be very different.

On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.

For the record C1 made a bit more than 10.5 tonnes payload.  12 tonnes was the target but it never got to it; one of the many reasons for the D1 redesign.

Offline Hempsell

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Re: Skylon
« Reply #233 on: 06/13/2011 11:17 am »
How do you handle the forces from venting the tanks? Just do them in two opposite directions?

(BTW, thanks for being so accessible on this site; it's great!)

That has not been worked out in detail but I suspect it will be in to the base area of the nacelles.

Offline Hempsell

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Re: Skylon
« Reply #234 on: 06/13/2011 11:19 am »
Will you be able to release information on the progress of the precooler tests? Or will it have to wait for the full report?

I think we had better actually do the test programme rather than tempt fate with progress reports and predictions.  I will give a heads up when we do have something to say but its going well at the moment.

Offline Hempsell

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Re: Skylon
« Reply #235 on: 06/13/2011 11:22 am »
Hi folks, I share RobLynn's skepticism about Skylon, given the difference in the weight of a couple of SSME's and the Sabre's, and given the very low density of the propellant mix. It seems to me that the main reason that Skylon works on paper is because of it's extraordinarily low structural weight: 53 tonnes unladen mass minus 19 tonnes leaves just 34 tonnes for everything else, and that's for a vehicle thats 83 meters long - longer than any commercial aircraft now flying.

Can anyone tell me what the mass of the individual propellants is? For the lighter C1 version I've read that LH2 is 66 tonnes and LOX is 150 tonnes, do those ratios hold for the D1?

No the ratios do not hold for D1 but I cannot tell you what they are.

Offline Crispy

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Re: Skylon
« Reply #236 on: 06/13/2011 11:36 am »
Thanks again for answering all our questions, Mark :)
It's the best thing about this forum - getting to talk to the people doing the real thing.

Offline RobLynn

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Re: Skylon
« Reply #237 on: 06/13/2011 04:44 pm »
Many in the Reaction Engines team have worked on pure rocket proposals (including myself on the Delta Clipper) and we are sure we are in a much better place.  But if someone wants to complete with a pure rocket system they are at liberty to do so.
Thanks for the reply, Looking forward to you guys getting fully funded!
The glass is neither half full nor half empty, it's just twice as big as it needs to be.

Offline Downix

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Re: Skylon
« Reply #238 on: 06/13/2011 04:59 pm »

Downix, those numbers are for the earlier C1 version of Skylon, payload for which was 12 tonnes to low equatorial orbit.
Those are the only numbers I have at this time.  I will assume that the design has been improved since then.  A team able to make a design with these weight numbers for an earlier model I doubt would make a gross mistake later on with upgrades.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Andrew_W

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Re: Skylon
« Reply #239 on: 06/13/2011 07:45 pm »
Thanks for the reply.


With regards to Andrew_Ws pure rocket alternative.  The initial figures seem to leave out TPS, recovery system (wings parachutes or rocket relight) and landing gear all add many tonnes.  You also need all the OMS and RCS kit and their propellants and the power generation system.  Put all these in and past studies suggest you exceed a take off mass of 1000 tonnes for the class of payloads we are dealing with.  The dry mass then works out more than SKYLON which parametrics suggest will be more expensive.

But they're the REL initial figures! I'm working on making only the changes to the C2 structure to accommodate the changed propellant mass ratios and heavier take-off mass, I've allowed a 7 tonne increase in structural mass to allow those changes, if I don't have TPS, recovery system, OMS and RCS kit and their propellants and the power generation system, and landing gear in my figures it means they're not in the REL figures for Skylon C2 unladen weight.


Part of the passion in pure rocket SSTO debates is very small changes in assumed achievable mass ratio makes massive differences in performance if 12 % TOM gets you 9.5 km/s, then at then 11% things are brilliant nearly 10 km/s so what is the problem but at 13 % you are looking at 9 km/s still well short of orbit.  Thanks to the rocket equation such vehicle are incredibly sensitive, now as Alan point out (but the original observation was I think Bob Parkinson) if the world were 10% smaller it would be very different.


That's why I've become a huge fan of aerial propellant transfer, even with the modest effort of refueling at 10-12,000 meters from an A380 your SSTO saves about a km/s from the ascent to orbit, in the great scheme of things the cost of and A380 tanker and hassle of in-flight refueling are minor penalties (but that's another story).

On the other side of the argument the main reason our structure masses are lower than conventional civil aircraft of comparable dimensions is the truss frame structure - like an airship.


That's the bit I think makes the difference to your numbers compared to other SSTO, but you can use such a truss frame structure irrespective of what form of engine you're using.
« Last Edit: 06/13/2011 09:38 pm by Andrew_W »
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

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