The Reaction Engines Skylon Master Thread (1)

[Cinder]

23 years later it looks like they might be vindicated.

Sheesh, you're easily pleased.. they've done one test, on the ground, without even a supersonic wind tunnel.

This is the first step on a very long journey, at least wait until they get something flying before declaring victory yeah?

Might was the word. While it takes one deal-breaker to wrap it up at any point in development (could happen tomorrow for all we know), it'll take till NET some arbitrary number of commercial flights before a positive conclusion and "vindication".

[flymetothemoon]

Well perhaps no earlier than some way into the flight test programme. We were talking about this recently in the thread. 100s of flights in the flight test programme to include real missions to IIS for example... Because you CAN. Because this is a different paradigm.

Within months - all being well - confidence could be built like it has never been built in any other spacecraft. And that would be long before the end of the flight test programme

[Hempsell]

I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

We have done supersonic wind tunnel test of both SKYLON (up to Mach 12) and the nacelle intake alone.  However the core SABRE engine (just like a jet) can be fully developed on the test stand.  We can do this because the core engine does not know what speed it is flying at apart from a rise in intake air temperature.

I can confirm SKYLON is still at the D1 configuration and is on target to meet the performance defined in the User Manual although the quoted high altitude performance is a little optimistic.  The User Manual was always intended to be part of the validation of the performance for D1 and at the moment we can meet those requirements. I am sorry but at the moment D1 will be kept under wraps, (too much new IPR) but the SKYLON you see is a good indication of what you will get.

The business plan assumes a minimum of 30 sales, this is not a number pulled out of thin air but based on a market survey conducted by successful aircraft sales organisation.

The test flight programme does assumed around 2 flights a week for each of the test SKYLONs at the peak but is more complex than the discussion here suggests.  2018 to 2020 can be more than 2 years.  26 flights are not orbital but tests of the abort options.  If the flights go well the reliability is proven before the 400 flights are complete so operations can be started before the test programme is complete.  Mostly test flights will fly a test payload but many also fly the secondary Systems such as the upper stage or the passenger module. We also hope to fly 16 missions to the ISS during this test programme.

We need to get this programme over as quickly as possible because until we start delivering operations SKYLONs we do not start earning money, and the interest on the borrowed money adds to the project debts at a fantastic rate.  However just because we have to prove this flight rate during the test programme does not mean any of the operators have to match it, they can launch at whatever rate suits their business..

The 40 passengers was an early assessment and I think the 24 shown in the User Manual is closer to what we will achieve, but we are in serious preparation on certification of the system and the impact of these requirements have not been fully assessed.  I think it is too early to made definitive statements about how many passengers SKYLON will be able to carry in the end.

I must also backtrack on the performance of the upper stage as quoted in the User Manual. This was the B1 configuration which on review was found a little optimistic on the mass. The B2 performance has been published in the Journal of the British Interplanetary Society in a paper entitled "Technical and Operations design of the SKYLON Upper Stage", April 2010 pp 136-144.  Our best guess now is over 5 tonnes into GTO in reusable mode and over 7 tonnes in expendable mode – but these are fluid numbers due to the lower level of definition on the Upper Stage design and I think we can improve upon the B2 configuration.

[flymetothemoon]

Within months - all being well - confidence could be built like it has never been built in any other spacecraft. And that would be long before the end of the flight test programme

Ok. Even I thought months was at least misleading after I quickly submitted it. I really wanted to allude to the fact that I had read that missions to the ISS were hoped to be part of the test programme, so much confidence could be gained before even the end of the test programme, never mind commercial flights. Much more than any expendable could.

Thank you for the update Mark!

[simonbp]

I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

Thanks!

The website notes that the precooler testing has gone from "stage 1 to stage 2". Can you share any details about what the various stages are?

[Hempsell]

I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

Thanks!

The website notes that the precooler testing has gone from "stage 1 to stage 2". Can you share any details about what the various stages are?

I am sorry but we are not making that sort of detail public

[baldusi]

The test flight programme does assumed around 2 flights a week for each of the test SKYLONs at the peak but is more complex than the discussion here suggests.  2018 to 2020 can be more than 2 years.  26 flights are not orbital but tests of the abort options.  If the flights go well the reliability is proven before the 400 flights are complete so operations can be started before the test programme is complete.  Mostly test flights will fly a test payload but many also fly the secondary Systems such as the upper stage or the passenger module. We also hope to fly 16 missions to the ISS during this test programme.

How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.

[john smith 19]

23 years later it looks like they might be vindicated.

Sheesh, you're easily pleased.. they've done one test, on the ground, without even a supersonic wind tunnel.

This is the first step on a very long journey, at least wait until they get something flying before declaring victory yeah?

I was referring to the idea of a *privately* funded large scale space development project with money raised as a *commercial* venture IE no "assured access" payments or subsidies as people in Europe tend to call them because non USG customers won't buy your hardware at the prices they want to charge.

Actually it's the *current* step on a very long journey that started a *long* time ago and given the accumulated budget it's amazing it's gotten this far. It's fair to say that REL's development programme has been as well thought out as SNC's Dreamchaser in the way each stage has been leveraged by the previous one.

France had independent space launch before the UK.

Type in haste, re-post at leisure.

What I meant was that the UK is the *only* country with both and *renounced* independent launch capability. While other G7 nations never had it the UK did and gave it up. The rest who have it have kept it. Given the pittance it cost it saved very little and lost a very useful technology base.

Because of course the UK could always rely on those nice Americans to launch whatever little boxes govt boffins (who were beleived to be the only people who had any interest in this space thing) could devise. Not so easy when they turned into multi tonne Geo-synchronous commsats and an industry worth billions of pounds.

[douglas100]

France had independent space launch before the UK.

Type in haste, re-post at leisure.

What I meant was that the UK is the *only* country with both and *renounced* independent launch capability. While other G7 nations never had it the UK did and gave it up. The rest who have it have kept it. Given the pittance it cost it saved very little and lost a very useful technology base.

I kind of thought you meant that. But unfortunately I suffer from advanced nit-picking disease with little hope of cure. 

However, your description of UK Government mentality with regard to space is spot on.

[Hempsell]

How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.

The qualification flight test programme has two production prototypes (there are also two earlier full scale development vehicles which are probably not orbital). One is a pathfinder that undertakes the scoping test flights the other is a workhorse and it puts in a solid 204 flights to prove the airfame specified life.

Around 30 of the pathfinder flights are abort tests and do not reach orbit and so are not counted in the flight statistics. So we have a total of around 380 orbital flights available from the two airframes.

Once the workhorse has done 204 flights and the overall programme has around 300 orbital flights we will have proven the specified mission success reliability (99/%) to a better than 80% confidence level, assuming a perfect flight record, and at that point SKYLON can be made operational. Although we have assumed we would still do the remaining 80 or so test flights.

In the more likely event of some test flight aborts we have the additional orbital flights (up to the total of around 380) to prove the reliability to the required confidence level.

If an operator wants to start operations without the full proof of the airframe life or with a low proven mission success rate they can pick an earlier point in the test flight programme to begin their operations.

[Lampyridae]

How many prototype crafts are you expecting to use? What's the expected life of the airframe and engines? And the time between rebuilds of the engine? I'm trying to grasp the level of reusability.

The qualification flight test programme has two production prototypes (there are also two earlier full scale development vehicles which are probably not orbital). One is a pathfinder that undertakes the scoping test flights the other is a workhorse and it puts in a solid 204 flights to prove the airfame specified life.

Around 30 of the pathfinder flights are abort tests and do not reach orbit and so are not counted in the flight statistics. So we have a total of around 380 orbital flights available from the two airframes.

Once the workhorse has done 204 flights and the overall programme has around 300 orbital flights we will have proven the specified mission success reliability (99/%) to a better than 80% confidence level, assuming a perfect flight record, and at that point SKYLON can be made operational. Although we have assumed we would still do the remaining 80 or so test flights.

In the more likely event of some test flight aborts we have the additional orbital flights (up to the total of around 380) to prove the reliability to the required confidence level.

If an operator wants to start operations without the full proof of the airframe life or with a low proven mission success rate they can pick an earlier point in the test flight programme to begin their operations.

That's quite a staggering level of reliability you have right there. The test flights alone are more than double the shuttle's flight history. And 99% mission success, does that mean LOM of 1 in 100 or LOV of 1 in 100? I assume Skylon, unlike the big Roman candles we use now, can do intact aborts with payload?

[lkm]

I have been rather busy recently but I have just had a look at this thread I cannot address all the points raised but I have a few corrections

We have done supersonic wind tunnel test of both SKYLON (up to Mach 12) and the nacelle intake alone.  However the core SABRE engine (just like a jet) can be fully developed on the test stand.  We can do this because the core engine does not know what speed it is flying at apart from a rise in intake air temperature.

I can confirm SKYLON is still at the D1 configuration and is on target to meet the performance defined in the User Manual although the quoted high altitude performance is a little optimistic.  The User Manual was always intended to be part of the validation of the performance for D1 and at the moment we can meet those requirements. I am sorry but at the moment D1 will be kept under wraps, (too much new IPR) but the SKYLON you see is a good indication of what you will get.

Can you comment on whether the improved air breathing performance of the SABRE 4 cycle translates into similarly improved Scimitar performance in Lapcat 2?
A point I think that seems that seems to be missed is that the precooler engine technology is a fundamentally enabling one far beyond just Skylon. As game changingly disruptive as Skylon could be for launch a new generation of precooler hydrogen aircraft engines could be far more so for airlines.

[mmeijeri]

Are there any commercially viable applications of the SABRE heat exchanger technology outside the aerospace sector?

[Hempsell]

The 1% mission failure rate is a failure to deliver the payload and not a vehicle loss statistic. Unlike expendable vehicles this is not the same because as you point out we have a full abort capability from every point in the mission.

The specified vehicle loss rate is better than 1/10,000 flights but it is not possible to directly prove than with any practical test flight programme, so it is inferred from the test flight anomaly record.

Both these are specified values for entry into service proven by the test flight programme.  It is expected that the real inherent reliability will be much better than that and that, as the operational record is generated, the Weibull function will improve it further in mature operation.

I cannot comment on details of the Sabre 4 or its relation with other pre–cooled engines – sorry.

The heat exchangers are eyewateringly expensive so we have not yet identified any non-space applications were it makes economic sense – not even jet engines.

[Seer]

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

[john smith 19]

That's quite a staggering level of reliability you have right there. The test flights alone are more than double the shuttle's flight history. And 99% mission success, does that mean LOM of 1 in 100 or LOV of 1 in 100? I assume Skylon, unlike the big Roman candles we use now, can do intact aborts with payload?

Only by ELV vehicle failure rates. In terms of the architecture Skylon is rather closer to the X15 programme. 199 flights with LOV only occurring when there were *substantial* changes to the architecture (big drop tanks, spray on ablative TPS or hanging a dummy scramjet nacelle on the vehicle). The core architecture (no bits dropping or being burned off, no routine extensive refurbishment) flew many times with no major issues.

Keep in mind while SABRE operates at high pressures (but still less than 75% of the SSME at most) the turbo pumps are driven by pure hot Helium, which is *much* better behaved than the high temperature Hydrogen with high pressure steam of the SSME pump drive system.

[lkm]

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

As I understand it the upper speed of Skylon airbreathing is pretty fixed as determined by this:

http://www.islandone.org/Propulsion/LACE.html

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622

[Warren Platts]

Mr. Hempsell, I wish to thank you again for taking the time to answer questions on this forum!

With the recent announcement of the new Planetary Resources Inc. (PRI) some discussion of getting precious metals like PGM's and possibly Au has been revived somewhat. With wholesale prices at $50,000+ USD/kg, it would be worth it to bring back to Earth. The gold market, in particular, could probably absorb at least $50B/year without depressing the price. But this would require bringing back up to 1000 mT/year of Au. This much downmass could possibly help out the economics of Skylon since it wouldn't have to deadhead it back to Earth with an empty cargo bay all the time.

Q: What can you tell us about the downmass capabilities (esp. in terms of mass and cost) of Skylon?

[john smith 19]

Mr. Hempsell, I wish to thank you again for taking the time to answer questions on this forum!

With the recent announcement of the new Planetary Resources Inc. (PRI) some discussion of getting precious metals like PGM's and possibly Au has been revived somewhat. With wholesale prices at $50,000+ USD/kg, it would be worth it to bring back to Earth. The gold market, in particular, could probably absorb at least $50B/year without depressing the price. But this would require bringing back up to 1000 mT/year of Au. This much downmass could possibly help out the economics of Skylon since it wouldn't have to deadhead it back to Earth with an empty cargo bay all the time.

Q: What can you tell us about the downmass capabilities (esp. in terms of mass and cost) of Skylon?

Note that REL is not planning to operate Skylon but to sell it to users. It would be up to the users how they used it. An interesting question would be how much propellant would be needed to get Skylon to orbit and then de-orbit it with whatever down mass you are targeting.

[Seer]

Do you know why the top speed in air breathing mode is mach 5.14? If you could boost the speed to mach 6, there would be a substantial payload gain.


 I remember reading somewhere that the temperature in the ramjet burners was a limiting factor, is that correct? If so could you use a higher temperature material or active cooling to allow higher speeds? The material specified for the burners is C/SiC I think, but there is a newer material which can withstand higher temperatures - up to 3000 F.  Its called tufroc and is used on the x-37 heat shield.

As I understand it the upper speed of Skylon airbreathing is pretty fixed as determined by this:

http://www.islandone.org/Propulsion/LACE.html

See Hempsell's response here:

http://forum.nasaspaceflight.com/index.php?topic=22434.msg632622#msg632622

Thanks for the link to that lace derivation, but as I understand that is a simplified derivation which assumes the hydrogen that is used to cool the air is dumped overboard rather than burnt in the ramjets. The top speed  then should be higher and the limiting factor is thermal considerations.