Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 441538 times)

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #680 on: 10/13/2015 03:10 PM »
The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #681 on: 10/15/2015 07:29 PM »
The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/

Here's the paper, a pretty good read I think.

It covers a lot of stuff we pretty much already knew but it's nice to see it all set out together in a paper.

SABRE 4 is what we thought with all the trade-offs we discussed and and they're working at bringing down the cost of making everything.

Things that jumped out at me as new:
A new SUS design
                  "This design is shorter and lighter than previous versions
                   increasing the allowable payload length from 4.4m to
                   8.6m and the reusable mode GTO payload from
                   6387kg to 7259kg. "

New mission modelling
                 "SKYLON D1 could place 17 tonnes into a 185 km circular orbit"

and
                " The vehicle can
                  recover to any airfield with compatible latitude at least
                 6 times per day from any orbit, and can recover to an
                 Equatorial airfield from a low inclination orbit (less
               than 40 degrees) on any pass. It was also found that
                the vehicle is capable of operating from any airfield,
               overflying any location on Earth, and recovering to the
              same airfield within a single orbit."


Now I wonder who would find that last part useful?
« Last Edit: 10/15/2015 07:35 PM by lkm »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #682 on: 10/15/2015 11:00 PM »
The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/
                " The vehicle can
                  recover to any airfield with compatible latitude at least
                 6 times per day from any orbit, and can recover to an
                 Equatorial airfield from a low inclination orbit (less
               than 40 degrees) on any pass. It was also found that
                the vehicle is capable of operating from any airfield,
               overflying any location on Earth, and recovering to the
              same airfield within a single orbit."


Now I wonder who would find that last part useful?
Actually anyone who's serious about servicing an on orbit asset, like a hotel for example, or collecting   the results of an on orbit manufacturing plant.
"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 t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #683 on: 10/16/2015 10:58 AM »
The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/

Here's the paper, a pretty good read I think.

I think it's fascinating that as we find out how frost control works.....it's suddenly irrelevant :-).  So much thinking and wondering about what it was and all for nothing.

Also thrust vectoring seems to be mentioned very often in papers that I found on Google about Dual Throat Nozzles.  I wonder if they intend to use it?
« Last Edit: 10/16/2015 11:00 AM by t43562 »

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #684 on: 10/16/2015 12:30 PM »
...
Also thrust vectoring seems to be mentioned very often in papers that I found on Google about Dual Throat Nozzles.  I wonder if they intend to use it?

Could you say more? Skylon designs have always had gimbaling nozzles as far as I know. What would be different about dual throat nozzles with SABRE 4?

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #685 on: 10/16/2015 12:35 PM »
The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/
                " The vehicle can
                  recover to any airfield with compatible latitude at least
                 6 times per day from any orbit, and can recover to an
                 Equatorial airfield from a low inclination orbit (less
               than 40 degrees) on any pass. It was also found that
                the vehicle is capable of operating from any airfield,
               overflying any location on Earth, and recovering to the
              same airfield within a single orbit."


Now I wonder who would find that last part useful?
Actually anyone who's serious about servicing an on orbit asset, like a hotel for example, or collecting   the results of an on orbit manufacturing plant.
That's a different problem, surely: being able to overfly any point on the Earth and land in one orbit is not the same as being able to rendezvous with an orbiting asset in one orbit.
« Last Edit: 10/16/2015 12:36 PM by adrianwyard »

Offline t43562

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #686 on: 10/16/2015 12:52 PM »
...
Also thrust vectoring seems to be mentioned very often in papers that I found on Google about Dual Throat Nozzles.  I wonder if they intend to use it?

Could you say more? Skylon designs have always had gimbaling nozzles as far as I know. What would be different about dual throat nozzles with SABRE 4?

I'm a layperson and what I could say isn't worth reading but... I did read up about a UAV project in the UK once that was aimed at demonstrating "fluidic" controls - FLAVIR.    As I understand it, fluidic vectoring uses smaller flows e.g. at the side of an exhaust, to influence the direction of the main flow.   How this works with dual-throat nozzles, I don't understand but there are a lot of papers about it e.g. from NASA.

The result, as I understand it, is a much lighter system than mechanical thrust vectoring and the more vectoring you have the less control surfaces you need so you get less drag.  But again I am an ignoramus and I'm just typing what I have inexpertly read about.  It may not make any sense for the part of SABRE4 which is basically rocket-like rather than jet-like.
 

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #687 on: 10/16/2015 01:42 PM »
I think it's fascinating that as we find out how frost control works.....it's suddenly irrelevant :-).  So much thinking and wondering about what it was and all for nothing.

Also thrust vectoring seems to be mentioned very often in papers that I found on Google about Dual Throat Nozzles.  I wonder if they intend to use it?
I'd be surprised at that.

The FLAVIR work you mentioned is not a dual throat nozzle. It's a main flow with 2 side flows, which use fluidic effects (the Coanda effect particularly IIRC) to divert the  main thrust up or down (or in principle with another set of side flow channels left or right). In theory the payoff is smaller, faster valves shift the control flow, which shifts the main flow.

But a dual chamber nozzle is truly one chamber inside the other, a bell within a bell.

The only one of these I'm aware of was the Lance tactical missile. The centre bell was the 50 000lb  booster to get off the launcher then the outer bell (technically an annular combustion chamber) gave 5000lb for cruising.

Development had some problems but I suspect that had more to do with the storable propellants, ablative cooling and long series mfg than the actual concept. Since SABRE engines are not ablattively cooled or use storables I think most of those problems would be absent.

[EDIT BTW FLAVIR was a remarkable programme. Most of the work resulted in actual flight vehicles, although by normal standards they were tiny. ]
« Last Edit: 10/16/2015 01:45 PM by john smith 19 »
"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 Citizen Wolf

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #688 on: 10/16/2015 10:29 PM »
On page 3 of the report it says:

**Also, due to the higher pre-cooler exit temperature compared to SABRE 3, the frost control system is no longer required.**

?? What exactly does that mean? They're not getting rid of the heat exchangers, so why don't they need the frost control? Below 0 C and ice forms. Why don't they need frost control now? What temperature will the heat exchangers reduce the intake airflow down to in SABRE 4?
« Last Edit: 10/16/2015 10:41 PM by Citizen Wolf »
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Offline 93143

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #689 on: 10/16/2015 10:49 PM »
The thing with SABRE 3 was that it used the same combustion chamber and nozzle for airbreathing mode as for rocket mode.  This meant that the airbreathing pressure ratio had to be very very high, which meant that the air going into the big end of the compressor had to be very very cold if the small end of the compressor was to survive very long.

Now that they're using a separate chamber, that opens up partway down the nozzle, they don't need rocket-class chamber pressures, so the pressure ratio is lower and the air can be much warmer before compression without damaging the engine.
« Last Edit: 10/16/2015 10:52 PM by 93143 »

Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #690 on: 10/16/2015 11:17 PM »
On page 3 of the report it says:

**Also, due to the higher pre-cooler exit temperature compared to SABRE 3, the frost control system is no longer required.**

?? What exactly does that mean? They're not getting rid of the heat exchangers, so why don't they need the frost control? Below 0 C and ice forms. Why don't they need frost control now? What temperature will the heat exchangers reduce the intake airflow down to in SABRE 4?
If you read the patent on SABRE 4 you'll see that in this cycle the precooler exit temperature is designed to never fall below 400K with the bidirectional valve in the cycle directing helium around the precooler to maintain that. 


The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/
                " The vehicle can
                  recover to any airfield with compatible latitude at least
                 6 times per day from any orbit, and can recover to an
                 Equatorial airfield from a low inclination orbit (less
               than 40 degrees) on any pass. It was also found that
                the vehicle is capable of operating from any airfield,
               overflying any location on Earth, and recovering to the
              same airfield within a single orbit."


Now I wonder who would find that last part useful?
Actually anyone who's serious about servicing an on orbit asset, like a hotel for example, or collecting   the results of an on orbit manufacturing plant.

I was thinking more along the lines of being able to responsively launch a Skylon with an ISR package in the payload bay and have it overfly any location on Earth from an airfield in CONUS.

My query about the engines is are they throttling by translating the nozzle adjusting throat area, we know it has to translate anyway and this is something I believe has been explored before with this type of nozzle.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #691 on: 10/17/2015 12:51 AM »
I was thinking more along the lines of being able to responsively launch a Skylon with an ISR package in the payload bay and have it overfly any location on Earth from an airfield in CONUS.
Given the expanded latitude range that would certainly seem to be possible.

Note that right now the only payload REL are committed to supplying (not necessarily building) is the Skylon Upper Stage.

Any operator, or customer of an operator, would have to supply that hardware themselves. I'd also not that under normal circumstances there is no reason for Skylon to fly "upside down." However an "Earth Observation" mode could be included in the standard flight control software to roll the vehicle 180deg, open its doors and then close and roll it backward.
Quote
My query about the engines is are they throttling by translating the nozzle adjusting throat area, we know it has to translate anyway and this is something I believe has been explored before with this type of nozzle.
A running theme of REL work has been to push the SoA  (or the common state of practice) only where absolutely necessary.

I'm not quite clear what you're suggesting. Do you mean some kind of Pintle injector? Making the whole inner chamber some kind of pintle?

Conventional practice has the whole engine gimbal but people have done engines where only the thrust chamber(s) move, although this needs high pressure fluid gimbals rated to chamber pressure, not tank pressure.

For throttling I'd guess they can either indirectly throttle the pump drive turbines by controlling heat addition through the pre burner or (with a more direct action) have divert valves to divert some of the propellants back to the pump inlets. These techniques have history going back to the RL10 and J2 (and possibly the RZ20 built by Rolls Royce in the late 60's).
"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 Citizen Wolf

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #692 on: 10/17/2015 09:35 AM »
Ikm
**If you read the patent on SABRE 4 you'll see that in this cycle the precooler exit temperature is designed to never fall below 400K with the bidirectional valve in the cycle directing helium around the precooler to maintain that.**

Ah, 400K, I see. That's well above freezing point. Thanks for the info. :)    Well, so much for the frost control!

@93143
I understood that the noozles were now separated in SABRE 4 and that had changed the thermodynamics of the flows. I just wasn't clear on what the pre-cooler exit temperature was. I just figured (before I saw the report) that the precooler still brought the airflow down below 0C. I guess they have much more control over the heat-exchanger thermodynamics than I imagined.  (As an aside, I wonder how much on-the-fly control could be engineered into such a system).

BTW, your explanation also gave me a better understanding of the system. Many thanks!
« Last Edit: 10/17/2015 09:44 AM by Citizen Wolf »
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Offline lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #693 on: 10/17/2015 10:00 AM »
I was thinking more along the lines of being able to responsively launch a Skylon with an ISR package in the payload bay and have it overfly any location on Earth from an airfield in CONUS.
Given the expanded latitude range that would certainly seem to be possible.

Note that right now the only payload REL are committed to supplying (not necessarily building) is the Skylon Upper Stage.

Any operator, or customer of an operator, would have to supply that hardware themselves. I'd also not that under normal circumstances there is no reason for Skylon to fly "upside down." However an "Earth Observation" mode could be included in the standard flight control software to roll the vehicle 180deg, open its doors and then close and roll it backward.

My thinking was these are their latest mission analysis studies conducted since they began their relationship with the AFRL and perhaps this was indicative of the sorts of questions they were asking.
 
My query about the engines is are they throttling by translating the nozzle adjusting throat area, we know it has to translate anyway and this is something I believe has been explored before with this type of nozzle.
A running theme of REL work has been to push the SoA  (or the common state of practice) only where absolutely necessary.

I'm not quite clear what you're suggesting. Do you mean some kind of Pintle injector? Making the whole inner chamber some kind of pintle?

Conventional practice has the whole engine gimbal but people have done engines where only the thrust chamber(s) move, although this needs high pressure fluid gimbals rated to chamber pressure, not tank pressure.

For throttling I'd guess they can either indirectly throttle the pump drive turbines by controlling heat addition through the pre burner or (with a more direct action) have divert valves to divert some of the propellants back to the pump inlets. These techniques have history going back to the RL10 and J2 (and possibly the RZ20 built by Rolls Royce in the late 60's).

The SABRE 4 ends the airbreathing mode by translating the entire airbreathing nozzle backwards until the airbreathing throat closes, as it does so the area of the airbeathing throat decreases. Other expansion-deflection nozzles designs  throttle thrust by varying the throat area through translating the pintle so if the SABRE 4 airbreathing chambers move with the nozzle then the SABRE 4 can throttle thrust in the same manner. So in a sense that is the SoA for ED nozzles.

Offline francesco nicoli

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #694 on: 10/17/2015 11:31 PM »
do you expect substantial costs reduction from getting rid of frost control?

Offline Star One

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #695 on: 10/18/2015 09:20 AM »

The IAC update seems to have happened but I can't find any crumbs of news or comments about it:

https://iafastro.directory/iac/paper/id/31601/summary/
                " The vehicle can
                  recover to any airfield with compatible latitude at least
                 6 times per day from any orbit, and can recover to an
                 Equatorial airfield from a low inclination orbit (less
               than 40 degrees) on any pass. It was also found that
                the vehicle is capable of operating from any airfield,
               overflying any location on Earth, and recovering to the
              same airfield within a single orbit."


Now I wonder who would find that last part useful?
Actually anyone who's serious about servicing an on orbit asset, like a hotel for example, or collecting   the results of an on orbit manufacturing plant.
That's a different problem, surely: being able to overfly any point on the Earth and land in one orbit is not the same as being able to rendezvous with an orbiting asset in one orbit.

I imagine the USAF took note of that, or rather were already aware of that.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #696 on: 10/18/2015 05:11 PM »
do you expect substantial costs reduction from getting rid of frost control?
Probably not much.

You've sunk the funds getting it to work. The HX's will be a bit simpler but I suspect not much simpler. The bulk of them will still be the LH2 network and that's going to be get much simpler.
I think it's fascinating that as we find out how frost control works.....it's suddenly irrelevant :-).  So much thinking and wondering about what it was and all for nothing.
Apparently so. But note it's taken REL about 30 years to get here and AFAIK all other groups working in this area (and there are a small number) tagged air cooling and frost control as the problems for these kinds of engines.

The attraction was you traded engine complexity for weight which meant less deadweight to get to orbit as you'd burnt off the LH2.

Trading higher engine weight for lower fuel is not an intuitively obvious way to go. You have to dig deep into the thermodynamics and engineering to get there, and only then can you discard the frost control.
My thinking was these are their latest mission analysis studies conducted since they began their relationship with the AFRL and perhaps this was indicative of the sorts of questions they were asking.
Probably not.

The work with ARFL was for SABRE, the engine.

These analyses apply to SKylon, the vehicle, which AFAIK had nothing do to with the AFRL contract.

However it is interesting they validated their trajectory analysis codes against a NASA system, although It's not clear where they got that from. Quite a lot of NASA stuff is available as source code (like their combustion modelling codes).


Quote

The SABRE 4 ends the airbreathing mode by translating the entire airbreathing nozzle backwards until the airbreathing throat closes, as it does so the area of the airbeathing throat decreases. Other expansion-deflection nozzles designs  throttle thrust by varying the throat area through translating the pintle so if the SABRE 4 airbreathing chambers move with the nozzle then the SABRE 4 can throttle thrust in the same manner. So in a sense that is the SoA for ED nozzles.
I think you're talking about the inlet end of SABRE. While it's technically a pintle I think most people call it an aerospike. I imagine changing overall air flow is part of the throttling process and that's certainly going to be part of the design for the ground test engine.

While REL's work does seem to have a pintle in the core of the test engines it looks like a straight cylinder to me and I suspect they'll want to keep the engine throttling process as simple as possible.
"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 lkm

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #697 on: 10/18/2015 06:00 PM »
do you expect substantial costs reduction from getting rid of frost control?
Probably not much.

You've sunk the funds getting it to work. The HX's will be a bit simpler but I suspect not much simpler. The bulk of them will still be the LH2 network and that's going to be get much simpler.
There is the benefit that you've lost a fourth liquid system from the engine which operationally must mean lower maintenance costs.


My thinking was these are their latest mission analysis studies conducted since they began their relationship with the AFRL and perhaps this was indicative of the sorts of questions they were asking.
Probably not.

The work with ARFL was for SABRE, the engine.

These analyses apply to SKylon, the vehicle, which AFAIK had nothing do to with the AFRL contract.

However it is interesting they validated their trajectory analysis codes against a NASA system, although It's not clear where they got that from. Quite a lot of NASA stuff is available as source code (like their combustion modelling codes).
AFRL is also looking at vehicle concepts.


The SABRE 4 ends the airbreathing mode by translating the entire airbreathing nozzle backwards until the airbreathing throat closes, as it does so the area of the airbeathing throat decreases. Other expansion-deflection nozzles designs  throttle thrust by varying the throat area through translating the pintle so if the SABRE 4 airbreathing chambers move with the nozzle then the SABRE 4 can throttle thrust in the same manner. So in a sense that is the SoA for ED nozzles.
I think you're talking about the inlet end of SABRE. While it's technically a pintle I think most people call it an aerospike. I imagine changing overall air flow is part of the throttling process and that's certainly going to be part of the design for the ground test engine.

While REL's work does seem to have a pintle in the core of the test engines it looks like a straight cylinder to me and I suspect they'll want to keep the engine throttling process as simple as possible.

No, I'm talking about the engine nozzle, the patent for it makes it clear. Pintle or centrebody is what I've read it as in ED papers.
Quote
"19. A nozzle arrangement according to claim 1, further comprising an actuator arrangement that is arranged to move the second portion of the nozzle between the two positions. "

Offline adrianwyard

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #698 on: 10/18/2015 07:13 PM »
lkm may know a better source, but here are links to the nozzle patent application and figures:

Text:
http://www.freshpatents.com/-dt20150416ptan20150101337.php

Figures:
http://images1.freshpatents.com/imageviewer/20150101337-p20150101337


Offline Bubbacub

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #699 on: 10/18/2015 08:01 PM »
The last few pages of this thread (in which I've been lurking for years) have got me thinking. It seems as if the cooling requirements have decreased significantly since the change in engine design from sabre 3 to sabre 4, so much so that frost control is no longer an issue.

My question is if this decrease in cooling requirements could allow for a change to methane as a the cryogenic fuel. This could significantly reduce the size and weight of skylon's tanks (and reduce the developmental costs and headaches from dealing with liquid H2). Of course a smaller skylon would make re-entry more difficult - if you believe reaction engines understanding of atmospheric re-entry.

I know that the trades around reduced ISP and increased propellant density are complex. However there does seem to be a recent trend, given today's tank building expertise and from lessons learnt from designs like, for example, the x33 to compromise with a lower ISP fuel to gain a benefit from the reduction in weight of tankage and insulation etc.

Over a 200 cycle lifetime there would also probably be fairly significant cost savings not only in terms of the cost of fuel but also the systems and infrastructure required to store and pump the fuel at the various launch sites.

Is this an obviously answerable question? Or is it something that could go either way and would require a complete vehicle redesign and modelling to answer?

In any event I thought it was something worth thinking about - especially given how reaction engines have demonstrated great flexibility in their thought processes by deciding to ditch frost control - a technology which they have spent the better part of twenty years perfecting. It takes a lot of strength of will and character to ditch the fundamental, truly unique part of their business in order to optimise the final vehicle. If they are willing to ditch frost control perhaps they would be willing to ditch liquid hydrogen?

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