Author Topic: The Reaction Engines Skylon Master Thread (5)  (Read 440287 times)

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1580 on: 06/14/2016 06:29 PM »
Which is a shame, it would be nice to believe there was some weight behind this article where Nextbigfuture believes the Reaction Engine Skylon Spaceplane will be fully funded as a result of SpaceX's potential dominance

Don't read anything into NextBigFuture articles. It's just a one-man science blog. Outside of some conference-blogging, there's never new information in the articles. Certainly, in the case of space-related topics, nothing you wouldn't have seen on NSF.

The author is usually just regurgitating press releases, science papers, or trying to do an "overview" type of article from a handful of different (online) sources, sometimes with a mushing together of concepts. (The Skylon article seems to be an example of the latter.)

For regular readers, NextBigFuture is basically just having someone else trawl the net for science stories for you; summarised so you can see if you care enough to click-through to the primary source. You get used to the vagaries of the author.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1581 on: 06/14/2016 09:57 PM »
It may be easier to obtain funding for a new class of engine that can be strapped to an existing vehicle
What existing vehicle would that be? XS1 seems too far gone for them to be an entrant and ATK seem quite tightly linked into the SR72 powerpoints powerplant project
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than to punt for a novel engine for a novel vehicle which requires novel infrastructure? or to put it anouther way
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AFRL officials views a single-stage-to-orbit Skylon space plane as "technically very risky as a first application [...]
This remains just a bizarre piece of logic. REL did an EU design study specifically for M5 cruise for the EU. While the core elements are similar the overall design is radically different because the task is radically different. The USAFRL should know this.

If the SABRE test engine delivers its promise the only logical thing to put it on is a single stage to orbit spaceplane. If you just want a precooled engine then it's not SABRE.

It comes down to this. A 2 stage design would essentially be the original Faget concept space shuttle (hopefully without the high risk stall maneuver he was looking at).

Such a design needs 2 engines and 2 airframes to get funded, develop and test.

There are a few ways to side step some of those issues, but not many.

Build the aircraft equivalent of a "biamese" rocket. 2 Identicalaircraft with the same engines and airframe.  SABRE sort of plays into this concept if your issue is you doubt REL's Skylon concept is infeasible. Note for maximum cost reduction the engines and airframes must be identical.

Slightly down from this would be identical airframes with different SABRE versions. The booster has the full moving spike inlets but flies with empty LOX tanks (remember, identical hardware --> both vehicles can be certified together) the upper stage has sealed nacelles (identical aerodynamics AFAP for flight certification)  and runs purely in rocket mode, with a reduced LH2 load. Same tanks, different propellant load. It's not the maximum payload to orbit plan, but it is the minimum budget plan short of the reprising the STS orbiter-plus-moster-RATO-packs-plus-monster-drop-tank concept, which we all got to appreciate.

Above that in terms of cost (and the most conventionally structured development plan) would be where you're looking at 2 separate vehicles (with separate mfg programmes, followed by separate then combined test programmes to integrate them together) with 2 separate engines.

Best case for this is that USAFRL has an existing rocket engine they can use for the 2nd stage. Worst case is this is a development from scratch.  :(

A TSTO is probably the safe bet if you don't have an engine that can give you (at least for part of the journey) an Isp of 3000+ secs.

Once that's on the table you should really reconsider your options.  :(
« Last Edit: 06/14/2016 10:46 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 Robotbeat

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1582 on: 06/14/2016 11:59 PM »
TSTO is the best bet if you don't want to solve the problems you're likely to uncover from both a dramatically new engine concept and an extremely good mass fraction airframe/TPS simultaneously.

One miracle at a time.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1583 on: 06/15/2016 01:03 AM »
Note for maximum cost reduction the engines and airframes must be identical.

Incorrect. This is the two-is-more-than-one myth again. A single design that can perform the two tasks is not necessarily going to be cheaper to develop than two designs that do one each. In fact, given the demands of re-entry, the opposite is likely to be true. For a TSTO built around SABRE, a biamese may be the worse possible design possible.

And you certainly don't want to use the same engines on both stages (you don't want SABRE or a derivative on the second stage.)

Similarly,

Such a design needs 2 engines and 2 airframes to get funded, develop and test.

With a TSTO, the upper stage engine would be a conventional rocket engine. That will not be the same development costs as the first stage hybrid air-breathing engine. For the first experimental version of the system, you can even use a conventional upper-stage off an existing system. That reduces your development cost to just the first stage. Since the re-entry for the upper-stage is vastly more demanding than the first stage, deferring development of a reusable second stage saves a lot, and allows you to fly hardware sooner.

I'm not arguing that the USAF idea for TSTO is necessarily superior to Skylon, but two-is-more-expensive-than-one is not a valid argument against it.

[edit: corrected stupid]
« Last Edit: 06/15/2016 01:05 AM by Paul451 »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1584 on: 06/15/2016 07:50 AM »
TSTO is the best bet if you don't want to solve the problems you're likely to uncover from both a dramatically new engine concept and an extremely good mass fraction airframe/TPS simultaneously.

One miracle at a time.
If SABRE fully checks out on the ground you'll basically waste most of it's design features. If you just want precooled air inlets then it's not SABRE at all. It's jet engine with a heat exchanger up front.

This should still generate significant revenue for REL, but it's not getting them anywhere near orbit.  :(

Regarding truss structure. NASA Langley did a study in 1969 comparing Aluminum with AlBe and Be tubing. The straight Al alloy structure (the "heavy" design) weighed 3lbs but could carry a 250lb load, roughly 83 1/3:1 load to mass.

So I think a well designed truss structure can support very significant loads.
"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 john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1585 on: 06/15/2016 07:51 AM »
Incorrect. This is the two-is-more-than-one myth again. A single design that can perform the two tasks is not necessarily going to be cheaper to develop than two designs that do one each.
Let me get this straight.

A TSTO using 2 unique stage designs and engines will be cheaper to design and build IE the overall budget will be lower, than a biamese with a single structural and engine design
Quote
In fact, given the demands of re-entry, the opposite is likely to be true. For a TSTO built around SABRE, a biamese may be the worse possible design possible.
No one goes to a biamese design for performance. They use it because the budget won't support the cost of 2 full vehicle and possibly engine design and the integration of the 2 vehicles, which might involve redesign as well. I did not state this but I thought it was fairly obvious.
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With a TSTO, the upper stage engine would be a conventional rocket engine.
Which was noted as a possible development option if you have an engine of appropriate size, or one that can be clustered to give the necessary thrust or you are in the position to size SABRE to the upper stage engine ahead of time. So now you're down to SABRE and 2 unique vehicles.
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That will not be the same development costs as the first stage hybrid air-breathing engine. For the first experimental version of the system, you can even use a conventional upper-stage off an existing system. That reduces your development cost to just the first stage. Since the re-entry for the upper-stage is vastly more demanding than the first stage, deferring development of a reusable second stage saves a lot, and allows you to fly hardware sooner.
So basically an XS1 done by the USAFRL.
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I'm not arguing that the USAF idea for TSTO is necessarily superior to Skylon, but two-is-more-expensive-than-one is not a valid argument against it.
Ah, I see our grounds for disagreement.

I was looking at how to fly SABRE and deliver a fully reusable launch system. You merely want to stick a payload in orbit.

You seem to be under the impression there is a shortage of space launch systems.

There is not. 

What there is a shortage of are fully reusable launch systems (1 or 2 stage) so the only part that gets "expended" is the payload (and you have down mass), with a turnaround time from previous launch measured in (at most) weeks and with a time from request (assuming you have a payload to hand) to launch of days or hours that you can treat as an asset not a ticket to ride and that you can buy and sell as an asset.

That's something no one has. It's something quite a lot of payload people would like and it's something that SABRE can help supply.
"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 Alf Fass

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1586 on: 06/15/2016 08:04 AM »
TSTO is the best bet if you don't want to solve the problems you're likely to uncover from both a dramatically new engine concept and an extremely good mass fraction airframe/TPS simultaneously.

One miracle at a time.
If SABRE fully checks out on the ground you'll basically waste most of it's design features. If you just want precooled air inlets then it's not SABRE at all. It's jet engine with a heat exchanger up front.

This should still generate significant revenue for REL, but it's not getting them anywhere near orbit.  :(

Regarding truss structure. NASA Langley did a study in 1969 comparing Aluminum with AlBe and Be tubing. The straight Al alloy structure (the "heavy" design) weighed 3lbs but could carry a 250lb load, roughly 83 1/3:1 load to mass.

So I think a well designed truss structure can support very significant loads.

One thing that does worry me about the Skylon truss structure is something I saw in an interview with a crewman on the Wellington bomber, while he thought the framing was great, he recounted how flexible the Wellington's fuselage was, he said the plane virtually wriggled its way across the sky, with the fuselage continuously bending and twisting in flight.

I imagine that the designers of Skylon will have to engineer a far more ridged frame structure given the rigidity that I assume the aeroshell will have.
When my information changes, I alter my conclusions. What do you do, sir?
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Offline Paul451

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1587 on: 06/15/2016 08:25 AM »
Incorrect. This is the two-is-more-than-one myth again. A single design that can perform the two tasks is not necessarily going to be cheaper to develop than two designs that do one each.
Let me get this straight.
A TSTO using 2 unique stage designs and engines will be cheaper to design and build IE the overall budget will be lower, than a biamese with a single structural and engine design

Yes.

It will also be faster to develop.

No one goes to a biamese design for performance.

No one goes to a biamese in reality.

You seem to be under the impression there is a shortage of space launch systems.

I'm not. The USAF wants a launcher that can operate out of airports and quickly replace US satellites in the event of a major kick-off with an a-sat capable nation.

Delta/Atlas/F9 ain't such beasts, and are vulnerable to attacks on launch sites.

And they obviously don't trust that Skylon can be built for a reasonable price or on a reasonable schedule.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1588 on: 06/15/2016 11:41 AM »
One thing that does worry me about the Skylon truss structure is something I saw in an interview with a crewman on the Wellington bomber, while he thought the framing was great, he recounted how flexible the Wellington's fuselage was, he said the plane virtually wriggled its way across the sky, with the fuselage continuously bending and twisting in flight.

I imagine that the designers of Skylon will have to engineer a far more ridged frame structure given the rigidity that I assume the aeroshell will have.
AFAIK the wellington structure was a single shell. Skylons is a space frame, with 2 layers of members. I would expect it to be much more rigid to stop it contacting the tanks which occupy most of the space frame, rather than to cope with skin rigidity.
« Last Edit: 06/15/2016 11:43 AM 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 john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1589 on: 06/15/2016 06:23 PM »
Why would there be? We develop multistage rockets all the time. Something as sophisticated and high performance as Skylon and its airframe is FAR harder. It will be more expensive, by Reaction Engines' own estimates!
It seems I have not been clear enough on my assumptions.

My OP on this subject had the words

Quote from: john smith
Build the aircraft equivalent of a "biamese" rocket. 2 Identicalaircraft with the same engines and airframe.  SABRE sort of plays into this concept if your issue is you doubt REL's Skylon concept is infeasible. Note for maximum cost reduction the engines and airframes must be identical.
Emphasis added.

Being the USAF I expected they to be looking at a winged vehicle. SABRE is also a very poor fit to a VTO LV so no I would expect designing 2 large aircraft with very different designs to be very expensive.

It would seem people who only think in terms of cylindrical tanks, with nothing wrapped around them, have trouble adjusting to the concept.

Obviously I must take more care to spell exactly what I mean to ensure comprehension by all readers. 
"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 Star One

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The Reaction Engines Skylon Master Thread (5)
« Reply #1590 on: 06/16/2016 11:42 AM »
Alan Bond to be guest of honour at BIS summer get together on the 30 July.

http://www.bis-space.com/2016/01/18/16053/bis-space-conference-at-charterhouse
« Last Edit: 06/16/2016 11:43 AM by Star One »

Offline momerathe

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1591 on: 06/16/2016 02:16 PM »
Why would there be? We develop multistage rockets all the time. Something as sophisticated and high performance as Skylon and its airframe is FAR harder. It will be more expensive, by Reaction Engines' own estimates!

IIRC REL actually addressed this directly at some point. Paraphrasing from memory, with a reusable TSTO there are actually three vehicles that need to be flight tested: the first  stage, the second stage, and the first and second stage together. This makes for a hard combinatorial problem. The flight dynamics of the Skylon airframe, OTOH are relatively bog-standard.

In other words, going TSTO might de-risk the engine, but it would add risk to the airframe development. Obviously they have confidence in their engine technology.

Rockets have significantly simpler flight dynamics and, moreover, there's a wealth of institutional knowledge on building multistage rockets that doesn't exist for aircraft.
thermodynamics will get you in the end

Offline Robotbeat

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1592 on: 06/16/2016 03:37 PM »
Yeah, I've heard that argument before, but Skylon is anything but bog standard.

I think Reaction Engines shouldn't let perfect be the enemy of the good, here. Far better to actually fly than to just talk about it because the initial investment step is simply far too high.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline momerathe

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1593 on: 06/17/2016 08:29 AM »
Well, AFRL have kindly offered to do that for them. :)

Less flippantly, what they really have to do is demonstrate a fully working engine - which is what they're working on. At that point any number of options open up.

I've somewhat lost track of the discussion - is the NTV still a thing?
thermodynamics will get you in the end

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1594 on: 06/17/2016 09:12 AM »
Yeah, I've heard that argument before, but Skylon is anything but bog standard.
Only in areas where where it can't afford to be.  Most of it's construction techniques have been suggested or used in other contexts, such as MLI and truss structures. Even the water cooled brake idea is SOP (in truck racing). Key risks are more in the materials area and structural interaction over the whole M0-23-0 range.
Quote
I think Reaction Engines shouldn't let perfect be the enemy of the good, here. Far better to actually fly than to just talk about it because the initial investment step is simply far too high.
Undoubtedly.

The problem is moving to a 2 winged stage design, which is needed for full reusability. Skylons in rocket mode already has the best possible Isp and if you're worried about the structural design AFAIK all other are worse, requiring more of the mass to be set aside for the structure. I think it's fair to say most of the benefits of staging in other designs are simply delivered by the high Isp of SABRE.

So if you can't design a 2nd winged stage with lower structural mass fraction than Skylon (the "safe" option because we're talking risk reduction here. Although at M5+ A lifting body design would be possible if you can figure out how to land it ) the only other option is the expendable rocket, IOW the XS-1 approach .

Note this is the broad outline of the constraints and it's possible that at the margins an option for a fully reusable 2 stage vehicle exists. Perhaps Skylons structural design is actually conservative compared to some other approaches, allowing a heavier structure for the 2nd stage, rather than the straight propellant-tanks-with-engines-at-bottom which seems the only lighter weight option.

Perceptions that a 2 stage winged system is somehow "safer" to design are just that, perceptions.
Once you see the constraint map I can't help thinking "Let's go for broke. See what the budget is, build the smallest SABRE you can and the smallest Skylon around it you can. It might put 10Kg in LEO but it's a) fully reusable and b)can be returned to Earth after it's been in orbit. "

This is still the USAF Research Laboratory. Research is about taking calculated risks. 
"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 Asteroza

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1595 on: 06/20/2016 01:29 AM »
Following that train of thought, what are reasonable lower bounds on size for SABRE cycle designs, if you want to follow the minimum demo path with a mini-Skylon? What is the bricklifter equivalent, able to place a 3U cubsat in orbit? REL is loath to make anything less than full size, mostly due to LH2 turbine design issues, but AFRL is under no such constraint (though considering the recent demise of the air launch project again...)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1596 on: 06/20/2016 09:45 AM »
Following that train of thought, what are reasonable lower bounds on size for SABRE cycle designs, if you want to follow the minimum demo path with a mini-Skylon? What is the bricklifter equivalent, able to place a 3U cubsat in orbit? REL is loath to make anything less than full size, mostly due to LH2 turbine design issues, but AFRL is under no such constraint (though considering the recent demise of the air launch project again...)
That is a very tough question to answer.

SABRESkylon is a system. If you shrink SABRE you have to think about the issues of shrinking Skylon.

REL do have a horror of scale models because they have scale effects, things that are highly non linear with size. The other issue is scaling up from test samples. Using small modules of large systems makes this much easier as much less analysis is going to be needed to do the scaling.

For SABRE I'd start by asking what is the smallest part of the engine already? The rest of the design I could scaled down by reducing the number of modules (and accepting the thrust loss as a consequence) but this part is either the smallest you can get or needs a major redesign to go smaller, possibly triggering module redesigns as well, giving a small engine with no pedigree you can use in the final version. It's no longer a SABRE-lite, with few key modules of every subsystem. It's a complete reimplementation of a SABRE at a smaller scale.  :(

But that scaling is likely the easy part.

Aerodynamic phenomena scale very badly. A 10-20cm nose radius may have relatively  low heating but drop that to a 2cm radius and the stagnation heating will skyrocket. What was viable in Pyrosic or RCC may not even be viable in the UHTC materials like Hafnium Diboride (assuming you could get big enough pieces that aren't too brittle and can be machined to adequate tolerances). Likewise transpiration cooling might need to cover a substantial part of the (model) wing due to boundary layer effects, which again scale badly.

Likewise they truss members are (IIRC) about 30cm long. You can make them shorter but you'd need to make them smaller in diameter so the end connectors remained a fraction of the link mass, but that fraction would be rising.

Essentially you would retain the aspect ratio of the payload bay but accept whatever the design can lift as the payload. I've no real sense how far you could go down with this plan.  Ithink the SABRE 4 cycle, needing lower thrust chamber pressures, helps a bit

Essentially it would be a very tricky re-balancing act, akin to the original SABRESkylon design process.

I'd love to see a fully orbit capable Skylon the size of a large executive jet. Once you demonstrate self ferry, launch on demand and rapid turnaround everything changes.

But I expect the physics places strong limits on how small you can make the airframe, and hence how small an engine is needed to fly the mission.

And I think those limits are pretty high.  :(
"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 Nilof

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1597 on: 06/20/2016 10:26 AM »
Yeah, I've heard that argument before, but Skylon is anything but bog standard.
Only in areas where where it can't afford to be.  Most of it's construction techniques have been suggested or used in other contexts, such as MLI and truss structures. Even the water cooled brake idea is SOP (in truck racing). Key risks are more in the materials area and structural interaction over the whole M0-23-0 range.
Quote
I think Reaction Engines shouldn't let perfect be the enemy of the good, here. Far better to actually fly than to just talk about it because the initial investment step is simply far too high.
Undoubtedly.

The problem is moving to a 2 winged stage design, which is needed for full reusability. Skylons in rocket mode already has the best possible Isp and if you're worried about the structural design AFAIK all other are worse, requiring more of the mass to be set aside for the structure. I think it's fair to say most of the benefits of staging in other designs are simply delivered by the high Isp of SABRE.

So if you can't design a 2nd winged stage with lower structural mass fraction than Skylon (the "safe" option because we're talking risk reduction here. Although at M5+ A lifting body design would be possible if you can figure out how to land it ) the only other option is the expendable rocket, IOW the XS-1 approach .

Note this is the broad outline of the constraints and it's possible that at the margins an option for a fully reusable 2 stage vehicle exists. Perhaps Skylons structural design is actually conservative compared to some other approaches, allowing a heavier structure for the 2nd stage, rather than the straight propellant-tanks-with-engines-at-bottom which seems the only lighter weight option.

Perceptions that a 2 stage winged system is somehow "safer" to design are just that, perceptions.
Once you see the constraint map I can't help thinking "Let's go for broke. See what the budget is, build the smallest SABRE you can and the smallest Skylon around it you can. It might put 10Kg in LEO but it's a) fully reusable and b)can be returned to Earth after it's been in orbit. "

This is still the USAF Research Laboratory. Research is about taking calculated risks.

You do NOT need wings or lifting bodies at all for reuse. Winged reentries are the root of all evil. Reducing peak g-loads and peak heating seems like a good trade at first, but it moves the heating problem to a near-equilibrium heating situation which forces you into a lot of bad trades that tend to increase shielding mass. Wings add mass, are useless for most of the flight, and add reentry problems that are arguably harder than the ones they solve.

I mean, which one would you rather do? Quickly pour a shot glass of liquid nitrogen on your hand, or keep it in -20C freezing salt water for a few hours? What kind of gloves would you need to protect your hand against one or the other?

Blunt-body reentry with high gees and ablative shielding add less mass than wings would. Lift is naturally much easier to get at high gees so maintaining the maximum load at the design level is easier. Any structural reinforcements required also give you more safety margin on the way up.

I would argue that three different wingless vehicles are much easier to design than a single winged vehicle that has to work from mach 0 to mach 25.
« Last Edit: 06/20/2016 10:31 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline momerathe

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1598 on: 06/20/2016 10:48 AM »
You do NOT need wings or lifting bodies at all for reuse.

No, but it cuts the required takeoff thrust by your L/D ratio. IIRC the SABRE thrust in airbreathing mode isn't enough for vertical takeoff, without scaling the engine up considerably.

Quote
I would argue that three different wingless vehicles are much easier to design than a single winged vehicle that has to work from mach 0 to mach 25.

Well yes, that's obvious. Is that actually what AFRL are proposing though?
thermodynamics will get you in the end

Offline Nilof

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Re: The Reaction Engines Skylon Master Thread (5)
« Reply #1599 on: 06/20/2016 11:00 AM »
You do NOT need wings or lifting bodies at all for reuse.

No, but it cuts the required takeoff thrust by your L/D ratio. IIRC the SABRE thrust in airbreathing mode isn't enough for vertical takeoff, without scaling the engine up considerably.

But for TSTOs it gives you nothing. Liftoff T/W barely cuts into the dry mass that has to be brought with you into orbit at all.

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I would argue that three different wingless vehicles are much easier to design than a single winged vehicle that has to work from mach 0 to mach 25.

Well yes, that's obvious. Is that actually what AFRL are proposing though?

It is what the USAF will likely be contracting for standard workhorse launches in a few years, without any government R&D money required.
« Last Edit: 06/20/2016 11:04 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

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