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#1 2012-04-28 13:16:06

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Reaction Engines

Have these guys been discussed before?

http://www.bbc.co.uk/news/science-environment-17874276

They seem pretty confident about their abilities, and I guess if they have the engine, the rest might follow.

It would be a first for the UK to have any really strong contribution to the space effort, so that would be nice.

edit copied posts on topic:
http://newmars.com/forums/viewtopic.php … 17#p100817

Nik wrote:

FWIW, check out Alan Bond's SABRE engine...

http://www.aau.ac.uk/rel.htm
http://en.wikipedia.org/wiki/SABRE

http://www.reactionengines.co.uk/index.html
Look under current projects...


http://newmars.com/forums/viewtopic.php … 10#p105510

GCNRevenger wrote:

Another trick is combining jet and rocket engines into a single unit, like Reaction Engines' concept http://www.reactionengines.co.uk/sabre.html . While I doubt their SSTO plane would be practical, it might make a great first stage engine.


http://newmars.com/forums/viewtopic.php?id=8190
Reaction Engines secure funding.


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#2 2012-04-28 16:15:41

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Louis:

They're a long way from flying yet,  but I really do hope it works.  I know how to do the same job with a parallel-burn combination of rockets and ramjets in a two-stage airplane,  but this would be loads better.  Single stage at realistic mass fractions (and that is one big hell of an if!!!!!) would always be better. 

Skylon's biggest problem has always been lack of funding.  Fix that,  and one only must contend with technical results.  Technical results is always a faster path than funding,  for everything I can remember.  And,  I'm an old guy.

GW

edit adding in content:
http://newmars.com/forums/viewtopic.php … 02#p117002

GW Johnson wrote:

Beyond that,  we're looking for Star Trek-style impulse engines and warp drive.  The physics ain't there yet for them,  much less the technology. 

Scramjet (supersonic-combustion ramjet) on the other hand features (at worst) a constant area chamber,  and usually gently-expanding at around 5 degrees half angle.  There is no throat contraction at all,  but locating the final expansion bell axially can make-or-break obtaining a burn at all.  This technology is still very far from being ready-for-prime-time,  the recent X-51 flights notwithstanding.  There’s no good way to reconcile these conflicting geometries except by one-shot/throwaway ejected components,  and even that is very most certainly not a trivial exercise,  or a “sure thing”. 

And,  we have not addressed inlet geometry incompatibilities between ramjet and scramjet at all.  They are huge,  more especially in the internal ducting lines,  surprisingly enough.  The external compression features are actually quite similar,  which is terribly misleading.  Failure to get this right causes as many violent explosions in scramjet test articles as does too-low a scramjet takeover Mach.  It is quite catastrophic,  and (so far) quite incompatible. 

Integrating ramjet-or-scramjet with rocket is even worse.  Most rockets have a very large area ratio contraction from chamber to throat:  on the order of 10+.  And the exit bell area expansion ratios exceed 10,  often by a very,  very large margin.  I know of no variable-geometry techniques to accomplish this kind of geometry change,  except one-shot/throwaway ejectable insert items. 

You can go from rocket to ramjet that way,  but you absolutely cannot go back to rocket.  How are you going to change back to rocket in a combined-cycle engine,  if your trade studies say that you want to do that?  I don’t think anybody on Earth has a practical answer to that,  excepting maybe the Skylon folks with their SABRE engine,  and I am very definitely not even sure of that!  (I hope they do,  but I am most definitely not going to bet the farm on it.)

And that’s why I think parallel-burn options for the differing engine types are way-to-hell-and-gone far superior to any combined-cycle proposals I have ever heard of.  I have seen many of those for the last 4.5 decades.    None has ever led anywhere,  before.  Not a good track record. 

But parallel-burn works,  both ways.  Try that.  We can do it right now.  All-existing technologies.  Not trivial,  but very definitely do-able. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#3 2012-04-28 17:09:04

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

GW Johnson wrote:

Louis:

They're a long way from flying yet,  but I really do hope it works.  I know how to do the same job with a parallel-burn combination of rockets and ramjets in a two-stage airplane,  but this would be loads better.  Single stage at realistic mass fractions (and that is one big hell of an if!!!!!) would always be better. 

Skylon's biggest problem has always been lack of funding.  Fix that,  and one only must contend with technical results.  Technical results is always a faster path than funding,  for everything I can remember.  And,  I'm an old guy.

GW

Well it would be nice if the UK could finally make a contribution to us getting off the planet. The UK had quite a nice space effort going in the 50s and early 60s but what with our military commitments and slow growth it was abandoned.

Do you think it's down to a question of using advanced lighter materials as components? They must be carrying a lot of mass with that cooling equipment forming part of the craft.

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http://newmars.com/forums/viewtopic.php … 20#p110420

Terraformer wrote:

Hmmm... so a ramjet-turbojet integrated engine is feasible? I presume it could be used to fly the carrier plane back after it's launched it's payload? Of course, if you can build it into an SSTO spaceplane...

It certainly begs the question of why Reaction Engines are working on the SABRE engine - surely the mass benefit of cutting out a few tonnes of engine mass don't warrant the extra complexity?

I imagine such an Spaceplane would fly up on jet power to about 20km, before shutting down the jet and lighting the rockets. Total required delta-V could come to say 9km/s, with the first 2km/s being jet power. Perhaps a mass ratio of 10 could be achieved. If the craft is 20 tonnes and delivers a 10 tonne payload, a payload fraction of around 3 percent could be achieved, though you're talking about a GLOW of 300 tonnes... assuming a runway could be found for it, and the average cost of the fuel comes to 250 dollars a tonne, we're talking about 7.5 dollars per kilogram in orbit in fuel costs. If the price is double this, it's still ridiculously cheap.


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#4 2012-04-28 17:17:52

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Louis:

No,  the real problem is one of making heat transfer occur as fast as the other propulsion processes,  when it truly and fundamentally does not want to be that fast.  Skylon's engine is basically a liquid air cycle engine.  No one else has ever made liquid air that fast,  ever.  But,  Reaction Engines just might.  I'm rootin' for 'em. 

GW

edit to add content
http://newmars.com/forums/viewtopic.php … 18#p111418

RGClark wrote:
RGClark wrote:
GW Johnson wrote:

For Bob Clark:  airbreather thrust,  particularly ramjet,  is very strongly (dominantly) dependent upon flight speed and altitude air density.  The nozzle thrust is calculated same way as a rocket (chamber total pressure,  gas properties,  pressure ratio across the nozzle,  and nozzle geometry),  the pressure is just lower and the expansion ratio a lot less.  You do need to worry about the difference between static and total chamber pressure,  unlike most rockets. 
The ram drag is the drag of decelerating the ingested stream of air into the vehicle.  Its massflow multiplied by its freestream velocity (in appropriate units of measure) is the way that is done.  But,  nozzle force minus ram drag is only "net jet" thrust.  There are several more propulsion-related drag items to account.
There is spillage drag for subcritical inlet operation (which also means reduced inlet massflow!),  additive or pre-entry drag for ingested stream tubes in contact with the vehicle forebody,  and the drag of boundary layer diverters or bleed slots,  quite common with supersonic inlets.  None of those are simple to calculate "from scratch" (we use wind tunnel test data to correlate empirically a coefficient for each as a function of Mach and vehicle attitude angles),  and taken together they are often quite a significant force. 
If you subtract that sum of drags from net jet thrust,  you have the "local" or "installed" thrust,  corresponding with just plain airframe drag.  Most airframers work in that definition.  If you don't,  then you have to add that sum of propulsive drags to the airframe drag to get the corresponding proper drag for "net jet" thrust-drag accounting (not very popular outside the propulsion community).

Thanks for the detailed response. That's actually a little too much detail for what I need. I read your post on ramjet boosters:

Sunday, August 22, 2010
Two Ramjet Aircraft Booster Studies
http://exrocketman.blogspot.com/2010/08 … e-boe.html

I noted that you were able to get better payload with more shallow launch angle but it created a problem for retrieving the first stage booster, since it went so far downrange. If I'm reading it correctly you were able to double the payload mass with the shallow angle, presumably using aerodynamic lift.
What I'm trying to determine if I can increase my payload just going to the range turbojets can get to, ca. Mach 3+. I intend to use the jets to get to medium altitude for a turbojet, ca. 15,000 m. But I need to get to a good angle as well as reaching its max speed. Another problem is that I don't know if it can get to max speed while climbing.
I looked at the case of the SR-71 and the XB-70 Valkyrie. These had more thrust than I wanted but that added weight because jet engines are so heavy. In any case I noted the climbing rate. From that it seemed doable, considering the high effective Isp, that you could reduce propellant mass that way. The problem is this is for a SSTO application and I can't afford the weight. What I wanted was the engines to put out in the range of 1/7th the vehicle weight to reduce the jet engine mass. What I don't know is how will that effect the climb rate, and will it even be able to reach supersonic now.
Note that an advantage of the SSTO is that you can get the better payload by flying a shallow angle and not have to worry about recovering the booster stage.


   Bob Clark


I discussed previously on NewMars the reasons why I think it should be possible to do a partially airbreathing SSTO with current jet engines in this post copied below from before the server crash.

====================================================

...Looking at the numbers though I'm convinced now you can even make a single stage to orbit vehicle with a combined ramjet/rocket engine, and without having to use scramjets.
The idea is to combine the turbo-ramjet/rocket into a single engine. This is what Skylon wants to do with their Sabre engine. But the Sabre will use hypersonic airbreathing propulsion up to Mach 6.5 before the rockets take over. This will require complicated air-cooling methods using heat exchangers with flowing liquid hydrogen for the Skylon.

However, just being able to get to say the Mach 3.2 reached by the SR-71 would take a significant amount off the delta-V required for orbit. Of course if the ramjet could get to Mach 5 that would be even better but key this would be doable with the existing engines of the SR-71. Note too the engines of the XB-70 Valkyrie bomber could operate at Mach 3 and as far as I know they didn't have ramjet operation mode. So it might not even be necessary for the engines to have a ramjet mode, turbojet might be sufficient.

The problem with using jets for the early part of the flight of an SSTO has been they are so heavy for the thrust they produce, generally in the T/W range of around 5 to 10. While rocket engines might have a T/W ratio in the range of 50 to 100. But a key point is the jet engine will be operating during the aerodynamic lift portion of the flight where the L/D ratio of perhaps 7. The XB-70 for instance had a L/D of about 7 during cruise at Mach 3. So if we take the T/W of the jet engine to be say 7 and the L/D to be 7, then the thrust to lift-off weight ratio might be about 50 to 1 comparable to that of rockets.

BTW, it is surprising there has been so little research on this type of combination with the jet and rocket combined into one. You hear alot about turbine-based-combined-cycle (TBCC) where it combines turbo- and scram-jets and rocket-based-combined-cycle (RBCC) , where the exhaust from a rocket is used to provide the compression for a ramjet. But not this type of combined turbojet/rocket engine. It doesn't seem to have an accepted name for example. It would not seem to be too complicated. You just use the same combustion chamber for rocket as for the jet. Probably also you would want to close off the inlets when you switch to rocket mode. 

For the calculation the delta-V and propellant load would be feasible, note that for a dense propellant SSTO might require as much as 300 m/s lower delta-V than a hydrogen fueled SSTO, in the range of about 8,900 m/s, so I'll use kerosene as the fuel. Hydrogen might have an advantage though in being light-weight if what you wanted was horizontal launch. Say you were able to get to Mach 3+ with the jets, 1,000 m/s. The delta-V to supplied by the rocket-mode is then 7,900 m/s. But note also you can get to high altitude say to 25,000 m. This might subtract another 300 m/s from the required rocket-mode delta-V, so now to 7,600 m/s.

A bigger advantage than this of the altitude is the fact that you get the full vacuum Isp during rocket-mode, call it an exhaust velocity of 3,600 m/s for kerosene rockets. Note this results in a mass-ratio for the rocket mode portion of e^(7,600/3,600) = 8.3, less than half that usually cited for a kerosene-fueled all rocket SSTO. Note the fuel required for the jet-powered portion would only be a fraction of the dry mass rather than multiples of it based on the fact the 1,000 m/s jet-powered speed is only a fraction of the 10,000 m/s or so effective exhaust speed of jet engines.

Note this brings the kerosene fuel load to be about that of hydrogen fueled SSTO's, except you still have the high density of kerosene. With modern lightweight materials this should be well doable.


  Bob Clark
=======================================================


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#5 2012-04-28 17:46:17

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

GW Johnson wrote:

Louis:

No,  the real problem is one of making heat transfer occur as fast as the other propulsion processes,  when it truly and fundamentally does not want to be that fast.  Skylon's engine is basically a liquid air cycle engine.  No one else has ever made liquid air that fast,  ever.  But,  Reaction Engines just might.  I'm rootin' for 'em. 

GW

Me too!

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http://newmars.com/forums/viewtopic.php … 23#p111423

GW Johnson wrote:

Skylon's SABRE is a liquid-air cycle engine.  They think they can solve the heat transfer problem to liquify the air as it comes in,  with the cold hydrogen.  Heat transfer is the slowest of the physical processes,  which is why liquid air cycle engines were never attempted before.  But,  I hope they can do it. 

Gas turbine engines can be built that have pretty good T/W.  Isp looks good on subsonic fanjets,  not so good on supersonic-capable low-bypass ratio turbojets,  and really bad when you light the afterburner.  The combustor can has to run very lean on fuel to hold turbine inlet temperatures under about 1800 F nor normal flights,  under 2000 F for temporary high-power operation.  Really exotic materials can add about 200 F more to those figures.  But you hit those conditions with turbine somewhere between about M 3.2 to 3.6,  almost no matter what design you use. 

Most of the combined cycle proposals I have seen compromise performance of each component just to build one device instead of two.  (Maybe SABRE can get around that,  we'll see.)  Most of these combined-cycle things end up pretty complex and heavy,  as a geometry change is almost invariably involved.  The best of these is the ejector ramjet my old friend Joe Bendot did at Marquardt.  It adds a big rocket inside the duct of the ramjet. 

On takeoff,  the rocket thrust induces some airflow through the ramjet to generate static thrust.  Isp is closer to rocket than ramjet.  Once you've reached the speed at which the inlet functions properly (usually M1.5+),  you can fly on ramjet alone at high speed.  This will work as an accelerator up to around 60,000 feet altitude,  where frontal thrust density drops too low due to low air density. 

At that point you have to turn the rocket back on,  and use both together at blended Isp,  which floats down toward rocket levels as you climb higher into unusably-thin air.  Run the rocket alone,  on into space,  at rocket Isp.  SSTO.

But rocket Isp won't be as high as you are used to,  because being inside the duct interferes with free plume expansion,  especially in near-vacuum.  Typically,  lowered Isp raises GLOW of an SSTO no matter what kind of propulsion or airframe design you choose. 

I actually like the parallel-burn approach better,  because neither device is compromised,  and you can run any blend of the two without variable geometry.  It actually works out no heavier,  and averages higher performance than the combined cycle designs.  Rocket-ramjet (maybe to M6,  and rocket-turbojet (M3.4+/- on turbo) would be two good candidates.

The air turboramjet could beat the M3.4+/- limit in turbine,  if 100% air bypass from ahead of the compressor face was used.  No one has ever built one,  but I think it could be done without too much fuss and bother.  If you can shut down the turbine and cut off all its airflow,  bypassing straight to the afterburner,  you can run the afterburner as a true ramjet.  Capability could be as high as M6.  M5 anyway.  Hard,  but do-able.

As for the book,  I have several topics roughed out now,  but only about 30% or so of them.  None are in final form.  The science is not too hard to write down,  it's the art that's hard.  I did some of that the other day,  on really how to size ramjet system geometries for several different ramjet systems and weapon/launch applications.  Still sweating.  Or swearing.  (Both,  maybe.)  I never wrote that stuff down before,  I just did it,  and noticed I was one of very few around the country able to do it that fast and well.  Neither has anyone else ever written sizing procedures down,  as near as I can tell.

GW


http://newmars.com/forums/viewtopic.php … 20#p116820

GW Johnson wrote:

All the numbers I have run point to two stages with all known non-nuclear rocket and ramjet technologies and materials that we have.  The numbers just aren't there for SSTO,  not at practical structural fractions,  and payloads big enough to be worthwhile. 

Fundamentally,  there's no reason why both stages of a TSTO cannot be reusable,  and this is true whether you design for HTO or VTO.  A practical SSTO will require some sort of propulsion breakthrough (yes,  I know it can technically be done right now,  just with impractically-small payload fractions).  I have a lot of hopes pinned on Skylon with its Sabre engine for such a breakthrough,  but I'm not betting the farm on it. 

GW


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#6 2012-04-29 18:40:33

Rune
Member
From: Madrid, Spain
Registered: 2008-05-22
Posts: 191

Re: Reaction Engines

I've also been following Skylon for a number of years. They are certainly shooting high in their ambitions! Full-fledged SSTO, HTOL, no less. The whole shebang. It is a harsh road they are traveling, especially funding-wise, but it could very well end up working and getting european space efforts into the history books. The first real SSTO would indeed be a very big deal, and the precooler seems pretty much done (a full-sized prototype is undergoing testing right now, as is shown on the video). It's a definite maybe, and I hope they succeed, get their funding, start selling spaceplanes, and enter my personal hall of fame.


Rune. As a side project, they are also developing the world's first hypersonic antipodal airplane, the LAPCAT A2. O_O


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#7 2012-04-30 06:38:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

Rune wrote:

I've also been following Skylon for a number of years. They are certainly shooting high in their ambitions! Full-fledged SSTO, HTOL, no less. The whole shebang. It is a harsh road they are traveling, especially funding-wise, but it could very well end up working and getting european space efforts into the history books. The first real SSTO would indeed be a very big deal, and the precooler seems pretty much done (a full-sized prototype is undergoing testing right now, as is shown on the video). It's a definite maybe, and I hope they succeed, get their funding, start selling spaceplanes, and enter my personal hall of fame.


Rune. As a side project, they are also developing the world's first hypersonic antipodal airplane, the LAPCAT A2. O_O

Space X should buy them up now, open a European operation.

edit content adding
http://newmars.com/forums/viewtopic.php … 23#p126623

Antius wrote:

Based upon the information provided by GW, I have investigated the options for a two-stage launch vehicle.  The first stage is provided by a horizontal take-off ramjet aircraft, which burns jet fuel and is boosted to ~400mph by lox-jet fuel rockets within its wings, at which point ramjet thrust takes over.  I have not subjected this stage to detailed analysis, but have assumed that the vehicle will release the upper stage at a speed of Mach 6 (2km/s) at a height of 100,000’ (30km).

The second stage will be fuelled by LOX-jet fuel.  The additional delta-V required to reach orbit is 6.75km/s.  Assuming acceleration takes place at 5g, gravity losses work out to be 1.25km/s, which is only slightly lower than the upper stage upward release velocity of 1.4km/s, assuming second stage release takes place at 45 degree angle.  I have taken exhaust velocity to be vacuum exhaust velocity of 3500m/s.  With these values, the mass ratio of the upper stage is 6.88.  My assumption is that (initially at least) the upper stage will be expendable, which increases payload mass and reduces design complexity.  A reusable upper stage can be developed later on if cost-benefit analysis shows it to be worthwhile.  The traditional coupling mechanism between stages is explosive bolts.  However, this raises the potential for single point failure across a large number of bolts and is not very compatible with lower stage reusability and rapid turn-around.  Hydraulic clamps may be a better alternative if the mass penalty can be tolerated.

My initial preference for the expendable stage was maximum possible design simplification.  This led me to favour pressure fed fuel feed systems, thus avoiding the need for turbo-pumps.  The engine combustion chamber would work at a pressure of 20bar.  At such low pressure, it could be ablative lined carbon steel, with the exit nozzle being carbon steel and preferably radiatively cooled.  The low chamber pressure does not impact performance as the engine will be firing in a near vacuum.  Tank pressures would be 30bar.

My calculations indicate that even using spherical pressurised tanks it was very difficult to reach the required mass ratio with safety factors of 3.  To overcome this difficulty would require either the use of maraging steels, which cost ~$100/kg or the use of more than one stage.  Alternatively, a lower safety factor could be used, but this would push up quality control costs.  All of these appear to be counterproductive for an expendable stage, which needs to be cheap and easy to mass produce, rather like a bullet.  However, the low chamber pressure would appear to allow the use of gas jet feed pumps, which have no moving parts and should be very cheap to produce.  The gas can be provided by an electrically heated boiler.  Lithium ion batteries appear to provide sufficient energy density to power the heaters without severely impacting the mass ratio.  The use of jet pumps is possible only for engines with relatively low chamber pressures.  Assuming tanks are pressurised to 3bar feed pressure and are constructed from alloy steel with yield stress of 600MPa, then the tank mass ratio reduces to ~2% (i.e. the empty mass of the tank is 2% full mass, ignoring valves).

Attitude control during the 135 second acceleration can be accomplished using some combination of nozzle gimbaling or cold gas (nitrogen) jets, as the required impulse is modest.  The elimination of gambling would allow further simplification of the engine (i.e. fixed nozzle).

Overall a simple, mass produced upper stage would appear to be workable.  Assuming a mass ratio of 2 for the 1st stage and a 10% empty mass for the 2nd stage, the overall mass ratio would be 44.  If total take-off mass is 1000 tonnes, payload to orbit would be 22.7 tonnes.  To deliver payload at a cost of $100/kg, the total launch cost must be no greater than $2.3million.  This is a tall order, and requires that the upper stage be manufactured for not much more than $1million each.  It also requires that the vehicle is able to use conventional facilities (airports) with minimal additional ground infrastructure (hence the choice of propellants).

Just realised I forgot to account for the Earth's spin.  That knocks 500m/s of the orbital speed velocity change and reduces overal mass ratio to 32.  Quite a significant improvement.


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#8 2012-04-30 07:02:30

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 3,291
Website

Re: Reaction Engines

No, SpaceX is trying to run with established technology and make it cheaper; Skylon are going for cutting edge R&D. A merger would do neither good...

edit more content:
http://newmars.com/forums/viewtopic.php … 51#p128051

SpaceNut wrote:

From an old friend:

Shaun wrote:

Skylon is gradually moving forward. smile
The European Space Agency (ESA) has granted approval for the Skylon jet plane that will be able to take us anywhere in the world in four hours to be equipped with the revolutionary Sabre (Synergistic Air-Breathing Rocket Engine) technology.

http://www.reactionengines.co.uk/images … en_610.jpg

I still LOVE the look of this beast!
What's not to like about a single-stage-to-orbit (SSTO) vehicle which might take off from a level runway, move 15 tonnes to LEO, and then land on a level runway again?


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#9 2012-04-30 11:21:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

Terraformer wrote:

No, SpaceX is trying to run with established technology and make it cheaper; Skylon are going for cutting edge R&D. A merger would do neither good...

Depends how you look at it. I think there would be synergy for both. I think it would complement SpaceX's range, meaning that in due course it could come to dominate space and lunar tourism. Essentially Skylon would be offering a passenger service - and passengers aren't that heavy a payload.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#10 2012-04-30 15:18:13

Terraformer
Member
From: Lancashire
Registered: 2007-08-27
Posts: 3,291
Website

Re: Reaction Engines

SpaceX has Dragon... I think Skylon should acquire SpaceX, so that SpaceX is a British company... tongue

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GW Johnson wrote:

My information may be obsolete,  but the last time I heard, they were running some kind of tests on the SABRE engine,  and had done some sort of test (probably a bench test of some kind) that convinced them their high speed heat exchange scheme would work.  They seem to have accounted for how to prevent ice clogs from the humidity n the air,  too.   

The airframe shape proposed for Skylon appears to have mid-mounted wings with tip-mounted engines.  They seem aware of the air capture and compressor blading temperature problem,  because the mission profile calls for airbreathing to Mach 5 at some high altitude although still down in the air,  then all-rocket from there to orbit.  At Mach 5 and 85,000 feet on a standard day,  the total temperature (near static once decelerated in the inlet) is 2252 R = 1251 K,  and that's without any air compression enthalpy rise,  which is a huge effect.  Even turbine blade designs are only good for about 2660 R = 1480 K.  You see the problem for real compressor blade materials.  You have to build them at least as tough as turbine blades. 

What concerns me is reentry,  which starts at Mach 25-ish,  and ends the hypersonics on a slender shape at about Mach 5.  The shocks shed by the tip-mounted engines are going to impinge-upon (and cut completely through) the wings.  That's the same shock impingement problem I tried to describe in post 16 just above.  I have very serious doubts about the Skylon airframe shape proposal,  as a result. 

You simply cannot have parallel nacelles and expect to survive,  no matter if you used solid silica phenolic heat shield materials (very heavy indeed) on the impingement zone.  The X-15 airframe shape could have survived Mach 6+ without that scramjet test article mounted in parallel,  but not with it (and almost didn't).  Shapes like the SR-71 cannot survive at Mach 6. 

There's a very good reason all entry shapes used so far do not feature any parallel-mounted nacelles or any other parallel-mounted structures.  Your driving temperature in degrees K for heat transfer is roughly numerically equal to your speed in meters/second all during entry hypersonics,  but your film coefficients are an order of magnitude or two higher than you would ever expect (higher than most stagnation correlations), even at only Mach 6 or so,  in a shock-impingement zone.  The material heats to melting and erodes away in a matter of seconds. 

Hypersonic aerothermo is a bitch,  ain't it?

GW


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#11 2012-04-30 16:03:02

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

Terraformer wrote:

SpaceX has Dragon... I think Skylon should acquire SpaceX, so that SpaceX is a British company... tongue

There's no comparison between sitting upside down on top of a rocket (aka a bomb) and the future offered by Skylon: a much more plane like experience to get you into space.

Something like Skylon is needed for longer term development of space tourism I think.

Edt more content

http://newmars.com/forums/viewtopic.php … 13#p138513

Yuri Pilipishin wrote:
GW Johnson wrote:

To this I would add the comment that no combined-cycle engine concept is an off the shelf item ready-to-apply, any more than scramjet is. Both have been “15 or 20 years away” since the 1960’s,  same as controlled fusion.  You cannot go to a manufacturer anywhere and buy one.  They don’t work yet,  except as very limited,  extremely-experimental devices.

If under "combined-cycle" you mean something like SABRE engines of Skylon, then it's agreed. These combined devices seems impossible in real world; too much adverticement with no results.

GW Johnson wrote:

That being the case, I see no practical applications for spaceplane concepts except as multi-stage devices to low Earth orbit, and then only for delivery of people at low payload fraction, not bulk cargo.

Surely, spaceplanes are not intended to bring lots of tons of cargo on orbit; instead, they could fly to orbit very frequently, with minimal price per kilogram.

But also, you forget my invention of multiple and multistage refueling; this made it possible for reusable spaceplanes to reach Moon, Mars, asteriods, and so on.

To bring a lot of cargo on orbit, surely it's better to use reusable rockets (not as much re-launches as for spaceplanes, but much more cargo per one launch). If someone would be interested, I have a project (it's my intellectual property, either) of such a completely reusable rocket (taking as a prototype rocket Energiya):
http://lychakivsky.dreamwidth.org/7959.html

GW Johnson wrote:

And I don’t think anybody will ever do that job with a turbojet-powered first stage. The frontal thrust density is just too impossibly low for anything like that to ever be practical! You’re much better off with rockets that can produce gobs of thrust from a small package at takeoff, just when you need it most, because your takeoff weight is so heavy.

Let me remember you Ukrainian "Mriya" aircraft. It is not only the most powerful cargo aircraft in the world - it also is intended to be exactly the said turbojet first stage for space launch. Maybe, you heard about MAKS project (small shuttle with external fuel tank) or "Air launch" (two-staged rocket system; as far as I'm informed they even evolutionize it to complete reusability), both intended to start from the top of "Mriya".

GW Johnson wrote:

The statement that "supersonic ramjets" are 1 < M < 6 is NOT actually correct in real practice.  There are low speed designs that cover 0.7 < M < 2-ish,  and high-speed designs that cover 1.8/2.5 < M < 4-to-6 (limited at both ends more by airframe drag relative to available thrust).  They differ by some very specific geometric features that you just cannot convert back-and-forth.

In my project, ramjets should start at M2.5 h=25km, and climb upward to M5(6) h=50 km. So they could be specialized for that altitudes and velocities (by "some very specific geometric features", as you have said).

GW Johnson wrote:

I don't think you'll like the engine inert weights or the required frontal cross-sections for a turbojet first stage, either. The numbers entirely rule out vertical takeoff,  and it looks rather ridiculous for horizontal takeoff,  if your payload is bigger than a small dog.

Why? If we take, just for estimate, turbojet engines of Soviet Tu - 144: it's four engines enable take-off weight of more than 200 000 kg (with the aerodynamic characteristics, very similar to my spaceplane); so, if we'd implement my concept of spaceplane with those engines, we would end up with final cargo on LEO estimately 2 000 - 3 000 kg (which is already not bad). And those engines were implemented in 1960s; now, after half a century pass, I think it would be possible to implement more powerful engines, so take-off weight could be nearly 500 000 kg, and final cargo on LEO - estimately 5 000 kg. That would made achiveable all the claimed functionality: including manned trip to Moon, Mars, and asteroids.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#12 2012-05-01 06:21:19

Rune
Member
From: Madrid, Spain
Registered: 2008-05-22
Posts: 191

Re: Reaction Engines

Well, I'd rather see both companies compete to bring the cost down and not get stuck with a single provider of reusable launch services. You know, bring the cost down as much as it is possible. Plus, different business models. Reaction engines wants to sell the vehicles, SpaceX wants to sell launch services. Other than that, both should be similarly comfortable for a passenger. Oh, and skylon is almost every bit a bomb as a rocket is, only it has less oxidizer at the point where the atmosphere can burn the H2 with no problems, and no escape system (it is a rocket most of the way to orbit, after all).


Rune. Let the best rocket win.


In the beginning the universe was created. This has made a lot of people very angry and been widely regarded as a "bad move"

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#13 2012-05-01 09:22:46

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Well,  passenger safety with a launch rocket such as Falcon-9 or Falcon-Heavy depends upon a good escape system.  I think Spacex's use of the capsule itself fully powered as the escape vehicle,  is a better idea than the old escape tower we used on Mercury and Apollo.  You have coverage from ignition all the way to orbit.  The tower didn't work after jettison. 

With an airliner-like vehicle (such as Skylon),  you have to make the craft "utterly reliable" so that no escape system is needed (sounds hauntingly familiar,  like "make the ship unsinkable",  right?  Well,  that's exactly what you have to do). 

That's what we tried to do with shuttle,  and failed.  A fragile heatshield,  exposed to debris impact in a side-mounted cluster,  is two strikes against you right there.  Add foam insulation that peels off,  and you kill a crew.  We did. 

That's why Skylon is proposed as an unmanned cargo vehicle.  Flying it like that for a while will uncover all the "gotchas",  which can be fixed in a follow-on design that could be manned.  That's actually the smart way to do it.  Because of its unique engines,  Skylon is really a feasibility demonstration vehicle.  Until we've flown it for a while. 

Any high-energy vehicle,  be it a vertical launch rocket or some kind of spaceplane,  will be risky.  That is just plain unavoidable.  But it can be managed and designed-for.

Feasibility of spaceflight itself is no longer in doubt.  For passenger service,  we need to get the safety-of-flight engineers in on the ground floor of all vehicle designs from now on.  After 50+ years,  we're finally doing that.  They did it at Spacex,  and I'm proud of them for it. 

Actually,  there was a way to have saved both shuttle crews,  and it was not what they implemented.  My idea was hindsight-only for Challenger,  but afterward it was never done,  which is why Columbia's crew died.  I couldn't get NASA to listen to me.  Outsider,  "not invented here",  and all that jazz.  But to this day I still show spaceflight crew escape concepts on my resume as something I consult in. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#14 2012-05-01 16:28:48

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

GW Johnson wrote:

Well,  passenger safety with a launch rocket such as Falcon-9 or Falcon-Heavy depends upon a good escape system.  I think Spacex's use of the capsule itself fully powered as the escape vehicle,  is a better idea than the old escape tower we used on Mercury and Apollo.  You have coverage from ignition all the way to orbit.  The tower didn't work after jettison. 

With an airliner-like vehicle (such as Skylon),  you have to make the craft "utterly reliable" so that no escape system is needed (sounds hauntingly familiar,  like "make the ship unsinkable",  right?  Well,  that's exactly what you have to do). 

That's what we tried to do with shuttle,  and failed.  A fragile heatshield,  exposed to debris impact in a side-mounted cluster,  is two strikes against you right there.  Add foam insulation that peels off,  and you kill a crew.  We did. 

That's why Skylon is proposed as an unmanned cargo vehicle.  Flying it like that for a while will uncover all the "gotchas",  which can be fixed in a follow-on design that could be manned.  That's actually the smart way to do it.  Because of its unique engines,  Skylon is really a feasibility demonstration vehicle.  Until we've flown it for a while. 

Any high-energy vehicle,  be it a vertical launch rocket or some kind of spaceplane,  will be risky.  That is just plain unavoidable.  But it can be managed and designed-for.

Feasibility of spaceflight itself is no longer in doubt.  For passenger service,  we need to get the safety-of-flight engineers in on the ground floor of all vehicle designs from now on.  After 50+ years,  we're finally doing that.  They did it at Spacex,  and I'm proud of them for it. 

Actually,  there was a way to have saved both shuttle crews,  and it was not what they implemented.  My idea was hindsight-only for Challenger,  but afterward it was never done,  which is why Columbia's crew died.  I couldn't get NASA to listen to me.  Outsider,  "not invented here",  and all that jazz.  But to this day I still show spaceflight crew escape concepts on my resume as something I consult in. 

GW


Oddly, perhaps, when you think about it, there is no escape system on an ordinary jet airliner.  So passengers wouldn't be at more risk really. In fact, I would expect the safety record to be better for the Skylon.  It would seem to avoid some of the dangers of rockets/the Space Shuttle...e.g. exploding rockets on the ground, bits falling off and hitting the fuel tanks etc.  If you avoid icy weather as well, is it going to be so dangerous?

What was your escape concept for the Space Shuttle?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#15 2012-05-01 17:27:09

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Louis:

Both shuttle accidents showed pressure cabin separation from the rest of the debris (I witnessed this with my own eyes during Columbia's destruction,  right from my front yard).  Structurally,  the weak point was the cabin to cargo bay joint,  where the structure went from a closed tube to an open tube (no strength in the bay doors). 

If you take the spin off the pressure cabin (pressurized or not,  the crew should be in suits,  who cares if it is punctured in some way),  you can use the compartment between cockpit (two levels) and cargo bay as a sacrificial "heat shield",  with nothing more than a stabilizing drogue from the nose. 

Once the noisy hypersonics quiet down,  you are are low-supersonic decelerating toward M1/20kft max q,  and only dozens of seconds from impact.  You quickly blow the hatch,  and jump out on personnel chutes with an oxygen bottle.  No wings,  so we don't need the silly pole and tractor rocket motors. 

We have known since WW2 that crews were unable to bail out from spinning airplanes due to centrifugal forces.  In fact,  that problem was the original rationale behind ejection seats. 

But for a shuttle pressure cabin,  a de-spin drogue is simply more practical. 

We have also known since WW2 that bailout from a non-spinning airplane is easy.  Just don't do it above about M1 or thereabouts,  because of the nonsurvivable wind blast (known since the early 50's).  Which transonic point is some 20kft on the typical ballistic re-entry trajectory,  even for debris. 

GW

Last edited by GW Johnson (2012-05-01 17:30:42)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#16 2012-05-02 03:35:48

Glandu
Member
From: France
Registered: 2011-11-23
Posts: 106

Re: Reaction Engines

Louis, for most airplane crashes, 'chutes would not have saved the day. The most frequent scenarii are

_failed take-off(Concorde, Gonesse, 2001, less than 10 km from my home) : you are not high enough for a 'chute to save you.
_failed landing : everything is OK, you're going to the track, and crash.
_unexpected crash where you thought you could go, and in fact that damn mountain was higher.
_misinterpretation of the instruments(Rio-Paris crash in 2009, where even the crew did understand far too late that the ariplane was losing altitude quickly. Last sentences were "
_I don't believe it, we're gonna hit!
_I don't understand, what's happening?")

The only case where it could be useful would be a complete engine shut-off, with no engine recovery possible, above the ground. That's not a common scenario. There are 'chutes on military aircraft because they all share another scenario : shot down by the enemy. Scenario where 'chutes can save your life 50% of the time. Scenario that airliners are not supposed to share.

Spacecrafts, at least in the beginning, will be far smaller & less reliable. 'chutes there will be far more useful in case of failure, & failures will happen far more often. When I took this A320 to come back from Krakow 10 days ago, we were more than 100 inside. Giving 'chutes to more than 100 people, then having them jump from a limited number of doors, without getting eaten by the reactors? Well, better try to survive the crash.


"I promise not to exclude from consideration any idea based on its source, but to consider ideas across schools and heritages in order to find the ones that best suit the current situation." (Alistair Cockburn, Oath of Non-Allegiance)

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#17 2012-05-02 07:51:38

Rune
Member
From: Madrid, Spain
Registered: 2008-05-22
Posts: 191

Re: Reaction Engines

GW Johnson wrote:

Louis:

Both shuttle accidents showed pressure cabin separation from the rest of the debris (I witnessed this with my own eyes during Columbia's destruction,  right from my front yard).  Structurally,  the weak point was the cabin to cargo bay joint,  where the structure went from a closed tube to an open tube (no strength in the bay doors). 

If you take the spin off the pressure cabin (pressurized or not,  the crew should be in suits,  who cares if it is punctured in some way),  you can use the compartment between cockpit (two levels) and cargo bay as a sacrificial "heat shield",  with nothing more than a stabilizing drogue from the nose. 

Once the noisy hypersonics quiet down,  you are are low-supersonic decelerating toward M1/20kft max q,  and only dozens of seconds from impact.  You quickly blow the hatch,  and jump out on personnel chutes with an oxygen bottle.  No wings,  so we don't need the silly pole and tractor rocket motors. 

We have known since WW2 that crews were unable to bail out from spinning airplanes due to centrifugal forces.  In fact,  that problem was the original rationale behind ejection seats. 

But for a shuttle pressure cabin,  a de-spin drogue is simply more practical. 

We have also known since WW2 that bailout from a non-spinning airplane is easy.  Just don't do it above about M1 or thereabouts,  because of the nonsurvivable wind blast (known since the early 50's).  Which transonic point is some 20kft on the typical ballistic re-entry trajectory,  even for debris. 

GW

Question: wouldn't the hypersonic airflow shake the very non-aerodynamic broken cabin into complete destruction? Never mind the superheated air finding the thermally soft spots, wherever they are, and burning through them like a blowtorch, getting the heat into the airframe, the astronauts would be long dead plastered on the wall by then in this scenario. Unless you redesign the whole primary structure with designed failure points that result in a self-stabilizing detached cabin, or something. Also, how do you test that this works, never mind modeling it for design? You sacrifice a couple orbiters?


Rune. Just nit-picking, but I imagine these are the kind of things that went through their minds. smile


In the beginning the universe was created. This has made a lot of people very angry and been widely regarded as a "bad move"

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#18 2012-05-02 09:37:29

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Rune:

I've seen a lot of re-entering satellites,  and I watched Columbia re-enter in pieces,  although I didn't know it was Columbia until about 10 minutes later.  Thinking back on what I saw,  and watching the video footage others took over-and-over,  I pretty well figured out what I saw. 

The ship lost its wing to the foam impact damage at about M12 over the Texas-New Mexico border.  (It was photographed over New Mexico at M15 intact but streaming debris from an obviously-failing wing.)  It tumbled and immediately lost its other wing,  vertical fin,  and bay doors to the hypersonic wind blast. 

2-3 seconds later the windshield caved in,  ripping the top off the flight deck,  and the 4 astronauts there were ripped out from under their seat belts in pieces.  3000-5000 psf q does that.  No time to burn,  just blunt wind blast pressure forces.  Those 4 torn-apart astronauts were the body parts that rained down just east of Dallas,  a little cooked,  but not burnt. 

We knew about the vulnerability of the windscreen to direct hypersonic stream impingement when I was a grad student in 1973.  Found it in wind tunnel tests,  and found the narrow range of AOA where the stream safely jumps over the cockpit,  as a separated flow.  Lose attitude control,  you're dead. 

When it was over Dallas at about M6 or 7,  that's when I saw it from outside Waco,  Texas,  to my north about 100 miles slant range.  The heavy engine thrust structure had already separated.  It and the fuselage (cabin still attached) led the debris stream.  The wings were fluttering along behind,  along with the chunks of bay doors and the fin,  and a whole cloud of smaller pieces,  maybe 2 dozen or so.  The fuselage and thrust structure were tumbling.  I could not see them tumble,  but they were leaving characteristically-braided contrails. 

I watched it go eastward until the contrails dimmed as the hypersonics faded into "mere" supersonics.  Between Dallas and Tyler,  I saw the fuselage break up as a fan of pieces,  leaving the cabin tumbling alone and still mostly intact,  except for the lost flight deck roof.  A contact at NASA confirmed to me that the three on the mid deck were still alive at that point,  although I hope the gee-force pounding had beaten them unconscious.  That's the last I saw of it,  visually.

Seconds later the cabin decelerated to about M1/20kft,  and was crushed by the rapidly-rising wind pressures again.  My contact at NASA said that's when the 3 mid deck astronauts died by blunt force trauma,  not upon impact with the ground seconds later.  If stabilized so as not to tumble,  it would not have crushed like that. 

Clearly,  lots of the structures survived the re-entry in recognizable condition.  This includes uniform patches and plastic parts from the interior.  No,  this stuff doesn't burn up on re-entry the way all the "experts" always said it did all these years.  There isn't time to burn,  it decelerates quite rapidly.  The pieces literally heat-sink their way through reentry on a transient. 

As for crew survival,  you separate the cabin from the cargo bay with a shaped charge,  and stream an inflated drogue from the nose to take the spin off the cabin.  If there’s enough warning time,  the flight deck crew can evacuate down to the middeck.  Otherwise,  windshield failure and flight deck roof loss is very likely before the drogue can stabilize it.  As it slows to “mere” supersonic speed,  you blow the hatch.  All survivors on the mid deck have but seconds to jump before impact,  but that’s better than no chance at all. 

It was the same with Skylab in 1979.  Fragile thin-shell aluminum remained intact as one single radar return down to 40 nautical mile altitude,  about halfway through reentry (around M12,  just like Columbia).  Minutes later,  although the solar wings and telescope mount were gone,  the main body was still in one piece when it completed reentry just off the western Australian coast. 

It finally broke up over land at about M1/20kft,  while ballistically falling into rapidly rising q at low altitudes as the path angle quickly steepened downward.  Of 85-90 tons at reentry,  they picked up 75 tons of debris in Australia.  Nope,  these things most definitely do not "burn up". 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#19 2012-05-02 14:19:43

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Louis:

I went and looked at Reaction Engines' web page,  and crawled around a bit just looking.  Things have changed since I first ran across them a few years ago. 

Most or all of the essential engine component technologies are now funded development programs of this or that agency.  If these component technologies can be made to work about as thought,  then the system can really be built.  Like most web sites,  it's quite optimistic,  but I saw enough "meat" to know for sure it's "real",  meaning this thing might eventually fly.  They do have a long way to go proving all the engine components.  And then there's some airframe components that will have to be proven,  most notably the heat shield. 

A look at their web site was reminiscent of looking at XCOR Aerospace's site,  except Reaction Engines is fairly big by comparison.  Yet,  I know that XCOR's Lynx suborbital tourist spaceplane is "for real",  too.  You should go visit their site. 

I've sat in their Lynx mockup,  and it's simple enough even I could fly that spaceplane.  My contacts there tell me Lynx number 1 is being built this year on their hangar floor. 

XCOR is about 30 guys and gals in one hangar at the Mojave,  CA municipal airport.  They've made their living so far selling rocket engines with the life,  restart,  and maintenance characteristics one expects from FAA-certified aircraft engines.  They're definitely "for real",  too.  Watch them,  I think they'll impress you next year. 

Most of the rest of the flightline at that airport is owned by Burt Rutan / Scaled Composites.  Last time I saw Burt in person was 1985.  Didn't get to go visit him,  when I visited XCOR recently (who's looking for ramjet help from me). 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#20 2012-05-02 16:18:30

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,854

Re: Reaction Engines

GW Johnson wrote:

Louis:

I went and looked at Reaction Engines' web page,  and crawled around a bit just looking.  Things have changed since I first ran across them a few years ago. 

Most or all of the essential engine component technologies are now funded development programs of this or that agency.  If these component technologies can be made to work about as thought,  then the system can really be built.  Like most web sites,  it's quite optimistic,  but I saw enough "meat" to know for sure it's "real",  meaning this thing might eventually fly.  They do have a long way to go proving all the engine components.  And then there's some airframe components that will have to be proven,  most notably the heat shield. 

A look at their web site was reminiscent of looking at XCOR Aerospace's site,  except Reaction Engines is fairly big by comparison.  Yet,  I know that XCOR's Lynx suborbital tourist spaceplane is "for real",  too.  You should go visit their site. 

I've sat in their Lynx mockup,  and it's simple enough even I could fly that spaceplane.  My contacts there tell me Lynx number 1 is being built this year on their hangar floor. 

XCOR is about 30 guys and gals in one hangar at the Mojave,  CA municipal airport.  They've made their living so far selling rocket engines with the life,  restart,  and maintenance characteristics one expects from FAA-certified aircraft engines.  They're definitely "for real",  too.  Watch them,  I think they'll impress you next year. 

Most of the rest of the flightline at that airport is owned by Burt Rutan / Scaled Composites.  Last time I saw Burt in person was 1985.  Didn't get to go visit him,  when I visited XCOR recently (who's looking for ramjet help from me). 

GW


Do you know the guys at Armadillo, GW?  I like the look of their DIY rocket for Mars. Looks like something the Mars settlers might be able to build themselves after a few years.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#21 2012-05-03 17:23:02

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Louis:

No,  I've never met the Armadillo guys.  I went to their website and crawled around a bit,  including looking at their Stiga-2 movie. 

That test reminded me very strongly of the US Army Bumper-WAC test ca. 1950.  Stiga-2 was a high-performance single stage sounding rocket.  Bumper-WAC was a 2-stage rig made of a captured V-2 and an Army WAC-Corporal missile.  Bumper-WAC actually reached about 200 miles (300 km) up.  Same sort of profile.  Neither had active roll control. 

The ballute test was really intriguing.  It was clearly deployed and inflated in vacuum just after apogee.  I could see the air drag stabilizing the cluster somewhat,  just before the strap failed.  I have to wonder if the point mass of the nose cone bouncing around,  midway out the strap,  isn't why it failed. 

Myself,  I would have used separate ballutes for the main rocket body and the nose cone.  Straps are more durable without extra point masses banging around.  At least,  that's been my experience. 

GW

edit adding content
http://newmars.com/forums/viewtopic.php … 36#p160336

GW Johnson wrote:

What I have seen regarding the SABRE engine is encouraging.  There is still a lot more testing to do before it could possibly fly.

I'm not too enthusiastic about the Skylon airframe designs I have seen.  With tip-mounted engines,  the shocks shed by the engine inlet spikes will impinge the wing leading edges.  Above about Mach 6,  there are no known materials but ablatives that might possibly survive this,  and any ablatives will have to be very thick and heavy,  and single-use,  if they can survive at all,  which I doubt.

Reentry starts at Mach 25.  I think the shocks will cut the wings off the bird during reentry. It may even have problems on ascent from about Mach 6 on up.  Depends upon how fast they are flying when they exceed about 200,000 feet altitude.

I say what I say about shock impingement heating,  because it amplified the already-horrific hypersonic heating by a factor of 7-ish,  on the X-15 flight that was severely damaged by this.  That was only Mach 6.7.

GW

elderflower wrote:

Sabre engine, {if it can be made to work!} will solve many of the SSTO problems.
https://www.reactionengines.co.uk/news/ … conditions


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#22 2012-05-14 06:07:56

Impaler
Member
From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Reaction Engines

Assuming the Engine proves viable the proposed Vehicle should be extremely affordable, probably an Order of Magnitude over the ideal expendable Rocket targets (SpaceX).  The only downside I see is the relatively small payload size of 12 tons, about half of what current Heavy lift rockets can manage.  Assuming the vehicle can't practically be enlarged then I would see Skylon falling into more of a Tanker role delivering LOX & LH2 to stations and dry boosters in LEO, I bet it would be desirable from payload size and construction standpoint to make versions of the vehicle that replace the cargo bay and straddling LOX tanks with one continuous LOX tank, just size all the tanks such that the vehicle has the right ratio of remaining fuel to dispense to the delivery point.  I bet you could squeeze another ton or two of payload with that.

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#23 2012-05-14 10:44:11

Rune
Member
From: Madrid, Spain
Registered: 2008-05-22
Posts: 191

Re: Reaction Engines

GW Johnson wrote:

Rune:

I've seen a lot of re-entering satellites,  and I watched Columbia re-enter in pieces,  although I didn't know it was Columbia until about 10 minutes later.  Thinking back on what I saw,  and watching the video footage others took over-and-over,  I pretty well figured out what I saw. 

The ship lost its wing to the foam impact damage at about M12 over the Texas-New Mexico border.  (It was photographed over New Mexico at M15 intact but streaming debris from an obviously-failing wing.)  It tumbled and immediately lost its other wing,  vertical fin,  and bay doors to the hypersonic wind blast. 

2-3 seconds later the windshield caved in,  ripping the top off the flight deck,  and the 4 astronauts there were ripped out from under their seat belts in pieces.  3000-5000 psf q does that.  No time to burn,  just blunt wind blast pressure forces.  Those 4 torn-apart astronauts were the body parts that rained down just east of Dallas,  a little cooked,  but not burnt. 

We knew about the vulnerability of the windscreen to direct hypersonic stream impingement when I was a grad student in 1973.  Found it in wind tunnel tests,  and found the narrow range of AOA where the stream safely jumps over the cockpit,  as a separated flow.  Lose attitude control,  you're dead. 

When it was over Dallas at about M6 or 7,  that's when I saw it from outside Waco,  Texas,  to my north about 100 miles slant range.  The heavy engine thrust structure had already separated.  It and the fuselage (cabin still attached) led the debris stream.  The wings were fluttering along behind,  along with the chunks of bay doors and the fin,  and a whole cloud of smaller pieces,  maybe 2 dozen or so.  The fuselage and thrust structure were tumbling.  I could not see them tumble,  but they were leaving characteristically-braided contrails. 

I watched it go eastward until the contrails dimmed as the hypersonics faded into "mere" supersonics.  Between Dallas and Tyler,  I saw the fuselage break up as a fan of pieces,  leaving the cabin tumbling alone and still mostly intact,  except for the lost flight deck roof.  A contact at NASA confirmed to me that the three on the mid deck were still alive at that point,  although I hope the gee-force pounding had beaten them unconscious.  That's the last I saw of it,  visually.

Seconds later the cabin decelerated to about M1/20kft,  and was crushed by the rapidly-rising wind pressures again.  My contact at NASA said that's when the 3 mid deck astronauts died by blunt force trauma,  not upon impact with the ground seconds later.  If stabilized so as not to tumble,  it would not have crushed like that. 

Clearly,  lots of the structures survived the re-entry in recognizable condition.  This includes uniform patches and plastic parts from the interior.  No,  this stuff doesn't burn up on re-entry the way all the "experts" always said it did all these years.  There isn't time to burn,  it decelerates quite rapidly.  The pieces literally heat-sink their way through reentry on a transient. 

As for crew survival,  you separate the cabin from the cargo bay with a shaped charge,  and stream an inflated drogue from the nose to take the spin off the cabin.  If there’s enough warning time,  the flight deck crew can evacuate down to the middeck.  Otherwise,  windshield failure and flight deck roof loss is very likely before the drogue can stabilize it.  As it slows to “mere” supersonic speed,  you blow the hatch.  All survivors on the mid deck have but seconds to jump before impact,  but that’s better than no chance at all. 

It was the same with Skylab in 1979.  Fragile thin-shell aluminum remained intact as one single radar return down to 40 nautical mile altitude,  about halfway through reentry (around M12,  just like Columbia).  Minutes later,  although the solar wings and telescope mount were gone,  the main body was still in one piece when it completed reentry just off the western Australian coast. 

It finally broke up over land at about M1/20kft,  while ballistically falling into rapidly rising q at low altitudes as the path angle quickly steepened downward.  Of 85-90 tons at reentry,  they picked up 75 tons of debris in Australia.  Nope,  these things most definitely do not "burn up". 

GW

Ingenious though the idea may be, what I get out of it is mainly that you can't make a shuttle-like vehicle safe. Not as safe as a capsule. That "Lose attitude control,  you're dead", which would also be true for skylon I'm sure, will give old-fashioned capsules an edge forever, and the added point of a rocket escape system finishes the discussion, IMO. The capsule is just more fail-safe from the beggining, about the only system you really need working to survive a crash is an emergency parachute, or a rocket landing system. You can put both on, and add redundancy. Proof? Recently the russians had two soyuzes lose all control during reentry and executed ballistic flights (that is, they fell like rocks). They didn't even ground the craft while they worked the problem, and it didn't make the news, much less kill anyone.

And if someone tells me a skylon can be flown several times and reused, and therefore is more reliable, the same can be said of a proper reusable capsule. So if skylon is ever to be made into a manned transport, the payload I suggest is a independent capsule with an escape system. But, you know, skylon's proper use is to put bulk stuff like propellant cheaply on orbit in huge quantities and regularly, not to carry people in style, and that hopefully it can do.

And Impaler, 12 mT is nothing to be sneered at. You can't launch a lunar mission on that, sure, but you can service 99% of the satellite market (with the possible exception of the huge DOD GEO comm spy birds). Hell, most LEO satellites are just a couple of tons. Buy, I don't know, Fregat stages for the final insertion, and you can service anywhere up to GEO anything that is currently commercially built. Arianne V's 20mT to LEO payload mainly means they need to dual-launch big GEO birds and have room to spare for several secondary payloads to not waste room.


Rune. Oh, and thanks for the detailed description, GW. I actually listened to a classmate analyze the accident in class last year, but from the "why the leading edge failed" POV, nothing on what had happened afterwards.


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#24 2012-05-14 11:56:10

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,027
Website

Re: Reaction Engines

Any spaceplane will resemble an airliner in its safety aspects.  It's just too hard to get a lot of folks out.  The more on board,  the worse this problem is.  So,  like airliners,  we will have to pay very careful attention to making them as safe as is humanly possible.  That's the way to build a passenger spaceplane. 

I think the choice between vertical launch rocket and horizontal spaceplane (one stage or two) depends really on the intrinsic value vs size of the cargo.  Using Atlas-5 and Falcon-Heavy as examples,  launching 25+ metric tons to LEO can be done for something like $1000-2500 per pound (as crude as this is,  $2000-5000/kg),  but only at the max payload capability of the vehicle. 

That last phrase is the key.  Some payloads will fall below that max flyable value for any launcher,  and it would be "wasteful" in a financial sense to launch them on rockets meant to haul much more.  The various spaceplane ideas could possibly have lower launch costs,  but the payload is a much smaller fraction of launch weight in systems like that. 

I think the spaceplanes will be carriers of smaller items (including crews if we really can make them safe enough).  The great massive things will fly mainly on vertical launch rockets.  So says "Cassandra".

As for launching propellants to LEO,  pre-tanked stuff comes in many sizes.  Big ones ought to fly on vertical launch rockets,   little ones perhaps on spaceplanes. 

Really "hard" tanked items could be shot into space by a light gas gun,  with a small solid motor for circularization.  That could be done for well under $100/lb.  Maybe even $10-20.  We'll see.  But your tanks (or other items) must withstand a 1000's-of-gees launch,  like artillery shells. 

GW Johnson


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#25 2012-07-18 12:27:52

Rune
Member
From: Madrid, Spain
Registered: 2008-05-22
Posts: 191

Re: Reaction Engines

Just a quick de-lurk to post this, because it sounds quite important. Seems the folks at REL are finally taking their shot at getting the Skylon program started:

Europe’s Next-gen Rocket Design Competition Included Surprise Finalist

FARNBOROUGH, England — Astrium Space Transportation and OHB AG will lead two consortia to perform a design of a new heavy-lift launch vehicle for the European Space Agency (ESA) following a bidding competition that included a surprise third bidder in Reaction Engines Ltd. of Britain, ESA Director-General Jean-Jacques Dordain said here July 10.

The British bidder, a company that for more than a decade has been designing a spaceplane using a radical new engine design for atmospheric and orbital flight, was not selected for what ESA calls its New European Launch Service.

But ESA, whose Estec technology directorate in Noordwijk, Netherlands, has been monitoring Reaction Engines’ work for the past couple of years, was sufficiently impressed with the proposal to ask its launcher directorate to engage with the company starting this month.

Considering REL's only really equipped to deal with the heat exchangers and general design, and the actual effort would require a lot of additional contractors that could be spread geographically through ESA's member states, who knows, they may even have a shot. Rolls-Royce building the SABREs while the various EADS divisions design the airframe? And Astrium for the orbital systems so everybody is happy, except maybe the germans.


Rune. I know it's a beautiful impossibility, but I still wish they get the green light.


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