swala - ramjet / rocket vehicle

[libra]

Hollaway & The Space Review

http://www.thespacereview.com/article/2933/1

http://www.thespacereview.com/article/3652/1

Basically
- MAGLEV trolley up to 400 km per hour
- ramjets to mach 5
- expendable solid-fuel kick stage to orbit

Thread to discuss that concept. Be civil please. The author himself may (or may not) come and discuss the thing.

[edzieba]

Rather than going to all the trouble of trying to dump and recover the ramjets (and the tanks?) and haul the 'spaceplane' to orbit with solids, just dump the entire spaceplane and use the solids as an expendable upper stage. You only 'expend' the motor casing and nozzle, which for solids are far cheaper than the tanks and engine of a liquid fuelled stage. It also means the 'spaceplane' does not actually need to go to space or survive re-entry, and you can use the weight savings to put on actual landing gear rather than needing to try and land on a moving trolley.
In addition, the fixed linear trolley could be replaced with a much more flexible launch from a carrier aircraft, which is a proven technology (e.g. B52 launches of the X1, X15, the D21 drone, numerous target drones, etc) with much greater launch site and target orbit flexibility, and potentially one with existing suppliers (Virgin's Cosmic Girl, NG's Stargazer, Stratolaunch's Stratolaunch).

It mainly seems to be an unnecessary convolution of the various existing air-launch schemes, and does not even approach solutions to the common problems thereof.

[Asteroza]

I thought the general design rule of thumb for ramjets is a 2 mach spread though? to go from sub-mach to mach 5, is this going to use two sets of ramjets, or a fancy variable inlet (which will not be light)?

The stated mach 5 demoed by the stuck throttle ASALM missile with a fixed inlet is usually trotted out as a near term pseudo-hypersonic weapon, but cruise was supposed to be mach 4.5, and it was a solid rocket integrated engine so what was the cutover speed from solid boost to air breathing mode?

[ChrisWilson68]

Anything with the word "expendable" in it is no longer an advanced concept at a time when SpaceX and Blue Origin are both working on fully-reusable launch vehicles.

The swala concept is strictly inferior to a fully-reusable vehicle.

[ChrisWilson68]

The article is full of misconceptions.

Here are the misconceptions in just one paragraph of the article:

The essential contradiction of hauling oxygen up through an atmosphere full of the stuff was ignored.

No, it wasn't ignored.  There's a trade-off.  Everyone knew that air-breathing was an option.  They went with carrying the oxygen instead of breathing it from the air because of the disadvantages of air-breathing options.

So were the benefits that this atmosphere bestows in the form of providing lift to airfoils.

Again, no, they weren't ignored.  Everyone involved in rockets was familiar with aircraft and their airfoils.  This was not the route chosen for space launch because airfoils have disadvantages in addition to advantages.

So in my article I suggested that launching a space plane off a speeding railroad wagon using ramjets was a much more efficient way of getting up to the top of the atmosphere.

This was simply a claim without running the actual numbers by a non-expert in the field.  Many others who have devoted their lives to space launch, had extensive education in it, and accomplished a lot in the field, have run the numbers and decided that rockets are the more efficient method.

This was a stalking horse: I wanted to see what practical objections there were to this idea. None emerged.

There have been lots of objections -- there are multiple threads on NSF full of such objections.  There are books written about the subject.  The author of this article simply didn't do his research if he is claiming there are no practical objections.

[John Hollaway]

I am very grateful to an anonymous benefactor for this forum, which gives me the opportunity to explain and discuss the Swala concept with an informed audience. I believe Swala represents the future of space launch, not just because it is superior to multi-stage rocketry, but because the industry is overdue a technical transformation. 

Any healthy business undergoes such revolutions, but they can be seen most clearly in the transport sector.  Sails were replaced by steam (and then diesel engines), steam locomotives were replaced by diesel (and then electricity), propellers driven by internal combustion were replaced by gas turbines (and then turbofans).  The duration of the initial technologies ranged from over 100 years (for steam locomotives) to about 20 years (for the turbofan).  And space launch? Taking the first successful V2 launch in early 1944 as marking the start, then it is a 77 year-old-technology.  By contrast the first electric railway locomotive was built in Scotland in 1841, just 35 years after William Trevithick’s first steam locomotive. Significantly this, primitive though it was, suffered destruction by railway workers who saw it as a threat to their jobs.

So, I believe the rocket launch business is well overdue for revolutionary innovation.  Coming in from the cold, as it were, I was struck by the persistence of the fundamental technology since 1945 and the failures (80-odd) of all the attempts at alternatives (principally spaceplanes).  Nothing worked.  But there was one common feature – those failures were, without exception as far as I could tell, promoted by rocket scientists.

Ever since the 1950s the space business has used technology driven both by its availability from the V2 engineers, and the urgent need to build ICBMs.  Over the years this has been tweaked until there is very, very little left that can be done (metallic hydrogen?).  Yet, as the sad history of alternatives shows, there has been no successful attempts to break away from the tunnel vision that has fixated the industry for the past 70 years.  Reusability is marvellous – all praise to Mr. Musk’s rocket scientists - but bringing a booster back to earth in one piece requires 30% of the payload to be replaced by extra fuel and oxidiser.  The true test will be when they are routinely used to carry up astronauts.

In any event, as the originator of the Swala concept, I must expect flak.  To make it easier for detractors, here are all the links to the Swala concept.

First, the nine articles I have had published in The Space Review since I started to promote this revolutionary idea (not all of them deal with Swala, but I like to think they are all relevant) –
An alternate, rocket-free history of spaceflight: www.thespacereview.com/article/2841/1
Space launch lite: the Swala concept: www.thespacereview.com/article/2933/1
Echoes from the past: the Mars dilemma: www.thespacereview.com/article/3000/1
Has the space launch industry been too focused in the last 70 years? www.thespacereview.com/article/3209/1
The end of a very long honeymoon: www.thespacereview.com/article/3294/1
NASA’s dilemma: governments don’t do innovation: www.thespacereview.com/article/3533/1
Mining asteroids: appealing to our romantic side? www.thespacereview.com/article/3586/1
Spaceplanes: the triumph of hope over experience: www.thespacereview.com/article/3601/1
The ramjet mystery: www.thespacereview.com/article/3652/1

There are two videos on the Swala concept:
1) A short (2 minute) one giving the basics:
2) A showier ten-minute one where I am the rather wooden presenter:

There is also a rather elderly website www.swalarlv.com - but carrying some useful links.

I think that’s about it – so please let’s hear from you, even if it is to remind me that ‘everybody knows’.

Thank you for persevering

John

PS A small correction to Libra's introductory post; launch is on a carriage on a linear motor track, not a maglev track (too expensive).

[John Hollaway]

And my own mistake - the V2 work started 77 years ago, but the first successful flight (and the ensuing bombardment, which I can just remember) was 75 years ago.

[john smith 19]

I thought the general design rule of thumb for ramjets is a 2 mach spread though? to go from sub-mach to mach 5, is this going to use two sets of ramjets, or a fancy variable inlet (which will not be light)?

The stated mach 5 demoed by the stuck throttle ASALM missile with a fixed inlet is usually trotted out as a near term pseudo-hypersonic weapon, but cruise was supposed to be mach 4.5, and it was a solid rocket integrated engine so what was the cutover speed from solid boost to air breathing mode?

The usual rule of thumb that ramjet designers have used is that a fixed geometry design could cope with 3 Mach numbers.

However
More modern designs have tended to be solid fuel, so can't really use techniques like "thermal choking" to broaden the Mach range by changing the fuel injection pattern.
 
I have suggested an X-programme to study the true limits of (subsonic combustion) ramjets would be a good use of research funds. But no one seems interesting in refining "known" technology when there is the ridiculously complex SCramjet to study instead.

[john smith 19]

And my own mistake - the V2 work started 77 years ago, but the first successful flight (and the ensuing bombardment, which I can just remember) was 75 years ago.

Welcome to the site.

Basic membership of this site is free and basic membership allows you to create a thread if you wish.

You're quite right that ramjets can generate thrust at sub M1 speeds. The Germans in WWII did quite a lot of work on this which was captured in an AGARD conference in the mid 50's. It is available for download here

Sub sonic ramjet design and mfg methods have been studied in the M0.7-0.9 range for use in target drones.
Papers for this exist in the open literature.

What you're describing in terms of payload is essentially the Pegasus rocket but with 1, not 3 solid stages. It weighs 23 tonnes and still needs a carrier aircraft to lift it to about 30 000 feet before it is launched.

This concept is generically referred to as "Assisted Single Stage To Orbit," but the dual fuel (liquid for the ejectable ramjets and solids for main stage) make it more like the Atlas "Stage-and-a-half" approach.

Boeing studied a full aSSTO design as the "Reusable Aero Space Vehicle" or RASV in the mid 70's. Their design report is here. They studied launch sled design quite extensively, as well as the issue of landing gear weight. It's a good read for any serious student of HTO launch systems.
As a general note NTRS is a rich site of NASA and NACA data. An Ozone powered ramjet for orbit keeping was already being studied in the 1950's.

Now to your specific concept.

In aerospace work there is the idea of a "Technology Readiness Level." Normally a 9 point scale. 1 is roughly "Demonstrated on a lab bench and does not break the laws of physics" and 9 being "Tested at full scale across all real life environments"

(sub sonic combustion) Ramjet TRL is high. Solid fuel rockets are TRL 9, Winged re-entry is TRL 9, but an electromagnetic catapult is way down (BTW the first attempts to launch an aircraft from a carrier flight deck with an EM catapult took place in the late 1940's). It's just entered service for speeds well below your target. There is no history of landing anything on such a platform. 

T/W of fixed ramjets is around 7:1 (SCRamjets seem to be about 2:1, which a number SCramjet proponents are very reluctant to admit). Modern large turbo fans are around 10:1. Rockets can hit 150:1.

The Isp of jet engines is around 3000. That lets you get away with a lot of structure. Ramjets are (AFAIK) not so good and will be considerably worse below M1. Likewise solids have much lower Isp than liquids (300secs is a really good solid. 280 is more likely)
[EDIT Those numbers were way too generous. A double base propellant (basically an explosive, not a fuel) can achieve a vacuum Isp of 300s, but the stuff in the Shuttle SRB's was about 243secs at sea level. ]
. Buying one OTS means you're at the mercy of the solids mfg for a large part of your reusable costs. It also gives you the worst Isp at a time when you'd like the best

BTW dropping ramjet pods has been discussed (on this site) in the context of a high TRL multi stage RLV (jet engined Launch Assist Platform to about M2.4, rocket fuel fueled ramjets to M5.5, winged rocket vehicle to orbit). Basically using the known current limits of various technologies and seeing what sort of architecture could you construct with them with minimal risk.

But the 2 biggest issues are
1) Your insistence on an EM catapult means you have exactly one viable launch direction. The real market needs access to other orbital inclinations and your system does not provide this.  The landing concept is completely untested (anywhere) and would need serious investment to lower the perceived risk of such a system

2) Financial. Why invest in this when investors can invest in something else that's a lot less risky and gives better returns? Your assumption that a ground launched, liquid and solid fueled reusable space plane can deliver 0.5tonnes while weighing 20 tonnes is very optimistic, given the range of propellants you're planning to use.

A designer needs to always be asking the question of themselves "Is this the best solution to this part of the design, or simply because I want to see if it will work" ?

[RobLynn]

I thought the general design rule of thumb for ramjets is a 2 mach spread though? to go from sub-mach to mach 5, is this going to use two sets of ramjets, or a fancy variable inlet (which will not be light)?

The stated mach 5 demoed by the stuck throttle ASALM missile with a fixed inlet is usually trotted out as a near term pseudo-hypersonic weapon, but cruise was supposed to be mach 4.5, and it was a solid rocket integrated engine so what was the cutover speed from solid boost to air breathing mode?

Stratolaunch can get you to ~10000m and ~200m/s.  Diving from there to 4000m can get you up to about 400m/s (M1.3) a much nicer ignition speed for a ramjet, without necessity of developing lots of tricky launch catapults  and subsonic ignition M5 capable ramjets etc.  Still unlikely to be worth while compared to simpler pure rocket solutions.

[John Hollaway]

Dear Readers - thank you for your comments, which are both useful and surprisingly restrained with this upstart.  I am going to answer them but first I want to put up three posts which in themselves will answer much thoughtful criticism.

I think that to start this first post I should repeat the essential aspects of the Swala spaceplane concept, a single-stage-to-orbit reusable spaceplane.  This statement itself at once brings controversy because, while Swala indeed has only a single stage rocket motor, to make this achievement possible it jettisons the heavy ramjets that have taken it to the upper stratosphere, parachuting them back for reuse. So, it can be argued that Swala does discard the equivalent of a stage; I will leave you to make up your own mind.

The Swala launch concept (‘Swala’ is the Swahili word for a gazelle) will carry a payload of about 500kg into low earth orbit (LEO). Launch and landing are up from and back to a carriage running on the same linear induction motor (LIM) track. For the launch this accelerates the vehicle to a speed of about 400km/h, at which point the ramjets will be generating enough thrust for take-off. Its capture on return uses a modified aviation instrument landing system to bring the approaching vehicle down on to the carriage, which is accelerated to match the speed of the vehicle as it glides in.  By eliminating the need for landing gear, the Swala spaceplane is uniquely light and efficient.

It will be able to achieve a height of at least 30km (100,000ft) by using the oxygen in the air instead of hauling up liquid oxygen – have a look at this Space Review article to get an idea of its feasibility – http://www.thespacereview.com/article/3652/1 and of some intriguing possibilities that these underrated units may offer.

Once the ramjets flame-out they are parachuted back for recovery and reuse. Thereafter, as explained, it uses a conventional solid fuel motor to carry it to low earth orbit (LEO) whose ratio of propellant to non-propellant will be about 12:1. All three propulsion systems - the linear motor, the ramjets and the solid fuel motor - have effectively no moving parts.

The objections to this concept focus principally on the use of ramjets with a fixed inlet to handle both subsonic and supersonic airflow regimes.  However, the use of the LIM system, both for launch and capture, has drawn criticisms as well, principally because this has never been done before.  So we will start with these.

A linear motor is a conventional electric motor laid out flat.  Linear electric motors, like the conventional sort, can be either induction or synchronous.  After discussion with manufacturers (they are much used in luggage handling systems and fairground rides) the linear type appears the best for the Swala concept.  This is principally because the carriage does not need to be nudged forward to get it working (therefore they are used on electric cars) and the armature (the aluminum ‘fin’ that fits between the line of coils above which the carriage runs) is much smaller.  A LIM track is also rather cheaper although its efficiency in terms of power factor is lower.  However, as the power is needed in short, sharp bursts this is not too important. 

Here is the Swala vehicle LIM launch compared to that of a Navy Super Hornet:

Aircraft           Super Hornet                          Swala
Mass                   30,000 kg                                 30,000 kg
Take-off Speed   78 m/s (280 km/hr)                 111 m/s (400 km/hr)
Acceleration   3.3 g                                          2 g
Launch Track    90 m                                         314 m
Launch Energy   110 MJ                                 185 MJ
Launch Duration   2.4 s                                         5.7 s


It can be seen from this table that the requirements of a Swala LIM launch at 400km/hr are not all that different from what is being routinely achieved on aircraft carriers. However, the 185MJ of power needed is equivalent to 52 kWh of energy used in 5.7 seconds.  This is a lot, and will be a heavy drain on the electrical infrastructure at Machrihanish, the old air force base on the Atlantic where I expect the first launches to occur.  To avoid the expense of batteries and/or capacitors it may be necessary to schedule launches in the small hours.

This is the point at which you will say ‘but ramjets will not generate sufficient power to lift a 30 ton vehicle at 400km/hr.  You are in good company; that is what the patent examiner said.  The document that led him (or her) to issue the patent can be downloaded from the Swala web site at http://swalarlv.com/The%20Swala%20Project%20-%20Welcome_files/Ramjet%20Thrust%20at%20Subsonic%20Speeds.pdf
I won’t go through the arguments again here, read the paper and let me have your comments.

Before I leave the matter of the LIM launch and capture, the latter feature has also brought a fair chorus of ‘it can’t be done.’  This is probably simply because it has not been done up to now.  But even this is not quite true - 
the Swala video at
has a clip showing big (15 ton) X 47B drones landing routinely on aircraft carriers; they have been doing this since 2013.  If you check on the internet you will find that drones are taking off from and landing on truck load-beds and you can see a fixed-wing drone landing on a moving platform at , a feat achieved by Germany’s Aerospace Centre (DLR).  So it can be done, a fact borne out by discussions with instrument landing specialists, who were not particularly fussed by the concept.

That will do for the present; my next post will deal with the main event, which is the arrogant assumption in the Swala concept that a one-size-fits-all ramjet can be built that will carry the vehicle up from 400km/hr to Mach 5 (and beyond).  And yes, for a time I was hornswoggled by the universal chorus from my advisers to the effect that the diffuser-choked inlet of a supersonic ramjet, needed to break up the shock front that formed at such speeds, could never be used at subsonic speeds because this would prevent sufficient air entering to give the thrust required.  But it can be overcome, in a way which is obvious in retrospect.  Post 2 arriving shortly

[John Hollaway]

This is the second of three posts -

The preceding post told of the innovative use of a linear electric motor to launch and capture the Swala vehicle, an innovation that I discovered the US Navy had already pre-empted.  But now for the next stage, where there is a seemingly impervious barrier.  Using ramjets to fly the vehicle up from launch to the high stratosphere was a no-no - there seemed to be no way in which a ramjet could function in both the subsonic and supersonic airflow regimes.  Any attempt would be thwarted by too much air flowing in above Mach 1 and too little below that speed.  It was a low spot in the evolution of the Swala concept, and the villain was the diffuser necessary to throttle the inlet airflow at supersonic speeds and break up the shock front that formed there.

And then I glanced at a picture of Boeing’s ASALM missile, which famously had a stuck fuel valve that caused it to hit over Mach 5.5 at 20,000 feet.  Despite this it had no obstruction in the inlet, which was a simple rectangular orifice.  What it did have was a protruding ‘chin’, which did the job of a diffuser – an external diffuser. 

I am a slow thinker; it was weeks later, sadly musing on the uniform professional resistance to my great idea, that I suddenly realised that all the experts I had consulted had only worked with missiles, not spaceplanes.  Apart from ASALM these missiles were universally designed so that the ramjet inlet was concentric around an ogive.  Swala, by contrast, had its ramjets positioned under its wings, and so a ‘chin’ could be installed above their inlets in the form of a fairing.  The fairing itself could function both as a fuel tank and as a flotation chamber to assist in recovering these units from the ocean.  Eureka moment!

Right, next problem.  But less of a problem, more of a question mark.  How high and how fast would the ramjets take the Swala vehicle?  Readers of this article - http://www.thespacereview.com/article/3652/1 will find that 30km and Mach 5 have been achieved consistently enough for them to be made realistic targets.

But could this be higher? Faster?  Here is a thought experiment.

The great, expensive bugbear of supersonic flight is thermodynamic heating.  Coping with it requires exotic, expensive materials, carbon fibre, titanium alloys and so on.  But if you are going to go high and fast you will have to price this feature in.  Aluminum, even its heat resistant alloys, is only good up to about Mach 2.5.

I was musing on this as I looked at the reports of the French Stataltex tests of ramjet-powered missiles in the early 1960s.  30 seconds into their flight these were experiencing stagnation temperatures at the tip of the ogive of well over 500ᵒC, getting as high as 800ᵒC after a minute, when their velocities were close to Mach 5.  Other, less well documented, tests gave similar figures.

Then I remembered that, here again, the Stataltex was a missile, and ramjet-powered missiles, perhaps without exception, got their initial momentum from solid rocket motors.  So I looked, and yes, these rockets were accelerated by such motors to near Mach 3 in just 20 seconds – no wonder their skins were already at over 500ᵒC when the ramjets started to drive them upwards ever faster.

So, the thought experiment.  Suppose we control the speed of ascent such that the skin temperature never rose above 250ᵒC, comfortably within the strength limits of aluminum-silicon hypereutectic alloys.  Remember, we are not dealing with a rocket but a spaceplane, an aircraft with controllable speed and conformation.  Now let us continue this relatively slow climb (not running out of fuel - frustratingly all the notable performances I have found – NACA, ASALM, Stataltex – ran out of fuel before their speed was explored to the limit).  As we get higher, the thinning of the air will reduce compression and skin friction, and the vehicle can speed up.  I knew from the evidence of the Stataltex missiles that ramjets travelling at over Mach 4.5 could still be accelerating at 30km (100,000 ft), where the air density is one thirtieth of that at sea level.  How much further and faster?

At 40km the air is one three hundredth that at sea level, and to approach the performance of the Stataltex missiles at 30km, ramjets would have to exceed orbital speeds!  This seems extremely unlikely, but the Swala proof-of-concept work described here should establish what can be achieved, and thus just how big its solid fuel motor needs to be.

And re-entry?  The Swala vehicle will have no deadlines to meet, and its return can be as leisurely as its ascent, extending over many hours.  Given this, there seems to reason why it should not keep its speed down to a point where, again, thermodynamic heating is held to a level that allows the use of aluminium alloys. 

The proof of concept work will directly answer these two persistent questions -
1.   Can a ramjet generate enough power at subsonic speed to get the Swala spaceplane to take off?
2.   Can the vehicle be guided back to land on to the launch carriage whose speed matches it?

As you will have seen, there are positive answers in the literature to these two questions, but they are historical or circumstantial and investors will want current and tangible evidence.  To provide this, the initial flight testing will be on a 1/10th scale vehicle.  This will be essentially constructed of aluminum alloy, limiting its speed at lower altitudes to about Mach 2.5.

However, it will not be used for the development of the launching and capture hardware and software. The danger of an expensive crash will be avoided by using pulse-jet radio-controlled model aircraft for this research and development. These units, a favorite at model aircraft shows, have a 1m wingspan and can travel at over 200km/h, but will cost a fraction of the 1/10th scale vehicle.

Once the software and hardware are ready, the small-scale Swala vehicle will be launched and captured using a roof platform on a Tesla Model S dual-motor electric car, equipped with the responsive guidance system and electromagnets. With its speed-limiting software disconnected this can reach the launch speed that the small ramjet units used will require (about 250km/h) for the thrust needed.  The testing of the launch and capture systems will be followed by flight testing to maximum altitude and speed, to destruction if necessary, to determine the limits of ramjet operation.  From the data acquired, the Proof of Concept document will be created, and with this the raising of capital for the full-scale project can commence.

The next post wraps up my inputs with the arguments for the size of the solid fuel rocket, and with thoughts on the market and the cash flow.

[John Hollaway]

Having dealt with the arguments over the launch and capture of the Swala spaceplane and its use of ramjets, this post completes my ten cents worth with a discussion about the size of the solid fuel rocket needed and finishes with thoughts on the market for its services and the possible cash flow arising from this.

It has been rightly pointed out that the enormous velocity required for orbital free-fall makes the speed needed to merely get the vehicle to the edge of space look relatively puny.  We can achieve Mach 5 at 30 kilometres, but, pace the arguments for going higher and faster in the previous post, we need to get to the equivalent of Mach 26 at 150 kilometres using a single stage rocket.

It is here that the rigors of the Tsiolkovsky equation make themselves felt.  The likely weight of the non-propellant part of the Swala vehicle after it has jettisoned its ramjets is as follows:

Component   Mass kg
Shell                     1,300
Payload                500
Guidance/control    300
Total                     2,100
 
So this is what has to be carried to orbital speed and altitude.  If we assume that the exhaust velocity of our rocket is around 2,800 metres a second, then the equation says we will have a propellant to non-propellant ratio of about 10:1.  Let us take this as 12:1 to allow for gravity and residual drag, then we will have a total vehicle mass of 25.2 tons of propellant and 2.1 tons of non-propellant, 27.3 tons in all.

Critics point out that this means Swala is not much further ahead with its propellant to non-propellant ratio than a typical multi-stage conventional rocket launch.  The reply to this is twofold: first the Swala vehicle is fully reusable.  With a conventional rocket - as the Falcon 9 reusable booster has demonstrated – about 30% of the payload is lost to the extra fuel and oxygen needed for bringing the booster back down again.  This loss of payload pushes the propellant to non-propellant ratio to above that of the Swala vehicle.

Secondly, thermodynamics means that rockets are very inefficient at low velocities when the exhaust carries away a great amount of kinetic energy.  If you go to https://en.wikipedia.org/wiki/Rocket#Energy_efficiency then you will see that rocket efficiency is about 5% in the first part of the launch.  Ramjets are not very efficient either (apart from within a limited speed range), but they do not carry up their oxygen with them for that part of the flight – about 2.5 tons of it for a ton of fuel.  Consequently, in practical terms their fuel consumption – their carbon footprint if you like – is a fraction that of a conventional rocket.

The outcome of this argument is best seen in the market potential and profitability of the Swala proposal.  ‘Smallsats’ – satellites with an individual mass of 200kg or less – now dominate the market.  The consultancy Euroconsult predicts that up to 3,600 smallsats are likely to be launched in the next decade.  In particular, ’cubesats’, weighing about 6kg apiece, will be the most numerous from now on.  Over 700 were launched from 2012 to 2017, and they represented 87% of all satellites launched in 2017, a total of 335 smallsats being launched in that year.

Much to the point, rockets usually have one or two customers with big satellites who dictate the launch date and the orbit, both often inconvenient to the owners of the small satellites sharing the payload with them.  The Swala Spaceplane will offer launches at need and on call, a feature so valuable that many satellite owners will probably be happy to pay a premium arising from not taking up the full payload capacity.

For investors in Swala, the capital requirement is relatively modest for the launch industry.  A cash flow projection, using a capex of $150m and a build-up to one hundred launches a year after 6 years from start, with prices at the equivalent of $3,000/kg – the SpaceX gold standard - gives an IRR of 24%.

To wrap up - the Swala concept benefits from tunnel vision in the space launch industry, which has used essentially the same technology since the 1940s.  Consequently, although Wikipedia records over eighty attempts to create a true spaceplane, these were, as far as I can tell, all designed by rocket engineers – and so they employed rockets in whole or in part.  Variations have employed air-launches from aircraft or balloons, but the amount of energy required to attain orbital altitudes and speeds have meant that these contributions are insufficient for a practical SSTO vehicle.  By using ramjets whose initial launch is from a linear motor track, it will at last be possible for a spaceplane to attain heights and speeds that allow a simple single-stage solid fuel motor to take it into low earth orbit.

The Swala development means that all the advantages offered by a successful reusable spaceplane will finally become attainable.  In addition to inserting satellites in orbit, the Swala vehicle could take astronauts and supplies to the International Space Station (ISS), collect and return to earth malfunctioning satellites or space junk and act as a true shuttle, carrying up components to assemble vehicles to explore other planets, in the same way that the ISS was built, but at a fraction of the cost.

Yes, Swala is novel. But the launch business is overdue for a disruptive technology, perhaps long overdue.  Electric locomotives were in use fifty years after the steam ones, jet turbines were powering aircraft forty years after the propeller-driven ones began powered flight.  It is now 75 years since the first V1 rockets rose vertically on an alcohol and liquid oxygen propellant, and nothing fundamental has changed since then.  But the Swala concept, like all disruptive technology, will be successful because it is essentially an economic revolution, making access to space not only an order of magnitude cheaper, but an order of magnitude more accessible to people and projects with limited cash resources.

Anyway, thank you for persevering with this, I know it’s a lot to take on board - now it’s your turn!  Let’s hear from you.  I’ll comment on issues that have already been raised by you shortly.

[john smith 19]

And then I glanced at a picture of Boeing’s ASALM missile, which famously had a stuck fuel valve that caused it to hit over Mach 5.5 at 20,000 feet.  Despite this it had no obstruction in the inlet, which was a simple rectangular orifice.  What it did have was a protruding ‘chin’, which did the job of a diffuser – an external diffuser. 

I am a slow thinker; it was weeks later, sadly musing on the uniform professional resistance to my great idea, that I suddenly realised that all the experts I had consulted had only worked with missiles, not spaceplanes.  Apart from ASALM these missiles were universally designed so that the ramjet inlet was concentric around an ogive.  Swala, by contrast, had its ramjets positioned under its wings, and so a ‘chin’ could be installed above their inlets in the form of a fairing.  The fairing itself could function both as a fuel tank and as a flotation chamber to assist in recovering these units from the ocean.  Eureka moment!

Inlet design is actually a complex field. There is an AGARD conference or two on this as well. IIRC the "chin" inlet is good for designs where the direction of travel may have to change quite a lot.

But could this be higher? Faster?  Here is a thought experiment.

There has been at least one thread on this site discussing an X programme to do this.

Then I remembered that, here again, the Stataltex was a missile, and ramjet-powered missiles, perhaps without exception, got their initial momentum from solid rocket motors.  So I looked, and yes, these rockets were accelerated by such motors to near Mach 3 in just 20 seconds – no wonder their skins were already at over 500ᵒC when the ramjets started to drive them upwards ever faster.

So, the thought experiment.  Suppose we control the speed of ascent such that the skin temperature never rose above 250ᵒC, comfortably within the strength limits of aluminum-silicon hypereutectic alloys.  Remember, we are not dealing with a rocket but a spaceplane, an aircraft with controllable speed and conformation. 

It's surprising how things in the aerospace world start out as an expedient idea and gradually mutate in to "This is how it's done, because it's always been done this way" folklore.

It looks like people have conflated 2 things together. That faster acceleration to operating speed is better than slower and that skin friction heating is going to happen at high speed anyway, so why worry about that caused by the initial booster burn?

But as you've seen space launch <> constant altitude cruise (even if its a missile)

Congratulations on spotting something that looks like a law of nature, but was in fact just the common state of practice. 

What you're looking for is more like a constant dynamic pressure trajectory, where the speed build up matches the rate at which outside air pressure falls. Modern flight computers (IE the programmable digital type) can be much more flexible in this regard.

And re-entry?  The Swala vehicle will have no deadlines to meet, and its return can be as leisurely as its ascent, extending over many hours.  Given this, there seems to reason why it should not keep its speed down to a point where, again, thermodynamic heating is held to a level that allows the use of aluminium alloys. 

There are 2 issues here. If it's an equatorial launch then it will come over the launch site on every orbit but if not then your design will need up to a days duration as the Earth moves under it. Winged vehicles have better cross range than capsules but it's a lot simpler to just wait until its ground track is more or less over the landing site than design for high cross range.
[EDIT BTW I noticed that Swala is depicted as a high wing monoplane. It has been known since the 50's that high wing designs could give better cross range but at the expense of severe heating issues.
The fact that Shuttle, Buran and the X37b are all low wing designs is not an accident. During re-entry they all put the fuselage behind the wing. It may not sound that important, but it is.  On the subject of Swala design you should also be aware that an aircraft with a mass ratio better than 4:1 IE <25% of the vehicles GTOW is structure, are very rare. AFAIK the best was the Virgin Global Challenger. Jettisoning the engines and eliminating the landing gear will certainly help to a point, but I'd still be wary that a solid rocket can get the job done. ]

The proof of concept work will directly answer these two persistent questions -
1.   Can a ramjet generate enough power at subsonic speed to get the Swala spaceplane to take off?
2.   Can the vehicle be guided back to land on to the launch carriage whose speed matches it?

I don't think 1 is that much in doubt. As you will have seen from the AGARD conference on German work big subsonic ramjets are quite capable of being built and generating substantial thrust. The US were looking at M0.7-0.9 ramjets as low cost power plants for target drones. A design is available on the internet.

The real doubts around ramjets for this task are

1) Can you design a ramjet that starts at a sub Mach1 speed, generates enough thrust to go through the sound barrier (there is a serious drag rise in the transonic regime. It falls off quite lot at >M1.2. That's the only other time Concorde's after burners were used) and can continue accelerating? Can you do this with a single configuration, or do you need to dynamically schedule different sets of injectors to do "thermal choking"? [EDIT worst case  you look at the multiple configuration changes (including a moving inlet) of the SR71 J85 nacelle. The bare J85 had a T/W ratio of about 5.5:1. with the nacelle it was about 1/2 that but the nacelle was utterly vital in order to make the concept work. Avoiding most (all?) of that complexity would be an excellent goal  BTW the SAIC consultancy (who've been asked to critique other air breathing launch concepts) reckon you need a thrust of about 0.7 GTOW  to get through M1 (although the Ryan Firebee II drone went supersonic with an engine thrust 1/2 its GTOW (with a RATO pack behind it) ]

2)Can it be done with acceptable fuel consumption. Rising drag losses (as the difference between outside velocity and speed the inlet needs to drop the airflow to in order for the ramjet to operate increase) and the associated increase in thrust (and hence fuel consumption) to overcome them have been the justification for the SCramjet (and it's consumption of > $10Bn in US funding over 6 decades without a single operational vehicle being delivered).

3) Can you do this with acceptable T/W ratio? The rule of thumb for ramjets seems to have been about 90lb of thrust per square inch of inlet area, or about 622 KPa in SI units.  But AFAIK that was for ramjets operating wholly at M1+. Sub M1 compression is likely to be less effective, but how much less?

While I've found NACA, NASA and DoD ramjet work relatively easily (up to 48" in dia, which is a beast) I've never come across any reports on testing a ramjet for an external transonic environment.  [EDIT IE accelerating through the range M0.8-1.2]

Which suggests this is truly "Terra Incognita"

As you will have seen, there are positive answers in the literature to these two questions, but they are historical or circumstantial and investors will want current and tangible evidence.  To provide this, the initial flight testing will be on a 1/10th scale vehicle.  This will be essentially constructed of aluminum alloy, limiting its speed at lower altitudes to about Mach 2.5.

That should pick up any problems with the transonic transition.

However, it will not be used for the development of the launching and capture hardware and software. The danger of an expensive crash will be avoided by using pulse-jet radio-controlled model aircraft for this research and development. These units, a favorite at model aircraft shows, have a 1m wingspan and can travel at over 200km/h, but will cost a fraction of the 1/10th scale vehicle.

Once the software and hardware are ready, the small-scale Swala vehicle will be launched and captured using a roof platform on a Tesla Model S dual-motor electric car, equipped with the responsive guidance system and electromagnets. With its speed-limiting software disconnected this can reach the launch speed that the small ramjet units used will require (about 250km/h) for the thrust needed.  The testing of the launch and capture systems will be followed by flight testing to maximum altitude and speed, to destruction if necessary, to determine the limits of ramjet operation.  From the data acquired, the Proof of Concept document will be created, and with this the raising of capital for the full-scale project can commence.

The next post wraps up my inputs with the arguments for the size of the solid fuel rocket, and with thoughts on the market and the cash flow.

The question about the landing would be around the fact that (having jettisoned the ramjet packs) it's a glider, while the landing pad can only accelerate or decelerate (which should be scaled to limits of the full size EMAILS, rather than what the Tesla is capable of).

[Elmar Moelzer]

The key to RLVs is the speed at which they can be reused and the cost of refurbishment.
And SSTO RLVs need to show an operational advantage over TSTO RLVs. If your SSTO is harder to reuse than a conventional TSTO, then there is no point to making an SSTO.
From my layman perspective, you RLV design is not exactly "gas and go". For one the ramjets need to be fished out of the ocean, inspected for damage from water landing, probably cleaned thoroughly as well.
Then there are the solid fuel rocket engines, which are usually not easy to reuse. They need to be completely replaced between flights. I am not sure that this can be done quickly and cheaply.
IMHO (and I may be wrong), once SRBs are involved, you might just as well make a two stage version with an expendable solid rocket second stage (since the solid rocket engines are essentially junk anyway). That would safe you a lot of trouble between flights and make the whole design a lot simpler since you do not need to worry about TPS for the first stage. You have more headroom for GLOW and can pack a landing gear and keep the engines attached for landing too.

[john smith 19]

It is here that the rigors of the Tsiolkovsky equation make themselves felt.  The likely weight of the non-propellant part of the Swala vehicle after it has jettisoned its ramjets is as follows:

Component   Mass kg
Shell                     1,300
Payload                500
Guidance/control    300
Total                     2,100
 
So this is what has to be carried to orbital speed and altitude.  If we assume that the exhaust velocity of our rocket is around 2,800 metres a second, then the equation says we will have a propellant to non-propellant ratio of about 10:1.  Let us take this as 12:1 to allow for gravity and residual drag, then we will have a total vehicle mass of 25.2 tons of propellant and 2.1 tons of non-propellant, 27.3 tons in all.

I've just realized what I'm missing from your analysis.

There is no mention of the fuel mass for the ramjets.

Gary Olsens old ramjet notes indicate that ramjets operating in subsonic airflow can have Isps in the 200sec range. However they also note they could operate as far as M7, with Isps at about 1700secs (from a peak in the 2000's).

While airflow will be 4x bigger than just the O2 they need for combustion that will still be a substantial mass of fuel that needs to be carried but I'm not sure where you have factored this in.

I will note that an aircraft with a mass fraction below about 26% of GTOW is very demanding. Even eliminating the landing gear means it will still have to be very lightly constructed given the SRM Isp.

[John Hollaway]

I must apologise for the delay in replying to the various comments - family commitments is my rather lame excuse.

First edzieba and his point about simply using a modified  Swala spaceplane as a carrier aircraft to take the solid fuel rocket to launch altitude.  A rather similar scheme was the basis for Bristol Spaceplane’s (David Ashford) proposals (http://bristolspaceplanes.com/projects/spacecab/) and for the NASA-funded catapult-scramjet-rocket proposal of 2009 - https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090034160.pdf

The main problem here is that while the spaceplane is recovered, nothing else is.  That includes the expensive and reusable carbon-filament casing of the SRM, its gimballing or vanes, the associated avionics and thrusters for positioning and the equipment associated with the payload bay.  With the advent of the reusable boosters of SpaceX, $3,000/kg is no longer a fantasy and the Swala vehicle needs to be fully reusable if it is to offer a competitive price.

Asteroza – I discuss in my posts why the perception that ramjets can only be designed for subsonic or supersonic regimes arose from the need to have them powering missiles.  The twin under-wing motors of Swala lend themselves to the ‘chin’ concept to control the shock front effect, and hence allow them to operate in both regimes, not necessarily efficiently, but with Isp values  high enough to give the thrust needed.   My mentor in these matters, Gary Johnson of McGregor,  Texas, recollects hearing that the ASALM vehicle actually reached Mach 6 before running out of fuel.

John Smith 19 – your main points are that the  EM catapult means one  launch direction and that it is unattractive financially.

On the first, the nature of a spaceplane means that it has directional capability; my thought was that if we launched from the unused airbase at Scotland’s Machrhanish airport we would fly round and jettison the ramjets over the north sea, avoiding oil and gas fields (and now wind farms), with the vehicle now in the azimuth and inclination for satllite insertion.

 On the finances  I hesitate to go public with a definitive cash flow, despite the high technology readiness of the concept, as I know how easy it is to produce a good, or bad, IRR at this stage of the development of an idea.  Nonetheless  the finances look attractive because every component is well proven and there are effectively no moving parts in the propulsion systems.

RobLynn – the linear motor is not a tricky launch catapult, but by this stage is well-established technology dating from the 1960s.  My main concern here has been with the electrical infrastructure at Machrihanish, delivering such a lot of power over so short a time.

John Smith 19 again – thank you for putting all that work into your analysis of the proposal – much appreciated, and I will follow up your suggestions.  I’ll deal with one point, which interests me greatly.  The sole reason for a high wing Swala vehicle was that I had done some gliding in my youth, and all the gliders I had flown were high wing.  Arising from your comment I checked and found that every spaceplane to this date had a low wing configuration, presumably so that there was a broad heat-insulated surface to handle reentry heating during the nose-up condition this requires.

But – I still wonder why reentry has to be so swift, less than an hour, normally.  Doing the calculation, here is my take on a 10-hour reentry using the Stefan-Boltzman constant; the vehicle heats up to not much over 400ᵒC.  I realise this is simplistic but it does suggest that it would be worth investigating.

Mass of vehicle   1500   kg Kinetic energy of vehicle   30   MJ/kg So kinetic energy to be lost       45,000    MJ Likely area of Swala vehicle    100   sq.m So kinetic energy per sq.m. to be lost   450   MJ/sq.m 1 MJ is equal to -   278   W.h So energy to be removed by emission -   125.1   kW.h/sq.m Duration of reentry   10   hrs So power to be lost       12,510    W/sq.m Stefan-Boltzman Constant   5.7E-08    Vehicle temperature T = (EXP(LN(W/sq.m/S-B constant)/4)   685   deg K

Anyway, thank you all very much.  More later, but please keep your comments coming.

[John Hollaway]

Again for John Smith 19 – yes, the fuel question is what drove me to write that article for The Space Review where I queried what was going on with ramjets as very high altitudes and very high speeds and which led to this forum, for which I am very grateful.  Specifically, there appears to be a ballistic (zoom, coast) benefit that cannot be accounted for by conventional calculations.  This realisation was sparked off by Glenn Olson’s comments –
‘In 1951 NACA launched a ramjet powered missile which reached an apogee of 159,000 ft. This missile was launched at a 75 degree angle and ran out of fuel at 67,200 ft and Mach 2.92. This missile could have reached astronaut-wings altitude with almost any combination of a) steeper launch angle (it was still doing over 1,000 fps at apogee), b) more fuel (it started with only 25 lbs or 11% of its mass), and/or c) bigger engines (it had two 6.6 inch diameter engines).’

Putting the numbers into the metric system (which, you will have to excuse me, I am most comfortable with) this missile was on a 75ᵒ ballistic trajectory from 20,483 metres and Mach 2.92 and this took it to 48,463 metres. If one uses the ballistic formula, then under these conditions it should have peaked at just under 40,000 metres, leaving aside drag.  So where did it get the energy to go up another 8-odd kilometres? 

This becomes very important when the fuel mass is significant.  The spreadsheet is attached with the calculation, and yes, the fuel is a fair weight. Of a 33-ton launch-ready vehicle, 2.8 tons is kerosene for the ramjets…however, if that remarkable missile performance noted by Glenn Olson is correct, then it could be significantly less.

[John Hollaway]

SWALA AND THE MONEY

(The Swala project, as you know, has been placed in the ‘Advanced Concepts’ section of the forum, meaning that it rubs shoulders with proposals for the Halo Drive, the Space Elevator and so on.  I would argue strongly that the Swala concept is not all that advanced, just novel, in the sense of a novel juxtaposition of existing technology.  All three components – linear motors, ramjets and solid fuel rockets are at a Technology Readiness Level of 8 or 9. (The TRL sequence is an awkward one to use when employing old technology in an alternative way.)  Conveniently, this means that we can put some costs together for the proposal that have a rather higher degree of confidence than its competitors.)

Starting with the capital costs.

The LIM track is going to be the most expensive single item.  A track that would enable a 1g acceleration of a 33 ton (metric tons) launch-ready Swala vehicle to 400km/hr would be about 620 metres long – say a kilometre for safety and braking (and for capture on return).  It would require about 200MJ of power (about 300kN in thrust) to use this, with a duration of about 11 seconds and with a peak voltage requirement of about 15kV. 

A costing of the track was kindly provided by Bertola Luca, lead author for this paper on using a LIM to reduce the fuel cost of aircraft launches -
https://content.sciendo.com/view/journals/aee/64/4/article-p535.xm

He estimated that the cost of the Swala LIM track, excluding civil works, power electronics and any energy storage system, would be about $35m.  As you may have gathered, the intention is to launch (and recover) the Swala vehicle at the old Machrihanish air force base on the Mull of Kintyre, facing the Atlantic west of Glasgow.  Here there is a 3km taxiway and numerous structures available, and to turn this into an operational LIM launch site could require another $25 million – say $60 million all told.  If the electrical infrastructure in the area is inadequate, then this could go up to cover the cost of batteries and capacitors. 
 
The big question mark is the cost of the Swala vehicle itself, which will have to include some development charges confirming ramjet performance.  To get an idea of what this may amount to, we can take the case of the US Navy’s T-18 Hornet carrier aircraft, which can be seen in the Swala video ( being launched using a LIM track (the Navy calls it EMALS for Electromagnetic Aircraft Launch System).  These aircraft are approximately the same size as the Swala vehicle and cost about $30 million apiece thirty years ago, or about $60 million today.  Obviously, a T-18 is much more complex than a Swala vehicle, but that price would allow for development costs.

So the LIM track and the Swala vehicle add up to a capital cost of about $120 million.  My instinct is to add on a 25% contingency, which will bring it up to $150 million, with a 18 – 20 month development and construction period, $100m in year 1 and $50m in year 2.

Operating costs will be low.  The electricity cost of a launch, even allowing for poor power factors, is effectively negligible in relation to the fuel costs, and the kerosine cost, of about $2 a litre would be under $6,000. The 25 tons of solid fuel will cost about $5 a kilogram - $125,000, and assuming we use cold gas thrusters, then they might add another couple of thousand dollars.  Somebody amongst the readers will have some idea of the control and monitoring costs; what I propose is that we simply assume that the operating cost per launch will be $600,000, including in that perhaps $100,000 for maintenance and then half a million for everything else..

How many launches could a Swala vehicle be expected to handle?  It will be flown up (and re-enter) relatively slowly to keep thermodynamic heating down, so let us assume a life of 500 launches and captures.  Then, with the first two years taken up with development and construction, the launch pattern might be –

Year   No. Launches
Year 1   0
Year 2   3
Year 3   10
Year 4   20
Year 5   50
Years 6-10   100

If we take the SpaceX gold standard of $3,000 a kilogram (and assuming that by hook or by crook we get full value for every payload), then the cash flow projection could look like the attached spreadsheet, which gives a 24% pre-tax internal rate of return.

A pre-tax internal rate of return of 24% is not particularly mind-blowing for an early-stage projection of what is a revolutionary break-through, but the $3,000/kg is a very low bar.  The key is the availability, not the affordability – here is a quote from Richard Peckham of Airbus who told a British Parliamentary Enquiry in 2016 that one of the impediments to growth facing satellite companies was the ongoing challenge of securing a low-cost launch slot. Currently, a small satellite provider has to ‘hitchhike’ on a launch for a bigger satellite.  He described this arrangement as placing the smaller, secondary payload at “the mercy of the main customer - If somebody is going to launch a two-tonne satellite and you want to put your 100 kg on it, you are reliant on when that goes.  If it gets delayed because the programme of the main guy paying for the launch is delayed for some reason, you are stuck.”

At that time the cost to launch was probably anything between $5,000 and $50,000/kg.  If Swala raised its rates to $4,000/kg without denting its market its IRR would leap to 35%.  At $5,000/kg it would be 43%.

[john smith 19]

SWALA AND THE MONEY

The LIM track is going to be the most expensive single item.  A track that would enable a 1g acceleration of a 33 ton (metric tons) launch-ready Swala vehicle to 400km/hr would be about 620 metres long – say a kilometre for safety and braking (and for capture on return).  It would require about 200MJ of power (about 300kN in thrust) to use this, with a duration of about 11 seconds and with a peak voltage requirement of about 15kV. 

Closer to 630m (about 628m using Newtons formulae for this with g=9.82m/s^2) than 620, and 12 secs to be on the safe side. That really suggests some kind of energy storage system, given the very short, very intense power release but very low rate.

A costing of the track was kindly provided by Bertola Luca, lead author for this paper on using a LIM to reduce the fuel cost of aircraft launches -
https://content.sciendo.com/view/journals/aee/64/4/article-p535.xm

This is not loading. I don't know if anyone else is having trouble.

He estimated that the cost of the Swala LIM track, excluding civil works, power electronics and any energy storage system, would be about $35m.  As you may have gathered, the intention is to launch (and recover) the Swala vehicle at the old Machrihanish air force base on the Mull of Kintyre, facing the Atlantic west of Glasgow.  Here there is a 3km taxiway and numerous structures available, and to turn this into an operational LIM launch site could require another $25 million – say $60 million all told.  If the electrical infrastructure in the area is inadequate, then this could go up to cover the cost of batteries and capacitors. 

There are cost studies on mass drivers which also cover this sort of technology. "Power electronics" is actually quite a big part of the hardware and by power electronics standards is both high power (IE high current and voltage) and fast
 

The big question mark is the cost of the Swala vehicle itself, which will have to include some development charges confirming ramjet performance.  To get an idea of what this may amount to, we can take the case of the US Navy’s T-18 Hornet carrier aircraft, which can be seen in the Swala video (https://www.youtube.com/watch?v=6B1o4nxmNXU)being being launched using a LIM track (the Navy calls it EMALS for Electromagnetic Aircraft Launch System).  These aircraft are approximately the same size as the Swala vehicle and cost about $30 million apiece thirty years ago, or about $60 million today.  Obviously, a T-18 is much more complex than a Swala vehicle, but that price would allow for development costs.

What ??

That's to buy a copy. The development cost was (at least) in the 100s of $m

The nearest thing Swala reminds me of was the XCOR "Lynx" sub orbital rocket plane. I don't think Jeff Greason discussed funding openly, and having it piloted (with a space for a passenger) would have increased costs, but your figure seem very low. The head of REL said they'd talked to BAe about doing an (uncrewed)  flight test vehicle to go past the air breathing to rocket transition (around M5.5) and BAe (who are an investor in REL) said they wouldn't do it for less than ŁBn1 

Can you get cheaper than old "Billions Above Estimate" ? I think so, but you'll have to do your homework to find someone who will take the risk (and by that I mean have you put up all the money in order for them to take the risk, which means the only risk is to their reputation).

Operating costs will be low.  The electricity cost of a launch, even allowing for poor power factors, is effectively negligible in relation to the fuel costs, and the kerosine cost, of about $2 a litre would be under $6,000. The 25 tons of solid fuel will cost about $5 a kilogram - $125,000, and assuming we use cold gas thrusters, then they might add another couple of thousand dollars.  Somebody amongst the readers will have some idea of the control and monitoring costs; what I propose is that we simply assume that the operating cost per launch will be $600,000, including in that perhaps $100,000 for maintenance and then half a million for everything else..

$5/Kg for solid fuel sounds like the 1970's price for the Shuttle SRB fuel load.

I'd be very doubtful that you could get that price in the 2nd decade of the 21st century, unless you plan to mfg the solid rockets in house, which brings you into explosives handling issues (which is what they are) 
As usual the closer to off-the-shelf you can get the better. That's before you have to consider issues of ITAR contamination, where suddenly the US Government can decide who you can approach to sell a launch too and what you can tell them about your LV's capabilities. 

You'll also need to factor in recovery teams for the ramjets (ramjets that can operate from sub M1 to M5 are quite sporty. Developing a design cheap enough to throw away would be pretty challenging).

Regarding the control issues.
Before Challenger the Shuttle was run by 5 processors (quadruplicate redundant with a 5th running a completely different software system) clocked at 0.4MHz with a memory of about 1 meg byte each. Jet engine controllers have been based on the Z80 and M68000 processors (like the Sinclair Spectrum or the original generation Apple Macintoshes).

Processing power is not the issue, but mechanical actuators (and the power to drive them) are more likely a bigger problem.
I'll note the Shuttle OMS's engines (6000lb each) used electric motor gimballing and the Vega LV has had 13 successful launches with electric TVC controlling a first stage thrust of 2200 Kn.

I think your vehicle development costs are unrealistic. I know you're expecting that once it's burnt off its fuel and released its payload Swala will be relatively "fluffy" and begin a slow glide down but there is simply no way you're going to avoid some kind of TPS. Engine and TPS are the two big issues with any RLV, of however many stages you plan to use.

[EDIT
You're right about convenience costs and how this class of payload is typically a secondary payload and primary payloads (often the USG) are deeply paranoid about letting anything with the remotest chance of failing in a way that could damage their mission fly with them.

The OSC (now NG) Pegasus was designed to meet that launch market but AFAIK its flight rate and all solid 3rd party supplied engines make it the most expensive ELV in terms of $/lb to LEO.

I'd also question the market analysis of what proportion of the market needs (or could adopt) a launch on the planned axis of the EM track?
It's a big mistake to assume all LEO payloads just want to be in LEO somewhere, anywhere.  All those who want to a different orbital path will involve a plane change, either by Swala during the launch or by the payload itself. These usually need quite high delta v changes, implying substantial loss of payload on Swala or substantial propellant burn from the payload once in orbit.

If Swala's normal track is fine for most of the market then it would be competitive with ELV's.  Probably best to say with this orbital plane you can deliver X Kg to this altitude down to Y Kg at this (higher)

One joker would be what payload could you put on a Lunar, or a near escape, trajectory? The idea would be to point out that a LEO capable vehicle can also put a payload on course for more distant destinations than just LEO. Suddenly a cubesat to Mars (without a state sponsor) is no longer impossible. ]

[Asteroza]

That link for LIM paper was missing a l at the end, but I get SSL errors due to unknown CA as well.

https://content.sciendo.com/view/journals/aee/64/4/article-p535.xml

[John Hollaway]

For John Smith 19.  Yes the link to 'Electromagnetic launch systems for civil aircraft assisted take-off' seems to have stalled.  You can get it by googling this title and downloading it from Researchgate.

The costing of the Swala vehicle?  It is a very simple structure with none of the systems associated with a fighter aircraft, and the stab at a price of $60 million works out at about $25,000 a kilogram.

But I much appreciate the effort you have put into your commentary.

[john smith 19]

For John Smith 19.  Yes the link to 'Electromagnetic launch systems for civil aircraft assisted take-off' seems to have stalled.  You can get it by googling this title and downloading it from Researchgate.

I was able to down load  a copy.

The costing of the Swala vehicle?  It is a very simple structure with none of the systems associated with a fighter aircraft, and the stab at a price of $60 million works out at about $25,000 a kilogram.

But I much appreciate the effort you have put into your commentary.

HTOL RLV's are unlike any other aircraft. They operate over a Mach range of roughly 0-M23_0 and have to accommodate huge shifts in the Centre of Gravity (since they are mostly propellant) and huge shifts in Center of Pressure (as they move across the Mach range). In liquid propellant designs some (or all) of one can be offset by varying the other, but that's not an option for solids.

And that's before you get into the heating issues.

All of which makes their design a very delicate balancing act to ensure that every aspect is good enough to do it's job while not hurting the performance of the rest of the vehicle during the rest of the ascent and descent.

About the only obvious way to simplify the design task (other than being uncrewed, which helps a lot in some ways) is to not pursue single orbit abort to launch site. This design "feature" (insisted upon by the USAF) wasted 10s of 1000s of hours of wind tunnel time during the design of the Shuttle.

[EDIT Eliminating the landing gear in principle eliminates openings in the underside of the vehicle which would probably be the most thermally stressed area. Likewise putting a lot of the major systems components in a compartment behind the nose payload bay (OMS/RCS thruster propellant, batteries, GNC) or on trays in front of the solid rocket "cartridge" would make their servicing difficult once near ready for launch but quite easy for the rest of the time, again trading better structural integrity (openings imply doors, latches, hinges and special TPS pieces, all of which add cost during mfg and servicing, as Shuttle found)  ]

Waiting a day for an uncrewed vehicle to come back over the ground track of its launch site would need a longer duration power system (but how much would actually be doing during that day with no crew to support?) but would substantially reduce design constraints regarding cross range.

I think you're seriously underestimating the design cost of the vehicle, but that's just my opinion. I don't have figures to back it up.

[Jim]

About the only obvious way to simplify the design task (other than being uncrewed, which helps a lot in some ways) is to not pursue single orbit abort to launch site. This design "feature" (insisted upon by the USAF)

not true

[john smith 19]

About the only obvious way to simplify the design task (other than being uncrewed, which helps a lot in some ways) is to not pursue single orbit abort to launch site. This design "feature" (insisted upon by the USAF)

not true

Would you agree it wasted 1000s of hours of wind tunnel time (and no doubt a great deal more in the design offices) for an abort mode that was never used and placed very substantial pressures on the design team that (ultimately) they could not deliver it in full?

[john smith 19]

Nonetheless  the finances look attractive because every component is well proven and there are effectively no moving parts in the propulsion systems.

Superficially, no.

Had you said "No valves" that would almost be true, except for the ramjet fuel supply and any pressurizing gas.

A true no moving parts design means.

1) Pyrotechnic valves to seal fluids before use then they run until empty (or you fire another one in a drainage pipe
2) Vehicle is statically trimmed to have no control surfaces. Over a range of M23 that would an extraordinary achievement.
3) The angle of takeoff is set by the sled and the nozzle on the SRM is fixed, needing no TVC system. Or (like the M-72 anti tank missile) steering is done by firing individual rocket "squibs" to turn it.

The payoff in simplicity (in some ways) would be substantial, but so is the fixed costs. I was told a straight 15mm explosive bolt  would be about $400, along with a $400 ignitor. You need both and they are usually used in pairs for redundancy. That's $1600  for a single simple pyrotechnic function.

AFAIK the Pegasus XL has no control surfaces but does have TVC on the rocket nozzle, which would seem about a simple a design as you could get. But with the rocket spent you have no aerodynamic controls on descent. Obviously since Pegasus is expendable that's not a problem for NG.
Could you get by with just aerodynamic controls on ascent to get you at the right attitude (and stay there) before you left the atmosphere?
Would RCS thrusters have the strength to do attitude control outside the atmosphere without active SRM TVC?
I don't know.
If either (or both) worked you could significantly simplify the main expendable component, while bringing in the need for gap seals, bearings and drive mechanisms.

[Jim]

Would you agree it wasted 1000s of hours of wind tunnel time (and no doubt a great deal more in the design offices) for an abort mode that was never used and placed very substantial pressures on the design team that (ultimately) they could not deliver it in full?

It was not a design driver.  And it was easy to do.   AOA was almost the first mission.  And it was legitimate abort mode.  If you are talking the cross range requirement for a VAFB AOA?, Then NASA by default had a similar requirement.  Any NASA mission from VAFB would need the cross range for a safe intact AOA.   Also, it was shown that a straight wing orbiter was never viable, it never could have made the transition from high AOA entry attitude to a gliding landing.

[rarchimedes]

I know that a lot of time and effort have been put into this concept, but that doesn't make it realistic. Just starting with the idea that a 1500 kg vehicle with 100 m² wing area could be constructed to handle all the loads of these various regimes is nothing short of hilarious. Also, scaling this thing up to something with the ability to carry humans to the ISS or any other orbit would mean upping everything by an order of magnitude, and you are not building that thing for the budget you have indicated. Skylon is a bit more complicated than Swala, but has a putative budget as of 2004 dollars of over 12 billion and counting. It descends fairly gradually, but still requires a ceramic skin to survive reentry.

From what I can see, neither Swala nor Skylon can scale past 20,000 kg to orbit and Swala seems unlikely to scale past 10,000 kg. At least Skylon does not require some high-risk, Rube Goldberg contraption to land back on Earth. There has been an attempt here to compare to a carrier landing, but it is at least an order of magnitude smaller a target, not to mention that I see no probability of hitting the power for a go around.

And as several others have commented, there is the minor problem of stabilizing the whole thing and its various parts as things are shed. That means a lot of control authority and lots of power for those controls as well as orbital controls.

My overall bet is that all the betting money in the UK will go to the Skylon and it may be built, but Swala won't.

Here's a mod that can be built much simpler than what you have explained. Having seen the world land-speed record go above the speed of sound, it is not impossible to get your vehicle up above 500 kmh to as much as 1000 kmh using regular jet propulsion on the ground to push your vehicle on its own wheels or a cart of some type, not needing a mag track of any variety. Getting that much extra speed on the ground can probably allow for a stronger air frame, maybe with landing gear. And now, your ramjet doesn't have the same problems with efficiency at low speed. Landing can be on that same jet cart if you want to go that way.

[CameronD]

Here's a mod that can be built much simpler than what you have explained. Having seen the world land-speed record go above the speed of sound, it is not impossible to get your vehicle up above 500 kmh to as much as 1000 kmh using regular jet propulsion on the ground to push your vehicle on its own wheels or a cart of some type, not needing a mag track of any variety. Getting that much extra speed on the ground can probably allow for a stronger air frame, maybe with landing gear. And now, your ramjet doesn't have the same problems with efficiency at low speed. Landing can be on that same jet cart if you want to go that way.

Maybe it's not impossible to get to 1000 kmh using regular jet propulsion on the ground, but that doesn't mean it's a safe or sensible thing to do on a regular basis.  After all, speed doesn't kill - it's the sudden stop that hurts.
 

[John Hollaway]

I think that we have run out of steam with this forum; there have been no posts for a couple of months, and I have run out of comments.  I am very grateful to all the subscribers for assisting in my education.  I believe the Swala concept has come through the challenges relatively unscathed.  No fatal flaws have been shown up; if you believe there are, please e-mail me at [email protected]; I should be delighted to take up the cudgels again – or to learn more.  Now for the serious business of raising capital for the proof of concept work.
Thank you all again
John Hollaway

[john smith 19]

I think that we have run out of steam with this forum; there have been no posts for a couple of months, and I have run out of comments.  I am very grateful to all the subscribers for assisting in my education.  I believe the Swala concept has come through the challenges relatively unscathed.  No fatal flaws have been shown up; if you believe there are, please e-mail me at [email protected]; I should be delighted to take up the cudgels again – or to learn more.  Now for the serious business of raising capital for the proof of concept work.
Thank you all again
John Hollaway

I'll admire your willingness to proceed but there's a big difference between what is technically possible, and what people are willing to fund, especially when there are a growing number of LV companies in the marketplace

It's true that technically they are much of a muchness (liquid fueled TSTO ELV's) but that is about the lowest risk development path. A winged vehicle (without a high Isp engine) is a very challenging design (although Boeing with RASV thought it possible, if you used Hydrogen as the fuel).

I'll wish good luck. I'm quite sure you'll need it.

[mlorrey]

I thought the general design rule of thumb for ramjets is a 2 mach spread though? to go from sub-mach to mach 5, is this going to use two sets of ramjets, or a fancy variable inlet (which will not be light)?

The stated mach 5 demoed by the stuck throttle ASALM missile with a fixed inlet is usually trotted out as a near term pseudo-hypersonic weapon, but cruise was supposed to be mach 4.5, and it was a solid rocket integrated engine so what was the cutover speed from solid boost to air breathing mode?

Ramjets produce thrust at any velocity above 0kph, and have been  productively used in  operational aircraft (French interceptors) from 200mph on upwards. The French Nord Griffon II, which looks like a Large Mouthed F-16 Falcon, was a ramjet interceptor that had a small turbojet in the core to get it up to ramjet operational speed.
Simple ramjets are designed for a set velocity range and altitude (BOMARC missile being one example) but as such are incredibly simple designs that are cheap to produce. With adjustable ram cones and variable exhaust nozzles (like the turkey feathers used on fighter plane engines today) a ramjet can fly a wide range of speeds. Utilizing active cooling of both ram spike and nozzzle with fuel, and Mass Injection Pre-Compressor Cooling techniques that have been used on turbine jets as well as ramjets, you can cause the air to enter the combustion chamber cooler and denser, so it can operate at a higher velocity. Note that a simple BOMARC missile with a stuck-open fuel injector, no adjustable geometry, went to Mach 5.5 before it burned out on one 'failure' test flight.

[Donosauro]

Note that a simple BOMARC missile with a stuck-open fuel injector, no adjustable geometry, went to Mach 5.5 before it burned out on one 'failure' test flight.

That's very interesting. Any chance you could provide a citation? By "burned out," do you mean it ran out of fuel?

[mlorrey]

Note that a simple BOMARC missile with a stuck-open fuel injector, no adjustable geometry, went to Mach 5.5 before it burned out on one 'failure' test flight.

That's very interesting. Any chance you could provide a citation? By "burned out," do you mean it ran out of fuel?

The source I had gotten that from years ago is no longer online, but correlates also to an ASLAM test flight that suffered a similar fuel control failure in 1980 that also peaked out at Mach 5.5, significantly above its operational speed, again, with minimal inlet adjustability, no shifting of the inlet from Ram to SCRAM configurations, and most importantly,  no MIPCC to cool and densify the inlet air. MIPCC tests on aircraft like the F-4 Phantom showed it can cause the engine to double its operational velocity, so if a standard ramjet can peak at mach  5.5, one  ought to be  able to reach Mach  8-9 with MIPCC, though  with a slight hit to the Isp of the air breathing system, it would still be significantly greater than any rocket engine. An LH2 ramjet/scramjet should get 2500 sec Isp, and kerosene gets about 1500 sec, though this  may  vary depending on whether you are using inlet heat to crack  the kerosene into lighter fractions for chamber combustion or not. The large molecules of Kerosene take longer to burn, though that also depends what grade you are using, JP-3,4,6,7,8 or RP-1...

[rarchimedes]

Citing sources does not equal applicable science. Just because a fairly slow F4 Phantom can double its velocity has nothing to do with doubling the velocity of something already above Mach 4. Drag increases with the square of velocity is a simple and standard and proven quantity. Let us assume for a moment that the doubling or almost doubling of velocity were to occur with a vehicle currently above Mach 4. All the parts of that vehicle, including the MIPCC would need to be able to withstand that increased velocity. Nothing we have or have had can sustain Mach 8-9-10 speeds for very long without melting. Use it or lose it, meaning that the time in that regime must accelerate the vehicle such that it can reach an atmospheric level where resistance is low enough to allow survival, which means essentially "space" before the vehicle melts or decelerate sufficiently to no longer be in danger.

We shall see how reasonable this whole approach is with the fate of the British Skylon SSTO. It is going to require a semi-equatorial airport with extremely thick runways of amazing length to support enor4mous takeoff and landing loads. Those are required for a vehicle with the following spec: (from wikipedia)

Length: 83.133 m^[9]:4 (272.75 ft)

Wingspan: 26.818 m ^[9]:4 (87.99 ft)

Height: approx 13.5 m ^[9]:4 (44 ft)

Empty weight: 53,400 kg^[9]:6 (117,000 lb)

Loaded weight: 325,000 kg^[9]:6 (717,000 lb)

Fuselage diameter: 6.3 m (20.67 ft)

Powerplant: 2 × SABRE 4 synergistic combined cycle rocket engine, 2,000 kN^[9]:6 (450,000 lbf) each

The hydrogen fueled jets at takeoff will damage almost any runway surface and the braking loads on this thing will create heat that has not been dealt with before. Also, there appears to be little potential to scale this beast beyond its initial design spec. Since my concept of the SWALA runway boost/landing vehicle involves only ordinary jet engines, most of these problems go away. Runway loading, however, does not. I would suggest running on rails, which greatly expands the areas where runways can be built.

As for the dangers of being overflown by the vehicles described in this post stream, we have Edwards AFB and the New Mexico Proving Grounds for such purposes and Edwards has landed such hypersonic vehicles for some decades now(the Shuttle and others). And we all know for what Alamogordo has been used in the past. Since all the land speed records have been accomplished on dry lake beds in California like Edwards, Swala as proposed could be done there as could any number of similar proposals. 

Lastly,"Ramjets produce thrust at any velocity above 0kph'', is a true statement without meaning, a non sequitur. The efficiency at slower speeds than the design range is not usable and the ranges at which any ramjet is efficient are far above zero. That is why there are no pure ramjet vehicles. With the land speed record above Mach 1, it should not be too hard to use jet propulsion to raise a vehicle to efficient ramjet speeds. Because of obvious factors, if the same device is to be used for landings, the speed should be kept subsonic.

[edzieba]

The hydrogen fueled jets at takeoff will damage almost any runway surface

Existing hydrogen-fuelled jet aircraft have not had this issue (and one can even convert existing Kerosene turbines to run on Hydrogen). A pure LH2-LOX rocket may do nasty things to a runway, but H2 air-breathing turbine exhaust will differ little from Kerosene turbine exhaust (beyond being less sooty). The air-breathing SABRE at takeoff is in effect a low-bypass turbojet.

[mlorrey]

Citing sources does not equal applicable science. Just because a fairly slow F4 Phantom can double its velocity has nothing to do with doubling the velocity of something already above Mach 4. Drag increases with the square of velocity is a simple and standard and proven quantity. Let us assume for a moment that the doubling or almost doubling of velocity were to occur with a vehicle currently above Mach 4. All the parts of that vehicle, including the MIPCC would need to be able to withstand that increased velocity. Nothing we have or have had can sustain Mach 8-9-10 speeds for very long without melting. Use it or lose it, meaning that the time in that regime must accelerate the vehicle such that it can reach an atmospheric level where resistance is low enough to allow survival, which means essentially "space" before the vehicle melts or decelerate sufficiently to no longer be in danger.

In fact, the point of MIPCC is COOLING, and would be injected, at least in the case of the engine, into the airstream along the surface of the compression ram. Furthermore, SHARP thermal protection materials, such as hafnium boride and zirconium diboride are both stronger and have far greater thermal protection capabilities than CC, inconel or tungsten. Thirdly, the use of fuel as a coolant for heated surfaces, and using the heating as the means of cracking the kerosene into CO and H2 for injection into the engine is superior to  tanked LH2 since LH2 is so non-dense (1/10th the density of kerosene) it requires such large fuel tanks that it creates far more drag  that cannot be overcome by cooling with the cryogenic temp LH2 since the hydrogen has such low capacity to absorb heat compared to the carbon in the kerosene. This is why the Skylons obsession with LH2, like NASAs, will end in failure for that entire program.
The F-4 MIPCC experiments proved that the densification of MIPCC maintained its engine advantage for the full range of flight, the only limiter then was the ability of the F-4 to tolerate high speed heating friction, since it was not designed for that, however current SCRAMjet Xplane tests have also used MIPCC and leading edge thermal cracking of kerosene. Furthermore, Russian hypersonics have been utilizing electromagnetic energy to dissipate shock wave forces and reduce friction along leading edges, energy generated from MHD exploitation of the jet engine airstream thermodynamics.

We shall see how reasonable this whole approach is with the fate of the British Skylon SSTO. It is going to require a semi-equatorial airport with extremely thick runways of amazing length to support enor4mous takeoff and landing loads. Those are required for a vehicle with the following spec: (from wikipedia)

Length: 83.133 m^[9]:4 (272.75 ft)

Wingspan: 26.818 m ^[9]:4 (87.99 ft)

Height: approx 13.5 m ^[9]:4 (44 ft)

Empty weight: 53,400 kg^[9]:6 (117,000 lb)

Loaded weight: 325,000 kg^[9]:6 (717,000 lb)

Fuselage diameter: 6.3 m (20.67 ft)

Powerplant: 2 × SABRE 4 synergistic combined cycle rocket engine, 2,000 kN^[9]:6 (450,000 lbf) each

The hydrogen fueled jets at takeoff will damage almost any runway surface and the braking loads on this thing will create heat that has not been dealt with before. Also, there appears to be little potential to scale this beast beyond its initial design spec. Since my concept of the SWALA runway boost/landing vehicle involves only ordinary jet engines, most of these problems go away. Runway loading, however, does not. I would suggest running on rails, which greatly expands the areas where runways can be built.

As for the dangers of being overflown by the vehicles described in this post stream, we have Edwards AFB and the New Mexico Proving Grounds for such purposes and Edwards has landed such hypersonic vehicles for some decades now(the Shuttle and others). And we all know for what Alamogordo has been used in the past. Since all the land speed records have been accomplished on dry lake beds in California like Edwards, Swala as proposed could be done there as could any number of similar proposals. 

Lastly,"Ramjets produce thrust at any velocity above 0kph'', is a true statement without meaning, a non sequitur. The efficiency at slower speeds than the design range is not usable and the ranges at which any ramjet is efficient are far above zero. That is why there are no pure ramjet vehicles. With the land speed record above Mach 1, it should not be too hard to use jet propulsion to raise a vehicle to efficient ramjet speeds. Because of obvious factors, if the same device is to be used for landings, the speed should be kept subsonic.

The hydrogen fuel, which I'm not a fan of for good reason, is so low mass that the aircraft will not damage the runway, at all. Assuming a vehicle of that size will also have the dry mass of a B-36 Peacekeeper is assumption of facts not in evidence, the Skylon gross wet mass is less than that of a 747 fully loaded. Even if  it were heavier, there are plenty of runways designed for such large aircraft, because, ba-bing, they were built during the cold war in expectation of needing to accommodate the heaviest strategic bombers, and feature runway concrete from 1-2 meters thickness. There is no need for rails. Heck, the training base I was stationed at in my first few months in the military in cornfield illinois had 6 foot thick  concrete  runways. SAC built these in a number of places for good reason.
Ramjet efficiency at subsonic speeds is still significantly greater than that of a rocket engine, and TBCC engines have been built. Aerojet's Pyrojet TBCC has a mach 4 class turbine engine that handles low speeds transitioning to SCRAMjet mode in the hypersonic range.
 I am not sure why you would posit ANY need to land or take off at supersonic speeds.
15years ago I had proposed something similar to your swala concept, the X-106,  taking an F-106 airframe, and radically rebuilding it to be a reusable spaceplane utilizing a Merlin rocket engine, belly scramjet, and underwing ramjets that would be dropped off and recovered. The aircraft would either take off under rocket power, ignited ramjet at 400kt and be refuelled  in flight, then go  for hypersonic, drop  the rams, then ignite  the Merlin at mach 8 and go for orbit. https://www.f-106deltadart.com/piwigo/picture.php?/8012
I covered a few of the issues involved in thermal protection and fuel use here: http://www.islandone.org/Launch/boron-sharp-article.htm

[john smith 19]

We shall see how reasonable this whole approach is with the fate of the British Skylon SSTO. It is going to require a semi-equatorial airport with extremely thick runways of amazing length to support enor4mous takeoff and landing loads.

Of which the US SAC already has at least 3, built in the late 1940's for the B36 (possible 4 as Mildenhall in the UK had a visit from a B36, although I'm not sure if it was fully loaded).
Not exactly the cutting edge of civil engineering.

As for it's GTOW.  It's lower than that of an Airbus A380 and a Boeing 777.

The hydrogen fueled jets at takeoff will damage almost any runway surface

Are you aware that NASA ran tests to run turbofans on LH2 in the 1970's? I've never seen any reports of runway damage as a result. Perhaps your statement should have a "IMHO" in front of it?

and the braking loads on this thing will create heat that has not been dealt with before.

Given a) All airliners have to pass a fully loaded braking test at just below take off speed to get certified and b) Several aircraft exceed Skylon's GTOW you would be wrong.
Given Skylon's high proportion of propellant it's landing weight will be substantially lower than conventional aircraft and have a very short landing run.

Also, there appears to be little potential to scale this beast beyond its initial design spec.

Want to try that with another "IMHO" in front of it?

I'll presume you're just not very well informed rather than being an actual troll. You are now a bit better informed.

[john smith 19]

In fact, the point of MIPCC is COOLING, and would be injected, at least in the case of the engine, into the airstream along the surface of the compression ram. Furthermore, SHARP thermal protection materials, such as hafnium boride and zirconium diboride are both stronger and have far greater thermal protection capabilities than CC, inconel or tungsten.

Lighter than tungsten, yes. More oxidation resistant (without a coating) than CC, yes. But you'd also need to add much more brittle and with a much lower TRL than any of those materials (or just straight molybdenum, which is pretty oxidation resistant, fairly ductile and and be welded).

Thirdly, the use of fuel as a coolant for heated surfaces, and using the heating as the means of cracking the kerosene into CO and H2 for injection into the engine is superior to  tanked LH2 since LH2 is so non-dense (1/10th the density of kerosene) it requires such large fuel tanks that it creates far more drag  that cannot be overcome by cooling with the cryogenic temp LH2 since the hydrogen has such low capacity to absorb heat compared to the carbon in the kerosene. This is why the Skylons obsession with LH2, like NASAs, will end in failure for that entire program.

Statements like this have so many hidden assumptions in them that they are pretty meaningless without stating all the context. I recommend anyone with such firm convictions in their PoV to go out and raise the money for their preferred approach and demonstrate its superiority.

You might like to keep in mind that the reason why the Martin Suntan vehicle lost to the SR71 was not that it was felt an LH2 M3 aircraft was impossible but the grave doubts over the vacuum insulated tank technology

however current SCRAMjet Xplane tests have also used MIPCC and leading edge thermal cracking of kerosene. Furthermore, Russian hypersonics have been utilizing electromagnetic energy to dissipate shock wave forces and reduce friction along leading edges, energy generated from MHD exploitation of the jet engine airstream thermodynamics.

Could you provide references for those statements? IIRC the X43b used RCC but no active cooling. I think Zubrin was involved in some project for the USN but I don't recall wheather it got to flight test.

Ramjet efficiency at subsonic speeds is still significantly greater than that of a rocket engine, and TBCC engines have been built. Aerojet's Pyrojet TBCC has a mach 4 class turbine engine that handles low speeds transitioning to SCRAMjet mode in the hypersonic range.

As are all air breathing systems. I will note the USAF designed a low cost subsonic ramjet in the M0.7-0.9 range for target drone applications. The tough part about Swala's use of them is continuing to operate from M0.7-M3+ IE through the subsonic to supersonic transition.

I am not sure why you would posit ANY need to land or take off at supersonic speeds.

Indeed. RASV had a higher takeoff speed than Skylon. 

[CameronD]

Thirdly, the use of fuel as a coolant for heated surfaces, and using the heating as the means of cracking the kerosene into CO and H2 for injection into the engine is superior to  tanked LH2 since LH2 is so non-dense (1/10th the density of kerosene) it requires such large fuel tanks that it creates far more drag  that cannot be overcome by cooling with the cryogenic temp LH2 since the hydrogen has such low capacity to absorb heat compared to the carbon in the kerosene. ...

I'll pipe in here to say no.  Absolutely no.  Fuel is regularly used as a coolant, but even if it were possible to crack kerosene into CO and H2 (and I'm yet to be convinced it is) the equipment required to do so, and to deal with all of the various by products and other contaminants like sulphur, would render the system so inefficient, complex and heavy that the vehicle would never leave the ground.  You'd do better cracking water.

[john smith 19]

I'll pipe in here to say no.  Absolutely no.  Fuel is regularly used as a coolant, but even if it were possible to crack kerosene into CO and H2 (and I'm yet to be convinced it is) the equipment required to do so, and to deal with all of the various by products and other contaminants like sulphur, would render the system so inefficient, complex and heavy that the vehicle would never leave the ground.  You'd do better cracking water.

Cracking is a routine process in the petrochemicals industry. The heat can be generated either from exo thermic chemical reactions in other parts of a particular product flow or combustion of some part of the feedstock to raise high pressure steam. Catalysts can lower the pressure and temperature requirements and improve specificity, narrowing the range of products.

AFAIK Zubrin was involved some sort of USN project to use this process to build a hypersonic ramjet that didn't need stored H2 to fly, presumably using a SCramjet.  I know nothing more than this.
So the outline (using heated catalysts to split long molecules into shorter molecules) certainly exists and even more recent attempts have been made with very selective fuels like JP10 (essentially one chemical)

Coking is a big issue and while better catalysts have been found I don't think anyone has found the perfect one.

But that stuff can be done in small samples in a lab, with computer simulation for assistance. IIRC some of the new stuff uses artificial zeolites to crack the fuel to imidenes and 5 mols of H2.

This is not a conventional heat exchanger. 

It is an HX wrapped around the surface of a flight vehicle with bulk injection of the fuel at one end leading to bulk collection of the cracked reaction stream from the other for onward flow to the engine(s).

With an internal catalytic layer to lower the skin temperature (allowing a thinner, lighter skin to be used)

Engineering such a component with no leaks (or at the least no leaks that cannot be repaired) with an even internal coating layer will be extremely difficult with little or no control over the shape of the vehicle it's going to be wrapped around. 

This may be an acceptable trade off to avoid LH2 in military systems.

Wheather or not it could be justified in a privately funded project versus other options with LH2 as the fuel is another matter.

Like the SCramjet it's one of those ideas that sounds quite simple and something like it already exists.
The troubles start (like the SCramjet) when you come out of the lab and try to scale it up. It's not impossible, but it is very difficult to engineer. 

 

[mlorrey]

Thirdly, the use of fuel as a coolant for heated surfaces, and using the heating as the means of cracking the kerosene into CO and H2 for injection into the engine is superior to  tanked LH2 since LH2 is so non-dense (1/10th the density of kerosene) it requires such large fuel tanks that it creates far more drag  that cannot be overcome by cooling with the cryogenic temp LH2 since the hydrogen has such low capacity to absorb heat compared to the carbon in the kerosene. ...

I'll pipe in here to say no.  Absolutely no.  Fuel is regularly used as a coolant, but even if it were possible to crack kerosene into CO and H2 (and I'm yet to be convinced it is) the equipment required to do so, and to deal with all of the various by products and other contaminants like sulphur, would render the system so inefficient, complex and heavy that the vehicle would never leave the ground.  You'd do better cracking water.

Sorry bro, you are about 15 years behind the times. US ONR launched a JP-10 fueled SCRAMJET powered FASTT vehicle in 2005. The JP-10 was used for active cooling, of both leading edges, compression ramp, and exhaust thrust ramp, which provided the energy to crack the JP-10 into H2, CO, and methane which were then injected into the scramjet combustion zone.
https://www.newscientist.com/article/dn8485-scramjet-missile-powered-by-jet-fuel/

If you are going to post negativity about tech here you should at least be doing your homework to know what the tech is.

[john smith 19]

Sorry bro, you are about 15 years behind the times. US ONR launched a JP-10 fueled SCRAMJET powered FASTT vehicle in 2005. The JP-10 was used for active cooling, of both leading edges, compression ramp, and exhaust thrust ramp, which provided the energy to crack the JP-10 into H2, CO, and methane which were then injected into the scramjet combustion zone.
https://www.newscientist.com/article/dn8485-scramjet-missile-powered-by-jet-fuel/

True.  This paper discusses fairly recent US work in the field, including that project, the X51 and the gun launched test article using ethylene. The last liquid fueled gun launched ramjet design I'm aware of used the much more toxic carbon disulphide. It got to about M3 and gave the projectile about a 300Km range.

But note these tests have been of missile sized vehicles at most, not launch vehicle sized (and certainly without wings) and IIRC the report points out (page 6 diagram) that the coking limit for keroscine derived fuels puts their operating maximum mach limit at M8. Above that  you're looking to switch to H2 fuel or full rocket.

As usual it's a trade off.  The military want kero based fuel because it avoids cryogens on a military vehicle. Would a company developing some kind of ram/scramjet engine system feel it was easier? The pragmatic approach of Johns Hopkins dual mode (liquid fuel from M2-8 say, then H2) is an option.

The real question with any SCramjet system is wheather or not the design tools are there so you can design a vehicle below full scale with the confidence when you scale up it will behave exactly as you predict from the flight tests at sub scale.

So far the comment by at least one advocate has been essentially "Build one (at full scale) and throw it away," partly because they tend to use the whole body of the vehicle as part of the engine, so any changes have huge knock on effects throughout the whole design.
That does not inspire confidence. 
Meanwhile the X51 longest flight of any SCramjet powered vehicle anywhere is 210 secs.
It's underwhelming for a technology that's sunk (in the US) at least $10Bn since 1960 and delivered no operational system.

[mlorrey]

Sorry bro, you are about 15 years behind the times. US ONR launched a JP-10 fueled SCRAMJET powered FASTT vehicle in 2005. The JP-10 was used for active cooling, of both leading edges, compression ramp, and exhaust thrust ramp, which provided the energy to crack the JP-10 into H2, CO, and methane which were then injected into the scramjet combustion zone.
https://www.newscientist.com/article/dn8485-scramjet-missile-powered-by-jet-fuel/

True.  This paper discusses fairly recent US work in the field, including that project, the X51 and the gun launched test article using ethylene. The last liquid fueled gun launched ramjet design I'm aware of used the much more toxic carbon disulphide. It got to about M3 and gave the projectile about a 300Km range.

But note these tests have been of missile sized vehicles at most, not launch vehicle sized (and certainly without wings) and IIRC the report points out (page 6 diagram) that the coking limit for keroscine derived fuels puts their operating maximum mach limit at M8. Above that  you're looking to switch to H2 fuel or full rocket.

As usual it's a trade off.  The military want kero based fuel because it avoids cryogens on a military vehicle. Would a company developing some kind of ram/scramjet engine system feel it was easier? The pragmatic approach of Johns Hopkins dual mode (liquid fuel from M2-8 say, then H2) is an option.

The real question with any SCramjet system is wheather or not the design tools are there so you can design a vehicle below full scale with the confidence when you scale up it will behave exactly as you predict from the flight tests at sub scale.

So far the comment by at least one advocate has been essentially "Build one (at full scale) and throw it away," partly because they tend to use the whole body of the vehicle as part of the engine, so any changes have huge knock on effects throughout the whole design.
That does not inspire confidence. 
Meanwhile the X51 longest flight of any SCramjet powered vehicle anywhere is 210 secs.
It's underwhelming for a technology that's sunk (in the US) at least $10Bn since 1960 and delivered no operational system.

The military intelligently  wants on board tankage of hydrocarbons because it has high energy density (that  is not per kg, but per cubic meter). H2 has very low volumetric energy density, hence it requires, in addition to complex  and dangerous cryogenic handling, much larger tanks for the same dV of a much smaller hydrocarbon tank. Tank volume matters to hypersonics, because  a hypersonic vehicle must be highly streamlined, and has limited  interior volume. A vehicle bloated by a huge H2 tank will not only necessarily be more massive, but have significantly greater  aerodynamic drag, thus limiting its maximum speed to much  less than that claimed potential. The "experts" say H2 can be used on hypersonics to  mach 25 flight, but  that simply is  not the  case, because H2 takes up too much space causing too much drag. H2 is a great fuel, but terrible payload.
Yes,longer chain hydrocarbons have serious coking issues, though jet fuels issues with coking  have far  more to do with the presence of sulfur in them than the  long  chains. More highly refined RP-1 helps  to remove most of the coking issues, allowing active cooling thermal management to simultaneously crack RP-1 into methane and H2 (and introducing water to  improve cracking is  actually exothermic so you can use this cracking reaction to power  fuel pumps), so that the scramjet combusts methane and H2 to maximize Isp, so you can get speeds higher than Mach 8, closer to M12-14, at which point the SCRAMjet should be transitioning to rocket mode anyways with onboard  LOX to power into orbit. It is really a waste of energy to try to go any faster in atmosphere, the atmospheric  losses to dV grow exponentially and eliminate all Isp advantages beyond that point.

[edzieba]

Sulphur presence is orthogonal to coke formation. Forming coke is dependant on operating temperature: get too hot, and coke forms. That itself puts a speed (+altitude) limit on your craft if you use heat sunk to fuel to provide leading edge cooling. On top of that, unless your scramjet can handle arbitrary hydrocarbon mixes you also need to precisely manage leading edge heat in order to crack the stored fuel down to the fraction desired for burning within the engine. With heat dependant on speed + pressure (and thus altitude) this ends up with a vehicle that must travel at a certain constant speed and altitude combination in order to operate its engines.
On top of that, cracking RP-1 (or any other long-chain hydrocarbon or hydrocarbon mix) in order to output Methane or H2 will result in residual Carbon. Even Propane - the shortest chain amenable to non-cryogenic storage - is going to give you one wayward Carbon atom for every two Methane molecules you crack it into (assuming 100% perfect process chemistry), and that Carbon coke needs to be rejected somehow or end up as solid in your plumbing.