The essential contradiction of hauling oxygen up through an atmosphere full of the stuff was ignored.
So were the benefits that this atmosphere bestows in the form of providing lift to airfoils.
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 a stalking horse: I wanted to see what practical objections there were to this idea. None emerged.
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?
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.
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!
But could this be higher? Faster? Here is a thought experiment.
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.
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.
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 kgShell 1,300Payload 500Guidance/control 300Total 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.
SWALA AND THE MONEYThe 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 (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.
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..