I have a question Garry, it's not related to viruses but with the creation of Zirconium scramjet cruise missile, what's the likeliness that scramjets find their way on to S-400/S-500 SAM missiles? Will it allow the missiles to have increased speed and range but with smaller dimensions, or is this just pure fantasy and not applicable to SAM missile fundamental properties?
It is all about design compromise. Ramjets are like jet engines and are relatively efficient... though for use in aircraft the key is re usability, so a jet aircraft is more efficient than a rocket powered aircraft for day to day flights. when the goal is to get to space however the jet just can't give enough speed so the Space Shuttle and Buran are rocket powered, which is expensive but to get to orbital speeds there really is no current alternative in terms of jet engines.
With designs of missiles low cost becomes critical as these engines will only be used once, so rocket and ramjet and now scramjet are the three competing options. In terms of volume a ramjet requires internal space to burn the fuel, though modern Russian ramjets use that internal space to fit a rocket engine to get the missile up to speed before the ramjet is started which means multi stage rockets are not so critical, though technically it is a multi stage rocket/ramjet.
The critical technology however is scramjet engines which in theory have no top speed, yet are fundamentally simple devices with few moving parts and no blades or shafts or "turbine" sections.
The huge advantage of a scramjet is the ability to throttle.
Solid fuel rockets are baked like cakes. to make them lighter they have the centre hollow, so instead of burning from one end to the other like a fuse, they burn from the centre outward, which means the walls of the rocket can be made thinner and lighter because as the rocket burns the pressure pushes out sideways is supported by the remaining fuel left to be burnt. Making the hold up the middle star shaped increases the surface area of the rocket fuel burning. the inner layer that burns first is high energy fast burning fuel generating high thrust to launch the missile and accelerate it rapidly to high speed. the next layer is slower burning that takes much longer to burn and does not accelerate the missile, it just allows it to cruise without losing speed for a few minutes.
A missile has a peak speed where drag overcomes the thrust and so any extra thrust is largely wasted... once the missile gets to that speed then continuing to burn at full thrust is a waste of energy. Simple calculations can be made to determine how long the high energy fuel should burn with the remaining fuel being much slower burning to maintain speed for much much longer and greatly extending flight range.
For S-400 et all the calculations are made easier because they are all ground launched and start from zero speed.
An AAM on the other hand might be launched from a hovering helo, or a high flying MiG-31 at mach 2.6.
Ramjets are efficient high speed jet engines where air is sucked in, fuel is added and burned and is blasted out the back generating thrust. You can throttle up and down depending on where you are and where you want to go.
Ramjets were tested on the I-15 Polikarpov Biplane and don't need to be moving through the air at very high speed to work, though obviously they are most efficient at higher speeds.
Solid fuel technology has improved significantly, so the Solid rocket SA-11 and SA-17 replaced the rocket ramjet SA-6 in service some time ago. For very long range however the turbojet powered Granit has been replaced by the ramjet powered Onyx... the range is shorter, but the missile is about 4 tons lighter too... the Granit is 7 tons and the Onyx is about 2.5 tons in the air launched model.
Scramjets offer even higher speed and efficient use of fuel with the added benefit of a throttle, but the main problems remain volume and of course the need for rocket launch.
Creating a scramjet S-400 likely wouldn't make it smaller or lighter, so I doubt they will bother, but for very long range very high speed missiles scramjet propulsion will probably be the mode of choice.
Scramjets characteristics are still relatively unknown, so Ramjets would be the safer bet. Ramjets also allow for the missile to throttle down to around Mach 1, which could improve range dramatically.
A scramjet is merely a ramjet that is designed so that the fuel can be burned at supersonic speed. The intake ramp on an F-16 was simplified and fixed which is what limits it to mach 2 or less. The intake ramp contracts at high speed and reduces the amount of air coming in the front of the aircraft at high speed. With its simplified fixed ramp the F-16 can't go faster than mach 2 because the air coming in is coming in too fast and would choke its engine. A scramjet on the other hand could take air coming in at any speed and still produce thrust.
the ramjets tested on the I-15 biplane increased flight speed by something like 85km/h and could be operated at speeds as low as 100km/h.
Like any engine aircraft combination certain configurations will be efficient, so you might find that a missile with a ramjet engine might operate best at around mach 2.5 or so, but scramjets would likely operate most efficiently above mach 5-6.
The Russians put a scramjet engine on the nose of an SA-5 SAM which replaced the warhead and guidance section with a small scramjet engine and fuel, so the missile is launched... its solid rocket boosters burn and fall away, the main rockets burn till the missile gets to about 15,000 m altitude and mach 5, when the scramjet engine on the nose of the missile is started. It accelerates the entire missile from mach 5 to mach 6.5 and burns for about 180 seconds... in other words about 3 minutes.
In those three minutes of burn time when the small scramjet operates the missile covers about 350km.
The limit of a turboprop engine is the speed of sound, the limit of a turbojet engine is about mach 3 in conventional mode. The limit of a ramjet engine is mach 5-6 or so. The limit for a scramjet is heat. If you had materials that could take the heat and speed a scramjet can take you to orbital speeds... into space... though in space it would no longer function of course.