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I have the impression that no scramjet has been realized so far. But the engine of 3M22 Zircon is reported to be a scramjet. Is it really a scramjet?

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  • $\begingroup$ Perhaps the hypothetical design you're thinking of is a shcramjet, not a scramjet? en.m.wikipedia.org/wiki/Shcramjet $\endgroup$
    – Someone
    Sep 9, 2023 at 2:41
  • $\begingroup$ @Someone: Why do you think so? The US program only just started testing: en.wikipedia.org/wiki/Hypersonic_Air-breathing_Weapon_Concept $\endgroup$
    – Hans
    Sep 9, 2023 at 2:55
  • $\begingroup$ The schramjet is still hypothetical, and the name is quite similar, so I was wondering if you heard/read that shcramjets are still hypothetical, and thought it was referring to scramjets. $\endgroup$
    – Someone
    Sep 9, 2023 at 3:07
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    $\begingroup$ @Someone: I see. This is the first time I heard of schramjet. Good to know. $\endgroup$
    – Hans
    Sep 9, 2023 at 3:36

1 Answer 1

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Speculatively possible.

I've searched if the manufacturer has made such a claim. However, they aren't making any claims. The only explicit claims they make is a press reprint about the specifications: that it flies at 2.65 km/s at an altitude of 20 km. Your link includes verified range figures of 350, 450, then 1000 km.

Perhaps one could determine if it's likely to be a scramjet indirectly, by analyzing if this performance could have been reached by another type of engine. First checking rockets:

  • The first 2.65 km/s of delta-V goes towards acceleration. For a (very good) solid rocket motor at Isp~=265, that requires Wi/Wf=e, in other words, 63% of the missile's mass just to get it to speed. 70% or more if the motor is discarded.
  • The Breguet equation for range in sustained aerodynamic flight is R = V * L/D * Isp * ln (Wi/Wf).
  • At a roughly estimated L/D=3 and fuel weight fraction of 0.35, R = 2650 * 3 * Isp * 0.43 ~= 3400 * Isp, for range in meters.
  • Solid rocket propellant would produce Isp in the 230-270 range, giving a range of 850 km. This is close enough to 1000 km if some speed is traded for range or L/D exceeds 3.

It's not easy to research a weapon that's still under a lot of secrecy. I had hoped that Russian-language articles would be closer to the source, as they usually are, but all are clearly the work of analysts not involved in the missile's development. This is the best I've managed to find. It confirms again that the missile uses a synthetic hydrocarbon fuel (JP-10 equivalent) and "a special ramjet engine, which is characterized by supersonic combustion". That would be the definition of a scramjet. Another article digs into listing every test, including launch footage, and attempting to estimate the missile's exact shape and dimensions from OSINT.

Mass is not advertised, but considering that the Zircon is a bit smaller than the missile it replaces, it can't be more than 3,000 kg total. That leaves a maximum weight of 900 kg for the second stage. With 35% for fuel and 30% for airframe+engine, its weight budget falls 20-25% short of that required to fit a 300 kg warhead and at least 100 kg in avionics.

So, it's possible to achieve the 350-450 km range from early tests without using a scramjet engine. A combination of rockets or air-augmented rockets could reach this velocity and range. For the later long-range tests, the warhead would have to be removed or greatly reduced.

Overall, a rocket engine is very unlikely. This missile is a successor of a long line of ramjet missiles. Its shape clearly indicates an airbreathing engine inside. The manufacturer doesn't explicitly state they're using a scramjet, but regular ramjets or other engines can't run at Mach 7. Scramjet engines have been studied and tested extensively, in various forms, and could realistically be used there.

Changing the equations to use a rocket to get to half speed, then a scramjet for the rest brings different math:

  • Accelerating to 1.3 km/s with a solid rocket requires 40% mass in fuel, or 45% with the motor.
  • Assuming a very conservative 700s Isp for the main engine, the remaining 1.4 km/s will take 1-1/e^(1400/7000)=18% mass in fuel.
  • The Breguet equation, after removing 18% spent on acceleration, computes as R = 2650 * 3 * 700 * ln(0.82/0.65) ~= 1,292,927, i.e. ~1,290 km.
  • To reach the target range of 1,500 km, fuel fraction has to be increased a bit. At 40% fuel, estimated range increases to 1,738 km, so it would be in between.
  • For a second stage at 1650 kg total, possible weight breakdown computes as 660 kg (40%) fuel, 550 kg airframe+engine, 340 kg warhead, 100 kg guidance.

The missile looks like it has a smaller booster than 45% by weight, though. But it's possible, considering that the second stage has a non-circular shape.

More likely, the missile uses a dual-mode ramjet, rather than a straight scramjet. Unlike the rest I've had to refer to, this article comes from a trusted source, having been published by the Von Karman Institute and republished by NATO.

Dual mode ramjets are a cross between ramjets and scramjets, able to operate in both subsonic and supersonic combustion modes. A DMR allows for an earlier takeover from booster to primary engine, improving range and payload capacity.

Of particular interest is the joint program between MBDA (French missile manufacturer) and MAI (Russian aviation research center) to develop a "wide range ramjet" and a "dual mode ramjet", covering the range from Mach 2 to Mach 12. The program was extensive on both sides, with a lot of prototypes. According to the article, testing at MAI's hypersonic wind tunnel has validated Mach 2-7.5 wide-range ramjet engines. It appears that this program has culminated in the Meteor missile using a wide-range ramjet and the Zircon missile using a dual-mode ramjet engine.

A DMR is also more consistent with modest statements about a "special ramjet supporting supersonic combustion", rather than an entirely different engine.

With a dual-mode ramjet, range estimates change:

  • Solid rocket booster is needed up to 700 m/s, consuming 26% mass in fuel, or 30% including the motor.
  • At the same 700s Isp for the DMR, the remaining 2 km/s will take 1-1/e^(2000/7000)=25% mass in fuel.
  • Using another 15% for cruise, Breguet computes as R = 2650 * 3 * 700 * ln(0.75/0.60) ~= 1,241 km.
  • At 2000 kg, the second stage might include 800 kg fuel, 600 kg airframe+engine, 400 kg warhead, and 200 kg guidance.

That version is consistent with current and intended range, is on the lower end for booster size, and leaves margins for heavier guidance or lighter launch weight. 2,850 kg is assumed here, but it could be as little as 2,000-2,400 kg with a lighter airframe or guidance package. It's also possible that the ramjet takes over a little later, maybe at Mach 3, driving a larger booster and a smaller second stage.

Summary

  • The missile's specifications are consistent with a scramjet engine.
  • A dual-mode ramjet is also a possibility, consistent with the missile's specifications, history, appearance, and research programs.
  • Test results are not consistent with other engine types. Rockets could replicate them, but with no room for a warhead.
  • The engine appears to be a "live prototype" that's still being improved. It falls short of the theoretical abilities of a scramjet, being more similar to an early iteration.
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  • $\begingroup$ Care to look at my follow-up question aviation.stackexchange.com/q/100838/37156? $\endgroup$
    – Hans
    Sep 11, 2023 at 13:34
  • $\begingroup$ @Hans Seen it. It's a very difficult question to answer. Much of that knowledge is TS/SCI or local equivalent. While there's some hope that scramjets will result in hypersonic passenger aircraft, right now their most likely application is missiles that destroy billion-dollar warships without warning. I'll try to respond with what I can produce based on open data. $\endgroup$
    – Therac
    Sep 11, 2023 at 14:07

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