eloise wrote:For the sake of discussion

Photo of AIM-120B and Meteor's booster and fuel

Capture.PNG

Meteor's booster is 69% the length of AIM-120B's propellant

Meteor's ramjet propellant stage (not including control valve,fuel injector, MSIU, IB-igniter) is 40% the length of AIM-120B's propellant

Because the IPS of ramjet engine is 3 times better than traditional rocket motors

=> Meteor ramjet propellant stage worth 40*3 = 120% the length of AIM-120B propellant

In total, 120+69 = 189%.

Is it correct to think Meteor is similar to AIM-120B with 189% fuel?

When trying to make that comparison, there are lot of known unknowns, and a bunch of unknown unknowns as well

Instead of comparing actual missiles, I'll try to ballpark what ISP advantage a VFDR powered missile might have over a conventional solid rocket motor.

I imagine that ~20% of the propellant mass can be shaved off to account for the inlets and gas generator hardware that isn't needed on the conventional missile. Of the remaining ~80% fuel mass, maybe half of it is used for the booster to get the missile up to speed. The remaining ~40% is not devoid of oxidizer (the graphic describes it as "oxygen deficient"), so let's call it 2.5x ISP compared to a conventional solid rocket. That means we get 40% + (40% x 2.5) = 140% ISP, or a mere 40% advantage. Is that enough to overcome the increased drag of the inlets? Maybe in some (possibly most?) flight profiles, but probably not in all of them.

Obviously, I'm pulling the 20% and 2.5x numbers out of my posterior, but whatever those values are, they have to be accounted for. The ISP multiplier in particular will vary greatly with speed. I would expect something like 2.5x for the optimal speed (Mach 3 maybe?), but less as the speed goes up or down from there.

My gut tells me that Meteor will have a massive advantage over an AIM-120D when chasing down a bandit running away at low altitude, but the Slammer launched from altitude on a lofted trajectory will come very close to the performance of the Meteor, and may even beat it.