TerraN, now you're getting me all messed up
I thought we were specifficly discussing beamriding systems. In those, contrary to your discription, there's no seeker in the missile head to look for reflected laser / radar energy. The operator keeps his crosshairs centered on the target, causing a coaxially mounted laser / radar emitter to emitt in the same direction. The sensors in the tail of the missile then try to keep the missile centered in that beam were the signal is at it's strongest. And I don't really believe a laser based system is at a speed / agility disadvantage here, since there is a working SAM system based on that principle. The RBS 70 is capable of engaging maneuvering airplanes.
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I have now also looked back at the video with the ATF-10 operation. Looks like the missile's sensor feed is indeed transmitted to the operator via fibre optic cable to allow him to command the missile. Would be interesting to know if the missile is able to continue tracking autonomously if the cable is cut.