> could an adversary surround the warhead with absorbent chaff as a countermeasure
That would require a constant stream of chaff (it would get left behind pretty quickly without any thrust), and would need to be shot out in the opposite direction of travel (lowering the missile speed the entire time), and require the chaff and its launch mechanism to be part of the payload (increasing weight).
That would require a constant stream of chaff (it would get left behind pretty quickly without any thrust), and would need to be shot out in the opposite direction of travel (lowering the missile speed the entire time), and require the chaff and its launch mechanism to be part of the payload (increasing weight).