>A surface-to-air missile -- after its fuel is burnt out and its payload is detonated -- is basically nothing more than a thin tube.
No, no, no. Modern SAM missiles have either a continuous rod warhead, a quite substantial affair that on detonation will spread shrapnel to a substantial range, or, even worse in this context, are kinetic killers like the HVM Starstreak the UK DoD is deploying. A kinetic killer is a heavy metal rod with some guiding fins that is propelled to hypervelocity (Mach 3.5 for the Starstreak) by a first stage. The Starstreak has 3 of these. There's a strong possibility that they stay intact after hitting their target, as aircraft are more flimsy than armoured combat vehicles, or even worse, some of the 3 will miss the target. What happens then is easy to guess: is goes on a ballistic trajectory at a high Mach speed, and in a dense urban area, may hit something fragile and cause some damage. Each of the 3 Starstreak submunition has as much energy as a 40mm Bofors shell.
So your scenario of "they'll gently come down" is far off target.
Edit: the Starstreak submunitions also have an explosive payload so they won't stay intact neither on hitting nor missing the target. The raining shrapnel caveat still applies, but shrapnel slows down beyond a few hundred meters.
That edit is an important caveat: the Starstreak is not a kinetic killer, but a kinetic penetrator. Half its weight is explosives, and after those detonate, the rest would turn into very small bits.
Of course an intact Starstreak submunition is very definitely something you that wouldn't want landing on your roof. But fragments from half a mile overhead? Not such a problem. Certainly not pleasant, and possibly a bit dangerous -- but probably no more than things that London drivers do hundreds of times every day already.[1]
[1] NB: I'm not a weapons engineer, but I do live in London. So to that degree, at least, I know of what I speak.
No, no, no. Modern SAM missiles have either a continuous rod warhead, a quite substantial affair that on detonation will spread shrapnel to a substantial range, or, even worse in this context, are kinetic killers like the HVM Starstreak the UK DoD is deploying. A kinetic killer is a heavy metal rod with some guiding fins that is propelled to hypervelocity (Mach 3.5 for the Starstreak) by a first stage. The Starstreak has 3 of these. There's a strong possibility that they stay intact after hitting their target, as aircraft are more flimsy than armoured combat vehicles, or even worse, some of the 3 will miss the target. What happens then is easy to guess: is goes on a ballistic trajectory at a high Mach speed, and in a dense urban area, may hit something fragile and cause some damage. Each of the 3 Starstreak submunition has as much energy as a 40mm Bofors shell.
So your scenario of "they'll gently come down" is far off target.
http://en.wikipedia.org/wiki/Starstreak http://en.wikipedia.org/wiki/Continuous-rod_warhead
Edit: the Starstreak submunitions also have an explosive payload so they won't stay intact neither on hitting nor missing the target. The raining shrapnel caveat still applies, but shrapnel slows down beyond a few hundred meters.