Why did they kidnap the astronauts instead of kill them?

Maybe I missed something or I am thinking about it too much, but I don't understand why Spectre just didn't launch missiles towards the spacecraft and destroy them in order to have war break out between the US and USSR instead of kidnapping them.

Anyone could use missiles. SPECTRE was demonstrating a superior technology and convincing the US that Russia was in possession of it, and vice versa. Besides, a hidden missile base would not be as impressive as what Ken Adam conceived. Moreover, Bond needed the astro/cosmonauts' help suiting up in order to replace the SPECTRE pilot (although it would have made more sense for one of them to have gone).

I'm probably the one overthinking it.

Oh yes I know Bond needed the astronauts help it's just that Specter does not want this to happen of course, so I was wondering their motivation for keeping the astronauts alive.

Also, even if a missile is not as impressive, I thought that firing missiles at a Russian spacecraft and an American one, would be enough to provoke war, perhaps even more so, as oppose to kidnapping with technology?

Plus I thought a hidden missile base would be just as impressive as long as Ken Adam made it just as goodlooking, like a hollowed out volcano and all.