<i>Columbia</i>&#x27;s last mission wasn&#x27;t an ISS mission. They had a pretty limited amount of time before it became hard to breathe. There was a potential rescue option in the form of <i>Atlantis</i> which was already being prepped for another mission and could have been redirected to pick up the <i>Columbia</i> astronauts, but it would have been a big rush and would have required getting things rolling fairly rapidly after they became aware of the ice strike.