airship...
<<That a shuttle be permanently positioned at the ISS in order to perform SAR missions in near-Earth orbit>>
<<That future missions rigourously incorporate the ability to "proceed by their own means to the ISS". >>
I think you are not understanding the problems of "orbit". It is massively difficult to rendevous when it is the aim of the mission. To do so on an ad hoc basis, particularly when something has gone wrong = degraded capability is just impractical.
If you persue this line, the best place for the "lifeboat" is on earth. At that point it has the potential to be launched into the desired orbit - i.e. match that of the "stricken" craft. If you go this route, then a criteria for launch is that this lifeboat is "ready to go".
<<If future space missions are to be pursued, then it is high time that these cease to be regarded as a "dice with death".>>
IMHO you've summed it up here. What value do you place on human life, particularly when those whose lives are at risk know far better than you and I the risks, and accept them.
Interesting website:
http://nasaproblems.com
In the 2 shuttle accidents to date, I do not think an escape capsule would have been of any value...
NoD