[r9etb]

5- a rescue vehicle prepositioned at the ISS for the express purpose of emergency rescues via orbital navigation docks with shuttle
6- shuttle personnel transfer into orbital rescue vehicle for return trip to ISS

There's your problem right there. At a minimum, this little maneuver requires a plane change of 24 degrees, and in reality a net plane change much larger.

The delta-V required to perform a plane change is given by:

delta-V = 2 * V * sin(plane change/2)

At LEO, the orbital velocity V is about 7700 m/sec, so the minimum net delta-V is 3200 m/sec -- which requires an enormous amount of propellant. (In reality, you'd probably have to budget at least 10,000 m/sec for a generic rescue capability, which is ruinously expensive.)

[freepersup]

If the shuttle expends it's remaining onboard fuel in an all out effort to reposition itself into the deepest (?) orbit possible (under the circumstances),

and if the ISS expends it's remaining onboard fuel in an all out effort to reposition itself into the shallowest (?) orbit possible (under the circumstances),

would there now be a realistic chance for a rescue with such a proposed rescue vehicle ?

Granted, it's all hypothetical as we play out the 'what if' scenarios.

One cannot dismiss the possibility that someday, something else may go wrong with the shuttle (in this example) while in Earth orbit. re: Murphy's Law

As an 'after market' add on to the ISS, a unit or module expessly designed as a berth for a rescue vehicle, seems conceiveable from a design and production stand point. One of the future modules could be re-engineered to accept and support the rescue vehicle, with costs proportional to what other modules of unique and specific purpose and or design cost.

I believe this aspect is realistic.

I must confess that I am illiterate regarding the discipline of aeronautical engineering and likewise in the sister field of astronomical physics, so I am not going to portend otherwise.

However, I would like to participate in pro-active problem solving, concerning the 'what if's' of future emergencies in space flight, and more particular, specific to the shuttle program.

If we close the gap between the shuttle and the ISS, would a rescue vehicle now be a viable option ?

Could fuel, of sufficient quantity, (to propel the rescue vehicle), be shuttled to the ISS for storage and future use ?

In this scenario, it is a given that the shuttle would be sacrificed (if need be) to save the lives of the crew, and it is a given that the ISS would be sacrificed (if need be) to save the lives of the crew, in an all out effort to rescue the stranded, imperiled shuttle occupants.

For obvious reasons, the current occupants of the ISS would have to escape the ISS using the onboard capsule, once re-positioned, should such a rescue maneuver result in the future demise of the ISS.

The rescue vehicle could be designed to either return to Earth, along the lines of a Mercury capsule, or, return to the ISS, where the crew would await rescue by more traditional space vehicles of the US of A, or Russia.

Granted the US of A would have to implement a major space program akin to the Apollo project, if a space rescue vehicle lacked the ability to return to Earth. Otherwise, dependency for rescue would fall to the Russians exclusively, as they would have to launch a 'taxi service' to the ISS in order to return the shuttle crew to Earth.