The only US-allied nations with runways long enough to land a space shuttle are Spain, Canada, France, and India. For a polar mission the Canadian runway is no more useful than the American runways, and the Spanish and French runways are too far from the Pacific Ocean, where the orbiter needs to come down. Perhaps the shuttle could make two orbits and then land in India, using those big heavy wings for crossrange.

However, I am looking at the Wikipedia list of runways in service today. I'm not about to embark on looking at historical data.

Compared to the cost of building/certifying/maintaining/launching a shuttle based nuclear capability - the relative cost of building redundant landing sites is trivial. Although I am surprised that the salt-lakes or groom lake runway couldn't be used for a shuttle landing site on a polar orbit.

The core shuttle design to have rocket engines on the orbiter makes substantially more sense if there was at one point a planned orbital delta-v component. Orbital delta-v really only makes sense for military applications involving satellite capture/servicing or nuclear strike. As all of these can be better done with missiles/robots, there isn't much advantage in a space shuttle except for the case where the payload must be returned from orbit. On a polar trajectory the only use cases where this would make sense are spy satellite returns or weapons missions. Replacing the spy satellite entirely is obviously cheaper than returning and refurbishing it - which leaves a weapons use case which was likely discarded sometime late in the program when it was determined to be logistically infeasible or difficult to pull off.

Not in the Pacific, but RAF Machrihanish could also be used.

That's nowhere near the ground path of a polar launch from either Vandenburg nor the Cape on the first few orbits, though.

True, I was responding to your post "the only...nations...".

Oh, I see, thanks.

Yes, most (maybe all) shuttle rollouts were less than the 10000 length of the Machrihanish runway, but that's really cutting it close. SLF Florida is 15000 feet. But I guess if the situation is so bad that the shuttle needs to come down outside the US, it's probably not going to be used again so why not mow the grass at the end of the runway.

According to wikipedia Machrihanish was "certified" as an emergency shuttle landing site. Local rumor is that it was used for SR-72/Aurora, black project flights. Lots of conspiracy theories, e.g. https://www.theregister.com/2000/07/10/top_secret_us_plane_c...