Which is why the USAF never had a plane shot down over the USSR as Gary Powers will certainly be glad to confirm. It’s also the reason no US planes ever fly over Syria, Irak, Afghanistan, Pakistan or any of the numerous conflict zones that the US is involved in. Also note: My point is not that satellites are useless, they are much more useful for continuous spying and surveillance, but there are numerous mission profiles that a plane can fulfill much better.
When you control the sky’s you don’t need to fly at 6000 mph.
We have bases in Pakistan and Afghanistan, for example.
Which mission profiles are you describing that are actually needed to fly at hypersonic speed? A lot of these countries are quite small for that speed. A 100 miles a minute.
I’m pointing out that the legality of overflying a country has always been and still is a lesser concern.
Mission profiles better suited to a plane than a satellite: anything that requires loitering, returning to a target, anything that requires a curved path that a satellite cannot fly or anything that requires close up - optics on satellites are good, but fundamental physics limits the achievable resolution. Hypersonic speed might not be required to fulfill the actual mission, but it allows shorter response times on all spots. It also would allow evading most intercept attempts.
Typically above 60,000ft (FL600) is considered to be outside of a nation's airspace[1] (by ICAO at least) - which is one of the reasons why the U2 was designed to cruise at 60,000-70,000ft (FL600-FL700). The SR-71 could cruise up to 85,000ft (FL850).
So, technically and at least according to ICAO, these birds flew/fly above a nation's sovereign airspace. That doesn't stop a nation-state from attempting to down one of these birds, of course.
60,000 feet is the limit of controlled airspace, i.e. if you fly above it air traffic control will not guide you to make sure you don't collide with other aircraft. It's not related to sovereign airspace, the area where a country has the right to decide who may fly.
I think the general rule is that sovereign airspace covers air-breathing planes but not spacecraft. From your link:
> There is no international agreement on the vertical extent of sovereign airspace, with suggestions ranging from about 30 km (19 mi)—the extent of the highest aircraft and balloons—to about 160 km (99 mi)—the lowest extent of short-term stable orbits. The Fédération Aéronautique Internationale has established the Kármán line—at an altitude of 100 km (62 mi)—as the boundary between the Earth's atmosphere and outer space, while the United States considers anyone who has flown above 80 kilometres (50 mi) to be an astronaut.
