Improved missiles are now able to shoot down the U2, and maybe get close to the SR-71. That makes these planes a liability now, when over developed territories such as the former USSR.

Both were formerly useful, and have been brought out of retirement, when required for tasks that a satellite could not perform, or was not in position for.

I wouldn't be surprised if the x37 mini-spaceplane was primarily useful as a surveillance platform.

This has probably been true since at least 1960.

I wouldn't be surprised if the x37 mini-spaceplane was primarily useful as a surveillance platform.

Eh. It takes an Atlas V to launch the X-37.

At 90 million a launch, and months to prep, it's not exactly something one can crank out with a frag order on a day's notice.