Again - physics suggests that what you heard in the 70s was also untrue.That was my thought at first. While not the same it is mind-blowing (at least to me) that mil sats in the 70's were supposedly capable of reading print of a magazine cover. Tech advances pretty rapidly and that over 50 years ago.
There is a limit to resolution based on the physics of the camera lens and of the air through which the light must travel.
Astronomy has been working against those limits for nearly a century. While there have been advancements, reading magazine covers from space is fantasy.
So is seeing through walls without x-rays. The sensors in space are passive. And there is no part of the normal spectrum of emission that is capable of penetrating walls.
Objects emit passive radiation, based on temperature. The Planck black body curve applies. For satellites to see x-rays from an object, through walls, that object has to be roughly as hot as the sun.
https://en.wikipedia.org/wiki/Planck's_law
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