> Unless by the early 1950s the US and possibly others were launching objects into orbit, and their doing so has been a closely guarded secret even until now.

Because of the very public competition between the US and the former USSR, any rocket technology successes would have become public very quickly. For example, Alan Shepard's 1961 suborbital flight was rather lame by modern standards and much less than the USSR had already accomplished, but it was front-page news. And after Sputnik launched, late in 1957, heads figuratively rolled among American rocket scientists because we were late in a very public race to orbit.

This doesn't refute the possibility you suggest, it only makes it unlikely.

> If we rule out ETs for the sake of argument, and if these weren’t atmospheric effects or artifacts from the nuclear tests themselves, then small objects were in orbit at the time and either they were launched from Earth or the planet happened to be crossing paths with them.

I like your approach -- don't assume the least likely possibility, consider all the alternatives first. As Carl Sagan liked to say, "Extraordinary claims require extraordinary evidence."

It's too bad that the evidence is so poor. The photographic resolution isn't good enough to either eliminate or accept a number of possibilities.