... when the reflections were the best possible from the standpoint of being on the earth, would AO 51 then be visable?

In a word, no. It's too small. A spacecraft of that size would be a very dim object. Even in a dark sky (if you can still find one!) you'd need at least binoculars to have a chance.

InstantTrack includes a very basic algorithm for estimating the visual magnitude of a satellite based on its size. InstantTrack says that AO-51 would be about the brightness of a magnitude 10 to 13 star, when it's illuminated by the sun and it's dark on the ground. A magnitude 9 star would require a very dark sky to see, so a magnitude 10 or dimmer star would not be a naked-eye object.

Now that estimate is based on a sphere, not on a "glint" specular reflection. You may be familiar with the so-called "Iridium flare", where an extraordinarily bright reflection is seen briefly from an Iridium satellite when the geometry is exactly right. That happens because the Iridium satellites have extremely tight attitude control (and because they have large flat surfaces). AO-51's attitude is constantly varying by small amounts, and it's spinning. There would be no way to predict exactly when a glint might be geometrically possible, and the duration of the glint would be fleeting indeed. I don't believe it would be possible to see it.

73 -Paul kb5mu@amsat.org