Why do some artificial satellites decrease and increase in brightness multiple times? I just observed a satellite almost directly above me travel for a few minutes while constantly dimming and then getting brighter. It did this for about 3 minutes until it faded out. I also observed a satellite with similar behavior on July 4th. I was thinking the satellite might be rotating, but I do not know of any satellites that rotate. Then I thought it could be a piece of space junk, but I don't think they get big enough to be visible from the ground. Does anyone know why the brightness of some satellites change while others remain constant? I am in the Northwest of the US. (Northern hemisphere)
I do not know for sure, but you are viewing the satellites by the reflection of sunlight. As the satellite moves across the sky, the Sun-satellite-you angle changes, therefore there is no reason to expect that the brightness should stay the same.

As for why it should fade and brighten again - if you imagine the satellite to consist of a number of surfaces, these surfaces may essentially cast a beam of light onto the Earth, which move across the Earth's surface. The satellite will brighten as one of these beams crosses you. I suppose this could happen several times for the same satellite.

The extreme examples of this are the Iridium satellite that "flare up" to magnitude -8, before fading in a matter of seconds.