[Bender2]

Re: It is a well-known optical illusion that occurs with satellites that change their reflectance because they are tumbling. As they flicker in brightness, they appear to be moving in a zig-zag or jerky motion.

That may be it, but the point of light I saw was not flickering at all. It was a strong, steady point of light doing a jitterbug while moving in a rough northeast to southwest orbit.

[Kirkwood]

The illusion can also be seen even if the light is not flickering, but flickering tends to intensify it. It is a very intense illusion when the visual field is mostly empty as in the case of the night sky. The illsuion is based on the microsaccadic motion of your eyes as they try to intensely fixate a small target. The microsaccades are due to normal physiological motor activity of the extraocular muscles.