Prowler is (or was) one of the most secret and enigmatic objects in existence. It was probably an experimental satellite for close covert inspection of Soviet geostationary satellites. I have posted on the background story of this object in more detail before. Clandestinely launched from Space Shuttle STS-38 in 1990, its launch and existence have never been acknowledged by the US government.
The images below were made on October 25 and 27, using the 61-cm F/10 Cassegrain of Sierra Stars Observatory in Marklee
Both images have an exposure time of 30 seconds. The brightness difference between the two images is mostly due to a difference in phase angle.