STS-48 UFO with "Abrupt Turn"
Video footage from NASA's Space Shuttle Discovery on September 15, 1991, during the STS-48 mission, shows some objects that display unusual motion. This video has resulted in speculation and debate that the objects may have been self-propelled.
In a detailed paper published in New Frontiers in Science (Vol. 3 No.1, Fall 2003) and viewable here as a PDF, Lan Fleming builds on a 1999 paper by Mark Carlotto that analyzed the objects in the video sequence using a frame overlay method at regular time intervals of 1/3 second. Fleming applied the same method of frame overlay, and did it over "considerably longer periods of elapsed video time than those originally covered by Carlotto."
Fleming concluded: "All of the objects in the STS-48 video discussed here were near or below the resolution of the camera and they do not differ in appearance from small debris particles near the shuttle. This lack of resolution has been cited as one of the reasons to assume that the objects are, in fact, shuttle debris. But it is obvious that other objects in the video that also "look like" debris particles in a single video frame are actually stars. It is the uniform linear motion of the stars when the video is run that clearly distinguishes the stars from any nearby shuttle debris. Similarly, it is the curvilinear motions of the unidentified objects in the video and the change of some of them from linear to curvilinear trajectories (and back again to linear in the case of M11) that most strongly distinguishes them from drifting shuttle debris. These trajectories are inconsistent with those of debris propelled either by a shuttle thruster or by sublimation. They are, however, consistent with the flight paths of large self-propelled objects moving around the curvature of the Earth."
James Oberg, former NASA employee and current "space journalist and historian" has a different, more prosaic take on the STS-48 video. In an interview for an article on Atlas Obscura, he asserts that the artifacts in the video are what he calls "space dandruff" - small flakes of ice, pieces of insulation and other fragments that have come off the space shuttle.