|The woo is out there|
|Aliens did it...|
|...and ran away|
The STS-75 incident is an alleged UFO sighting where the bright spots seen moving in video coverage of a Space Shuttle mission are interpreted as a swarm of
alien spacecraft UFOs around the orbiter. It has no "official" name and it's usually described with some combination of "Shuttle," "STS-75," "Tether," "UFO," and "incident."
STS-75 (the 75th mission of NASA's Space Shuttle) was launched in February 1996. One of its objectives was the deployment of the Tethered Satellite System Reflight (TSS-1R) experiment. Research in electrodynamic space tethers is interesting to scientists because of the potential for cheap propulsion and power generation in Earth orbit, something useful for satellites and space stations. 
The tether allowed STS-75 to dangle a satellite from a 20 kilometer (12 mile) cable and check how much current the Earth's magnetic field would induce in the cable. But the tether broke before it was completely deployed and, together with the satellite, drifted away from the orbiter.
Why the tether broke
Basically, because of unforseen pinholes in the insulated cover of the tether, air trapped under the insulation bubbled out of the pinholes into the vacuum of space. The approximately 3500 to 5000 volts being generated across the tether converted the air bubbles into a plasma (which is a great conductor of electricity) that short circuited to the metal body of the shuttle, and -- pop! -- the current was enough to melt the cable.
As seen on video
NASA mission video recordings of the tether experiment show what appear to be a number of bright objects swirling around the tether. Astronaut Franklin Chang-Diaz explained the bright spots seen near the tether were "a little bit of debris that kind of flies with us" that was illuminated by the sun.
Since the shuttle and all its contents were weightless and orbiting the Earth at 17,600 miles per hour, anything that gets detached from it (like ice crystals) would tend to hang around nearby and "fly with" the shuttle.
A routine water dump[Note 1] had taken place just before the tether experiment. Shuttle water dumps are known to create clouds of debris particles, many of which linger around the shuttle for several hours before drifting off. And the camera's image intensifier circuit is known to distort bright objects, creating circular image artifacts that appear "notched" - reflecting the notched shape of the camera's aperture.
Gotta be aliens
Some UFOlogists were not satisfied with such a boring explanation. So they examined the video looking for evidence that would prove the existence of aliens, quickly cooking up a counter-narrative.
They decided the bright spots had to be Buick-sized alien ships located some distance away, because the video showed the spots appearing behind the tether. Naturally, they rejected more rational explanations, e.g. the debris was overexposed by bright sunlight giving the illusion it was behind the tether. (Hey, they don't call it UFOlogy for nothing)
Other (more creative) UFOlogists saw the bright spots as an "undiscovered" naturally existing life form, like an amoeba, only bigger. According to cranky geniuses, these flashing, blinking tribbles are pseudoscientifically magical:
“”[They] exist in a spectrum not visible to the naked eye under normal conditions. They appear to be total harmless, feeding off electrical or other energy. If you look closely at the footage you will observe them increasing in brightness near electrical storms. With this in mind it is not in the least surprising to find them swarming around the electrodynamics tether which is NASA's attempt to harness the very energy that they feed on."
|—The Secrets of the Universe|
According to crank thought-leaders, these space amoeba are friendly and can teach mankind how to avoid nuclear war and live in peace, if we'd only stop messing with their "food" and attempt to communicate with them. It's not the least bit surprising to us that this particular fantasy borrows shamelessly from old Star Trek episodes.
- International Flight No. 184, STS-75 Columbia Spacefacts
- "The Exploration of the Earth's Magnetosphere": The Space Tether Experiment" NASA.
- UFO believers claim NASA footage of 'tether incident' proves aliens exist Houston Chronicle
- STS-75 Shuttle 'Tether' Video Analysis by James Oberg
- Amoeba Like Life Forms "Critters" - Critters and UFO's - STS 75 Thelivingmoon.com
- See the Wikipedia article on the TSS-1 and TSS-1R missions.
- UFO NASA's unexplained tether overload incident, one of the myriad YouTube videos about the incident, notable for being uploaded in 2006, surviving to 2012 and getting 1 400 000 views
- STS-75 Shuttle 'Tether' Video Analysis by James Oberg, 2000, mirrored on Rense.com, of all places
- The Tether Incident (Space Shuttle Mission: STS-75), thread at the Bad Astronomy and Universe Today Forum, started 2 May 2011