NASA's Secret Footage of the STS-75 Tether Incident

On February 25, 1996, something amazing happened on the Space Shuttle Columbia, which was about 184 miles above Earth. What started as a groundbreaking scientific experiment to make electricity from space ended with a broken tether, a drifting satellite, and some of the most controversial footage in NASA's history. The "tether incident" on the STS-75 mission has fascinated scientists, skeptics, and believers for almost 30 years, making people wonder what happened that is still not fully understood.

The Mission - Space Shuttle Columbia during the STS-75 mission in February 1996, carrying the Tethered Satellite System experiment that would capture some of the most controversial footage in space exploration history.

The Big Experiment

The Tethered Satellite System (TSS-1R) was one of NASA's most creative ideas. It was a joint U.S.-Italian mission to use the Earth's magnetic field to make electricity. Commander Andrew Allen was in charge of the seven-person crew. The crew included Pilot Scott Horowitz, Payload Commander Franklin Chang-Diaz, Mission Specialists Jeffrey Hoffman, Claude Nicollier, and Maurizio Cheli, and Payload Specialist Umberto Guidoni. The mission took off on February 22, 1996, with not only astronauts on board but also the lofty goal of changing how spacecraft get their power.

The idea was simple but very complicated from a technological point of view. NASA gave the deployer assembly and the tether itself, which is a 12.8-mile-long (20.7 km) braided cable made of copper wire, Kevlar, nylon, and Teflon insulation and is only 2.54 millimeters thick. The Italian Space Agency (ASI) gave a 1.6-meter-diameter, 518-kilogram spherical satellite. The plan was to send this satellite into space with a tether that would connect it to Columbia. The tether would then drag the satellite through the ionosphere, which is the electrically charged upper atmosphere, at orbital speed.

The conducting tether would act like a giant dynamo as it moved through Earth's magnetic field, making electricity through electromagnetic induction. Scientists thought the system could create voltages higher than 3,500 volts and currents close to one ampere. This was a ground-breaking example of how to generate electrodynamic power in space. There were going to be twelve investigations: six from NASA, five from the Italian Space Agency, and one from the U.S. Air Force, all of which were meant to look into how a tether system works in the ionosphere.

The Deployment and the Break

The first deployment started on February 25, 1996, but it was delayed by one day because the onboard TSS computers had to be fixed. The satellite slowly opened up from its cradle on a 40-foot extendable boom in Columbia's payload bay. For almost five hours, everything went well. The deployment rate started at only 0.012 meters per second and slowly rose to 2.2 meters per second. It then slowed to 1 meter per second as the satellite got closer to its maximum extension.

The scientific data that came back was amazing. The tether was creating voltages and currents that were much higher than what theory said they should be. In some cases, the currents that were collected were two to four times higher than what Parker-Murphy theory said they should be. The experiment was going very well at 19.7 kilometers of deployment, with the tether set to -3,500 volts.

Then, at 8:29:35 p.m. On February 26, 1996, at 8:00 a.m. EST, disaster struck.

Mission Specialist Jeffrey Hoffman's voice crackled over the communications system: "The tether has broken at the boom!" "It is going away from us."

The crew watched helplessly as the satellite and its 12-mile-long tether sped away from the shuttle at a speed of about 100 miles per hour (24 meters per second). The tether had suddenly broken near the top of the deployer boom, even though it was only supposed to hold 65 newtons (15 pounds) of load.

The Crew - The seven-member crew of STS-75 in their orange launch suits: Commander Andrew Allen, Pilot Scott Horowitz, Payload Commander Franklin Chang-Diaz, and Mission Specialists who witnessed the tether incident.

Mission Control quickly confirmed that Columbia and the astronauts were not in any danger. Because of how orbits work, the satellite and tether naturally broke away from the orbiter and spiraled off into a higher orbit. The crew was told to film the boom and broken tether for analysis after the flight. Some of the most talked-about footage in the history of space exploration would come from what they filmed.

The Investigation: What Really Went Down?

NASA quickly called together the TSS-1R Mission Failure Investigation Board to find out what caused the tether to break. The investigation found a sad story of mistakes in manufacturing and engineering in what should have been a carefully controlled experiment.

After the flight, the tether was checked and found to be burned, with signs of burning and a final tensile failure of only a few Kevlar strands. The Board found that an electrical arc had started in the Lower Tether Control Mechanism (LTCM), sending a 1-ampere current to the ground of the orbiter. The arc kept going on and off for nine seconds while the broken part of the tether moved through the deployer mechanisms at a speed of one meter per second. The arcing caused a lot of burning of the tether material, and the normal load eventually broke the tether at the burn point while it was still on the 12-meter deployer boom.

The breach in the tether's FEP (fluorinated ethylene propylene) insulation layer was found to be the main cause. The breach let the high-voltage conductor, which carried -3,500 volts, arc through to the grounded deployer hardware. But why did the insulation break?

The investigation found big problems with how the tether was made. The fabrication took place in a regular manufacturing shop, not a clean room. Records from the manufacturing process showed that making the tether was "very difficult" because there were many problems with the extrusion and braiding steps. Investigators found both metallic and non-metallic contamination in the FEP insulation layer of the flight tether, which was the worst thing they found. There was metallic debris in the LTCM, the deployer boom assembly, and the reel housing that was big enough to break through the FEP insulation. This included a small piece of silver-plated wire and aluminum shavings.

The tether was wound around its flight reel with a tension of 50 newtons, which caused compressive forces of up to 35 newtons per millimeter on the inner layers. This pressure was strong enough to push small pieces of debris through the insulation layer over the three and a half years that the tether was on the reel between the TSS-1 and TSS-1R missions. The problem got worse because Teflon tends to "cold-flow" when it is under constant pressure.

The Board said, "Foreign object penetration, or damage to the FEP insulation layer during manufacturing or handling, is the most likely cause of the breach of the insulation layer." A $443 million experiment had been lost because of contamination that could have been avoided with proper clean-room procedures.

The Strange Video

While engineers looked at burned tether pieces and metallurgical samples, the video footage taken after the tether break also caught people's attention.

Mission Control told the crew to film the drifting tether with Columbia's onboard cameras, which included low-light television (LLTV) and cameras that some sources say could see infrared light. There has been a lot of debate, analysis, and argument about what was shown in that video since it came out.

The Tethered Satellite System - Technical diagram showing the satellite deployment configuration with the tether, particle sensors, and deployer mechanisms used in the TSS-1R experiment.

The video shows the 12-mile-long tether against the black of space. The sunlight makes it look like a bright line. But there are many bright objects around the tether, maybe dozens or even hundreds. They look like disks with a dark spot or notch in the middle, which makes them look like donuts. Some things look like they are pulsing or changing brightness. Most controversially, some things seem to go behind the tether, which means they are very big—maybe even miles wide—if they really are that far away.

The crew's audio commentary has added to the mystery of the event. One astronaut says, "We see a long line, a few things that look like stars, and a lot of things swimming in the foreground." "There's a lot of stuff swimming around out there," another voice says. People who think the objects moved on purpose have latched onto the word "swimming."

Astronaut Franklin Chang-Diaz, who has been to space seven times, first described the objects as "a little bit of debris that kind of flies with us," lit up by sunlight. NASA would later say that ice crystals, shuttle debris, and other ordinary particles reflecting sunlight made things look strange because of camera effects.

The Theory of Optical Artifacts

The most common scientific explanation is that optical artifacts are strange things that happen with camera optics that can make small, close objects look big, far away, and strange.

The cameras used on STS-75 missions had telephoto zoom lenses and used Silicon Intensifier Target (SIT) Vidicon tube technology. These lenses had a round mirror or aperture system. When these kinds of cameras focus on something far away, like the tether, while things that are closer, like ice particles, stay out of focus, the closer things look like bright, enlarged disks instead of points.

The "donut" or "notch" look comes from how the camera's optics are made. The telephoto lens assembly had guide shafts that held the lens elements. There were usually three shafts, with one vertical to a close pair. When light from things that aren't in focus goes through this assembly, the shadows of the guide shafts make notches in the picture that comes out. The number and placement of notches can change based on the zoom level and where the object is in the field of view.

Photographers and astronomers have written a lot about this phenomenon. The word for the pretty quality of out-of-focus blur is "bokeh." When you take pictures through a circular aperture with things in the way, the objects will look like donuts. This is something that astronomy fans do on purpose to check the collimation of their telescopes.

John Tindall from the History Channel said that the camera images were too bright because of the bright sunlight, which made things look brighter than they really were. This made it look like they were behind the tether instead of in front of it. This is a well-known optical illusion: when a camera is focused on something far away, things that are close by but out of focus can look like they are in the background because they are bigger and don't move with respect to the focal plane.

Astronaut Tom Jones, who flew on STS-80 later in 1996, talked about the tether incident directly in 2016. Jones looked over the footage because NASA had gotten a lot of questions about "UFOs" that people saw on NASA TV. He said, "I looked at the video and thought, 'Oh, I know what this is—this is just ice crystals floating along beside the ship for the first couple of days of the flight.'" He stressed that what seemed important to people on the ground watching the video was "a complete non-event" to the astronauts looking out the windows.

The Argument for Strange Behavior

However, the optical artifact explanation has not satisfied everyone, especially those who have done thorough analyses of the footage. Critics cite particular behaviors that appear incongruent with drifting debris or ice crystals.

Some things in the video seem to change direction suddenly, making turns of 45, 90, or even 180 degrees. Computerized analysis of flight paths indicates velocities and trajectory alterations that appear atypical for passive debris influenced solely by orbital mechanics and minor thruster effects. Some of the objects seem to be moving at very different speeds, with some speeding up, slowing down, or hovering.

The apparent interaction with the tether itself is perhaps the most interesting part. The broken tether still had the electrical potential it had built up—over 3,500 volts—and was basically a 12-mile-long charged antenna sending electromagnetic energy into the plasma environment around it. Some scientists think that if these were plasma instead of ice particles, they might be drawn to or interact with this electromagnetic field.

A recent study that came out in a scientific journal said that some of these things could be between 0.1 and 4 square kilometers in size and move at speeds of up to 28 kilometers (17.4 miles) per second, but only if they were really at the distance of the tether. But these calculations are based on the idea that the objects are the same distance from the tether, which the optical artifact theory directly contradicts.

Story Musgrave, a veteran astronaut who flew six shuttle missions and is known for his scientific and thoughtful approach, talked about similar strange videos from space missions. Musgrave said he "cannot explain" some of the unexplained sightings, but he didn't say they were caused by alien spacecraft. People who want proof for the strange hypothesis have noticed that he is hesitant to completely dismiss such footage.

The Scientific Setting

To accurately assess the STS-75 footage, comprehending the environment is essential. The shuttle was flying through the ionosphere, which is the upper part of the Earth's atmosphere (about 60 to 600 miles above the surface) where solar radiation ionizes gases in the atmosphere, turning them into a plasma of free electrons and ions. This is an electrically active place where strange optical and electromagnetic events can happen.

The TSS-1R experiment was made to look into this setting. As the conductive tether moved through Earth's magnetic field, it made an electric field that moved at about 100 volts per kilometer. This electromagnetic interaction with the ionospheric plasma had effects that were stronger than what we thought they would be, which shows that we didn't fully understand how these processes worked.

The tether stayed electrically charged and kept interacting with the plasma around it after it broke. Electrical discharge effects can ionize or light up any particles, debris, or gas molecules nearby, creating glowing effects. There are many ways that the space around an electrically charged object can make visible light, such as electrical discharge, fluorescence of gases in the atmosphere, charging of particles, and other plasma effects.

The shuttle also makes the area around it outgassing, ice particles from water vapor, paint flecks, insulation fragments, and other debris. Cameras on almost every shuttle mission caught floating objects, especially in the first few days after launch when the payload bay was opened and systems were turned on.

The Effect on Culture

No matter what the objects in the footage really were, the STS-75 tether incident has had a lasting effect on culture. It became a key case for UFO researchers and was featured in many documentaries, such as "Out of the Blue," "Secret NASA Transmissions" by Martin Stubbs, and conversations in Dr. Steven Greer's "Unacknowledged" series. YouTube and social media are still sharing enhanced versions of the footage, and the most interesting parts are often highlighted in comments.

The event happened at a very important time in the conversation about UFOs. In the middle of the 1990s, the subject became popular again, partly because of pop culture like the TV show "The X-Files," which started in 1993. People who were ready to question official explanations liked the idea that NASA might be capturing and hiding proof of strange events.

NASA saw the event as mostly an engineering failure and a reminder of how important it is to follow the right manufacturing steps and check the quality of the work. The TSS-1R tether break taught us things that changed how we do tether experiments and high-voltage systems in space in the future. No subsequent mission has endeavored to deploy an electrodynamic tether of comparable length, although the concept continues to hold theoretical significance for spacecraft propulsion and power generation.

The Questions That Are Still Unanswered

What can we say for sure about the STS-75 tether incident almost thirty years later?

We know exactly what caused the tether to break: contamination during manufacturing led to a breach in the insulation, which caused electrical arcing and burning, which led to the structure failing. This isn't a mystery; it's a warning about how important it is to follow clean-room procedures and good high-voltage engineering practices when building space hardware.

It's still not clear what the things in the video are. The explanation for the optical artifact is scientifically sound and fits with what we know about how cameras work. If the lens is set for the distant tether and small particles are close to the camera, they will look like large, bright disks with geometric patterns that are determined by the aperture structure. If you overexpose them, they will look brighter and give you false depth cues.

But this explanation only works if all the things we saw were small particles that were close to the camera. Even though this is the simplest explanation and fits Occam's Razor, it is still hard to prove for every single object in hours of footage. Some of the movement patterns look strange at first glance and need to be looked at frame by frame to figure out how they fit together. They could be explained by thruster firings, orbital mechanics, and camera motion.

The overarching inquiry—whether anomalous phenomena exist in space that current scientific paradigms cannot elucidate—persists. The ionosphere is a complicated place where our knowledge of plasma physics, electromagnetic interactions, and even ball lightning and other electrical phenomena is still growing. It may be too soon to assume that all strange observations are just normal misidentifications, just as it may be too soon to assume that they are evidence of aliens visiting Earth.

The Legacy

The STS-75 mission, aside from its contentious footage, yielded significant scientific data during the tether's deployment. The collection of electrical currents two to four times greater than expected showed that theoretical models of current collection in ionospheric plasma were not complete. This discovery has ramifications for forthcoming electrodynamic tether applications, encompassing proposed systems for satellite de-orbiting, orbit maintenance, and power generation.

The mission also showed that it is possible to deploy long tethers in space, even though the full deployment was not finished. Researchers looked at the tethered system's dynamics, how tether charging and interaction with the plasma environment affect it, and the problems that high-voltage systems face in space in more detail than ever before.

The seven astronauts who flew STS-75 probably remember the mission more for the scientific discoveries and the lessons learned from the tether break than for the footage that caused a lot of controversy later. When the tether broke, they stayed calm and professional, which showed the kind of training and attitude needed for space exploration.

The video itself has turned into a kind of Rorschach test. What you see in those glowing, pulsing things against the black of space depends a lot on what you bring to the viewing. A skeptic sees camera artifacts and debris; an enthusiast sees proof of something amazing; and a scientist sees a chance to learn more about plasma physics and optical phenomena.

The STS-75 tether incident may have left us with the most important lesson: space is still a frontier where the extraordinary and the ordinary can be hard to tell apart. The ionosphere is a place where radiation, magnetic fields, and electrically charged particles all interact in complex ways. We are just starting to learn about it. The things in the video could be ice crystals, plasma phenomena, optical artifacts, or something else entirely. They show how we are still trying to understand the universe around us.

The incident serves as a reminder that questioning official explanations, demanding thorough analysis, and maintaining openness to possibilities while adhering to the scientific method are all crucial for the advancement of human knowledge. No matter what the truth is, it should be looked into carefully, with evidence-based analysis instead of just rejecting it or accepting it without question.

As we keep sending more advanced cameras and sensors into space, future missions may help us answer the questions that STS-75 raised. Until then, the tether incident is still an interesting example of how cutting-edge science, technical failure, strange images, and the human need to find meaning in the unknown all come together.

The 12-mile-long tether, which is still in orbit around Earth, holds not only the memory of a failed experiment but also the mystery of what the cameras saw on that day in February 1996. This mystery still fascinates and inspires people decades later.