Episode 151: STS-75 - Tethers in Space are a Snap! (TSS-1R)

On STS-75 we’ll take another try at the Tethered Satellite System. It didn’t work so great on STS-46, but with much of the same crew and it should be a snap. Also on this flight, starting fires in space, and disembodied consciousnesses.

Episode Audio #

Photos #

For more photos, head over to our friends at Wikiarchives.space: https://wikiarchives.space/index.php?/category/870

Post-Flight Presentation #

The post-flight presentation has a lot of great footage. The Mt. Everest shot I mentioned begins at 18:08.

“UFO” Footage #

Here’s the low-light camera footage of TSS that got the UFO people all worked up.

Transcript #

NOTE: This transcript was made by me just copying and pasting the script that I read to make the podcast. I often tweak the phrasing on the fly and then forget to update the script, so this is not guaranteed to align perfectly with the episode audio, but it should be pretty close. Also, since these are really only intended to be read by myself, I might use some funky punctuation to help remind myself how I want a sentence to flow, so don’t look to these as a grammar reference. If you notice any egregious transcription errors or notes to myself that I neglected to remove, feel free to let me know and I’ll fix it.

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Hello, and welcome to The Space Above Us. Episode 151, Space Shuttle flight 75, STS-75: Tethers in Space are a Snap!

Last time, we flew a little further out into space than usual, following the Galileo Orbiter-and-Probe all the way out to Jupiter. We rode along as the probe withstood 250 G’s of deceleration and temperatures 8 times hotter than the space shuttle during reentry. We repeatedly dove towards the Jovian moons Io, Europa, Ganymede, and Callisto, using their gravitational pulls to tweak our orbit. We learned that Europa is maybe the solar system’s biggest gusher, with a malleable outer layer and liquid core. And we did it all on no more than 40 bits per second of data. On today’s mission we’ll again be flying in close proximity to mysterious spheres flying in space, but on a considerably different scale.

That’s because today we’ll be carrying one of the stranger payloads to ever fly on the space shuttle: the Tethered Satellite System, or TSS. Visually, TSS is a 1.6 meter wide bright white ball with a couple of odd looking extendable appendages sticking out of it. But once it’s deployed, its most striking feature, the one that made it so unusual, becomes apparent: it was attached to the shuttle by a long white tether. This is weird because typically when we deploy a satellite out of the payload bay, the crew goes to great lengths to ensure that it cleanly separates and never touches the orbiter again. But TSS is a little weird.

If this concept sounds familiar to you, there’s a good reason. TSS actually first flew four years earlier, on STS-46. I’ll leave the details to Episode 121, but the flight did not go as planned. In fact, it ended up being sort of an embarrassment. Before spooling out even 300 meters of tether, the experiment came to a more or less literal grinding halt thanks to protruding 6 millimeter long bolt. The bolt had been added late in the process, after testing had been completed, when there was some concern about how securely the reel was mounted to the payload bay. The reel wasn’t loose or anything, but you always want plenty of extra margin just in case something unexpected happens, so the bolt was added. Unfortunately, those integration tests exist for a reason, and by bypassing them, the reel sure was securely attached to the payload bay.. and most of the tether was trapped on the reel. There was no option but to wind TSS back in and move on to the other objectives of the flight.

Well today, TSS is getting another chance with TSS-1R. The “R” stands for “reflight”. Getting a reflight wasn’t a guarantee. For every experiment flown on the space shuttle, there are others that have to be left on the ground. I’m sure there was a principal investigator out there with plenty of good reasons for why their experiment should fly at all instead of giving this weird tether apparatus a second shot.

But there were a few good reasons to try again. First, there was likely a political angle to it, or at least a diplomatic angle. TSS had been developed by the Italian Space Agency, which doesn’t get access to the sort of resources provided by the space shuttle every day, so the STS-46 failure was a severe disappointment. Giving the experiment another shot would help maintain good will between NASA and their Italian counterparts.

But diplomacy and international friendship weren’t the only reasons to try again; the experiment had plenty of merit on its own. Tethers in space held the potential to be incredibly useful. First, just by having a long cable in space some cool stuff could be done. You could put a spacecraft on one end and a counterweight on the other and spin the two and suddenly you’ve got artificial gravity. And you could potentially lower stuff down into the extreme upper atmosphere. As we’ve learned, studying this region is difficult for a variety of reasons, so being able to trail an instrument package through it and make direct measurements for long periods of time would be great. It would also be possible to lower models of proposed vehicles and use the upper atmosphere as a hypersonic wind tunnel.

And the possibilities further expand when you consider that the Earth has a very convenient magnetic field. What happens when you drag a long conductive cable through a magnetic field? You induce a current! This is cool because it provides an alternative to solar panels but also, by studying that current it’s possible to learn more about the Earth’s magnetic field. But the coolest possibility is what happens if you send your own current down the line. For one thing, you can make a super low frequency antenna, but what’s even cooler is that when you send a current down the tether, the Earth’s magnetic field pushes back. If this could be done reliably while maintaining control, satellite operators might have a new way to change a spacecraft’s orbit without expending their limited supply of propellant. So yeah, tethers are pretty cool.

But as you might suspect, with thousands of meters of a thin tether in weightlessness come thousands of potential problems. How do you damp out oscillations? What if you get more than one type of oscillation going at once? What happens if tension is lost? And what failure modes haven’t even been considered yet?

Well, we’ve got a crew of seven who are eager to find out. Actually, just like how this flight will be reflying the primary payload of STS-46, it’ll also be reflying most of the crew of STS-46, along with three European astronauts.

Commanding the mission was Andy Allen, who we last saw flying as Pilot on STS-62. His command of this flight makes perfect sense since he was the Pilot on STS-46, the first flight of TSS. Not only that, on his previous flight, STS-62, the shuttle carried the US Microgravity Payload 2 experiment, and today Columbia will be carrying USMP-3! This is Allen’s third and final flight.

Joining Allen up front is our Pilot for STS-75: Scott Horowitz. Scott Horowitz was born on March 24th, 1957 in Philadelphia, Pennsylvania but would tell you that he’s from Thousand Oaks, California. He earned a bachelor’s degree in engineering from California State University at Northridge, followed by a master’s and doctorate in aerospace engineering from the Georgia Institute of Technology. I’m guessing that’s why his nickname was “Doc”. He then joined up with the Air Force, learning how to fly and becoming a T-38 instructor pilot and performing research at Williams Air Force Base in Arizona. He next was deployed to Germany, flying the F-15 fighter for two years, before returning to the United States and graduating from Test Pilot School at Edwards. Throughout all of this, he somehow taught graduate level classes on aircraft design, aircraft propulsion, and rocket propulsion. Finally, in 1992, likely surprising nobody, NASA scooped him up as an astronaut. This is his first of four flights.

Behind Horowitz we find a familiar face: Mission Specialist 1, Jeff Hoffman. Hoffman has been with us for a while now, first flying on STS-51D, which improvised the fly-swatter to try to rescue Syncom IV-3, and we most recently saw him on STS-61, the first Hubble servicing mission. With this flight, Hoffman marks his fifth and final mission. But that doesn’t mean you have to see him go. Hoffman was the professor of the excellent MIT course “Engineering the Space Shuttle”, which is freely available online at the time of this recording. Hoffman brings in some real heavy hitters. Want to hear about the origins of the shuttle? Let’s get Dale Myers. Mission control? How about Chris Kraft and Wayne Hale? EVA? Hoffman himself shares his lessons learned. If you’re listening to this show, you’ll surely love it. Again, “Engineering the Space Shuttle”. Anyway, that’s still in the future. For now, this is Hoffman’s fifth and final flight.

Moving to the middle seat, we meet Mission Specialist 2, Maurizio Cheli. Maurizio Cheli was born on May 4th, 1959 in Modena, Italy. He graduated from the Italian Air Force Academy and then in what must have been one heck of a culture shock headed over to the Vance Air Force Base in Oklahoma to learn how to fly. He then returned to Italy, flying the F-104G fighter. He continued his education by graduating from the Italian Air Force War College and then the Empire Test Pilot’s School in the UK. He served in a variety of roles at the Italian Air Force Flight Test Center near Rome, flying dozens of types of aircraft and racking up thousands of hours of flight time. In 1992 the European Space Agency selected him as part of the second group of ESA astronauts and he joins the crew as a full Mission Specialist. This is his first and only flight.

Moving down to the middeck we run into another old friend, Claude Nicollier. When we last saw Claude he was helping his spacewalking crewmates from inside the crew cabin on STS-61, the first Hubble servicing flight. One of those spacewalking crewmates was none other than Jeff Hoffman, who he was flying with again today. In fact, Nicollier’s first flight was STS-46, the original TSS flight, which also had him flying with Hoffman. I’m going to go out on a limb here and assert this without digging through the full archives, but I’m pretty sure Hoffman and Nicollier are the only astronauts to fly together three times. Prove me wrong, internet. In any case, this is Nicollier’s third and fourth flight, but his last with Hoffman.

Mission Specialist 4, and Payload Commander for TSS-1R, was another one of our frequent flyers: Franklin Chang-Diaz. When we last saw him, he was flying alongside Cosmonaut Sergei Krikalev on STS-60, and watching the Wake Shield Facility hang out on the end fo the robot arm. Chang-Diaz is joining us for the 5th time and still has two more flights to go.

And last but not least, Payload Specialist 1, Umberto Guidoni. Umberto Guidoni was born on August 18th, 1954 in Rome, Italy. He earned a Bachelor’s Degree and Doctorate in Astrophysics from the University of Rome doing post-doc work in plasma physics at the Thermonuclear Research Centre of CNEN, Brazil’s nuclear energy agency. He returned to Italy as a staff scientist at the Italian National Energy Committee, working on solar panel research. Next he moved to the Space Physics Institute, working as a co-investigator on one of the original TSS experiments, developing laboratory simulations of electrodynamic tether phenomena, and integration of his experiment with the TSS satellite. In 1989 he was selected as one of two Italian scientists who might fly as a Payload Specialist alongside TSS. He served as backup for STS-46, assisting with on-orbit operations from Houston. When TSS was chosen to fly again, Guidoni was selected to fly with it, making this his first of two flights.

So just to recap that, Commanding this flight was the Pilot from STS-46, we’ve got three Mission Specialists from STS-46, and the backup Payload Specialist from STS-46. There’s a lot to be said for having a cohesive team!

In order to allow for around the clock operations, we will be once again splitting up into multiple shifts, but we’ll actually be taking it one step further. In addition to a Red team and a Blue team, we’ll also have a White team that would be focusing on electric power generation experiments on TSS. The Red team was Pilot Horowitz, Mission Specialist Cheli, and Payload Specialist Guidoni, the Blue team was Mission Specialists Nicollier and Chang-Diaz, and the White team was Commander Allen and Mission Specialist Hoffman. Once TSS operations were done, the White team would join the Blue team.

On February 22nd, 1996, the countdown proceeded smoothly, with no unplanned holds, and at 3:18 PM Eastern Standard Time, Space Shuttle Columbia lifted off the pad for the 19th time. The slow buildup of tension of the countdown soon lead to spikes of adrenaline when the pilot crew scanned their instruments and noticed that the left main engine was reporting only 40% of the expected combustion chamber pressure. This surely lead to even more adrenaline when instead of an RSLS pad abort, the twang completed, Columbia rocked back to vertical, and the solid rocket boosters ignited! With one engine at 40% the crew wasn’t going to experience an RSLS abort on the pad, they were going to become the first crew to execute a hair-raising RTLS (Return to Launch Site) abort! .. or were they? After a quick consultation with the ground, it turned out to be a local instrumentation error. Ground telemetry confirmed that the engine was performing at the expected 104% of rated thrust and all was well. Though presumably also performing at 104% of rated thrust were the pilot crew’s hearts. Thankfully, they had the rest of the ascent to recover since the remaining ride uphill was nice and routine.

As the crew opens the payload bay doors and settles in for their lengthy stay on orbit, how about a fun fact? On one of the onboard IBM laptops used to help control the TSS experiment was a free operating system, usually just used for hobbies, nothing big and professional like GNU. That’s right, less than five years after it was first created, Linux was flying in space. To some of you that won’t mean much, but I guarantee that a lot of computer nerds thought that earlier sentence sounded awfully familiar. That’s because I adapted it from the opening line of a famous email written by Linux’s creator, Linus Torvalds, announcing the start of the project. The little operating system that could had taken yet another step to the big leagues. But I’ll leave the twists and turns of the Linux story to some computer history podcast.

TSS deployment was scheduled for Flight Day 3 but there was still plenty of prep work to do before that could happen, and unfortunately that prep work didn’t go completely smoothly. First, the encoder, which told the crew how much tether had been spooled out, was somehow already set to 23 meters instead of zero, but that was easy enough to fix. There was also some trouble with the data display control system but that was fixed with a cable swap. More problematic was a multiplexer/demultiplexer that essentially kept rebooting itself. These devices were used to move data around on the orbiter’s network of data cables in such a way that the same cables could be shared between different devices. This way the orbiter didn’t need to be weighed down with even more cabling that it already had. With this multiplexer/demultiplexer rebooting, the ground was losing critical telemetry from the TSS payload. So the decision was made to push back the deploy by a day to give the ground more time to troubleshoot.

24 hours later the ground had worked it out and the crew was ready to try again.

First, the telescoping boom that TSS rested upon needed to be raised to its full height, nearly 12 meters above the payload bay. The boom looked like a boxy girder that you would make out of K’Nex or similar building toys. By raising TSS up above the payload bay, the risk of the round little satellite making contact with the orbiter was greatly reduced.

But before we release TSS, let’s think about which way we want it to go. In order to ensure that the tether went where desired, it was important to carefully choose Columbia’s attitude for this deploy process. As we’ve learned from rendezvous missions, the geometry of two spacecraft in low earth orbit dictates their relative motion. Setting aside perturbations from drag, the lumpiness of the Earth, spacecraft thrusting, and so on, let’s consider two spacecraft in the same orbit: the shuttle and TSS. If TSS was deployed directly in front of or behind Columbia, along the direction of travel, then the two spacecraft actually still be in the same orbit, just at slightly different points on that orbit, what’s called its true anomaly. So TSS would just sit there indefinitely. Of course, in the real world it would eventually drift away since it can’t be placed perfectly and there are disturbing forces but we’ve set aside those issues for now. If TSS were deployed to the left or right of Columbia, then we’ve actually slightly changed the inclination of the satellite. Once we let go, TSS will start to drift back towards the shuttle. If it were able to pass through it like a ghost, it would continue on to the same lateral distance it started from but on the other side, and then start moving back again, endlessly oscillating back and forth. Neither of these are super useful.

But if we deploy TSS upward or downward, along the vector between the orbiter and the Earth, now we’ve got something we can use. We’ll look at the upward case since that’s what STS-75 actually went with. If TSS were deployed above the shuttle, it would now be in a slightly higher orbit, which would make it slightly slower than Columbia. So from the point of view of the crew it would start to fall back while also moving upward. Columbia would essentially be dragging TSS behind it sort of like a kid running with a balloon. The longer the tether gets, the more TSS can drift behind Columbia. But what’s strange about this is that TSS will be in this higher and slower orbit but will be pulled faster by the lower and faster shuttle. What happens when a satellite goes faster? It goes up! So now we again force TSS into a higher orbit which would normally be even slower and the feedback loop continues. Eventually, TSS will end up almost right above the shuttle. It’s the same gravity gradient stabilization effect that we used on LDEF years ago. You can also picture this as a person standing in place and spinning around while holding a ball on a string. Once things stabilize, the ball will be right in front of the person, pulling the string taut. But instead of a person spinning around, it’s Columbia spinning around the Earth. This is also nice because it’s a stable configuration, with TSS gently pulling on the tether and maintaining tension. So that’s exactly what they went with.

In order to ensure that TSS and the tether wouldn’t contact the orbiter, first its telescoping boom was raised about 12 meters above the payload bay, nearly 40 feet. Next, the crew turned Columbia around so it was flying backwards with its belly facing the earth, and then pitched its nose 40 degrees down. This essentially pointed the payload bay along the path that the satellite would take. 72 hours into the mission, TSS was released and the planned two days of tether activities began.

TSS started out 18 meters above the payload bay but that wasn’t enough for the relative motion effects to really be significant, so at first it helped things along by using some small nitrogen thrusters. This pulled the shiny white ball up and away, maintaining tension as the tether was slowly spooled out. At first this was really really slow, only around one centimeter per second.

This seemed obvious once I thought about it, but for some reason I thought it was pretty funny that the tether the crew watched extend above their heads was literally the same tether that four of them had watched four years earlier. 300 meters had been trimmed off the end to account for any damage caused by everyone’s least favorite bolt, but other than that it was literally the same thing. Also, while I’m sort of on a tangent, I wanted to mention that the official NASA press kit, when describing the appearance of the tether, compared it to a quote “long white shoelace.” Why a shoelace, I’m not really sure.

Anyway, TSS rose up up and away, and the two-and-a-half millimeter wide tether extended off into the aether. Over the course of five hours, the satellite moved further and further away, with the speed of the tether ramping up to a maximum of 2.2 meters per second, around 5 miles an hour. As it began to approach the planned 20.7 kilometer limit, the tether began to slow down a bit so it wouldn’t just come to a sudden halt.

Around this time a lot of exciting things were happening. All the instruments on TSS were working great, the tether was taut and exhibited nice benign dynamics, and it was generating a current. The tether was white thanks to its protective coating, but at its heart was a copper core, making it conductive. Dragging the conductive tether through the magnetosphere would induce a current, but of course for it to be a current, the loop needs to be closed. To do this, electron guns were mounted in Columbia’s payload bay, which fired them off into space. The electrons would skip the insulated outer sheath of the tether and find TSS, which was coated in a special electron-friendly paint. Then they would rush down the tether back to Columbia and complete the circuit. Scientists on the ground were already seeing something like three times more voltage than had been expected, up to 3500 volts. The returned current hit as high as 480 milliamps. So combine that with P equals I V and we find that TSS was generating almost 1.7 kilowatts of power. That’s some serious power! You could easily run a satellite, or even a small house on that.

Around this time, Jeff Hoffman noticed an interesting phenomenon. Rather than being perfectly straight, the tether seemed to have developed a long arcing bow. This wasn’t really troubling but it was sort of interesting since he hadn’t expected it. And what do we do when we see something weird in space? We document it! So Hoffman got out a video camera and began filming the distant TSS and tether, both of which were shining brilliantly white thanks to them reflecting sunlight. Suddenly, he noticed a distinctive rippling pattern appear in the tether, and with a sinking feeling of deja vu, he knew that the 19.7 kilometers of deployed tether had gone slack. The last time this happened it was because of the mechanical interference in the deployment reel, which brought the experiment to an early end. Hoffman looked to the boom and instantly understood two things, one very bad, and one very good. He grabbed the radio and called down these two facts in the same order: “Houston, the tether has broken at the boom. The tether has broken, it is going away from us.”

The bad news here was obvious. The tether was broken and that was the end of the TSS experiment as it had been planned. But the fact that the breakage had happened on the shuttle end was actually very good news. If it had broken on the TSS end, then nearly 20,000 meters of tether would be flying back towards the orbiter. They would have had to quickly cut the bottom of the tether and then scooted out of the way. Instead, with the tether severed at the boom, TSS was no longer constrained and orbital mechanics were free to kick in again. TSS was going much faster than it normally would have in its higher orbit, so it and the tether, clumped and tangled near the bottom, flew away at around 24 meters per second, up and away from the shuttle. With no immediate danger, the crew focused on documenting the state of the tether in the last few minutes before orbital sunset when they lost sight of it.

As luck would have it, at the moment the tether snapped, the four crew members who were awake were the four who had flown together on STS-46. I can only imagine the looks they exchanged when they realized that once again, the Tethered Satellite System had not gone according to plan.

We’ll talk about why this happened in a bit, but first it’s worth noting that the experiment actually wasn’t quite over yet. At the moment of the snap, TSS had safed its instruments but was actually completely fine, happily running on battery power. Before long, technicians on the ground were able to send commands directly to TSS and instructed it to turn its instruments back on. Over the next few days, as the batteries drained, they were able to collect some more data and downlink instrument readings from the wayward spacecraft.

Thanks to their new relative orbits, within a few days Columbia passed within 90 kilometers of TSS and its tether, and there was actually some discussion of an attempted rescue rendezvous, but unfortunately there wasn’t enough propellant to try. Double unfortunately, as they got closer, the crew focused a special low light video camera on TSS, creating some video footage that would become a mainstay of UFO crazies on the internet. I’ll explain.

When the tether broke, it created a fair amount of debris. It wasn’t necessarily dangerous but there was a bunch of tether fragments, little blobs of the copper core, and stuff like that that had been sprayed out at the moment that the tether snapped. On top of that, the shuttle had been performing its usual waste water dumps. So in the general orbital neighborhood of Columbia and TSS were a bunch of little reflective pieces of debris and ice crystals. Combine that with some optimal lighting and a low light camera, and you’ve got a recipe for a UFO conspiracy theory.

Why? Because in the footage, you can see the tether, once again pulled straight by the gravity gradient, brightly reflecting in the distance. And in the foreground you can see a whole bunch of little out-of-focus bits of debris floating around around in a bunch of different directions, reflecting brightly in the amplified sunlight. Each out of focus bit of debris looks like a fuzzy ball with a notch cut in it due to an artifact of the camera. Well, that’s what you would see as somebody who knows something about spaceflight history. What the UFO people apparently see is a swarm of super advanced spacecraft behind TSS, investigating it and trying to get it to stop eating their electric food source. I’m not joking. The UFO people apparently aren’t bothered by the fact that if the points of light were behind the nearly 20 kilometer long tether then each one must be at least several hundred meters across and clearly visible from the ground, but I guess that’s the least of their problems.

Alright, so what happened? Why did the tether snap? The short version is that electrical arcing burned through enough of the tether that the 6.8 or so kilograms of tension was enough to snap what was left. For the much much longer version, shoot me an email at jp@thespaceabove.us and I’ll send you the 365 page failure investigation report. For something in the middle.. it turns out that making a 22 kilometer long tether that can survive the rigors of spaceflight is not the easiest thing in the world. At some point in the lengthy manufacturing process, little bits of foreign material were introduced to the tether. Stuff like metal shavings and other little things. That’s not great but wouldn’t be enough on its own to cause a problem. But when the tether was wound onto its reel, it was under a great deal of tension, which had the effect of compressing the tether (and any foreign bodies) against itself. And it sat like that for years before STS-46 and then again before STS-75. As it unspooled, a portion of the tether with a damaged sheath was revealed and thanks to the 3500 volts of potential built up by the tether, an electric arc formed between the damaged area and the orbiter structure. The arc lasted intermittently for nine seconds as the tether moved from the lower mechanism up into the boom, burning away at the tether until finally, it snapped.

This was actually exactly what the crew guessed almost immediately. By using some powerful telephoto lenses, Hoffman was able to get a closeup look at the broken end of the tether that was still in the boom. The tether end was frayed and charred. All that was left to do was wind the remaining tether back on the reel, retract the boom, and turn to the other work to be done on the flight. In one bit of irony, if scientists had known that the voltage would be as high as it was, Hoffman speculated that they likely only would have extended the tether out to 10 kilometers, and the damaged portion would never have been exposed. Oh well.

The official NASA material twice called TSS a quote “scientific adventure” and they were more right than they could have known.

Luckily, there was plenty else on board to keep the crew occupied. The most engaging one, and the one I suspect they had the most fun with, was a new experiment glovebox that had been installed on the middeck. This, again, is one of those things you’ve likely seen where an experiment is contained inside a transparent box that has gloves built into the side of it, so the crew can operate the experiment while keeping whatever it is safely confined inside the box. It also provided an opportunity to test the new glovebox design for use on the ISS.

Inside the box was something that we definitely want to keep contained: fire. Yes, we’re once again setting stuff on fire in orbit. It was extremely important to understand the behavior of fire and smoldering materials in microgravity for pretty obvious reasons: if we don’t understand fire, we can’t detect fire and suppress it before it becomes a lethal hazard. On Earth, we detect fire by putting smoke and heat detectors up near the ceiling. This works because the fire heats up the air, which makes it less dense. And thanks to gravity, the more dense air scoots down, pushing the hot air up, conveniently allowing us to detect smoke and heat and fire. In space, of course, there is no up. In fact, fire can sometimes operate backwards from how you might expect. On this particular experiment, a slight breeze was introduced into the scenario to see how the fire would behave. It actually would burn towards the breeze since that was the source of fresh oxygen. And when material smoldered, since it had no upward direction to go, it just meandered around in these weird oddly unsettling patterns. It sort of looks like a fire spider.

In an oral history, Hoffman recalled quote “We had a lot of fun burning things. We eventually burned all the fuel they had given us, and we offered to start tearing up flight books and things but they said, “No, you’ve done enough.” We had a great time. Bunch of little kids building fires in space. That was fun.”

The other major experiment on board actually required as little crew interaction as possible. The US Microgravity Payload 3 experiment was, as you may have guessed, the third flight of the USMP suite of material science experiments that we’ve seen previously fly on STS-52 and STS-62. As you’ll recall, these were a handful of experiments were operated remotely from the ground and were seeking to use the weightless environment to study effects that were not possible on the ground. Stuff like nailing down the critical point of xenon, crystals-crystals-crystals, dendritic growth of metals, and so on. I’ll refer to you to the STS-52 and STS-62 episodes for more details.

What’s different about this flight is that with two shifts, the crew would be operating around the clock. Apparently, when they found out, the scientists operating the experiments were horrified! With the previous flights, eventually the crew went to sleep and stopped moving around, and they could count on around 8 hours of smooth flying in which to do science. But now, at all times, someone would be awake and potentially bouncing around the crew cabin.

Not to worry though, as usual, astronauts are a pretty adaptable bunch. First, the USMP experiments were only performed when one shift was asleep, so they’d only have half the crew to deal with. Second, the crew understood the needs of USMP and were happy to accommodate. Part of the experiment involved flying some very sensitive accelerometers, so scientists could know what sorts of disturbances their experiments had been subjected to. The crew simply put the realtime data from those accelerometers onto a laptop computer in the cabin, and kept an eye on it. Pretty soon, through trial and error, they figured out what made big disturbances, what didn’t, and how to live alongside the sensitive experiments.

It turns out, this is actually pretty incredible for the crew. We once again turn to Jeff Hoffman’s oral history for a quote: “In order to accomplish this, though, they had to declare that these eight-hour periods - when the other shift was asleep - were the co-called quiescent periods. They weren’t allowed to give us experiments to do, any jobs. So for the best part of a week for eight hours a day we just had to float and look out the windows. I felt as if I were a space tourist. It was really quite extraordinary. You basically had to float, because any time you touched the wall, you would cause a disturbance.”

He later continued, saying “I found that without any feedback from your body if you’re truly relaxed you could actually almost lose a sense of physical reality. I would just be floating there as a disembodied consciousness, which was really a very unique and pleasant experience." It sounds both incredible and a little freaky. The crew got even more time to experience the joys of weightlessness because the USMP experiments were going so well that an extra day was added to the flight.

After the drama of TSS-1R, life onboard the lengthy mission continued with a steady rhythm. Footage shot on board shows the usual antics such as the crew making balls of water to slurp out of the air. Claude Nicollier decided that the water wasn’t complete without a goldfish swimming around in it, and added a few. Thankfully for anyone concerned about the well-being of the fish, it was the little cheese crackers. Don’t worry, it confused Danny Concannon too. Hoffman took the usual water drop fun and added a little spin to it, rotating a blob of water until it spread into two blobs connected by a thin bridge, which eventually broke, sending the two blobs of water flying.

At one point during the flight, Columbia passed near the Himalayan mountains, and the crew shot some really incredible footage. First, they managed to zoom way in and find Mt. Everest, which in a few months would see its busiest and deadliest climbing season to date. But then what’s amazing was as Columbia continued on over the Pacific Ocean, the crew kept the video camera trained on the massive mountains, and you can clearly see them sticking up over the limb of the Earth, slowly setting as the orbiter continued on. It’s rare to really get a sense of the 3D nature of the Earth from space, so that footage caught me off guard and really made an impression. If you want to see it for yourself, it’s in the STS-75 post-flight presentation, which is easy to find online but I’ll link it in this episode’s announcement tweet and, if I ever get around to making it, the show notes page.

Lastly, near the end of the flight, two crew members gathered together on the flight deck for a photo op. Jeff Hoffman and Franklin Chang-Diaz held up a sign that read “2000 hours”. It was in celebration of the fact that as the flight drew to a close, Jeff Hoffman became the first person to spend 1000 hours on the space shuttle. And in a stroke of good luck, bad weather extended the mission by one more day on top of the extension given for USMP, and those last 24 hours pushed Chang-Diaz past the 1000 hour mark as well. So between the two of them they had more than 2000 hours of flight time. 1000 hours is 41 days and 16 hours and is a pretty impressive accomplishment. Commander Allen, with his test pilot background, pointed out that logging 1000 hours in any vehicle is a significant milestone, but being the first to do so is a special honor. So good job, Jeff and Franklin.

As I mentioned, the temperamental weather at the Kennedy Space Center pushed the flight out by one more day, but after the 2000 hour celebration it was time to once again suit up, close the payload bay doors, and head home. After an uneventful entry and landing, Columbia rolled to a stop, closing out a mission lasting 15 days, 17 hours, 40 minutes, and 21 seconds.

At first this mission might seem like kind of a mixed bag, and I guess that’s fair, but in a lot of ways it was a wild success. First of all, USMP-3, the glovebox combustion experiments, and a number of other smaller science experiments all worked great, and time-wise, those were the bulk of the mission. But even with TSS-1R the flight is more of a success than it might seem.

Let’s get the obvious out of the way.. yes, the payload was lost when a manufacturing flaw lead to a powerful electric arc burning away its tether. It was a potentially dangerous situation, it lead to the unplanned loss of a spacecraft, and frankly, after the debacle of STS-46, it was pretty embarrassing.

But also, a ton of science had gotten done. Scientists discovered that the tether generated way more voltage than expected, they learned about the dynamics of long tethers being dragged around in space, and they were even able to continue operating experiments after the tether snapped. After this flight we’re not going to be seeing tethers in space again, at least not in the shuttle program, and I think that’s really a shame. Yeah, it didn’t go as expected, but we learned so much! The crew spend hundreds of hours working in simulators and learning how to properly handle the dynamics of a wobbling tether in space. Scientists proved that a significant amount of power could be generated, and that the tether could be controlled, if manufactured flawlessly. To me, this flight proves that tethers are a worthwhile concept to pursue. So hopefully, in the not too distant future, we’ll once again see the incredible and perplexing sight of a brilliant white tether fading off into the black. We just won’t tell the UFO people.

Next time.. Norman Thagard had such a good time living on Mir that Shannon Lucid has decided to drop by. Let’s give her a ride!