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Episode 178: STS-91 - A Farewell to Mir (Bringing Thomas Home)

On STS-91 we’ll try out a new external tank, learn a little physics, and find out what Mir upper management thinks about the state of the space station. Oh, we’ll also bring Andy Thomas home and wave farewell to Mir forever.

Episode Audio>

Episode Audio #


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Space Shuttle Discovery lifts off on STS-91
Mir awaits!
The combined STS-91 and Mir crew
Mission Specialist Wendy Lawrence floating in a sea of cargo
Valery Ryumin and Talgat Musabayev in Mir

Post-Flight Presentation>

Post-Flight Presentation #

If you’d like to see the mission in motion you can check out the post-flight presentation here:


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.

Hello, and welcome to The Space Above Us. Episode 178, Space Shuttle flight 91, STS-91: Прощание с Миром: A Farewell to Mir

Before we begin, I just wanted to take a quick moment for something personal. A couple weeks ago, the day after I got the news about my Dad I woke up after only a few hours of sleep and tried to juggle getting work stuff all set, finding a cat-sitter, packing to head home, and deciding what to do about the podcast. I realized that I had about 30 minutes available to write, record, edit, and post a message to the podcast feed explaining what was going on. This ended up being sort of a perfect amount of time since it didn’t really give me too much of a chance to overthink things. As I explained, I mostly posted it out of some sense of normality and just generally wanting to keep folks in the loop. What I did not expect was the outpouring of emails, messages, and well-wishes from people who listened to that episode. During my time back home, scrolling through the incoming messages was definitely a source of comfort, so for that I thank you all. As way of thanks, I’d like to tell a brief story that was mentioned in Dad’s eulogy and was one of his central quote-unquote “legends” as far as I’m concerned.

During the eulogy, one of Dad’s life-long friends said a line that got a laugh, saying “Undeterred, they became hobos.” What’s great was that this wasn’t even a joke. After getting home from the Vietnam War and getting out of the Army, Dad went down to Florida to join a friend in working construction. That went pretty well, but the oil crisis eventually popped up and new construction shut down and he and his friend were out of a job. Undeterred.. they became hobos! They decided to go and see the country through a combination of hitchhiking and hopping on freight trains. So yeah, literally hobos. Somehow they made their way to California, and that’s where a friend of a friend of a friend snuck them into a rail yard so they could hide in a box car, which for some reason had always been a dream of my dad’s. After several miserable days bouncing 6-12 inches in the air on the floor of the box car in stifling heat, they found themselves on a new train that was transporting new pickup trucks.They sat in the beds of the trucks, which was exposed to the elements but a lot better than the super hot box car. At one point the conductor or engineer or whatever apparently got sick of seeing them climbing around back there and moving from truck to truck because suddenly they realized the train was slowing down, before stopping completely, in the middle of nowhere. A train worker hopped out of the caboose and came stomping up to the train car that was holding the trucks. My Dad and his friend hid from view but the guy yelled up “Hey you guys! I know you’re up there! You better stay put! I don’t wanna pick up your guts! If you don’t stay put I’m wiring ahead to the next station!” And then he just walked away and got back on the train and it started moving again. You have to wonder how much it cost them to stop the train just to yell at these two doofuses.

Somewhere in Iowa they decided that life on the rails wasn’t all it cracked up to be and began hitchhiking back to Florida. They made it all the way to Titusville, just across the water from the Kennedy Space Center, and all they had left was a single dime and a raw potato. They took their last remaining dime and put it in a payphone to call some people they knew who lived in Titusville.. and the phone ate their dime. Because of course it did.

That’s just one example of the ridiculous stories he would tell, and retell, whenever given the chance, whether you wanted to hear it or not. I once asked him what his worst job was and two hours later I got the answer: can factory. Even now, the stories don’t end, as I have been sifting through thousands of slides, photos, and negatives, scanning them into my digital archive, though now I have to interpret the stories myself. Why was he so excited to ride in a box car? What’s the story behind this photo of him on a gas powered scooter? Is that a real rifle he’s holding in his kitchen in this photo labeled “Age 8”? The stories go on. And I’m sure he would be glad to know that some of his stories were being heard around the world thanks to this crazy hobby of mine, even if he never did quite understand it.

Anyway, thanks again for all your kind words, support, and understanding. Let’s get back to it.

Last time, we covered one of the most scientifically sophisticated flights of the entire shuttle program, STS-90: Neurolab. Between confusing rats, sticking needles in nerves, taking a spin in the Crazy Chair, and playing catch, this 16 day mission used the unique environment of weightlessness to shed new light on how the nervous system functions. While there are still some science-focused flights to come, from here on out there is a definite move towards the shuttle being more of the “space truck” it was originally envisioned to be.

Case in point, today’s mission, STS-91. Today we’ll be visiting Mir for the last time, bringing astronaut Andy Thomas home and bringing, well, no one to replace him. But while we’re at it we’ll bring a bunch more supplies for our Russian partners, do what we can to help with that whole Spektr situation, and allow the upper management of the Mir program to see first-hand what it’s like on board the station. Let’s just jump right into it and meet the crew.

Commanding the mission is someone who has practically been treating Mir as his vacation home: Charlie Precourt. He was Pilot for STS-71, the first Mir docking, and was Commander for STS-84, the Linenger/Foale swap. And with this flight he becomes the only American to visit Mir three times. This is his fourth and final flight.

Joining Precourt at the front of the flight deck is today’s pilot: Dom Gorie. Dominic Pudwill Gorie was born on May 2nd, 1957 in Lake Charles, Louisiana. He earned a Bachelor’s in Ocean Engineering from the US Naval Academy and 11 years later also picked up a Master’s in Aviation Systems from the University of Tennessee. After graduating from the Naval Academy he became a Naval Aviator, flying the A-7E Corsair and the F/A-18 Hornet, and graduating from Test Pilot School. He also flew 38 combat missions as part of Operation Desert Storm. Along the way he logged over 6700 hours in the air, flying more than 35 different aircraft. He was selected as an astronaut in 1994 and this is his first of four flights. And it’s worth noting that on his third flight, he’ll command the first flight of friend of the show Dan Tani, so we have that to look forward to.

Behind Gorie we find mission specialist 1 and frequent flyer: Franklin Chang-Diaz. This is the sixth time we’re seeing Franklin so I’m not sure what else there is to say about him. I guess I could say that he would likely be a fan of the show’s sign-off, since after leaving NASA he became the founder and CEO of the space propulsion company Ad Astra, working on groundbreaking plasma rocket technology, so that’s pretty cool. When we last saw him he was waving goodbye to the TSS experiment as it drifted away after its tether broke. Lucky for him, there are no tethers in sight on this, his sixth of seven missions.

Sitting in the middle of the flight deck is today’s flight engineer, Mission Specialist 2, Wendy Lawrence. Of course, we know Lawrence from her flight on STS-86 when she helped deliver Dave Wolf to Mir so he could serve out a mission that she thought she’d be doing herself. As a sort of consolation prize for having her long duration mission snatched away due to an ill-fitting space suit, Lawrence was assigned to this flight even before STS-86 had launched. In fact, within five hours of landing on STS-86 she got a call from Charlie Precourt inviting her to the STS-91 crew meetings. She pushed him off a few weeks while she debriefed on STS-86 but now here she is. And while the surprise reshuffle left her with less to do on STS-86, today she’ll be helping out the orbiter crew and supervising the transfer of cargo to and from the station. This is her third of four flights.

Moving downstairs, we find our last spaceflight rookie for this flight, Mission Specialist 4 Janet Kavandi. Janet Kavandi was born in Springfield, Missouri, and Missouri is where she stayed as she picked up a Bachelor’s and Master’s in Chemistry from Missouri Southern State College Joplin and the University of Missouri Rolla, respectively. She later picked up a Doctorate in Analytical Chemistry from the University of Washington in Seattle. She was in Seattle because she was working for Boeing, serving as the lead engineer of secondary power for the Short Range Attack Missile II and worked on thermal batteries for the Sea Lance and Lightweight Exo-Atmospheric Projectile programs. Along the way she helped support some familiar programs such as the Inertial Upper Stage and Get-Away Specials. She was selected as an astronaut in 1994 and this is her first of three flights.

And last but certainly not least, Mission Specialist 4, Valery Ryumin. Valery Ryumin was born on August 16th, 1939 in Komsomolsk-on-Amur in the far east of Russia. And as you may have guessed, he may be new to the space shuttle, but he is no rookie. He graduated from the Kaliningrad Mechanical Engineering Technical College with a specialty in “Cold Working of Metal” and also graduated from the Department of Electronics and Computing Technology of the Moscow Forestry Engineering Institute with a specialty in Spacecraft Control Systems. In between those two he also found time to spend three years as a tank commander in the army. In 1973 he was selected as a cosmonaut, first flying in 1977 on Soyuz-25, which was intended to be the first crewed flight of the new Salyut 6 space station, which was kind of like Mir if it only had the base block. Unfortunately, the docking mechanism failed and Ryumin and his commander had to head home after only a couple of days. But two years later he returned and this time spent around six months on the tiny station. The next year he was back for another 185 days. Since then he rose through the ranks at Energia, serving as the flight director for Salyut 7 and for Mir, helping to design both stations. And as the Russian head of the Shuttle-Mir program, he was the Russia counterpart to Frank Culbertson. I don’t really have any definitive source for this but I kind of get the impression that he just sort of assigned himself to this flight so he could take a look around on Mir for himself. And as I mentioned last week, he has a strikingly gigantic head. I’ll post photos, it’s crazy. This is his fourth and final flight.

A couple weeks before the launch, STS-91 met a significant milestone by passing a propellant loading test of its external tank. This was significant because this wasn’t just any external tank, it was the fancy new Super Lightweight Tank. Seriously, that’s what they called it. Which I guess makes sense because ever since 1983 the tank was called the Lightweight Tank, so what else are you going to call a lighter weight version? The Super Lightweight Tank used a combination of new metal alloys and a machined orthogrid along with other tweaks to shave off as much mass as possible. If you’re curious, an orthogrid is basically just what it sounds like: an orthogonal grid. Rather than attaching long metal elements called stringers to stiffen the large tank, they started with a thicker sheet of metal and then machined out thousands and thousands of squares, leaving behind a grid of thicker metal that maintained rigidity while the machined-out squares were thin and light. The tank lived up to its name with a dry weight that was around 3,400 kilograms, or an incredible 12%, less than its predecessor, for a total dry weight of around 26-and-a-half-thousand kilograms. That’s pretty impressive considering that when filled, it carried around 733,000 kilograms of propellant, nearly 28 times more than its own mass. To bring those numbers down to Earth a bit, a standard 12 ounce soda can weighs about 25 times more when full than when empty. So the Super Lightweight Tank was doing even better, while also being just a bit bigger.

All of this effort was worth it because while it didn’t quite make it all the way into orbit, the External Tank is propelled almost all the way into orbit. This means that for each kilogram of mass saved in the tank, you get almost a full kilogram of extra payload. Building the ISS was going to require lofting a lot of mass, and with its relatively high inclination orbit demanding even more performance, every bit of payload savings was a big deal.

On June 4th, 1998, after a smooth countdown with no unplanned holds, Space Shuttle Discovery leapt off of the pad at 6:06 and 24 seconds AM, Eastern Daylight Time, kicking off STS-91. First time flyer Janet Kavandi said quote “Until I felt the SRBs go off, I didn’t really fully anticipate what was going to happen. It brought tears to my eyes; I was actually crying on the way up, not because I was scared, but because it was just a flood of emotion as I felt all the power and everything thrusting us into space.” end quote. And since I got that entire quote from his book The Twenty-First Century in Space, I’ll once again thank Ben Evans and remind you all to check out his work!

Before we even get to Mir, we have to take a little bit of a step back and learn some physics. That’s because riding in the back of the payload bay was the first iteration of the Alpha Magnetic Spectrometer, or AMS-01. In a sense, this experiment existed because the decision was made to build the ISS. Without getting into the whole tortured history, in the early 1990s there were two major scientific projects in the United States that somehow found themselves as rivals for the same slice of government funding. One was a gigantic particle accelerator called the Superconducting Super Collider, or SSC, and the other was the International Space Station, or ISS.

As you know, the ISS did not get canceled, which means that the SSC did, in a big blow for the particle physics community in the United States. In a move that I guess was taking lemons and making lemonade, Nobel Prize winning physicist Samuel Ting began a campaign to fly a particle physics experiment on the ISS: the Alpha Magnetic Spectrometer. Fast-forwarding through a number of years and here we are with AMS-01, which was serving both as a proof of concept as well as a calibration opportunity for a larger version that would eventually fly on the ISS, creatively named AMS-02.

The broad goal of AMS was to answer two questions: where’s all the antimatter, and what the heck is dark matter? If physicists were right about the start of the universe, there should have been an equal amount of matter and antimatter, but when we look around us we pretty much just see matter. So AMS sought to answer question “where is all the antimatter?” It was possible that entire galaxies of antimatter were out there in the universe, and if that was the case AMS should be able to detect antimatter cosmic rays flying through space. But if large amounts of antimatter were not detected, scientists would have to go back to the drawing board when trying to answer the antimatter question.

At the same time, AMS would be looking for evidence of “dark matter”. Dark matter is sort of a misnomer. It’s not literally dark. I mean, it might be, but that’s not why it’s called that. When astronomers looked at distant galaxies and figured out how fast they were rotating the answer turned out to be “way too fast for our current understanding of physics to be right.” Astronomers had a few options. One option would be to decide that in a wild coincidence, from our point of view in space every galaxy was just about to spin itself into pieces, regardless of how far away it was and thus how far back in time those events were. Another option would be to decide that the laws of physics, specifically gravity, are different in different times and places of the universe. Neither of those options are pretty appealing for scientists who are looking for a general theory that explains how the universe works. So they went with another option. If we assume that the part of the galaxy we were seeing was actually just a small fraction of the overall mass, then its rate of rotation would line up with expectations. But that would imply that there was a crazy amount of unseen matter out there. The name given to this large majority of unseen, unknown stuff was, you guessed it, dark matter. So it’s more like “mystery matter” than “physically dark matter”, but again, who knows.

OK, so that all sounds pretty cool. But how do you actually do that? How do you even try to answer those questions? This is why I kind of love AMS. The folks who built it had to solve some pretty tricky engineering problems but at its heart, AMS is very simple. Fly a big magnet in space, wait for stuff to fly through it, watch how fast it was going and how its path bends. That’s it. Really I think we just want to know how the path bends, but since that will depend on the particle’s speed, we also need to record the speed. We can learn a lot just by watching the paths that particles take in a magnetic field. An electron weighs practically nothing so is really easy to deflect, so it flies around in these crazy spirals. A proton has the opposite electric charge of an electron, so it will deflect in the opposite direction but it weighs nearly 2000 times as much as an electron so its path bends much more slowly. But what if you see something that bends in the direction of a proton but moves like it has the mass of an electron? That, dear listener, is antimatter: a positron, or anti-electron. Similarly, a particle that bends like an electron but an electron that weighs nearly 2000 times more, that’s an antiproton. And if a bunch of unexpected antimatter was found flying around, that would be an important clue in the search for where it all went. That’s the basic idea. Record how fast a particle is going and how it bends, and you can tell what sorts of particles are flying through the detector. But of course, once you get into the nuts and bolts it’s a little more involved.

First, we need a big donut-shaped magnet. OK fine, go get a bunch of neodymium and get to work. Next we need to know how fast the incoming particles are going when they enter the magnet. For this, we use a type of sensor called a time-of-flight scintillator. With this we can measure what time a particle enters the experiment and what time it hits the bottom, and since we built the experiment we know what that distance is and we can figure out the speed.

Next, we need to know how the path of the particle is curved as it passes through the magnet. To do this, we have 1,921 sensors arranged in six horizontal layers in the experiment. A particle passing through the experiment will pass through each layer, which records its position. From that, scientists can just connect the dots and figure out its trajectory. At the bottom of the experiment is a ten centimeter layer of aerogel that sits above 168 phototubes, which are basically cameras which look for particles interacting with the aerogel. This final layer helps to differentiate between protons and more exotic stuff like pions and muons.

Believe it or not, that’s the simple version. Since we’ll be talking about this again when we someday get to STS-134 which, spoiler alert, will deliver AMS-02 to the ISS, and since this isn’t actually a physics podcast I’ll just reiterate AMS’s job as: big magnet bends particle paths.

OK, so this is all great, and the detector was doing its job in the payload bay, but there was just one problem.. the Ku-band antenna wasn’t working. Or, put into NASA-speak, quote: “After Ku-band activation, the system failed to radiate any radio frequency energy when placed in the communication mode.” The Ku-band antenna, again, is that funny little antenna that sits on a robot arm at the forward starboard corner of the payload bay. By using a higher frequency radio signal and by pointing the antenna directly at TDRS satellites, tracking them as the orbiter flies around the world, the Ku-band antenna provided data rates to the ground that were much higher than something like an S-band omnidirectional antenna. Ku-band is great for stuff like live television broadcasts, getting lots of telemetry about the orbiter itself, and critically in this case.. data from experiments. So without this antenna, scientists on the ground couldn’t get any live data from AMS. The data was still getting recorded, but it was important to get the data on the fly in case the system needed to be calibrated. And that calibration was extra important because the results of this flight would dictate the design of the bigger version destined to fly on the ISS. Plus, there was always a chance that the onboard recorder failed too, in which case the data would just be completely lost.

The crew got to work trying to figure out what was wrong with the antenna, starting with the old classic of turning it off and on again. When that didn’t work, they started taking apart electronics. The hope was that the issue lay in the electronics inside the crew cabin, in which case maybe the faulty part could be repaired or bypassed. Unfortunately, it soon became apparent that the problem lay outside of the crew’s ability to repair it mid-flight. The crew were able to switch things over so that AMS data could be downlinked to ground stations via S-band, which was slower and had more limited coverage than TDRSS. It was better than nothing, but it severely limited the amount of data that could be received during the mission.

AMS ended up operating for 184 hours during the mission, recording over 200 million events, but fewer than 19 hours of that data was downlinked before landing. This actually proved to be sufficient, but I’m sure that Dr. Ting and his team were sweating bullets as they watched the data trickle in.

And just so we can turn our attention fully to Mir, I’ll tell you now how the AMS results shook out. No dark matter was found, but some antimatter was indeed detected.. buuut no more than would be expected from cosmic rays interacting with the interstellar medium. Put another way, there was no surprise excess of antimatter. And importantly, no anti-helium was detected, which would have been a major finding. As always in science, this shouldn’t be construed as a failure, but just as more data. The results set an upper limit on how much antimatter could be out there, if it was indeed out there. I was trying to think of a good analogy for this and my brain came back with this insane sentence which I’m just going to pass on to you: it would be like saying “well, if there are any raccoons in my backyard there probably aren’t thousands of them, because I looked through my window for five minutes and didn’t see any raccoons.” This brings me to my new science experiment proposal: the SRS, or Space Raccoon Spectrometer.

Oh hey, what’s that looming in the overhead flight deck windows? It’s Mir! Here to save me from this bizarre raccoon tangent!

Yes, even though the Ku-band antenna failed at actually doing Ku-band communications, its secondary function as a rendezvous radar was still working just fine. The pilot crew maneuvered Discovery to a point about 200 meters below Mir and began working their way up. Thanks to an interview for the Smithsonian-published book “Space Shuttle: The First 20 Years” we can get a little insight into what it’s like flying the shuttle in prox ops from mission commander Charlie Precourt. He said, quote “For a pilot, the response of the shuttle is totally different from that of an airplane. You pulse the jets, then you wait for the response. It takes a while for the input to take effect. Say you want to move directly above the space station. You’d do some ‘up’ pulses with your hand controller as well as some pitch change pulses to rotate the vehicle as you move up. You do a set number of pulses, predicting what the response will be. Then you stop and wait 45 seconds or so to see what happens. Then you correct it. It’s not aggressive control; it’s patient, timely inputs. If it’s not where you thought it was going to be after 45 seconds, you shouldn’t wait too much longer. If you do, you might need a much bigger correction.” End quote

And it’s a good thing Precourt sounds like a patient and steady-handed commander, because during the approach there was one minor hiccup with our old friend RPOP. RPOP, again, stands for Rendezvous and Proximity Operations Program and it’s an application that runs on a laptop mounted near the aft flight deck windows. Its job is to show the shuttle commander where the orbiter will go, relative to the target, in the next few minutes. It basically serves as a situational awareness tool that helps clarify the counterintuitive motions associated with flying two low Earth orbit spacecraft in close proximity.

An important feature of RPOP is the ability to show multiple trajectories that use multiple data sources as input. This is a nuance of spaceflight that I think is lost on a lot of people who don’t have to deal with the really nitty gritty aspect of navigating in orbit, and certainly was lost on me until I began working on OSAM-1: you sort of have to choose what flavor of truth you’d like to use since when you are in space you’re never completely sure where you are and where you’re going. Of course, as Heisenberg tells us, that’s true all the time, but I’m not talking about quantum mechanics here. Stuff in low earth orbit moves very fast and is usually pretty far away from anything else. This means that any measurement of its position and velocity, also known as a state vector, has more uncertainty in it than a lot of people might expect. The result is that rather than your knowledge of a spacecraft’s position looking like a point, it’s more like a bubble. Specifically, a bubble that’s super stretched out in the direction of travel since, by definition, that’s the direction it’s moving fastest. Think of it like this: imagine measuring the altitude of a car as it drives down the highway and then measuring it again a tenth of a second later. Unless it’s falling out of the sky, the two values will be pretty close. Now try this again but instead measure the car’s distance to the side of the road. Again, the two values will be pretty close, even if you’re in a turn. But now measure how far the car has moved down the road in that time. The number will be way bigger. In a tenth of a second, a car that’s moving at highway speed might clear three meters in a tenth of a second. So if your timing is off by a little bit you’ll still be mostly right about its altitude and its position relative to the side of the road, but you could be significantly wrong about how far down the road the car is. The same problem applies in space, but instead of maybe a few meters of uncertainty, depending on how safe you want to be, the bubble could be a few hundred meters tall and wide, and few dozen kilometers long.

And you can combine this with the fact that the modeling of the problem won’t be perfect. We won’t know the absolute precise drag area of the orbiter or its absolute precise mass or the absolute precise density of the air outside, and so on. So errors build up. When you’re flying all on your own this is no big deal. But when you’re trying to very gently nudge up against a Russian space station, this uncertainty becomes an issue.

OK fine, so what to do? What you do is have multiple different methods of calculating your state vector. By the time Discovery was right outside of Mir it was relying on a propagated version of its old state vector, the rendezvous radar, the Trajectory Control System, and the laser rangefinder. So RPOP had the ability to show multiple solutions at once, basically saying “hey, according to the radar, we’re going to move like this. But according to the laser rangefinder we’re going to move like this.” Which solution the commander considers to be true is sort of subjective and requires judgment. When you’re really far away you probably shouldn’t believe the laser rangefinder since it can’t even see the station at all and will be reporting nonsense. But as the orbiter got closer, the high precision of the laser rangefinder meant that it was much more trustworthy than the more coarse solutions from the propagated state vector or the rendezvous radar. In fact, during the final parts of prox ops, it was expected that those last two solutions would start to diverge and the crew would just ignore them.

Since the final parts of prox ops are a pretty tense time, the crew wouldn’t necessarily want to dedicate the mental bandwidth to ignoring a solution that they knew was wrong. With that in mind, the RPOP developers provided a button the crew could press to hide those solutions when they began to diverge. The problem today was that when the crew hit the button, it also turned off the solution from the Trajectory Control System, which is one of the solutions the crew would want to have during prox ops. The crew tried resetting RPOP and once again some of the less precise solutions diverged and once again they tried to turn them off and once again the TCS went with it.

In the end this was actually more of a nuisance than a serious problem, but nuisances and distractions during critical phases of flight have a way of growing into much bigger issues.

The reason that this problem caught my eye, and why I gave it maybe more time than was strictly necessary, is 1) it’s nice to kind of trick you all into a spaceflight physics lesson once in a while and 2) because RPOP was one of the inspirations for a tool me and my team are making for the OSAM-1 flight dynamics ground code: the Trajectory Monitor. Our Trajectory Monitor has a similar feature where we show our future trajectory as predicted by different force models and input states. Essentially, we show where the spacecraft thinks it’s going and we show where we on the ground think it’s going, with our faster computers and more accurate physical modeling. This way if it looks like it’s going to be in trouble a few hours from now we can potentially intervene and fix the problem. Or critically, if the spacecraft thinks everything is fine but we can see that it is, in fact, going to be in trouble, we can call for an abort. So this story about RPOP failing to show critical data during a critical phase of flight really made the hair on the back of my neck stand up as I took a few notes to make sure that our version of this tool doesn’t do the same thing!

Anyway, despite the slight hiccup from the otherwise very useful RPOP, Space Shuttle Discovery finally closed those few meters it left open back on STS-63, and docked with Mir approximately 43 hours after liftoff.

We’ve been through this part of the story a few times so I’ll spare you the numbers and little details, but Andy Thomas transitioned back to being a shuttle astronaut, and thousands of kilograms of equipment and water crossed the hatch going in both directions. I will note that Fuel Cell 3 was having a minor problem which was resulting in it leaking water overboard. So to help with that the ground turned the water tank pressure down during the crew sleep periods. This meant it took a little time to repressurize every day when the crew woke up, which meant that less water was available at the middeck galley resulting in only about 80% as much water transferred as usual. But somehow, 101% of the total cargo they planned to transfer actually got transferred, so I guess they found some extra stuff to deliver or bring home.

The entire crew would have been excited to cross through the Docking Module and visit Mir, but I have to imagine that this especially applied to Valery Ryumin. He hadn’t been to space in nearly 18 years and in that time he had become a lead designer at Energia, which meant that Mir was his baby. And after working on it for decades he was finally seeing it in person for the first time. For Musabayev and Budarin it must have been somewhat bizarre to be literally off the planet and then suddenly have their like, boss’s boss’s boss’s boss show up to take a look around, though they were glad that someone from upper management was seeing the state of things for themselves.

Ryumin was reportedly “displeased” with the staggering clutter and mess onboard the station, saying he thought it made work for the cosmonauts extremely difficult. In an oral history interview with Charlie Precourt, Precourt recalls how on the first day at Mir Ryumin said to him “Charlie, this place is in bad shape. I don’t know how they live up here. This is awful. This is worse than I imagined. This is unbelievable. This is unsafe.” Precourt responded “Well, this is the way it’s been for the last four years. I’ve been telling you this for the last two missions i debriefed.” And Ryumin responded “Yeah, but, you know, when you don’t get to see it for yourself, you hear these stories, you just don’t imagine how bad it really is.” Ryumin was getting to experience for himself the result of the ground just completely losing control of inventory management on the station, which he estimated to have happened back around 1989. Precourt talked about seeing boxes of food up there that were labeled for John Blaha and even Shannon Lucid, who had been home for two years. Ryumin vowed that they would learn the lesson and do better on the ISS.

But by the third day Ryumin had relaxed a little, saying “Well, you know, I think I could get used to staying up here and being here. Maybe I’ll just stay.”

There was one funny moment when Ryumin found a bunch of literal garbage behind a wall panel and radioed down asking for permission to get rid of it. But I guess mixed in with all the garbage were important cables so mission control denied his request. Ryumin was irritated not only to have his request shot down but also because he couldn’t really argue back or overrule them.. because when on the ground he had always made a big deal out of making sure the on-orbit crews adhering to decisions made by mission control! To quote Michael Scott, well well well, how the turn tables.

The entire crew spent the week zipping around, making sure that the right cargo was in the right place on the right spacecraft. During that time, spaceflight rookie Janet Kavandi discovered how interesting Mir’s node is. She talked about how much fun it was to float there and just look around in the various directions. Quote “Since there could be no ‘up’ or ‘down’ in a vehicle such as this, it was very amusing to look into one module and see people ‘standing’ on the wall, working on an experiment. In the adjacent module, someone might be jogging on a treadmill on the ceiling. Beneath you, you might see someone else having a meal underneath your feet. Above your head, you’d hear the thumping of a body coming toward you, and you’d have to move aside to make room for them to pass.” End quote.

With no new experiments to set up or new long term resident to instruct, docked operations flew by and a little under four days after arriving, it was already time to go. Pilot Gorie was given the chance to perform the undocking and subsequent flyaround at a distance of around 75 meters, which was pretty nice of Charlie Precourt. As they backed away, Andy Thomas watched out the window, later saying quote “It was fascinating, because, you know, I’d spent four and a half months on Mir, but it was inside Mir. I really didn’t see the outside of the vehicle. I’d seen it briefly when we first docked, but not a lot. So the fascinating part was that as we pulled away and did a fly-around, I was able for the first time to get to see the outside of what had been my home for twenty weeks. That was really interesting. I’d say, “Oh, yes, I know that window. I used to look out that window. Oh, is that what that was? I wondered what that thing was.” And so that was kind of fun” end quote.

And actually, the combined crews still had one more bit of business to accomplish. A few minutes before orbital sunrise, when the lighting conditions would be ideal, Musabayev and Budarin injected a tracer gas through a port in Spektr’s hatch and into the depressurized module. The gas, a mix of acetone and biacetyl, was expected to become ionized and show up as a dull glowing green cloud in the low angle of the orbital sunrise. If the cloud could be spotted near Spektr it might give a clue as to where the leak was located. This had actually been attempted two days earlier while Discovery was still docked, with everyone watching from the various windows on the combined spacecraft, but with no luck. And it turns out this second attempt, with the Discovery crew peering back at the station, was no more successful. The leak remained elusive. Oh well, it was a good idea. Pilot Gorie blipped Discovery’s thrusters, and the orbiter drifted away. No American would ever see Mir up close again.

The few days between undocking and returning home passed uneventfully, with the Alpha Magnetic Spectrometer doing its thing in the payload bay while the crew kept a close eye on it, as well as tending to the orbiter and some onboard experiments. Yes, there were some crystals, no, we’re not gonna talk about them. One interesting item of note was that the RMS was taken out for a spin in order to take a look at the side of the orbiter. Remember that leaky fuel cell? Well, it was completely harmless, and was even known about before launch. But that “completely harmless” label came with the footnote: as long as it wasn’t growing a big giant icicle out of the port that was leaking the water. Such an icicle could break off and then damage the thermal protection system, which would be no good. The port in question was on the starboard side, a little aft of the crew cabin, close to where the delta wing merges into the main fuselage. Since the RMS is mounted at the forward port side, this meant that it had to bend over at sort of an awkward angle in order to take a look at that part of the orbiter, but Kavandi was able to get it into position and inspect the port. There was a little ice around the port itself, but no scary icicle to worry about, but it was better to have checked.

After an uneventful reentry and landing, Space Shuttle Discovery touched down at the Kennedy Space Center, wrapping up 9 days, 19 hours, 54 minutes, and 0 seconds in space. Of course, this also wrapped up 812 days of continuous American presence in space, and when we add Norm Thagard’s mission to the continuous stints of NASA-2 through -7, we get a total of just under 916 days with Americans living on Mir. The Shuttle-Mir program was now in the history books, and podcasts, and it was time for the ISS to take center stage.

But before we say goodbye to Mir forever, we should take one last look back at the seven incredible missions NASA astronauts performed there, as well as learn a bit about the station’s ultimate fate. But jeez, that sounds like it could take a while. Maybe even an entire episode. So…

Next time, we take a whirlwind tour through all the Shuttle-Mir missions again, venture back inside Spektr, and wonder why Taco Bell is unfurling a giant target in the South Pacific Ocean.

Ad Astra, catch you on the next pass.