Episode 177: STS-90 - Of Mice and Medicine (Neurolab)

On STS-90 we’ve got dozens of nervous system experiments to get through, we’ll play some catch, take a whirl in the crazy chair, and we’ll wonder where NASA got 2000 crickets.

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

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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 177, Space Shuttle flight 90, STS-90: Of Mice and Medicine

Last time, we watched some spacewalks through the window, played some video games, and wondered just how many fires a single space station could endure as we rode along on NASA-7 with Andy Thomas, the last astronaut to live and work on Mir. We’ll still see a little of Mir when we go to pick Andy up, and I’ve got a retrospective episode planned, but with the end of NASA-7, astronauts were out of the long duration spaceflight game.. for now. While Thomas was working on Mir, life continued on Earth, and even above it! Today we’ll cover the one shuttle mission that flew during Thomas’s lengthy mission: STS-90.

STS-90 is a mission that’s sort of the last of its kind. We still have some upcoming missions that will be dedicated to science, but the great majority of the remaining flights are related to the ISS or Hubble, and none will have such a singular focus on a single field of scientific inquiry. Now, a concept like “focus” can be pretty qualitative and tough to pin down, so here’s something a little more definitive about this mission: not counting the unpressurized pallets cause they’re kind of boring, this is the final flight of Spacelab. Spacelab, of course, is the European-made big pressurized can that was placed in the orbiter’s payload bay, greatly expanding the capability of the shuttle and transforming it into an on-orbit laboratory. First introduced way back on STS-9, with none other than the great John Young in command of the mission, Spacelab would go on to fly 16 times in total, including today’s flight.

Spacelab essentially made the orbiter into something in between the space truck it was originally envisioned as, and something like a space station. It was as if for two weeks at a time, NASA had a one-module space station at its disposal. As always seems to be the case in spaceflight, the program cost more than expected and didn’t always have as quick as a turnaround as hoped, but there is no denying that Spacelab was a huge success. According to Space Shuttle historian Dennis Jenkins, in only its first decade of flight, Spacelab supported more than 760 experiments, resulting in more than 1000 peer-reviewed articles, 2000 talks and abstracts, and 250 master and doctoral theses. And by 2009 an incredible 5,475 publications had resulted from Spacelab experiments.

Inside Spacelab for its final flight was Neurolab, an investigation into how the nervous systems of humans and animals are affected by spaceflight. For part of the reason why this mission is sort of the last of its kind, we can turn to an oral history interview with Dr. John Charles, the principal investigator of the Lower Body Negative Pressure device we’re so familiar with. He said, quote, “The investigator community themselves realized early in planning for SLS-1 that they were interfering with each other. They couldn’t do all the things they wanted to do just because somebody else’s final state, after the astronaut’s finished doing that investigation, becomes the next guy’s initial condition. That initial condition doesn’t mimic what happens in regular spaceflight, it mimics what happens when your astronaut has just finished drinking a gallon of some sort of metabolic tracer fluid or something.” end quote. So with SLS-1 flying in 1991 that means that as early as the late 80s scientists were realizing that their experiments were sort of stepping on each other. Clearly that does not mean that useful science couldn’t be done, but it does make planning the mission and the experiments much more complex and difficult.

So really what scientists needed was a way to do these experiments without cramming them all into the same frantic two week period. They needed time for crew members to return to a baseline. Basically –stop me if you’ve heard this before– they needed a space station. So yeah, at this point in the program, all roads lead to the ISS.

We’ll get into what exactly Neurolab entails once we make it to orbit. But first, let’s meet the crew.

On this flight we’ve got more rookies that we’ve seen since all the way back on STS-73, eighteen flights ago. So with apologies to the newbies, the bios will be a little shorter than usual. Or at least I’ll try.

Commanding this flight was Rick Searfoss. This was his first time in the Commander’s seat, but we know Searfoss from STS-76, where he was the Pilot and helped to drop off Shannon Lucid for her extended stay on Mir. This is Searfoss’ third and final flight.

Joining Searfoss up front was today’s Pilot, Scott Altman. Scott Altman was born on August 15th, 1959 in Lincoln, Illinois, growing up in nearby Pekin, Illinois. He graduated from the University of Illinois with a degree in Aeronautical and Astronautical engineering and set off to join the Air Force. Unfortunately, he found he was too tall for the Air Force, but apparently the Navy has more lenient height limits, and Altman was soon in training to be a naval aviator. He completed two cruises while flying the F-14A before heading over to the Navy’s Test Pilot School. Around the same time he went back to school and picked up a Master’s in Aeronautical Engineering. After returning from a deployment that saw him serve as strike leader over Southern Iraq, he was selected as an astronaut, reporting to JSC in March of 1995. Altman has already sort of blown up my “shorter biographies” plan but there’s one more anecdote of his that I simply can’t not include: he’s the real Maverick. Or rather.. his squadron happened to be at Miramar when the 1986 film Top Gun was being shot, and he and three other lucky pilots were deemed mature enough to handle the unconventional flying requested by the filmmakers, with Altman filling in for the fictional Maverick. This granted Altman unusual permission to do some stuff that would normally get your wings revoked before you knew what hit you, including stuff like buzzing the tower. I’ve also seen multiple sources, including Altman himself, claim that he was the actual person to flip off the Soviet pilot while inverted in the famous scene. Though, since there’s no way those two planes actually could have been that close I’m guessing he had to use his imagination a bit for that scene. This is his first of four spaceflights, where flying inverted is a little easier.

Behind Altman was find Mission Specialist 1, Rick Linnehan. We know Linnehan from STS-78, one of the Spacelab-based life sciences flights. Linnehan is actually a veterinarian, and as both a vet and the payload commander, he was the ultimate authority when it came to the numerous animals onboard the flight. Yes, some of these animals would be paying the ultimate price for science, but Linnehan’s job was to make sure that they were comfortable and cared for and that their sacrifices were not in vain. He said quote “I can guarantee the animals are well-fed, well-housed, and well-cared for. It’s my duty to check every day to make sure everything looks good as far as their food, water, and general health. I have absolute authority, on-orbit, if I need to, to stop an experiment if an animal becomes sick.” end quote. This is his second of four flights.

Moving over to Linnehan’s left, we find Mission Specialist 2, Kay Hire. Kathryn Hire was born in Mobile, Alabama, but actually considers Merritt Island in Florida to be home. If that location sounds familiar to you, it’s because it’s also the home of the Kennedy Space Center, so it makes sense that Hire is the first KSC employee to be selected as an astronaut. She graduated from the US Navy Academy before being commissioned as a Naval Officer, and ten years later picked up a Master’s from the Florida Institute of Technology. After graduating from the Navy Academy, she spent the next few years flying all around the world doing oceanographic research before going to work for NASA as a Space Shuttle Engineer, working on the vehicle itself and stuff like the crew access arm. In 1993 she became the first woman assigned to a combat aircrew as part of Patrol Squadron Sixty-Two. As Mission Specialist 2, Hire is today’s Flight Engineer, and she’ll be helping Searfoss and Altman keep the orbiter happy and healthy while the science team toils away in Spacelab. This is her first of two flights.

Moving downstairs, we meet Mission Specialist 3, Dave Williams. Dave’s actual first name is Dafydd, spelled D-A-F-Y-D-D. I’m not entirely sure how to pronounce that but it doesn’t really matter since he went by Dave. However you say it, Dafydd Williams was born on May 16th, 1954 in Saskatoon, Saskatchewan in Canada. He earned a Bachelor’s in Biology from McGill University before continuing on to earn a Master’s in Physiology, Doctorate of Medicine and Master of Surgery. He spent a few years working in surgery and emergency medicine, including evaluation of CPR training and methods to identify high-risk trauma patients. As part of his postgraduate studies he became interested in neurophysiology in vertebrates, specifically looking at how hormones modify sleep-wake cycles, which would eventually make him perfect for this flight. In 1992 the Canadian Space Agency selected him to become an astronaut, where he performed several ground-based roles, including a 7-day simulated mission. In 1995 he was selected as a full Mission Specialist and this is his first of two flights.

And joining the main crew were two Payload Specialists! Payload Specialist 1 was Jay Buckey. Jay Buckey was born on June 6th, 1956 in New York, New York. His undergrad work was in electrical engineering and he went on to get his Doctorate in Medicine from Cornell. He’s actually been lurking in the background of our narrative for a while now, serving as backup Payload Specialist back on STS-58. Well, this time he got the nod for this, his one and only spaceflight.

And last but certainly not least, Payload Specialist 2, Jim Pawelczyk. James Pawelczyk was born on September 20th, 1960 in Buffalo, New York, but he would say he’s from nearby Elma, New York. He earned one Bachelor’s degree in Biology and another in Psychology, a Master’s in Physiology, and a PhD in Biology. He was a visiting scientist at the Department of Anesthesia in Copenhagen, and helped work on the book “Blood Loss and Shock”. This is his only spaceflight.

And there’s the crew! OK, I’m pretty sure that I failed at my goal of making that shorter than usual, but it’s not my fault that astronauts are interesting people!

The first launch attempt for STS-90 needed to be scrubbed before the crew even boarded due to a failed network signal processor, without which the orbiter would not be able to send and receive voice and data signals. No problem though, a technician popped on over to the Orbiter Processing Facility and dug one out of Endeavour, resulting in only a 24 hour recycle. Though even a slip of a single day is a little more exciting on this flight. Thanks to the animals on board as part of the nervous system studies, technicians had to carefully lower themselves down into Spacelab to retrieve their lockers and make sure they were well cared for during the downtime. I hope that the privileged few who got to go spelunking in Spacelab over the years got some sort of exclusive mission patch.

The next day it was time to try again, and everything proceeded smoothly. First time flyer Jim Pawelczyk recalled what it was like to arrive at the launchpad, which at this point was almost completely deserted. He said you get off the van and you’re all alone while a helicopter circles overhead. You’re wearing 86 pounds of spacesuit and survival gear while wearing two full layers of long underwear, all in the thick and humid Florida air. And I checked the historical weather logs, at that time of day it would’ve been 82 degrees Fahrenheit or about 28 Celsius and since it’s Florida, guaranteed to be humid. Pawelczyk described his seat as not being very comfortable, but after squirming around to get in the right position and strapped in by a technician, it was a huge relief to finally hook into the suit cooling system. He described it as “as refreshing as a swimming pool on a hot summer day.”

As Pawelczyk enjoyed his recumbent swimming pool, the hours ticked by, and on April 17th, 1998, at 2:19pm Eastern Daylight Time, Space Shuttle Columbia leapt off of the pad and STS-90 was underway. 10 seconds after SRB separation, Columbia was the first orbiter to try a new performance-enhancing technique and fired its OMS engines for 102.4 seconds. My understanding here is that while the thrust from the engines was maybe helpful, it wasn’t the real reason for doing the burn. In fact, the mission report even notes that they can’t accurately determine how much additional velocity was imparted by the OMS engines since their effect was so small compared to the SSMEs. But the 1800 kilograms of OMS propellant expended during the burn was that much more mass that the main engines didn’t have to push to orbital velocity, enabling 112 additional kilograms of payload. I didn’t see a rationale for why it was OK to burn off 1800 kilograms of OMS fuel before the mission ever got going, but I suspect it has to do with the small size of the propellant tanks in the forward RCS module. My guess would be those smaller tanks are always the limiting factor, which left more than enough extra in the rear tanks, so they might as well use it. Though if that’s true I have to wonder why they didn’t just leave the propellant out of the tanks in the first pace. If I had to guess on that it would be related to prop sloshing or maybe just not wanting to validate liftoff in a new configuration. Or maybe the additional thrust was making a bigger difference than I thought. In any case, engineers must have liked the results because this would be the norm on most flights going forward.

So between the new OMS burn and the new roll to heads up, ascent is getting even more exciting than it used to be! 8 minutes and 27 seconds after lifting off, the main engines shut down, and it was time to get to work.

Spacelab activation was delayed by 40 minutes due to high carbon dioxide levels inside, but that soon dropped and the crew were able to start activating the laboratory. Inside were mice, rats, fish, snails, and crickets, adding up to over 2000 animals who had just made the ride of their lives. These 2000 animals, along with the seven big ones in the bright orange suits, would be participating in 26 experiments: 11 performed on the crew, and 15 on the animals. Specifically, the slightly awkwardly phrased themes of the experiments were: autonomic nervous system, sensory motor and performance, vestibular, sleep, neuronal plasticity, mammalian development, neurobiology, and my favorite, which is just listed as “aquatic”. But in general they were trying to ask the question of how gravity, or the lack of it, affects the nervous system, and how the nervous system adapts to change. After all, isn’t it kind of weird that humans only take a couple days to adapt to weightlessness after an entire lifetime, and evolution of the species, in 1G? How does the brain do that?

A good number of the 2000 animals in Spacelab were crickets, which kind of seems like cheating to pad the numbers, but I guess if you’re gonna bring a bunch of crickets somewhere you might as well go all in. Crickets are a handy animal to bring to space for a couple of reasons. One reason is that they have a pretty simple and well understood nervous system, so it should be more straightforward to study it and see how it was affected by a stint in weightlessness. Crickets are also handy because they will turn their heads from side to side depending on how you tilt them, I guess just keeping their heads upright. They can do this because, just like us, crickets have an organ that determines which way is up or down. For humans, it’s a part of our inner ear that has some small crystals that basically roll around inside a small space. For crickets.. it’s some other thing. I don’t know, this isn’t a cricket podcast. Scientists were curious to see if crickets that developed in space would end up with a smaller gravity sensing organ since they weren’t getting any useful signals from them. They also wanted to see what the space crickets would do when they returned to Earth. Would they be able to figure out which way is up and which is down? Thanks to their head tilting, it should be easy to see.

The gravity sensing organs actually grew to their usual size, but scientists found that there were changes in how it connected to the nervous system. They also found that while the parts of the brain responsible for handling gravity data were significantly changed, the crickets’ behavior was not. Which meant that somehow the crickets were compensating and adapting in a way that was not exposed by this experiment. So if anyone out there has always wanted to fly some crickets in space, there’s your excuse.

Moving over to the crew as subjects, we have the Visual-Otolithic Interactions in Microgravity experiment and the Spatial Orientation of the Vestibulo-Ocular Reflex experiment. These two combine into what I call “the crazy chair”. It seems like scientists are always trying to find excuses to load astronauts into crazy chairs and probably make them barf. For this one, a crew member would load themselves into this big chair that looked sort of like an ejection seat. Once inside, they would seal themselves off from any light from the rest of Spacelab, and position a special camera that can watch the movement of their eyes. Then, the chair would start spinning at 45 rpm, the same as a vinyl record. One of the fast ones! With no visual stimuli, the crew member’s brain only had their inner ears to rely on for data, so after a few minutes they would actually stop feeling like they were spinning and instead feel like they were tilted in a direction that depended on how the chair had been oriented. By studying their eye movements during this adaptation phase, scientists could learn how the brain switched its understanding of how it was moving. The post-flight presentation includes some video shot from the chair and man, it really gets going. I wouldn’t even want to get in this thing on the ground, let alone in space.

One question scientists sought to answer on this mission was if there is a critical period of development where if gravity is not present, an organism will never learn how to properly handle it. As way of example, if you take someone who was blind from birth due to an eye defect and then as an adult fix their eyes, they still won’t be able to see properly, at least not without a lot of time and effort. That’s because for all those years that the eyes weren’t sending any data, the part of the blind person’s brain that normally is dedicated to vision got bored and started lending a hand to other tasks. So when a bunch of vision data suddenly starts flowing in, the brain doesn’t know how to handle it and sort of has to start from scratch. So scientists wondered if there was a similar phenomenon for animals.

With that in mind, a number of mice and rats of various ages, and thus at various stages of development, were brought along on Spacelab. To be honest, I’m a little confused on which experiments involved mice and which involved rats, since several sources and interviews with the crew seem to mix them up. So while there were definitely both mice and rats, I’m just going to call them all rats. That way rather than being unsure of if I’m right or wrong on this, I’ll just know for sure that I’m wrong, and that somehow seems better. Apologies to any space mice listening.

Mission Specialist Rick Linnehan found that the rats adapted very quickly in a way that was similar to a human crew, and maybe even faster. Within a day or two they would could be seen pushing off of the walls of their cage to float over to another wall. He would also spot them floating around in the middle, nibbling on some food they were holding with their front legs as if they were drifting around in a pool. Then they would let it go, push off, go get some blobs of water to sip on, then go back and retrieve their floating food. He said quote “Some of them were so relaxed, like it was no big deal to them. It takes us humans a while to get used to manipulating things in freefall, and these guys were doing it on the second day.” end quote.

The crew also found that the rats would get around much like they did, by primarily using their forelimbs and sort of dragging themselves along while hindlimbs followed. Once they had their space legs, they had no problem scooting around a little jungle gym in their enclosure.

Once everyone was back on the ground, scientists found evidence that supported the idea of a critical period for developing motor skills. The space rats had an unusual way of walking, where they seemed to be only using their forelimbs, just like how they had learned in space. Additionally, their walk was unusually low to the ground since their brains weren’t firing the muscles that are responsible for lifting you up as part of a normal walk cycle. They also found that parts of the space rats’ brains seemed to have developed more than the ones that had stayed on the ground. The scientists speculated this may have been caused by the extra engagement the space rats got from being able to explore their enclosure’s walls and ceiling while the Earth rats only had the floor to explore. But it seems that this may have been a double edged sword, because once back on the ground, the space rats’ development slowed, perhaps because they were under-stimulated by being constrained to a boring 2D floor, so the Earth rats eventually caught up.

So while these results aren’t likely to be a concern until pretty far into the future, it has serious implications for humanity as a space-faring civilization. I’m pretty sure this was obvious already, but there was now concrete evidence that trying to raise a human baby in weightlessness probably wouldn’t be a great idea. Setting aside the concern about various messy fluids that are a problem even in 1G, let alone weightlessness, the baby’s brain would be eagerly trying to learn how movement and limb coordination works at a time when the rules of movement were very different than usual. It also raises questions about how that development would work in a place like a Mars base, where the gravity is only one third that of Earth’s.

Moving back to experiments on the crew, we have an unpleasant but interesting look at what role the nervous system plays in adapting to spaceflight, or re-adapting to life on Earth. Over the years, NASA had found that around 60% of astronauts returning to Earth were unable to stand for 10 minutes without needing to take a break and sit down. And sometimes they would suddenly faint in a way that was similar to someone standing up too fast and having the blood rush out of their head. But what was interesting about this was that some of these returning astronauts who were having trouble seemed to have a normal blood pressure. So even if it was temporary, why were they suffering from low-blood-pressure-like issues?

To study this, for one last time we’re busting out an experiment that we all know very well but haven’t heard about in a long time. Well, actually we sort of briefly heard about it in the intro but let’s pretend that didn’t happen. The Lower Body Negative Pressure device. As you’ll recall, this was sort of a weird sleeping bag that a crew member would partially enclose themselves in, cinching the bag tight around their upper body, with their legs inside. The pressure in the bag would be lowered, causing their legs to very slightly expand, which mimicked the cardiovascular challenge of returning to Earth. The original idea of this experiment was to see if regular stints in the LBNP device would keep the cardiovascular system from getting too accustomed to weightlessness, easing the transition back to Earth. That didn’t really work out, but now scientists had the perfect device for this experiment. A crew member would have a tiny little acupuncture-sized needle inserted into a nerve just below the knee (that’s the unpleasant part) and would then do a few rounds in the LBNP. The probe stuck into the nerve allowed the signals from the brain to the blood vessels to be collected as the pressure in the LBNP was lowered and the astronaut felt more like they were back on Earth. This essentially let scientists wire tap the call between the brain and the blood vessels. The principal investigator of the experiment said that finding a nerve is a really tricky task, even on the ground, so he was impressed that the astronauts were able to get it done in space.

In a different experiment, Mission Specialist Dave Williams had so much fun with one activity that he thought they could make an amusement park ride out of it. The actual experiment involved him sticking his head into a box that blocked off his view of Spacelab. Bizarrely, the moment he did that, he would feel like he was upside down. Take the box off, and he’s right side up again. Put the box back on, upside down, even though intellectually he knew that he was right side up with respect to Spacelab, with his head near the ceiling and his feet in some loops on the floor. He speculated that because every astronaut gets a puffy head from fluids no longer being pulled down by gravity that his brain felt like he was upside down, why else would there be all this extra fluid in his head? Normally, the image of a right side up Spacelab was apparently enough to counteract that sensation, but the second the image was gone, the brain fell back on its other sensors and again determined that it was upside down. Williams said “They were running video as part of the experiment and I probably looked like a pigeon sticking my head in and out like that.”

And that actually seamlessly leads into another experiment, where the crew donned a virtual reality headset. The goal here was essentially to study the effect that Williams had discovered on his own. When a crew member put on the VR headset, they would see an image of Spacelab. But rather than sitting still, the image would rotate around, as if Spacelab was a big rolling cylinder. After a little while of this, the brain would get kind of confused and decide that rather than Spacelab moving, the astronaut was moving! Scientists wanted to know how strong this effect was and how quickly it would set in. The press kit also noted that quote “Portable head-mounted virtual reality displays such as the one developed for this Neurolab experiment can be useful by providing visual prostheses for individuals with vestibular impairment.” And I’ll add that they’re also pretty great for simracing and Beat Saber.

In another examination of the crew’s adaptation to weightlessness they were presented with a deceptively simple task: catch a falling ball. But actually, when you think about it, catching a ball isn’t simple at all! First, your brain has to process the signals from the eyes to try to determine the state vector for the ball: where it is and where it’s going. Then it has to propagate that state vector out into the future, determining where the ball will be as it continues. Then it has to choose a point within reach of your hand and fire who knows how many nerve signals to coordinate the muscles of your shoulder arm and wrist to be in the right position. And then it has to accurately predict when the ball will make contact with your hand so you can close your fingers around it and grasp the ball. So the question was.. how much does your brain factor gravity into all that? And can it adapt when it’s no longer there?

This actually makes a huge difference. In space, at the time scales we’re talking about here, the ball essentially doesn’t have any acceleration. It just continues in a straight line at a constant velocity. And then also, your muscles don’t have to fight against gravity. So if the brain were to naively apply the same algorithm as usual, the ball would be much higher than expected since it wasn’t being accelerated downwards, and your arm would be jerked up too early and to a higher position since the muscle movements to fight against gravity were no longer needed.

To study this, before lifting off scientists had crew members sit in a chair and dropped a ball from the ceiling next to them. The crew member would reach out and catch the ball, and special sensors on their arms, hands, and the ball would allow scientists to track the motion. It basically looks like one of those motion capture suits they use in video games and movies. Then, once on orbit, they would basically do the exact same thing. Similar chair, similar motion tracking, similar ball. The difference, of course, is that there was no gravity. So when the ball was released, it moved at a constant velocity from Spacelab’s ceiling to floor as the crew member reached out to grab it.

Catching the ball was actually pretty easy, since it took around two seconds to reach the astronaut’s hand, but there were still some pretty interesting changes to observe. As you might expect, their arm muscles tensed and began moving earlier than they needed to, likely based on decades of experience of a falling object accelerating pretty quickly. They also found that the arm would stop or even reverse course when the crew member realized they were too early. Again, this might sound kind of basic, but it gives some insight into how the brain handles the task of catching a flying object. It’s not just relying on that initial state vector, it’s targeting, just like how the code I write at work figures out where and how big a maneuver should be. Your brain guesses when the time to contact is, observes the ball, notes that it was wrong and the difference between expectation and reality to make a new guess, observes, notes that it was wrong, and so on until contact. The fact that our brains apparently just inherently have the ability to run a targeter against some differential equations is pretty wild if you think about it, and it’s cool that some of the underlying details can be discerned with such a simple task.

Crawling down the tunnel from Spacelab back to the middeck and flight deck, we find that the orbiter has been running like a champ this whole time. In general, the issues experienced on the flight were small and easy to handle. Stuff like a cold thruster needing to be warmed up, or the waste collection system’s dump valve failing, requiring rerouting to some contingency water containers. But 7 days and 9 and a half hours into the mission, something broke that had the potential to be a show stopper: the RCRS broke down. The RCRS, again, is the Regenerative Carbon Dioxide Removal System, and is part of the Extended Duration Orbiter equipment, which is now unique to Columbia after being taken out of Endeavour. By using some clever chemistry to absorb CO2 from the crew cabin and then vent it out into space, the RCRS allowed for greatly extended missions since the crew would no longer be constrained by the number of lithium hydroxide canisters onboard. There were some lithium hydroxide canisters onboard as a backup, but not enough to last the entire planned mission duration. The crew put some time into debugging the RCRS, switching it to another controller, but that didn’t solve the problem. For now, they installed some lithium hydroxide canisters and went to sleep while the ground figured out how to handle it.

The next day the ground had a plan and Commander Searfoss and Pilot Altman worked to take the device apart and bypass a problematic valve that was allowing ambient air to mix. Around 18 hours after it first failed, the RCRS was back up and running and everyone could breathe a sigh of relief, which the RCRS then promptly scrubbed of CO2.

The RCRS problem ended up having essentially no impact on the mission, even though its initial failure did keep the crew up past their usual bedtime. But maybe the lack of impact was because their sleep was already sort of disrupted since, you guessed it, it was another one of the experiments. The nature of shuttle missions means that crews are not presented with ideal sleeping conditions. Orbital requirements often have them launching at a weird point in their usual sleep cycle, the lighting cues are all wrong thanks to the 15 or 16 sunsets and sunrises every day, other crew members might be bumping around while they try to sleep, and they’re in the midst of what is probably the most busy and important two week period of their lives. So it’s no surprise that more than half of shuttle crew members end up using some sleep medication during their brief flights. Scientists wanted to better understand how the crew’s sleep was affected by space. This could result not only in improved conditions for future space crews, but also for people on the ground who are required to disrupt their sleep cycle: medical personnel, people suffering from jet lag, night shift workers, and other roles like that.

With all this in mind, the crew would both be experimenting with melatonin to help regulate sleeping cycles as well as using a portable sleep monitor. Mindful of how the wires and electronics of the sleep monitor might disrupt the very sleep it was trying to study, the experiment’s principal investigator had assured the crews that it was designed to be comfortable to wear. He said that he had worn it while sleeping and actually preferred it, claiming to have slept better. The crew were pretty skeptical. Mission Specialist Linnehan recalled quote “Picture putting a colander on your head, taping it down with duct tape, then lying down and trying to sleep. It took forever to get on, it was not comfortable, and it did impede our sleep. But that’s the nature of the work. To measure things, you have to wear the equipment.”

One thing that was kind of funny about sleeping in space is that Dave Williams said that he somehow felt better when he turned over in his sleep even though physically it made no difference, it was purely psychological. It made me wonder if he was aware that Leroy Chiao did the same thing on STS-65, the IML-2 flight. Which also gives me an excuse to remind you about IML-Man.

Unfortunately, the usual frantic space shuttle conditions weren’t the only reason for disrupted sleep. Partway through the mission, the crew checked in on some of the young rats and discovered that they were actually really struggling and several had died. It was actually sort of a lucky break they even realized when they did. They had checked in ahead of schedule just to see how the rats were doing, and the answer was “not great”. The problem was that some of the mother rats were struggling to adapt to space and thus were dehydrated, which meant they weren’t lactating or caring for their pups. Linnehan recalled how for four or five days the science crew would care for each one of them individually: washing them, warming them, and giving them fluids. They ended up sacrificing some once in a lifetime opportunities to view the Earth from space, and quite a bit of their own sleep schedule, resulting in what Linnehan called “Blurrolab”, but they just couldn’t in good faith ignore them. In the end, they lost around 50% of the neonatal rats, but Linnehan predicts that without their intervention it would’ve been more like 90%. Having a veterinarian running the science turned out to be a pretty good idea after all.

Despite the orbiter crew having managed to save enough resources for another day-and-a-half on orbit, the decision was made to head home at the scheduled time. They potentially could have gathered more data, but they already had a sufficient amount. Plus, there was a bad weather front moving in that threatened a Kennedy landing, and with time sensitive experiments there was a desire to not land at Edwards. So everything was packed up, Spacelab’s hatch was closed, the crew pulled on the launch and entry suits, and cruised through an uneventful entry, one which would prove to be Columbia’s final daytime landing. The crew and their ark of 2000 animals came to a stop 15 days, 21 hours, 49 minutes, and 58 seconds after lifting off. And with that, the last Spacelab mission, and one of the last shuttle flights primarily dedicated to science, was in the books.

The mission was so successful that serious consideration was given to re-flying the exact same crew, orbiter, and payload, STS-94 style. A three month gap in the launch manifest had opened up due to delays in ISS construction and such a flight could be done without impacting the schedule. But concerns over schedule risk prevailed and the idea was shelved. Of course, to add insult to injury, the three month gap widened and it was later clear that the re-flight could have happened after all.

In a 2011 oral history, original shuttle astronaut Rhea Seddon, who had been payload commander of the Space Life Sciences 2 mission on STS-58, spoke about this flight saying that it was a shame that it was the last of its kind. They had confronted and solved a lot of the challenges that doing this type of science in space presented. But in the face of limited flights and a daunting ISS build schedule, similar flights were shelved, waiting for the full potential of the ISS to be unlocked. But even once the ISS was flying, the facilities weren’t in place and the crew size wasn’t large enough to support this kind of work. Reading ahead, it looks like the capability to study mice on the ISS was finally achieved.. in 2014, sixteen years after this flight, and three years after the final space shuttle mission.

I’m really leaning on this idea because it highlights the sorts of difficult decisions that have to be made with the space program. It’s only possible to fly so many missions every year and only so much stuff can fly on each flight. Just like how we have to wonder what could have been done with ten flights that didn’t go to Mir, we have to ask what would provide more value? Using the shuttle to build the ISS or to fly a couple dozen more Spacelab missions? I’m certainly no expert on this front but I tend to think that NASA made the right call here, even if science capability on the ISS came online slower than hoped. The ability to study a topic for weeks, months, or years on the ISS is something that Spacelab simply could not provide. But I do sympathize with Rhea Seddon’s regretful sentiments.

But all of that is in the future. So as to not end on a dour note, here’s something a little more uplifting. While summing up his thoughts on the mission in the STS-90 results publication, payload commander Rick Linnehan said “STS-90 was one of the most important scientific missions that NASA has ever flown. The in-flight experiments that we conducted, and were a part of, were first-class science, and the information that was gathered will significantly contribute to the understanding of many physiologic and disease processes that occur in Earth’s populations. These data will also contribute to future spaceflight initiatives involving long-duration flights and, someday, planetary exploration.” Someday, Rick. Someday.

Next time.. we’ll add another “last” to our list as we go pick up Andy Thomas on STS-91 and drift through the myriad modules of Mir for one last time.

Ad Astra, catch you on the next pass.