 Nope, that was not a joke. I really did ask Mike Collins, the command module pilot from Apollo 11, about his underwear. Now the sound isn't great because this was a bit of a last minute, oh he's free, I'm going to go jump and ask him this question while I have a chance. So I've added some subtitles and captions to help you guys actually hear the exchange between Mike and I. So here goes. What percentage of insanity do you run? High. On board, I can figure out where this is, but Neil just says to you, be ready for your underwear, Mike, be ready for your underwear, be ready for your underwear to do it. No, I think that's it. Do you have any idea what this is about? None. Zero. I think they are making fun of me because I don't remember any liquid cool garment in my underwear, maybe that's why I think they remember something like those lines, but with these words, I don't know if it's the odd ones. I think I will put these odd lines in the other ones so hard because no one knows what exactly is going on in the cabin at the moment, right? No. I think you have that same hair all the time. That sounds like it's a pair of underwear and not only a cold undergarment in the cabin. No, the liquid cool was built into the underwear. But I didn't have any. When we think about working on the moon, we probably think about staying warm because as we know with no atmosphere, there's nothing to trap the sun's lovely warmth, but really, the issue is staying cool. No matter what you are doing, whether you are lying on the couch watching TV or whether you are lifting and going for a personal best at the gym, your body is burning calories. Those calories transfer into energy. In the couch example, that energy is mainly used to keep your organs working. In the gym example, it's mainly going towards muscle recruitment to help you lift that heavy weight. But not all of the calories your body burns is used as energy. A fair bit is actually lost through heat. We've all seen this happen. You go for a walk or run outside on a hot day and you start to sweat. This is your body overheating and attempting to cool itself. You sweat, the sweat evaporates, and it cools the body. And as we know, we don't really like to be too hot. It's uncomfortable, but it can also cause physiological problems like dehydration and lightheadedness. So there are two things that we can do to deal with heat. We can either cool the environment, which for most of us involves turning on the air conditioning, or we can make it so that less heat is transferred from our skin. We can actually physically cool your skin, say putting an ice pack on your arm or on your abdomen or on your back to help your body stay cooler. In any case, the heat that we put out from our own bodies is measured in British thermal units, or BTUs. And one BTU is defined as the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. So think of a human as a machine. The harder the body works, the higher its heat output is. But a human is a very low efficiency machine. A small increase in work will translate to a sharp increase in thermal output. Think of it like a bank of computers in a small room. A human will also overheat if he isn't cooled while working. But unlike computers, the human won't just shut down and reboot. He could die. The fact that humans lose heat when they exercise or work was not exactly unknown to NASA when it started developing the spacesuits for the lunar EVAs, or moonwalks. But it was the first time that human physiological responses to heat were actually integrated into a system. A human astronaut working on the moon is basically the same as our human machine or bank of computers working in a confined space. To prevent overheating, you can either cool the environment, in this case the microenvironment of the suit, or you can prevent heat transfer to the skin by using some kind of cooling system. NASA actually looked at the former option first. In the mid-1960s when the first Gemini missions were flying, the suits had evolved into a four-layer garment that used oxygen channeled through the suit for ventilation, cooling, and for breathing. But it really wasn't an ideal solution. To cool an astronaut during peak work intensity, the flow rate of the gas was so high that it was so noisy and actually created high winds inside the suit. This in turn led to headaches and nausea. And it was only so good as a cooling method, as evidenced by Gene Cernan's spacewalk on Gemini 9. Cernan worked so hard on that spacewalk, and the suit couldn't cool him effectively, that almost immediately his visor fogged over, he was blind, and he sweat so much, he actually lost about 10 pounds during that spacewalk. NASA knew it had to come up with some other system, and so turned to liquid cooling garments. NASA started looking into liquid cooling garments in 1964, and a single demonstration at the manned spacecraft center proved that this was a very good path forward for keeping astronauts cool in space. A test subject wearing a liquid cooling garment and a full pressure suit exercised to a point where he was producing about 1,300 BTUs of heat per hour. The suit he was wearing was designed to remove about 3,400 BTUs of heat per hour. He was actually so cold, he started shivering. It was clear that liquid cooled suits were the best way forward to keep astronauts cool on the moon. What developed from these early tests was the Apollo liquid cooled garment. This was a water cooled nylon undergarment that really looked like long underwear, but there were plastic tubes running through it. The cool liquid flowed through these channels close to the body to carry away excess metabolic heat and to stop external heat from reaching the skin, causing heat stress and fatigue. Attached to liquid cooled garment was a bio belt that carried instruments to measure all of the astronauts vital functions while working on the moon. It also allowed for real time measurements of the temperature of the water running over their skin, giving doctors on the ground a very good indication of just how hard the astronauts were working. And there are some interesting charts to show you just how hard the astronauts actually worked on the moon. This first chart shows an average output in BTUs for different activities. You can see Apollo 11 lunar exploration from Aldrin's measurements, as well as Gene Cernan's Gemini 9 spacewalk. Note that the spacewalk was significantly higher than the lunar EVA. This second chart shows in more detail the output from both Armstrong and Aldrin during each individual exercise during their EVA on Apollo 11. Of course, not all astronauts wore the liquid cooled garment. Only the commander and lunar module pilot would be working and walking on the moon's surface, and so only they had the fancy underwear with these liquid tubes woven through the material. So what I asked this question, I really did have a completely different answer in mind as what I was expecting him to say. Now, I learned in Charlie Duke's memoirs, Moonwalker, that there was a very particular set of steps that the astronauts would go through when using the facilities. And by facilities on Apollo, I mean a bag. So on Apollo missions, there wasn't exactly a bathroom with a running faucet such that if you got something dirty, you could clean it in the sink or clean yourself in the sink if you got dirty. So it became common practice for astronauts to strip down totally naked when using the facilities, a.k.a. poop bag. So that's actually kind of what I was thinking was happening at this moment when Neil Armstrong asked Mike Collins if he was ready for his underwear. In my head, it was that Mike Collins had stripped down to use the facilities and Neil was dressing him like the commander does, playing the role of a dad or something. Of course, unsurprisingly, when you're dealing with spaceflight, not only are these guys absolute professionals, but they are always thinking about the mission. So even the gentle joshing between astronauts is really about hardware, about in this case, the liquid cooling garment. So that's my little moment from Space Fest 8 in Tucson with Mike Collins that I really wanted to share with you guys. Let me know your thoughts and your questions and things you'd like to see covered in future episodes in the comment section below. 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