Do-It-Yourself Podcast "Micro-g" Transcript
My name is Nancy Rabel Hall. I work at the NASA Glenn Research Center in Cleveland, Ohio. And my job is that of a project scientist and a project manager. And I work on experiments that fly on the space station.
Gravity is the force of attraction between two objects. Basically, gravity is what keeps you here on Earth. If you were to take an object, and you let it go, it will fall due to what's called the acceleration of gravity (acceleration due to gravity). Gravity is pulling objects toward the center of the Earth. If the ground was to suddenly disappear, I would continue to fall to the center of the Earth. If I'm standing on a scale, what that scale is reading is the force of gravity pulling on you, and it shows up as your weight.
Microgravity is a condition that exists when a person is in a state of free fall. In other words, what's happening is you are falling at the same rate of acceleration that gravity is pulling on you, so you are essentially in what we refer to as microgravity.
NASA is interested in microgravity because objects and materials behave differently when in a microgravity environment. If we're going to go and visit other planets or asteroids, we need to understand how the human body, how the space vehicle we're going to use, as well as how substances behave when you're in a microgravity environment.
NASA studies the behaviors of different materials. One thing we know is that liquids behave differently in the presence of microgravity. Fluids have a tendency to form what's called a sphere or ball. Think about blowing a water bubble. We know that is due to a scientific property called surface tension. Something else we study is combustion, or what happens when an object burns. Here on Earth if you light a candle, you get this traditional hour-glass shape that you get on a candle due to what's called forced convection. You have the hot gases, which are lighter rising to the top, and the cooler gases staying at the bottom. So you get this little tear shape; however, in microgravity you don't have this forced convection so the flame actually forms almost like a sphere.
If you've ever gone down the steps in a school or your home and you've jumped off that last step, you've actually experienced microgravity. The key thing about microgravity is ... what's happening in a microgravity environment is you are being accelerated or pulled at the same rate gravity is pulling you down. So if you were to jump in the air, for that split second before you come down, you are experiencing microgravity.
As you're going over a roller coaster, what you're experiencing is similar to what the astronauts experience. Think about it: as you're going up the roller coaster, right before you go over that first hill, you have this feeling in your stomach and then as you're going down that hill it feels like you're floating out of your seat. Well that whole situation as you're going right over the roller coaster and down is similar to what the astronauts experience. So if you've ever been on roller coasters or ever jumped off a swing, you have experienced microgravity.
Think about what happens when you throw a ball. If you start with a ball and you let it go, gravity immediately has it falling. If you throw the ball; watch the shape that the ball does. The ball does this curve. It does not go horizontally and then all of a sudden think "oh my goodness, there's gravity" and fall straight down. No, instead it does a curve shape. If you threw the ball even harder, it would continue to travel horizontally for a little bit, but you'd still see that curve. Now if I was strong enough and I could throw the ball at 17,500 miles an hour, what would happen is it would continue to fall around the Earth. That's what's happening to the space station astronauts. They're in a state of free fall. So them, a scale, everything in the shuttle (station) is falling at the same rate. They are, in essence, in what's called apparent weightlessness. If the astronauts were to try to stand on a scale, the scale is floating; the astronaut is floating; there's no force pulling on the scale. So the scale would read zero if the astronauts were to try to stand on the scale.
As a result of the astronauts going up in space and spending time in the space station, one of the interesting things we found out is that the astronauts are affected especially in the area of what's called bone loss. Here on Earth because gravity is pulling you down, you have a constant force on your bones. But in microgravity, you don't have that force pulling down on you so what we've noticed is astronauts lose what's called bone mass, and they lose about 1 percent bone mass per month. Now, the reason that's a concern is because, if you think what the bones do, the bones help keep you together. So if your bone becomes brittle, then it's easy to break. So if anyone's ever broken their arm or leg, you know that you really can't do much with that. It hampers what you can do in regard to playing sports or anything else. If you think about a mission where you're going to have astronauts going to another planet, if their bone becomes brittle, then they won't be able to do their jobs. So one of the things we do in a program called our human research program is we try to study and understand what happens to human physiology, what happens to an astronaut's body when they're in a state of free fall.
We're always sending up experiments; we're always doing research; and we're looking at different things. We're studying what's called the physical sciences -- looking at fluid physics and combustion research. We're also doing work in the human research program looking at how microgravity affects humans. We're also doing stuff in life sciences looking at when we send things like butterflies or spiders. How do spiders make webs in space? Is there a way we can make a web like a spider does -- which is very thin but very strong? We're also looking at lots of different areas in crystal growth. So all these different areas have benefits to different people.
Imagine yourself -- first time -- going into space. You don't know what to expect because there is no gravity button here on Earth. What I mean is there is no button where you can hit and turn off gravity. We try to get ready to get this experience before we go into space by studying what other people have done. We look at video; we talk about it. But there is nothing that's on Earth that can really help us to get ready. We have a zero-gravity airplane that sometimes we get to fly in, which is really fun. The airplane climbs up really high and then dives down towards the planet Earth. While it's diving down, we are all in the middle of the airplane kind of in a free fall. It feels like you're floating in space, but then, of course, the airplane has to pull up before it hits the ground. Then all of a sudden, we feel really heavy -- like two or three gravities -- so two or three times heavier than what we normally feel. So we go up and down, up and down, and that kind of makes people sick sometimes. So, that's not a perfect example of zero gravity, but it's the best we can do. So once we do get up in space, we have to take, especially for the first time, it takes a few days to get accustomed to it. I'll tell you what: Once you get used to being weightless in microgravity, it's a lot of fun. You can fly around like Superman; try my patented Iron Man technique; or anything -- it's because you feel normal except you can fly, and you can lift up really heavy things and move them around. It's a lot of fun in microgravity.
Each time we go out into to space on a spacewalk, it's a little bit dangerous and it's definitely really difficult. It's also a lot of fun, especially when you've trained really well for it and you know what you're doing, so it's not that scary. You open up the door, and you see beautiful planet Earth floating below. You float outside. You make sure you have your safety tethers connected so you won't float away. You don't learn that just by studying it in a book; we actually practice it a lot here on planet Earth. The best place, the only other place that you can kind of simulate being in space is inside of a big swimming pool. Here at the Johnson Space Center, we call it the Neutral Buoyancy Laboratory, or the NBL. I've spent a lot of time getting ready for my spacewalks -- both the American spacewalks and the Russian spacewalks -- by spending time here at the Neutral Buoyancy Laboratory. And we have a full mock-up of the International Space Station, especially the airlock. We practice opening the hatch. Of course when we open the hatch, we see a scuba diver's face there; we don't really see planet Earth. It's just like being in space. We practice setting our safety tethers. We practice turning the bolts and putting out the scientific experiments and bringing them back in, and doing it safely and efficiently. And, sometimes, you don't even know what you're going to do on your mission because the unknown things happen. Something breaks that we weren't expecting. So we get a good set of skills here. And to build up (a) good set of skills, we need to practice things over and over inside the Neutral Buoyancy Laboratory. So we wear a real spacesuit, and we stay inside the water for six hours practicing all the necessary skills to have a safe spacewalk, and it paid off on one of my missions. We had an unexpected spacewalk because a part of the space station broke. We just put on our suits and went outside, moved things around, turned a few bolts, replaced the power module, and we were back in business. And nobody was worried about it at all because we had really good training.
Once you're in space -- in microgravity -- you can move really heavy things around. Not only can you move yourself around, like flying, but things that normally on planet Earth that you can't move around, like three or four hundred pounds, are really easy. And I remember when we were still building the space station, the space shuttle came up to visit us aboard the space station. They brought this really big module. We picked it up with a robot arm and connected it to the space station. On the inside it had all kinds of cargo including like a 1200-pound water recycling rack. And I remember my friend, Don Pettit, came up with that mission, and he and I were moving this rack around, just two of us moving a 1200-pound rack, and we were standing on the ceiling or on the walls and just moving it gently along. And I'll tell you what, it would take like six or seven of us to do it on the planet and we would probably bump into the walls, but in space, 1,200 pounds, no problem.
Newton pretty much said it succinctly when he said a body that's in rest wants to stay at rest and one that is in motion wants to keep moving. So you can pick up something heavy, but then you also have to use the same amount of effort to slow it down or to stop it. That's why when we move heavy things in space, you'll see us taking it nice and easy because it takes a lot of effort to get it moving, and then it's gonna take just as much effort to get it stopped.
In microgravity, there (are) a lot of fun things to do. You can play with your food. It floats around -- gets a little messy after a while, so I don't recommend it. But it is a lot of fun. But I think one of the more fun things to do is to fly. You can move around any way you want. You can touch the ceiling. You can hang around upside down all day, and you don't even feel it. Like, if you're hanging upside down on the planet Earth and the blood rushes to your head, (it's) not that way in space.
A quick flying lesson -- is that when you're in space, you don't want to fly around really fast because there is nothing to stop you, nothing to slow you down, except like maybe your head or your hands or something. So, you don't want to fly around too fast next time you go to space.
Gravity is a force that governs motion throughout the universe. It holds us to the ground; it keeps the moon and the station in orbit around the Earth, and the Earth in orbit around the sun. It is best described as the attraction between any two masses, most apparent when one mass is very large, like the Earth. The acceleration of an object toward the ground caused by gravity alone near the surface of the Earth is called normal gravity, or 1 g
. This acceleration is equal to 9.8 meters per second squared (m/sec²), or 32.2 feet per second squared (ft/sec²).
Well, what is microgravity? The International Space Station and (we) astronauts aboard are traveling at approximately 28,000 kilometers per hour (kph), or 17,500 mph. And we're essentially falling around
the Earth, creating weightlessness. The weightlessness that is felt in free fall on a ride at an amusement park or on the International Space Station when it circles around the Earth is microgravity. Objects in a state of free fall in orbit are said to be weightless. The object's mass is the same, but their weight would register zero on a scale. Weight varies depending on if you're on Earth, the moon or in orbit, but your mass always stays the same.
If you drop an apple on Earth, it falls at 1 g
. If an astronaut on the space station drops an apple, it falls too. It just doesn't look like it's falling; that's because they're all falling together. The apple, or the onion, the astronaut and the space station, all falling together.
On Earth, our heart pumps oxygen-rich blood up to the brain, and then Earth's gravity helps pull the blood back down to the lower parts of the body. Since the brain is the capstone of our proverbial pyramid, our heart has to work especially hard to pump blood up to it. But in weightlessness, there's a difference. The blood volume in our head and chest increases. For those of you who know me, you recognize that my face is now rounder and puffier than typical on Earth.
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