I'm not the first. I could probably start every musing with that statement. Today, I am not the first to contemplate building a better space station (or spacecraft in general). The problem that comes up in the media a lot with space travel is human health - particularly long term negative effects on the persons known as astronauts in micro- or null gravity. There are a whole host of other issues to be aware of including radiation, outer hull perforation, fuel, atmosphere, food, etc. But the idea that your bones figuratively evaporate calcium when there is no load strain placed on them is cause for real concern. NASA and Roscosmos just launched the first year long stay for several Cosmonauts and Astronauts to study the longterm effects of space on human health. The findings should be quite interesting.
I loved seeing the movie interstellar. It was gorgeous, well acted, bleak, and at the same time vastly hopeful about our ability to overcome obstacles. I felt the movie did a neat job sidestepping the human impact on the Earth's climate (probably to bring a wider audience), and instead focused on a somewhat realistic doomsday-style virus or affliction that attacked plants. The dark-humourist in me laughed about corn being the last of the crops we could grow. Out of all the mega food crops we grow now, it is perhaps the least nutritional to humans. It has other uses, true, and I'm getting off topic.
So in that movie, humans are forced to start thinking about an exit strategy from Earth because they (we) have no food. The main character, played by Matthew McConaughey, straps himself into a rocket, blasts off to space with his crew, and then couples their flight vehicle with a travel vehicle and blasts off (again) for an outer solar system wormhole. All of this is very cool, but what the spaceship does while in flight reminded me of this idea we used to beat up a little bit in my introductory astronomy and physics classes: spin the station.
Many times in sci-fi, the author or creator will have some vague, physics-defying technology that generates a directed gravitational field for shipboard survival and comfort. With that technology out of the way, we are free to explore the stars in our own time, not worrying about the horrible effects of bone loss and reduced heart strength. Application of sci-fi style space travel therefore encounters a problem at the start: we don't have any clue how to start generating gravitational fields other than good old fashioned "add mass to it" methods. Mass, as it turns out, is quite effective at keeping a gravitational field, as it is a property of mass itself. Another problem: unfortunately, of the four base forces we can observe in the universe (there are probably at least 5, but we can't even detect the fifth one yet), gravity is 10^-38 as strong as the nuclear strong force (the thing that holds protons together in a nucleus). What that means for our "add mass to it" method is it requires a lot of mass to get comfortable gravity, say about the amount found on Earth (go figure). That is too much to make a space ship out of (unless you think Earth is a spaceship, then congratulations astronaught, you have arrived). There is a way to get around this, and it requires us to think of gravity from a slightly different frame of reference.
Gravity is a force (duh). We feel the effects of gravity in different ways depending upon our circumstances, but in general our feet take the brunt of the opposing force of the ground acting on our bodies, while gravity pushes on our heads (okay, on all of us and it doesn't push, but just picture it okay?). This concept is key though. We feel "gravity" because the ground pushes on our feet upwards. That can seem counterintuitive, but read Newton's Three Laws of Motion and you'll get there.
Armed with the knowledge that my feet are gravity detectors and that they can't think for themselves, I am confident that I can trick them to think that there is "gravity" in situations where our mind would understand that this is less than true. Well, still true, but "free fall reference frame" introduces another page of explanation so just go with it. I just have to push up on my feet, preferably at a steady acceleration, and my feet will report to my brain that we are experiencing gravity. Picture an elevator: going down makes the elevator floor accelerate downward, reducing the force it is applying to your feet, and they report you have less gravity (again, because they are dumb). The opposite is true when you go up. Silly feet.
I keep talking about acceleration though, when this is about gravity or even about a better space station. We're getting there. When I said gravity is a force, I wasn't kidding. On Earth and in many places humans can explore, Newtonian physics dominates, and so his equations work for describing things like forces. Newton's equation for force is F=ma where F is force (gravity), m is mass (you, earth, elevator, etc.) and a is acceleration of that mass. On Earth, we have the force of gravity competing with the force the ground exhibits on your feet. They generally balance out so you don't fall to the middle of Earth or fly out into space. When you jump from a perfectly good airplane for no reason, you don't have the ground pushing against you, just the air. So the air slows you down because it is putting a force on you, but gravity is winning and down you go. The ground will balance that when you get there. Hopefully you brought a parachute. In space, when you jump out of a perfectly good airplane, you suffocate, but before that happens, you experience weightlessness (or less/no gravity - stupid feet). This is because gravity is pulling you toward the center of the earth (that's what gravity do), but you keep missing the ground because you are going sideways, or what we commonly call orbiting.
I'm going way wide on this, so let's get back to simulating gravity.
So since we want to trick our feet into thinking there is gravity, we need to push on them with something (artificial ground) while our heads are accelerating "downward". If we had an infinite amount of fuel and nothing to run into, we could just build a platform to stand on, and then accelerate it in one direction forever. Problem solved. New problem: we don't have infinite fuel, we need supplies, and orbits make it really hard to travel in straight lines...ever. So another way to make something feel like it is accelerating downward is to spin it. Down becomes away from the center, and the hull of a ship acts as the ground pushing against your feet. "Aha!" you might exclaim aloud, he's talking about centrifugal force, and my response is, "No I'm not!" The force being applied in a centrifuge is centripetal force, and that is what I'm talking about. You might ask yourself, "what's the difference" to which I would point you to a Wikipedia article and move on. Once your done there, we'll continue...
Okay, so spinning a hollow object that you can stand in sounds like the right idea. We run into some issues when we realize that size matters and the distance you are from the spinning object determines how much force you feel. To understand this idea, think about a wheel on a bicycle. If you spin that wheel so that the rim goes by the same point, say your finger, every second, you may notice something further down on one of the spokes, closer to the hub: it also goes by the same point every second. But the point on the rim needs to travel further than the point on the spoke. If time is equal, but distance is different, then velocity must be different (D=rt is the common equation in grade school. It's simple but it works for this demonstration). Now picture your head vs your feet. If you stand in our spinning spaceship, your body is like a spoke on the wheel, where your feet touch the rim and your head is closer to the middle. That means your feet are traveling faster than your head, and because your spinning, the velocity turns (pun intended) into acceleration. Remember above when we talked about acceleration on a mass being a force? Well this is why your feet would feel more "gravity" than your head by a percentage related to how far away you are from the center of the spinning spaceship. This is not difficult physics, I promise, but it is probably getting hard to hold in your head. I encourage you to draw some pictures, or better yet, get some string and start trying this out. For our purposes here, I'll tell you the conclusion: the farther you are from the center of rotation, the smaller the % difference in force between your head and your feet. Another upside is that you don't have to spin as fast to get the same force (this is useful when trying to reduce the Coriolis effect. That almost inspired another long explanation of misunderstood but commonly cited physics terms...but just google it instead). So how big of a spacecraft are we talking about?
A spacecraft would need to be approximately 448 meters in diameter to allow for a roughly 30 second "orbital" period and 1g of gravitational force. That's huge. Putting this in perspective, the International Space Station (ISS) is about the size of an American football field or 109 meters from end to end. That is pretty big, and it has taken us many years to put that thing together...and it doesn't spin. Now imagine the engineering marvel that is a spinning spaceship, or even cooler the parts of a spinning spaceship and how they interact/seal against the non-spinning parts. The engineering challenge starts to balloon when you attempt to solve this problem in one sitting, in one head. Thankfully, humanity has a lot of heads, and while time may be short according to some, it is still time and we do still have it.
I've written a lot, so I want to stop here. I might pick this topic up again in the future. Perhaps explore some real-life plans to make artificial "gravity" a reality. For now, I am bursting with other ideas and so need a break...
So in that movie, humans are forced to start thinking about an exit strategy from Earth because they (we) have no food. The main character, played by Matthew McConaughey, straps himself into a rocket, blasts off to space with his crew, and then couples their flight vehicle with a travel vehicle and blasts off (again) for an outer solar system wormhole. All of this is very cool, but what the spaceship does while in flight reminded me of this idea we used to beat up a little bit in my introductory astronomy and physics classes: spin the station.
Many times in sci-fi, the author or creator will have some vague, physics-defying technology that generates a directed gravitational field for shipboard survival and comfort. With that technology out of the way, we are free to explore the stars in our own time, not worrying about the horrible effects of bone loss and reduced heart strength. Application of sci-fi style space travel therefore encounters a problem at the start: we don't have any clue how to start generating gravitational fields other than good old fashioned "add mass to it" methods. Mass, as it turns out, is quite effective at keeping a gravitational field, as it is a property of mass itself. Another problem: unfortunately, of the four base forces we can observe in the universe (there are probably at least 5, but we can't even detect the fifth one yet), gravity is 10^-38 as strong as the nuclear strong force (the thing that holds protons together in a nucleus). What that means for our "add mass to it" method is it requires a lot of mass to get comfortable gravity, say about the amount found on Earth (go figure). That is too much to make a space ship out of (unless you think Earth is a spaceship, then congratulations astronaught, you have arrived). There is a way to get around this, and it requires us to think of gravity from a slightly different frame of reference.
Gravity is a force (duh). We feel the effects of gravity in different ways depending upon our circumstances, but in general our feet take the brunt of the opposing force of the ground acting on our bodies, while gravity pushes on our heads (okay, on all of us and it doesn't push, but just picture it okay?). This concept is key though. We feel "gravity" because the ground pushes on our feet upwards. That can seem counterintuitive, but read Newton's Three Laws of Motion and you'll get there.
Armed with the knowledge that my feet are gravity detectors and that they can't think for themselves, I am confident that I can trick them to think that there is "gravity" in situations where our mind would understand that this is less than true. Well, still true, but "free fall reference frame" introduces another page of explanation so just go with it. I just have to push up on my feet, preferably at a steady acceleration, and my feet will report to my brain that we are experiencing gravity. Picture an elevator: going down makes the elevator floor accelerate downward, reducing the force it is applying to your feet, and they report you have less gravity (again, because they are dumb). The opposite is true when you go up. Silly feet.
I keep talking about acceleration though, when this is about gravity or even about a better space station. We're getting there. When I said gravity is a force, I wasn't kidding. On Earth and in many places humans can explore, Newtonian physics dominates, and so his equations work for describing things like forces. Newton's equation for force is F=ma where F is force (gravity), m is mass (you, earth, elevator, etc.) and a is acceleration of that mass. On Earth, we have the force of gravity competing with the force the ground exhibits on your feet. They generally balance out so you don't fall to the middle of Earth or fly out into space. When you jump from a perfectly good airplane for no reason, you don't have the ground pushing against you, just the air. So the air slows you down because it is putting a force on you, but gravity is winning and down you go. The ground will balance that when you get there. Hopefully you brought a parachute. In space, when you jump out of a perfectly good airplane, you suffocate, but before that happens, you experience weightlessness (or less/no gravity - stupid feet). This is because gravity is pulling you toward the center of the earth (that's what gravity do), but you keep missing the ground because you are going sideways, or what we commonly call orbiting.
I'm going way wide on this, so let's get back to simulating gravity.
So since we want to trick our feet into thinking there is gravity, we need to push on them with something (artificial ground) while our heads are accelerating "downward". If we had an infinite amount of fuel and nothing to run into, we could just build a platform to stand on, and then accelerate it in one direction forever. Problem solved. New problem: we don't have infinite fuel, we need supplies, and orbits make it really hard to travel in straight lines...ever. So another way to make something feel like it is accelerating downward is to spin it. Down becomes away from the center, and the hull of a ship acts as the ground pushing against your feet. "Aha!" you might exclaim aloud, he's talking about centrifugal force, and my response is, "No I'm not!" The force being applied in a centrifuge is centripetal force, and that is what I'm talking about. You might ask yourself, "what's the difference" to which I would point you to a Wikipedia article and move on. Once your done there, we'll continue...
Okay, so spinning a hollow object that you can stand in sounds like the right idea. We run into some issues when we realize that size matters and the distance you are from the spinning object determines how much force you feel. To understand this idea, think about a wheel on a bicycle. If you spin that wheel so that the rim goes by the same point, say your finger, every second, you may notice something further down on one of the spokes, closer to the hub: it also goes by the same point every second. But the point on the rim needs to travel further than the point on the spoke. If time is equal, but distance is different, then velocity must be different (D=rt is the common equation in grade school. It's simple but it works for this demonstration). Now picture your head vs your feet. If you stand in our spinning spaceship, your body is like a spoke on the wheel, where your feet touch the rim and your head is closer to the middle. That means your feet are traveling faster than your head, and because your spinning, the velocity turns (pun intended) into acceleration. Remember above when we talked about acceleration on a mass being a force? Well this is why your feet would feel more "gravity" than your head by a percentage related to how far away you are from the center of the spinning spaceship. This is not difficult physics, I promise, but it is probably getting hard to hold in your head. I encourage you to draw some pictures, or better yet, get some string and start trying this out. For our purposes here, I'll tell you the conclusion: the farther you are from the center of rotation, the smaller the % difference in force between your head and your feet. Another upside is that you don't have to spin as fast to get the same force (this is useful when trying to reduce the Coriolis effect. That almost inspired another long explanation of misunderstood but commonly cited physics terms...but just google it instead). So how big of a spacecraft are we talking about?
A spacecraft would need to be approximately 448 meters in diameter to allow for a roughly 30 second "orbital" period and 1g of gravitational force. That's huge. Putting this in perspective, the International Space Station (ISS) is about the size of an American football field or 109 meters from end to end. That is pretty big, and it has taken us many years to put that thing together...and it doesn't spin. Now imagine the engineering marvel that is a spinning spaceship, or even cooler the parts of a spinning spaceship and how they interact/seal against the non-spinning parts. The engineering challenge starts to balloon when you attempt to solve this problem in one sitting, in one head. Thankfully, humanity has a lot of heads, and while time may be short according to some, it is still time and we do still have it.
I've written a lot, so I want to stop here. I might pick this topic up again in the future. Perhaps explore some real-life plans to make artificial "gravity" a reality. For now, I am bursting with other ideas and so need a break...
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