JSC (AV) - Skylab 4 - Science Demonstration - Gyroscope - TV 4 Part 1

Description

#A224 SKYLAB 4 KINESCOPE A224 TAPE 9, PART 3 of 3 Hello from Skylab. What I'm gonna' talk to you about today is the subject of cotational stability, or gyroscopes. Now, rotational stability is the we're gonna' say it's the propensity or the ability of a body to maintain its attitude in space without rotating around, and of course, that's something we need when you fly in space because you want to look at the sun or if you want to look at the stars or at the earth, you want to do it from a stable platform, you don't want to do it from a tumbling platform. In the spacecraft today, there's two different ways that we maintain attitude stability - in the Apollo system, they used thrusters, little gas jets, to maintain a fixed attitude in space. In Skylab here, we use very large gyros - gyroscopes in order to do that. Now let me just show you. Now what I have here is just one of the little hand gyroscopes that you can buy at the dimestore, and first of all, I want to show you what a body does when its in zero-G and that's when you let it go, it just drifts. Now if you translate that body, or if you hit it, it moves in translation and also tumbles - you notice it tumbles the whole time, and we can hit it in a different direction, and it just keeps on tumbling and moving in the direction you need it. There's no damping, there's no effort on the part of the body to maintain itself in the position that it was in in the beginning let's see what happens when you get with the gyroscope. First of all, before we look at a gyro, let me do a little bit of drawing here, a little bit of cartoon work here for you. Now let's say that this is a gyro disc right here and this is the speed axis that the disc spins on. Now if we spin the gyro in this direction, the disc, then let's just by definition say that this is the spin axis right here. The spin axis is in that direction. Now what the physicist and the engineer used to remember this sort of thing is what we call a right-hand rule. That is if your fingers follow the spin or the rotation of the disc, your thumb points in the direction of the spin axis, so the principle of precession says, if we have that disc spinning like this and we pash down on it over here like that with a force, that the disc will rotate in this plane, in other words, it will rotate so that the back end of the disc goes down and the front end of the disc goes up. And what it seems like and this really isn't much of what you call rigorous physics that I'm telling you, but what it would seem is that if you put a force here, the disc carries the force around to the 90 degrees in the direction of rotation and then does the deflection over there, 90 degrees away, and that is the principle of precession. So let's see just exactly what it looks like in this little gyro that we have right here. Now I'm going to spin it up, now what I have done is Page 2 I have set the spin axis here up like that, and I've got my string wrapped so that we get the right-hand rule, that is that the spin is to the right with the force factor uh the spin factor up, and here we go. All right? There's my gyro, there's my string, looking to get tangled now I'm going to turn this little rascal loose there. Okay? And I'm going to use these two soda straws in order to provide the forces that I need. Now I've got this gyro spinning quite fast now, and notice when I hit it with a straw or deflect it - see it moves in translation doesn't it, just exactly the way it did before. But you notice that when I hit it, it doesn't want to tumble or drift in rotation - it maintains its rigidity in space, and this is the principle that's very widely used in spacecraft. Now, remember I told you that the spin axis is up this way and the rotation is this way, and that's the way I've got it set up on this gyro now. Now, if I push on that side of the disc, I expect the gyro to tip this way and show the bottom to you, so let's see what happens if I do that. I also have a little trouble with friction here, wanting to run it off the straws. Now you see what I did - I was going like this with it, but it was precessing 90 degrees from the way I was trying to get it to go. Now something else here that's very interesting is the fact that this thing did not precess just exactly this way - it rotated a little bit in that direction, too, and we'll talk about that a little bit more later. Now the next thing I want to do - let's try doing it this way - and get a wheel going a little slower speed - get it going at about half the speed we had initially. Uh I think it's going at about half the speed now now, I don't know if you can see this very well on your screen, but the spin axis, the very tip where the bearing is is starting to wobble a little bit and we're at a slower speed now now what I'm gonna' try to do is make this gyro stand up again, now I know it's spinning this way, and the spin axis is away from you, so in order to make it spin this way, I've got to push here in order to make that part go down. So, I'll take it and I'll see, I'm pushing on the side, and it's precessing 90 degrees, but do you notice we also didn't just get pitching 90 degrees, we got that coupling again - I'm calling it coupling for right now - now, let's slow this thing down just a little bit more. I'm going to try to slow it down so slow that you could almost see the spokes going have to be careful not to touch it or you'll end up either tumbling it or with a handful of gyro. Now it's going so slow, you can almost see the spokes go around. Now let's tip it again. This time I'm going to try to tip it forward - if I want to tip it down, I need to push here, which means I want to put a force on it like SO. Now, I think if we can get Page 3 our cameraman to zoom in now, you might be able to see the wobble in the axis there, the spin axis. Also you notice that I really got a lot of coupling this time, too. It's really - it's really from where we started, it's about this way - it's about 20 degrees rotation in this direction - it just came in while I was doing through a precession. The reason for that is friction - it's the friction between these two soda straws that I've got right here, and the axis, when I put my soda straws on the axis to cause this thing to precess, the friction is also causing a torque - and that causes it to precess a little bit in the other direction, which is, again, precession caused by friction. Now let's talk a little bit in summary about what we said here. Number 1 - did you notice that this gyro rotates only as long as I am putting a force on it - a torque on it - with my soda straws. But as soon as I take the torque off, it stops where it is, it freezes and maintains its position. Also, I think one of the things that we've learned here that we should remember is the fact that the faster the gyro goes, the less effect friction has on it, and also the faster the gyro goes, the less wobble there is, or the more stability - spin stability there is. So it would seem then that if you keep your gyro going very fast, you'll have less wobble and therefore, the bearings that your gyro is mounted on will have less friction and this will cause you to have a bearing that will stay cool, that will operate without giving you a lot of noise. By noise, I mean little wobbles, little bits of information sent to your computer that will make it think it's doing things it's really not doing. So let's review again now. The spacecraft systems - the Apollo systems uses a little gyro like this, a set of them, and it uses these gyros to remember its orientation. What we do is before we spin up the gyro, we set it in a direction, set the axis in the direction we want to have it go in, then we spin up the gyro on electric motors, and then that gyro stays there and it remembers where it is, and anytime our spacecraft drifts away from that attitude, the gyro tells the computer, the computer commands the thrusters to maintain our attitude. Now in the case of Skylab, we also use little gyros like this to remember our attitude, however, when they feed their information to a computer, the computer then feeds information to these huge gyros, and these three huge gyros that we have to maintain the attitude of our spacecraft are 22" in diameter, they weigh 140 lbs a piece, their wind thickness right here is about 4", and the speed at which our gyros operate is about 9,027 revolutions per minute, so essentially, the computer sends torques to this big gyro and puts pressure on Page 4 it, and so the big gyro being connected to our spacecraft precesses and moves our spacecraft in the way we want it to, so in review, we apply torques to the big gyros, and the big gyros apply a torque to the spacecraft to maneuver it to the position we want it to. Now, I wanted to tell you before I close (garble) on M-509 backpack also has these rate gyros in it, and it has a little (garble) gyros that are used for attitude sensing or remember the attitude and it also has some very small (garble) like we have to maneuver our spacecraft. We have them also on our backpack and they maneuver the backpack. We have found that this particular backpack this particular type of a gyro system is extremely stable, and a very good way to control the spacecraft. Well, I hope that this little demonstration has showed you something. I hope that this kind of demonstrates graphically to you just exactly what a gyro does. Thank you.

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Records of the National Aeronautics and Space Administration

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Moving Images Relating to Documentary Stock Footage