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August 24, 2019

FOSSUM: Hi. My name’s Mike Fossum. I’m the commander of Expedition 29. Welcome to the International Space Station. Today we’re gonna talk some about how the Space Station and other spacecraft manage to maintain their attitude in space. There’s really two ways we can go about doing this. One way would be to use small rockets or jets — thrusters — to push the Space Station and keep it in the attitude that we want to maintain. The problem with using thrusters is that that requires a lot of fuel, which we have to launch from the surface of the Earth up to the Space Station and keep it resupplied. We have a much more ingenious way. It’s using angular momentum, or gyros, and that’s what the discussion today is all about. Okay. So, how do we use this, then, to control a spacecraft? Well, it’s — I about said it’s easy, but it’s not really a simple concept. We use systems called control moment gyros, or CMGs for short. It’s an attitude-control device that’s used in controlling the orientation of spacecraft. The CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor’s angular momentum. Now, these gimbals are used to keep objects level in an unstable environment. As that rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the aircraft. Now, we have four of these CMGs — control moment gyros — on the International Space Station that control its orientation in space. The CMGs are steel wheels that spin at a constant speed of 6,600 rotations per minute. That means, in one minute, the wheel rotates 6,600 times. Each CMG has gimbals, and these can be repositioned to any attitude or orientation. As the CMG is repositioned, that resulting force causes the ISS to move or twist. Using multiple CMGs permits the ISS to be moved to new positions or permits the attitude to be held constant. Now, on Earth, we could demonstrate this very easily with a wheel off a bicycle. Front wheel is usually the easiest. And it functions as a simple gyroscope. Spinning the wheel — Once you get the wheel spinning, hanging on to the axle of the wheel, which is the axis of our CMG, and then you try tilting it, and you’ll feel the very strange forces which are acting not intuitive at all. You’ll notice there’s a friction that’s increased and also that resistance. When you get that wheel spinning in a plane and you try to tilt that axis of rotation — the axle of the wheel — you can feel it definitely twisting in your hands. That’s exactly the same force that we use to control the International Space Station. We can demonstrate some of these principles of a gyroscope in space or what these controlled gyros do. I have here — and it’s not rotating right now. The gyroscope inside here is not rotating. And I can float it here in space, and then I can give it a little nudge on the top and the bottom, and you see nothing unusual happens. I gave it just a tiny little nudge, and let me get it from the side here so you can see it from this side, too. And the gyroscope is not spinning at this point. A little nudge on the top and the bottom, and it’s very well-behaved. It tumbles just exactly like you’d expect it to. That’s because there’s no real — The gyroscope itself is just a mass inside right now. It doesn’t have any angular momentum itself right now. So, let’s get the string inserted into it and get this control gyro spun up to speed. And watch the difference. All I’m doing here is wrapping this string around the axle of the gyroscope inside here. Okay, let’s give it a good spin. Watch this. Okay, we’ve got a good spin going. Okay, there’s some friction, so the frame — One, it’s got a little wobble. Let’s try to work that out. And then I’m gonna give it that little push on the top and the bottom. It didn’t start tumbling. Did you see that? It’s holding it fairly stable. Let’s look at it from the side. If I stop the gyroscope… I can get it to tumble like that. Now it’s out of control. Before, with it spinning, it’s exhibiting stability. There’s friction and things like that in this. This is actually — It’s a toy. It’s a demonstrator that you can make at home. And it’s that friction that’s causing it to really wobble and go a little bit unstable, but it’s that riding force where it takes a lot more energy to get it to move once its angular momentum is set and it’s turning like that. So, let’s sum up our exploration of angular momentum and gyroscopes. The angular momentum of a rotating object remains constant unless it’s acted on by an external torque. Gyroscopes, which possess angular momentum, keep the ISS oriented and pointed in a favorable position. Take a look at the world around you and find other ways gyroscopes are used. Thanks for joining us on the International Space Station. Have a great day.

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  1. you said you use gyroscopes to control the attitude?? I understand you could control the rotation or orientation of the spacecraft with the gyros but, how could you affect to the linear momentum(to control attitude) just with gyros?
    Thanks and hello from Spain:)

  2. is the orientation of the gyroscope stable relative to the direction of down or relative to its initial orientation?

    in other words if an ideal gyro were spun up on the ISS and could run indefinitely would it appear to rotate relative to the orientation of the ISS?

  3. This man is not in space. He is suspended on wires in front of a green screen with computer animated gyro and necklace. He sees the objects on off-screen monitors. Please research "NASA fraud."

  4. What is the GYRO pulling against since there is no fuel exiting the station, what happens to Newtons third law of equal and opposite reaction ??? Looks like angler momentum is the term used to describe the hooks that the GYROS will pull against to change the station position. So Newtonian 3 law does NOT apply here… Wow… what "they" can't explain is what the GYROS pull against in empty space vacuum.. Maybe It's invisible and not seen by humans as the Earth hurls through space at 66,000 miles through space.. Like one driving a car at 60 MPH with the windows shut, not knowing that the air pressure pushing against the car is there, you only have to crack open the window a little to feel the force… However in space there is no air just something that is there because GYROS interact with this invisible force to pull against it to re-orient the space station. Why is it So.. !!! Al…

  5. Reading a script in a sound studio against a green screen. The gyroscope, necklace and wrist watch floating effect done with augmented reality CGI.

  6. Could you use strikes of electricity on a free floating gyro to rotate it and to keep it stable. I ask this, with the thought that an electrical Arc has a pushing force.

  7. The ISS is close enough to the earth to experience only the 'y' force gravity component, so the gyro will always stay vertical to the plain of the earth. However since they tell us that space is weightless, then there is no 'y' component. This is totally confusing. Is space weightless or is this filmed on the earth?

  8. Where the wobble might hinder the gyroscope example, it does give a great example of the low margin of error when engineering something for use in microgravity environments.

  9. this version .. 40 years ago…. in another space station …. is head and shoulders better!!
    Friction? the whole point is that your in a weight-less no gravity place, maybe things were better 40 years ago?
    Gyroscopes in Space 1973 NASA; Skylab Science Tutorial Program #4; Owen Garriot

  10. great video, would love to see any other experiments using gyros in space, a good way to reduce the effects of friction has to be magnetic bearings. would making the gyro spin up to 66000 RPM make the moving force 10 times stronger? so many questions bounce around my head, have you developed a variable density gyro using magnetics? whats the fastest speed you have got a gyro in space up to and what happened? i have subscribed to your channel and i am working my way through your 5 year video posting.


  12. Awesome presentation! I love seeing the oscillating stabilization effect in free fall. Euler would love this. Difficult math even 300 years later. Thanks.

  13. 4:03 How are his glasses staying on his face? Did they glue them on or something? Shouldn't they float off his face because of the momentum (like everything else in the ISS, apparently) in a weightless environment?
    I have glasses and they fly off my face if I move my head too fast, so why doesn't it happen here? They stay firmly cemented on his noggin like they should on the ground.

  14. One of the few videos tsken from soace I've ever watched. And the first one used to demonstrate a principle in that way.

  15. sir, there is a very high possibility that you may be an illegitimate brother of elon musk.
    just trolling 😉 thank you nasa for these very informative videos.

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