I thought we talked about how you actually steer and 0.12 ton spacecraft that's up in orbit around the Earth, such as such as the Hubble Space Telescope.

Our pride.

Enjoy.

So where is that?

I mean, obviously that's on your test.

Where's the real one?

No one's up there orbiting around the Earth.

It was designed so that it could be in an orbit that would be accessible by the space shuttle so that if and when things went wrong, we could send astronauts up there to fix it.

And thank goodness that we did.

Because there's been several issues with Hubble in its wonderful, long lifetime that these astronauts left, risking life and limb to help us out, I have managed to solve, which has made it such an incredibly long lasting and successful mission.

Mike Massimino Sze reflection Ah, in the half shroud of the Hubble Space Telescope, he prepares Thio open the doors of protective doors over the fixed head star trackers and the rate sensor units.

Well, I want to talk about the physics behind how you actually get a telescope like this point in the direction that you want it to point and keep it there, and it's actually surprisingly simple physics.

And it's all down to the conservation of angular momentum.

Now you might see in in some science fiction shows like Battlestar Galactica or something like that, but they maneuver spacecraft with thrusters.

You've got these jets and propellants on Newton's Law says that if you scored a jet propellant in one direction, you move in the opposite direction.

But for many reasons, that's not ideal for a telescope like Hubble.

First of all, you don't want to be spreading some sort of material like propellant in the atmosphere around your telescope.

It will cause a fog.

It'll can condense on your instruments, and fundamentally, it's a finite L.

A resource, and so eventually you'll run out.

The pointing system behind Hubble consists of several elements.

First, too, helped tell how it's pointing.

We use gyroscopes, and you might be familiar with gyroscopes like this.

This was a Christmas president.

Our house this year on the thing about a gyroscope is that once you get it spinning, it stays pointing in the same direction, and that's because of the conservation of angular momentum.

So once get the the gyroscope spinning it doesn't like to move in a different direction so I can lift this coffee cup up, and I can tilt it.

But you'll notice that the axis of the spin keeps pointing the same direction.

And so the gyroscopes on the Hubble Space Telescope work in the sense that they keep pointing in one direction.

And if the telescope starts to move, the sensors in the telescope will feel a force field gyroscope pushing back, resisting that motion.

And that's a diagnostic that tells the cyst the spacecraft system that it's pointing it's trying to.

It's trying to move or point in a different direction.

So the normal complement of gyroscopes on the Hubble Space Telescope it's six.

And that gives you extra redundancy because normally you need three to be operating, one pointing in each perpendicular direction to tell you which way you're going.

But the gyroscopes without the only pointing mechanism that the whole space telescope has, it actually has these four black bars that you see here on the outside and those air called magnetic talker bars.

And they're kind of meat because they use the fact that the Hubble Space Telescope is operating in Earth orbit, which means it can feel the magnetic field of the earth.

And so they're electromagnets that could be switched on and off and actually provide a torque perpendicular to the magnetic field of the Earth and help moved the telescope in that way.

The magnetic tor crowbars link up to the final piece of the steering puzzle because we've talked about how you know where you're pointing and how you know if you start moving in orientation.

But how do you actually make the telescope spin on its axis?

And for that, there are four flywheels.

They're called reaction wheels that could be spun up or spun down by an electric motor.

And so again, it's all just simple conservation of angular momentum.

You cause a reaction wheel to spin up in one direction.

The rest of the telescope has to move in the other direction to compensate.

Everything I've talked about with Hubble really relied on intervention by people to keep it going to replace the Giro's and the flywheels as well.

The reaction wheels were replaced.

Two of them failed over 18 years and were replaced a cz well, all of these things have moving parts right Um, and so all of those things are subject to failure.

When you think of other telescopes that air spent sent up now, they may not be so accessible.

They may be going to a little branch point or being in an earth trailing orbit.

So, for example, the James Webb telescope, exactly.

It's going to be much further way and completely outside any hope of intervention in the future.

So instead of he's very vulnerable Giro's that are subject to working parts and wires that are corroding and things like that.

James Webb actually uses a different kind of gyroscope, which has no moving parts.

A tall and it's called a hemispherical resonator gyroscope.

And essentially, it's not much difference, then a wine glass.

So if you take a wine glass or anything else, that sort of resonates and you get it going.

If you put it on a turntable, you'll notice something.

This is This is exactly what G.

H.

Brian discovered back in 18 90 that if you think about what's happening with the vibrations in this wine glass, if I strike it, if you could look at it in very slow motion, you'd see it deforming this way and then deforming that way would be squashing in and out in two different directions.

If you put that on a turntable and you spun it around, you would expect to hear a beat sort of a wall wall wall sound as you turned around as each one of those nodal points came into view.

What he found was that as you did, that you didn't hear the fora beats per revolution that you would expect.

You only heard about 2.4, which means the vibrating pattern is trailing the rotation of the physical object.

What that means is that you have, just like with the gyroscope, which exerted a force when you tried to move it.

You Now, um bye.

Noting the vibrations of this hemispherical object, you can again get a sense of whether it is moving or not.

And so on.

James Webb.

I essentially have ah, little courts hemisphere these these air very, very finely machined and incredibly sensitive instruments, and it's vibrating at a resonant frequency.

And then just a little electrical sensors will will be able to sense whether or not it's moving.

And the wonderful thing about this is that It works better in a vacuum, all right?

And so it'll actually were better in space than it does on the ground and has no moving parts.

And again, you know, it's much less likely to fail than the old mechanical spinning gyroscope.

So fingers crossed that when James Webb goes up, it will carry the full complement of these gyroscopes and that they'll work for the lifetime of the mission until it reaches the very top, at which point it will stop.

And the thing is really good.

Yeah, like a really, really good put yet, Um, let just sort of stopped throwing the engine unfolding.

In that time, the antenna will fold out so I can talk to Earth, and then the whole thing moves upwards.