Speaker 1: Hey, Jorgey, are you good at navigating? Depends on what
Speaker 1: do you mean by navigating? Do you mean navigating the
Speaker 1: complex issues of how to lead a good life? Then no,
Speaker 1: I haven't figured that one out. But if you mean
Speaker 1: like getting somewhere, I have a phone with GPS, so
Speaker 1: I guess i'm pretty good. Well, what have you lost
Speaker 1: your phone? Like? Or civilization crumbled? Do you know how
Speaker 1: to oriente yourself in the woods? Well? I imagine I
Speaker 1: could use a map and a compass, right, do you
Speaker 1: mean like a basic old school compass or the compass
Speaker 1: app on your phone? Okay, yeah, that's a good point.
Speaker 1: I only have the compass on my phone. But I
Speaker 1: guess you could probably find a low tech original you know,
Speaker 1: og compass. Yeah, that would let you get low tech
Speaker 1: original lost. I guess there's civilization crumbles were all lost.
Speaker 1: I am morehammy cartoonist and the creator of PhD comics. Hi,
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
Speaker 1: UC Irvine, and I've never honestly been lost in the woods. Well, well, yeah,
Speaker 1: I think that's self evident, because you're talking to us
Speaker 1: right now. If you were lost in the woods, I'm
Speaker 1: not sure we would have from you again. Maybe I'm
Speaker 1: calling you from my secret woods hideout, or even I
Speaker 1: don't know where it is, although if you have Wi
Speaker 1: Fi there and are able to record, I'm not sure
Speaker 1: you're that lost. Yeah, that's true. But I've often gone
Speaker 1: on long backpacking trips and wonder if I really could
Speaker 1: get myself out of the woods if I had to. Yeah,
Speaker 1: it's pretty tricky because I guess it's hard to see
Speaker 1: above the trees and know where you are right. I
Speaker 1: can't see the forest for the tree. It's definitely a
Speaker 1: particular skill of figuring out how the map represents the
Speaker 1: world you're seeing around you, and how to figure out
Speaker 1: where on the map you are. Well, I'm glad you're
Speaker 1: not lost in the woods, Daniel, it's what of my
Speaker 1: recurring nightmares. Welcome to our podcast Daniel and Jorge Explain
Speaker 1: the Universe, a production of our Heart Radio in which
Speaker 1: we try to avoid being lost in the woods of physics.
Speaker 1: We try to navigate our way through all of the
Speaker 1: confusing issues about this incredible universe, figure out how we
Speaker 1: can actually understand it, what we can make sense of,
Speaker 1: how big our map of the intellectual cosmos. We really
Speaker 1: can illuminate it. So I think of this podcast as
Speaker 1: your GPS for the entire universe, helping you know where
Speaker 1: things are and how to get there. Because slowly, over
Speaker 1: hundreds or thousands of years, we have started to build
Speaker 1: a map of how the universe works. We have a
Speaker 1: literal map of like what's physically out there in the universe,
Speaker 1: but we also have a conceptual map one that tells
Speaker 1: us how things work, how they explain the experience we see,
Speaker 1: and what they predict about what is to come. Yeah,
Speaker 1: because it is a pretty big universe and there's a
Speaker 1: lot out there for us to explore and to check out,
Speaker 1: and so having a map is a really good thing.
Speaker 1: Do you know where we sit in the universe? And
Speaker 1: it turns out that, we say it in a very
Speaker 1: small corner of one tiny galaxy that's part of a
Speaker 1: giant supercluster. And it's amazing we've been able to figure
Speaker 1: that out just looking at the night sky from this
Speaker 1: little piece of rock. Why do you call our galaxy tiny?
Speaker 1: I think it's pretty impressive. Well, you know, it could
Speaker 1: be bigger. You know, always use a bigger house, right,
Speaker 1: I don't know. I have friends that moved into a
Speaker 1: bigger house, and they found themselves just screaming at each
Speaker 1: other from opposite ends of the house all the time.
Speaker 1: I think they were happier in their tiny, little cramp department.
Speaker 1: Sounds like they needed an intercom, which is like technology
Speaker 1: from the eighties seventies. Yeah, exactly. And so if we
Speaker 1: lived in Andromeda, we'd have an even bigger galaxy to
Speaker 1: explore to find those aliens unless we had some sort
Speaker 1: of like alien galactic intercom where we could just talk
Speaker 1: to everybody. Yeah, you could have like a quantum warp
Speaker 1: tunnel the intercom. But the universe is quite vast, even
Speaker 1: beyond our tiny or large galaxy, depending on how you
Speaker 1: see it. And it's incredible that we have been able
Speaker 1: to figure out what's out there. Remember when you look
Speaker 1: at a map of the superclusters or our galaxy, that
Speaker 1: those are constructed from painstaking work to figure out where
Speaker 1: everything is. We don't have cameras above the Milky Way
Speaker 1: or outside of the galaxy. We've basically only ever observed
Speaker 1: things from Earth or from very very close to Earth,
Speaker 1: and those technological eyeballs we have built have allowed us
Speaker 1: to piece together this concept of where we are in
Speaker 1: the cosmos. Yeah, it's amazing what we've been able to
Speaker 1: piece together just from our little viewpoint using basically like
Speaker 1: two pieces of glass. Right, the original telescopes were che
Speaker 1: tube and two pieces of glass. I mean they're a
Speaker 1: little fastier now, but essentially the same thing. Yeah. I
Speaker 1: think you're glossing over a couple of crucial details, like
Speaker 1: the shape of that glass, but yeah, those are the
Speaker 1: basic ingredients. Yeah, and so we've been able to look
Speaker 1: at the stars and other galaxies from our point or
Speaker 1: an Earth, but we've also been able to look at
Speaker 1: the sky from the sky. We now have more than
Speaker 1: a few space telescopes out there in orbit and beyond
Speaker 1: orbit looking at the rest of the universe. Yeah, we
Speaker 1: have two really awesome sets of technology ground based telescopes
Speaker 1: that can get really really big tens of meters across
Speaker 1: for the primary mirrors, but those can be obscured by
Speaker 1: all the air that's between us and space. That air
Speaker 1: wiggles and shimmys and makes a little bit unclear to
Speaker 1: see what's out there. So we have this other awesome
Speaker 1: set of eyeballs we built that are actually out there
Speaker 1: in space above the atmosphere and can see much more clearly,
Speaker 1: although they can't yet be quite as large, So it's
Speaker 1: a complementary set of eyeballs. Now, these are not literal eyeballs, Like,
Speaker 1: we didn't send eyeballs into space, did we. Well, it
Speaker 1: depends on your definition of eyeballs. Right, they're not human
Speaker 1: biological eyeballs, but they're more like cameras. Right. They take
Speaker 1: pictures which are then transmitted to your eyes. Are they
Speaker 1: in the shape of a ball at least there are
Speaker 1: definitely some balls on them, right, we'll talk about it
Speaker 1: in the podcast. But they have spinning wheels and spinning balls,
Speaker 1: which are crucial elements of their operation. Oh all right, well,
Speaker 1: so technically there are they are eye and balls. But
Speaker 1: it is amazing that we have space telescodes. It's pretty cool.
Speaker 1: It's like, literally we build spaceships that are nothing but
Speaker 1: or spacecraft that are nothing but a telescope. Right, that's
Speaker 1: their only function, and they're out there in space doing
Speaker 1: their job. They're sort of like robotic space telescope spacecraft. Yeah,
Speaker 1: they're sort of like distant robot eyeballs that we connect
Speaker 1: to our own minds. It is really incredible. And you know,
Speaker 1: the telescopes here on Earth. That makes sense how they work.
Speaker 1: You want to look at something, you can turn the telescope,
Speaker 1: you point it at that thing that you want to watch.
Speaker 1: But the telescopes that are out there in space, it's
Speaker 1: a little harder to understand, like how those work, how
Speaker 1: they keep track of where they are, how you can
Speaker 1: turn and telescope in space? And a bunch of listeners
Speaker 1: wrote in and ask me how does that work? So
Speaker 1: do they end the program? We'll be tackling the question
Speaker 1: how do space telescopes point themselves? Now? I guess, Daniel,
Speaker 1: The question I guess is like, if you telescope here
Speaker 1: on Earth, you're grounded to the Earth, so you sort
Speaker 1: of know where you are and which way you're pointing.
Speaker 1: But maybe the question that the listeners were wondering is like,
Speaker 1: if you have a telescope out there in space, like,
Speaker 1: how do you know where you are? And how do
Speaker 1: you know which way you're pointing? Yeah, I think there's
Speaker 1: two different parts to it, right, is how do you
Speaker 1: know which direction you are pointing? And then also how
Speaker 1: do you change your direction? Right? How do you actually
Speaker 1: turn something that's up in space? Because here on the
Speaker 1: ground you can push against the ground it's like connected
Speaker 1: to something that you can push against. But up in space, right,
Speaker 1: it's harder to move things around, especially if you wanted
Speaker 1: to last four decades. M I see, because I guess
Speaker 1: anything that you do, like if you have jets or anything,
Speaker 1: then that means that you're expending energy. Yeah, and more
Speaker 1: specifically mass, right, jets have to push out something. You
Speaker 1: have to throw something out the back of the jet
Speaker 1: in order to get the momentum. You mean, we count
Speaker 1: to throw something at them from here, like to you know,
Speaker 1: knock them into the linement. That was definitely one of
Speaker 1: the plans, So I think it was pretty far down
Speaker 1: on the list. Maybe zap them from Earth with lasers
Speaker 1: also was pretty far down on the list. Oh, but
Speaker 1: that would be pretty good, wouldn't it. That's what our
Speaker 1: strategies for turning asteroids that are coming towards Earth. So
Speaker 1: maybe we would also work for spacecraft. Yeah, you know,
Speaker 1: it would indowd used lasers. Actually, I think that would
Speaker 1: work if you had like sales on the telescope and
Speaker 1: you could just push it from Earth with lasers. That
Speaker 1: would be really cool. I can't imagine what could go
Speaker 1: wrong or why there might be an issue with building
Speaker 1: an enormous space laser. They should high NASA obviously because
Speaker 1: we have good ideas. I'll be expecting an email as
Speaker 1: soon as we're done with this podcast. Well, as usually,
Speaker 1: we were wondering how many people had there had thought
Speaker 1: about the space telescopes out there in space and how
Speaker 1: they turned themselves to point at different stars. So thanks
Speaker 1: to everybody who answered these questions for the podcast. If
Speaker 1: you would like to participate for our future episodes, please
Speaker 1: please please do right to me two questions at Daniel
Speaker 1: and Jorhey dot com. We'd love to hear a huge
Speaker 1: variety of voices from all over the world. So think
Speaker 1: about it for a second. If you earned space pointing
Speaker 1: a telescope, how would you turn yourself. Here's what people
Speaker 1: had to say. I haven't thought about it. Maybe by
Speaker 1: using some geroscopes, either this cameramount that you pointed at
Speaker 1: the North Star and then it's basically calibrated to turn
Speaker 1: to compensate for the rotation of the Earth, which is
Speaker 1: like very consistent. So I'm assuming that space telescopes would
Speaker 1: do the same. I would guess that the space telescopes
Speaker 1: point themselves the same way that Alon Musk's SpaceX rockets
Speaker 1: do with the air pressure thing, I don't know, maybe
Speaker 1: either that or like a ion engine, I don't know.
Speaker 1: I learned that the James Webb telescope has a set
Speaker 1: of wheels that spin and apply some torque, so the
Speaker 1: whole thing making the twist a little okay, I think
Speaker 1: I actually remember this one from a previous episode in
Speaker 1: which we said that it was actually very hard to
Speaker 1: orient yourself in space, with the exception of being able
Speaker 1: to use pulsars, which you described as sort of like
Speaker 1: celestial guiding points that flash very consistently and can therefore
Speaker 1: somehow be used to triangulate your location, assuming that you
Speaker 1: already have the known location of two or more pulsars.
Speaker 1: I believe they use gyroscopes in order to orient themselves,
Speaker 1: or perhaps they off gas, you know, shooting little jets
Speaker 1: in particular directions in order to orient themselves in order
Speaker 1: to point themselves in a particular direction, and they use
Speaker 1: the background stars to orient themselves correctly. All right, pretty
Speaker 1: technical answer here, but pretty imaginative. Yeah, our listeners have
Speaker 1: thought about flying through space, how to get around, how
Speaker 1: to turn, how to know where you're pointing. We got
Speaker 1: some pretty smart folks listening to the podcast. Yeah, let's
Speaker 1: flatter our audience. You guys are awesome, beautiful and brilliant.
Speaker 1: But I feel like the answer is here, and we're
Speaker 1: also a little confused about what we're asking in the question,
Speaker 1: like are we asking like how does a space telescope
Speaker 1: orient itself? Like how do we how does it know
Speaker 1: which way it's pointing? And also how does it turn
Speaker 1: to point at something it wants to look at. Yeah,
Speaker 1: I think we're asking both questions and have different answers,
Speaker 1: both of which are really fascinating. So I think all
Speaker 1: of that is involved. I mean, you have your eyeball
Speaker 1: out in space, you wanted to look at something in particular,
Speaker 1: you got to solve both problems. You gotta know where
Speaker 1: it is now and how to change its position. M
Speaker 1: do you think there's a there's like a joystick somewhere
Speaker 1: in NASA or Houston Control Center that points these telescopes?
Speaker 1: Like who gets to move that joysting? And I wonder
Speaker 1: if there's a red button on the top of that
Speaker 1: joystick and if it actually fires something or if it
Speaker 1: just has a little like sound effect peo pew, or
Speaker 1: maybe if you press the button like a flag pops
Speaker 1: out at the end of Hubble boom, or I wonder
Speaker 1: if anyone that NASA has never been tempted to turn
Speaker 1: the telescope around and point it at Earth, like, what
Speaker 1: could it look at? What could it see? You could
Speaker 1: take a selfie with Hubble? Right? Yeah, oh man, do
Speaker 1: you probably find all of NASA selling those selfie opportunities.
Speaker 1: Hubble is quite delicate, and if too much light enters
Speaker 1: its aperture it could damage it. They have to be
Speaker 1: very careful about not pointing it, for example, towards the Sun.
Speaker 1: And I wonder if even the Earth might be too
Speaker 1: bright a source for Hubble. Well, I guess it would
Speaker 1: have to be night selfies. Then all right, well, let's
Speaker 1: dig into this question of how based telescopes orient themselves,
Speaker 1: how they know which way they're pointing at, and then
Speaker 1: if they want to point somewhere in particular, how do
Speaker 1: they move themselves to point in that direction. So, first
Speaker 1: of all, Daniel stepped us through this. Why this is
Speaker 1: important and heart wells important because we want to choose
Speaker 1: what we are seeing. Remember that the telescopes don't see
Speaker 1: all of space, right, It's not like when you look
Speaker 1: out of the night sky and you stare up and
Speaker 1: you basically see the whole sky, or at least the
Speaker 1: part that's not blocked by the earth. A telescope is
Speaker 1: very very narrow aperture in comparison, and so you're only
Speaker 1: really looking at a small portion of the sky, and
Speaker 1: you want to get to pick which portion of the
Speaker 1: sky you are looking at. Are we studying this galaxy,
Speaker 1: are we studying that star over there? Are we tracking
Speaker 1: something that's moving? So you definitely want to have control
Speaker 1: over where your telescope is pointed. Yeah, it's sort of
Speaker 1: like you say, it has a very narrow field of view.
Speaker 1: I imagine it's sort of like walking around your neighborhood
Speaker 1: looking through a straw or something like that. Right, that's
Speaker 1: what it means to have a narrow field of view.
Speaker 1: Like if you close one eye and the other eye
Speaker 1: could only look through a drinking straw, your field of
Speaker 1: view moop be super narrow, and it'd be pretty hard
Speaker 1: to know where you are. And anybody who looked through
Speaker 1: a telescope has that experience. Your telescope sort of towards
Speaker 1: the thing you're looking for, and then you look through
Speaker 1: the telescope and you don't see it and show wiggle
Speaker 1: the telescope around and try to find the object. It's
Speaker 1: not easy when you're looking through a telescope to find
Speaker 1: that particular object has to be pointed very very close
Speaker 1: for you to even see it. And a straw is
Speaker 1: a great example, but it's actually not even dramatic enough.
Speaker 1: Some of these telescopes, their field of view is so small.
Speaker 1: It's more like looking at a grain of saying you
Speaker 1: hold at arm's length, right, that's the fraction of the
Speaker 1: sky these telescopes can look at at one time. It's
Speaker 1: like looking at a straw. That's the width of a
Speaker 1: grain of salt, and a meter lungs what you're saying, Yeah,
Speaker 1: that's exactly right. So some recent images, for example from
Speaker 1: James Webb, where they focus on the deep, deep sky,
Speaker 1: they point at one particular place in the sky and
Speaker 1: they take a bunch of pictures of that one spot.
Speaker 1: And the reason you want to hold it there for
Speaker 1: a long time is that the things that they're looking
Speaker 1: at are quite dim. You know, these distant galaxies don't
Speaker 1: send a whole lot of photons per second, so you
Speaker 1: want to build up a crisp image of them. You've
Speaker 1: got to wait as many seconds as possible to get
Speaker 1: as many photons as possible. So you have to keep
Speaker 1: pointing in the same direction for as long as possible. Yeah,
Speaker 1: and I imagine that's extra hard because first of all,
Speaker 1: like that thing that you're looking at might be moving,
Speaker 1: but also like the space telescope is moving, right, and
Speaker 1: like these space telescopes are usually an orbit around something,
Speaker 1: either the Earth or I guess mostly the Earth, but
Speaker 1: either a near orbit or far orbit. Yeah, we're always
Speaker 1: moving relative to the Sun. And even if these distant
Speaker 1: objects aren't effectively moving relative to our galaxy, You're right,
Speaker 1: our position is moving, and so you have to do
Speaker 1: something to stay on target. You can't just turn it
Speaker 1: and point and take pictures. The things you're looking at
Speaker 1: will change as you orbit the Sun, and so you
Speaker 1: have to do work. I have to do something to
Speaker 1: keep pointing in the same direction. M okay. So then,
Speaker 1: and that's hard to do to move your space telescope
Speaker 1: because basically there's nothing to push against in space. Exactly,
Speaker 1: if you're swimming in a swimming pool and you want
Speaker 1: to turn, what do you do. You hold your arms
Speaker 1: out and you push against the water. Right, You're pushing
Speaker 1: against something, and so you turn. But in space, what
Speaker 1: is there, right, There's no air, there's no water, there's
Speaker 1: nothing to push against, and so turning yourself is much
Speaker 1: harder because there's nothing immediately there for you to push against,
Speaker 1: for you to like boost off of right. And but
Speaker 1: usually satellites and spacecraft the way they navigate and turn
Speaker 1: and move around, they have rockets, right, or at least
Speaker 1: some sort of like a listener suggested, like an ion engine.
Speaker 1: And the crucial thing here is conservation of momentum. If
Speaker 1: you're stationary and you want to get moving, then to
Speaker 1: conserve momentum, you have to throw something going the other direction.
Speaker 1: That requires mass right the same way that like if
Speaker 1: you fire a bullet, you feel a recoil. If you're
Speaker 1: out in space you turn on a rocket, then basically
Speaker 1: the motion of your ship is the recoil from firing
Speaker 1: the rocket, because it's basically shooting a bunch of tiny
Speaker 1: bullets out the back of the rocket. The rocket is
Speaker 1: not just flames, it's throwing mass out the back of it.
Speaker 1: So you don't just need fuel to run the rocket.
Speaker 1: You need some sort of propellant something to throw out
Speaker 1: of the rocket to move your ship. And that's true
Speaker 1: both for motion and for rotation. And so if you
Speaker 1: need a mass to do it, then eventually you're going
Speaker 1: to run out because you can only bring a limited
Speaker 1: amount of mass. So the goal is to figure out
Speaker 1: a way to turn your telescope without using some kind
Speaker 1: of propellant, right, because I guess if you're using a propellant,
Speaker 1: even if there are like ion atoms or molecules, you're
Speaker 1: going to run out eventually, right, You are going to
Speaker 1: run out eventually. And if you spend billions of dollars
Speaker 1: and decades to develop this thing, then you want it
Speaker 1: to last as long as possible. So you're going to
Speaker 1: try to avoid at all costs having things that run out.
Speaker 1: Can you make it electric like an electric car? Yeah,
Speaker 1: you can make it electric, and an ion engine essentially
Speaker 1: is electric, but it still has to throw something out
Speaker 1: of the back, right, it's throwing ions which have been
Speaker 1: accelerated by electric fields. And just bring like a really
Speaker 1: big gas tank, like one that will last one hundred years, right,
Speaker 1: Because these missions usually don't have like an unlimited lifespan, right,
Speaker 1: They usually come with like an expiration date. You can't
Speaker 1: do that. But then the gas tank is big, which
Speaker 1: means it's heavy, which means you need more gas to
Speaker 1: launch it. And usually you want to use all of
Speaker 1: your available space and mass to design it for science
Speaker 1: rather than having a huge fuel tank on the back
Speaker 1: of it. I see. So I guess if you can
Speaker 1: figure out a smarter way to turn out there in space,
Speaker 1: then you could have more science than your rugget bigger
Speaker 1: telescope exactly, more science and more years of science because
Speaker 1: you wouldn't run out of something. Then you need to
Speaker 1: turn the thing also be greener, I imagine, right for
Speaker 1: the space ecosystem, you'd be less pollution. That's true exactly,
Speaker 1: and so for all of our neighbors out there, we
Speaker 1: should be consider it. All right, Well, that's why it's
Speaker 1: important and hard to turn a space telescope and orient
Speaker 1: it out there in space. And so let's get into
Speaker 1: how you would actually do this and how you would
Speaker 1: find yourself if you were lost in space. So let's
Speaker 1: dig into that. But first let's take a quick right,
Speaker 1: all right, we're talking about space telescopes, which are telescopes
Speaker 1: in space basically finally a well named physics object. Well,
Speaker 1: I know, right, and we're talking about how they point
Speaker 1: themselves out there in space. So let's tackle maybe the
Speaker 1: first question is, if you're on telescope out there in space,
Speaker 1: how do you know where you are? And how do
Speaker 1: you know where you're pointing? So these telescopes typically have
Speaker 1: multiple ways to figure out where they are pointing. First
Speaker 1: of all, they just have a bunch of sensors. Like
Speaker 1: the Hubble, for example, has several different kinds of sensors.
Speaker 1: It has a sensor that tells it where the Sun is,
Speaker 1: which helps it know where it's pointing, but also helps
Speaker 1: it avoid pointing into the Sun accidentally. It also has
Speaker 1: sensors for magnetic field, so that you can use the
Speaker 1: Earth's magnetic field to help figure out where it is.
Speaker 1: And then there are sensors that look at stars, and
Speaker 1: there's like a known star map and helps it get
Speaker 1: an orientation roughly for where it is, So to get
Speaker 1: a rough idea for where it is and orient itself,
Speaker 1: it has essentially maps the Sun, the magnetic field, and
Speaker 1: the stars that give it a sense for where it is. Yeah,
Speaker 1: that's usually how they do it in science fiction, Like
Speaker 1: if you're in a spaceship and you land in a
Speaker 1: place you're not quite sure where you are. Usually the
Speaker 1: way you orient yourself is by looking at the stars
Speaker 1: around you, and if you sort of know where they're
Speaker 1: supposed to be, you can figure out where you are
Speaker 1: relative to them. That's the idea, right Basically, they're looking
Speaker 1: at the constellations. They're looking at the constellations, and Hubble
Speaker 1: is not a traveling spacecraft, so it will never appear
Speaker 1: in Andromeda and have to figure out where it is.
Speaker 1: It's always going to be orbiting the Earth, and so
Speaker 1: we know what the stars look like when you're orbiting
Speaker 1: the Earth, and so you just need a few examples
Speaker 1: of particular known stars and you can roughly figure out
Speaker 1: where you are. So those are the sort of lower
Speaker 1: precision instruments, sort of baseline that Hubble uses to figure
Speaker 1: out where it's pointing. But it also has much more
Speaker 1: precise way to measure how it's so not just like
Speaker 1: look at the map and figure out where you are,
Speaker 1: but also understand how far you have turned right. And
Speaker 1: so in internal to Hubble and almost all of these spacecraft,
Speaker 1: they have gyroscopes. Gyroscopes are these balls that's been really
Speaker 1: really fast, and so they're insensitive to the motion of Hubble,
Speaker 1: and they can measure sort of how far it's turned.
Speaker 1: M Yeah, that's pretty cool. We use gyroscopes here on
Speaker 1: Earth all the time also to measure how things turn.
Speaker 1: But I guess you know as an engineer, the trickling
Speaker 1: thing with gyroscopes is that they tell you how much,
Speaker 1: if whether you've turned and how much, But over time
Speaker 1: they're sort of not calibrated to something fixed like the
Speaker 1: sun for example, exactly. And so if you're holding a
Speaker 1: gyroscope and you turn, the gyroscope stays pointing in its
Speaker 1: original direction, and so you can measure I turned thirty
Speaker 1: six point two degrees. So it's a relative measurement, as
Speaker 1: you say, it tells you how far you have turned,
Speaker 1: doesn't tell you where you're actually pointing. That's why Hubble
Speaker 1: has this combination of having the rough sensors to tell
Speaker 1: it the absolute measurements like on pointing and is part
Speaker 1: of the sky or that part of the sky or
Speaker 1: this part relative to the sun, plus these gyroscopes to
Speaker 1: measure very precisely how far it has turned. So it
Speaker 1: needs a combination of these sensors to get an absolute
Speaker 1: sense for where it is pointing in the sky. Because
Speaker 1: I guess if you're using a sensor to track where
Speaker 1: the sun is. You're basically talking about a camera, right,
Speaker 1: and so maybe a camera is not that accurate. Yeah,
Speaker 1: it's basically a low tech camera, and the precision of
Speaker 1: that is limited by like the pixels of the camera
Speaker 1: and also basically the width of the object you're looking at.
Speaker 1: And so the gyroscopes give you the most precise measurement
Speaker 1: of how far you have turned. And these things need
Speaker 1: to be again, super duper precise. Like when Hubble is
Speaker 1: focusing on something and trying to keep it in its
Speaker 1: field of view, it's like holding a laser beam focused
Speaker 1: on a dime two hundred miles away. That's how precise
Speaker 1: we're trying to be. You mean, like how stead of
Speaker 1: your hand needs to be basically right, Yeah, exactly, And
Speaker 1: so you're focusing on a dime that's two hundred miles away,
Speaker 1: plus you're moving relative to that dime, and so it's
Speaker 1: not just about being steady, it's about slowly tracking, it's
Speaker 1: about turning your telescope so you can keep on it.
Speaker 1: So these gyroscopes are super duper important to the operation
Speaker 1: of these based telescopes, and Hubble has been going for decades,
Speaker 1: and because these things are so important, they actually went
Speaker 1: up in two thousand and nine and replaced all six
Speaker 1: of them. Hobble has six of these things, six gyroscopes.
Speaker 1: I met six gyroscopes. Yeah, and each one spins at
Speaker 1: like twenty thousand rpm. Why do they need to be replaced, Well,
Speaker 1: eventually they degrade. You know, there's always some amount of
Speaker 1: friction in those things, so they'll rub against each other,
Speaker 1: they'll slow down, they'll heat up, and nothing is a
Speaker 1: perpetual motion machine, right, and so eventually these things do
Speaker 1: need to be replaced. No, when you say it needs
Speaker 1: to be accurate to the point where you can spot
Speaker 1: a dime two hundred miles away, is that when you're
Speaker 1: tracking something, you know, when you're trying to stay focus
Speaker 1: on a star? Or is that more for finding stars
Speaker 1: and things like that? I imagine in the gyroscopes maybe
Speaker 1: don't really help you to find a star. Yeah, the
Speaker 1: gyroscopes don't tell you what's out there at all. They
Speaker 1: just tell you how far you have turned. And the
Speaker 1: scientists need to decide where they want to look. So
Speaker 1: maybe they've seen something already in the sky near another object,
Speaker 1: then they want to appear more closely, or they've seen
Speaker 1: it maybe in the infrared using Spitzer, and now they
Speaker 1: want to get optical images of it. So they have
Speaker 1: to already know where in the sky to look. So
Speaker 1: they have like galactic coordinate systems they used to orient
Speaker 1: to say where something is in the sky relative to
Speaker 1: the plane of the galaxy, for example, And so you
Speaker 1: have to know basically where something is and then go
Speaker 1: look at it. Is there like a galactic coordinate system. Oh. Absolutely.
Speaker 1: When you look at the maps, for example, of the
Speaker 1: cosmic microwave background, those are relative to the plane of
Speaker 1: the galaxy. So the galaxy runs through the middle of
Speaker 1: those like a line through the middle of that oval.
Speaker 1: And then you go above and below the galactic plane.
Speaker 1: It's arbitrary, right, You could pick an access anywhere in space,
Speaker 1: and so we pick it relative to the Milky Way
Speaker 1: center to the like basically the main axis of the
Speaker 1: Milky Way. Yeah. And if you are out camping and
Speaker 1: lost in the woods and you look at the sky,
Speaker 1: you see the sort of Milky Way of stars across
Speaker 1: the night sky, and that is the plane of the galaxy, right,
Speaker 1: if you're looking above it or below, you're looking out
Speaker 1: from the galaxy, because remember, our galaxy is kind of
Speaker 1: like a disc, and if you're looking at that line
Speaker 1: and you're looking through the galaxy, which is why it
Speaker 1: looks so milky, because there's so many more stars and
Speaker 1: gas and dust and all that kind of stuff. So
Speaker 1: that's the galactic coordinate system. We used to talk about
Speaker 1: where things are in space. Well, that gives you the direction,
Speaker 1: but like, where's the origin of this coordinate system. It's
Speaker 1: at the center of the Milky Way. If you look
Speaker 1: at that oval, for example, and you put a dot
Speaker 1: in the very very center of it, that's where the
Speaker 1: black hole is. But then when we look at our
Speaker 1: night sky, it's going to be a little different than that. Right,
Speaker 1: that's right, we don't see that entire thing. But you
Speaker 1: can map the sphere of things that we can see
Speaker 1: onto that coordinate system. But you have to like a
Speaker 1: little bit of an angle change because we're not at
Speaker 1: the center of the galaxy, right exactly, we're not at
Speaker 1: the center of the galaxy. And also our solar system
Speaker 1: is filted a little bit, so you have to know
Speaker 1: where the Sun is relative to the center of the
Speaker 1: galaxy in order to map that on cool But then
Speaker 1: you said it uses sort of a cameras to see
Speaker 1: the constellations in a way or a map of the stars.
Speaker 1: Does it actually do that, like does it actually like
Speaker 1: track certain stars or constellations? And is that one of
Speaker 1: those maps you can buy in Hollywood Boulevard to the Stars. Yeah.
Speaker 1: So Hubble has a bunch of these different systems, right,
Speaker 1: has the course sun sensors, has a magnetic sensing system.
Speaker 1: Then it has star trackers, right, and the star trackers
Speaker 1: determines Hubble's altitude by looking at the location and brightness
Speaker 1: of stars that it sees, So it has a broader
Speaker 1: field of view than Hubble sort of main camera. And
Speaker 1: this lets it like identify unique patterns throughout the sky,
Speaker 1: which a computer then maps to star maps internal to
Speaker 1: Hubble and lets it figure out like if there's a
Speaker 1: correction or if it's slightly pointed in the wrong direction.
Speaker 1: And then the fine guidance system uses the gyroscopes and
Speaker 1: everything else to sort of fine tune everything. Now that's interesting.
Speaker 1: They had to go and replace those gyroscopes. Is that
Speaker 1: something we can do pretty easily? Like how do we
Speaker 1: do that? We need to send a rocket with people
Speaker 1: or do we send robots it's not something we can
Speaker 1: do very easily. We have to send astronauts up there
Speaker 1: because it's a complicated job, and so it was done
Speaker 1: in two thousand and nine, but that was the last time,
Speaker 1: and it's not something that we can do for James
Speaker 1: Webb for example. James Webb. Remember it's not in Earth orbit,
Speaker 1: it's out at a Lagarrange point. It's much much further away,
Speaker 1: and it's not a place where we can send humans.
Speaker 1: So either we have to develop robotic repair people or
Speaker 1: we just can't replace it. So James Webb actually has
Speaker 1: a slightly different technology than Hubble does. M what does
Speaker 1: the James Webb telescope do? So Hubble has these spinning balls.
Speaker 1: They're like mechanical, right, But James Webb tried to look
Speaker 1: for something that was less mechanical, that didn't require something
Speaker 1: spinning a really high speed, because that seems like sort
Speaker 1: of easy to mess up, like a little grain in
Speaker 1: there can really mess it up. So James Webb actually
Speaker 1: uses this weird technology. It's a quartzemisp fear that resonates
Speaker 1: in a particular way, sort of like if you have
Speaker 1: a wine glass and you rub your finger around it.
Speaker 1: It resonates and it makes like a ringing sound. That's
Speaker 1: that wine glass like flexing a little bit. You can't
Speaker 1: see flexing, but it's actually shaking a little bit. And
Speaker 1: if you like rotated the wine glass, then the sound
Speaker 1: would rotate with it. So what happens in the gyroscope
Speaker 1: inside James Webb is that the quartz hemisphere resonates in
Speaker 1: this very particular way. It's surrounded by electrodes that are
Speaker 1: like driving the resonance. They can also detect any slight
Speaker 1: change in its orientation, Like if James Webb rotates around
Speaker 1: this quartz hemisphere, they will hear the resonance impacting the
Speaker 1: telescope at a different location. Well, it's pretty fascinating and
Speaker 1: so I guess those don't wear out. The hope is
Speaker 1: that they don't wear out as fast. Right, everything will
Speaker 1: wear out eventually. This is still moving. Every time James
Speaker 1: Webb moves, it moves relative to these gyroscopes, and so
Speaker 1: there's a potential for friction there. But you don't have
Speaker 1: a spinning mass, right, and so it's less kinetic energy,
Speaker 1: it's less mechanical, and so the hope is that it
Speaker 1: will last longer. And so that's how it orients itself.
Speaker 1: And so if you wanted to point to like a
Speaker 1: particular galaxy out there that you know about, um, do
Speaker 1: you still have to kind of like tan around you think, like,
Speaker 1: do you think there's someone and NASA with the joystick
Speaker 1: going back and forth, back and forth, opened out, Oh
Speaker 1: there it is. Or do you think they can just
Speaker 1: go like point to here, boom, it's pointing there. I
Speaker 1: don't know the details, but I'm pretty sure it's not
Speaker 1: a joystick. I think they type in the coordinates and
Speaker 1: Hubble like pans over. This thing happens very slowly, like
Speaker 1: when Hubble turns, it turns about as fast as a
Speaker 1: clock does. It's a hubble, for example, can turn ninety
Speaker 1: degrees and about fifteen minutes. This is not something you
Speaker 1: want to spin around very quickly. I see, So it
Speaker 1: just takes a while with the joystick. I hold the
Speaker 1: joystick for a while. Yes, it takes patience with a joystick.
Speaker 1: Probably they do have a joystick that's not actually doing anything.
Speaker 1: It's just connected like the large change on collider and
Speaker 1: the the center. They have a big red button you
Speaker 1: can press that sets off lots of alarm bells and
Speaker 1: flashing lights, but doesn't actually shut anything down. Wow, that
Speaker 1: sounds like something the fire department did not approve. All right, well,
Speaker 1: that's how space telescopes orient themselves. How they know where
Speaker 1: they're looking at in the night sky or I guess.
Speaker 1: And if you're if you're in space, every every night
Speaker 1: is the night sky. It's always night in space. Yeah,
Speaker 1: unless you're looking at the Sun, I guess. But now
Speaker 1: let's talk about how space telescopes move, how they actually
Speaker 1: turn to look at a particular star or galaxy or nebula.
Speaker 1: So let's get into that, but first let's take another
Speaker 1: quick break. Or we're talking about how space telescopes point themselves.
Speaker 1: That's that seems very like self accusatory. I mean, like,
Speaker 1: what's the point of space telescopes? No, like they have
Speaker 1: to point at them they're pointing themselves at themselves. I mean,
Speaker 1: some you've got to do it, right. How introspective are
Speaker 1: space telescopes? I guess they're not really pointing themselves. We
Speaker 1: are pointing them, right, somebody is doing it. Yeah yeah, right,
Speaker 1: the joystick. It's not like they're up there just deciding
Speaker 1: on their own. Hey I'm going to look at Andromeda today.
Speaker 1: Yeah yeah, I'm sure there's the NASA joystick person listening
Speaker 1: to this brain now going, hey, I point the space
Speaker 1: tells cooes. Do you think space telescodes point themselves? That's right?
Speaker 1: What do you think the garbage takes itself out just
Speaker 1: because you're not doing that well? We talked about how
Speaker 1: space telescopes can know which way they're pointing out out
Speaker 1: there in space, because I guess it's pretty disorient can
Speaker 1: be disorient thing. If you're out there in space, you're
Speaker 1: sort of it's hard to know which way is up
Speaker 1: and down exactly. And so the second question now is
Speaker 1: how do they actually turn? How do they like if
Speaker 1: you're looking in one way looking at a star and
Speaker 1: you want to look at the star over there, how
Speaker 1: do you make that term? Because, as we talked about,
Speaker 1: you don't want to rely on propellants or rockets or
Speaker 1: ion engines because those are kind of costly. They maybe
Speaker 1: you might run out at some point in the future. Yeah,
Speaker 1: and those would be nice, right, you'd like to do that.
Speaker 1: It's sort of an easy solution because it lets you
Speaker 1: have a net force. Right, you have your space telescope,
Speaker 1: you throw something off the side, you're applying a force
Speaker 1: to that object. That object applies to force back to you.
Speaker 1: You turn or you move and make some sort of sense.
Speaker 1: But as we said, that requires some mass, and so
Speaker 1: now we need a solution that doesn't have any net
Speaker 1: force or no net torque on the object. Right, you
Speaker 1: have to figure out how to turn the telescope without
Speaker 1: applying an overall force to it. Oh, I see what
Speaker 1: you're saying. Because if you are applying an overall net
Speaker 1: force or torque, that means you're expending energy in the universe, right, yeah,
Speaker 1: and not just energy momentum. Right. So if you're going
Speaker 1: to turn this thing from the outside, you're like, put
Speaker 1: your hand on it and turn it, then you're applying
Speaker 1: a force to it, right, Or if you're on the
Speaker 1: telescope and you're throwing a rock off the side of it,
Speaker 1: you're using some mass. You're expending momentum. So what we
Speaker 1: want is a way to turn the telescope without changing
Speaker 1: its total momentum, because changing its total momentum, by Newton's laws,
Speaker 1: requires something else to balance that momentum, which means something
Speaker 1: else with mass, and there's nothing else out there. It's
Speaker 1: just floating out in space. How do you turn the
Speaker 1: telescope without applying some overall force to it. That's the
Speaker 1: physics puzzle, Like how do you change your absolute orientation
Speaker 1: without changing your overall angular momentum? Kind of Yeah, imagine,
Speaker 1: for example, you're on ice skates and you're on a
Speaker 1: super duper slippery surface. How do you turn? Or you
Speaker 1: can't push against the ice because you're on ice skates
Speaker 1: in a super slippery So how do you turn your direction?
Speaker 1: How do you change which way you are pointing? That's
Speaker 1: basically the puzzle, right, So if you could push against
Speaker 1: the side, that'd be great, but there is no side.
Speaker 1: If you could like throw a rock, then that'd be great,
Speaker 1: but you can't do that. So the question is how
Speaker 1: do you turn on this slippery surface? Right? Or I
Speaker 1: was thinking it's more like, you know, if you were
Speaker 1: stuck out there in space, like if you're an astronaut.
Speaker 1: So imagine you're an astronaut and your space suit and
Speaker 1: you're out there and base whether you're looking away from
Speaker 1: your spaceshipe or away from the Earth, and you want
Speaker 1: to turn around to look at your spaceship or Earth,
Speaker 1: but you've run out of fuel and maybe in your jetpack,
Speaker 1: how do you turn yourself around, Like, you can't just
Speaker 1: like grab something and pull yourself to look the other way.
Speaker 1: And you can't just like flail your arms because it
Speaker 1: would be hard to sort of change your orientation. Yeah,
Speaker 1: even just flailing your arms won't do it, right. You
Speaker 1: can't by flailing your arms apply any overall force to yourself.
Speaker 1: So this seems like an unsolvable problem, and the way
Speaker 1: to solve it is to find a loophole is to say, well,
Speaker 1: what if I don't want to turn the whole telescope.
Speaker 1: What if I only want to turn part of the telescope.
Speaker 1: So imagine like an invisible dividing line. You say, this
Speaker 1: part of the telescope I want to turn because it's
Speaker 1: got the cameras on it, and this other part of
Speaker 1: the telescope has the electronics and all the other stuff.
Speaker 1: They can't see anything, so I don't really care about
Speaker 1: that one. So instead of turning the whole telescope, what
Speaker 1: if you just want to turn part of the telescope
Speaker 1: one way? You can do that by turning the other
Speaker 1: part the other way. I imagine, for example, having two
Speaker 1: ice skaters that are ski getting together. One of them
Speaker 1: can start spinning if they push against the other one. Right,
Speaker 1: So instead of turning the whole telescope, just turn the
Speaker 1: part of the telescope you want to actually use to
Speaker 1: look at the universe by pushing it against another part
Speaker 1: of the telescope, or maybe instead of iceicators. You can
Speaker 1: imagine our stranded astronaut out there in space. You know,
Speaker 1: they can't look in a particular way by themselves, but
Speaker 1: if they had a buddy or a friend, like, one
Speaker 1: of them could push against the other one and at
Speaker 1: least one of them can look back at Earth or
Speaker 1: at their spaceship. Exactly. If you don't care what your
Speaker 1: buddy gets to see, then you can turn in one
Speaker 1: direction by pushing against him or her. And that's exactly
Speaker 1: what they do. On the space telescopes. They have a
Speaker 1: little part of it called at a buddy. It's got
Speaker 1: a little space telescope. Buddy, it's got the important part
Speaker 1: and the not important part, and the non important part
Speaker 1: is just there to help the other part turn. It's
Speaker 1: at the buddy, the sidekick, right, and so on a
Speaker 1: space telescope, this is called a reaction wheel. Essentially, it's
Speaker 1: a little piece which turns the opposite direction that the
Speaker 1: spacecraft does, so spacecraft says, I want to go that way.
Speaker 1: Then the reaction wheel turns the other way in order
Speaker 1: to balance it. So you're not changing the overall angular
Speaker 1: momentum of this thing at all. You're only changing the
Speaker 1: angle momentum of the part that you care about and
Speaker 1: the part you don't care about. The sidekick gets the
Speaker 1: opposite angular momentum, so physics is happy and you get
Speaker 1: to point the part that you want in the right direction.
Speaker 1: M So I'm imagining like inside of the space telescope,
Speaker 1: there's basically like a just a big disc maybe right,
Speaker 1: or like a big donut or cylinder that's that you
Speaker 1: can spin. Is that the idea? That's exactly the idea.
Speaker 1: So if you want to turn like clockwise, you would
Speaker 1: turn the donut or the disc counterclockwise. M Imagine you
Speaker 1: two astronauts. One of them ones to turn clockwise, so
Speaker 1: he pushes against the other one and one of them
Speaker 1: turns one way, the other one turns the other way.
Speaker 1: Now on the space telescope, you don't want like a
Speaker 1: second telescope to push against, so you shrink the other
Speaker 1: part down as much as you can make it massive
Speaker 1: and make it spin really, really fast, so it can
Speaker 1: store a lot of angular momentum. And so the space
Speaker 1: telescope has one of these for each direction it might
Speaker 1: need to turn interesting like up and down, the side
Speaker 1: to side, in front, the back exactly. So you need
Speaker 1: three of these to control your direction complete the in space.
Speaker 1: Usually they have extras just in case one of them breaks.
Speaker 1: But they're called reaction wheels or momentum wheels, and they
Speaker 1: are fixed in place on the sort of on the
Speaker 1: side of the telescope. They spin many many times, like
Speaker 1: a thousand or four thousand times a minute. M Now,
Speaker 1: I guess maybe I have two questions. One is okay,
Speaker 1: so I'm out there and floating a space, and I
Speaker 1: want to turn clockwise, So I spin my little wheel counterclockwise,
Speaker 1: and that gets me to turn clockwise while the spinning
Speaker 1: wheel is spinning inside of me. Now, let's say I
Speaker 1: want to stop because I certainly I got some angular
Speaker 1: momentum turning. How do I stop turning? Do I just
Speaker 1: spin the wheel the other way? Just spin the wheel
Speaker 1: the other way exactly, And so you can apply whatever
Speaker 1: torque you want to yourself as long as you're applying
Speaker 1: the opposite torque to the wheel and that works in
Speaker 1: both directions, and so the wheel isn't like ever stationary.
Speaker 1: What you're doing is you're speeding the wheel up or
Speaker 1: slowing the wheel down, and I do that with a
Speaker 1: little electric motor which is solar powered. So it is
Speaker 1: sort of like your Tesla as you said earlier, yeah,
Speaker 1: or like the Prios, right, or any any car with battery.
Speaker 1: Like when you break, you're putting energy into the battery,
Speaker 1: and then when you need to accelerate, you take energy
Speaker 1: from the battery. So basically the same concept, right, Basically
Speaker 1: the same concept exactly. So you want to change your orientation,
Speaker 1: you have to change the speed of the wheel to
Speaker 1: create a torque on the rest of the object. And
Speaker 1: so this thing spins really really fast, so it can
Speaker 1: store a lot of ing the momentum, but it's still
Speaker 1: really small and low mass compared to the actual telescope,
Speaker 1: which means you can't turn the telescope very quickly. But
Speaker 1: that's good, right, you don't want this thing jerking around.
Speaker 1: They're not super dupe or powerful, but you don't ever
Speaker 1: need to ever change the telescope's direction really really quickly.
Speaker 1: It sort of feels like you got something for free
Speaker 1: or something for nothing, you know, do you know what
Speaker 1: I mean? Like that was pointing one way and then
Speaker 1: I did something, and now I'm pointing it another way.
Speaker 1: But I didn't lose really any energy. Yeah, there's two
Speaker 1: different aspects of this, energy and momentum. So momentum conservation
Speaker 1: is satisfied. Because part of U spunum one way, the
Speaker 1: other part supund the other way, so it adds up
Speaker 1: to zero. Just like your two astronauts, they could also
Speaker 1: split apart if they push against each other, right, they
Speaker 1: could float away in space when you could get back
Speaker 1: to the spaceship, and the other one could be lost
Speaker 1: to infinity, and that would satisfy conservation momentum. There'd be
Speaker 1: no net force on the pair of them, even though
Speaker 1: there is a force relative between them, So momentum is satisfied.
Speaker 1: But you're right, we are using energy, so this is
Speaker 1: not for free. You need to speed up that reaction
Speaker 1: wheel or slow down that reaction wheel. That requires some energy,
Speaker 1: and so this thing is not for free. It does
Speaker 1: use some energy, but it doesn't need any propellant. Right.
Speaker 1: A rocket uses both energy and propellant, has to have
Speaker 1: some math to throw at the side. This doesn't require
Speaker 1: any propellant, though it does use some energy. Yeah, I
Speaker 1: guess what I mean. Like in the two astronaut example,
Speaker 1: if you and I are in space and I'm like, Daniel,
Speaker 1: save yourself. I'm going to push you towards the spaceship
Speaker 1: to save yourself, and I push you. You're moving towards
Speaker 1: the spaceship, but I'm not. I'm moving away from the spaceship.
Speaker 1: But then I'm what if? And then but then suddenly
Speaker 1: it's like I changed my mind. I'm like, wait, wait, wait, no,
Speaker 1: that was a terrible idea, and I pull on the
Speaker 1: rope that was attached between us to bring us back together. Technically,
Speaker 1: we would not, like, our center of mask would not
Speaker 1: have moved. That's right, right. Our center of masks cannot
Speaker 1: move without some external force. Right. So even if you
Speaker 1: don't change your mind and I drift back to the spaceship,
Speaker 1: you're drifting away from the spaceships. Our center of mass
Speaker 1: is not changing, right, right. But on the spinning example
Speaker 1: with the space telescope, I kind of it sort of
Speaker 1: feels like you did get away with something, right. It's
Speaker 1: like you spun the mass one way and then you
Speaker 1: spun it the other way and now you're you're in
Speaker 1: a different spot. Your total orientation change direction. Well, part
Speaker 1: of the spaceship changes direction and another part changes direction
Speaker 1: in the opposite way. So the total angle momentum hasn't changed. Right.
Speaker 1: But then when you slow down to stop, you spin
Speaker 1: it the other way, and presumably it's the same amount
Speaker 1: of momentum that you need to take out or put
Speaker 1: back in. And so you and the wheel are in
Speaker 1: the same spot you started with, but both of you
Speaker 1: are pointing in a different direction. Though you're both pointing
Speaker 1: in a different direction, but the angular momentum hasn't changed.
Speaker 1: You've expended some energy, but the angular momentum isn't different. Yeah, right,
Speaker 1: it sort of feels like you're getting something for free. Well,
Speaker 1: it's sort of like if the astronauts push against each
Speaker 1: other and they're further away, it costs some energy to
Speaker 1: change that configuration, but it didn't change the overall momentum. Yeah,
Speaker 1: but in the astronaut example, they didn't move if they
Speaker 1: come back together. But in the wheel case, do you
Speaker 1: do sort of like move, You're not pointing in a
Speaker 1: different direction, right, Well, in the astronaut a case, imagine
Speaker 1: we're connected by ropes and you push against me, so
Speaker 1: that I drifted back towards the ship, and you drift
Speaker 1: away from the ship. And then you change your mind,
Speaker 1: and so you tug on the rope to stop my motion,
Speaker 1: which also stops you. Now we're further apart than where
Speaker 1: we were, but we have no change in our center
Speaker 1: of mass, no change in our overall momentum. We've lost
Speaker 1: is you spend some energy pushing me away and then
Speaker 1: pulling me back, So in the same way, when you're
Speaker 1: orienting the telescope, you've changed its overall configuration, but there's
Speaker 1: no change in its overall angle momentum. That you have
Speaker 1: spent some energy to change the directions of both parts,
Speaker 1: the telescope and the reaction wheel. Interesting, so well, well,
Speaker 1: I feel also that the other part question I had
Speaker 1: is it isn't spinning a little wheel basically the same
Speaker 1: as flailing your arms, Like if I was stuck out
Speaker 1: there in space, could I also just like gonna spin
Speaker 1: my arm and that would reorient myself? If you could
Speaker 1: turn your arm effectively into a reaction wheel, then yes,
Speaker 1: I don't know if you really could get your arm
Speaker 1: to spin independently along the same access though I had
Speaker 1: to think about the biomechanics of it. Actually, you're an
Speaker 1: expert in that, aren't you. I'm not sure if you
Speaker 1: really can have it spinned independently, or if when you're
Speaker 1: moving in or way, if you're moving in a circle,
Speaker 1: if you're effectively pushing back on your body. But yes,
Speaker 1: if you, for example, ripped your arm off and attached
Speaker 1: it via mechanical axle to your body, then by spinning
Speaker 1: it you could change your direction. That seems a little dramatic,
Speaker 1: but I think the answer, since you say that I'm
Speaker 1: the expert, I think the answer is yes, I think
Speaker 1: you could do that. It's kind of the reason why
Speaker 1: when you jump off a cliff into the water, for example,
Speaker 1: or of a diving board, people flail their arms. They
Speaker 1: sort of like moving like a windmill, and that because
Speaker 1: they're trying not to fall on their face in the water. Yeah. Well,
Speaker 1: I'll trust you whether that's possible. I prefer the cleaner
Speaker 1: physics but more gory example where you actually pull the
Speaker 1: arm off, but I trust you that it's possible even
Speaker 1: without filling your arms. All right, we're in space. You
Speaker 1: can rip your arm out, but they don't have to
Speaker 1: look back at the spaceship, although I'm not sure what
Speaker 1: you're going to do once you get the spaceship. Are
Speaker 1: you going to open the door? And I'll do my
Speaker 1: way and we'll see how that goes? All right, Well,
Speaker 1: we'll see if the door was designed to be opened
Speaker 1: one handed, just space was designed for arm removal. I'm
Speaker 1: not saying it's more practical. I'm just saying the physics
Speaker 1: of it is clearer. I see, I see, And that's
Speaker 1: more important than your arm. I guess in this scenario,
Speaker 1: if it's just hypothetical and I want to give the
Speaker 1: accurate physics answer, then yes, I prefer the more gruesome
Speaker 1: but clear physics scenario, right right. I think as an engineer,
Speaker 1: I would try my way first if it works, rather
Speaker 1: than getting to the physics dogma here. All right, but
Speaker 1: you can be expending valuable oxygen as you do your experiment.
Speaker 1: All right? So then is this how the James Webb
Speaker 1: space does coupe orient itself? Do they have? Does it
Speaker 1: have these spinning wheels? Do the Hubble also do this? Yeah?
Speaker 1: So basically every spacecraft does this. James Webb has six
Speaker 1: of these reaction wheels that are spinning that help it
Speaker 1: turn Hubble has these things. Kepler has these things, and
Speaker 1: Kepler is a fascinating story because these things failed on Kepler,
Speaker 1: which made it very, very difficult for Kepler to do
Speaker 1: its mission. What happened? So Kepler launched two thousand and nine,
Speaker 1: had four of these reaction wheels you only nearly need three,
Speaker 1: but it had a spare just for good measure. And remember,
Speaker 1: Kepler is a telescope that's looking for planets to eclipse
Speaker 1: their stars. So you got to watch a star for
Speaker 1: a while, for a long time to see it's one
Speaker 1: ten thousands drop in brightness as a planet goes across
Speaker 1: the star, so you really got to be focused on it.
Speaker 1: A few years into itsmission, in two thousand and twelve,
Speaker 1: one of these things failed and they didn't understand why.
Speaker 1: But that's okay. They were had four, so they had
Speaker 1: one spare. They're okay with three, and then the next
Speaker 1: year they lost weight. I have a question, like, you
Speaker 1: need one for every direction, right up, down, left, and
Speaker 1: right from the back. Which one is your spare? Like?
Speaker 1: Can you spur point in all three directions? Yeah? Good question.
Speaker 1: I don't know the answer. I guess the engineers have
Speaker 1: probably figured that out. Okay, So then Kepler lost one
Speaker 1: and they activated to spare and then what happened, And
Speaker 1: then they lost another one in twenty thirteen, so now
Speaker 1: they only had two, which limits how the spacecraft can
Speaker 1: turn right. And this thing has to be able to
Speaker 1: turn in three D to track an arbitrary star. So
Speaker 1: people were pretty bummed. They spent a lot of time
Speaker 1: and money on this spacecraft, and it also cost money
Speaker 1: to operate. It's not like once you have it up
Speaker 1: there in space it's free, it's saying, costs millions of
Speaker 1: dollars to operate the deep space network and the people
Speaker 1: and all electronics and everything. So it's a real question
Speaker 1: of like you just shut the thing down or do
Speaker 1: you try to figure out another way to operate this telescope.
Speaker 1: I wonder I'm guessing the answers no, because otherwise it
Speaker 1: would have figured that out. But I wonder if you
Speaker 1: can just use two to orient yourself in any direction
Speaker 1: in space? You know what I mean, because orientations in
Speaker 1: space are these kinds of weird transformations where you can, like,
Speaker 1: if you wanted to point to the right, you could,
Speaker 1: but you don't have something that turns you to the right.
Speaker 1: You could maybe point down, turn left, or you know,
Speaker 1: turn the other way and then switch back and do
Speaker 1: some weird complicated maneuver to get you to point right. Well,
Speaker 1: these things are orthogonal from each other, and so having
Speaker 1: only two basically only lets you map out a plane
Speaker 1: in a three D space. But like it, used one
Speaker 1: to turn one way, then that reorients the other one,
Speaker 1: doesn't it, So you essentially kind of can point in
Speaker 1: any direction. No, yeah, that's a really good point, and
Speaker 1: I think that that's essentially what they tried to do.
Speaker 1: But you still need help in that third direction because
Speaker 1: you don't want to drift right. You don't want to
Speaker 1: drift in that third direction. And once you've turned and
Speaker 1: pointed at the star, now you've used your two reaction
Speaker 1: wheels along those two planes, which means you're susceptible. You're
Speaker 1: always susceptible to moving in that third dimension. And so
Speaker 1: in order to correct, you would then need to turn
Speaker 1: twice basically in order to correct, which you'd bring you
Speaker 1: off of the star. So they actually came up with
Speaker 1: an ingenious way to try to prevent that from happening. Oh,
Speaker 1: I see what you're saying is that if you could
Speaker 1: point anywhere you want with maybe two reaction wheels active,
Speaker 1: but you wouldn't be able to maybe track a star smoothly. Yeah,
Speaker 1: you might have to take like zig zags, right, and
Speaker 1: which means you couldn't keep it in your field of view.
Speaker 1: So then what did they do? So they came up
Speaker 1: with this really cool scheme to use the sun. Right,
Speaker 1: the Sun is actually pushing on these things. Remember our
Speaker 1: conversation earlier about like zapping a solar sail attached to
Speaker 1: telescope with lasers from Earth. They basically are doing that,
Speaker 1: except they're using sunlight instead of lasers from Earth. So
Speaker 1: as it moves around the Sun, the solar wind and
Speaker 1: the photons push against the solar panels on Kepler, and
Speaker 1: so now instead of compensating for that, they're using that
Speaker 1: to help keep it stable. Interest in using the solar wind, Yeah,
Speaker 1: they're actually using the photon pressure, right, not just the
Speaker 1: solar wind, but the actual photon pressure. It's like a
Speaker 1: solar sale. So the solar panels are in sort of
Speaker 1: like a hexagon around Kepler. And if the pointy part
Speaker 1: where the solar panels meet, if that thing is oriented
Speaker 1: right along the direction of the photons, then it sort
Speaker 1: of stays stable and it's turned a little bit, then
Speaker 1: it's unstable. So they can use that orientation to help
Speaker 1: either push on the spacecraft or to keep it stable,
Speaker 1: but would that help it track a start? It really
Speaker 1: limits what they can do. They can only look at
Speaker 1: sort of a couple different places in the sky, but
Speaker 1: for a couple of spots and its orbit around the Sun,
Speaker 1: they can use the Sun to compensate for the lack
Speaker 1: of the third reaction wheel and keep it stable and
Speaker 1: keep a tract on a planet for a little while.
Speaker 1: So it's not a complete recovery of its abilities by
Speaker 1: any means, but it's a partial recovery of the science
Speaker 1: mission cool. Well, that's a pretty clever technology, I guess,
Speaker 1: although I feel like they should change the name from
Speaker 1: reaction wheels to flailing arms. It's a really big bummer
Speaker 1: that these things went bad. They've been trying to understand
Speaker 1: what happened, and in twenty seventeen there's a paper that
Speaker 1: came out that suggests that it's due to geomagnetic storms
Speaker 1: from the Sun. Basically, the Sun has like some big
Speaker 1: energetic event, it dumps out a bunch of plasma and
Speaker 1: a coronal mass ejection and as this passes through the spacecraft,
Speaker 1: it interferes with the operation of the reaction wheel. Wow. Yeah,
Speaker 1: that's pretty cool and also a pretty convenient story to
Speaker 1: make up for the fact that era the thing you
Speaker 1: design did not last as much as you thought it would. Yeah,
Speaker 1: and these reaction wheels are very specialized technology. This one
Speaker 1: manufacturer that has been putting these things out it's called Ithaco,
Speaker 1: and their reaction wheels have failed not just on Kepler
Speaker 1: but also on other spacecraft. So James Webb actually went
Speaker 1: to a different manufacturer to produce these things. So we're
Speaker 1: hoping that James Webb's reaction wheels lasts a lot longer.
Speaker 1: And so that is a pretty clever way to turn
Speaker 1: yourself in space to have these reaction wheels. And so
Speaker 1: basically the space teal skills use them. Do other spacecraft
Speaker 1: use them like the voyage you're used at, or do
Speaker 1: some of these like the Parker Solar Probe does it
Speaker 1: use that too? Some other spacecraft do use these kind
Speaker 1: of things, But remember they're very slow, so they're not
Speaker 1: great for navigation. They're really just great for like very
Speaker 1: gentle orientation. Another example is light Sale Light Sale is
Speaker 1: one of these things that's testing out the ability to
Speaker 1: sail on sunlight. There's a huge solar sale that it's
Speaker 1: using to gather momentum and navigate around the solar system.
Speaker 1: But they also want to be able to steer this thing,
Speaker 1: and so they have a reaction wheel on it to
Speaker 1: try to turn it sort of towards an away from
Speaker 1: the sun to change how it's sailing. So then it
Speaker 1: only needs one wheel. It only needs one wheel. Yeah,
Speaker 1: though it's also sort of experimental craft, and so I
Speaker 1: think they're trying to be simpler and cheaper. Everybody would
Speaker 1: love to have more of these wheels, and a lot
Speaker 1: of the spacecraft have a combination of reaction wheels and
Speaker 1: chemical thrusters. Chemical thrusters are for when you've like saturated
Speaker 1: your reaction wheel you can't turn anymore because it's already
Speaker 1: spinning in it's max rpm, or when you need to
Speaker 1: turn faster than you can with your reaction wheels, that
Speaker 1: you want to use your chemical thrusters very sparingly because
Speaker 1: you just use up the mass and then eventually you're
Speaker 1: run out cool Well overall, a pretty clever solution to
Speaker 1: move yourself, at least in orientation in space. Yeah, it's
Speaker 1: a very clever idea. And when I think we'll be
Speaker 1: using for a long time in the future, if we
Speaker 1: can make these things more reliable and if they don't
Speaker 1: require tearing your arm off, yes, let's try that solution. Second,
Speaker 1: So first zapping with lasers, second tearing your arm off.
Speaker 1: Kind that's right, I'm gonna be up up there is
Speaker 1: space going yes, season, go ahead and shoot the lasers
Speaker 1: at Daniel and let me know if that works. And
Speaker 1: if it does, then you can shoot them in me.
Speaker 1: But I'm going to be flailing my arms out here
Speaker 1: and I'll see you back at the space ship. I
Speaker 1: wonder if that big earth laser for zapping astronauts also
Speaker 1: has a joystick? And who gets to run that one?
Speaker 1: Oh man? Yeah? Yeah, And what kind of training the
Speaker 1: prison needs to do? You know, play a lot of
Speaker 1: asteroids maybe, or a lot of Halo. Perhaps you want
Speaker 1: someone who can get a good head shot the first
Speaker 1: try Fortnite experts. All right, Well, hopefully you did not
Speaker 1: get lost in this discussion, and we navigated your brain
Speaker 1: to understanding how space tells coopes move and orient themselves
Speaker 1: to look at the universe out there and This is
Speaker 1: crucial to our ability to understand what is out there
Speaker 1: in the universe and to continue to build that physical
Speaker 1: and conceptual map of how the universe works. Thanks for
Speaker 1: joining us, See you next time. Thanks for listening, and
Speaker 1: remember that Daniel and Jorge Explain the Universe is a
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