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00:00:00 --> 00:00:02 Andrew Dunkley: Hi there. Thanks for joining us. Once again,
00:00:02 --> 00:00:05 this is a Q and A edition of Space Nuts. My
00:00:05 --> 00:00:07 name is Andrew Dunkley. Great to have your
00:00:07 --> 00:00:09 company. Uh, we will be answering audience
00:00:09 --> 00:00:12 questions exclusively on this episode. We'll
00:00:12 --> 00:00:15 never do it again. Yes, we will. Uh, we're
00:00:15 --> 00:00:17 going to be, um, looking at
00:00:18 --> 00:00:20 a, uh, concept that Ross has put up about,
00:00:20 --> 00:00:23 uh, black holes equaling dark matter. Uh,
00:00:23 --> 00:00:25 we'll explain that. Or he will and we'll try
00:00:25 --> 00:00:28 and tear it apart. Uh, Sandy is
00:00:28 --> 00:00:31 asking about navigation in space.
00:00:32 --> 00:00:35 Uh, John is talking relativity, time,
00:00:35 --> 00:00:38 black holes and the big crunch. I
00:00:38 --> 00:00:40 knew we'd get a question about the big crunch
00:00:40 --> 00:00:42 because we talked about it so recently. And
00:00:43 --> 00:00:45 the speed of re entry is a question from
00:00:45 --> 00:00:48 Andy. We'll deal with all of that on this
00:00:48 --> 00:00:50 episode of space nuts.
00:00:50 --> 00:00:52 Voice Over Guy: 15 seconds. Guidance is internal.
00:00:53 --> 00:00:55 10, 9. Uh, ignition
00:00:55 --> 00:00:58 sequence start. Uh, space nuts. 5, 4, 3,
00:00:58 --> 00:01:01 2. 1, 2, 3, 4, 5, 5, 4,
00:01:01 --> 00:01:04 3, 2, 1. Space nut astronauts
00:01:04 --> 00:01:05 report it feels good.
00:01:06 --> 00:01:08 Andrew Dunkley: And with us once again is Professor Fred
00:01:08 --> 00:01:10 Watson, astronomer at large. Hello, Fred.
00:01:11 --> 00:01:14 Professor Fred Watson: Hi, Andrew. Good to talk again. Uh, it
00:01:14 --> 00:01:16 seems like only a few minutes ago that we
00:01:16 --> 00:01:17 were talking. It does, doesn't it?
00:01:17 --> 00:01:20 Andrew Dunkley: Yes, that's called relativity, I think.
00:01:20 --> 00:01:21 Professor Fred Watson: Time dilation. Yeah.
00:01:21 --> 00:01:24 Andrew Dunkley: Um, I'll tell you something funny. We had our
00:01:24 --> 00:01:26 granddaughters around last night. They were
00:01:26 --> 00:01:27 supposed to stay the night, but they both
00:01:27 --> 00:01:29 chickened out so dad had to come and pick
00:01:29 --> 00:01:30 them up at 9 o'.
00:01:30 --> 00:01:30 Speaker C: Clock.
00:01:30 --> 00:01:33 Andrew Dunkley: But um, um, they were, um,
00:01:33 --> 00:01:35 having a bit of fun and um, they liked doing
00:01:35 --> 00:01:38 craft. And one of them built a telescope with
00:01:38 --> 00:01:41 a piece of paper and was looking through it.
00:01:41 --> 00:01:43 And Judy said, what have you made? And it was
00:01:43 --> 00:01:46 the four year old she said, I made
00:01:47 --> 00:01:48 a looking through thing.
00:01:50 --> 00:01:52 That's what a telescope. It's a looking
00:01:52 --> 00:01:52 through thing.
00:01:53 --> 00:01:56 Professor Fred Watson: Um, which is nearly what they were
00:01:56 --> 00:01:58 originally called before the telescope was
00:01:58 --> 00:02:01 intended of a time
00:02:01 --> 00:02:04 device. Device for seeing afar. Uh,
00:02:05 --> 00:02:06 yeah, it's.
00:02:06 --> 00:02:07 Andrew Dunkley: Well, m. Looking through things.
00:02:07 --> 00:02:08 Professor Fred Watson: Looking through thing. Yeah.
00:02:08 --> 00:02:09 Andrew Dunkley: Very cute.
00:02:09 --> 00:02:11 Professor Fred Watson: I love that. Yeah. Um,
00:02:12 --> 00:02:14 yeah, you know, you know, you don't know what
00:02:14 --> 00:02:16 you might have, you know, released in that
00:02:16 --> 00:02:19 child's brain. She might become the
00:02:19 --> 00:02:22 next great astronomer. Uh, uh, using a
00:02:22 --> 00:02:24 looking through thing to make discoveries
00:02:24 --> 00:02:25 about the universe.
00:02:25 --> 00:02:27 Andrew Dunkley: Yeah. Yeah. Well, that's why we called it
00:02:27 --> 00:02:30 Vera. No, her name's. Her name's
00:02:30 --> 00:02:31 Felicity.
00:02:32 --> 00:02:34 Professor Fred Watson: That's a good name as well. I like it.
00:02:34 --> 00:02:37 Andrew Dunkley: It is nice. Shall we get to
00:02:37 --> 00:02:38 our first question?
00:02:38 --> 00:02:39 Professor Fred Watson: Oh, all right.
00:02:40 --> 00:02:43 Andrew Dunkley: All right. Uh, if black holes are, uh, the
00:02:43 --> 00:02:46 center of most galaxies, uh, and have
00:02:46 --> 00:02:48 been eating up matter almost from the
00:02:48 --> 00:02:50 Beginning of the universe. Can this be a
00:02:50 --> 00:02:53 possible explanation of dark matter? The
00:02:53 --> 00:02:55 black holes have eaten it.
00:02:56 --> 00:02:59 Now this, uh, comes from Ross Simon. I
00:02:59 --> 00:03:01 uh, had to smile when I read his name because
00:03:01 --> 00:03:03 Ross Simon used to be a famous newsreader on
00:03:03 --> 00:03:06 the Australian Broadcasting Corporation's TV
00:03:06 --> 00:03:09 news service. I remember Ross. He was, he was
00:03:09 --> 00:03:12 brilliant. Might be the same one. You
00:03:12 --> 00:03:12 never know.
00:03:12 --> 00:03:14 Professor Fred Watson: I was gonna say it's not the same Ross, is
00:03:14 --> 00:03:16 it? I hope so.
00:03:16 --> 00:03:18 Andrew Dunkley: It would be lovely. But, uh, it's not.
00:03:19 --> 00:03:21 Professor Fred Watson: Yeah. So, um, whether or not you are the
00:03:21 --> 00:03:24 famous Ross Simon. Ross, lovely to hear
00:03:24 --> 00:03:27 from you. Uh, and um, I mean
00:03:27 --> 00:03:29 it's, it's, it is tempting,
00:03:30 --> 00:03:32 uh, to lump black holes and dark
00:03:32 --> 00:03:35 matter together. Indeed. Um, that was
00:03:36 --> 00:03:37 looked at as being one of the first
00:03:38 --> 00:03:40 explanations of dark matter. Uh,
00:03:40 --> 00:03:43 that we've got space full of black holes
00:03:43 --> 00:03:45 that we don't see because they're black
00:03:45 --> 00:03:48 holes, um, and that they might account
00:03:48 --> 00:03:50 for the dark matter. This was the so called
00:03:50 --> 00:03:53 macho theory. Massive compact halo
00:03:53 --> 00:03:56 objects, uh, which was
00:03:56 --> 00:03:58 popular in the 80s,
00:03:59 --> 00:04:02 um, because it was only in the late
00:04:02 --> 00:04:04 70s that people started taking the idea of
00:04:04 --> 00:04:07 dark matter seriously when we realized
00:04:07 --> 00:04:09 that um, something like
00:04:10 --> 00:04:13 80% of the matter in the
00:04:13 --> 00:04:15 universe is invisible to us.
00:04:16 --> 00:04:19 Uh, now that's perhaps
00:04:19 --> 00:04:21 slightly different from what Ross is asking
00:04:21 --> 00:04:23 about because he's talking about material
00:04:23 --> 00:04:25 being sucked into black holes. Uh, and
00:04:25 --> 00:04:28 um, that is certainly
00:04:28 --> 00:04:31 something that happens. But that's not matter
00:04:31 --> 00:04:34 that's missing. That's just gone. Uh,
00:04:34 --> 00:04:37 the bottom line is that the universe as we
00:04:37 --> 00:04:39 see it today has this mystery in
00:04:39 --> 00:04:42 that we know that there is stuff there that
00:04:42 --> 00:04:44 has a gravitational effect. It holds galaxies
00:04:44 --> 00:04:46 together, it holds galaxy clusters together,
00:04:47 --> 00:04:49 causes uh, gravitational lensing
00:04:50 --> 00:04:52 all over the place. Um, but
00:04:52 --> 00:04:55 we have no way of detecting what it is other
00:04:55 --> 00:04:58 than through its gravity. So it's, it's. Some
00:04:58 --> 00:05:00 people used to call it missing matter. It's
00:05:00 --> 00:05:03 not missing. It's definitely there. Uh, this
00:05:03 --> 00:05:06 dark matter is around and it's probably in
00:05:06 --> 00:05:08 the rooms that you and I are sitting in, uh,
00:05:08 --> 00:05:11 at the moment. Uh, because it, it tends to be
00:05:11 --> 00:05:13 where normal matter is and we can.
00:05:13 --> 00:05:15 Andrew Dunkley: Judy and I were actually talking about a dark
00:05:15 --> 00:05:17 matter the other day, but you know, I won't
00:05:17 --> 00:05:18 elaborate.
00:05:20 --> 00:05:22 Professor Fred Watson: Uh, well, what you do in your spare time,
00:05:22 --> 00:05:24 Andrew, is entirely up m to you,
00:05:25 --> 00:05:26 especially with your wife. Um,
00:05:27 --> 00:05:30 um, so, yeah, so, so, but, um, but the,
00:05:30 --> 00:05:33 the, the black hole thing did come
00:05:33 --> 00:05:36 in because of this theory back in the 80s
00:05:36 --> 00:05:38 that Machos massive compact halo objects,
00:05:38 --> 00:05:41 objects that um, kind of dead
00:05:41 --> 00:05:44 stars or orphan planets or more Especially
00:05:44 --> 00:05:47 black holes might be, uh, the
00:05:47 --> 00:05:49 source of dark matter. The source of this GR
00:05:50 --> 00:05:53 we see present in large, on large scales
00:05:53 --> 00:05:56 like galaxy clusters and galaxies. What ruled
00:05:56 --> 00:05:58 that out was, uh, work carried out at a
00:05:58 --> 00:06:00 number of observatories, including here, uh,
00:06:00 --> 00:06:03 in Australia, uh, in fact, in a survey
00:06:03 --> 00:06:06 which was called macho, uh, looking for
00:06:06 --> 00:06:09 these things. Uh, and it was, um,
00:06:09 --> 00:06:11 that if you, if you had a universe full of
00:06:11 --> 00:06:14 black holes that you can't see, you would
00:06:14 --> 00:06:16 still be able to detect them by what's called
00:06:16 --> 00:06:18 gravitational microlensing. Because
00:06:18 --> 00:06:20 occasionally one of these black holes would
00:06:20 --> 00:06:22 pass in front of a distant star. Uh, and
00:06:22 --> 00:06:25 because black holes distort the space around
00:06:25 --> 00:06:27 them that behaves like a lens. And
00:06:27 --> 00:06:30 you magnify the light of the distant star.
00:06:30 --> 00:06:33 So you get a microlensing event has a
00:06:33 --> 00:06:35 very characteristic shape. It's a star
00:06:35 --> 00:06:37 getting brighter, uh, to a
00:06:37 --> 00:06:40 sharp cusp and then fading away again quite
00:06:40 --> 00:06:43 symmetrically. Uh, and we do
00:06:43 --> 00:06:46 see them. They're caused by normal stars and
00:06:46 --> 00:06:48 their planets. But in the numbers that you
00:06:48 --> 00:06:51 would have to have for black holes to
00:06:51 --> 00:06:54 be dark matter, they are not
00:06:54 --> 00:06:56 there. There weren't enough. The numbers were
00:06:56 --> 00:06:59 far too low. And that's when the emphasis
00:06:59 --> 00:07:01 shifted to WIMPs, the weakly interacting
00:07:01 --> 00:07:03 massive particles, which is just one class
00:07:03 --> 00:07:06 of, uh, subatomic particles that we think
00:07:06 --> 00:07:08 dark matter might be. So that's where the
00:07:08 --> 00:07:11 theory stands at the moment. So black holes,
00:07:11 --> 00:07:14 uh, you know, and I think Ross is
00:07:14 --> 00:07:16 talking about supermassive black holes at the
00:07:16 --> 00:07:17 centers of galaxies. Yes, They've been
00:07:17 --> 00:07:20 swallowing stuff up for 13.8 billion years,
00:07:20 --> 00:07:23 as far as we can tell. Um, but they don't
00:07:23 --> 00:07:25 explain why today in
00:07:26 --> 00:07:28 universe, um, something like 4/5 of the
00:07:29 --> 00:07:31 matter in the universe is invisible to us.
00:07:32 --> 00:07:35 Andrew Dunkley: Yeah, um, well, there's so many things we
00:07:35 --> 00:07:37 don't understand. And as yet, uh,
00:07:37 --> 00:07:40 which was brought up in a question recently,
00:07:40 --> 00:07:43 we have not been able to capture
00:07:43 --> 00:07:46 or identify, uh,
00:07:46 --> 00:07:47 a dark matter particle. So, um,
00:07:49 --> 00:07:52 until we can find some absolute proof
00:07:52 --> 00:07:55 and study it, we're probably going
00:07:55 --> 00:07:58 to just keep working with theory, I would
00:07:58 --> 00:07:58 imagine.
00:07:58 --> 00:08:00 Professor Fred Watson: Yeah, there are, um,
00:08:01 --> 00:08:04 techniques that can be brought to bear. Um,
00:08:04 --> 00:08:06 one of the theories about
00:08:06 --> 00:08:09 dark matter is that if
00:08:09 --> 00:08:12 that while dark matter particles don't
00:08:12 --> 00:08:14 interact with normal matter particles, they
00:08:14 --> 00:08:16 may interact with each other. In other words,
00:08:16 --> 00:08:18 if you bring two dark matter particles
00:08:18 --> 00:08:19 together, it's thought they might annihilate
00:08:20 --> 00:08:23 and produce a signal in gamma radiation.
00:08:23 --> 00:08:25 So you get this flash of gamma rays which
00:08:25 --> 00:08:28 might have a characteristic spectrum. And
00:08:28 --> 00:08:29 people are looking for that
00:08:30 --> 00:08:33 phenomenon in the centers of
00:08:33 --> 00:08:35 galaxies because that's where you would
00:08:35 --> 00:08:38 expect the dark matter to be at its densest.
00:08:38 --> 00:08:39 So it's where you would expect the dark
00:08:39 --> 00:08:41 matter particles to interact with each other.
00:08:42 --> 00:08:45 Um, so far the results have been a bit mixed
00:08:45 --> 00:08:47 on that. But it's one possible way that we
00:08:47 --> 00:08:50 might eventually discover, uh, what
00:08:50 --> 00:08:50 dark matter is.
00:08:52 --> 00:08:55 Andrew Dunkley: Maybe dark matter is like a, uh, negative
00:08:55 --> 00:08:57 photograph. Remember in the days of manual,
00:08:57 --> 00:09:00 um, photography, you'd take the film and
00:09:00 --> 00:09:02 it would be negative, and then you turn it
00:09:02 --> 00:09:05 into the photograph. Maybe dark matter
00:09:05 --> 00:09:06 is the negative of the universe.
00:09:07 --> 00:09:09 Professor Fred Watson: Well, yeah, I mean,
00:09:11 --> 00:09:14 there might well be, uh, a way that
00:09:14 --> 00:09:17 there is a sort of dark. What can I
00:09:17 --> 00:09:19 call it? A dark particle physics.
00:09:20 --> 00:09:23 A whole, uh, sweep of
00:09:23 --> 00:09:26 subatomic particles which
00:09:26 --> 00:09:29 fall under what we lump together as dark
00:09:29 --> 00:09:31 matter. But it's not just a single particle,
00:09:31 --> 00:09:32 it's many different ones. Just like the
00:09:32 --> 00:09:35 particles of normal matter. The 16 normal,
00:09:35 --> 00:09:38 uh, matter. Sorry, 16 subatomic
00:09:38 --> 00:09:40 particles. They include forces as well as
00:09:40 --> 00:09:42 matter when you count the 16. But you know
00:09:42 --> 00:09:44 what I mean, You've got this suite of
00:09:44 --> 00:09:46 different particles that make up normal
00:09:46 --> 00:09:47 matter. Maybe there's a suite of different
00:09:47 --> 00:09:50 particles that in some ways are a negative,
00:09:50 --> 00:09:53 uh, um, that make up dark matter.
00:09:54 --> 00:09:55 So I think that's not a bad one.
00:09:56 --> 00:09:57 Andrew Dunkley: We've been assuming it's just the one thing.
00:09:57 --> 00:09:59 It could be all sorts of things.
00:10:01 --> 00:10:03 Professor Fred Watson: There could be atoms and molecules made out
00:10:03 --> 00:10:05 of dark matter because
00:10:06 --> 00:10:09 they interact with each. I don't know. Look,
00:10:09 --> 00:10:11 I'm not a particle physicist, but, um, the
00:10:12 --> 00:10:14 possibilities seem, not exactly endless
00:10:14 --> 00:10:16 because particle physics has certain rules
00:10:16 --> 00:10:19 that you've got to follow. Uh, but I'm
00:10:19 --> 00:10:21 still pretty optimistic that we're going to
00:10:21 --> 00:10:22 get to the bottom of dark matter, uh,
00:10:23 --> 00:10:26 hopefully while I'm still al. Because I want
00:10:26 --> 00:10:26 to know.
00:10:27 --> 00:10:30 Andrew Dunkley: Yeah, we all do. We all do. Uh, thanks for
00:10:30 --> 00:10:31 the question, Ross. Uh, really good
00:10:31 --> 00:10:32 discussion point.
00:10:32 --> 00:10:34 We get a lot of questions about dark matter
00:10:34 --> 00:10:36 and black holes. Uh, while we're on the
00:10:36 --> 00:10:38 subject of black holes, there was, uh, an
00:10:38 --> 00:10:41 article released on the BBC, uh,
00:10:41 --> 00:10:44 early this year. Uh, I know it's still early
00:10:44 --> 00:10:44 this year, but.
00:10:44 --> 00:10:44 Professor Fred Watson: Right.
00:10:44 --> 00:10:46 Andrew Dunkley: You know, I'm talking the 3rd of January,
00:10:46 --> 00:10:48 where scientists captured the first ever
00:10:48 --> 00:10:51 visual proof of two supermassive black holes
00:10:51 --> 00:10:54 in a death spiral. So we're really starting
00:10:54 --> 00:10:56 to be able to find out more and more,
00:10:57 --> 00:11:00 uh, through our increased technology and the
00:11:00 --> 00:11:03 capacity to observe and create images
00:11:03 --> 00:11:05 of these things. So, uh, that was pretty
00:11:05 --> 00:11:07 exciting story. I read that one the other
00:11:07 --> 00:11:09 day. I thought I'd, um, give it a mention.
00:11:09 --> 00:11:11 But, um. Yeah, they,
00:11:11 --> 00:11:14 uh, of Course, uh, the popular
00:11:14 --> 00:11:17 press, uh, created their own photo which
00:11:17 --> 00:11:19 has absolutely got nothing to do with it.
00:11:20 --> 00:11:23 But, uh, yeah, it sells the story,
00:11:23 --> 00:11:26 doesn't it? Um, but uh, they've got the image
00:11:26 --> 00:11:28 of these two black holes, um,
00:11:29 --> 00:11:31 basically getting ready to devour each other.
00:11:31 --> 00:11:33 I think the big one will win.
00:11:35 --> 00:11:37 Professor Fred Watson: Yes, probably. Well, you.
00:11:37 --> 00:11:37 Andrew Dunkley: Thanks, Ross.
00:11:38 --> 00:11:39 Professor Fred Watson: Yeah, probably.
00:11:39 --> 00:11:41 Andrew Dunkley: Yeah, thanks, Ross. Good to hear from you.
00:11:44 --> 00:11:46 Professor Fred Watson: Okay, we checked all four systems and.
00:11:46 --> 00:11:48 Speaker C: Being with a go space nats, our.
00:11:48 --> 00:11:51 Andrew Dunkley: Uh, next question comes from Sandy.
00:11:53 --> 00:11:55 Speaker C: G', day, Fred and Andrew. It's Sandy here
00:11:55 --> 00:11:57 from Melbourne again. Thanks for a cracking,
00:11:57 --> 00:12:00 ah, show as usual. Um, my question today
00:12:00 --> 00:12:03 is about navigation in the solar system for
00:12:03 --> 00:12:05 the various spacecraft that we've sent into
00:12:05 --> 00:12:08 deep space. Being a sci fi
00:12:08 --> 00:12:10 nerd, my mind naturally goes to fancy
00:12:10 --> 00:12:13 graphics of star charts and orbit parts on a
00:12:13 --> 00:12:16 giant screen. However, wanted to
00:12:16 --> 00:12:18 ask how mission planners at various space
00:12:18 --> 00:12:21 agencies plot orbits. Do they take
00:12:21 --> 00:12:23 into account objects like asteroids for any
00:12:23 --> 00:12:26 close calls or is the space so vast
00:12:26 --> 00:12:29 it's not really necessary? Thanks heaps,
00:12:29 --> 00:12:30 Sandy. Cheers.
00:12:31 --> 00:12:33 Andrew Dunkley: Thank you, Sandy. Good, uh, to hear from you.
00:12:33 --> 00:12:34 I don't think we've heard from Sandy in a
00:12:34 --> 00:12:37 little while, but, um. Yeah, um,
00:12:38 --> 00:12:39 he does a lot of great
00:12:41 --> 00:12:44 astrophotography and he's got a pretty
00:12:44 --> 00:12:46 amazing setup that he's shown me in the past
00:12:46 --> 00:12:48 about, uh, how he does it. Computers all
00:12:48 --> 00:12:51 plugged into telescopes and yeah, all this
00:12:51 --> 00:12:53 great software. It's a bit out of my league.
00:12:54 --> 00:12:56 Um, I might get there one day. Uh,
00:12:56 --> 00:12:59 navigation in space, plotting orbits, all
00:12:59 --> 00:13:02 that kind of jazz. Um, I
00:13:02 --> 00:13:05 must confess I struggle to get my head around
00:13:05 --> 00:13:07 it. Uh, it's not like driving a car. You've
00:13:07 --> 00:13:10 got to do, um, you know, when it comes to
00:13:10 --> 00:13:12 space, you've got, um, much less
00:13:12 --> 00:13:15 resistance, much, uh, more, much
00:13:15 --> 00:13:18 more reaction to minute, um,
00:13:19 --> 00:13:22 thrust and micro thrust and all
00:13:22 --> 00:13:23 sorts of other things. But you've got to be
00:13:23 --> 00:13:25 looking in all directions, not just, you
00:13:25 --> 00:13:28 know, on the plane of the planet. When
00:13:28 --> 00:13:31 you're driving a car type of thing. I don't
00:13:31 --> 00:13:33 know what I'm trying to say, but, um. Yeah.
00:13:33 --> 00:13:34 How does it all work, Fred?
00:13:35 --> 00:13:38 Professor Fred Watson: Uh, it's. It's sort of
00:13:38 --> 00:13:40 the equivalent of plotting things on a
00:13:40 --> 00:13:42 screen, but not quite the same. Um,
00:13:43 --> 00:13:45 but yeah, you know, the,
00:13:46 --> 00:13:49 uh, idea that, um. Excuse me
00:13:49 --> 00:13:52 a minute. Um, I'm sorry, I've got this cough.
00:13:52 --> 00:13:54 Sandy's, uh, idea that we
00:13:55 --> 00:13:58 need to take into account. I'm all right. I'm
00:13:58 --> 00:14:00 all right. Yeah,
00:14:01 --> 00:14:03 we need to take into account the positions of
00:14:03 --> 00:14:04 asteroids and things of that sort. That's
00:14:04 --> 00:14:07 exactly right. Um, so when you,
00:14:07 --> 00:14:10 um, chart, uh, the
00:14:10 --> 00:14:13 pathway through space, which
00:14:13 --> 00:14:15 is all done numerically, you know, it
00:14:15 --> 00:14:18 doesn't. We can make displays of them, and
00:14:18 --> 00:14:21 I think people do as well. But the
00:14:21 --> 00:14:24 reality is that the real hard core is locked
00:14:24 --> 00:14:26 up in the numbers and the equations. Um, what
00:14:26 --> 00:14:29 you have to do is to, uh, at any
00:14:29 --> 00:14:32 instant along the orbit, uh, of the
00:14:32 --> 00:14:34 spacecraft. Because it is always an orbit.
00:14:35 --> 00:14:37 Usually, uh, for something, you know, going
00:14:37 --> 00:14:39 between the planets, it will be in orbit
00:14:39 --> 00:14:41 around the sun. Uh, that's the way
00:14:41 --> 00:14:44 orbital mechanics work. As, uh, soon as you
00:14:44 --> 00:14:47 switch on your thrusters, then you change
00:14:47 --> 00:14:50 that orbit. Uh, but when all the
00:14:50 --> 00:14:52 thrusters are off and your main engines are
00:14:52 --> 00:14:54 off, you are following a trajectory which is
00:14:54 --> 00:14:56 essentially an orbit. Um,
00:14:57 --> 00:15:00 not always a closed one. It could be an open
00:15:00 --> 00:15:02 orbit, uh, which is what's happening to the
00:15:02 --> 00:15:04 five spacecraft that are leaving the solar
00:15:04 --> 00:15:06 system. Uh, but that
00:15:06 --> 00:15:09 orbit, uh, the future position
00:15:09 --> 00:15:12 of your spacecraft is dictated by the
00:15:12 --> 00:15:15 gravitational influence. Not just of the sun
00:15:15 --> 00:15:17 and the Earth and probably the Moon, but all
00:15:17 --> 00:15:20 the planets. All of them exert a
00:15:20 --> 00:15:22 gravitational pull. Uh, and, um,
00:15:23 --> 00:15:25 um, that goes down to the asteroids as well.
00:15:26 --> 00:15:27 If you're passing through the asteroid belt,
00:15:28 --> 00:15:30 you need to know where they all are, all the
00:15:30 --> 00:15:32 ones which are known. And there's more than a
00:15:32 --> 00:15:34 million known asteroids now.
00:15:35 --> 00:15:38 You would have them kind of built into your
00:15:38 --> 00:15:40 software that's looking, uh, at
00:15:41 --> 00:15:42 the direction that your spacecraft is going
00:15:42 --> 00:15:44 in. If there was any risk of a collision, it
00:15:44 --> 00:15:47 would flag that. And, um, it would also
00:15:47 --> 00:15:50 take into account the gravitational influence
00:15:50 --> 00:15:52 of any close encounters of asteroids. So
00:15:52 --> 00:15:55 it's a very precise science, um,
00:15:56 --> 00:15:58 as you know, because we know
00:15:59 --> 00:16:01 when, for example, the New Horizons, uh,
00:16:01 --> 00:16:04 flyby of Pluto a decade ago,
00:16:04 --> 00:16:07 uh, in 2015, um, the precision
00:16:07 --> 00:16:09 with which that was executed was
00:16:09 --> 00:16:11 unbelievable. And it's because of orbital
00:16:11 --> 00:16:13 mechanics and how well we understand these
00:16:13 --> 00:16:16 gravitational influences, uh, that let you do
00:16:16 --> 00:16:19 that. Um, so, uh, yes, space navigation,
00:16:19 --> 00:16:22 in some ways it's easier, uh, than navigating
00:16:23 --> 00:16:25 on, uh, than driving a car. Because
00:16:25 --> 00:16:28 with driving a car, you've always got the
00:16:28 --> 00:16:31 unpredictability of the other road users.
00:16:31 --> 00:16:33 The great thing about orbital mechanics is,
00:16:34 --> 00:16:36 you know, what the other planets, the other
00:16:36 --> 00:16:37 asteroids and all the rest of it are going to
00:16:37 --> 00:16:40 do. And just one other
00:16:40 --> 00:16:42 adjunct to this, if I may. Um,
00:16:43 --> 00:16:46 uh, some years ago, there was, um, several
00:16:46 --> 00:16:48 papers which talked about the interplanetary
00:16:48 --> 00:16:51 superhighway. Uh, and these are
00:16:51 --> 00:16:53 effectively low energy trajectories between
00:16:53 --> 00:16:56 the planets. And it's based on exactly what
00:16:56 --> 00:16:59 I've just been Saying you can map where, um,
00:16:59 --> 00:17:02 the gravitational pull of all the objects
00:17:02 --> 00:17:04 will take you. And it turned out that
00:17:05 --> 00:17:07 if you can put um, a spacecraft at one of
00:17:07 --> 00:17:10 your Lagrange points, these gravitationally
00:17:10 --> 00:17:13 stable points, then leading from that
00:17:13 --> 00:17:15 are these various low energy pathways that
00:17:15 --> 00:17:17 take you to the Lagrange points of other
00:17:17 --> 00:17:20 planets. Uh, and that's the interplanetary
00:17:20 --> 00:17:22 superhighway. It might take you decades to
00:17:22 --> 00:17:25 get, uh, um, from
00:17:26 --> 00:17:28 the Earth Lagrange points to something like
00:17:28 --> 00:17:31 Mars or Jupiter's Lagrange points. It's a
00:17:31 --> 00:17:34 very slow process, but it does exist.
00:17:35 --> 00:17:38 Almost like an imaginary highway which is
00:17:38 --> 00:17:39 changing all the time as the planets go
00:17:39 --> 00:17:41 around in their orbits. Uh, just an
00:17:41 --> 00:17:44 interesting aspect of the navigation in
00:17:44 --> 00:17:44 space.
00:17:45 --> 00:17:47 Andrew Dunkley: Yeah, I would imagine that a lot of
00:17:47 --> 00:17:50 this, uh, would be pre
00:17:50 --> 00:17:53 programmed into the uh, computers of
00:17:53 --> 00:17:56 these vessels. Um, they do
00:17:56 --> 00:17:58 everything ahead of time because these things
00:17:58 --> 00:18:01 are on autopilot, the long haul spacecraft
00:18:01 --> 00:18:03 that are going out to do these missions.
00:18:04 --> 00:18:07 Uh, so it would. And I've been
00:18:07 --> 00:18:10 in the cockpit of a commercial uh,
00:18:10 --> 00:18:13 airliner, um, long before you can't
00:18:13 --> 00:18:15 do that anymore. Long before we had any
00:18:15 --> 00:18:17 issues like that. And
00:18:17 --> 00:18:20 watching the process, the plane flies itself
00:18:21 --> 00:18:24 and the pilots sit back and tell dad jokes to
00:18:24 --> 00:18:27 the tower. Um, that's what happened.
00:18:28 --> 00:18:30 But I would imagine it's the same in space.
00:18:30 --> 00:18:33 All these things are pre programmed, pre
00:18:33 --> 00:18:35 calculated, uh, and then
00:18:35 --> 00:18:38 contingencies built in just in case something
00:18:38 --> 00:18:40 gets in the way that you didn't anticipate.
00:18:40 --> 00:18:43 Um, they modify the
00:18:43 --> 00:18:46 spacecraft to sense a problem and go around
00:18:46 --> 00:18:47 it, I would imagine.
00:18:49 --> 00:18:52 Professor Fred Watson: Yeah. In fact
00:18:52 --> 00:18:55 the likelihood of something, it's so
00:18:55 --> 00:18:57 predictable. And our uh, knowledge
00:18:58 --> 00:19:00 of the sort of
00:19:01 --> 00:19:03 congestion in space, if I can put it that
00:19:03 --> 00:19:06 way, is so deep that um,
00:19:06 --> 00:19:08 it's unlikely that something's going to come
00:19:08 --> 00:19:10 along to surprise you. You suddenly see
00:19:10 --> 00:19:13 something ahead that you've got to avoid, uh,
00:19:13 --> 00:19:15 because that avoidance might actually be very
00:19:15 --> 00:19:17 difficult. Um, you can do things. So
00:19:17 --> 00:19:20 apparently, perhaps the best example
00:19:20 --> 00:19:22 I can give you again, it goes back to New
00:19:22 --> 00:19:25 Horizons and that is that once the
00:19:25 --> 00:19:27 Jupiter encounter, sorry, the Pluto encounter
00:19:27 --> 00:19:30 had happened, uh, back in July
00:19:30 --> 00:19:32 2015, um,
00:19:33 --> 00:19:35 they looked for other potential targets
00:19:36 --> 00:19:39 and eventually found the object
00:19:39 --> 00:19:41 Arrokoth that was discovered as part of
00:19:41 --> 00:19:44 surveys looking for future targets. And they
00:19:44 --> 00:19:46 worked out at what point they had to
00:19:47 --> 00:19:50 apply a thrust to the spacecraft to change
00:19:50 --> 00:19:52 its trajectory so that it would intersect
00:19:52 --> 00:19:55 with Arrokoth. And it all happened,
00:19:55 --> 00:19:58 you know, perfectly smoothly. Um,
00:19:58 --> 00:20:00 I think it was a couple of years later when
00:20:00 --> 00:20:03 the Arrokoth, uh, flyby took place. I Can't
00:20:03 --> 00:20:05 remember when it was. Maybe even a bit later
00:20:05 --> 00:20:08 than that. Maybe five years later.
00:20:09 --> 00:20:12 But yeah, that all happened. That was the
00:20:12 --> 00:20:14 nearest thing to, oh, there's something
00:20:14 --> 00:20:17 ahead, we need to change course to either
00:20:17 --> 00:20:19 interact with it or avoid it. Um, and it was
00:20:19 --> 00:20:21 a very leisurely process.
00:20:22 --> 00:20:24 Andrew Dunkley: And you're right about, uh, navigation on the
00:20:24 --> 00:20:27 planet on roads being much more dangerous.
00:20:27 --> 00:20:29 We were walking along the street the other
00:20:29 --> 00:20:31 day and somebody turned right off the main
00:20:31 --> 00:20:34 road into our, uh, part of town and,
00:20:34 --> 00:20:37 uh, went to the right hand side of the
00:20:37 --> 00:20:38 traffic island instead of the left.
00:20:38 --> 00:20:40 Professor Fred Watson: Right where we were walking.
00:20:42 --> 00:20:42 Yeah.
00:20:42 --> 00:20:44 Andrew Dunkley: Ah, I don't think she noticed, to be honest.
00:20:44 --> 00:20:46 Honest, she just went up the wrong.
00:20:46 --> 00:20:48 Professor Fred Watson: Side of the road. Hm.
00:20:48 --> 00:20:51 Andrew Dunkley: Anyway, it happens, but we, we always keep an
00:20:51 --> 00:20:53 eye out for that kind of thing. Um, there you
00:20:53 --> 00:20:54 go, Sandy. Thanks for the question. The
00:20:54 --> 00:20:57 answer is easy peasy, really.
00:20:58 --> 00:21:00 Professor Fred Watson: With modern computers, it's a lot harder if
00:21:00 --> 00:21:02 you're doing it by hand. Yeah.
00:21:03 --> 00:21:05 Andrew Dunkley: All right. This is a Q and A edition of Space
00:21:05 --> 00:21:07 Nuts with Andrew Dunkley and Professor Fred
00:21:07 --> 00:21:08 Watson.
00:21:11 --> 00:21:14 Space Nuts. Okay. Uh, our next question
00:21:14 --> 00:21:17 comes from John in 27
00:21:17 --> 00:21:19 parts. Hey, guys. Love the show. Every time I
00:21:19 --> 00:21:22 listen to a new episode, my mind goes crazy
00:21:22 --> 00:21:23 thinking about new possibilities and
00:21:23 --> 00:21:25 questions. I have two questions about
00:21:26 --> 00:21:29 time dilation. Uh, in general
00:21:29 --> 00:21:31 relativity, uh, if general
00:21:31 --> 00:21:34 relativity causes time to be observed at
00:21:34 --> 00:21:36 different rates, would that mean
00:21:36 --> 00:21:39 someone orbiting very close to one of the
00:21:39 --> 00:21:41 first black holes in existence would
00:21:41 --> 00:21:44 experience a universe that has existed for a
00:21:44 --> 00:21:46 much shorter period of time?
00:21:47 --> 00:21:49 Uh, as a follow up to this, if the
00:21:50 --> 00:21:52 new theory about the Big Crunch turns out to
00:21:52 --> 00:21:55 be true, would the finite
00:21:55 --> 00:21:58 time of the universe form the Big Bang
00:21:58 --> 00:22:01 to, uh, uh, from the Big Bang to the Big
00:22:01 --> 00:22:04 Crunch be considerably shorter if again,
00:22:04 --> 00:22:07 you were orbiting close to a black hole,
00:22:07 --> 00:22:09 uh, we see the universe as being
00:22:09 --> 00:22:12 13.79 billion years old.
00:22:12 --> 00:22:15 And uh, new estimates put the big crunch
00:22:15 --> 00:22:18 at 20 billion years into the
00:22:18 --> 00:22:20 future. My brain hurts thinking that these
00:22:20 --> 00:22:22 timescales could be considerably different
00:22:22 --> 00:22:25 due to time dilation. All the best, John. Uh,
00:22:25 --> 00:22:27 from Suffolk in the uk.
00:22:29 --> 00:22:30 There's a lot in there.
00:22:31 --> 00:22:33 Professor Fred Watson: Um, yeah. And so, so
00:22:34 --> 00:22:37 it's quite complicated because time
00:22:37 --> 00:22:39 dilation depends, uh, on your
00:22:39 --> 00:22:42 vantage point. So yeah, if you're in
00:22:42 --> 00:22:45 orbit around a black hole, uh, you're in an
00:22:45 --> 00:22:47 intense gravitational field.
00:22:47 --> 00:22:50 Andrew Dunkley: You're also stuffed. But we'll just deal with
00:22:50 --> 00:22:51 that another time.
00:22:52 --> 00:22:53 Professor Fred Watson: Um, yeah,
00:22:55 --> 00:22:58 you experience time just at the normal rate.
00:22:59 --> 00:23:00 Uh,
00:23:02 --> 00:23:05 what, um, an outside observer looking at you
00:23:05 --> 00:23:08 would see would be your time going very
00:23:08 --> 00:23:11 slowly. The time would be Dilated. So,
00:23:11 --> 00:23:14 um, I suppose what we're talking about
00:23:14 --> 00:23:16 here is that in terms of
00:23:17 --> 00:23:19 what you might call the frame of rest of the
00:23:19 --> 00:23:22 universe itself, uh,
00:23:22 --> 00:23:25 that's what we
00:23:25 --> 00:23:27 see when we look at the universe in general.
00:23:27 --> 00:23:30 And that's what gives us the 13 point, 13.79
00:23:30 --> 00:23:33 or 13.8 billion year age of the
00:23:33 --> 00:23:36 universe. Um, your perception of that,
00:23:36 --> 00:23:38 so that time effectively wouldn't change,
00:23:39 --> 00:23:41 uh, but your perception of it if you were in
00:23:41 --> 00:23:43 orbit around the black hole would. It would
00:23:43 --> 00:23:45 probably appear to look as though it was
00:23:45 --> 00:23:47 going very quickly. Uh, but that's because
00:23:48 --> 00:23:50 your time's slower. And uh,
00:23:51 --> 00:23:53 likewise, um, uh,
00:23:54 --> 00:23:56 with the density of the universe being
00:23:56 --> 00:23:59 higher, uh, at earlier
00:23:59 --> 00:24:02 stages, yes, we do know time dilation takes
00:24:02 --> 00:24:04 place. You can actually see that, uh,
00:24:04 --> 00:24:07 because, um, when scientists, uh,
00:24:08 --> 00:24:10 look at, uh, the light curves of
00:24:10 --> 00:24:13 supernovae, exploding stars, they have a
00:24:13 --> 00:24:15 light curve. Their light increases and then
00:24:15 --> 00:24:18 decreases, uh, in a more gradual
00:24:18 --> 00:24:21 way with a very characteristic shape. Uh,
00:24:21 --> 00:24:24 those light curves, uh, are dilated, they're
00:24:24 --> 00:24:26 stretched when we look at ones in the early
00:24:26 --> 00:24:29 universe. So the phenomenon does happen,
00:24:29 --> 00:24:32 but, but, um, it doesn't happen at a
00:24:32 --> 00:24:35 level that's going to significantly shorten
00:24:35 --> 00:24:37 our, um, perception. You know, the
00:24:37 --> 00:24:40 universe's perception of its own history. If
00:24:40 --> 00:24:42 I put it that way. I think I'm talking a
00:24:42 --> 00:24:44 little bit in riddles here, but I hope John
00:24:45 --> 00:24:47 follows me, that it really is all about your,
00:24:48 --> 00:24:50 um, frame of rest, as we call it, your
00:24:50 --> 00:24:53 vantage point, uh, on the universe. Because
00:24:53 --> 00:24:55 that's what time dilation is all about. It's
00:24:55 --> 00:24:57 about people seeing time going differently,
00:24:57 --> 00:25:00 depending on their viewpoint. Our viewpoint
00:25:00 --> 00:25:03 here, uh, from Earth is probably
00:25:03 --> 00:25:06 that of the universe as a whole, effectively,
00:25:06 --> 00:25:09 uh, because we are not in an intense
00:25:09 --> 00:25:12 gravitational field. The gravitational
00:25:12 --> 00:25:14 field of the sun is the strongest thing we
00:25:14 --> 00:25:17 feel that keeps the Earth in orbit. But it's
00:25:17 --> 00:25:18 nothing like what you would find around a
00:25:18 --> 00:25:21 black hole. And so we've got probably a
00:25:21 --> 00:25:24 fairly unbiased view of the
00:25:24 --> 00:25:25 universe and its history.
00:25:26 --> 00:25:28 Andrew Dunkley: Now, uh, are we in a gravity well?
00:25:30 --> 00:25:32 Professor Fred Watson: Yeah, we are. I mean, the, the Earth itself
00:25:32 --> 00:25:34 creates a gravity well and that's what keeps
00:25:34 --> 00:25:36 us stuck to the Earth. Because the
00:25:36 --> 00:25:39 gravitational potential at your head
00:25:39 --> 00:25:41 is a little bit different from what it is at
00:25:41 --> 00:25:43 your feet. And that's what's pulling you
00:25:43 --> 00:25:46 down. The change in shape of space. There you
00:25:46 --> 00:25:47 go.
00:25:47 --> 00:25:48 Andrew Dunkley: All right.
00:25:48 --> 00:25:49 Professor Fred Watson: I'm not spaghettifying you.
00:25:50 --> 00:25:52 Andrew Dunkley: No, no. So, um,
00:25:53 --> 00:25:54 did we unpack everything there?
00:25:58 --> 00:25:59 Professor Fred Watson: Yeah, I think so. I think we. I think we've
00:25:59 --> 00:26:02 covered most of it. Okay, look,
00:26:02 --> 00:26:05 I know. Sorry. Go ahead.
00:26:05 --> 00:26:07 Andrew Dunkley: No, I was going to say that, uh, he also
00:26:07 --> 00:26:08 asked if the Big Crunch would happen
00:26:10 --> 00:26:12 faster than the expansion.
00:26:12 --> 00:26:15 Professor Fred Watson: So. Yes. So that I kind of, you know, lumped
00:26:15 --> 00:26:17 that into the. The fact that the times that
00:26:17 --> 00:26:20 we observe from, uh, our location in the
00:26:20 --> 00:26:22 universe, probably. Yes. 20 billion years
00:26:22 --> 00:26:24 down the track seems about right from the Big
00:26:24 --> 00:26:26 Crunch. If the recent desi results.
00:26:27 --> 00:26:29 Yeah, it's what happens. Um, um.
00:26:30 --> 00:26:32 Uh, I was going to say that,
00:26:33 --> 00:26:35 like you, John, uh, these things make my
00:26:35 --> 00:26:38 brain hurt. So don't think it's
00:26:38 --> 00:26:41 peculiar to, uh, um, a
00:26:41 --> 00:26:44 few people. Uh, I think most physicists,
00:26:45 --> 00:26:47 you know, they get their. They really have to
00:26:47 --> 00:26:49 get their heads around the things, like
00:26:51 --> 00:26:52 seeing things from different vantage points.
00:26:52 --> 00:26:55 It's not entire. Uh, it's not intuitive at
00:26:55 --> 00:26:55 all.
00:26:56 --> 00:26:59 Andrew Dunkley: No, no. All right, John, thank you. And I
00:26:59 --> 00:27:01 hope all is well in Suffolk. That's, uh,
00:27:01 --> 00:27:04 that's basically like one of.
00:27:04 --> 00:27:05 One of the easternmost points of England,
00:27:05 --> 00:27:06 isn't it?
00:27:06 --> 00:27:08 Professor Fred Watson: I used to live in Suffolk. Oh, there you are.
00:27:08 --> 00:27:11 Uh, yeah, not. Not far from Cambridge, which
00:27:11 --> 00:27:14 is in Cambridgeshire, but Suffolk. I was over
00:27:14 --> 00:27:16 the border in Suffolk. Uh, you're right,
00:27:16 --> 00:27:18 Suffolk. Uh, Norfolk and Suffolk are the two
00:27:18 --> 00:27:20 counties in East Anglia. That sort of
00:27:21 --> 00:27:23 semicircular bit that sticks out not very,
00:27:23 --> 00:27:25 very much north of the Thames Estuary.
00:27:25 --> 00:27:26 Andrew Dunkley: There you go. All right.
00:27:26 --> 00:27:27 Professor Fred Watson: Very pretty.
00:27:27 --> 00:27:27 Andrew Dunkley: Thanks, John.
00:27:28 --> 00:27:28 Professor Fred Watson: Yeah.
00:27:28 --> 00:27:29 Andrew Dunkley: Yes.
00:27:30 --> 00:27:32 Good to hear from you. Our final question
00:27:32 --> 00:27:34 today comes from Andy.
00:27:35 --> 00:27:38 Speaker D: Hi, guys, this is Andy from London. I'm a new
00:27:38 --> 00:27:40 listener to your podcast and quite new to
00:27:40 --> 00:27:43 science, so forgive me if this is a stupid
00:27:43 --> 00:27:46 question, but I was just wondering, um, when
00:27:46 --> 00:27:49 craft re enter atmosphere and they have to
00:27:49 --> 00:27:51 come in at a certain angle to stop from
00:27:51 --> 00:27:53 burning up, um,
00:27:54 --> 00:27:57 why do they not just come through slowly to.
00:27:57 --> 00:27:59 To get away with the friction effect
00:28:00 --> 00:28:03 which causes, uh, the heat. Thanks.
00:28:04 --> 00:28:07 Andrew Dunkley: Thank you, Andy. Um, and thanks for finding
00:28:07 --> 00:28:09 space Nuts and being a new listener. Uh,
00:28:09 --> 00:28:11 you've only got 590 odd
00:28:11 --> 00:28:14 episodes to catch up now, so. Yeah,
00:28:14 --> 00:28:17 have fun with that. We've certainly had fun
00:28:17 --> 00:28:20 with it. Um, I think we've had this question
00:28:20 --> 00:28:23 before, maybe asked a different way. Um,
00:28:27 --> 00:28:29 And when it comes to a spacecraft, we're
00:28:29 --> 00:28:31 orbiting the planet, which is essentially,
00:28:31 --> 00:28:33 it's just constantly falling. You're just
00:28:33 --> 00:28:36 maintaining a velocity that stops you falling
00:28:36 --> 00:28:39 in. Um, you do have to
00:28:39 --> 00:28:42 slow down to re enter so that that
00:28:42 --> 00:28:42 arc is,
00:28:45 --> 00:28:47 you know, reduced or increased, can't
00:28:47 --> 00:28:49 remember which. Uh, and then you fall through
00:28:49 --> 00:28:52 the atmosphere. Um, you can't stop
00:28:52 --> 00:28:54 and just sort of ease your way back in
00:28:55 --> 00:28:58 as against a space elevator, which would be
00:28:58 --> 00:29:00 able to do that if we ever build
00:29:00 --> 00:29:03 one. Uh, but that's a different set. But a
00:29:03 --> 00:29:06 space elevator is essentially not orbiting.
00:29:06 --> 00:29:09 It is stationary to a point on
00:29:09 --> 00:29:10 the planet, which means it goes up and down.
00:29:11 --> 00:29:12 Is that making sense?
00:29:13 --> 00:29:15 Professor Fred Watson: Yeah, um, yes, it is.
00:29:16 --> 00:29:17 Andrew Dunkley: That's good.
00:29:17 --> 00:29:19 Professor Fred Watson: That's the first time ever everything you've
00:29:19 --> 00:29:21 said is correct. Um, space elevators are, uh,
00:29:22 --> 00:29:25 hypothesized. Buzz, uh, Aldrin told me
00:29:25 --> 00:29:27 that night I had dinner with him, it's never
00:29:27 --> 00:29:29 going to happen. And he was quite right
00:29:29 --> 00:29:32 because, um, the space elevator has to sit on
00:29:32 --> 00:29:34 the equator. Uh, uh, every spacecraft in the
00:29:34 --> 00:29:36 sky crosses the equator. So you're always
00:29:36 --> 00:29:39 going to get things banging into, uh, will
00:29:39 --> 00:29:42 be very difficult to build one, uh, you know,
00:29:42 --> 00:29:44 apart from the structural thing, uh, so
00:29:44 --> 00:29:46 neglecting the space elevator for a minute,
00:29:46 --> 00:29:48 what you said is absolutely right. In order
00:29:48 --> 00:29:51 to stay in orbit, you have to achieve
00:29:51 --> 00:29:54 basically a horizontal velocity of about
00:29:54 --> 00:29:56 8 kilometers per second. Uh,
00:29:57 --> 00:29:59 and that's, uh, otherwise you just fall back
00:29:59 --> 00:30:02 to Earth. So that's what all
00:30:02 --> 00:30:05 the, you know, the, the huge amount of
00:30:05 --> 00:30:07 fuel that is carried by a rocket being
00:30:07 --> 00:30:10 launched. That's what it's all about. It's
00:30:10 --> 00:30:12 about getting up to a height of 2 or
00:30:12 --> 00:30:15 300 km and getting that
00:30:15 --> 00:30:17 orbital velocity, getting that horizontal
00:30:17 --> 00:30:20 velocity of 8 kilometers per second. So,
00:30:21 --> 00:30:22 um, what you could do,
00:30:24 --> 00:30:27 uh, is, and, you know, going, this
00:30:27 --> 00:30:29 is hopefully helping Andy,
00:30:29 --> 00:30:31 uh, if you, you had
00:30:32 --> 00:30:35 unlimited amounts of fuel, you could
00:30:35 --> 00:30:38 turn the rocket round, uh, from its orbital
00:30:38 --> 00:30:40 position and fire, uh,
00:30:40 --> 00:30:43 your rockets to act as a braking system
00:30:43 --> 00:30:45 to slow the thing down. And then you could
00:30:45 --> 00:30:48 gently tiptoe down through the atmosphere,
00:30:48 --> 00:30:50 constantly firing your rockets. It's actually
00:30:50 --> 00:30:53 what, um, Musk does with
00:30:53 --> 00:30:56 his, uh, Falcon rockets.
00:30:57 --> 00:30:59 He's got enough fuel left that he can bring
00:30:59 --> 00:31:02 the empty spacecraft back down intact,
00:31:02 --> 00:31:05 uh, and use it again, uh, without
00:31:05 --> 00:31:07 needing a heat shield. Um,
00:31:08 --> 00:31:10 so you could do that. Uh, and he's
00:31:10 --> 00:31:13 demonstrated that we can. Uh, but it
00:31:13 --> 00:31:16 turns out that, uh, it's much more
00:31:16 --> 00:31:19 effective to use this process called
00:31:19 --> 00:31:22 aerobraking, where you actually use the
00:31:22 --> 00:31:25 atmosphere itself to slow the
00:31:25 --> 00:31:27 spacecraft down, uh, because you don't need
00:31:27 --> 00:31:29 any fuel for that. You just need something
00:31:29 --> 00:31:31 that's going to stop it burning up. Uh, so
00:31:31 --> 00:31:34 getting from this 8km per second down
00:31:34 --> 00:31:37 to a few, you know, a meter or two per
00:31:37 --> 00:31:39 second, uh, for a splashdown or a touchdown,
00:31:40 --> 00:31:43 uh, is the tricky bit. And you've got to,
00:31:44 --> 00:31:46 uh, you know, you've got to use whatever
00:31:46 --> 00:31:49 means are at your disposal. And the easiest
00:31:49 --> 00:31:51 one is aerobraking using the atmosphere
00:31:51 --> 00:31:53 itself to slow you down. I should point out
00:31:53 --> 00:31:56 that, um, I think the first stage Falcon
00:31:56 --> 00:31:59 rockets, they're not at orbital velocity. Uh,
00:31:59 --> 00:32:00 when they turn around and come back, they
00:32:00 --> 00:32:03 haven't got up to that 8km per second because
00:32:03 --> 00:32:05 there's a second stage that lets them do that
00:32:05 --> 00:32:08 and they still burn up basically coming back
00:32:08 --> 00:32:11 into the atmosphere. The second stages.
00:32:11 --> 00:32:14 Um, but yeah, good question. Not a stupid
00:32:14 --> 00:32:15 question at all.
00:32:15 --> 00:32:17 Andrew Dunkley: No, no. And, and you know,
00:32:19 --> 00:32:21 it's rocket science. I mean we
00:32:21 --> 00:32:24 often say when something's not difficult,
00:32:24 --> 00:32:25 it's not rocket science. This is rocket
00:32:25 --> 00:32:28 science. Um, orbital speeds
00:32:28 --> 00:32:31 are, ah, significant. They're to stay
00:32:31 --> 00:32:34 out there, they've got to, um, do
00:32:34 --> 00:32:35 17 miles an hour.
00:32:35 --> 00:32:37 Professor Fred Watson: Hour, uh, which is eight kilometers per
00:32:37 --> 00:32:38 second. Yeah.
00:32:38 --> 00:32:41 Andrew Dunkley: Mark 25. Um, to slow
00:32:41 --> 00:32:43 down so that you can return to Earth safely,
00:32:43 --> 00:32:46 you've got to go from that speed to
00:32:46 --> 00:32:49 subsonic speed. Uh, and
00:32:49 --> 00:32:52 using fuel to do that would be exhaustive.
00:32:52 --> 00:32:54 Professor Fred Watson: Yeah, that's right. That's exactly right. You
00:32:54 --> 00:32:57 know, basically you're looking at the
00:32:57 --> 00:33:00 same amount of hardware
00:33:00 --> 00:33:03 in terms of a rocket and its fuel to
00:33:03 --> 00:33:05 get you up there. You'd need the same amount
00:33:05 --> 00:33:07 to bring you back just to do a gentle
00:33:07 --> 00:33:10 touchdown on the Earth. M.
00:33:10 --> 00:33:13 Um, notwithstanding the first stage
00:33:13 --> 00:33:15 recovery that we're starting to see with.
00:33:15 --> 00:33:17 Well, not starting. They've been doing it for
00:33:17 --> 00:33:20 10 years with the Falcon 9 rockets.
00:33:20 --> 00:33:23 Andrew Dunkley: M. Yeah, I'm sure the technology will improve
00:33:23 --> 00:33:25 and we'll find better ways, but at the
00:33:25 --> 00:33:27 moment, using the atmosphere as a free
00:33:27 --> 00:33:30 braking system. Yeah, yeah, works really
00:33:30 --> 00:33:33 well. Except when it doesn't. But that's only
00:33:33 --> 00:33:35 happened a couple of times. Yeah, um,
00:33:35 --> 00:33:38 yeah, thank you Andy. Great question though.
00:33:38 --> 00:33:40 Uh, really appreciate it. And don't forget,
00:33:40 --> 00:33:42 if you've got questions for us, you can send
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00:33:44 --> 00:33:47 spacenutspodcast.com spacenuts
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00:33:52 --> 00:33:55 finally figured that out. Ask me anything
00:33:55 --> 00:33:58 ama. Uh, and you just fill in the blanks. Uh,
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00:34:08 --> 00:34:11 spacenuts IO uh, while you're there
00:34:11 --> 00:34:13 you might want to hit the supporter button
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00:34:18 --> 00:34:21 essential. We do not demand that of you,
00:34:21 --> 00:34:23 never will. But uh, we do have a lot of
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00:34:35 --> 00:34:38 Um, and we do appreciate our supporters very,
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00:34:45 --> 00:34:47 appreciate it greatly.
00:34:47 --> 00:34:49 Uh, I think we're all done. Fred. Thank you
00:34:49 --> 00:34:49 so much.
00:34:51 --> 00:34:53 Professor Fred Watson: Uh, a pleasure, Andrew. Great to hear from
00:34:53 --> 00:34:55 the listeners, as always. Great questions,
00:34:56 --> 00:34:58 uh, get my mind, mind thinking again.
00:34:59 --> 00:35:02 Uh, so thank, uh, you everybody and thanks,
00:35:02 --> 00:35:04 uh, to you, Andrew too, for keeping on the
00:35:04 --> 00:35:05 rails.
00:35:06 --> 00:35:09 Andrew Dunkley: Uh, I do my best and sometimes I don't,
00:35:09 --> 00:35:11 but yes, thank you, Fred. We'll see you next
00:35:11 --> 00:35:14 time. Professor Fred Watson, astronomer, uh,
00:35:14 --> 00:35:16 at large. And thanks to Huw in the studio who
00:35:16 --> 00:35:17 definitely does keep it all together.
00:35:17 --> 00:35:19 Although he couldn't be with us today
00:35:19 --> 00:35:21 because, um, he re entered his garage at
00:35:21 --> 00:35:24 excess velocity, couldn't get down to some
00:35:25 --> 00:35:27 sonic speed. And, uh, well, he'll be in
00:35:27 --> 00:35:29 traction for, for a couple of weeks. Uh, from
00:35:29 --> 00:35:31 me, Andrew Dunkley. Thanks for your company.
00:35:31 --> 00:35:33 You'll see on the next episode of Space Nuts.
00:35:33 --> 00:35:34 Bye Bye.
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