This is a Q and A edition of Space Nuts. We will be answering audience questions exclusively on this episode. We're looking at a concept that Ross has put up about black holes equaling dark matter, we'll explain that. Sandy is asking about navigation in space. John is talking relativity, time, black holes and the big crunch. And the speed of re entry is a question from Andy. We'll deal with all of that on this episode of space nuts.
For more Space Nuts visit www.spacenutspodcast.com (https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support (https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support?utm_source=rss&utm_medium=rss&utm_campaign=rss) .
Episode link: https://play.headliner.app/episode/31188641?utm_source=youtube
00:00:00 --> 00:00:02 Hi there. Thanks for joining us once
00:00:02 --> 00:00:05 again. This is a Q&A edition of Space
00:00:05 --> 00:00:06 Nuts. My name is Andrew Dunley. Great to
00:00:06 --> 00:00:08 have your company. Uh we will be
00:00:08 --> 00:00:10 answering audience questions exclusively
00:00:10 --> 00:00:13 on this episode. We'll never do it
00:00:13 --> 00:00:15 again. Yes, we will. Uh we're going to
00:00:15 --> 00:00:19 be um looking at uh a concept that Ross
00:00:19 --> 00:00:22 has put up about black holes equaling
00:00:22 --> 00:00:24 dark matter. We'll uh we'll explain that
00:00:24 --> 00:00:26 or he will and we'll try and tear it
00:00:26 --> 00:00:29 apart. Uh Sandy is asking about
00:00:29 --> 00:00:33 navigation in space. Uh John is talking
00:00:33 --> 00:00:36 relativity, time, black holes, and the
00:00:36 --> 00:00:39 big crunch. I knew we'd get a question
00:00:39 --> 00:00:40 about the big crunch because we talked
00:00:40 --> 00:00:44 about it so recently. And the speed of
00:00:44 --> 00:00:46 re-entry is a question from Andy. We'll
00:00:46 --> 00:00:49 deal with all of that on this episode of
00:00:49 --> 00:00:50 Space Nuts.
00:00:50 --> 00:00:55 >> 15 seconds. Guidance is internal. 10 9
00:00:55 --> 00:00:57 ignition sequence start.
00:00:57 --> 00:00:57 >> Space nuts.
00:00:58 --> 00:01:00 >> 5 [music] 4 3 2
00:01:00 --> 00:01:02 >> 1 2 3 4 5 5 4 3 2 1
00:01:02 --> 00:01:04 >> Space Nuts
00:01:04 --> 00:01:06 >> astronauts report. It feels good.
00:01:06 --> 00:01:08 >> And with us once again is Professor Fred
00:01:08 --> 00:01:11 Watson, astronomer at large. Hello Fred.
00:01:11 --> 00:01:14 >> Hi Andrew. Good to talk again. Uh seems
00:01:14 --> 00:01:16 like only a few minutes ago that we were
00:01:16 --> 00:01:17 talking.
00:01:17 --> 00:01:19 >> It does, doesn't it? Yes. Extra.
00:01:19 --> 00:01:20 >> That's called relativity I think. Time
00:01:20 --> 00:01:21 dilation.
00:01:21 --> 00:01:23 >> Yeah. Um, I I'll tell you something
00:01:23 --> 00:01:25 funny. We we had our granddaughters
00:01:25 --> 00:01:26 around last night. They were supposed to
00:01:26 --> 00:01:27 stay the night, but they both
00:01:27 --> 00:01:29 chickenened out, so dad had to come and
00:01:29 --> 00:01:32 pick them up at 9:00, but um uh they
00:01:32 --> 00:01:34 were they were um having a bit of fun
00:01:34 --> 00:01:36 and um they like doing craft. And one of
00:01:36 --> 00:01:39 them built a telescope with a piece of
00:01:39 --> 00:01:41 paper out of and and was looking through
00:01:41 --> 00:01:42 it and Judy said, "What have you made?"
00:01:42 --> 00:01:45 And it was the four-year-old. She said,
00:01:45 --> 00:01:50 "I I I made a a looking through thing."
00:01:50 --> 00:01:52 That's what a telescope is. It's a
00:01:52 --> 00:01:54 looking through thing. [laughter] Um,
00:01:54 --> 00:01:56 which is nearly what they were
00:01:56 --> 00:01:58 originally called before the telescope
00:01:58 --> 00:02:00 was in 10. Yeah,
00:02:00 --> 00:02:01 >> she's ahead of her time.
00:02:01 --> 00:02:04 >> Device for seeing a device for seeing a
00:02:04 --> 00:02:05 far. [sighs]
00:02:05 --> 00:02:08 >> Yeah. Well, a looking through things.
00:02:08 --> 00:02:08 Yeah.
00:02:08 --> 00:02:09 >> Very cute.
00:02:09 --> 00:02:11 >> I love that. Yeah.
00:02:11 --> 00:02:12 >> I um [snorts]
00:02:12 --> 00:02:14 >> Yeah. You know, you know, you don't know
00:02:14 --> 00:02:16 what you might have, you know, released
00:02:16 --> 00:02:19 in that child's brain. She might become
00:02:19 --> 00:02:22 the next great astronomer using a
00:02:22 --> 00:02:24 looking through thing to make
00:02:24 --> 00:02:26 discoveries about the universe.
00:02:26 --> 00:02:27 >> Yeah. Yeah. Well, that's why we called
00:02:27 --> 00:02:30 it Vera. No, her name's uh her name's
00:02:30 --> 00:02:32 Felicity. [laughter]
00:02:32 --> 00:02:33 >> That's a good name as well. I like
00:02:33 --> 00:02:34 Felicity.
00:02:34 --> 00:02:36 >> It [snorts] is nice.
00:02:36 --> 00:02:39 >> Uh shall we get to our first question?
00:02:39 --> 00:02:40 >> Oh, all right.
00:02:40 --> 00:02:43 >> All right. Uh if black holes are the
00:02:43 --> 00:02:46 center of most galaxies uh and have been
00:02:46 --> 00:02:48 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 --> 00:02:57 black holes have eaten it. Now this uh
00:02:57 --> 00:03:00 comes from Ross Simon. I had to smile
00:03:00 --> 00:03:02 when I read his name because Ross Simon
00:03:02 --> 00:03:03 used to be a famous newsreader on the
00:03:04 --> 00:03:06 Australian Broadcasting Corporation's TV
00:03:06 --> 00:03:09 news service. I remember Ross, he was he
00:03:09 --> 00:03:11 was brilliant.
00:03:11 --> 00:03:13 might be the same one. You never know. I
00:03:13 --> 00:03:14 >> was going to say it's not the same Ross,
00:03:14 --> 00:03:15 is it? [laughter]
00:03:15 --> 00:03:18 >> I hope so. It would be lovely. But, uh,
00:03:18 --> 00:03:19 if it's not.
00:03:19 --> 00:03:21 >> 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 --> 00:03:28 from you. Uh, and, um, I mean, it's it's
00:03:28 --> 00:03:32 it is tempting, uh, to lump black holes
00:03:32 --> 00:03:34 and dark matter together. And indeed,
00:03:34 --> 00:03:37 um, that was looked at as being one of
00:03:37 --> 00:03:40 the first explanations of dark matter,
00:03:40 --> 00:03:43 uh, that we've got space full of black
00:03:43 --> 00:03:45 holes that we don't see because they're
00:03:45 --> 00:03:47 black holes, um, and that they might
00:03:48 --> 00:03:50 account for the dark matter. was the
00:03:50 --> 00:03:52 so-called macho theory, massive compact
00:03:52 --> 00:03:55 halo objects
00:03:55 --> 00:03:59 uh which was popular in the 80s
00:03:59 --> 00:04:02 um because it was only in the late '7s
00:04:02 --> 00:04:04 that people started taking the idea of
00:04:04 --> 00:04:07 dark matter seriously when we realized
00:04:07 --> 00:04:12 that um something like 80% of the matter
00:04:12 --> 00:04:16 in the universe is invisible to us. Uh
00:04:16 --> 00:04:18 now
00:04:18 --> 00:04:20 that's perhaps slightly different from
00:04:20 --> 00:04:22 what Ross is asking about because he's
00:04:22 --> 00:04:23 talking about material being sucked into
00:04:24 --> 00:04:28 black holes. Uh and that is certainly
00:04:28 --> 00:04:31 something that happens. But that's not
00:04:31 --> 00:04:33 matter that's missing. That's just gone.
00:04:34 --> 00:04:36 Uh the the bottom line is that the
00:04:36 --> 00:04:39 universe as we see it today has this
00:04:39 --> 00:04:41 mystery in that we know that there is
00:04:41 --> 00:04:43 stuff there that has a gravitational
00:04:43 --> 00:04:45 effect. It holds galaxies together. It
00:04:45 --> 00:04:48 holds galaxy clusters together, causes
00:04:48 --> 00:04:50 uh gravitational lensing all over the
00:04:50 --> 00:04:54 place. Um but we have no way of
00:04:54 --> 00:04:55 detecting what it is other than through
00:04:55 --> 00:04:58 its gravity. So it's it's some people
00:04:58 --> 00:05:00 used to call it missing matter. It's not
00:05:00 --> 00:05:03 missing. It's definitely there. uh this
00:05:03 --> 00:05:05 dark matter is around and it it's
00:05:05 --> 00:05:07 probably in the rooms that you and I are
00:05:07 --> 00:05:10 sitting in um at the moment uh because
00:05:10 --> 00:05:13 it it tends to be where normal matter is
00:05:13 --> 00:05:13 and we think
00:05:13 --> 00:05:15 >> Judy and I were actually talking about a
00:05:15 --> 00:05:17 dark matter the other day but you know I
00:05:17 --> 00:05:19 won't elaborate.
00:05:19 --> 00:05:20 [gasps]
00:05:20 --> 00:05:22 >> Well what you do in your spare time
00:05:22 --> 00:05:23 Andrew is [laughter]
00:05:23 --> 00:05:25 entirely up to you especially with your
00:05:26 --> 00:05:30 wife. Um um so yeah so so but um but the
00:05:30 --> 00:05:33 the the black hole thing did come in
00:05:34 --> 00:05:36 because of this theory back in the 80s
00:05:36 --> 00:05:38 that match massive compact halo objects
00:05:38 --> 00:05:42 objects that are kind of dead stars or
00:05:42 --> 00:05:44 orphan planets or more especially black
00:05:44 --> 00:05:47 holes might be uh the source of dark
00:05:47 --> 00:05:49 matter the source of this gravitation
00:05:49 --> 00:05:52 that we we see present in large on large
00:05:52 --> 00:05:54 scales like galaxy clusters and
00:05:54 --> 00:05:57 galaxies. What ruled that out uh was
00:05:57 --> 00:05:58 work carried out at a number of
00:05:58 --> 00:06:01 observatories including here uh in
00:06:01 --> 00:06:03 Australia uh in fact in a survey which
00:06:03 --> 00:06:06 was called Macho uh looking for these
00:06:06 --> 00:06:10 things uh and it was that if you if you
00:06:10 --> 00:06:12 had a universe full of black holes that
00:06:12 --> 00:06:14 you can't see you would still be able to
00:06:14 --> 00:06:16 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
00:06:20 --> 00:06:22 would pass in front of a distant star
00:06:22 --> 00:06:24 and because black holes distort the
00:06:24 --> 00:06:27 space around that has behaves like a
00:06:27 --> 00:06:29 lens and you magnify the light of the
00:06:30 --> 00:06:32 distant star. So you you get a microl
00:06:32 --> 00:06:34 lensing event has a very characteristic
00:06:34 --> 00:06:37 shape. It's a star getting brighter uh
00:06:37 --> 00:06:39 to a sharp cusp and then fading away
00:06:40 --> 00:06:43 again quite symmetrically. Uh and they
00:06:43 --> 00:06:45 we do see them. They're caused by normal
00:06:45 --> 00:06:48 stars and and their planets. But in the
00:06:48 --> 00:06:50 numbers that you would have to have for
00:06:50 --> 00:06:54 black holes to be dark matter, they are
00:06:54 --> 00:06:56 not there. That they weren't enough. The
00:06:56 --> 00:06:58 numbers were far too low. And that's
00:06:58 --> 00:07:00 when the emphasis shifted to WIMPs, the
00:07:00 --> 00:07:02 weakly interacting massive particles,
00:07:02 --> 00:07:05 which is just one class of uh subatomic
00:07:05 --> 00:07:07 particles that we think dark matter
00:07:07 --> 00:07:08 might be. So that's where the theory
00:07:08 --> 00:07:12 stands at the moment. So black holes uh
00:07:12 --> 00:07:14 you know in the and and I think Ross is
00:07:14 --> 00:07:16 talking about super massive black holes
00:07:16 --> 00:07:17 at the centers of galaxies. Yes, they've
00:07:17 --> 00:07:19 been swallowing stuff up for 13.8
00:07:19 --> 00:07:22 billion years as far as we can tell. Um
00:07:22 --> 00:07:25 but they don't explain why today in
00:07:25 --> 00:07:28 today's universe um something like
00:07:28 --> 00:07:30 four-fifths of the m matter in the
00:07:30 --> 00:07:32 universe is invisible to us.
00:07:32 --> 00:07:35 >> Yeah. Um well there's so many things we
00:07:35 --> 00:07:37 don't understand and and and as yet uh
00:07:38 --> 00:07:39 which was brought up in a question
00:07:40 --> 00:07:43 recently, we have not been able to
00:07:43 --> 00:07:46 capture or identify a black uh a dark
00:07:46 --> 00:07:50 matter particle. So um yeah, until we
00:07:50 --> 00:07:53 can find some absolute proof and and
00:07:53 --> 00:07:56 study it, we we're probably going to
00:07:56 --> 00:07:58 >> just keep working with theory, I would
00:07:58 --> 00:08:01 imagine. Yeah, there's there are um
00:08:01 --> 00:08:03 techniques that can be brought to bear.
00:08:03 --> 00:08:07 Um one of the theories about dark matter
00:08:07 --> 00:08:11 is that if that while dark matter
00:08:11 --> 00:08:13 particles don't interact with normal
00:08:13 --> 00:08:15 matter particles, they may interact with
00:08:15 --> 00:08:16 each other. In other words, if you bring
00:08:16 --> 00:08:18 two dark matter particles together, it's
00:08:18 --> 00:08:20 thought they might annihilate and
00:08:20 --> 00:08:23 produce a signal in gamma radiation. So
00:08:23 --> 00:08:25 you get this flash of gamma rays which
00:08:25 --> 00:08:27 might have a characteristic spectrum.
00:08:27 --> 00:08:30 And people are looking for that
00:08:30 --> 00:08:34 phenomenon in the centers of galaxies
00:08:34 --> 00:08:36 because that's where you would expect
00:08:36 --> 00:08:38 the dark matter to be at its densest. So
00:08:38 --> 00:08:39 it's where you would expect the dark
00:08:39 --> 00:08:41 matter particles to interact with with
00:08:41 --> 00:08:44 each other. Um so far the results have
00:08:44 --> 00:08:46 been a bit mixed on that. But it's one
00:08:46 --> 00:08:49 possible way that we might eventually uh
00:08:49 --> 00:08:52 discover what dark matter is. May maybe
00:08:52 --> 00:08:55 maybe dark matter is like a negative
00:08:55 --> 00:08:57 photograph. Remember in the days of uh
00:08:57 --> 00:08:59 manual photography, you you'd take the
00:09:00 --> 00:09:01 film and it would be negative and then
00:09:01 --> 00:09:04 you turn it into the photograph.
00:09:04 --> 00:09:06 >> Maybe dark matter is the negative of the
00:09:06 --> 00:09:07 universe.
00:09:07 --> 00:09:11 >> Well, yeah. I mean, um you know, you
00:09:11 --> 00:09:14 there might well be a way that there is
00:09:14 --> 00:09:17 a sort of dark what can I call it? A
00:09:17 --> 00:09:22 dark particle physics. um um a whole uh
00:09:22 --> 00:09:27 sweep of subatomic particles which fall
00:09:27 --> 00:09:29 under what we lump together as dark
00:09:29 --> 00:09:30 matter. But it's not just a single
00:09:30 --> 00:09:32 particle. It's many different ones just
00:09:32 --> 00:09:34 like the particles of normal matter. The
00:09:34 --> 00:09:35
00:09:35 --> 00:09:38 >> uh normal matter part sorry 16 subatomic
00:09:38 --> 00:09:39 particles. They include forces as well
00:09:39 --> 00:09:41 as matter when you count the 16. But you
00:09:41 --> 00:09:43 know what I mean? You've got this this
00:09:43 --> 00:09:45 suite of different particles that make
00:09:45 --> 00:09:47 up normal matter. Maybe there's a suite
00:09:47 --> 00:09:49 of different particles that in some ways
00:09:49 --> 00:09:52 are a negative uh that make up um that
00:09:52 --> 00:09:56 make up dark matter. So I think that's
00:09:56 --> 00:09:57 we've been assuming it's just the one
00:09:57 --> 00:09:59 thing. It could be all sorts of things.
00:10:00 --> 00:10:01 >> Could be there could be, you know, they
00:10:01 --> 00:10:03 could be atoms and molecules made out of
00:10:03 --> 00:10:07 dark matter because they they interact
00:10:08 --> 00:10:09 with each other. I don't know it. Look,
00:10:09 --> 00:10:12 I'm not a particle physicist, but um the
00:10:12 --> 00:10:15 possibilities seem not exactly endless
00:10:15 --> 00:10:16 because particle physics has certain
00:10:16 --> 00:10:19 rules that you've got to follow. Uh but
00:10:19 --> 00:10:21 yeah, I I'm still pretty optimistic that
00:10:21 --> 00:10:22 we're going to get to the bottom of dark
00:10:22 --> 00:10:25 matter hopefully while I'm still alive
00:10:25 --> 00:10:28 cuz I want to know. Yeah, we all do. We
00:10:28 --> 00:10:30 all do. Uh thanks for the question,
00:10:30 --> 00:10:32 Ross. Uh really good discussion point.
00:10:32 --> 00:10:34 We get a lot of questions about dark
00:10:34 --> 00:10:36 matter and and black holes. Uh while
00:10:36 --> 00:10:37 we're on the subject of black holes,
00:10:37 --> 00:10:40 there was a an article released on the
00:10:40 --> 00:10:43 BBC uh early this year. Uh I know it's
00:10:43 --> 00:10:45 still early this year, but right, you
00:10:45 --> 00:10:47 know, I'm talking the 3rd of January,
00:10:47 --> 00:10:48 where scientists captured the first ever
00:10:48 --> 00:10:51 visual proof of two super massive black
00:10:51 --> 00:10:53 holes in a death spiral. So, we we're
00:10:54 --> 00:10:56 really starting to be able to find out
00:10:56 --> 00:10:59 more and more uh through our increased
00:10:59 --> 00:11:02 technology and the capacity to observe
00:11:02 --> 00:11:04 and and create images of these things.
00:11:04 --> 00:11:06 So, uh that was pretty exciting story. I
00:11:06 --> 00:11:07 read that one the other day. I thought
00:11:07 --> 00:11:10 I'd um give it a mention. But um yeah,
00:11:10 --> 00:11:14 they they 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
00:11:19 --> 00:11:20 it. [laughter] That's all right.
00:11:20 --> 00:11:23 >> But uh yeah, it sells the story, doesn't
00:11:24 --> 00:11:26 it? But uh yeah, they've got the image
00:11:26 --> 00:11:30 of these two black holes um basically
00:11:30 --> 00:11:31 getting ready to devour each other. I
00:11:32 --> 00:11:35 think the big one will win.
00:11:35 --> 00:11:36 >> Yes,
00:11:36 --> 00:11:37 >> probably. Well,
00:11:37 --> 00:11:38 >> thanks Ross.
00:11:38 --> 00:11:39 >> Yeah, probably.
00:11:39 --> 00:11:41 >> Yeah, thanks Ross. Good to hear from
00:11:41 --> 00:11:44 you.
00:11:44 --> 00:11:47 >> Okay, we checked all four systems and
00:11:47 --> 00:11:48 >> Space Nuts.
00:11:48 --> 00:11:53 >> Our next question comes from Sandy.
00:11:53 --> 00:11:54 >> Good day, Fred and Andrew. It's Sandy
00:11:54 --> 00:11:57 here from Melbourne again. Thanks for a
00:11:57 --> 00:12:00 cracking show as usual. Um, my question
00:12:00 --> 00:12:02 today is about navigation in the solar
00:12:02 --> 00:12:04 system for the various spacecraft that
00:12:04 --> 00:12:07 we've sent into deep space. Um, being a
00:12:07 --> 00:12:10 sci-fi nerd, my mind naturally goes to
00:12:10 --> 00:12:12 fancy graphics of star charts and orbit
00:12:12 --> 00:12:15 parts on a giant screen. However, wanted
00:12:16 --> 00:12:17 to ask how mission planners of various
00:12:18 --> 00:12:21 space agencies plot orbits. Do they take
00:12:21 --> 00:12:23 into account objects like asteroids for
00:12:23 --> 00:12:26 any close calls or is the space so vast
00:12:26 --> 00:12:28 it's not really necessary? Thanks,
00:12:28 --> 00:12:31 Heaps. Sandy, cheers.
00:12:31 --> 00:12:33 >> Thank you, Sandy. Uh, good to hear from
00:12:33 --> 00:12:34 you. I don't think we've heard from
00:12:34 --> 00:12:36 Sandy in a little while, but um yeah,
00:12:36 --> 00:12:41 he's um he he does a lot of great um
00:12:41 --> 00:12:44 astrophotography and he's got a a pretty
00:12:44 --> 00:12:46 amazing setup that he's he's shown me in
00:12:46 --> 00:12:48 the past about how he does it. Computers
00:12:48 --> 00:12:51 all plugged into telescopes and yeah,
00:12:51 --> 00:12:53 all this great software. It's a bit out
00:12:53 --> 00:12:55 of my league. Um I might get there one
00:12:55 --> 00:12:58 day. Uh navigation in space, plotting
00:12:58 --> 00:13:02 orbits, all that kind of jazz. Um I I
00:13:02 --> 00:13:05 must confess I struggle to get my head
00:13:05 --> 00:13:07 around it. Like it's not like driving a
00:13:07 --> 00:13:09 car. You've got to do um you know when
00:13:10 --> 00:13:12 it comes to space you've got um much
00:13:12 --> 00:13:15 less resistance, much more much more
00:13:15 --> 00:13:18 reaction to minute
00:13:18 --> 00:13:22 um thrust and micro thrust and all all
00:13:22 --> 00:13:23 sorts of other things. But you've got to
00:13:23 --> 00:13:25 be looking in all directions, not just,
00:13:25 --> 00:13:28 you know, on the plane of the planet
00:13:28 --> 00:13:30 when you're driving a car type of thing.
00:13:30 --> 00:13:32 I don't know what I'm trying to say, but
00:13:32 --> 00:13:35 um yeah, how how does it all work, Fred?
00:13:35 --> 00:13:39 >> Uh it's it's sort of the equivalent of
00:13:39 --> 00:13:40 plotting things on a screen, but not
00:13:40 --> 00:13:43 quite [clears throat] the same. Um but
00:13:43 --> 00:13:48 yeah, you know, the the uh idea that um
00:13:48 --> 00:13:51 [laughter] excuse me minute that I'm
00:13:51 --> 00:13:53 sorry, I've got this cough. Sandy's idea
00:13:53 --> 00:13:55 [clears throat] that we
00:13:55 --> 00:13:57 need to take into account I'm all right.
00:13:57 --> 00:14:00 I'm all right.
00:14:00 --> 00:14:02 Yeah, we need to take into account the
00:14:02 --> 00:14:04 positions of asteroids and things of
00:14:04 --> 00:14:06 that sort. That's exactly right. Um, so
00:14:06 --> 00:14:11 when you um chart uh a pathway
00:14:11 --> 00:14:14 through space, which is all done
00:14:14 --> 00:14:17 numerically, you know, it doesn't we can
00:14:17 --> 00:14:19 make displays of them and and I think
00:14:19 --> 00:14:22 people do as well, but the reality is
00:14:22 --> 00:14:24 that the real hardcore is locked up in
00:14:24 --> 00:14:27 the numbers and the equations. Um what
00:14:27 --> 00:14:30 you have to do is to uh at any instant
00:14:30 --> 00:14:32 along the orbit of the uh of the
00:14:32 --> 00:14:34 spacecraft because it is always an
00:14:34 --> 00:14:37 orbit. Uh usually for something like you
00:14:37 --> 00:14:38 know going between the planets it will
00:14:38 --> 00:14:41 be an orbit around the sun. Uh that's
00:14:41 --> 00:14:44 the way orbital mechanics work. Uh soon
00:14:44 --> 00:14:47 as you switch on your thrusters then you
00:14:47 --> 00:14:50 change that orbit. Uh but when all the
00:14:50 --> 00:14:52 thrusters are off and your main engines
00:14:52 --> 00:14:54 are off, you are following a trajectory
00:14:54 --> 00:14:58 which is essentially an orbit. Um not
00:14:58 --> 00:15:00 always a closed one. It could be an open
00:15:00 --> 00:15:01 orbit. Uh which is what's happening to
00:15:01 --> 00:15:03 the five spacecraft that are leaving the
00:15:03 --> 00:15:05 solar system.
00:15:05 --> 00:15:09 So uh but that orbit it's uh the future
00:15:09 --> 00:15:12 position of your spacecraft is dictated
00:15:12 --> 00:15:14 by the gravitational influence not just
00:15:14 --> 00:15:17 of the sun and the earth and probably
00:15:17 --> 00:15:19 the moon but all the planets. All of
00:15:19 --> 00:15:23 them exert a gravitational pull. Uh and
00:15:23 --> 00:15:25 um um that goes down to the asteroids as
00:15:25 --> 00:15:26 well. When you get if you're passing
00:15:26 --> 00:15:28 through the asteroid belt, you need to
00:15:28 --> 00:15:30 know where they all are. They would all
00:15:30 --> 00:15:32 all the ones which are known and there's
00:15:32 --> 00:15:35 more than a million known asteroids now.
00:15:35 --> 00:15:37 Uh you would have them kind of built
00:15:37 --> 00:15:40 into your software that's looking uh at
00:15:40 --> 00:15:42 the uh at the direction that your
00:15:42 --> 00:15:43 spacecraft is going in. If there was any
00:15:43 --> 00:15:46 risk of a collision, it would flag that
00:15:46 --> 00:15:47 and [clears throat] um it would also
00:15:47 --> 00:15:49 take into account the gravitational
00:15:49 --> 00:15:51 influence of any close encounters of
00:15:51 --> 00:15:54 asteroids. So it's it's a very precise
00:15:54 --> 00:15:58 science um as you know because we you
00:15:58 --> 00:16:01 know we know when for example the New
00:16:01 --> 00:16:05 Horizons uh flyby of Pluto a decade ago
00:16:05 --> 00:16:07 uh in 2015 um that the precision with
00:16:08 --> 00:16:10 which that was executed was unbelievable
00:16:10 --> 00:16:12 and it's because of orbital mechanics
00:16:12 --> 00:16:13 and how well we understand these
00:16:13 --> 00:16:16 gravitational influences uh that that
00:16:16 --> 00:16:19 let you do that. Um so uh yes space
00:16:19 --> 00:16:21 navigation in some ways it's easier uh
00:16:21 --> 00:16:25 than navigation on uh you know than
00:16:25 --> 00:16:26 driving a car because with driving a car
00:16:26 --> 00:16:28 you've always got to the predict
00:16:28 --> 00:16:31 unpredictability of the other road
00:16:31 --> 00:16:33 users. The great thing about orbital
00:16:33 --> 00:16:35 mechanics is you know what the other
00:16:35 --> 00:16:36 planets the other asteroids and all the
00:16:36 --> 00:16:39 rest of it are going to do. And ju just
00:16:39 --> 00:16:41 [clears throat] one other adjunct to
00:16:41 --> 00:16:44 this if I may. Um uh some years ago
00:16:44 --> 00:16:47 there was several papers which talked
00:16:47 --> 00:16:49 about the interplanetary superighway.
00:16:50 --> 00:16:52 Uh and these are effectively low energy
00:16:52 --> 00:16:54 trajectories between the planets and
00:16:54 --> 00:16:56 it's based on exactly what I've just
00:16:56 --> 00:16:59 been saying. You can map where um the
00:16:59 --> 00:17:02 gravitational pull of all the objects
00:17:02 --> 00:17:04 will take you. And it turned out that
00:17:04 --> 00:17:06 you can you if you can put um a
00:17:06 --> 00:17:08 spacecraft at one of your lrangee
00:17:08 --> 00:17:11 points, these gravitationally stable
00:17:11 --> 00:17:14 points, then leading from that are these
00:17:14 --> 00:17:16 various low energy pathways that take
00:17:16 --> 00:17:17 you to the the ground points of other
00:17:17 --> 00:17:19 planets. Uh and that's the
00:17:19 --> 00:17:21 interplanetary superighway. It might
00:17:21 --> 00:17:25 take you decades to get from uh from um
00:17:25 --> 00:17:28 you know from the Earth Lrange points to
00:17:28 --> 00:17:30 something like Mars's or Jupiter's
00:17:30 --> 00:17:32 Lrange points. It's a very slow process,
00:17:32 --> 00:17:36 but it it it does exist. This this
00:17:36 --> 00:17:37 almost like an imaginary highway which
00:17:37 --> 00:17:39 is changing all the time as the planets
00:17:39 --> 00:17:42 go around in their orbits. Uh just an
00:17:42 --> 00:17:43 interesting aspect of the of the
00:17:43 --> 00:17:45 navigation in space.
00:17:45 --> 00:17:49 >> Yeah, I imagine that a lot of this uh
00:17:49 --> 00:17:52 would be pre-programmed into the
00:17:52 --> 00:17:55 computers of these these vessels. Um
00:17:55 --> 00:17:58 they they do everything ahead of time
00:17:58 --> 00:18:00 cuz these these things are on autopilot.
00:18:00 --> 00:18:02 the the long haul spacecraft that are
00:18:02 --> 00:18:04 going out to do these missions.
00:18:04 --> 00:18:07 >> Uh so it would because and I've been in
00:18:07 --> 00:18:10 the cockpit of a a commercial uh
00:18:10 --> 00:18:13 airliner um long before you can't do
00:18:13 --> 00:18:15 that anymore, long before we had any
00:18:15 --> 00:18:17 issues like that. But um
00:18:17 --> 00:18:19 >> and and watching the process like the
00:18:19 --> 00:18:23 plane flies itself and the pilots sit
00:18:23 --> 00:18:25 back and tell dad jokes to the the
00:18:25 --> 00:18:27 tower. Um no, that's what happened.
00:18:27 --> 00:18:28 [laughter]
00:18:28 --> 00:18:30 But I I would imagine it's the same in
00:18:30 --> 00:18:32 space. All these things are
00:18:32 --> 00:18:35 pre-programmed, pre-calculated. Uh and
00:18:35 --> 00:18:37 then contingencies built in just in case
00:18:38 --> 00:18:39 something gets in the way that you
00:18:39 --> 00:18:42 didn't anticipate. Um they they modify
00:18:42 --> 00:18:45 the spacecraft to sense a problem and go
00:18:45 --> 00:18:49 around it. I I would imagine.
00:18:49 --> 00:18:53 >> Yeah. And in fact the you know the
00:18:53 --> 00:18:55 likelihood of something it's so
00:18:55 --> 00:18:59 predictable and our knowledge of of the
00:18:59 --> 00:19:02 of the sort of congestion in space if I
00:19:02 --> 00:19:06 can put it that way is so deep that um
00:19:06 --> 00:19:08 it's unlikely that something's going to
00:19:08 --> 00:19:10 come along to surprise you. You know you
00:19:10 --> 00:19:11 suddenly see something ahead that you've
00:19:11 --> 00:19:14 got to avoid. Uh because that avoidance
00:19:14 --> 00:19:16 might actually be very difficult. Uh you
00:19:16 --> 00:19:19 can you can do things. So perhaps the
00:19:19 --> 00:19:21 the the best example I can give you
00:19:21 --> 00:19:24 again it goes back to New Horizons and
00:19:24 --> 00:19:26 that is that once the Jupiter encounter
00:19:26 --> 00:19:29 sorry the Pluto encounter had happened
00:19:29 --> 00:19:32 uh back in July 2015
00:19:32 --> 00:19:35 um they looked for other potential
00:19:35 --> 00:19:39 targets and eventually found the object
00:19:39 --> 00:19:41 Arakov that was discovered as part of
00:19:41 --> 00:19:44 surveys looking for future targets and
00:19:44 --> 00:19:46 they worked out at what point they had
00:19:46 --> 00:19:49 to apply a thrust to the spacecraft to
00:19:49 --> 00:19:51 change its trajectory so that it would
00:19:52 --> 00:19:54 intersect with Araoth. And it and it all
00:19:54 --> 00:19:58 happened, you know, perfectly smoothly.
00:19:58 --> 00:20:00 Um I think it was a couple of years
00:20:00 --> 00:20:03 later when the Araoth uh flyby took
00:20:03 --> 00:20:04 place. I can't remember when it was,
00:20:04 --> 00:20:07 maybe even a bit later than that, maybe
00:20:07 --> 00:20:09 five years later. [clears throat] But um
00:20:09 --> 00:20:11 but that yeah, that that all happened.
00:20:11 --> 00:20:14 that was the the nearest thing to oh
00:20:14 --> 00:20:15 there's something ahead we need to
00:20:15 --> 00:20:17 change course to either interact with it
00:20:18 --> 00:20:20 or avoid it. Um and it was a very
00:20:20 --> 00:20:22 leisurely process and
00:20:22 --> 00:20:24 >> and you're right you're right about uh
00:20:24 --> 00:20:26 navigation on the planet on roads being
00:20:26 --> 00:20:28 much more dangerous. We were walking
00:20:28 --> 00:20:29 along the street the other day and
00:20:29 --> 00:20:31 somebody turned right off the main road
00:20:31 --> 00:20:35 into our uh into our part of town and
00:20:35 --> 00:20:37 >> uh went to the right hand side of the
00:20:37 --> 00:20:39 traffic island instead of the left right
00:20:39 --> 00:20:41 where we were walking.
00:20:41 --> 00:20:42 So
00:20:42 --> 00:20:44 >> yeah, I don't think she noticed to be
00:20:44 --> 00:20:45 honest. Honest, she just went up the
00:20:46 --> 00:20:48 wrong side of the road.
00:20:48 --> 00:20:50 >> Anyway, it happens. But we we always
00:20:50 --> 00:20:53 keep an eye out for that kind of thing.
00:20:53 --> 00:20:54 There you go, Sandy. Thanks for the
00:20:54 --> 00:20:56 question. The answer is easy peasy.
00:20:56 --> 00:20:58 Really [laughter]
00:20:58 --> 00:20:59 >> with modern computers.
00:20:59 --> 00:21:01 >> It's a lot harder if you're doing it by
00:21:01 --> 00:21:02 hand.
00:21:02 --> 00:21:03 >> Yes.
00:21:03 --> 00:21:05 >> All right. This is a Q&A edition of
00:21:05 --> 00:21:06 Space Nuts with Andrew Dunley and
00:21:06 --> 00:21:11 Professor Fred Watson.
00:21:11 --> 00:21:14 Space nuts. Okay, our next question
00:21:14 --> 00:21:18 comes from John in 27 parts. Hey guys,
00:21:18 --> 00:21:20 love the show. Every time I listen to a
00:21:20 --> 00:21:22 new episode, my mind goes crazy thinking
00:21:22 --> 00:21:24 about new possibilities and questions. I
00:21:24 --> 00:21:28 have two questions about time dilation.
00:21:28 --> 00:21:31 Uh in general relativity, uh if general
00:21:31 --> 00:21:33 re relativity causes time to be observed
00:21:33 --> 00:21:35 at different rates,
00:21:35 --> 00:21:38 would that mean someone orbiting very
00:21:38 --> 00:21:40 close to one of the first black holes in
00:21:40 --> 00:21:42 existence would experience a universe
00:21:42 --> 00:21:45 that has existed for a much shorter
00:21:45 --> 00:21:47 period of time?
00:21:47 --> 00:21:50 Uh, as a follow-up to this, if the new
00:21:50 --> 00:21:52 theory about the big crunch turns out to
00:21:52 --> 00:21:56 be true, would the finite time of the
00:21:56 --> 00:22:00 universe form the big bang to uh uh from
00:22:00 --> 00:22:02 the big bang to the big crunch be
00:22:02 --> 00:22:05 considerably shorter if again you were
00:22:05 --> 00:22:08 orbiting close to a black hole? Uh we
00:22:08 --> 00:22:11 see the universe as being 13.79
00:22:11 --> 00:22:14 billion years old and uh new estimates
00:22:14 --> 00:22:17 put the big crunch at 20 billion years
00:22:17 --> 00:22:20 into the future. My brain hurts thinking
00:22:20 --> 00:22:21 that these time scales could be
00:22:21 --> 00:22:23 considerably different due to time
00:22:23 --> 00:22:25 dilation. All the best uh John from
00:22:26 --> 00:22:29 Suffach in the UK. [gasps]
00:22:29 --> 00:22:31 >> Oh, there's a lot in there.
00:22:31 --> 00:22:35 Um yeah and and so it's it's quite
00:22:35 --> 00:22:39 complicated because time dilation uh
00:22:39 --> 00:22:41 depends on your vantage point.
00:22:41 --> 00:22:43 >> So yeah, if you're in orbit around a
00:22:43 --> 00:22:46 black hole uh you're in an intense
00:22:46 --> 00:22:48 gravitational field.
00:22:48 --> 00:22:50 >> You're also stuffed, but we'll just deal
00:22:50 --> 00:22:52 with that another time.
00:22:52 --> 00:22:52 [sighs and gasps]
00:22:52 --> 00:22:57 >> Um yeah, you're you experience time just
00:22:57 --> 00:22:59 at the normal rate.
00:22:59 --> 00:23:04 >> Yeah. um what uh what um an outside
00:23:04 --> 00:23:06 observer looking at you would see would
00:23:06 --> 00:23:08 be your time going very slowly. The time
00:23:08 --> 00:23:10 would be dilated.
00:23:10 --> 00:23:14 >> So um I I suppose what we're talking
00:23:14 --> 00:23:17 about here is that in terms of the what
00:23:18 --> 00:23:19 you might call the frame of rest of the
00:23:19 --> 00:23:22 universe itself.
00:23:22 --> 00:23:26 uh that's what we what we see when we
00:23:26 --> 00:23:28 look at the universe in general and
00:23:28 --> 00:23:31 that's what gives us the 13.79 or 13.8
00:23:31 --> 00:23:35 billion year age of the universe um your
00:23:35 --> 00:23:37 perception of that so that time
00:23:37 --> 00:23:39 effectively wouldn't change uh but your
00:23:40 --> 00:23:41 perception of it if you were in orbit
00:23:41 --> 00:23:43 around the black hole would it would
00:23:43 --> 00:23:45 probably appear to look as though it was
00:23:45 --> 00:23:48 going very quickly uh but that's cuz
00:23:48 --> 00:23:53 your time's slower. uh and likewise um
00:23:53 --> 00:23:56 uh with the you know the density of the
00:23:56 --> 00:23:59 universe being higher uh at earlier
00:23:59 --> 00:24:01 stages. Yes, we we do know time dilation
00:24:01 --> 00:24:03 takes place. You can you can actually
00:24:03 --> 00:24:07 see that uh because um when uh
00:24:07 --> 00:24:11 scientists look at the light curves of
00:24:11 --> 00:24:13 supernovi exploding stars, they have a
00:24:13 --> 00:24:15 light curve, their light increases and
00:24:15 --> 00:24:18 then decreases uh in a more gradual way
00:24:18 --> 00:24:21 with a very characteristic shape. Uh
00:24:21 --> 00:24:24 those light curves are dilated. They're
00:24:24 --> 00:24:26 stretched when we look at ones in the
00:24:26 --> 00:24:28 early universe. So the phenomenon does
00:24:28 --> 00:24:32 happen but um it doesn't happen at a
00:24:32 --> 00:24:34 level that's going to significantly
00:24:34 --> 00:24:37 shorten our um perception you know the
00:24:37 --> 00:24:39 the universe's perception of its of its
00:24:40 --> 00:24:41 own history if I put it that way. I
00:24:41 --> 00:24:43 think I'm talking a little bit in
00:24:43 --> 00:24:45 riddles here but I hope John follows me
00:24:45 --> 00:24:49 that it it really is all about your um
00:24:49 --> 00:24:50 your 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.
00:24:55 --> 00:24:57 It's about people seeing time going
00:24:57 --> 00:24:58 differently depending on their
00:24:58 --> 00:25:01 viewpoint. Our viewpoint here uh from
00:25:01 --> 00:25:04 earth is probably that of the universe
00:25:04 --> 00:25:07 of a as a whole effectively uh because
00:25:07 --> 00:25:09 we are not in an intense gravitational
00:25:09 --> 00:25:12 field. It the gravitational field of the
00:25:12 --> 00:25:14 sun is the strongest thing we feel that
00:25:14 --> 00:25:16 keeps the the earth in orbit but it's
00:25:16 --> 00:25:18 it's nothing like what you would find
00:25:18 --> 00:25:20 around a black hole. And so we've got
00:25:20 --> 00:25:24 probably a fairly unbiased view of the
00:25:24 --> 00:25:26 universe and its history. Now,
00:25:26 --> 00:25:29 >> are we in a gravity well?
00:25:30 --> 00:25:31 >> Yeah, we are. I mean, the the earth
00:25:31 --> 00:25:33 itself creates a gravity well. Uh, and
00:25:33 --> 00:25:35 that's what keeps us stuck to the earth
00:25:36 --> 00:25:39 because the gravitational potential at
00:25:39 --> 00:25:41 your head is a little bit different from
00:25:41 --> 00:25:43 what it is at your feet. And that's
00:25:43 --> 00:25:45 what's pulling you down, the changing
00:25:45 --> 00:25:46 shape of space.
00:25:46 --> 00:25:48 >> There you go. All right. Um,
00:25:48 --> 00:25:50 >> I'm not spaghettifying you.
00:25:50 --> 00:25:54 >> No. No. So, um, did we unpack everything
00:25:54 --> 00:25:57 there? [laughter]
00:25:58 --> 00:25:59 >> Yeah, I think so. I think we I think we
00:25:59 --> 00:26:00 covered most of it.
00:26:00 --> 00:26:02 >> Okay. Um,
00:26:02 --> 00:26:04 >> look, I know.
00:26:04 --> 00:26:05 >> Sorry. Go ahead.
00:26:05 --> 00:26:07 >> No, I was going to say that he also
00:26:07 --> 00:26:10 asked if the big crunch would happen
00:26:10 --> 00:26:12 faster than the expansion.
00:26:12 --> 00:26:15 >> So, yes. So that I kind of you know lump
00:26:15 --> 00:26:17 that into the the fact that the the
00:26:17 --> 00:26:19 times that we observe from our
00:26:19 --> 00:26:21 >> location in the universe probably yes 20
00:26:21 --> 00:26:23 billion years down the track seems about
00:26:23 --> 00:26:25 right for the big crunch if if the
00:26:25 --> 00:26:27 recent desi results yeah it's what
00:26:27 --> 00:26:28 happens
00:26:28 --> 00:26:33 >> um um uh I was going to say that like
00:26:33 --> 00:26:36 you John uh these things make my brain
00:26:36 --> 00:26:38 hurt so um don't think it's it's
00:26:38 --> 00:26:42 peculiar to uh to um to a few people we
00:26:42 --> 00:26:45 I think I think most physicists, you
00:26:45 --> 00:26:47 know, they get their they really have to
00:26:47 --> 00:26:50 get their heads around the things like
00:26:50 --> 00:26:52 seeing pe seeing things from different
00:26:52 --> 00:26:54 vantage points. It's not entire it's not
00:26:54 --> 00:26:56 intuitive at all.
00:26:56 --> 00:26:59 >> No. No. All right, John. Thank you. And
00:26:59 --> 00:27:01 I hope all is well in Suffach. That's uh
00:27:01 --> 00:27:04 that's basically what one of one of the
00:27:04 --> 00:27:06 eastern most points of England, isn't
00:27:06 --> 00:27:06 it?
00:27:06 --> 00:27:09 >> I used to live in Suffach. But uh yeah,
00:27:09 --> 00:27:11 not not far from Cambridge, which is in
00:27:12 --> 00:27:14 Cambridge High, but SuffK I was over the
00:27:14 --> 00:27:17 border in Suffach. You're right. SuffK,
00:27:17 --> 00:27:18 Norfolk and Suffach are the two counties
00:27:18 --> 00:27:21 in East Anglia, that sort of
00:27:21 --> 00:27:23 semic-ircular bit that sticks out not
00:27:23 --> 00:27:26 very much north of the Temp's Estie.
00:27:26 --> 00:27:27 >> There you go. All right.
00:27:27 --> 00:27:28 >> Very pretty country. Yeah.
00:27:28 --> 00:27:31 >> Yes. Good to hear from you. Our final
00:27:31 --> 00:27:35 question today comes from Andy.
00:27:35 --> 00:27:38 >> Hi guys, this is Andy from London. I'm a
00:27:38 --> 00:27:40 new listener to your podcast and quite
00:27:40 --> 00:27:42 new to science, so forgive me if this is
00:27:42 --> 00:27:45 a stupid question, but I was just
00:27:45 --> 00:27:48 wondering um when craft re-enter
00:27:48 --> 00:27:49 atmosphere and they have to come in at a
00:27:50 --> 00:27:54 certain angle to stop from burning up um
00:27:54 --> 00:27:56 why do the not just come through slowly
00:27:56 --> 00:28:00 to to get away with the friction effect
00:28:00 --> 00:28:04 which uh causes the heat? Thanks.
00:28:04 --> 00:28:06 >> Thank you, Andy. Um, and thanks for
00:28:06 --> 00:28:08 finding Space Nuts and being a new
00:28:08 --> 00:28:11 listener. Um, you've only got 590 odd
00:28:12 --> 00:28:15 episodes to catch up now. So, um, yeah,
00:28:15 --> 00:28:16 have [clears throat] fun with that. Uh,
00:28:16 --> 00:28:19 we've certainly had fun with it. Um, I
00:28:19 --> 00:28:21 think we've had this question before,
00:28:21 --> 00:28:27 maybe asked a different way. Um,
00:28:27 --> 00:28:29 and and when it comes to a spacecraft,
00:28:29 --> 00:28:31 we're orbiting the planet, which is
00:28:31 --> 00:28:32 essentially it's just constantly
00:28:32 --> 00:28:34 falling. you're just maintaining a
00:28:34 --> 00:28:38 velocity that stops you falling in. Um,
00:28:38 --> 00:28:41 you do have to slow down to re-enter so
00:28:41 --> 00:28:46 that that arc is is, you know, reduced
00:28:46 --> 00:28:47 or increased. Can't remember which. Uh,
00:28:47 --> 00:28:49 and and then you fall through the
00:28:49 --> 00:28:53 atmosphere. Um, you can't stop and just
00:28:53 --> 00:28:56 sort of ease your way back in as against
00:28:56 --> 00:28:58 a space elevator which would be able to
00:28:58 --> 00:29:02 do that if we ever build one. But that's
00:29:02 --> 00:29:04 a different set of but a space elevator
00:29:04 --> 00:29:07 is essentially not orbiting. It is
00:29:07 --> 00:29:09 stationary to a point on the planet
00:29:09 --> 00:29:12 which means it goes up and down. Is that
00:29:12 --> 00:29:13 making sense?
00:29:13 --> 00:29:16 >> Yeah. Um yes it is. [laughter]
00:29:16 --> 00:29:18 That's good. That's the first time ever.
00:29:18 --> 00:29:20 >> Everything you've said is correct. Um
00:29:20 --> 00:29:24 space elevators uh hypothesized Buzz
00:29:24 --> 00:29:26 Aldrin told me uh that night I had
00:29:26 --> 00:29:27 dinner with him it's never going to
00:29:28 --> 00:29:29 happen. And he he was quite right
00:29:29 --> 00:29:32 because um the space elevator has to sit
00:29:32 --> 00:29:33 on the equator.
00:29:33 --> 00:29:35 >> Uh every spacecraft in the sky crosses
00:29:35 --> 00:29:37 the equator. So you're always going to
00:29:37 --> 00:29:39 get things banging into it. Uh it would
00:29:39 --> 00:29:42 be very difficult to build one. Uh you
00:29:42 --> 00:29:44 know apart from the structural thing. Uh
00:29:44 --> 00:29:46 so neglecting the space elevator for a
00:29:46 --> 00:29:48 minute, what you said is absolutely
00:29:48 --> 00:29:50 right. In order to stay in orbit, you
00:29:50 --> 00:29:53 have to achieve basically a horizontal
00:29:53 --> 00:29:56 velocity of about 8 kilometers/s.
00:29:56 --> 00:29:56 >> [gasps]
00:29:56 --> 00:29:59 >> uh and that's otherwise you just fall
00:29:59 --> 00:30:03 back to earth. So that's what all the
00:30:03 --> 00:30:05 you know the the the huge amount of fuel
00:30:05 --> 00:30:07 that is carried by a rocket being
00:30:07 --> 00:30:09 launched that's what it's all about.
00:30:10 --> 00:30:12 It's about getting up to a height of two
00:30:12 --> 00:30:15 or 300 kilometers and getting that
00:30:15 --> 00:30:17 orbital velocity getting that horizontal
00:30:17 --> 00:30:20 velocity of 8 kilometers/s.
00:30:20 --> 00:30:25 So, um, what you could do, uh, is, and
00:30:25 --> 00:30:28 and you know, going, this is hopefully
00:30:28 --> 00:30:32 help helping Andy, uh, if you had
00:30:32 --> 00:30:35 unlimited amounts of fuel, you could
00:30:35 --> 00:30:37 turn the rocket round, uh, from its
00:30:37 --> 00:30:41 orbital position and fire uh, your
00:30:41 --> 00:30:44 rockets to act as a braking system to
00:30:44 --> 00:30:45 slow the thing down. And then you could
00:30:46 --> 00:30:47 gently tiptoe down through the
00:30:47 --> 00:30:49 atmosphere, constantly firing your
00:30:49 --> 00:30:53 rockets. It's actually what um Musk does
00:30:53 --> 00:30:56 with his with his uh Falcon rockets. He
00:30:56 --> 00:30:59 he he's got enough fuel left that he can
00:30:59 --> 00:31:01 bring the empty spacecraft back down
00:31:01 --> 00:31:05 intact uh and and use it again uh
00:31:05 --> 00:31:08 without needing a heat shield. Um so you
00:31:08 --> 00:31:11 could do that. Uh and he's demonstrated
00:31:11 --> 00:31:15 that we can. Uh but it turns out that uh
00:31:15 --> 00:31:19 it's much more effective to use this
00:31:19 --> 00:31:21 process called aerobreing where you
00:31:21 --> 00:31:24 actually use the atmosphere itself to
00:31:24 --> 00:31:27 slow the spacecraft down. Uh because you
00:31:27 --> 00:31:28 don't need any fuel for that. You just
00:31:28 --> 00:31:30 need something that's going to stop it
00:31:30 --> 00:31:32 burning up. Uh so getting from this 8
00:31:32 --> 00:31:34 kilometers/s
00:31:34 --> 00:31:37 down to a few, you know, a meter or two
00:31:37 --> 00:31:39 per second uh for a splashdown or a
00:31:39 --> 00:31:42 touchdown uh is the tricky bit. And
00:31:42 --> 00:31:45 you've got to uh you know you you you
00:31:45 --> 00:31:47 you've got to use whatever means are at
00:31:47 --> 00:31:49 your disposal and the easiest one is
00:31:49 --> 00:31:51 arrow braingreaking using the atmosphere
00:31:51 --> 00:31:53 itself to slow you down. I should point
00:31:53 --> 00:31:55 out that um I think the first stage
00:31:56 --> 00:31:57 Falcon rockets they're not at orbital
00:31:57 --> 00:32:00 velocity uh when they turn around and
00:32:00 --> 00:32:02 come back. They haven't got up to that 8
00:32:02 --> 00:32:04 kilometers/s because there's a second
00:32:04 --> 00:32:06 stage that lets them do that and they
00:32:06 --> 00:32:09 still burn up basically coming back into
00:32:09 --> 00:32:13 the atmosphere. the second stages.
00:32:13 --> 00:32:14 >> Good question. Not a stupid question at
00:32:14 --> 00:32:15 all.
00:32:15 --> 00:32:19 >> No. No. And and you know,
00:32:19 --> 00:32:22 it's rocket science. I mean, we we often
00:32:22 --> 00:32:24 say when something's not difficult, it's
00:32:24 --> 00:32:25 not rocket science. This is rocket
00:32:25 --> 00:32:29 science. Um orbital speeds are
00:32:29 --> 00:32:32 significant. They're they're to stay out
00:32:32 --> 00:32:36 there. They've got to um do 17 mph,
00:32:36 --> 00:32:38 >> which is 8 kilometers/ second.
00:32:38 --> 00:32:42 >> Yeah. Mark 25. Um, to slow down so that
00:32:42 --> 00:32:44 you can return to Earth safely, you've
00:32:44 --> 00:32:47 got to go from that speed to subsonic
00:32:47 --> 00:32:48 speed.
00:32:48 --> 00:32:49 >> Yeah.
00:32:49 --> 00:32:51 >> And using fuel to do that would be
00:32:51 --> 00:32:52 exhaustive.
00:32:52 --> 00:32:54 >> Yeah, that's right. That's exactly
00:32:54 --> 00:32:57 right. You know, you basically you're
00:32:57 --> 00:33:00 looking at the same amount of hardware
00:33:00 --> 00:33:03 in terms of a rocket and its fuel to to
00:33:03 --> 00:33:05 get you up there. you'd need the same
00:33:05 --> 00:33:07 amount to bring you back just to do a
00:33:07 --> 00:33:10 gentle touchdown on the earth.
00:33:10 --> 00:33:13 >> Um uh 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
00:33:17 --> 00:33:21 for 10 years with the Falcon 9 rockets.
00:33:21 --> 00:33:23 >> Yeah. Uh I'm sure the technology will
00:33:23 --> 00:33:25 improve and we'll find better ways but
00:33:25 --> 00:33:27 at the moment using the atmosphere as a
00:33:27 --> 00:33:28 free braking system.
00:33:28 --> 00:33:29 >> Yeah. Yeah.
00:33:29 --> 00:33:31 >> Yeah. Works really well.
00:33:31 --> 00:33:31 >> It does.
00:33:31 --> 00:33:33 >> Except when it doesn't. But that's only
00:33:33 --> 00:33:34 happened a couple of times.
00:33:34 --> 00:33:35 >> Yeah, it is.
00:33:35 --> 00:33:36 >> Um, yeah. [sighs]
00:33:36 --> 00:33:38 Thank you, Andy. Great question, though.
00:33:38 --> 00:33:40 Uh, really appreciate it. And don't
00:33:40 --> 00:33:41 forget, if you've got questions for us,
00:33:41 --> 00:33:44 you can send them through via our
00:33:44 --> 00:33:46 website, spacenutspodcast.com,
00:33:46 --> 00:33:48 spacenuts.io. You click on the little
00:33:48 --> 00:33:51 AMA link at the top. Uh, which means ask
00:33:51 --> 00:33:54 me anything. I finally figured that out.
00:33:54 --> 00:33:57 Ask me anything. AMA. Uh, and you just
00:33:57 --> 00:33:58 fill in the blanks. whether it's a text
00:33:58 --> 00:34:00 question or you can hit the start
00:34:00 --> 00:34:03 recording button and record a question
00:34:03 --> 00:34:06 for us. Um, any device with a microphone
00:34:06 --> 00:34:08 will do. spacenutspodcast.com or
00:34:08 --> 00:34:10 spacenuts.io.
00:34:10 --> 00:34:12 Uh, while you're there, you might want
00:34:12 --> 00:34:14 to hit the supporter button and um, you
00:34:14 --> 00:34:17 know, look at ways of supporting us uh,
00:34:17 --> 00:34:19 financially. It is not essential. We do
00:34:20 --> 00:34:22 not demand that of you. Never will. But
00:34:22 --> 00:34:24 uh, we do have a lot of people who
00:34:24 --> 00:34:26 volunteer to do that. In fact, it was
00:34:26 --> 00:34:27 the listener's idea in the first place
00:34:28 --> 00:34:29 to set that up for us. We didn't even
00:34:29 --> 00:34:31 think about it until someone said, "How
00:34:31 --> 00:34:33 do I contribute to the program?" And it
00:34:33 --> 00:34:36 all took off from there. Um, and we do
00:34:36 --> 00:34:38 appreciate our supporters very very
00:34:38 --> 00:34:41 much. Uh, thank you so much for thinking
00:34:41 --> 00:34:43 enough of us to put a couple of bucks
00:34:43 --> 00:34:46 behind um behind our words. We we
00:34:46 --> 00:34:48 appreciate it greatly. Uh, I think we're
00:34:48 --> 00:34:51 all done. Fred, thank you so much.
00:34:51 --> 00:34:53 Uh, a pleasure, Andrew. Great to hear
00:34:53 --> 00:34:55 from the listeners as always. Great
00:34:55 --> 00:34:58 questions. Uh, get my mind thinking
00:34:58 --> 00:35:01 again. [sighs] Uh, so uh, thank you
00:35:01 --> 00:35:03 everybody and thanks to you Andrew too
00:35:03 --> 00:35:06 for keeping on the rails.
00:35:06 --> 00:35:09 I do my best and sometimes I don't. Uh,
00:35:09 --> 00:35:11 but yes, thank you Fred. We'll see you
00:35:11 --> 00:35:13 next time. Professor Fred Watson,
00:35:13 --> 00:35:15 astronomer at large. And thanks to Hugh
00:35:15 --> 00:35:17 in the studio who definitely does keep
00:35:17 --> 00:35:18 it all together. Although he couldn't be
00:35:18 --> 00:35:21 with us today because um, he re-entered
00:35:21 --> 00:35:23 his garage at excess velocity. couldn't
00:35:23 --> 00:35:27 get down to subsonic speed and uh well
00:35:27 --> 00:35:28 he'll be in traction for a couple of
00:35:28 --> 00:35:30 weeks. Uh from me, Andrew Duckley,
00:35:30 --> 00:35:31 thanks for your company. We'll see you
00:35:31 --> 00:35:33 on the next episode of Space Nuts.
00:35:33 --> 00:35:34 Bye-bye.
00:35:34 --> 00:35:35 >> Space Nuts.
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