First, we join Ash from Brisbane as he ponders the enigmatic mechanics of spacecraft reentry. Using Apollo 13's nail-biting descent as a springboard, Fred demystifies the concept of 'bouncing off the atmosphere' and reveals the delicate balance between gravitational pull and atmospheric drag.
Next, Darryl from South Australia challenges us with the icy extremes of absolute zero. Why does this ultimate chill exist, and is there a corresponding 'absolute hot'? Fred delves into the physics of temperature and the motion of atoms, shedding light on the limits of the thermal universe and the possibility of an 'absolute heavy' or 'absolute light'.
Finally, Alex from London, by way of Indiana, brings us face-to-face with the enigma of dark energy. Is this mysterious force the antithesis of gravity itself? Our hosts explore the repulsive power that's pushing galaxies apart and the ongoing quest to unravel the secrets of the cosmos.
With each question, Andrew and Fred illuminate the wonders and oddities of the universe, blending humor with profound scientific insight. So, join the Space Nuts community, submit your own cosmic queries, and keep the spirit of discovery alive!
For more space-time odysseys and answers to your astronomical inquiries, subscribe to Space Nuts on your favorite podcast platform. Until we venture again into the vast unknown, keep your gaze to the stars and your curiosity alight!
Episode Chapters
(00:00) Welcome to Space Nuts: Astronomy and Space Science
(02:10) Ash from Brisbane questions the 'bouncing off the atmosphere' during spacecraft reentry
(10:45) Darryl from South Australia inquires about absolute zero and the limits of temperature
(17:30) Alex from London asks if dark energy could be considered antigravity
(25:15) Closing remarks and how to submit your questions to Space Nuts
Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts--2631155/support.
For more Space Nuts visit www.spacenuts.io or our HQ at www.bitesz.com
[00:00:00] Hi there, thanks for joining us again.
[00:00:01] This is Space Nuts where we talk astronomy and space science.
[00:00:05] My name is Andrew Dunkley, your host.
[00:00:08] Coming up on this episode,
[00:00:10] we'll be answering audience questions.
[00:00:12] Ash is looking at Apollo 13.
[00:00:16] Darrell is asking questions about absolute zero,
[00:00:20] which seems to be a common topic.
[00:00:21] I'm pretty sure we've had this one pop up previously,
[00:00:24] so we'll
[00:00:25] have a crack at that again obviously we didn't do it well enough before and Alex is focused on
[00:00:31] anti-gravity that's all coming up on this edition of Space Nuts. 15 seconds guidance is internal 10, 9, Ignition Sequence Start. Space nuts.
[00:00:45] 5, 4, 3, 2, 1.
[00:00:48] 1, 2, 3, 4, 5, 4, 3, 2, 1.
[00:00:50] Space nuts.
[00:00:51] Astronauts reported.
[00:00:52] Feels good.
[00:00:53] Joining me to solve all of those riddles and puzzles
[00:00:57] is Professor Fred Watson.
[00:00:59] Astronomert large.
[00:01:00] Hello, Fred.
[00:01:01] Hi, Andrew.
[00:01:02] How are you doing?
[00:01:03] Now, Fred, let's go to our Q&A segment.
[00:01:07] This is where we basically take questions from the audience,
[00:01:10] which are always welcome.
[00:01:11] Don't forget to send them into us.
[00:01:13] And we endeavor to answer them,
[00:01:15] or we just pretend we know the answer and then move on.
[00:01:18] And I mentioned at the beginning that Ash wanted to ask a question about Apollo 13. That's
[00:01:26] not quite accurate. What we, what he was asking about, he used Apollo 13 as an example of
[00:01:35] a situation that he doesn't quite get. Let's hand it over to Ash.
[00:01:39] Yeah, what I want done. Ash you from Brisbane again with another question for you
[00:01:47] I was recently watching the movie Apollo 13 my daughter and
[00:01:52] Coming towards the end of the movie where they're talking about
[00:01:56] their reentry of the command module the
[00:02:00] news reporter
[00:02:02] Said that to steep an angle and it will burn up on reentry. I get that.
[00:02:08] And then he goes on to say that I'm into shallow and the spacecraft will bounce
[00:02:14] harmlessly off the atmosphere, floating off into space, skipping off the atmosphere like a rock
[00:02:19] off a pond. Don't really get this one. Skipping off the atmosphere, is this something we've
[00:02:25] observed in the past? Or is it just something theoretical? I'm interested to hear your thoughts
[00:02:32] on that. Well, the show goes, come up.
[00:02:35] So Ash is bringing up an interesting point because we all understand the implications
[00:02:40] of coming into steep and hitting the atmosphere and burning up. We've seen that in recent years with disastrous effects and the loss of
[00:02:50] lives, unfortunately, on one particular occasion. But we don't think much about
[00:02:57] the bouncing off thing. And I've always just taken it for granted that that's
[00:03:00] gospel. And I suppose he brings up a very solid question as to
[00:03:07] have we ever witnessed this. So yeah, let's try and understand the concept a
[00:03:14] bit more bouncing off the atmosphere like a skipping stones across a lake.
[00:03:19] And I think that's the problem, Andrew, that we kind of use what I think is the wrong terminology.
[00:03:29] So yeah, I mean, we've all seen skimming stones
[00:03:33] where you skim across the lake, exactly as you've said.
[00:03:35] And that's what this sort of thing
[00:03:37] conjures up for you in your mind.
[00:03:40] But what you're actually doing is it's the angle of entry that is the critical thing.
[00:03:47] If you get it too shallow, sorry, too steep, then the velocity that you come in at is too high for the spacecraft's heat shield
[00:04:02] to cope with the frictional heat that you've got as it passes through the atmosphere.
[00:04:08] Because remember the atmosphere is just getting steadily more dense as you go down.
[00:04:12] And so that's catastrophic, as you've just said.
[00:04:16] And so then there's a sort of sweet spot where you can use the friction of the atmosphere to slow you down, atmospheric breaking. It's a balance between
[00:04:28] the thermal construction of the heat shield, how much temperature that will withstand it,
[00:04:34] and for how long, and how much of that heat is conducted through to the interior of the spacecraft. So that balancing act is very much sort of,
[00:04:48] you know, it's judging many different factors,
[00:04:55] steepness, temperature,
[00:04:58] resilience of the spacecraft, teach you all of that
[00:05:01] with the, to get the right angle of entry. So, but if you then change that
[00:05:08] to make it shallower, remember you're still, still in a gravitational situation. I mean,
[00:05:17] when the spacecraft is outside the atmosphere, basically the only force acting on it is gravity and that dictates its motion exactly. So when it enters the atmosphere that's when the thing is going to start
[00:05:30] slowing down. So if you enter at an angle that is too shallow the gravitational
[00:05:37] pull of the earth which the thing is feeling and it's going downwards it will also as it hits the outer parts
[00:05:47] of the atmosphere it will basically feel the deceleration of the atmospheric braking but there
[00:05:54] won't be enough if you're not at a steep enough angle there won't be enough gravitational braking
[00:06:00] and eventually even though the heat shield will heat up and everything,
[00:06:05] but eventually it won't actually come down to Earth.
[00:06:09] It will keep going through the upper atmosphere.
[00:06:12] Its orbit will be altered dramatically.
[00:06:14] In fact, it may even, as a result of that,
[00:06:17] going to orbit around the Earth because it's experienced sunbreaking,
[00:06:20] but it's still not being captured by the Earth in the sense that you want it to be,
[00:06:25] you want it to come in. This is actually about 11 kilometres per second. It's got to get
[00:06:29] hit the Earth's atmosphere out to slow down enough to come back in from the moon. So it's
[00:06:39] not a bounce. It's that gravity wins over atmospheric breaking. And what would happen, as I said,
[00:06:46] it's likely that it would come out of the atmosphere, but now be in an elliptical orbit
[00:06:52] around the earth. And so it's orbit, depending on just what the circumstances were, might
[00:06:58] turn into a long ellipse and go back. Now, there have been a contrary to popular belief, you're not going to be speed off into oblivion.
[00:07:08] Well, you would be, basically.
[00:07:10] Oh, I guess you'll be in the wrong orbit, and you don't have any means of changing the orbit.
[00:07:16]