Deep Space Radiation, Black Holes And Other Questions - Episode 14

hello it's scott manley here back with any other batch of questions from my supporters over at patreon and we're going to get right into uh yes axel s bomb asking what is the state of the art in radiation shielding for deep space missions thinking about missions to the gateway and the moon as well as transits to and from mars and presuming you're talking about radiation shielding for people because of course radiation shielding for electronics and other hardware is also important but yes think state of the art implies that there's radical improvements that can be made and yes there are technological concepts for uh like active radiation protection using magnetic fields that you know steer ionized particles away um really the thing that we mostly spend time on is looking at putting material between the people and the radiation because just having the radiation come in and have to plow through you know either propellant tanks or dedicated radiation shielding or even the poop of the astronauts yes you can actually in case you can use pupa's shielding and obviously you can also use the food as shielding um so yeah i mean if you think about radiation shielding on earth we tend to use heavy materials like concrete and lead or actually concrete with lead in it and whereas in space we actually tend to use lighter materials like polythene polyethylene is actually one of the most uh well-tested and well-studied materials for blocking radiation in space and part of the reason why we do one thing versus the other is the type of radiation we deal with on earth is mostly things like neutrons and gamma rays like sure there's alpha particles and beta particles but those tend to get you know they tend to get dealt with by the atmosphere it's those last two are the penetrating ones and those are the reason why you have these vests and or radiation shields or whatever that are lead because you want to block them in as shorter distance as possible and actually it turns out that blocking neutrons and blocking um gamma rays and stuff lead does a pretty good job because it puts a lot of electrons into a very small volume and it's the electrons which cause the gamma rays to scatter um but yet for space there's mainly there's two types of radiation space there's first of all uh radiation from the sun in the form of protons which is mainly protons or some other stuff and there's some x-rays and then there's cosmic rays which are coming those are even higher energy and those uh are mainly protons alpha particles and maybe some electrons so these come in from outside the solar system and actually the best way to shield against cosmic rays in space is the sun the sun's magnetic field actually protects the whole solar system from high-energy cosmic rays and when the sun is really active it actually reduces the amount of cosmic rays albeit you increase the amount of solar radiation you know solar proton radiation so yeah um it i think if you i think i saw one study that basically said the best time to go to mars is during solar maximum because that minimizes your amount of cosmic rays which are super high energy and go through anything and instead leaves you with high energy protons from the sun and those are much easier to shield against using um you know hydrogen-rich protection scattering systems and the other reason why hydrogen-rich systems work better than say lead is when you get up to the very large nuclei and you have these particles coming in they can hit the nuclei and they spillate they generate more secondary radiation so when you have just protons like hydrogen that there tends to be a lot less of that so yeah um i i think one source said that for a ro a reliable mission you would need something like 10 centimeters of aluminium over like some protected part of the ship where they could wait out a solar storm and yeah then it would be super manageable but really it does come down to managing this and deciding what you can accept and minimizing the time where you're exposed to a lot of material so that's a fairly long answer to start with and yes next question steven schmidt thinking about how important jupiter is to our solar system would it be possible to send some kind of long-term manned research mission there or are the radiation and electromagnetic hazards a field's too strong for human survival near jupiter what other problems would get in the way of this kind of mission well the main problem that we'd get in the way is it's a really long way you would have to go out there and spend a very long time out that way so yeah i love there's a painting i remember our place of space art that shows a person painting jupiter from the surface of io with volcanoes in the background that is never going to happen because there's way too much radiation uh basically the closer you get to jupiter the more radiation you get from that's trapped in jupiter's magnetic field the jovian equivalent of van allen belts and yeah i think io europa and ganymede they all have pretty much too high levels of radiation for you to spend a lot of time on the surface callisto on the other hand uh it actually seems to be much more manageable if you you look at the numbers so yeah if you wanted to mount a mission to callisto it wouldn't be too hard callisto probably has a fair amount of water ice and very likely has liquid water in places just not as much as say europa now of course if you want to avoid these radiation effects you can go under the surface and that really helps you a whole lot not going to happen in iowa because nobody likes swimming in you know molten lava europa you could actually in theory go scuba diving underneath the ice it's really really thick but the atmosphere or sorry the gravity of europa is low enough that it's at the high end of what is possible in scuba with highly technical gear but yeah a callisto is a good target as far as i'm concerned for a human mission but it is a very long time in space uh zach strong has got a couple of friends and i are working on a universe building project we thought it would help with an issue we had a hard time researching could a planet be shielded from a neutron star's radiation god we're all about radiation questions today aren't we i love it if it was orbiting a yellow blue similar star what would the sky look like from the planet's surface in either case well first of all it would depend on how far away you were from the neutron star so neutron stars have masses of greater than 1.4 solar masses because that's the chandra seeker like mass limit like there's a chandra seeker limit and a chandra seeker mass and there's actually they mean different things and i always forget which ones which but yeah neutron stars are remnants from stars so you've had a star that formed it went through its main sequence it went became a red giant cult you know has a core collapse supernova and you're left with a neutron star so whatever whatever that planet is that is orbiting another star in this star system and that means probably that the neutron star has to be a certain distance out right so it can't be too close it can't be like a neutron star orbiting at the distance of jupiter i don't think that would work from a stability point of view um now you say yellow blue similar star wouldn't be a blue star because if it were a blue star blue stars are high mass and they evolve too quickly you want a yellow or even a red star that will outlive the star that caused the supernova that left the neutron star behind could that protect the planet that's a very good question uh um again i would have to do the math on that but i think the dynamic constraints that basically says it has to survive the initial instability of you you basically got one heavy mass star and then it becomes a lower mass star after the supernova and yet this has to remain bound the whole time that probably puts constraints on how close they can be you might actually have it in a fairly eccentric orbit depending upon the age so i've got to think about that look it would be a pretty fabulous thing and the other thing about neutron stars is that when we think about pulsars we think about this like magnetic field sweeping out and blowing out radiation and they tend to be fairly collimated so you could design a neutron star which is preferentially throwing like it has its magnetic fields pointed away and it's not aiming at that planet or or you know first story you could have something where the most of the radiation goes out in a plane and there's times in this planet's life where it passes through these radiation belts and there's terrible storms and things like that but you know it's like there's a lot of places you can go with this story but yeah i mean the neutron star would be uh probably generating interesting aurora and and truthfully yeah it's uh it whatever the story needs i'm sure you could spend some time and come up with it that's what i'm gonna say but you could definitely make a livable planet in that uh but i would i would think a little about your orbit okay um seb would you rather fly a new shepherd or ride passenger in an f a 18 for 30 minutes as much as i love the f-18 and stuff i think new shepard is currently where i'd be at for the simple reason that i would be a passenger in either case and i prefer to go higher and see more whereas i know it's actually possible to buy rides in the back of fighter jets like mig i don't know migs or whatever so that would be more affordable so yeah just from a simple economic argument we'd go with new shepard but yeah realistically you know half hour flight and a fighter jet it's also more likely to make me sick it'd need a little bit of training to work up to it who knows alan thought of another one which means must have asked me a question previously you've talked about advanced gemini but what about big gemini or gemini as nasa would say and reports that was being considered as a lower cost replacement for the space shuttle so here's the thing um okay so basically big gemini was proposed by mcdonnell douglas uh i don't know sometime in the 60s and they basically so there was gemini and then there was the air force's blue gemini with the mar the manned orbiting laboratory where they would have like a big space station attached underneath the heat shield of the gemini and they would actually have a hatch in the heat shield and they would go in and they would have all these cameras to observe the ground right that's what the military was thinking you know before i think they were just wanting to have people fly in space because obviously corona was doing a pretty good job so big gemini was like let's scale this up even more let's have the basic gemini capsule and then like there's a row of seats behind it i think they could fit something like a dozen people in this and then potentially a cargo bay behind that and this was something was proposed like as a next step after apollo which is interesting because of course apollo was a more advanced capsule uh the thing about the gemini uh big germany was that also it would land under a rogallo wing so it would fly horizontally under a big soft parachute type wing and i know that some people at nasa thought it was a good idea because they thought that shuttle would take too long they wanted to have a space station with a dozen people in the early 1970s and they didn't think shuttle would be ready until too late so this was a sort of a smaller easier more likely to happen project but ultimately of course it never happened because you know funding a cut at nasa right the politicians were really interested in not paying for this and instead paying for the vietnam war and other things like that uh it could have it could have made sense if if things had lined up but equally the space shuttle you know the space shuttle could have also made more sense let's say scott f hey scott great name by the way please explain how an object falling into a black hole event horizon would appear to slow down and freeze on the surface as viewed from an outside observer due to time dilation wouldn't that mean that every object that ever fell into an event horizon would be recorded as a frozen image on the surface oh my god okay so so here's the thing these these visions of a black hole with the event horizon and the timelines never actually touching the event horizon as viewed by an outside observer like this is this is something that basically it sort of when you think about it initially it's like oh that's kind of mind-blowing and then the more you think about it it becomes amazingly mind-blowing right so it turns out if you do the math there's no point outside of a black hole where the event horizon is in the past so there's actually no way to actually see the event horizon that means you can never see the formation of the black hole right everything ultimately ends up in this hypothetical surface but yeah the event horizon around a schwarzschild like metric black hole it is it's an approximation it is a very accurate approximation it happens to match everything but if you imagine an object falling down from the outside observer it does appear to like slow down and stop above the event horizon but also it becomes red-shifted very rapidly so you can't see it anymore um also because the the if you imagine the object comes in you would think well wait a second if you've got the black hole here and you've got this tiny mass here doesn't this mean you've got like some sort of binary uh your non-spherical mass and yes except that it very quickly becomes spherical as as it approaches the event horizon so then that is from an outside observer so you can't see it that way the charge if you imagine an electric charge coming down and coming close well it turns out the electric charges they communicate their charge via photon exchange right you know electromagnetic forces are mediated by photon exchange and those get distorted so an electric charge comes down close to the event horizon it doesn't look like it's next to the event horizon because of the distortion it looks like it's at the center of the black hole so it all sort of fits together and makes sense um yeah what i'm basically saying is that these models that we use are really approximations if you're part of the black hole it's not necessarily a time that you are observed to be inside i don't know it's very complicated uh yeah like basically as far as you're concerned outside you're never going to see because the things get time dilated any uh non-sphericity is very quickly eliminated by changes to the the geometry yeah i'm yeah there's i'm going to get comments from people that actually understand i say what are you talking about scott okay hi scott hope you're well why don't rocket companies have a wider range of faring sizes i quite often see really small satellite and a big fairing and mostly because it takes a lot of testing to validate fairings with the aerodynamics and loads and if you build a bigger fairing that moves the center of mass uh sorry the center and drag forwards and therefore the center of mass backwards and you know if you took a falcon 9 and had to make a smaller fairing well that means now you've got two sections in the factory for two different fairing sizes it makes more sense to just make one type of fairing um there are some really interesting fairing designs for sure there's like a the lenticular fairing design that was the idea was you would fly up a huge circular mirror disc shaped mirror and ace a fairing that was side on there was also the um the large asymmetric fairing which sort of looked like a head of an arrow and they wanted to put certain large payloads they they advertised this they said they'd done the math on it and if there was a customer that wanted it they could fly it never happened it would fly on an atlas heavy which is something that never actually happened atlas 5 heavy which we would have three cores of the atlas 5. um yeah so yeah it basically comes down to the fact that building the fairings and approving the fairings is hard and the more production lines you have the more factory space you're taking for these things right if you're having to do just one thing it's going to cost much more than doing the other big thing that you've already got a production line for okay paul brundit for years manned space plane concepts have come and gone but with the exception of space shuttle none have come to reality we now have several different capsules but no dinosaur hermes manned dream chaser x37c are space planes just too hard to develop and do they offer no advantage over a capsule they are hard to develop the the geometry on a space plane is much more complicated and you inevitably end up with sharper corners like along the leading wing edges which means much higher thermal loads that means you need a heat shield which is not not homogeneous right it means your whatever thermal protection system if you've got tiles means much more geometry it does make everything a lot more complicated and the capsule is much simpler geometry also because you have to have the wings you inevitably get a worse surface area to volume ratio so you get less space inside it for the same mass of course there are advantages to capsules right they have much better cross-range capability lower g loading for the cargo and or passengers and the nice thing is the thing that dreamchaser really wants to offer is the ability to land at an airfield and pretty much have the stuff offloaded right away whereas if you look at the your dragon cargo it lands at sea gets recovered sails back and then the stuff gets offloaded so there's a you know there's a sort of prompt recovery of cargo advantage that uh your dream chaser is supposed to offer but yeah it's it's that a capsule is a much safer bet and it's much easier to develop and you get much better volume for the same amount of mass and that's why they're they're kind of popular nobody it's very rare that they need the level the advantages that space planes offer okay finally joe so we know starship flight plan requires refueling and space to go to mars after the starships final burn to get on the correct trajectory there should be still some fuel in the tanks to do a landing burn on mars will this fuel help keep the rocket cooled as it enters the atmosphere i would imagine all the cryogenic fuel would slam up against the side of the rocket as it slows down so um so you're sort of right there yes absolutely this uh propellant would slosh up against the side of the tanks and keep it cool but the starship can't rely on that first of all there's no propellant in the front section in the cargo so that's not going to help it secondly if you're returning from mars to earth then you have much less propellant than the tanks you only have enough propellant in those tanks to fill the headers the oxygen and the fuel oxides are in fuel header tanks and those are in the middle of the rocket far away from the edges so you absolutely have to rely on the heat shield right coming back from mars to earth by the way is going to be much hotter than arriving at mars i believe i think the velocities are going to be significantly higher and you've got less you know more gravity less uh anyway a point is yeah you cannot rely on that at all it's a nice thing to have but if you're getting to the situation where it makes a difference then you have lost heat shield tiles and you shouldn't ever be in that situation because you're not going to be able to guarantee it in some many conditions okay i think that's a pretty good episode i hope you enjoyed all that uh remember check out the patreon if you want to ask questions i've got a huge backlog and uh hopefully some of these questions have hopefully some of these have answered the questions that were burning in your your head i'm scott manley fly safe [Music] you

Channel: Scott Manley

Views: 309,463

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Id: qtWhv9Ic7Hg

Length: 21min 41sec (1301 seconds)

Published: Sun Jan 30 2022