Gravitic Spaceship Propulsion

Transcript

gravity is a fascinating Force it's what holds everything on our planet together and it might one day help us travel to other planets gravity is a strange thing on the one hand it's the oldest and best known of the fundamental forces on the other it's the weakest and least understood within that uncertainty May lie the keys to escaping this world and traveling to countless as others or building structures of incomprehensible scope and amazing purpose while we'll cover gravitic Technologies beside proportion in February today we'll focus solely on moving spaceships we'll explore everything from mundane uses of gravity for proportion like slingshotting around planets and the ooth effect to more hypothetical varieties such as space-time warping gravitational wave proportion anti-gravity Dark Energy negative matter frame drag the diametric differential pitch and bias drives and more that's a lot to cover so grab a drink and a snack hit those like And subscribe buttons and let's dive into the topic we might as well begin with the best known use of gravity for moving spaceships preventing them from moving by giving them a massive gravity well to drag themselves out of while also making them drag through a thick atmosphere this is where something like anti-gravity could change the game if you could simply ignore gravity or activate something that counters it it would be revolutionary anti-gravity is a somewhat vague term mainly from science fiction and probably should be divided into reversing gravity and nullifying it this brings up a key point about gravity unlike other forces it lacks a repulsive aspect only having an attractive one or so we think we could be wrong about that the the mysterious Force known as dark energy for instance acts a lot like a repulsive Gravity Force and we'll explore that later the ability to manipulate gravity would be a huge game Cher if we had it but it's worth noting that we already have some ability to manipulate gravity and even some forms of gravitic propulsion let's delve into three existing techniques gravity assist also known as the slingshot maneuver the ooth effect and tether propulsion most people are familiar with gravity assist or slingshot Maneuvers but the mechanism of speed gain and how it varies with the oorth effect can be confusing the gravity assist slingshot and the overo effect are both important techniques in orbital mechanics that allow spacecraft to gain speed or change trajectory efficiently however they operate under different principles and in different contexts here's a breakdown of their differences a gravity assist or slingshot maneuver uses the gravitational field of a large Celestial body like a planet or moon to change a spacecraft speed and direction as the spacecraft approaches the planet it falls in the planet's gravitational well gaining velocity this is part of why asteroid impacts are so severe even if an object is moving at the same speed as Earth when we cross paths it will generally gain velocity relative to us comparable to Earth's escape velocity as it falls into our gravity well when the spacecraft exits on the other side it has gained energy relative to its initial trajectory essentially the spacecraft borrows some of the plants orbital momentum giving it a speed boost without using its own fuel people often understand why this lets you change direction without fuel but they might wonder how it can increase speed after all if you fall past a planet you moving away from it again so shouldn't you lose the speed you gained and the answer is yes but only relative to that planet that planet is moving around the Sun or the sun around the Galaxy imagine hooking a physical tether to a planet like Jupiter as you cross paths you'd end up in orbit around it and in fact we'll discuss using a physical tether shortly but for now you're latched on picture this tether as being made of virtual gravitons when you go let's say 10 km/s away from the Sun toward what we will call Sol or east assuming the sun is at the center of the map and Compass directions align with the sun's ecliptic if you hold on to that for half a Jupiter year you could release on the other side of the solar system in any direction Jupiter like most celestial bodies orbits on an elliptical path moving faster when near the Sun and slower when further away this allows you to change your velocity relative to the solar system or even the Galaxy for Interstellar slingshots your riding along with someone else as that body changes speed the maximum gain is twice the celestial body speed relative to the Sun the momentum gain depends on the object's Mass how close you approach its speed relative to the sun and the incoming and outgoing trajectories Voyager 1 picked up about 10 km/ second from Jupiter which orbits at 13 km/ second Cassini during its mission to Saturn managed to fall toward the Sun use Venus revisit Venus again A year later then slingshot around Earth and finally shoot out to Jupiter which it used before reaching Saturn in 2020 7 years after launch Mercury is an optimal object for slingshot Maneuvers because it's small dense and orbits faster than the other planet with good timing you could fall from Earth swing past Mercury and fling yourself out of the solar system possibly passing by other planets along the way though this would be slow on an Interstellar scale it helps save fuel on launch or on arrival to slow down you could further speed up after slingshotting using conventional fuel or vice versa on arriv Rival by slingshotting around stars or black holes you could achieve impressive speeds potentially approaching a fraction of light speed but this requires us to move from a passive slingshot to an active one using the O birth effect now the overo effect does involve using Fuel and lets us get more out of it when moving toward another body at higher speeds that can seem weird that a spacecraft gains more kinetic energy from a propulsion maneuver like a rocket burn when it's moving at higher speeds particularly when it's deep within a gravitational well such as near a planet if we picture a ship approaching a planet or in a long elliptical orbit it is speeding up as it falls toward the planet and slowing down away from it if at the top of a long elliptical orbit you burn fuel to finish breaking away from it which is what we tend to visualize burn to get free you will actually do worse on this than burning as you drop toward the planet so let's imagine we're moving toward a planet to get some gravity assist and turn direction hooking around it it's weird to think about but the amount of speed you get from gravity is based on how strong the field is and how long you spend in it just like any Force more time under it more strength FAS or speed if you are approaching a planet at speed you will pass by it faster and spend less time in that gravity this normally balances out if you're not burning fuel because you might pass by in an hour or a day but you approach it gaining speed and leave it losing speed in the same time interval if you are falling toward a planet and not burning fuel to speed up you spend a lot of time falling now you burn fuel on your way out speeding up using it and while at top speed too so the time you spend leaving being ped on by gravity to slow you is decreased this cuts the period of time when gravity is hurting you most pulling back on you while closest to it and when it's strongest and this is one way to look at the ooth effect another is that when you burn your fuel you are going to increase your speed by a set amount of Delta V let's say you're approaching Earth initially at zero speed and you've got enough fuel to give you 5 km/s of Delta V left to yourself you're going to be going 11.2 km/s when you pass Earth then lose all that climbing away that's our escape velocity and it reflects the energy you gain then lose from gravity or 62.7 2 megga per kg Accelerate from the beginning to 5 km/s adding 12.5 5 m of kinetic energy per kilog of ship instead of reaching Earth at 11.2 km/s you'll be going 12.25 km/ second and be at 75 M of kinetic energy we must then spend 62.7 2 m to escape Earth again and that leaves us right back down again at 12.5 megga of kinetic energy or at 5 km/s when we are done simple conservation of energy there but if instead we use that Delta V right after we hit that maximum fall speed of 11.2 km per second we are now up to 16.2 km/s and now our kinetic energy which goes with the square of velocity is up to 131.0 m per kog now we pay that 62.7 2 MGA energy tax to leave Earth and we are left with 68.5 megga per kilogram and that is a kinetic energy equivalent to 11.7 km/ Second not the 5 km/ Second of Delta V our Rocket Fuel offord and that extra energy comes from the gravity of the planet you passed or any Celestial body so if I'm falling toward a black hole and born when I'm moving at 10% of light speed and having a kinetic energy of 450 trillion Jew ignoring special and general relativity for the moment and that 5 km/ Second Del Delta V increases your kinetic energy by 150 billion Jew thousands of times what our last example did and for the same rocket fuel now you have that left over when you fly off which you can since escaping a black hole works just fine so long as you don't cross that event horizon you have 150 billion jewles of kinetic energy per kilogram and your velocity change isn't 5 km/ Second when you escape but rather 548 km per second 110 times as much and about 2% of light speed and we could have dropped even closer to that black hole assuming secretion disc wasn't a threat and title force is not too bad and thus emerged even faster pretty impressive and using no new technology and I should note that close to poaches on plac like Jupiter or the sun can do good for us if not as much the same trick works for deceleration too you fall into a system at high speed approaching your destination drop that system sun and burn backwards lowering your speed by a set Delta V and shuing off tons of kinetic energy in the process and again this transfers energy by gravity a big reflective solar sail works great for this since the force on it is highest when closest to a star as for tether proportion also called momentum exchange tether this comes in a variety of forms but two channel regulars will be familiar with already are the classic space elevator and its a bridged cousin the Skyhook also known as a rotor Vader you may see those episodes for a deeper dive of those approaches but one that folks tend not to think of is connecting a tether to a spaceship from a space station or asteroid and using that to winch them in or slingshot them out in a much more traditional sense of that term than the slingshot maneuver uses if you're wondering how this uses gravity it's working with that in combination with a tether to allow some trajectory changes you could normally do with just gravity or at least not without burning a lot of fuel you could basically fall toward a planet or other Celestial body get harpooned with a tether or Harpoon it with a tether and use that in the fall to swing onto A New Path and with additional speed no special new Sciences involved here other than that very strong tensile materials and very good co Nation help but on to the topic of things involving new science or reasonably new science I was talking about using black hes a bit ago and very dense objects like black and neutron stars are great for slingshots and the oth effect but they also rotate very fast your typical porar or neutron star doesn't take a day to spin like Earth does or more like a month for our son but a second or even less mere milliseconds black cores are even denser and faster and both objects can create significant frame dragging frame dragging also known as the lens thuring effect is predicted by general relativity and we have confirmed it even around Earth itself where it is far or less in general relativity a massive object distorts the fabric of SpaceTime if the object is rotating it doesn't just distort SpaceTime it also drags it along in the direction of its rotation near a rap rapidly rotating Mass SpaceTime itself is Twisted in the direction of the rotation this means that objects in close proximity to the rotating Mass experience a dragging effect where their paths are slightly shifted due to this twisting of SpaceTime you could potentially surf along this to gain some speed as an additional option for ships moving near large bodies like slingshots in the aroth effect it would just stack up with those two to get you even more free speed stolen GR ically from the larger body or dumped into it to slow a ship instead but like those this depends on timely maneu taking you to objects not a novel form of spaceship Drive we've talked about creating micro black holes for proportion before usually by Hawking radiation or feeding matter into a black hole for high energy emissions exceeding what nuclear fusion could produce however if a spacecraft could generate a miniature rotating Mass with sufficient density and speed it might be able to create a localized frame dragging effect this generated effect could potentially be used to provide thrust by twisting SpaceTime around the spacecraft itself this is the basic notion behind theoretical drives like the bias diametric disjunction and Pitch drives which are more Concepts than a specific engine in this case what frame draging can be thought of as doing is making it so gravity is stronger in one direction of your ship than another so you're basically going to follow that direction we'll give some specifics on that in a moment like how negative matter might serve as a gravity drive but before I detail that a neat thing about gravity drives is that they are working on everything in a ship equally borrowing tital effects and thus allow safe high G acceleration normally when we accelerate an object the various bits of it are not experiencing identical Force at the same levels and instance this causes a lot of stress on bodies and ships that a gravitational field does not so a lot of our normal limits on acceleration rates go away with gravitic proportion if you're falling in a 100g gravity field near some dense body you're fine whereas a person on a 100g rocket sled is going to die and a ship that suddenly slams at 10g to the side to dodge some piece of space debris is going to injure or kill its crew as someone who was walking down a corridor might suddenly slam a meter to the the side at 10g or 14 m/s 31 mph that's the equivalent of falling 10 m on Earth or 33 ft that could also just as easily be falling up a couple meters onto your head or the equivalent of dropping 20 M or 66 ft and Landing head first you wouldn't have that with a ship accelerating in a gravitational field unless it was so sharp and narrow we had the kind of effects we experienced near black holes where gravity on your feet is significantly higher than on your head and rips you apart gravity pulls on everything equally and is stopped and slowed by nothing we know of it's not a force we can block like we might an electromagnetic field if we could that would be a path to anti-gravity or even gravity beams or waves or gravity lasers you float off a planet because your gravity reflecting paint on your ship pushes you away from gravity or prevents it affect continue and this was the method used in HG Well's 1901 sci-fi novel The forced Men in the Moon where the substance called cavorite negates gravity and such a material or field you could produce opens the doors to the classic Flying Saucer ignoring gravity or to neat gravity ignoring suspensor fields that let you move heavy objects with ease or fly around in the sky without wings or even build Citadel floating in the sky again we'll cover that that more in our gravity Tech episode a material like Cavite would be problematic in our universe since it would flat out permit you to violate conservation of energy but we've known that's had some exception since nearly when the book was written as conservation of energy has some issues with things like general relativity Hubble expansion dark energy and of course the big bang itself so we should not take for granted that conservation of energy rigidly prevents workarounds the long of physics may be inviable but if there are loopholes we could exploit there's no sign of an intelligent policing agency in forcing obedience it says that something like cite also allows perpetual motion machines which is itself a way to run a spaceship drive and thus would be a type of gravitic propulsion too there's a lot of ways some piece of clock Tech hyper Advanced borderline magical technology could allow us to move ships or generate power but there are some general approaches that we should highlight the first is the bias Drive which is an example of a clock tech engine that works not by warping space or time but by locally altering physical constants of the universe in this case the gravitational constant in front of and behind the ship letting essentially fall to its destination gravity becomes inherently stronger from One Direction by altering that constant to be bigger like the ones covering the electromagnetic force are this might involve something weak like finding a parallel universe that had a higher gravitational constant and sliding toward or into it or skimming or skipping along it in the case of warping SpaceTime itself this can provide normal proportion and potentially even faster than light proportion or time travel but see our warping reality episode for discussion of warp drives in detail beyond having no method to alter physical constants at this time it is likely that a bias drive would produce a singularity in the center of the ship if functional however such a ship would not need to expend any fuel to move from point A to B and a bias drive would appear to allow perpetual motion machines for producing electricity and power though it is entirely possible that techniques for changing physical constants might still conserve quantities such as energy and momentum we also have its cousin the diametric drive another hypothetical clock Tech reactionist Drive but one typically in visioned as running on negative mass and it is actually a subcategory of pitch drives which we'll get into in a bit the basic notion here is that you build a ship stretchy between two big globes one of positive regular matter and one of negative matter the former might be where all your people and cargo were at and it does not have to be of the same mass or rather opposite mass as the negative Mass section in the most commonly discussed version it is generally assumed that posit postive mass will attract both positive and negative mass and negative Mass particles would repel both positive and negative masses as a result two positive Mass particles will pull toward each other two negative Mass particles repel each other and a positive and negative Mass particle will actually shove the positive Mass away from the negative Mass while pulling the negative Mass toward the positive Mass resulting in the positive Mass particle being chased by the negative one so a ship running on this a type of diametric Drive will begin Falling Towards positive Mass globe on the front of the ship you could flip over to slow down or more likely just have several of the Globes positive and negative as packets you could pump around the ship like a fluid and rotate or stop the ship as needed by adjusting the distribution of that negative Mass your ship might be a ring or Taurus instead of a barbell now negative Mass proportion is a catchall term for any drive that iies on the properties of negative Mass generally how negative mass or energy should warp space to expand around it opposite of normal matter Contracting space around it or be pushed toward you if you shove on it not away as no negative Mass has ever been detected any negative Mass technology currently qualifies as clock Tech and this includes most warp drive and warhole proposals there are multiple versions of how negative Mass should operate depending on if it is negative inertial mass or gravitational Mass active or passive or some combination thereof Mass's thoughts are really be three different items that presumably all linked at some core level but which we might be able to tweak separately for movement so inertial mass is how things respond to force shovey on them to speed or slow them Force equals mass time acceleration and mass here is inertial mass if I could temporarily lower some means inertial Mass it would be easier to push momentum is masstimes velocity and again this is inertial mass here and due to conservation of momentum if we lowered something's inertial Mass temporarily then it would speed up and if we increased it it would slow down with no use of fuel either way this would be neat since a ship with an En noal Mass modulator would be able to use fuel to speed itself up get clear of orbital space on its in noal Mass reducer and suddenly leap up to speed it could then flip it on near an object it wanted to study and turn it higher to instantly slow down and presumably like with gravity drives slow everything uniformly so the crew didn't smear on the walls of the ship this was seem to massively violate conservation of energy too but maybe it's robbing it from something else and indeed it would be awesome to use in conjunction with the oorth effect but that is Enos man active and passive gravitational Mass active is how strong an object pours on others with gravity as based on its mass or its active gravitational Mass if the three can be separated while passive is how things respond to gravity if I can dial up a ship's passive gravitational Mass it will accelerate faster as it falls towards some bigger object then like with the timing and using the ooth effect I can switch it low as we pass that object and it begins trying to pull us backwards but with weakened effect active gravitational Mass alterations could let us generate a tractor beam to pull toward objects or pull them to us and indeed you might be able to make a gravity laser at that point to concentrate it at a great distance to yank on somebody and pull yourself toward it or it toward you or for bases to shove ships away to launch out of a gravitic cannon so to speak possibly a device more worthy than Mass driver than the one we usually discuss in that rule see Mass drivers for details if we can manipulate these or make gravity lasers we must consider that we may be able to generate gravity without mass at all and this is the concept behind the disjunction drive that the field might be destroyed from the object that created it in this case gravity and mass but it could be one of the other forces conceptually we might imagine a ship built near a large gravity well which was then disjoined from the mass gradient and potentially reattached the front of the ship so it constantly fell forward we might also disjoin something's anal Mass while leaving its gravitic mass in place or disjoin electrostatic or magnetic field from their generator this could also be a disjunction from a higs ban field needless to say if I can lower or raise something's mass in one or all of those three rows it may be possible to lower to 0 or even below zero which takes us back to negative mass or negative energy proportion and again we don't have any negative matter I personally doubt it exists so we can't be sure of its properties the pitch Drive is a hypothetical clock Tech reactionless Drive where a FAL force can be used to create an effective pressure difference on the ship to push it along diametric drives are a subcategory of pitch drives where there is a s for the force like a ball of negative Mass pitch drives in a wider sense do not require a source and would include technologies that simply cause some force or pressure difference to appear on your ship it may work on any field or Force which can be used to create an effective pressure difference on the ship to push it along much as an air foil in the atmosphere works and gravity drives don't need to be limited to spaceships either conceptually you might imagine that on one side of your propeller gravity is 10% lower and on the other side 10% higher so that as they spin the falling side fures more gravity while the other gets less and now it can spin without needing any fuel or motor it just spins under Gravity propelling your ship through an atmosphere this blatantly violates conservation of energy but again not all concern at the moment of course the dark energy that drives expansion of our universe which itself seems have gotten energy from nowhere to begin with seems to violate conservation of energy that's debatable and we looked at those arguments in our Dark Energy episode but what's undeniable is that galaxies are moving apart and that the further you are away the greater your speed we assume that this is because new bits of space time are randomly popping up everywhere all the time and that as a result over long distances predictable amounts of new space emerg between objects causing them to be further apart over time which is speed a growing distance over time this is not limited to the speed of light either if we could control or manipulate that we could put space directly in front of us or perhaps remove it SpaceTime costs actual energy to exist so adding new bits means energy went in there and if you could eat some up in front of you your distance would shrink and give you energy as you gobbled it up presumably some of the kins that the buus ram scoop which drags in hydrogen particles along your journey through Interstellar space and fuses them for energy to run our ship and its engines only here it's gobbly up SpaceTime there's only about one Jewel of energy per cubic kilometer of space which is really tiny but there is a lot of space and more of it emerging constantly so a ship that want to generate a 100 m radius cylinder of space behind it would only need one Jewel for 53 km of new space layer and this is the kind of space-time warping that gets around light speed so a 100 megawatt fion reactor powering some rotating habitat spaceship 100 m in radius and however long could in theory be traveling at 52 billion kilm per second or 17,6 66 times the speed of light which would mean the trip to Alpha centuri would take just over 2 hours it's a bit over 2 light years per hour or a bit under 50 light years day you could get to the Andromeda galaxy in a little over a century and to any corner of ours including the melanic clouds in under a decade that was a pretty arbitrary power supply in radius too but we can of course build 100 megawatt reactors and a ship of that size now Dark Energy isn't exactly gravity proportion but there's a Strange Relation there with one only being attractive and the other only repulsive and both being incredibly weak but dominating the universe in their ranges because the other forces all have attractive and repulsive versions they negate out much beyond the molecular scale even what we think of as powerful magnetic or electric Fields represents only a very tiny bias where almost everything else is balanced beyond that gravity dominates and is all attractive and beyond that dark energy does and both are tied into space time at a fundamental level apparently unlike the other stronger forces they may be unrelated but it felt like a good place to wrap up our discussion of gravitic propulsion with an FTR version and some hard numbers and calculations I doubt you could just make a cylinder of space like that more likely you'd have some more energy intensive cone but it's all hypothetical anyway sadly that is still true for most of our gravitic spaceship proportion options though as we saw today gravity is already a valuable tool for portion even now what's more gravity is still such a mystery that I'm more optimistic that as our understanding of it grows that doors to new novel and awesome proportion will open up for us to fall through to Strange New worlds we never know what awesome new text might help us in the future like the gravity drives we looked at today but in the meantime there's a lot of work to be done Paving our way to other worlds and helping with this world's problems many folks would like to help make a positive impact on the world and using your job to do that is a great approach after all you have 80,000 hours in your career that's 40 hours a week 50 weeks a year for 40 years it's a lot of time to make a difference but how do you find that job that really will make a difference and is right for you that's where 80,000 hours a nonprofit comes in they spent over a decade conducting research partnering with academics at Oxford University to figure out how you can have a fulfilling career while tackling some of the world's most pressing problems they provide all of that for free solid datadriven guidance and advice to help you help everyone else whether you're just starting your career thinking about switching past or just want to make a bigger difference where you are now 80,000 hours can help they are for tools like a free in-depth career guide to help you create a personalized plan a job board with hundreds of high impact rules a podcast featuring deep conversations with experts about solving Global challenges even an episode on solving the firmy Paradox if you join the newsletter now you'll get a free copy of their in-depth research-led career guide sent to your inbox just sign up at 8000 hour.org arthor Stop settling for generic career advice and platitudes get started planning a career that works on one of the world's most pressing problems sign up now at at 8000 hour.org ISAC arthor as a quick side note before we get to our upcoming schedule of episodes this episode airs on December 15th which is my mom Jean's 75th birthday and I want to thank her for amongst many other things giving me that early interest in both science and science fiction without both of which there wouldn't be this show speaking of the show we've got plenty more episodes still for this year starting Thursday with an extended and updated discussion of space elevators after that we'll be returning to the fmy Paradox to ask what very high-tech and autonomous civilizations might be like in the hermit shoplifter hypothesis then we'll wrap up 2024 with some predictions for the future as well as some discussion of how to make decent predictions if you'd like to get alerts when those and other episodes come out make sure to hit the like subscribe and notification buttons you also hope support the show by becoming a member here on YouTube or at patreon or check out other ways to help at Isaac arthor . net until next time thanks for watching and have a 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