WEBVTT 1 00:00:03.439 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.839 --> 00:00:31.039 Okay, let's unpack this. When you think about space travel, 8 00:00:31.440 --> 00:00:33.439 what's the first image that comes to mind. 9 00:00:33.399 --> 00:00:36.039 For most people? I bet it's that classic rocket line. 10 00:00:36.039 --> 00:00:41.079 Exactly, fire, smoke, this enormous vehicle just fighting its way 11 00:00:41.119 --> 00:00:43.960 off the planet. Maybe you know a Soyuz lifting off 12 00:00:43.960 --> 00:00:44.640 from Bacon Ore. 13 00:00:44.759 --> 00:00:47.159 It's an incredible sight, no doubt powerful. 14 00:00:46.880 --> 00:00:50.240 Definitely powerful. But that image, that very picture of a 15 00:00:50.359 --> 00:00:55.439 rocket launch, it actually highlights this this huge fundamental problem, 16 00:00:55.479 --> 00:00:58.560 a challenge that's really held back our bigger dreams for 17 00:00:58.640 --> 00:01:02.039 exploring deep space or well over a century now. 18 00:01:02.079 --> 00:01:06.040 It really has because despite all our advanced engineering, rockets 19 00:01:06.040 --> 00:01:07.920 still work on a pretty simple. 20 00:01:07.599 --> 00:01:09.200 Principle Judent's third law. 21 00:01:09.200 --> 00:01:11.599 That's the one for every action, there's an equal and 22 00:01:11.680 --> 00:01:15.400 opposite reaction. You burn fuel, throw that mass backwards. Really fast, and. 23 00:01:15.359 --> 00:01:19.239 The reaction pushes the rocket forwards. Simple physics, simple. 24 00:01:19.079 --> 00:01:22.359 But brutal and inescapable really. 25 00:01:22.200 --> 00:01:23.879 And needing to throw a mass away like that. That 26 00:01:24.000 --> 00:01:27.400 leads straight to the big mathematical hurdle, the one constantin 27 00:01:27.519 --> 00:01:30.239 Siolkowski figured out way back in nineteen oh three. 28 00:01:30.439 --> 00:01:32.480 Ah, Yes, the famous rocket equation. 29 00:01:32.840 --> 00:01:36.280 It basically spells out this limit the mass ratio problem. 30 00:01:36.480 --> 00:01:38.239 And people call it a tyranny for a reason. 31 00:01:38.400 --> 00:01:41.159 It absolutely is a tyranny. It traps us in this well, 32 00:01:41.200 --> 00:01:44.439 this vicious cycle. See the fuel you need to speed 33 00:01:44.519 --> 00:01:48.120 up your spacecraft. It's heavy, really heavy. 34 00:01:47.920 --> 00:01:49.760 And you have to carry that fuel on the rocket. 35 00:01:49.599 --> 00:01:51.719 Which means you need more fuel just to lift the 36 00:01:51.760 --> 00:01:52.840 first batch of fuel. 37 00:01:53.000 --> 00:01:57.040 It gets exponential, right, Skiolkowski's equation just lays it bare 38 00:01:57.840 --> 00:02:01.359 that desired speed change engineers call it to v It 39 00:02:01.400 --> 00:02:04.359 depends exponentially on how much of your rocket is fuel 40 00:02:04.560 --> 00:02:06.000 versus payload. 41 00:02:05.599 --> 00:02:08.840 And exponential here is well, that's punishing. 42 00:02:09.000 --> 00:02:10.400 Maybe give us a sense of that. Like, if you 43 00:02:10.439 --> 00:02:13.039 want to double your speed leaving Earth orbit. 44 00:02:12.919 --> 00:02:15.520 Yeah, good point. Doubling your speed might mean you need 45 00:02:15.599 --> 00:02:18.520 say five times the fuel, not just twice as much, 46 00:02:18.560 --> 00:02:21.520 maybe even more Wow. And for really ambitious stuff deep 47 00:02:21.520 --> 00:02:24.479 space or you know, a big dream interstellar travel, you 48 00:02:24.520 --> 00:02:25.599 need huge delta V. 49 00:02:25.840 --> 00:02:28.479 So the amount of fuel you need just skyrockets. 50 00:02:27.840 --> 00:02:30.639 Exactly the mass fraction, the percentage of your rocket that's 51 00:02:30.680 --> 00:02:33.479 just propelling it gets closer and closer to one hundred percent. 52 00:02:33.439 --> 00:02:36.560 Like ninety nine percent fuel, one percent. 53 00:02:36.199 --> 00:02:38.599 Space ship, or even ninety nine point nine to nine 54 00:02:38.639 --> 00:02:42.800 percent fuel. You're basically launching fuel to launch fuel to 55 00:02:42.879 --> 00:02:46.439 launch fuel. It makes high speed interstellar travels seem well, 56 00:02:46.520 --> 00:02:50.240 not just hard, but almost physically impossible. With chemical rockets, 57 00:02:50.280 --> 00:02:51.879 we just can't carry enough energy that way. 58 00:02:51.960 --> 00:02:54.800 Okay, So that sets up our mission for this deep dive. 59 00:02:54.840 --> 00:02:57.800 Then the sources you've looked at, they're all about breaking 60 00:02:57.800 --> 00:02:58.719 that cycle, aren't they. 61 00:02:58.800 --> 00:03:01.840 Precisely the big much in driving this is what if 62 00:03:02.000 --> 00:03:06.120 spacecraft didn't have to carry their propellant, What if they 63 00:03:06.120 --> 00:03:09.319 could just leave the fuel behind, find another way, find 64 00:03:09.360 --> 00:03:12.599 another way. And that's exactly what's explored in this really 65 00:03:12.680 --> 00:03:15.319 comprehensive new review. It popped up on the arcs of 66 00:03:15.560 --> 00:03:19.560 Preprint Server by Roma Nya, kezerashphili. 67 00:03:18.879 --> 00:03:20.639 Arxif right, the Physics preprint place. 68 00:03:20.800 --> 00:03:23.560 Yeah, and this review looks carefully at different ways to 69 00:03:23.560 --> 00:03:26.599 get propellent less propulsion, so systems that don't burn on 70 00:03:26.719 --> 00:03:30.439 board masks, but instead tap into forces and energy that 71 00:03:30.479 --> 00:03:31.879 are already out there in space. 72 00:03:31.960 --> 00:03:33.719 We're not just talking about making rockets a bit more 73 00:03:33.719 --> 00:03:34.479 efficient here. 74 00:03:34.360 --> 00:03:35.879 No, no, not at all. This is a whole different 75 00:03:35.919 --> 00:03:37.759 way of thinking, a paradigm shift, really. 76 00:03:37.840 --> 00:03:39.800 So the big takeaway right up front, the. 77 00:03:39.759 --> 00:03:42.800 Crucial point from the review is that these propellantless methods, 78 00:03:42.840 --> 00:03:46.159 they aren't just improvements. They could actually enable missions that 79 00:03:46.199 --> 00:03:49.879 are completely impossible right now with conventional rockets. 80 00:03:49.599 --> 00:03:52.080 Especially if you want to go far, like really far 81 00:03:52.639 --> 00:03:53.719 beyond Pluto, kind. 82 00:03:53.639 --> 00:03:57.120 Of far exactly. Getting rid of that need for propellant 83 00:03:57.280 --> 00:04:01.719 escaping the mass trap, it changes everything, mission design, what's feasible, 84 00:04:02.439 --> 00:04:03.039 the whole game. 85 00:04:03.240 --> 00:04:05.719 Right, So where do we start. There's one method that's 86 00:04:05.719 --> 00:04:08.360 actually been used for quite a while, hasn't it? Less 87 00:04:08.400 --> 00:04:10.120 future tech, more clever maneuvering. 88 00:04:10.319 --> 00:04:14.039 That's right, the gravity assist. It's probably the simplest propellantless 89 00:04:14.039 --> 00:04:17.680 technique and it's got a proven track record going back decades. 90 00:04:17.800 --> 00:04:20.079 We could call it maybe the easiest theft. 91 00:04:20.079 --> 00:04:22.480 Huh, I like that a theft of momentum. 92 00:04:22.519 --> 00:04:25.800 Conceptually, yeah, that's pretty much it. It's elegant. Really. You 93 00:04:25.920 --> 00:04:29.360 time a spacecraft's flight path very very carefully, so it 94 00:04:29.439 --> 00:04:33.519 swings close by a big planet like Jupiter or Venus. 95 00:04:33.240 --> 00:04:36.199 You fly past it on a specific path, a hyperbolic trajectory, 96 00:04:36.199 --> 00:04:37.759 I think is called correct. 97 00:04:37.759 --> 00:04:40.560 And as it swings by, the spacecraft and the planet 98 00:04:40.720 --> 00:04:43.720 exchange a bit of momentum. The planet has so much 99 00:04:43.800 --> 00:04:45.079 momentum it barely. 100 00:04:44.839 --> 00:04:47.199 Notices but for the tiny spacecraft. 101 00:04:47.240 --> 00:04:50.759 For the spacecraft, it's huge. It effectively steals a tiny 102 00:04:50.879 --> 00:04:54.199 fraction of the planet's orbital momentum, and that translates into 103 00:04:54.319 --> 00:04:58.160 a significant speed boost for the probe, completely free in 104 00:04:58.240 --> 00:04:59.000 terms of fuel. 105 00:04:59.160 --> 00:05:02.319 It's like a cosmic sling shot conservation of energy, doing. 106 00:05:02.120 --> 00:05:05.560 The work exactly. And the textbook example, the one everyone 107 00:05:05.600 --> 00:05:07.839 points to, has to be the Voyager Probes. 108 00:05:07.680 --> 00:05:10.800 AH Voyager one and two. The Grand Tour. 109 00:05:10.959 --> 00:05:13.639 The Grand Tour, Yeah, launched back in the late seventies. 110 00:05:13.639 --> 00:05:16.600 They took advantage of this really rare alignment of the outer. 111 00:05:16.399 --> 00:05:21.759 Planets Jupiter, Saturn, Uranus, Neptune, the visit at all four didn't. 112 00:05:21.759 --> 00:05:24.680 They did, using one gravity assist after another to hop 113 00:05:24.720 --> 00:05:27.519 from planet to planet, getting boosts along the way, and 114 00:05:27.519 --> 00:05:27.879 doing that. 115 00:05:27.839 --> 00:05:31.639 With chemical rockets alone, carrying enough fuel impossible. 116 00:05:31.240 --> 00:05:33.399 Just completely impossible. The amount of fuel needed would have 117 00:05:33.439 --> 00:05:37.240 been astronomical. Voyager is just the stunning example of how 118 00:05:37.279 --> 00:05:39.000 powerful orbital mechanics can be. 119 00:05:39.439 --> 00:05:42.959 It really is brilliant, a testament to clever engineering and physics. 120 00:05:43.720 --> 00:05:47.959 But there's always a butt, isn't there. The review mentions 121 00:05:48.000 --> 00:05:48.759 the trade offs. 122 00:05:49.079 --> 00:05:52.720 There are always trade offs. Gravity assists work, We've mastered 123 00:05:52.759 --> 00:05:56.720 the technique, but they have some pretty big practical limitations. 124 00:05:57.040 --> 00:05:59.160 You can't just decide to do one whenever you feel 125 00:05:59.199 --> 00:05:59.439 like it. 126 00:05:59.480 --> 00:06:03.439 No apps not, That's the main constraint. You are completely 127 00:06:03.480 --> 00:06:05.839 dependent on the planets being in the right place at 128 00:06:05.839 --> 00:06:06.639 the right time. 129 00:06:06.600 --> 00:06:08.920 Relative to each other and relative to where you want. 130 00:06:08.759 --> 00:06:12.800 To go exactly. These alignments are where the Voyager opportunity, 131 00:06:12.839 --> 00:06:15.399 for instance, only comes around once every one hundred and 132 00:06:15.439 --> 00:06:16.759 seventy six years. 133 00:06:17.079 --> 00:06:19.680 Wow. So mission planners aren't just looking at next Tuesday. 134 00:06:19.720 --> 00:06:23.279 They're looking decades ahead mapping planetary positions. 135 00:06:23.360 --> 00:06:25.279 They use these things called pork chop plots. 136 00:06:25.800 --> 00:06:27.279 Pork chop plots. 137 00:06:26.959 --> 00:06:30.680 Serious, seriously, they're graphs that show the possible launch windows 138 00:06:30.720 --> 00:06:34.160 flight times and energy needed. They basically highlight how you 139 00:06:34.199 --> 00:06:36.920 only get these narrow windows maybe a few weeks every 140 00:06:37.000 --> 00:06:39.680 few years or even decades to launch if you want 141 00:06:39.680 --> 00:06:42.000 to use a specific gravity assist. 142 00:06:41.639 --> 00:06:45.160 Path, so very limited opportunities, and the path. 143 00:06:44.920 --> 00:06:49.160 Itself it's totally inflexible. Once you launch, you're locked into 144 00:06:49.199 --> 00:06:53.639 that trajectory. It's dictated by celestial mechanics, by the cosmic clock, 145 00:06:54.160 --> 00:06:56.759 not by where you might want to go explore next week. 146 00:06:57.120 --> 00:07:01.360 So great for preplan tours, but not for flexible on 147 00:07:01.439 --> 00:07:05.759 demand exploration. If you need continuous thrust or the ability 148 00:07:05.800 --> 00:07:07.360 to change course easily. 149 00:07:07.040 --> 00:07:09.399 You need something else. You need to look beyond planets 150 00:07:09.439 --> 00:07:12.040 and start tapping into the energy sources that are always 151 00:07:12.040 --> 00:07:12.759 there in space. 152 00:07:13.000 --> 00:07:15.560 Okay, which takes us to the next step, moving away 153 00:07:15.560 --> 00:07:19.079 from these occasional gravitational boosts towards something more constant. And 154 00:07:19.120 --> 00:07:21.079 this is where I think you said it gets really interesting, 155 00:07:21.439 --> 00:07:23.519 harnessing sunlight itself. 156 00:07:23.199 --> 00:07:28.800 Exactly solar sales. This shifts the concept from borrowing momentum 157 00:07:28.839 --> 00:07:31.560 from a planet to catching momentum from the most abundant 158 00:07:31.639 --> 00:07:33.600 energy source in the Solar system. 159 00:07:33.639 --> 00:07:37.399 Sunlight solar pressure. Now I know some listeners might hear 160 00:07:37.480 --> 00:07:39.720 solar sale and think of old sci fi. Is the 161 00:07:39.759 --> 00:07:43.240 physics really solid here? How can light push something if 162 00:07:43.279 --> 00:07:44.800 photons don't have mass? 163 00:07:45.199 --> 00:07:48.480 It's fundamental physics. Actually, photons, the particles of light, might 164 00:07:48.560 --> 00:07:51.720 have zero rest mass, but they definitely carry momentum. So 165 00:07:51.959 --> 00:07:55.319 when photons hit something, they transfer that momentum. If they 166 00:07:55.319 --> 00:07:58.800 get absorbed, they transfer some, But if they get reflected, 167 00:07:58.839 --> 00:08:00.720 which is what a shiny sale is designed to do, 168 00:08:01.279 --> 00:08:04.240 they transfer about twice the momentum, like bouncing a ball 169 00:08:04.279 --> 00:08:04.879 off a wall. 170 00:08:05.079 --> 00:08:07.240 Ah. Okay, so the sails like a giant mirror. 171 00:08:07.360 --> 00:08:12.079 Essentially, yes, a huge, incredibly thin reflective membrane. It catches 172 00:08:12.120 --> 00:08:15.000 the momentum from countless photons hitting it, But the. 173 00:08:15.000 --> 00:08:18.519 Push from a single photon must be minuscule. 174 00:08:18.040 --> 00:08:22.480 Oh, absolutely tiny, infantesimal. But the sun is always shining, 175 00:08:22.560 --> 00:08:25.519 so that tiny push is constant. It's there two entred 176 00:08:25.519 --> 00:08:26.839 and forty seven week after week. 177 00:08:26.759 --> 00:08:29.959 Year after year, and over time, that constant, gentle push 178 00:08:30.079 --> 00:08:30.560 adds up. 179 00:08:30.680 --> 00:08:33.399 It adds up, It builds velocity, gradually, slowly at first, 180 00:08:33.480 --> 00:08:36.600 but persistently, And the most beautiful part, it uses zero 181 00:08:36.679 --> 00:08:38.399 fuel once it's deployed. Zero. 182 00:08:38.720 --> 00:08:42.360 That dream became reality thanks to Japan Space Agency JAXA. 183 00:08:42.559 --> 00:08:45.480 Right yes, with the Ikros probe. That was a fantastic 184 00:08:45.559 --> 00:08:47.799 mission back in twenty ten, a real game changer. 185 00:08:47.919 --> 00:08:48.440 What did it do? 186 00:08:48.720 --> 00:08:52.360 JAXA successfully deployed the square sale in space, controlled it 187 00:08:52.559 --> 00:08:54.600 and used it to fly the probe all the way 188 00:08:54.639 --> 00:08:56.360 to Venus, powered only by sunlight. 189 00:08:56.399 --> 00:08:59.120 Wow, just push by light, just push by light. 190 00:08:59.399 --> 00:09:01.639 It proved the works in the real world, not just 191 00:09:01.720 --> 00:09:03.440 on paper or in in computer models. 192 00:09:03.480 --> 00:09:07.600 Okay, so proof of concept check. But the review it 193 00:09:07.639 --> 00:09:15.519 really digs into the challenges the downsides. The engineering side sounds. 194 00:09:13.519 --> 00:09:18.120 Delicate, extremely delicate. Material science is the huge bottleneck here. 195 00:09:18.759 --> 00:09:20.960 For a solar sale to be effective, it needs to 196 00:09:20.960 --> 00:09:24.440 be incredibly light, but also incredibly large. We talk about 197 00:09:24.480 --> 00:09:27.480 aerial density, the mass per square meter. 198 00:09:27.639 --> 00:09:29.919 You want that number to be tiny, as low as possible. 199 00:09:29.960 --> 00:09:32.960 We're talking materials that are almost like smoke gossamer thin, 200 00:09:33.200 --> 00:09:35.600 maybe just a few milligrams per square meter, but the 201 00:09:35.679 --> 00:09:39.159 sale itself needs to be vast. Think multiple football fields 202 00:09:39.159 --> 00:09:39.960 in area. 203 00:09:40.120 --> 00:09:43.519 So imagine trying to unfold something thinner than kitchen plastic 204 00:09:43.559 --> 00:09:48.679 wrap but kilometers across in space without ripping it exactly. 205 00:09:48.720 --> 00:09:52.159 And then you have to keep it tensioned, stable, pointed correctly. 206 00:09:52.639 --> 00:09:54.159 It's an engineer's nightmak. 207 00:09:53.879 --> 00:09:55.240 What are these materials? Usually made of. 208 00:09:55.320 --> 00:09:58.840 Specialized plastics, often polymers like CP one or types of 209 00:09:58.919 --> 00:10:02.600 polymide film coated with a thin layer of aluminum for reflectivity. 210 00:10:02.919 --> 00:10:05.080 But they also have to be incredibly tough. 211 00:10:04.919 --> 00:10:06.840 Tough against what space is empty, right. 212 00:10:06.840 --> 00:10:10.879 Not quite empty enough. They have to survive years, maybe decades, 213 00:10:11.200 --> 00:10:15.279 bathed in intense ultraviolet radiation from the Sun, which degrades 214 00:10:15.320 --> 00:10:22.679 materials over time. Plus there's constant bombardment by tiny dust particles, micrometeoroids. 215 00:10:21.960 --> 00:10:25.480 H space dust. Even a tiny speck hitting that thin 216 00:10:25.559 --> 00:10:26.799 film at high speed. 217 00:10:26.600 --> 00:10:30.039 Could potentially cause a tear, and enough small tiers could 218 00:10:30.039 --> 00:10:33.519 affect the sale's structure, its tension, its ability to generate 219 00:10:33.559 --> 00:10:34.480 thrust efficiently. 220 00:10:34.720 --> 00:10:38.000 Okay, so materials and deployment are hard, Yeah, but there's 221 00:10:38.039 --> 00:10:41.759 a more fundamental physics limitation too, right, tied to distance. 222 00:10:41.919 --> 00:10:44.519 Yes, And this is a big one sunlight and therefore 223 00:10:44.559 --> 00:10:48.879 the radiation pressure it creates follows the inverse square law, meaning. 224 00:10:48.639 --> 00:10:50.679 The further you get from the Sun, the weaker the push. 225 00:10:50.799 --> 00:10:53.639 Dramatically weaker. The forest drops off with the square of 226 00:10:53.639 --> 00:10:56.159 the distance. So if you go from Earth's distance one 227 00:10:56.200 --> 00:10:59.720 astronomical unit or AU out to Jupiter, which is about 228 00:10:59.720 --> 00:11:01.080 five away. 229 00:11:00.879 --> 00:11:02.639 The force isn't five times weaker. 230 00:11:02.360 --> 00:11:05.639 It's twenty five times weaker five square oach. 231 00:11:05.759 --> 00:11:08.000 That's a massive drop in acceleration. 232 00:11:07.840 --> 00:11:10.840 It really is. It makes solar sales potentially great permissions 233 00:11:10.840 --> 00:11:13.960 inside the orbit of Mars, maybe out to the asteroid belt, 234 00:11:14.720 --> 00:11:18.679 but for deep space, going out past Jupiter to Saturn, Uranus, 235 00:11:18.759 --> 00:11:20.240 Neptune or beyond. 236 00:11:19.919 --> 00:11:22.559 The push becomes almost nothing, pretty much negligible. 237 00:11:22.600 --> 00:11:25.759 Your acceleration just fades away. So for exploring the outer 238 00:11:25.799 --> 00:11:29.559 Solar System or heading towards the stars, solar cells alone 239 00:11:29.879 --> 00:11:31.080 probably aren't the answer. 240 00:11:31.279 --> 00:11:33.759 Okay, So if sunlight pressure gets too weak out there, 241 00:11:34.519 --> 00:11:37.200 what else is constantly flowing outwards from the Sun that 242 00:11:37.200 --> 00:11:38.399 we could potentially push. 243 00:11:38.159 --> 00:11:40.240 Against that leads us to the solar wind? 244 00:11:40.440 --> 00:11:43.720 Uh, not light pressure, but actual particles exactly. 245 00:11:44.080 --> 00:11:48.480 The solar wind is this continuous supersonic stream of charged 246 00:11:48.559 --> 00:11:52.440 particles plasma mostly protons and electrons, that flows out from 247 00:11:52.480 --> 00:11:55.679 the Sun all the time, and crucially, it carries significant 248 00:11:55.679 --> 00:11:58.720 momentum and keeps a decent density much further out than 249 00:11:58.759 --> 00:11:59.720 where sunlight pressure. 250 00:11:59.759 --> 00:12:02.000 Because okay, so if we can push against that, maybe 251 00:12:02.039 --> 00:12:04.320 we can get thrust further out. Yeah, this brings us 252 00:12:04.320 --> 00:12:05.639 to magnetic sales. 253 00:12:06.679 --> 00:12:10.399 Mag sales, correct magnetic sales. It's a totally different concept 254 00:12:10.440 --> 00:12:11.799 from reflecting. 255 00:12:11.320 --> 00:12:13.960 Light because there's no physical sail, right, you can't reflect 256 00:12:14.039 --> 00:12:16.240 charged particles with a sheet of plastic right. 257 00:12:16.639 --> 00:12:20.200 Instead of a physical membrane, a mag sail uses loops 258 00:12:20.240 --> 00:12:25.639 of superconducting wire to generate a really powerful, large magnetic field, 259 00:12:25.919 --> 00:12:28.120 an artificial magnetosphere, essentially like. 260 00:12:28.120 --> 00:12:31.320 Earth's magnetic field, but generated by the spacecraft sort of. 261 00:12:31.440 --> 00:12:34.639 Yes, And when the charged particles of the solar wind 262 00:12:34.720 --> 00:12:36.399 hit this magnetic field. 263 00:12:36.120 --> 00:12:38.840 They get deflected like how Earth's field deflects the solar 264 00:12:38.840 --> 00:12:39.720 wind exactly. 265 00:12:40.120 --> 00:12:44.080 That magnetic field pushes the plasma particles aside, and by 266 00:12:44.159 --> 00:12:47.799 Newton's third law again, pushing the solar wind plasma away 267 00:12:48.279 --> 00:12:51.840 pushes the spacecraft forward. You're essentially sailing on the solar 268 00:12:51.879 --> 00:12:53.399 wind using a magnetic bubble. 269 00:12:53.519 --> 00:12:56.639 That sounds incredibly cool, and it avoids the whole problem 270 00:12:56.679 --> 00:13:00.679 of deploying and maintaining huge, fragile sheets of material. 271 00:13:00.919 --> 00:13:04.600 That's a major theoretical advantage. Yes, No, worries about UV 272 00:13:04.759 --> 00:13:08.600 degradation or micrometeoroid tears on a physical sale. 273 00:13:08.279 --> 00:13:10.440 And because the solar wind doesn't drop off as quickly 274 00:13:10.480 --> 00:13:11.519 as light pressure. 275 00:13:11.279 --> 00:13:14.799 The potential acceleration profile, especially in the outer solar system, 276 00:13:15.200 --> 00:13:18.279 could be much better than a solar sale, better performance, 277 00:13:18.519 --> 00:13:19.759 potentially more durable. 278 00:13:19.960 --> 00:13:24.519 Okay, sounds great. What's the catch? The review mentioned a 279 00:13:24.600 --> 00:13:26.679 massive technological chasim ah. 280 00:13:26.799 --> 00:13:30.399 Yes, the catch is well, it's the scale, the sheer 281 00:13:30.559 --> 00:13:32.279 mind boggling scale required. 282 00:13:32.320 --> 00:13:33.159 How big are we talking? 283 00:13:33.240 --> 00:13:36.480 To generate a magnetic field strong enough and large enough 284 00:13:36.480 --> 00:13:40.559 to effectively interact with the relatively low density solar wind, 285 00:13:40.759 --> 00:13:45.120 especially far from the Sun, you need enormous superconducting. 286 00:13:44.399 --> 00:13:46.080 Coils define enormous. 287 00:13:46.279 --> 00:13:50.399 The review polling from technical studies suggests these superconducting loops 288 00:13:50.480 --> 00:13:53.120 might need to be get ready for this up to 289 00:13:53.360 --> 00:13:55.440 fifty kilometers in radius. 290 00:13:55.519 --> 00:13:58.639 Wait kilometers fifty radius. 291 00:13:58.639 --> 00:14:02.120 Fifty kilometer radius, meaning the whole structure the magnetic field 292 00:14:02.200 --> 00:14:05.080 generator would be one hundred kilometers across once deployed. 293 00:14:05.240 --> 00:14:08.480 One hundred kilometers. That's bigger than any structure we've ever 294 00:14:08.480 --> 00:14:11.200 put in space by orders of magnitude. That's not a 295 00:14:11.240 --> 00:14:13.080 spacecraft that's an orbiting installation. 296 00:14:13.320 --> 00:14:16.960 We're heating on the core problem. The scale is just immense, 297 00:14:17.080 --> 00:14:19.480 and that's only part one of the challenge. There's more 298 00:14:19.679 --> 00:14:23.519 to get that magnetic field strength efficiently. The coils need 299 00:14:23.559 --> 00:14:25.240 to be super conducting. 300 00:14:24.919 --> 00:14:28.600 Meaning they have zero electrical resistance, but that only happens 301 00:14:28.600 --> 00:14:30.360 when they're incredibly cold. 302 00:14:30.080 --> 00:14:34.440 Exactly cryogenic temperatures. We're talking temperatures close to absolute zero. 303 00:14:34.639 --> 00:14:37.159 So you have this one hundred kilometer wide structure made 304 00:14:37.159 --> 00:14:40.200 of superconducting wire that needs to be kept freezing cold 305 00:14:40.879 --> 00:14:43.360 in space where sunlight is still hitting it. 306 00:14:43.639 --> 00:14:48.480 Yes, you need a massive, complex and incredibly reliable cryogenic 307 00:14:48.559 --> 00:14:52.440 cooling system cryocolers running constantly for potentially decades. 308 00:14:52.720 --> 00:14:56.600 The power requirements alone for that cooling system must be huge, 309 00:14:56.679 --> 00:15:00.840 not to mention just building, launching, and deploying one hundred colimater. 310 00:15:00.559 --> 00:15:04.440 Structure precisely, and the superconducting wire itself. It needs to 311 00:15:04.480 --> 00:15:08.000 be structurally strong enough to handle the immense magnetic forces 312 00:15:08.039 --> 00:15:11.120 trying to tear the coil apart while staying superconducting while 313 00:15:11.120 --> 00:15:14.919 being lightweight. We'd need breakthroughs in material science just for 314 00:15:14.960 --> 00:15:15.399 the wire. 315 00:15:15.639 --> 00:15:18.799 So the technology to build the structure, deploy it power 316 00:15:18.799 --> 00:15:22.000 the cooling maintain those temperatures reliably for years. 317 00:15:22.320 --> 00:15:26.360 It simply doesn't exist yet, not even close. We're researching 318 00:15:26.360 --> 00:15:30.519 things like high temperature superconductors or HTS, which could operate 319 00:15:30.559 --> 00:15:34.679 it slightly warmer though still very cool temperatures, reducing the 320 00:15:34.720 --> 00:15:35.440 cooling load a. 321 00:15:35.440 --> 00:15:37.720 Bit, but still needing significant cool. 322 00:15:37.519 --> 00:15:40.679 Well, absolutely compared to the ambient temperature of space. Even 323 00:15:40.840 --> 00:15:45.320 HTS needs serious refrigeration, the power generation, the thermal management, 324 00:15:45.440 --> 00:15:49.000 the deployment mechanisms for something that size. It puts mag 325 00:15:49.039 --> 00:15:53.000 sales firmly in the far future breakthrough category. For now. 326 00:15:53.120 --> 00:15:58.720 It's an incredible concept, but the engineering hurdles are just astronomical. Yeah, okay, 327 00:15:58.759 --> 00:16:02.320 So if the magsail is yes, potentially too big, too heavy, 328 00:16:02.360 --> 00:16:05.919 too complex with the cryogenics, is there a lighter way 329 00:16:05.960 --> 00:16:07.320 to push against that solar wind? 330 00:16:07.399 --> 00:16:10.759 Well, that's the thinking behind the next concept, electric sales 331 00:16:10.960 --> 00:16:13.519 or E sales electric not magnetic. 332 00:16:13.639 --> 00:16:14.360 How does that work? 333 00:16:14.440 --> 00:16:16.919 E sales try to achieve a similar goal using the 334 00:16:16.960 --> 00:16:19.600 solar wind, but with a different physical principle and hopefully 335 00:16:19.600 --> 00:16:22.120 a much lighter structure. Instead of a magnetic field, they 336 00:16:22.200 --> 00:16:23.120 use electric fields. 337 00:16:23.159 --> 00:16:26.039 Okay, how do you make an electric field push things 338 00:16:26.080 --> 00:16:26.559 in space. 339 00:16:26.879 --> 00:16:29.320 The idea is to deploy a number of very long, 340 00:16:29.559 --> 00:16:33.960 very thin conductive wires or tethers radially outwards from the spacecraft, 341 00:16:34.000 --> 00:16:36.240 maybe spun out using centrifugal. 342 00:16:35.759 --> 00:16:37.600 Force kilometers long These. 343 00:16:37.399 --> 00:16:41.600 Wire potentially tens of kilometers long, yes, but very lightweight. 344 00:16:42.519 --> 00:16:45.440 Then you use an electron gun on board the spacecraft. 345 00:16:45.519 --> 00:16:47.440 An electron gun what forour to. 346 00:16:47.480 --> 00:16:50.480 Shoot electrons away from the spacecraft and the tethers, leaving 347 00:16:50.519 --> 00:16:54.679 the tethers with a strong positive electric charge, maybe thousands 348 00:16:54.679 --> 00:16:55.639 of volts positive. 349 00:16:55.759 --> 00:16:58.120 Ah. I see where this is going. The solar wind 350 00:16:58.159 --> 00:17:01.039 is mostly positively charged protons. 351 00:17:00.759 --> 00:17:04.640 Exactly like charges repel, So the positively charged tethers create 352 00:17:04.680 --> 00:17:07.759 an electric field around them that repels the incoming positive 353 00:17:07.799 --> 00:17:09.319 protons of the solar wind. 354 00:17:09.519 --> 00:17:13.839 So you're pushing the solar wind away using electrostatics, not magnetism. 355 00:17:13.440 --> 00:17:16.200 Precisely, and again Newton's third law means pushing the wind 356 00:17:16.240 --> 00:17:18.920 away pushes the cell forward away from the Sun. 357 00:17:19.119 --> 00:17:23.160 And the big advantage here is replacing those massive crygenic 358 00:17:23.680 --> 00:17:25.599 superconducting coils with. 359 00:17:25.680 --> 00:17:29.599 Just long, thin wires and an electron gun, potentially a 360 00:17:29.720 --> 00:17:32.920 much much lighter system than a magsail. That's the main appeal. 361 00:17:33.079 --> 00:17:36.160 Escaping some of that enormous mass and complexity. 362 00:17:35.640 --> 00:17:38.640 Sounds like a definite improvement in terms of mass, but 363 00:17:38.720 --> 00:17:41.359 the review probably points out new challenges too. 364 00:17:41.720 --> 00:17:45.680 No free lunch, No free lunch in space propulsion. Unfortunately, yeah, 365 00:17:45.759 --> 00:17:48.519 E sales swap one set of problems for another. The 366 00:17:48.599 --> 00:17:52.680 review highlights issues with again materials and also power. 367 00:17:52.799 --> 00:17:56.279 Let's start with the materials. Kilometers of thin wires floating 368 00:17:56.279 --> 00:17:58.319 in space sounds fragile. 369 00:17:58.359 --> 00:18:01.200 They would be very thin, to say, mass very long 370 00:18:01.279 --> 00:18:03.839 to create a large enough for pulseivaria. That makes them 371 00:18:03.839 --> 00:18:08.240 incredibly vulnerable to micrometeoroids. Again space dust YEP, a single 372 00:18:08.319 --> 00:18:11.839 hit probably wouldn't be catastrophic. The designs often involve multiple 373 00:18:11.880 --> 00:18:15.599 tethers for redundancy, but cumulative damage over years from tiny 374 00:18:15.680 --> 00:18:19.440 impacts could degrade the tethers, potentially sever them, or cause 375 00:18:19.480 --> 00:18:23.240 oscillations that make navigation tricky. Maintaining the integrity of potentially 376 00:18:23.319 --> 00:18:26.640 hundreds of kilometers of deployed wire over decades is a 377 00:18:26.759 --> 00:18:27.680 huge challenge. 378 00:18:27.799 --> 00:18:30.440 Okay, so durability is one issue. What about power? You 379 00:18:30.480 --> 00:18:31.759 mentioned electron. 380 00:18:31.319 --> 00:18:35.440 Gun right, If mag sales need power for cryogenic cooling, 381 00:18:35.799 --> 00:18:39.759 E sales need continuous significant electrical power to run that 382 00:18:39.839 --> 00:18:40.599 electron gun. 383 00:18:41.000 --> 00:18:44.359 Why continuously don't you just charge the wires once? 384 00:18:45.000 --> 00:18:48.240 If only it were that simple. Space isn't a perfect vacuum. 385 00:18:48.279 --> 00:18:52.720 There's plasma everywhere. The electrons in the surrounding solar wind 386 00:18:52.759 --> 00:18:55.640 plasma are attracted to the positive tethers and will try 387 00:18:55.680 --> 00:18:58.720 to neutralize their charge. It's called plasma screening. 388 00:18:58.839 --> 00:19:01.599 So you're constantly fighting to keep the wires charged up. 389 00:19:01.759 --> 00:19:04.960 Exactly, you need to keep pumping electrons off the wires 390 00:19:05.000 --> 00:19:08.000 with the electron gun to maintain that high positive potential 391 00:19:08.039 --> 00:19:11.880 against the surrounding plasma. That requires a pretty beefy power 392 00:19:11.920 --> 00:19:15.960 source multikilowatt level, running constantly, efficiently and reliably for the 393 00:19:16.119 --> 00:19:18.519 entire mission duration potentially decades. 394 00:19:18.960 --> 00:19:21.799 So you trade the mag sales challenge of huge scale 395 00:19:21.839 --> 00:19:24.920 and cryo cooling for the E sales challenge of extreme 396 00:19:24.960 --> 00:19:27.279 wire fragility and continuous high power generation. 397 00:19:27.440 --> 00:19:30.000 That's a good summary of the trade off. Yes, still 398 00:19:30.039 --> 00:19:35.000 requires advanced materials, reliable long term power systems. Significant hurdles remain. 399 00:19:35.319 --> 00:19:38.319 Okay, Wow, we've covered quite a range here, from the 400 00:19:38.359 --> 00:19:41.920 tried and true gravity assist to light sales to these 401 00:19:41.920 --> 00:19:45.759