Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Okay, let's unpack this. When you think about space travel,
Speaker 2: what's the first image that comes to mind.
Speaker 3: For most people? I bet it's that classic rocket line.
Speaker 2: Exactly, fire, smoke, this enormous vehicle just fighting its way
Speaker 2: off the planet. Maybe you know a Soyuz lifting off
Speaker 2: from Bacon Ore.
Speaker 3: It's an incredible sight, no doubt powerful.
Speaker 2: Definitely powerful. But that image, that very picture of a
Speaker 2: rocket launch, it actually highlights this this huge fundamental problem,
Speaker 2: a challenge that's really held back our bigger dreams for
Speaker 2: exploring deep space or well over a century now.
Speaker 3: It really has because despite all our advanced engineering, rockets
Speaker 3: still work on a pretty simple.
Speaker 2: Principle Judent's third law.
Speaker 3: That's the one for every action, there's an equal and
Speaker 3: opposite reaction. You burn fuel, throw that mass backwards. Really fast, and.
Speaker 2: The reaction pushes the rocket forwards. Simple physics, simple.
Speaker 3: But brutal and inescapable really.
Speaker 2: And needing to throw a mass away like that. That
Speaker 2: leads straight to the big mathematical hurdle, the one constantin
Speaker 2: Siolkowski figured out way back in nineteen oh three.
Speaker 3: Ah, Yes, the famous rocket equation.
Speaker 2: It basically spells out this limit the mass ratio problem.
Speaker 2: And people call it a tyranny for a reason.
Speaker 3: It absolutely is a tyranny. It traps us in this well,
Speaker 3: this vicious cycle. See the fuel you need to speed
Speaker 3: up your spacecraft. It's heavy, really heavy.
Speaker 2: And you have to carry that fuel on the rocket.
Speaker 3: Which means you need more fuel just to lift the
Speaker 3: first batch of fuel.
Speaker 2: It gets exponential, right, Skiolkowski's equation just lays it bare
Speaker 2: that desired speed change engineers call it to v It
Speaker 2: depends exponentially on how much of your rocket is fuel
Speaker 2: versus payload.
Speaker 3: And exponential here is well, that's punishing.
Speaker 2: Maybe give us a sense of that. Like, if you
Speaker 2: want to double your speed leaving Earth orbit.
Speaker 3: Yeah, good point. Doubling your speed might mean you need
Speaker 3: say five times the fuel, not just twice as much,
Speaker 3: maybe even more Wow. And for really ambitious stuff deep
Speaker 3: space or you know, a big dream interstellar travel, you
Speaker 3: need huge delta V.
Speaker 2: So the amount of fuel you need just skyrockets.
Speaker 3: Exactly the mass fraction, the percentage of your rocket that's
Speaker 3: just propelling it gets closer and closer to one hundred percent.
Speaker 2: Like ninety nine percent fuel, one percent.
Speaker 3: Space ship, or even ninety nine point nine to nine
Speaker 3: percent fuel. You're basically launching fuel to launch fuel to
Speaker 3: launch fuel. It makes high speed interstellar travels seem well,
Speaker 3: not just hard, but almost physically impossible. With chemical rockets,
Speaker 3: we just can't carry enough energy that way.
Speaker 2: Okay, So that sets up our mission for this deep dive.
Speaker 2: Then the sources you've looked at, they're all about breaking
Speaker 2: that cycle, aren't they.
Speaker 3: Precisely the big much in driving this is what if
Speaker 3: spacecraft didn't have to carry their propellant, What if they
Speaker 3: could just leave the fuel behind, find another way, find
Speaker 3: another way. And that's exactly what's explored in this really
Speaker 3: comprehensive new review. It popped up on the arcs of
Speaker 3: Preprint Server by Roma Nya, kezerashphili.
Speaker 2: Arxif right, the Physics preprint place.
Speaker 3: Yeah, and this review looks carefully at different ways to
Speaker 3: get propellent less propulsion, so systems that don't burn on
Speaker 3: board masks, but instead tap into forces and energy that
Speaker 3: are already out there in space.
Speaker 2: We're not just talking about making rockets a bit more
Speaker 2: efficient here.
Speaker 3: No, no, not at all. This is a whole different
Speaker 3: way of thinking, a paradigm shift, really.
Speaker 2: So the big takeaway right up front, the.
Speaker 3: Crucial point from the review is that these propellantless methods,
Speaker 3: they aren't just improvements. They could actually enable missions that
Speaker 3: are completely impossible right now with conventional rockets.
Speaker 2: Especially if you want to go far, like really far
Speaker 2: beyond Pluto, kind.
Speaker 3: Of far exactly. Getting rid of that need for propellant
Speaker 3: escaping the mass trap, it changes everything, mission design, what's feasible,
Speaker 3: the whole game.
Speaker 2: Right, So where do we start. There's one method that's
Speaker 2: actually been used for quite a while, hasn't it? Less
Speaker 2: future tech, more clever maneuvering.
Speaker 3: That's right, the gravity assist. It's probably the simplest propellantless
Speaker 3: technique and it's got a proven track record going back decades.
Speaker 3: We could call it maybe the easiest theft.
Speaker 2: Huh, I like that a theft of momentum.
Speaker 3: Conceptually, yeah, that's pretty much it. It's elegant. Really. You
Speaker 3: time a spacecraft's flight path very very carefully, so it
Speaker 3: swings close by a big planet like Jupiter or Venus.
Speaker 2: You fly past it on a specific path, a hyperbolic trajectory,
Speaker 2: I think is called correct.
Speaker 3: And as it swings by, the spacecraft and the planet
Speaker 3: exchange a bit of momentum. The planet has so much
Speaker 3: momentum it barely.
Speaker 2: Notices but for the tiny spacecraft.
Speaker 3: For the spacecraft, it's huge. It effectively steals a tiny
Speaker 3: fraction of the planet's orbital momentum, and that translates into
Speaker 3: a significant speed boost for the probe, completely free in
Speaker 3: terms of fuel.
Speaker 2: It's like a cosmic sling shot conservation of energy, doing.
Speaker 3: The work exactly. And the textbook example, the one everyone
Speaker 3: points to, has to be the Voyager Probes.
Speaker 2: AH Voyager one and two. The Grand Tour.
Speaker 3: The Grand Tour, Yeah, launched back in the late seventies.
Speaker 3: They took advantage of this really rare alignment of the outer.
Speaker 2: Planets Jupiter, Saturn, Uranus, Neptune, the visit at all four didn't.
Speaker 3: They did, using one gravity assist after another to hop
Speaker 3: from planet to planet, getting boosts along the way, and
Speaker 3: doing that.
Speaker 2: With chemical rockets alone, carrying enough fuel impossible.
Speaker 3: Just completely impossible. The amount of fuel needed would have
Speaker 3: been astronomical. Voyager is just the stunning example of how
Speaker 3: powerful orbital mechanics can be.
Speaker 2: It really is brilliant, a testament to clever engineering and physics.
Speaker 2: But there's always a butt, isn't there. The review mentions
Speaker 2: the trade offs.
Speaker 3: There are always trade offs. Gravity assists work, We've mastered
Speaker 3: the technique, but they have some pretty big practical limitations.
Speaker 2: You can't just decide to do one whenever you feel
Speaker 2: like it.
Speaker 3: No apps not, That's the main constraint. You are completely
Speaker 3: dependent on the planets being in the right place at
Speaker 3: the right time.
Speaker 2: Relative to each other and relative to where you want.
Speaker 3: To go exactly. These alignments are where the Voyager opportunity,
Speaker 3: for instance, only comes around once every one hundred and
Speaker 3: seventy six years.
Speaker 2: Wow. So mission planners aren't just looking at next Tuesday.
Speaker 2: They're looking decades ahead mapping planetary positions.
Speaker 3: They use these things called pork chop plots.
Speaker 2: Pork chop plots.
Speaker 3: Serious, seriously, they're graphs that show the possible launch windows
Speaker 3: flight times and energy needed. They basically highlight how you
Speaker 3: only get these narrow windows maybe a few weeks every
Speaker 3: few years or even decades to launch if you want
Speaker 3: to use a specific gravity assist.
Speaker 2: Path, so very limited opportunities, and the path.
Speaker 3: Itself it's totally inflexible. Once you launch, you're locked into
Speaker 3: that trajectory. It's dictated by celestial mechanics, by the cosmic clock,
Speaker 3: not by where you might want to go explore next week.
Speaker 2: So great for preplan tours, but not for flexible on
Speaker 2: demand exploration. If you need continuous thrust or the ability
Speaker 2: to change course easily.
Speaker 3: You need something else. You need to look beyond planets
Speaker 3: and start tapping into the energy sources that are always
Speaker 3: there in space.
Speaker 2: Okay, which takes us to the next step, moving away
Speaker 2: from these occasional gravitational boosts towards something more constant. And
Speaker 2: this is where I think you said it gets really interesting,
Speaker 2: harnessing sunlight itself.
Speaker 3: Exactly solar sales. This shifts the concept from borrowing momentum
Speaker 3: from a planet to catching momentum from the most abundant
Speaker 3: energy source in the Solar system.
Speaker 2: Sunlight solar pressure. Now I know some listeners might hear
Speaker 2: solar sale and think of old sci fi. Is the
Speaker 2: physics really solid here? How can light push something if
Speaker 2: photons don't have mass?
Speaker 3: It's fundamental physics. Actually, photons, the particles of light, might
Speaker 3: have zero rest mass, but they definitely carry momentum. So
Speaker 3: when photons hit something, they transfer that momentum. If they
Speaker 3: get absorbed, they transfer some, But if they get reflected,
Speaker 3: which is what a shiny sale is designed to do,
Speaker 3: they transfer about twice the momentum, like bouncing a ball
Speaker 3: off a wall.
Speaker 2: Ah. Okay, so the sails like a giant mirror.
Speaker 3: Essentially, yes, a huge, incredibly thin reflective membrane. It catches
Speaker 3: the momentum from countless photons hitting it, But the.
Speaker 2: Push from a single photon must be minuscule.
Speaker 3: Oh, absolutely tiny, infantesimal. But the sun is always shining,
Speaker 3: so that tiny push is constant. It's there two entred
Speaker 3: and forty seven week after week.
Speaker 2: Year after year, and over time, that constant, gentle push
Speaker 2: adds up.
Speaker 3: It adds up, It builds velocity, gradually, slowly at first,
Speaker 3: but persistently, And the most beautiful part, it uses zero
Speaker 3: fuel once it's deployed. Zero.
Speaker 2: That dream became reality thanks to Japan Space Agency JAXA.
Speaker 3: Right yes, with the Ikros probe. That was a fantastic
Speaker 3: mission back in twenty ten, a real game changer.
Speaker 2: What did it do?
Speaker 3: JAXA successfully deployed the square sale in space, controlled it
Speaker 3: and used it to fly the probe all the way
Speaker 3: to Venus, powered only by sunlight.
Speaker 2: Wow, just push by light, just push by light.
Speaker 3: It proved the works in the real world, not just
Speaker 3: on paper or in in computer models.
Speaker 2: Okay, so proof of concept check. But the review it
Speaker 2: really digs into the challenges the downsides. The engineering side sounds.
Speaker 3: Delicate, extremely delicate. Material science is the huge bottleneck here.
Speaker 3: For a solar sale to be effective, it needs to
Speaker 3: be incredibly light, but also incredibly large. We talk about
Speaker 3: aerial density, the mass per square meter.
Speaker 2: You want that number to be tiny, as low as possible.
Speaker 3: We're talking materials that are almost like smoke gossamer thin,
Speaker 3: maybe just a few milligrams per square meter, but the
Speaker 3: sale itself needs to be vast. Think multiple football fields
Speaker 3: in area.
Speaker 2: So imagine trying to unfold something thinner than kitchen plastic
Speaker 2: wrap but kilometers across in space without ripping it exactly.
Speaker 3: And then you have to keep it tensioned, stable, pointed correctly.
Speaker 3: It's an engineer's nightmak.
Speaker 2: What are these materials? Usually made of.
Speaker 3: Specialized plastics, often polymers like CP one or types of
Speaker 3: polymide film coated with a thin layer of aluminum for reflectivity.
Speaker 3: But they also have to be incredibly tough.
Speaker 2: Tough against what space is empty, right.
Speaker 3: Not quite empty enough. They have to survive years, maybe decades,
Speaker 3: bathed in intense ultraviolet radiation from the Sun, which degrades
Speaker 3: materials over time. Plus there's constant bombardment by tiny dust particles, micrometeoroids.
Speaker 2: H space dust. Even a tiny speck hitting that thin
Speaker 2: film at high speed.
Speaker 3: Could potentially cause a tear, and enough small tiers could
Speaker 3: affect the sale's structure, its tension, its ability to generate
Speaker 3: thrust efficiently.
Speaker 2: Okay, so materials and deployment are hard, Yeah, but there's
Speaker 2: a more fundamental physics limitation too, right, tied to distance.
Speaker 3: Yes, And this is a big one sunlight and therefore
Speaker 3: the radiation pressure it creates follows the inverse square law, meaning.
Speaker 2: The further you get from the Sun, the weaker the push.
Speaker 3: Dramatically weaker. The forest drops off with the square of
Speaker 3: the distance. So if you go from Earth's distance one
Speaker 3: astronomical unit or AU out to Jupiter, which is about
Speaker 3: five away.
Speaker 2: The force isn't five times weaker.
Speaker 3: It's twenty five times weaker five square oach.
Speaker 2: That's a massive drop in acceleration.
Speaker 3: It really is. It makes solar sales potentially great permissions
Speaker 3: inside the orbit of Mars, maybe out to the asteroid belt,
Speaker 3: but for deep space, going out past Jupiter to Saturn, Uranus,
Speaker 3: Neptune or beyond.
Speaker 2: The push becomes almost nothing, pretty much negligible.
Speaker 3: Your acceleration just fades away. So for exploring the outer
Speaker 3: Solar System or heading towards the stars, solar cells alone
Speaker 3: probably aren't the answer.
Speaker 2: Okay, So if sunlight pressure gets too weak out there,
Speaker 2: what else is constantly flowing outwards from the Sun that
Speaker 2: we could potentially push.
Speaker 3: Against that leads us to the solar wind?
Speaker 2: Uh, not light pressure, but actual particles exactly.
Speaker 3: The solar wind is this continuous supersonic stream of charged
Speaker 3: particles plasma mostly protons and electrons, that flows out from
Speaker 3: the Sun all the time, and crucially, it carries significant
Speaker 3: momentum and keeps a decent density much further out than
Speaker 3: where sunlight pressure.
Speaker 2: Because okay, so if we can push against that, maybe
Speaker 2: we can get thrust further out. Yeah, this brings us
Speaker 2: to magnetic sales.
Speaker 3: Mag sales, correct magnetic sales. It's a totally different concept
Speaker 3: from reflecting.
Speaker 2: Light because there's no physical sail, right, you can't reflect
Speaker 2: charged particles with a sheet of plastic right.
Speaker 3: Instead of a physical membrane, a mag sail uses loops
Speaker 3: of superconducting wire to generate a really powerful, large magnetic field,
Speaker 3: an artificial magnetosphere, essentially like.
Speaker 2: Earth's magnetic field, but generated by the spacecraft sort of.
Speaker 3: Yes, And when the charged particles of the solar wind
Speaker 3: hit this magnetic field.
Speaker 2: They get deflected like how Earth's field deflects the solar
Speaker 2: wind exactly.
Speaker 3: That magnetic field pushes the plasma particles aside, and by
Speaker 3: Newton's third law again, pushing the solar wind plasma away
Speaker 3: pushes the spacecraft forward. You're essentially sailing on the solar
Speaker 3: wind using a magnetic bubble.
Speaker 2: That sounds incredibly cool, and it avoids the whole problem
Speaker 2: of deploying and maintaining huge, fragile sheets of material.
Speaker 3: That's a major theoretical advantage. Yes, No, worries about UV
Speaker 3: degradation or micrometeoroid tears on a physical sale.
Speaker 2: And because the solar wind doesn't drop off as quickly
Speaker 2: as light pressure.
Speaker 3: The potential acceleration profile, especially in the outer solar system,
Speaker 3: could be much better than a solar sale, better performance,
Speaker 3: potentially more durable.
Speaker 2: Okay, sounds great. What's the catch? The review mentioned a
Speaker 2: massive technological chasim ah.
Speaker 3: Yes, the catch is well, it's the scale, the sheer
Speaker 3: mind boggling scale required.
Speaker 2: How big are we talking?
Speaker 3: To generate a magnetic field strong enough and large enough
Speaker 3: to effectively interact with the relatively low density solar wind,
Speaker 3: especially far from the Sun, you need enormous superconducting.
Speaker 2: Coils define enormous.
Speaker 3: The review polling from technical studies suggests these superconducting loops
Speaker 3: might need to be get ready for this up to
Speaker 3: fifty kilometers in radius.
Speaker 2: Wait kilometers fifty radius.
Speaker 3: Fifty kilometer radius, meaning the whole structure the magnetic field
Speaker 3: generator would be one hundred kilometers across once deployed.
Speaker 2: One hundred kilometers. That's bigger than any structure we've ever
Speaker 2: put in space by orders of magnitude. That's not a
Speaker 2: spacecraft that's an orbiting installation.
Speaker 3: We're heating on the core problem. The scale is just immense,
Speaker 3: and that's only part one of the challenge. There's more
Speaker 3: to get that magnetic field strength efficiently. The coils need
Speaker 3: to be super conducting.
Speaker 2: Meaning they have zero electrical resistance, but that only happens
Speaker 2: when they're incredibly cold.
Speaker 3: Exactly cryogenic temperatures. We're talking temperatures close to absolute zero.
Speaker 2: So you have this one hundred kilometer wide structure made
Speaker 2: of superconducting wire that needs to be kept freezing cold
Speaker 2: in space where sunlight is still hitting it.
Speaker 3: Yes, you need a massive, complex and incredibly reliable cryogenic
Speaker 3: cooling system cryocolers running constantly for potentially decades.
Speaker 2: The power requirements alone for that cooling system must be huge,
Speaker 2: not to mention just building, launching, and deploying one hundred colimater.
Speaker 3: Structure precisely, and the superconducting wire itself. It needs to
Speaker 3: be structurally strong enough to handle the immense magnetic forces
Speaker 3: trying to tear the coil apart while staying superconducting while
Speaker 3: being lightweight. We'd need breakthroughs in material science just for
Speaker 3: the wire.
Speaker 2: So the technology to build the structure, deploy it power
Speaker 2: the cooling maintain those temperatures reliably for years.
Speaker 3: It simply doesn't exist yet, not even close. We're researching
Speaker 3: things like high temperature superconductors or HTS, which could operate
Speaker 3: it slightly warmer though still very cool temperatures, reducing the
Speaker 3: cooling load a.
Speaker 2: Bit, but still needing significant cool.
Speaker 3: Well, absolutely compared to the ambient temperature of space. Even
Speaker 3: HTS needs serious refrigeration, the power generation, the thermal management,
Speaker 3: the deployment mechanisms for something that size. It puts mag
Speaker 3: sales firmly in the far future breakthrough category. For now.
Speaker 2: It's an incredible concept, but the engineering hurdles are just astronomical. Yeah, okay,
Speaker 2: So if the magsail is yes, potentially too big, too heavy,
Speaker 2: too complex with the cryogenics, is there a lighter way
Speaker 2: to push against that solar wind?
Speaker 3: Well, that's the thinking behind the next concept, electric sales
Speaker 3: or E sales electric not magnetic.
Speaker 2: How does that work?
Speaker 3: E sales try to achieve a similar goal using the
Speaker 3: solar wind, but with a different physical principle and hopefully
Speaker 3: a much lighter structure. Instead of a magnetic field, they
Speaker 3: use electric fields.
Speaker 2: Okay, how do you make an electric field push things
Speaker 2: in space.
Speaker 3: The idea is to deploy a number of very long,
Speaker 3: very thin conductive wires or tethers radially outwards from the spacecraft,
Speaker 3: maybe spun out using centrifugal.
Speaker 2: Force kilometers long These.
Speaker 3: Wire potentially tens of kilometers long, yes, but very lightweight.
Speaker 3: Then you use an electron gun on board the spacecraft.
Speaker 2: An electron gun what forour to.
Speaker 3: Shoot electrons away from the spacecraft and the tethers, leaving
Speaker 3: the tethers with a strong positive electric charge, maybe thousands
Speaker 3: of volts positive.
Speaker 2: Ah. I see where this is going. The solar wind
Speaker 2: is mostly positively charged protons.
Speaker 3: Exactly like charges repel, So the positively charged tethers create
Speaker 3: an electric field around them that repels the incoming positive
Speaker 3: protons of the solar wind.
Speaker 2: So you're pushing the solar wind away using electrostatics, not magnetism.
Speaker 3: Precisely, and again Newton's third law means pushing the wind
Speaker 3: away pushes the cell forward away from the Sun.
Speaker 2: And the big advantage here is replacing those massive crygenic
Speaker 2: superconducting coils with.
Speaker 3: Just long, thin wires and an electron gun, potentially a
Speaker 3: much much lighter system than a magsail. That's the main appeal.
Speaker 3: Escaping some of that enormous mass and complexity.
Speaker 2: Sounds like a definite improvement in terms of mass, but
Speaker 2: the review probably points out new challenges too.
Speaker 3: No free lunch, No free lunch in space propulsion. Unfortunately, yeah,
Speaker 3: E sales swap one set of problems for another. The
Speaker 3: review highlights issues with again materials and also power.
Speaker 2: Let's start with the materials. Kilometers of thin wires floating
Speaker 2: in space sounds fragile.
Speaker 3: They would be very thin, to say, mass very long
Speaker 3: to create a large enough for pulseivaria. That makes them
Speaker 3: incredibly vulnerable to micrometeoroids. Again space dust YEP, a single
Speaker 3: hit probably wouldn't be catastrophic. The designs often involve multiple
Speaker 3: tethers for redundancy, but cumulative damage over years from tiny
Speaker 3: impacts could degrade the tethers, potentially sever them, or cause
Speaker 3: oscillations that make navigation tricky. Maintaining the integrity of potentially
Speaker 3: hundreds of kilometers of deployed wire over decades is a
Speaker 3: huge challenge.
Speaker 2: Okay, so durability is one issue. What about power? You
Speaker 2: mentioned electron.
Speaker 3: Gun right, If mag sales need power for cryogenic cooling,
Speaker 3: E sales need continuous significant electrical power to run that
Speaker 3: electron gun.
Speaker 2: Why continuously don't you just charge the wires once?
Speaker 3: If only it were that simple. Space isn't a perfect vacuum.
Speaker 3: There's plasma everywhere. The electrons in the surrounding solar wind
Speaker 3: plasma are attracted to the positive tethers and will try
Speaker 3: to neutralize their charge. It's called plasma screening.
Speaker 2: So you're constantly fighting to keep the wires charged up.
Speaker 3: Exactly, you need to keep pumping electrons off the wires
Speaker 3: with the electron gun to maintain that high positive potential
Speaker 3: against the surrounding plasma. That requires a pretty beefy power
Speaker 3: source multikilowatt level, running constantly, efficiently and reliably for the
Speaker 3: entire mission duration potentially decades.
Speaker 2: So you trade the mag sales challenge of huge scale
Speaker 2: and cryo cooling for the E sales challenge of extreme
Speaker 2: wire fragility and continuous high power generation.
Speaker 3: That's a good summary of the trade off. Yes, still
Speaker 3: requires advanced materials, reliable long term power systems. Significant hurdles remain.
Speaker 2: Okay, Wow, we've covered quite a range here, from the
Speaker 2: tried and true gravity assist to light sales to these
Speaker 2: more exotic magnetic and electric concepts pushing against the solar wind.
Speaker 2: Let's try and break it all together. What's the synthesis here?
Speaker 2: What does the review conclude when looking at all these options.
Speaker 3: Well, when you lay them all out gravity assist, solar sale,
Speaker 3: MAG sale, E sale, you see this clear spectrum. On
Speaker 3: one end you have gravity assists proven working now but
Speaker 3: totally inflexible. On the other end, you have mag sales
Speaker 3: and E sales potentially much higher performance, especially for deep space,
Speaker 3: but requiring technology that is frankly way beyond our current capabilities.
Speaker 3: Solar sales are somewhere in the middle.
Speaker 2: Let's quickly recap the killer limitation for each based on
Speaker 2: the review.
Speaker 3: Okay, gravity assists work great, but you're tied to rare
Speaker 3: planetary alignments, no flexibility, no autonomy.
Speaker 2: Solar sales proven concept, steady thrust near the Sun, but
Speaker 2: the materials are incredibly delicate and the thrust just dies
Speaker 2: off way too fast with distance because of the inverse
Speaker 2: square law useless for the outer solar system.
Speaker 3: Are beyond right, then mag sales great potential performance, avoids
Speaker 3: material degradation, pushes against the solar wind further out, but
Speaker 3: the showstopper is the scale those fifty kilometer radius superconducting
Speaker 3: coils needing constant cryogenic cooling just not feasible today, and E.
Speaker 2: Sales lighter than mag sales, also uses the solar wind,
Speaker 2: but you trade the massive coils for potentially fragile kilometers
Speaker 2: long tethers and the need for continuous high power electron
Speaker 2: guns to keep them charged. Still big tech hurdles exactly.
Speaker 3: So the big conclusion from the review, looking across all
Speaker 3: of this.
Speaker 2: What does it all mean for actually getting out there?
Speaker 3: It means there's no silver bullet, No single propellantless method
Speaker 3: solves all the problems right now. Each one has a
Speaker 3: critical flaw, whether it's flexibility, fragility, distance limits, or just
Speaker 3: requiring currently non existent technology.
Speaker 2: So the path forward probably isn't picking just one winner.
Speaker 3: Very unlikely. The review strongly suggests the future probably lies
Speaker 3: in combining these approaches. Maybe use a powerful launch stage,
Speaker 3: then a solar sale to get good initial acceleration out
Speaker 3: of the inner solar system, and.
Speaker 2: Then maybe deploy an E sale or mag sale once
Speaker 2: a solar cell becomes ineffective to continue accelerating using the
Speaker 2: solar wind.
Speaker 3: Something like that, or using gravity assists strategically in combination
Speaker 3: with continuous low thrust propulsion, hybrid approaches seem much more
Speaker 3: plausible than relying on a single magic solution, and.
Speaker 2: That idea needing these advanced propellantless methods, perhaps in combination,
Speaker 2: becomes absolutely critical when we talk about the really big goals,
Speaker 2: doesn't it, Yeah, interstellar travel.
Speaker 3: It's non negotiable for interstellar really. The review hammers this home.
Speaker 3: If you're serious about reaching another star system within a
Speaker 3: human lifetime or even a couple of centuries, chemical rockets
Speaker 3: just won't cut it. Because of that Silkovski mass ratio limit.
Speaker 2: You simply can't carry enough fuel.
Speaker 3: You can't, So leaving the propellant behind isn't just a
Speaker 3: nice to have for interstellar missions, it's probably the only
Speaker 3: way it could ever be feasible. It fundamentally changes the challenge.
Speaker 2: From a challenge of energy storage fuel to a challenge
Speaker 2: of energy harvesting light, wind, gravity.
Speaker 3: Perfectly put, it becomes about building incredibly efficient, large scale
Speaker 3: energy harvesting structures that can operate reliably for centuries.
Speaker 2: Which suddenly makes those huge engineering hurdles. The fifty kilometer coils,
Speaker 2: the super durable tethers. The decades long power sources seem
Speaker 2: less like science fiction pipe dreams.
Speaker 3: And more like the necessary entry ticket. They define the
Speaker 3: scale of engineering required if we actually want to become
Speaker 3: an interstellar species. It's less about building slightly better rockets
Speaker 3: and more about inventing fundamentally new ways to build and
Speaker 3: power things in space.
Speaker 2: This has been a really fascinating journey breaking free conceptually,
Speaker 2: at least from the tyranny of the rocket equation. We've
Speaker 2: looked at gravity assists, solar sales, magnetic sales, electric sales,
Speaker 2: each with its promise and its major roadblocks, flexibility, materials, scale, power.
Speaker 3: And maybe as we wrap up, it's worth focusing on
Speaker 3: that biggest technological gap, the mag sale scale. For instance,
Speaker 3: if we accept that something like a fifty kilometer superconducting
Speaker 3: structure kept near absolute zero for decades might be what
Speaker 3: it takes for truly fast deep space or interstellar travel,
Speaker 3: pose is a really interesting question for you, the listener,
Speaker 3: to think about. Go on, what kind of fundamental science
Speaker 3: needs to be discovered first before we can even think
Speaker 3: about designing the propulsion system. What breakthrough in say, material science,
Speaker 3: may be practical room temperature superconductors or in compact ultralong
Speaker 3: life power generation, maybe fusion power plants small enough for spacecraft.
Speaker 3: What needs to happen in the lab before the engineers
Speaker 3: can even start drawing up the blueprints for these proportion systems.
Speaker 2: It's a great point. We might not just be waiting
Speaker 2: for better engineering. We might be waiting for a whole
Speaker 2: new piece of physics or material science to unlock the
Speaker 2: path forward, the invention that enables.
Speaker 3: The invention exactly. The next leap in propulsion might start
Speaker 3: not in a rocket factory, but maybe with a discovery
Speaker 3: in condensed matter physics or advanced energy research. It really
Speaker 3: shifts your perspective on where the bottleneck lies.
Speaker 2: A powerful thought. Indeed, we need the science before we
Speaker 2: can build the sales to truly navigate the void. Thank
Speaker 2: you for joining us on this deep dive into leaving
Speaker 2: the fuel behind U
Speaker 3: S S