Hello SFIA Audio listeners, in this month's Nebula-exclusive, Big Alien Theory, we're asked if the reason alien civilizations might be rare is because most aliens are huge. To hear it and every episode early and ad free, plus hours of bonus content, check out go.nebula.tv slash Isaac Arthur and use my code IsaacArthur. Reaching for the stars has always been humanity's dream. What if we could climb later instead?
For centuries humanity has dreamed of reaching the stars, but until now we've relied on rockets, which have some real limitations on throughput if our goal is to get millions of people able to go back and forth to space every day. There are a number of alternatives we've looked at over the years, and recently we did an extended look at space elevators and followed it up by comparing the pros and cons of rockets compared to mass drivers.
essentially big railways or space cannons for launching cargo or even people into orbit. There are many innovative systems for transporting cargo and people to space, Today we'll be exploring several that build on the fundamental principle of that space elevator while differing in their execution. Our primary focus will be on Skyhook and Rotovator systems, along with Paul Birch's Jacob's Ladder concept.
often referred to simply as a space ladder. These approaches offer a way to escape Earth's gravity without relying on the explosive force of chemical propellants or the staggering cost of repeated rocket launches. Instead, they leverage tether-based systems, a revolutionary paradigm for space exploration that redefines how humanity reaches orbit and beyond.
In the case of the space ladder, these systems could be constructed near or even within cities, providing a safe, quiet, and high capacity mode of travel to space, even allowing daily commutes. By hard to see advanced physics and material science, tether systems create reusable and scalable infrastructure for space access. This includes orbital tethers, rotating cables, and massive structures extending from Earth's surface to space.
enabling the direct transport of people and goods. With Tether technology, space is no longer a distant and expensive frontier, instead it becomes an accessible and natural extension of human activity. akin to crossing oceans or flying across continents. These innovations represent a bold step toward a spacefaring civilization, where the sky is no longer the limit but merely the beginning.
I now believe that with Graphene Superlaminate, GSL, we have a material that can be produced affordably, with sufficient strength and length, to make a true space elevator feasible, as we discussed recently in the Space Elevator Update video. However, shorter tethers are far easier to construct and, as we'll explore today, may be deployable much sooner than a full-scale space elevator. We'll also see how Skyhook and Rotorator systems can work seamlessly alongside other technologies
such as more cost-effective and easier to build mass drivers, space planes, and reusable rockets. These systems complement one another. making space access cheaper and more efficient through their combined use with tether-based technologies. Imagine a cable that can catch spacecraft in flight, reducing the need for enormous fuel reserves,
or a ladder anchored to an orbital ring, offering a steady climb into orbit. These technologies promise a revolution in space logistics, lowering costs, improving sustainability, and enabling long-term human habitation beyond Earth. These are not just tools for exploration, they are humanity's stepping stones to becoming a space-faring civilization.
As we'll see later, these systems are not just effective for getting into space from Earth, they also hold great potential for use on Mars, Venus, and Mercury. with each environment benefiting from different strengths and adaptations in these systems. Indeed the latter system itself allows not just fast travel to space, but fast travel back.
for a rapid and cheap means of transport around Earth that no airplane can match. Now as we delve into skyhooks and rotavators, a key concept to understand is that if a spacecraft only needed to launch at half the speed required to reach orbit, it would use just one fifth of fuel. Savings extend far beyond fuel, as the reduced launch speeds mean significantly lower construction costs. High-speed launches require extreme engineering precision, driving costs far beyond the fuel itself.
Similarly, a mass driver designed to launch objects at lower speeds could be just a quarter of the length needed for full orbital velocities. These technologies fall into various categories and applications, but the first implementations are likely to work in tandem with existing rockets or hypersonic planes to achieve orbit, and those might get their boost out of a mass driver.
How does this work? First it's worth noting that technically Skyhook and Rotorator are two terms used to describe the same general concept. However, I seem to have unintentionally popularized the term Skyhook about a decade ago to be a particular variation of the Rotovator. That's where we did a couple episodes on the topic of Skyhooks and some of their history and experimental designs and plans.
See those episodes for more on that. Before that, rotovator was probably the more commonly used term, though both were relatively obscure even then. I preferred Skyhook because my speech impediment for saying the letter R was much worse at the time and Skyhook was simply easier to say than Votovator, which I tended to say as Votovator.
In science fiction, Skyhook often referred to more speculative technologies like anti-gravity. In recent discussions, I've used the term Skyhook to refer specifically to a tether that is radially oriented, or hangs straight down toward Earth. and Vodovator to describe a tether that spins end over end as it orbits. This distinction seems to have gained traction, so we'll stick with it here, starting with the simpler concept of the Skyhook.
Objects orbit Earth at a speed determined by their altitude or distance from the planet's center. This rule applies to any celestial body. The farther they orbit, the slower the object moves. an object needs to travel faster to orbit a more massive celestial body at the same distance. In Earth's case, objects just above the atmosphere orbit at a speed of about 7,788 meters per second, and complete a full orbit in roughly 90 minutes.
Earth is still spinning under you, so what qualifies as a full orbit varies on if we mean returns over the same spot or completes 360 degrees. That spin by Earth does give spaceships a boost, especially closer to the equator. Anyway, if we go about 2000 kilometers further up, to 2100 kilometers, the orbit period rises to a bit over 2 hours and the orbital speed drops to 6820 meters per second.
15,400 miles per hour. Now let's consider a fairly massive space station orbiting at 2100 kilometers altitude with a lightweight tapered tether attached to it that reaches down to an altitude of 100 kilometers. Chords can snap under their own weight, so tapering them to be thicker up top and thinner near the bottom lets us make them longer than one of the same thickness the whole way. We talked about that more in the Space Elevator Episode 2.
Regardless, the low end of that tether will be traveling around the Earth, just above the atmosphere, at just 5,228 meters per second, because it's orbiting in the same period the station above is, but the circle at Straci is a lot shorter Less distance over the same time means our slower speed. In this case, 1,592 meters per second slower than the station it is hanging from and a whopping 2,560 meters per second slower than the orbital velocity at 100 kilometers altitude.
which was 7,788 meters per second. Now if you want to place a payload into orbit you can send a rocket up, have it drop its payload off at the end of that tether and then fall back to the Earth. then the space station can simply winch that payload up the tether. The key difference here is that this rocket needs 27% less Delta V compared to what it normally takes for a rocket to get to orbit. Also if it's a reusable rocket,
it will need to shed 27% less delta V during re-entry. So how is this helpful? 27% may not seem like a lot, but remember that our brains are wired for linear thinking. Rocketry is governed by the exponential nature of the rocket equation. When the Delta V requirements on a rocket are reduced by 27%, this translates to a dramatically lower cost and complexity for the system. The fuel goes down to more like a half
And not only does that mean you only need to build half the rocket, but you can dramatically lower the insane construction costs involved for engineering a device meant to handle orbital rocket tolerances without exploding and to then repair and reuse that rocket. so we could easily be looking at an order of magnitude of cost decrease if not more. But again, how does this actually help? Now we have a ship hanging just above the atmosphere that also exhausts a downward pull on the station.
Here's where the tether comes in handy. You can climb it, this could be done by winching up cargo or passengers to the station which might have multiple tethers hanging down for redundancy in other cargo or by having the ship climb the tether itself. Alternatively, there could be a pod at the end of the Skyhook where people and cargo are transferred. The vehicle that brought them there could then detach and return to Earth while the pod climbs the tether to the station.
Depending on the circumstances, any of these approaches might work better than the others. When you reach the top of the tether, you will be moving at the z-less station speed, which is slightly below the normal orbital velocity for that altitude. Your climb also slows the station slightly as it transfers momentum to you. A very small burst of fuel would be enough to place you into a stable orbit, allowing you to transfer to your desired orbit as you leave the zenith station.
Alternatively, the station could provide an electromagnetic boost to get you up to speed, using a small mass driver or catapult system. This approach could save fuel and further streamline the process of achieving orbit. Earlier I mentioned that station having fuel pods and solar panels and this is part of why, the other was that the more mass it has the less it has its own speed and orbit destabilized when hooking a ship.
Now this is useful in its own right, as you now have a ship up in space that did not need to be built with the insane engineering and equally insane costs that one designated to get to orbit on its own needs. Fuel is not the main cost of sending things to space, so simply by allowing a reusable rocket or spaceplane that is vastly cheaper to build and maintain, we achieve huge launch savings.
But the cooler part is that the station can regenerate its momentum. Rocket fuel is not an efficient propulsion method, especially for achieving high Delta V, as the faster you want to accelerate, the less Delta V you get for the same amount of fuel, generally speaking. In contrast, efficient drives like ion engines provide 10-20 times more Delta V per unit of fuel.
but they operate at much lower thrust levels. You cannot launch a ship with an ion drive because it must exceed the downward acceleration caused by gravity, about 1g, and the more you exceed that the better. For example, a rocket accelerating at 4 Gs will use less fuel to reach orbit than one at 2 Gs. However, ion drives don't even come close to generating 1 G of force.
if your station is large and only loses say one hundred meters per second of velocity when a ship hooks to it and climbs you likely have several hours or even days before the next launch or hook During that time, the station can use an ion drive or another low-thrust, high-efficiency engine to regain the lost speed and momentum.
Around Earth, with its powerful magnetosphere, momentum regeneration can be achieved through electrodynamic tethering. This involves running an electric current through a long tether. This current interacts with the magnetic field, creating a force via the Lorentz effect that pushes the tether. In Earth's case, the magnetosphere provides a stable magnetic field for this interaction, allowing the tether to produce thrust without the need for traditional propellant.
While not fast, this method requires no propellants, relying solely on electricity which can be generated abundantly by solar panels. Skyhooks of this length spend a significant amount of time in Earth's shadow, less than half, but still a considerable portion. During periods outside the shadow, the surplus solar energy can be used to lift the station back into position while recharging its batteries. This setup is actually more efficient than solar power on Earth for a few reasons.
1. No interference from cloudy days, 2. Less time spent in shadow compared to Earth-based solar arrays, and 3. With an orbital period of only a couple of hours, the batteries only need to store energy for around 14 minutes, not half a day. This combination of electrodynamic tethering and solar power makes Skyhooks a sustainable and efficient system for maintaining momentum
and stability in orbit. The lower you hang that hook, the more air drag it's going to have too, which you have to regenerate. You could probably get away with keeping the Skyhook's bottom below the Karman line but hanging it at normal airplane altitudes probably would not be feasible. If you can get some place where an air-breathing jet can still function though, it will work even better.
and as we're seeing today, science is opening up new pathways to space. While today we explore incredible ways to make space more accessible, in the next exclusive episode, we're contemplating what happens if and when we reach the final frontier, not just of space, but of knowledge itself.
in the end of science we ask whether there will ever come a time when scientific discovery slows or even stops entirely could we one day know all there is to know and what happens to civilization when their great mysteries are solved is the end of discovery the beginning of decline or something far stranger explore these ideas in the end of science available now exclusively on nebula the largest creator owned streaming platform
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And you might be able to lower the tether the last bit into the air just for the hookup and then winch it back up when not in use, or use an elliptical orbit so it only dropped into the thicker air briefly twice per orbit, or a combination of both. Now, can we go longer than 2000 kilometers? Sure, the braking length of GSL is 4200 kilometers or 2600 miles. It's a bit more up there as gravity starts to weaken,
and braking length is based off normal Earth gravity, half the gravity, twice the braking length of a material. We discussed this in deeper detail in the Space Elevator Update. At a certain length you might as well abandon a skyhook in favor of a space elevator though, which requires no momentum regeneration and lets you leave straight from the ground. Like the space elevator, skyhooks work better at the equator,
where they can benefit from the free speed of Earth's rotation the most, but this is not required and thus works fine with existing launch sites. I think a 5,000 kilometer skyhook is perfectly plausible and that will result in a period of just under three and a half hours, and the hook at the bottom having a speed of about 3300 meters per second or 7400 miles per hour, and notably that's around the top speed of the NASA X-43.
so something we could reliably say an air-breathing spaceplane could achieve rendezvous with. An even slower speed would be nice, and we could build yet longer skyhooks, but again we're getting close to space elevator conditions at that point
since it's really only the lowest sections of the space elevator that are challenging for weight. We'll find a way to get a lower speed on the tip when we get to the Rotovator in a bit, and we'll see some other uses on other planets with lower gravity too, But one last thing to note for this style of Skyhooks is that they can not only be used in tandem with a rocket, spaceplane, or mass driver, they can also be used in tandem with each other.
You could just as easily make one 10,000 kilometers long, hanging just above our 5,000 kilometer long version, with a slower speed and with a tip hanging down that first Skyhook station that would pass by it occasionally and you make a transfer to it. going yet higher and not necessarily needing any onboard fuel. Rinse and repeat as needed, something we'll also do with the space ladders when we discuss them in a bit, giving them rungs you climb. There's no free lunch here.
but instead of having to produce a huge amount of thrust in mere moments, we can spread it out over a long period and use low thrust high efficiency engines powered by solar which undergo far less strain on the components involved. making for cheaper cost, easier engineering, and low risk of catastrophic failure. The primary advantage of a non-rotating skyhook over its counterpart, the Rotovator, which we'll discuss shortly, is that it doesn't spin.
It's just an abridged space elevator that isn't stationary to the ground. This makes it significantly easier to rendezvous with, as it remains predictable and consistently positioned at the same altitude. In contrast, a Rotorator swings around like a giant bolus in space, which can pose challenges and potential risks when dealing with other objects in orbit, potentially fatal ones, at least for long term and heavy use around Earth.
For new deployment around places like Mars or some new colony where there's not much stuff in orbit yet, they might be particularly beneficial. Now this brings us to the Rotovator. As the name suggests, it is a rotating and shortened or abridged version of a space elevator, designed to bridge the gap to orbit in a dynamic and efficient way.
The basic concept of a rotavator is that it rotates rather than simply hanging like a traditional skyhook. While a regular skyhook moves slower than orbital speed at its altitude, The Rotorator's spinning motion further reduces its relative speed to the ground at the bottom of its swing. Conversely, at the top of its swing the rotation adds to its speed, allowing it to hurl a spacecraft outward at high velocities.
The road reader spins through a vertical plane, similar to a ferris wheel rather than a merry-go-round. In fact, a larger version of this concept, designed for mining airless worlds, resembles a hybrid of a ferris wheel and a bucket excavator. See our episodes on Mining or Dismantling Planets for discussion of that. The Rotorator's primary advantage lies in its spinning motion, which allows it to impart additional momentum to payloads during the downward swing.
It will use the same methods of momentum regeneration as a skyhook but must regenerate more momentum as it transfers more, though it will require less compensation for atmospheric losses and can more easily dip to lower altitudes. On the other hand, because it spins like a bolus, the tetherer experiences additional strain from centrifugal force. This strain is at the maximum at the bottom of the spin,
where the combined forces of gravity and rotation exert the greatest stress, especially when clamping onto a vehicle to lift it into space. The rotavito's length and spin can be adjusted to suit the material strength and gravitational forces,
but it will generally need to be shorter than an equivalent skyhook. Its center of mass is positioned at the midpoint of the tether, where the spin pivots. This means its orbital period will be shorter than a skyhook's, as the skyhook's center of mass is closer to the top.
However, the strength of the Rotovator is limited to the segment from the midpoint to the end, rather than the entire length as is the case of the Skyhook. Additionally, the Rotovator doesn't require a large station at its midpoint, as it's not a destination like the Xena Station at the top of a Skyhook. Instead, the Rotorator serves as a mechanism to hook onto a vehicle and spin it up and out to space.
The middle point is just for adding mass in a place where it won't put strain on the tethers, to increase your total momentum so a vehicle hooking to you won't disrupt that much. and this is presumably mostly solar panels and ion drives as you don't have any real reason to have tons of radiation shielding or refueling depots, again this is not a port of call. The longer and faster you spin a rotator the better it performs,
but this also significantly increases the strain on the tether. Centrifugal force rises with length, but a key advantage is that tethers can't be tapered, thicker near the middle and thinner towards the tip, to reduce strain. Tapering allows the tether to exceed the normal breaking length of the material by concentrating strength where it's needed most, for example, the middle section supports more weight, while the lower sections bear progressively less.
Now, imagine a rotator orbiting Earth with a length of 2000 kilometers, its center position 1050 kilometers above sea level. This means its bottom tip would swing to just 50 kilometers above ground at its lowest point. The entire Rotovator orbits every 106 minutes, traveling at an orbital speed of 16,400 miles per hour, 7.33 kilometers per second.
Due to Earth's rotation beneath it, the rotavator would pass over the same point on the ground every 114 minutes, assuming a circular orbit around the equator to simplify things. To synchronize with launch operations we'd want the Rotavator's Spin to be a multiple of this, or at least half of it, since it has two tips that could service multiple launch sites. For example, it could complete a full rotation every 11.4 minutes,
allowing it to dip 10 times per orbit or spin more slowly, such as every 114 minutes to align with passing overhead most of the time. If launching is infrequent, slower rotations might suffice, For instance, a rotation of every 1145 minutes might be reasonable if launches are rare. However, spinning once every 25 orbits, every other day, would likely be too slow to be practical.
as shorter, faster spinning rotavators would work better for such tasks. For a rotavator we are discussing rotation periods faster than orbital periods. There are other possible applications besides spaceship assistance that a rotavator might be used for that might benefit from slower rotation. To illustrate, a rotovator spinning every 114 minutes would have a tip speed of 915 meters per second, 2050 miles per hour,
The acceleration at the tip would be just 0.085G, meaning the tether and any attached payload would experience only 8.5% more weight than normal. This makes it a relatively low stress system for both the tether and its payload. but it's not particularly impactful. The entire rotovator is moving at 7.3 kilometers per second, 16,400 miles per hour due to its orbital motion, while Earth rotates at 465 meters per second,
1040 miles per hour at the equator. When those combined with tip speed, the relative velocity for rendezvous drops to just under 6 kilometers per second, compared to the 8 kilometers per second normally required for orbit. If we increase the rotation speed by a factor of 4, completing a full rotation every 29 minutes, the tip speed jumps to 3660 meters per second, 8200 miles per hour.
This reduces the rendezvous speed to 3200 meters per second, comparable to what a 5000 kilometer long skyhook could achieve. However, the acceleration at the tip increases to 1.37 g, meaning the tip experiences 237% of normal gravity and weight at the bottom of the spin. Importantly, this system only requires a 1000 km tether, not a 5000 km tether.
making it a more compact and potentially viable alternative. If we increase the rotation to 7 times per orbital period, the tip speed rises to 6400 meters per second, 14,300 miles per hour.
reducing their rendezvous speed to 9300 meters per second or 465 meters per second at the equator, about 1000 miles per hour. However, the tether would experience 4.2g from centrifugal force, Pushing this further to 8 rotations increased the acceleration to 5.5g, plus Earth's gravity, and raised the tip speed to 7.32 kilometers per second, 16,374 miles per hour.
At this speed, the tip would effectively move backward relative to Earth's surface except at the poles. So, too fast to be useful, at least on Earth. We can imagine it being quite handy on a planet, a bit more massive than us, that we've settled or that some alien civilization arose on. The 7 rotation version seems feasible with materials suitable for a 5,000 kilometer skyhook, and would allow rendezvous with a relatively mundane hypersonic craft at 50 kilometers, 30 miles of altitude.
which is far more manageable for air-breathing jets. However, this setup poses challenges since the Tether repeatedly slams into relatively dense regions of the atmosphere at high speed, for about a minute every 16 minutes. The lower speed helps but the narrow rendezvous window adds further complications. We also can't realistically winch this tether up or down in so short a time to try to cut down an air drag like the Skyhook can as that would add even more strain.
Another key benefit of the Rotovator is the incredible launch speed it provides. When a spacecraft attaches at the top, 2050 kilometers up, it would be traveling at 13.7 kilometers per second. at an altitude where orbital speed is only 6.88 kilometers per second. This allows it to escape Earth's gravity well and head toward the Moon or beyond. However, the constant dipping in Earth's atmosphere drains momentum significantly.
making the system more efficient at higher altitudes or on airless worlds, but you limit the chance to use a more efficient air-breathing jet in tandem with it. For instance, on the Moon or Mercury, the Roto-Vito could dip right to the surface, grab cargo pods from a stationary platform, and launch them without atmospheric interference. It would also work well on Mars where the thinner atmosphere poses less resistance.
Another approach is to use eccentric orbits, where the Rotavito dips into the atmosphere only twice per orbital ellipse, with the remainder of the orbit far above the atmosphere. You could also combine technologies. For example, a skyhook extending into the atmosphere could be paired with a rotator above it to provide high launch speeds for departing spacecraft.
Alternatively, a rotavator could manage low atmosphere rendezvous speeds, followed by a skyhook or another rotavator to add even more velocity. In our earlier Skyhooks episode, we discussed unconventional orbital paths like the cardio rotavator and tandem systems, such as a Skyhook with a Rotovator hanging from it, or even a Rotovator with another Rotovator attached.
These tandem rotovators are designed to reduce centrifugal force strain on the tether by using a slower spinning primary tether with a shorter, faster spinning secondary tether at its end. While these configurations theoretically mitigate strain, Combining two spinning tethers presents significant practical engineering challenges, making them unlikely to be realized anytime soon. For more details on these advanced concepts, see that episode.
On airless worlds, I believe the Rotorator has an advantage over the Skyhook as there's no air drag to contend with, and the lower gravity on most of these worlds allows the tether to handle greater stress. On Venus however, where habitats must float in the clouds and gravity is somewhat weaker than Earth's, the Skyhook seems like a better option, especially when paired with a mass driver also floating in the atmosphere.
These work well with mass drivers in general, they also both get around the issue many moons or slow routine planets have with space elevators, in that they do not have to remain ground stationary and thus are not problematic on places where your tether might need to be a million miles long to work or around a moon where there is no stable geostationary orbit, or Clark orbit for places besides Earth.
Skyhooks and Rotovators both offer impressive throughput, but they are limited by how quickly they can regenerate momentum and how many you are willing to deploy. You might bring your propellant in from off-world though. such as making rocket fuel on the Moon and using that to let a skyhook more quickly regenerate momentum, though your efficiency suffers. They also pose challenges in managing orbital debris, as they sweep through significant areas of space.
and if damaged or off course could turn from a skyhook into a skywhip instead, a weapon we'll discuss another time. This brings us to Space Ladders, which we will discuss briefly before wrapping up our discussion today of Tether Systems besides the Space Elevator. Space ladders operate quite differently from the other two but have some big advantages. Namely, space ladders eliminate the need for launch vehicles entirely and can operate from virtually any location on the planet.
Space ladders rely on active support, with the original Jacob's Ladder concept proposed by Paul Birch in his paper on Orbital Rings from the early 1980s. Amusingly, Birch referred to the tether's end hook as a sky hook.
a term that's always been somewhat loosely defined as we've mentioned. For those familiar with Orbital Rings, you know their design well, but we won't dive deeply into them today, though they are worth revisiting in future discussions along with other active support launch systems.
The fundamental idea behind an orbital ring is to construct a large metal ring in space, encased within a hollow tube, and spin the two components at different speeds. The system is kept stable through magnetic suspension. As long as the combined momentum of the inner and outer rings match the orbital requirements for a given altitude, the structure remains in place regardless of the relative speed of its components.
While larger versions of these rings could support incredible feats, including constructing entire planets, we'll focus today on a simpler design, a thin orbital ring spinning just once per day. allowing it to remain stationary relative to Earth. The ring inside it spins much faster than orbital speed at that altitude, thus the whole thing remains up and more or less stationary to the ground.
At the equator, this works seamlessly, and here's where the skyhook aspect comes into play. Paul Borch developed his ideas before the advent of carbon nanotubes or graphene. and even Kevlar was a relatively new material at the time. For an orbital ring to remain truly stationary, it needs to either be positioned directly above the equator or tilted at an angle and anchored to the ground.
The latter requires additional engineering and stronger cables, and given that we're already discussing cables over 100 miles long, Borch likely assumed you'd simply tilt the ring and let procession slowly move it around the entire planet. This approach has the added benefit of enabling one ring to serve as a large global community. One ring to serve them all.
Skyhooks could then dangle from the orbital ring, moving at standard aircraft speeds to minimize air drag. These hooks could hang low enough for aircraft to rendezvous with them, allowing for efficient winching of payloads or passengers up to the ring.
descents would likely be less frequent and carefully coordinated to retrieve cargo or passengers. Multiple skyhooks could be distributed around the ring's circumference, ensuring consistent access across a wide area. Regarding momentum regeneration, Orbiter rings spend a significant amount of time in a planet's shadow much like we do on the surface. By default they are positioned just low enough in the atmosphere to benefit from some protection against radiation and micrometeors.
Solar panels can be attached to the ring to regenerate momentum by spinning the inner ring faster. We can also steal momentum from that inner ring to launch a spacecraft but we'll save that for another time. You'd also pair orbital rings with more conventional skyhooks or rotavators above them to further elevate objects, or even install another orbital ring further out. Alternatively, a mass driver could be run along the ring itself for additional functionality.
However, based on the strengths of the tethers we discussed in other contexts, you could take a different approach. Instead of using skyhooks, you could extend tethers down to the ground, often angled like guy wires, to keep the orbital rings securely lashed in place and prevent procession. You can also run power and communication lines on these. This approach is more infrastructure intensive
but offers unparalleled advantages. It allows for climber cables to extend at angles from a broad band around an orbital ring, potentially hundreds of miles wide, These climbers could transport passengers and cargo directly to the orbital ring from within a city, generating no more noise than a train, or even less, and requiring similar levels of acceleration.
and with no need of onboard fuel, just air reserve tanks and a parachute in case the tether snapped for some reason. This setup is the ultimate solution for moving large numbers of people and massive amounts of cargo to and from space daily. You could have hundreds of large rings at slightly different altitudes and angles, interconnected by short tethers. These rings could serve as any location on the planet, providing a low energy path to space directly from urban centers.
From there, ultra-high speed vacuum trains could connect orbital rings to other tethers reaching the ground anywhere on Earth, enabling global travel faster than any plane under the fraction of the cost. We've often discussed the benefits of Orbital Rings, see our episodes on Orbital Rings and Interplanetary Infrastructure for more of their applications.
However, this is a heavy infrastructure solution that likely would not be implemented until there are tens of thousands of people commuting to space regularly. There are other approaches to creating a space ladder beyond simply constructing a space tower. See our episode on Space Towers for more details. For example, you could use purpose-built lobstrom loops to hang a tether, allowing a rotator to snag a ship once it's above the atmosphere.
Orbital rings and loops don't have to be circular either, you could design one that touches the ground on Earth and reaches up to geostationary altitude at its apogee. These structures can also be built in successive layers. with one ring positioned 100 miles up, another at 200 miles, then 300 miles and so on. Larger increments such as thousands of miles become more viable as you move farther from Earth.
creating a series of steps along this space ladder for climbing into orbit. None of these designs is particularly expensive, their cost largely depends on the tether material, which could be relatively cheap if made from carbon based materials. Their main expense lies in the cost of launching the first tether into orbit. In conclusion, tether-based systems like skyhooks, rudivators, and space ladders represent a transformative leap in how humanity might access space.
These concepts, ranging from simple tethers to advanced orbital rings, offer scalable, sustainable, and cost-effective methods for moving people and cargo into orbits and beyond. either on their own or in tandem with proven technologies. By leveraging advanced materials, innovative designs, and the principles of physics we reduce the reliance on traditional rockets,
make them cheaper and easier to build where we do use them, and open up space to millions of people. While these technologies require significant initial investment and infrastructure, their long term potential is unparalleled. promising a future where space is as accessible as air travel is today, a stepping stone to a truly spacefaring civilization.