Chapter Three: The Gravity Well

Orbital Rings: The Ultimate Space Transit System

An orbital ring has the highest capacity of any conceptual mass transit system to space while also having virtually no impact on the ground. Since the ring itself sits well above the bulk of the atmosphere, it is not affected by the weather. It is invisible to the naked eye, even from the highest peaks or an airplane window. The anchor lines would appear as strange threads vanishing into space and would be visible only from close proximity.

The ring itself is located well above the flight ceiling of all air traffic, making it unreachable even by the most sophisticated high-flying military aircraft. The only vehicles that can reach it are rockets heading for space. The anchor lines span the distance from the ring to the ground, but they would be well marked and easily avoided by air traffic.

The bottom line is that once an orbital ring is built, it will have a very small environmental impact but an absolutely huge economic one. Just imagine a world where a person can have a regular job in space while still living on the Earth’s surface.

Spaceships can be launched from the orbital ring with sufficient velocity and a high degree of precision to reach Mars without needing any extra propellant beyond what is required to slow down for Mars’ orbital insertion. Transporting people, equipment, and supplies to space would cost less than airplane travel since there would be no fuel costs. Yes, building an orbital ring is a monumental task, but so was building the rail system, all the roads we drive on, and laying down all the fiber optic cables that make the Internet work. An orbital ring would have an impact comparable to those achievements and beyond.

Types of Orbital Rings

There are several types of orbital rings besides the one I will describe later. The particular design I favour is a continuous inner cable spinning faster than orbital velocity and fully enclosed in a sealed shell.

The disadvantage of this “closed” design is that it requires significantly more material to construct, making it practical only if that material is sourced from space.

The advantage is that it is much more stable than designs with a free-spinning cable that is only anchored at a few locations. A closed ring is also capable of being placed at a lower altitude than an “open” design since the inner shell can be made to operate at reduced pressure.

A closed orbital ring would utilize a circular orbit, so the force generated by the excess cable velocity would be uniform and aligned with the great-circle plane that the ring occupies. In other words, the stretch in the cable simply makes the orbit slightly higher. A great-circle plane is a plane that passes through the center of a sphere, as opposed to a segment plane, which does not pass through the sphere’s center.

An open orbital ring is somewhat different. It is described in Paul Birch’s paper titled “Orbital Ring System and Jacob’s Ladders”, published in the Journal of the British Interplanetary Society, vol. 35, 1982.

First of all, in Birch’s design, the cable would be anchored at as few as two locations. In that configuration, the cable’s orbit would be football-shaped rather than circular. The downline connectors would be placed at the two opposite ends of the orbit. The two support structures would absorb the extra force as they accelerate the cable. The biggest problem with this setup is that any disturbance, such as the moon passing overhead, could cause catastrophic failure since it would have half an orbit to amplify that disturbance, making the loop inherently unstable. Additionally, there is the issue that a maglev train cannot run over the bare cable, which drastically degrades the ring’s functionality. The significant advantage of this design is that the cable would need to spin only slightly faster than its natural orbital velocity, as all the extra force generated by that additional spin is concentrated at just two locations.

Another design that could work in either an open or closed configuration does not use a cable at all. Instead, it employs a series of small pellets placed in the orbital path previously occupied by the cable in other designs. Each individual pellet is then propelled by the support system, slightly altering its velocity in the process. This change in velocity provides the lifting force that was previously supplied by the cable.

The danger is that any misalignment of even one of the approximately 42 million pellets could lead to a catastrophe, as the relative velocity between the pellet and the platform is about 30 times the speed of a bullet. The figure of 42 million pellets is based on spacing them 1 meter, or about 3 feet, apart. To put that in perspective, a velocity of 30 times the speed of a bullet means that the kinetic energy would be 450 times greater than that of a bullet with the same mass, since kinetic energy is calculated as half times mass times velocity squared, or 0.5 times the mass of one bullet times 30 squared.

The last example also provides insight into how the cable works. You can think of each section of the cable as a separate piece that is slightly redirected when it interacts with the outer shell; it is this slight change in velocity that prevents the stationary outer shell from falling back to Earth. This change in velocity for the section is necessary because it is moving somewhat too quickly for the orbit it occupies; thus, the section is actually trying to move to a higher orbit, but the stationary structure is redirecting it to remain in its desired orbit.

We will perform the calculations in a later section of the book. For now, suffice it to say that it is the slight changes in velocity (i.e., direction) of each individual segment of the cable as it interacts with its support structure that provide the lift to that support structure. The support structure is stationary relative to the ground, whereas the inner cable is spinning faster than its natural orbital velocity.

This brings up another important point about the cable in the orbital ring. It exists solely to keep the pellets embedded in it on their proper path. The cable does not need to be very strong. The stiffness of the cable adds some safety, as even a slight brush between the inner cable and the outer shell at 28,000 km/h (17,400 mph) could cause a catastrophe. The cable keeps the individual pellets in the correct orientation and in line, thereby preventing such a catastrophe.

Public domain image courtesy or Wikipedia. https://en.wikipedia.org/wiki/Konstantin_Tsiolkovsky

Tsiolkovsky’s significant contributions include the formulation of the Tsiolkovsky rocket equation, which describes the motion of rockets, as well as his visionary ideas regarding space exploration and the potential for human life in outer space. He proposed the concept of using multi-stage rockets and emphasized the importance of liquid propellants for achieving the necessary speeds to escape Earth’s gravity. Additionally, Konstantin Tsiolkovsky imagined the possibilities of space habitats, interplanetary travel, and the use of artificial satellites long before these ideas became a reality.

Despite facing financial difficulties and lacking formal training, Konstantin Tsiolkovsky’s work laid the groundwork for future generations of rocket scientists and space explorers. His legacy is celebrated in various ways, including the naming of craters on the Moon and Mars in his honor. He passed away on September 19, 1935, but his visionary ideas continue to inspire scientists and engineers in the field of space exploration.

Another important figure in the imagining of megascale space infrastructure projects is Arthur C. Clarke. In his 1945 paper on geostationary satellites, he introduced the concept of artificial structures in orbit that could serve humanity on Earth, setting the stage for more ambitious megastructures like orbital rings.

Arthur C. Clarke was a groundbreaking British science fiction writer, futurist, and inventor, born on December 16, 1917, in Minehead, England. His fascination with science and technology began at an early age, leading him to pursue a career in science. He served in the Royal Air Force during World War II, where he worked on radar technology, which later influenced his writings.

Arthur C. Clarke is perhaps best known for his novel “2001: A Space Odyssey”, published in 1968, which was developed concurrently with Stanley Kubrick’s iconic film of the same name. The story explores themes of artificial intelligence, space exploration, and the evolution of humanity, and it has become a cornerstone of science fiction literature.

In addition to “2001,” Arthur C. Clarke wrote numerous other novels and short stories, including “Rendezvous with Rama”, “Childhood’s End”, and “The Fountains of Paradise”. His works often blended scientific accuracy with imaginative speculation, earning him a reputation as one of the “Big Three” science fiction writers of the time, alongside Isaac Asimov and Robert A. Heinlein.

Arthur C. Clarke was a visionary thinker who predicted the rise of satellite communication and the internet. He proposed the idea of a geostationary satellite in 1945. His contributions to both science fiction and real-world technology earned him numerous accolades, including the Hugo and Nebula Awards.

In his later years, Arthur C. Clarke lived in Sri Lanka, where he continued to write and lecture on science and space exploration. He passed away on March 19, 2008, leaving behind a legacy of pioneering ideas and literary achievements that continue to inspire generations of readers and scientists.

The first formal, detailed proposal for an orbital ring came from Paul Birch, a British engineer. Paul Birch‘s contributions were outlined in a series of papers published in the Journal of the British Interplanetary Society between 1982 and 1984, where he expanded on earlier ideas of space tethers and momentum-exchange systems, developing a detailed and practical framework for orbital ring construction.

Paul Birch described the orbital ring as a tension structure encircling the planet at low Earth orbit (approximately 300 to 500 km in altitude). He proposed the idea of a tension-supported structure encircling Earth at Low Earth Orbit (LEO).

Unlike space elevators, which require materials capable of withstanding extreme tensile forces from Earth’s surface to geostationary orbit, Birch’s design placed the ring in orbit, allowing centrifugal forces to support the structure dynamically. His orbital ring concept involved a rotating cable moving slightly faster than orbital velocity. Magnetic suspension or bearings would hold the ring aloft, and tethers could extend to the Earth’s surface, allowing elevator systems to transport materials and people to orbit.

Paul Birch’s work extended beyond Earth. He described how similar systems could facilitate the colonization of Mars, Venus, and other celestial bodies. His designs incorporated terraforming elements, showcasing the potential of orbital rings for planetary-scale engineering.

By NASA/svg by uploader – derivative of http://www.nas.nasa.gov/About/Education/SpaceSettlement/Nowicki/SPBI1271.GIF, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5810733

In the 2000s, the development of carbon nanotubes, graphene, and ultra-light composites reignited interest in orbital ring designs. These materials, known for their exceptional tensile strength, were considered essential for constructing orbital tethers and rings by many. As you will see in later chapters, however, those advanced materials are not actually required. They would undoubtedly improve the orbital rings by allowing them to be placed in higher orbits using thinner, stronger cables. The conductivity of graphene or carbon nanotubes would also enable power generated from the orbital ring’s solar panels to be transported directly to the surface rather than requiring transmission via microwave power transmitters. No other conductor is strong and light enough to be incorporated in the anchor lines.

Though SpaceX has not pursued orbital rings directly, the company’s work on reusable rockets and the Starship reflects a growing interest in cost-effective space infrastructure, aligning with the orbital ring goals of providing cheap and continuous space access. I will use the SpaceX Starship in later chapters for cost calculations as I describe the build process.

NASA has conducted space tether experiments, such as the Tethered Satellite System (TSS), which test the dynamics of long tether structures in space. Although these projects are not directly related, they provide valuable insights into how orbital rings might be stabilized and operated.

Not to be mistaken for orbital rings are the Ringworld megastructures made popular by Larry Niven in his 1970 novel “Ringworld” and the Iain M. Banks Culture series, as well as in the video game Halo. I mention this because it is the first thing many people cite when I talk about orbital rings. Other than the word “ring,” the two are not related.

Orbital rings are mentioned in a number of science fiction novels, including Kim Stanley Robinson’s books “Red Mars” and “2312.”

“Children of Time” (2015) by Adrian Tchaikovsky is a very interesting story in which intelligent spiders create an orbital ring using their spiderwebs. You will discover why that is so interesting later; however, I only recently read that fantastic book, and I wrote my first paper on how to build an orbital ring nearly ten years ago, using, you guessed it, artificial spider silk. I wrote that paper after reading an article in Wired Magazine about a company called Bolt Threads (https://www.wired.com/2015/06/bolt-threads-spider-silk/).

Other Space Transit Systems

Besides an orbital ring, there are numerous other proposals for space transit systems, including tethered rings, launch loops, space elevators, skyhooks, StarTram, Hyperloop to Space, mass drivers, space guns, space fountains, lightcraft, ground-launched space planes, assisted launch space planes, and multistage rockets.

These concepts can be further grouped into several categories, including rings and loops, tethers, initial launch systems, externally sourced propulsion, and conventional launch systems.

We will briefly examine each of these in the next few articles of this blog.

Keep following this blog, and don’t forget to check out the first book of the hard fiction saga, Orbital Ring Engineering, now available in hard cover and Kindle versions.