An Orbital is a rotating hoop-shaped megastructure which consists of an enormous band of material arranged in a ring with a diameter that is typically measured in millions of kilometres. The spin rate and diameter of the Orbital is made to simulate the length of day and surface gravity of a given planet along the entire inner surface of the megastructure. As the Orbital spins, the lithosphere, hydrosphere and atmosphere are held against the inner surface by centrifugal forces to maintain the desired type of ‘planetary’ environment. In this article, I will be describing an archetypical Orbital that is made to duplicate the same conditions as the Earth.
Credit: Al Brady
To create Earth-like conditions, the Orbital orbits the Sun at around the same distance as the Earth. The inner surface of the Orbital has the same sea level atmospheric pressure as the Earth, experiences a 24 hour day-night cycle and provides the same amount of gravitational acceleration as on the Earth’s surface. To do that, the Orbital will need to have a diameter of 3.71 million kilometres. Because the Orbital spins once every 24 hours, the velocity at its rim is 486000 kilometres per hour or 135 kilometres per second. An atmosphere is held against the inner surface of the Orbital by spin induced centrifugal forces. Walls that are over a hundred kilometres high line both rims at the inner surface of the Orbital. These immense walls along the rims maintain the atmosphere by preventing it from slipping off the edge into space.
Constructing the Orbital will be a challenge because there is still no known material strong enough to withstand the tremendous tensional stresses found within the structure of the Orbital. As always, this yet to be discovered material shall be termed unobtanium and it will be used in the construction of the stress carrying structure of the Orbital. The lithosphere, hydrosphere and atmosphere will all be constructed upon the inner surface of this unobtanium-based stress carrying structure. To construct the rim walls along the two edges of the inner surface of the Orbital, extremely low density and very high strength materials such as self-supporting diamondoid foam can be employed. Furthermore, self-supporting diamondoid foam can also be used to support the underlying contours of the topography.
The entire circumference of the Orbital along its inner surface measures 11.66 million kilometres and it takes light almost 40 seconds to travel that distance. Assuming that the Orbital has a width of 15000 kilometres, the total habitable area of the inner surface of the Orbital will be a staggering 175 billion square kilometres. An area like this is equivalent to 343 times the surface area of the whole Earth or 17800 times the surface area of the United States of America
An observer standing on the inner surface of the Orbital will see a sky that is similar to that seen from the Earth’s surface as the atmosphere overhead is entirely open to space. However, unlike on the surface of the Earth, the observer will be able to see the approach of dawn and dusk along the Orbital. Furthermore, the observer on the inner surface of the Orbital will be constantly aware of an impressive sight where the world at two ends of the horizon will appear to curve upwards and eventually meet overhead at a great distance of 3.71 million kilometres away.
Nights on the inner surface of the Orbital will be spectacular as the ringlight reflected from the illuminated portion of the Orbital will appear thousands of times brighter than the full moon on Earth. Due to the large amount of reflected light, astronomers on the inner surface of the Orbital will have a great difficulty in trying to observe the nigh sky. However, the dark and pristine vacuum of space is never too far away as the astronomers can easily carryout their observations from the outer surface of the Orbital. At night, an amateur astronomer with an average backyard telescope will be able to distinguish large geological features and any great megalopolis located far away, on the other side of the Orbital.
To create the day and night cycles, the Orbital is tilted at an angle of 23.5 degrees with respect to its motion around the Sun. If the Orbital has no axial tilt with respect to its motion around the Sun, it will eclipse the Sun all of the time from the perspective of an observer on the inner surface of the Orbital. The tilt of the Orbital creates 2 warm seasons and 2 cool seasons each year. The middle of each warm season is marked by a midsummer eclipse of the Sun and the middle of each cool season is marked by the Sun’s lowest position in the sky. Unlike on the Earth, the length of daylight on an Orbital will not vary, resulting in no long summer days or long winter nights. If the orbit of the Orbital around the Sun has some eccentricity, it can cause one warm season to be warmer than the other and one cool season to be cooler than the other.
Regions located near the towering walls along the rims of the inner surface of the Orbital will experience a more pronounced seasonal variation. If the Orbital goes around the Sun in a circular orbit with negligible eccentricity, the region in the immediate vicinity of one rim wall will be in shadow for half a year while the region near the other rim wall will receive extra light reflected from the rim wall itself. This means that during first half of the year, the region located near one rim wall will be cooler than the rest of the Orbital and during the second half of the year, the region located near the same rim wall will be warmer than the rest of the Orbital. During the same period, the opposite is true for the region located near the other rim wall.
Overall, seasonal variations on the Orbital will be very slight in comparison to those that occur on the Earth. The Coriolis Effect will not be significant on the Orbital because the only form of Coriolis Effect is the rising and falling air within the troposphere where most of the weather occurs. With a thickness of around 10 kilometres or so, the depth of the troposphere is insignificant as compared to the 3.75 million kilometres diameter of the entire Orbital. Without major temperature gradients and without the Coriolis Effect, the weather on the habitable inner surface of the Orbital will be gentler and more localized than the weather on the Earth.
Without a moon, the tidal effects on the Orbital will be weaker than those on the Earth since the only form of tides on the Orbital will be those generated by the Sun. With no contrasting cold polar oceans and warm equatorial oceans like those found on the Earth, natural circulation between the surface waters and the deep ocean waters cannot be established. Without such a circulation system, the deep ocean waters will become anoxic. In order to maintain rich oxygen-bearing waters throughout the entire depth of the oceans, artificial heating can be applied to the deep ocean waters at specific locations on the ocean floor to keep the circulation running. Additionally, the underwater topology can be carefully sculptured to enable the mixing of surface water with deep ocean water from tidal effects alone.
Towering walls that are similar to those found on the rims or exceedingly high mountain ranges called ‘bulkhead ranges’ can be used to contain and completely isolated alien environments and ecosystems that are very different from the standard Earth-like environment of the Orbital. Entire pristine prehistoric worlds that are populated by once extinct creatures can also be completely enclosed within these immense barriers. Panoramic views of or from these ‘bulkhead ranges’ will be especially breathtaking as these mountains tower over a hundred kilometres above the surroundings. In comparison, Earth’s Mount Everest is only 8848 meters in height. On the immense scale of the Orbital, mountains that far surpass the height of Earth’s Mount Everest or Mars’ Olympus Mons will appear as mere tiny bumps on the incredibly vast landscape.
‘Bulkhead ranges’ and other mountains of comparable heights rise from the dense and warm lower reaches of the atmosphere and terminate at summits reaching high above the atmosphere into the silent vacuum of space. These mountains are rather interesting as they rise through the full extent of the troposphere, stratosphere and mesosphere. In fact, these mountains are so high that they rise well above the ozone layer and even above the high-flying noctilucent clouds. The summit environments of these mountains are basically bare rock exposed to the vacuum of space. In order to reduce the mass of material required for such mountains, the interior bulk of these mountains can be entirely made of advance self-supporting diamondoid foam or other forms of exotic materials that have very low densities and very high strengths.
Journeying to a distant part of the Orbital will be a challenge due to the sheer size of the Orbital. Even for someone cruising at a speed of 10 kilometres per second onboard a high speed vacuum tube maglev train, it will still take almost 2 weeks to circumnavigate the entire Orbital. Hence, travelling to far-off places on the Orbital will require technologies similar to those employed for large scale commercial interplanetary space travel. Furthermore, interplanetary space voyages disembarking from the Orbital will be much simpler as a spacecraft released from the outer surface of the Orbital will already be travelling at a speed of 135 kilometres per second.