EOS: Earth Orbit Station

EOS is a large, spherical, rotating space station located in high Earth orbit.

EOS stands for “Earth Orbit Station”. The name references Eos, the Greek goddess of the dawn. Her brother was Helios, god of the Sun, and her sister was Selene, goddess of the Moon. This is apt since EOS is a sphere orbiting Earth, like Luna, and will be built from lunar materials. Also, EOS is solar-powered.





EOS is a sphere with diameter of 20 km. It has open circular entrances at the north and south poles with diameters of 2.26 km, and an open cylindrical core running through the centre with a diameter of 2.66 km. Spacecraft arrive and depart through these large circular openings and dock inside this cylinder where the level of artificial gravity is Luna-equivalent (0.165 g).

EOS’s axis of rotation is perpendicular to the ecliptic, making it almost parallel with Luna’s axis of rotation. The station completes one full rotation every 3 minutes, or 480 times per day. This rotation achieves two important effects:

  • It produces an artificial gravity effect within the station, via centripetal force.
  • It prevents any side of the station being exposed to sunlight or darkness for long periods of time, thereby preventing it from becoming too hot or too cold.

The outer hull is partly covered in solar panels. The total area of the external hull is approximately 1,257 km2, but we will probably not need to completely cover this area with solar panels. A ring of solar panels would initially be built around the space station’s equator, and then expanded towards the poles as energy requirements increase over time.

Polar regions will be dedicated to radiators, thrusters for station-keeping and stabilisation, and communications and other equipment. Windows will be located at the ends of each level.

To maintain a stable axis of rotation, the station’s mass is balanced around the axis by pumping water between large tanks located throughout the station.

Gravity levels

There are four concentric cylinders within the external spherical hull, which are levels within the station. Each has a different radius, and thus a different gravity level. The radius of each level is such that the level’s gravity level corresponds to a world of the Inner Solar System. In order of increasing radius and thus increasing gravity, the levels correspond to Luna, Mars, Venus, and Earth, and are therefore named Levels L, M, V, and E respectively. Mercury has almost the exact same level of gravity as Mars, therefore Level M represents Mercury as well.Screen Shot 2018-03-10 at 20.43.06Transit between the levels is achieved with elevators that run perpendicular to the axis of rotation. As someone “descends” from Level L to E, they will experience a steady increase in gravity, from Luna-equivalent to Earth-equivalent.

The different gravity levels will offer scientists the opportunity to conduct research in the gravity environments of the Inner Solar System worlds, without the need to go there. Astronauts and tourists could visit EOS on their way to other parts of the Solar System, for training in different gravity levels.

Perhaps the most important advantage of the different gravity levels is that they will enable comfortable accommodation to be provided for people from 5 worlds. This will make EOS an ideal location for conferences where interplanetary affairs can be discussed.

Orbital parameters

The intention is that EOS be placed between Earth and Luna, at the “one week” orbit. This orbit has a synodic period of exactly one week, and a sidereal period of 6.8684 days, which means it will return to the same place in the sky relative to Earth and the Sun at the same time each week. This orbital radius is 152,629 km, which is almost exactly 40% of the distance between Earth and Luna, and almost half the distance to Earth-Moon L1.

Unlike most of the Earth orbit space stations we will build during the early stages of orbital colonisation, this altitude places EOS above Earth’s magnetosphere for most of the time. Earth’s magnetosphere extends to about 65,000 km from Earth on the day side, and about 6,300,000 km on the night side.

When EOS is on Earth’s night side, it will be protected from cosmic radiation by the magnetosphere and Earth itself; however, most of the time it will not be protected, and will therefore require significant shielding mass.

Despite the additional mass and therefore cost associated with building at this altitude, the station will be an excellent location for researching Earth’s magnetosphere, the solar wind, and the radiation environment of near-Earth interplanetary space.

This orbit will deliver attractive views of the entire spheres of both Earth and Luna. It could become a popular destination for space tourists, and a useful way station between the two worlds. One of its primary functions could be a refuelling station for spaceships bound for various destinations throughout the Solar System.


Due to the large mass, most of the materials for construction are expected to come from Luna. Therefore, a reasonable industrial base on Luna, and the capacity to launch large payloads from the lunar surface, are prerequisites. Construction would probably not commence until the 22nd century, after settlements have already been established on both Luna and Mars, and lunar or asteroidal sources of oxygen, water, metals, silicon, carbon, etc. are available.

The space station may be constructed from lunar steel; an alloy of iron, magnesium, and perhaps other elements yet to be determined. The external hull will comprise trusses of steel beams, connected along the edges of a tessellated sphere. This will produce a very strong and stable structure. The four internal cylinders, for the levels, will also be constructed from steel trusses. Spokes will run from the equator through the centre of the sphere that will tie the sphere and the cylinders together, and prevent excessive outward bulge caused by centripetal force.

The solar panels on the external hull would also fabricated on Luna.

Features of the levels

Each level, other than Level L, will include areas for built environment, parks, and waterways. Dirt, concrete, and water will all help to provide radiation protection.
Under each level will be storage for water, oxygen, nitrogen, carbon dioxide, and other necessary resources; environment control and life support systems; and recycling and other systems. Every level will have both underground and aboveground structures, such as accommodation, farms, shops, offices, workshops, schools, and medical, research, and industrial facilities. The ceiling will be about 200 m above the datum on each level (excluding Level L), allowing an open, airy feel, with sunlight piped in from the external hull. Day-night cycles would be simulated within the station by opening and closing of light pipes.

Every level will feature accommodation suited to people from that world or approximate gravity level. This highlights one of the primary uses of EOS — it is where people from all over the System can come and meet, and attend conferences and so forth. If people from Mars want to meet with people from Earth, for instance, it may be too difficult for the Martians to meet on Earth, because Earth’s high gravity would be uncomfortable for them. However, at EOS, both parties could both find comfortable accommodation, and the Terrans could go to the meeting rooms on Level M to meet with the Martians.

Level L

This level is open to space and will not feature plants or waterways, but be entirely solid, most likely constructed of concrete and steel. Spaceships will enter and depart through the circular openings at the poles, and dock on Level L. It may be possible for arriving spacecraft to match the speed of rotation and dock with the moving surface of the level; otherwise, “docking rings” could be included that rotate at the same speed in the opposite direction relative to the space station, thus providing a stationary platform for spacecraft to dock. After docking, the rotational velocity of a docking ring would gradually change until it matched that of the station, so that alighting passengers and crew could easily and safely move into the station.

Level L is a tube almost 20 km long, with an area of over 16,000 hectares. In addition to docking bays, it will provide cargo storage, fuel storage and refuelling stations, workshops for spacecraft repairs and maintenance, laboratories for lunar-gravity research, and facilities for lunar- and zero-gravity sports and recreational activities.

Level M

On Level M, in addition to research facilities and accommodation for visiting Martians, there will be a large, enclosed section where the Martian environment will be simulated, including dirt, rocks, air, lighting, and gravity. Gravity is the one characteristic that cannot be simulated on Earth. This “Mars tank” will permit astronaut training and experimentation with robotics and other equipment in a realistic Mars environment, without the need to travel all the way to Mars. Although people will already be living on Mars by the time EOS is operational, it will still be convenient to have a facility like this close to Earth.

Level V

Level V will be dedicated to Venusian science and terraforming research. It will host a large and lush forest and a university where international and interplanetary conferences can be held.

To be honest, Level V is arguably superfluous, and it could be eliminated from the design to significantly lower the cost of the station. The university and forest could be located on Level E or M.

Level E

On Level E, a large, natural-looking river will flow through the centre of the level, with additional water features such as streams and waterfalls off to the sides, flowing into the river. Level E is 11 km wide, therefore, this creating strips of land over 5 km wide on each side of the river. The river will be suitable for swimming, boating, and other water-related activities.



I like to travel, read, write, code, and teach. My main interests are space settlement, planetary engineering, health and fitness, and human evolution.

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