7.8 km a second: what low Earth orbit means
Published
A low Earth orbit is any orbit that goes round in 128 minutes or less[1], and the region it uses lies below about 2,000 km[2]. Staying up there takes a speed of about 7.8 km a second[3].
The ISS as the example
The International Space Station flies in low orbit, about 400 to 420 km above the surface[4]. It moves at 7.67 km a second and goes round the Earth roughly every 93 minutes[5].
At the game’s 400 km the same physics gives about 7.67 km/s and an orbit of about 92 minutes (derived from Earth’s mass and radius), close to the station’s figures. From that height the horizon is about 2,300 km away and sits about 20° below level.
Two low-orbit points in the game
The game has two low-orbit places, both at 400 km:
- Over Sumatra, at 0°, 100° E.
- Over Ecuador, at 0°, 80° W: exactly opposite Sumatra on the globe, off Ecuador’s Pacific coast.
Each uses a sharper cut of NASA’s Blue Marble map, about 1.9 km a pixel, and Earth here is close enough to be drawn at true scale. NASA’s cloud map decides where it is cloudy; up close, cloud shapes are generated, drift with the winds of their latitude, and cast shadows. With the Sun fixed at a June morning, the Ecuador point is at local midnight, so it is dark, by choice.
- Sumatra links up to the 100° E geostationary point only, and down to the 25 km surface areas over Bukittinggi and Bangkok.
- Ecuador links up to the 140° W and 20° W points.
- The two never link: Earth is between them.
Low orbit to Bukittinggi takes about 7 minutes at 1 g; the 100° E geostationary point to low orbit over Sumatra, about 1.1 hours.
One simplification: in game a low-orbit point holds still over its spot. A craft truly at 400 km would pass over it about every 92 minutes, not hover.
How the places connect: Travel nodes.
Related
- 35,786 km up: why a satellite can hang still in the sky
- Bukittinggi: a highland town between two volcanoes, at 25 km
- 11 places, 14 links: how travel works in Hostile Flagship
- 384,400 km apart: the Earth and the Moon at true scale
Sources
- Low Earth orbit, Wikipedia.
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less
- Low Earth orbit, Wikipedia.
The term LEO region is used for the area of space below an altitude of 2,000 km (1,200 mi)
- Low Earth orbit, Wikipedia.
The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s
- Low Earth orbit, Wikipedia.
The International Space Station is in LEO about 400 to 420 kilometres (250 to 260 mi) above the Earth's surface
- International Space Station, Wikipedia.
Its orbit takes it at 7.67 km/s (27,600 km/h; 17,200 mph) roughly every 93 minutes around Earth