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A view from the International Space Station in a low Earth orbit (LEO) at about 400 km (250 mi), with yellow-green airglow visible at Earth's horizon, where roughly at an altitude of 100 km (62 mi) the boundary between Earth and outer space lies and flying speeds reach orbital velocities.
Low Earth orbit (LEO): geocentric orbits with altitudes below 2,000 km (1,200 mi). [7] Medium Earth orbit (MEO): geocentric orbits ranging in altitude from 2,000 km (1,200 mi) to just below geosynchronous orbit at 35,786 kilometers (22,236 mi). Also known as an intermediate circular orbit.
The Japanese Space Agency, JAXA, launched its Super Low Altitude Test Satellite, or SLATS (“Tsubame”), in 2017, whose orbit slowly decreased from an initial altitude of 630 km (391 mi) to operate at seven different altitudes, from 271 km (168 mi) to a final altitude of 167.4 km (104.0 mi).
For a satellite to be in a stable orbit (i.e. sustainable for more than a few months), 350 km is a more standard altitude for low Earth orbit. For example, on 1 February 1958 the Explorer 1 satellite was launched into an orbit with a perigee of 358 kilometers (222 mi). [5]
Hubble orbits in low Earth orbit at an altitude of approximately 540 kilometers (340 mi) and an inclination of 28.5°. [5] The position along its orbit changes over time in a way that is not accurately predictable.
In contrast, Earth satellites with perigees below 80 km are highly unlikely to complete their next orbit. It is noteworthy that meteors (travelling much more quickly) usually disintegrate in the 70–100 km altitude range, adding to the evidence that this is the region where the atmosphere becomes important.
Atmospheric pressure in low Earth orbit, around 500 km altitude [13] [14] 10 −7 Pa. 100 nPa Highest pressure still considered ultra-high vacuum [15] [16] 10 −6 Pa.
The speed is approximately 3 km/s (9,800 ft/s). High Earth orbit (HEO) Geocentric orbits with altitudes at apogee higher than that of the geosynchronous orbit. A special case of high Earth orbit is the highly elliptical orbit, where altitude at perigee is less than 2,000 km (1,200 mi). [9]