SPOILER! Kattints ide a szöveg elolvasásához!Space around the Earth is often divided into different orbital regimes that generally describe the dynamic characteristics of satellites. The most simple and relevant description of an orbit pertains to the minimum (perigee) and maximum (apogee) altitudes (e.g. 400 x 800 km) that a satellite achieves. In circular orbits, which make up the vast majority of satellites, perigee and apogee are almost equal.
The atmosphere almost entirely subsides by around 7o0km altitude, and so an object above this altitude will remain in orbit much longer than a lower satellite. Most cubesatellites are required to deorbit naturally within 25 years, and so they mostly have perigees well below 500 km. But once you leave the exosphere of the atmosphere, the time to deorbit (if ever) becomes MUCH greater. In 2007, China tested an anti-satellite (ASAT) weapon on a target in an 850 km circular orbit. Unfortunately, the large amount of debris produced by the collision will remain on orbit for at least a century or two, presenting a long-term space debris hazard.
Above around 1000 km, you start leaving the realm of Low Earth Orbit (LEO) and entering the broad expanse of Middle Earth Orbit (MEO). There are a couple of geodetic satellites in the 1,500-10,000 km altitude range, among which is LAGEOS. This satellite was the subject of significant perturbation analysis and was found to be in a stable orbit for at least 8 million years. The primary perturbations at these altitudes result from the gravitation of the Sun, Moon, the oblatness of the Earth, and from the transfer of momentum of solar particles to the spacecraft, a phenomenon known as solar radiation pressure (SRP).
The effect of SRP is much greater on smaller particles than larger objects due to the greater Area-to-Mass ratio. Smaller particles are therefore subject to much higher magnitudes of orbital perturbations, and could potentially deorbit faster than larger denser satellites. One such example would be the rapid orbital decay (~50 years) of milimeter-sized copper wires from ~3500 km launched as part of the MITLL Project West Ford.
Jumping in altitude out to ~20,200 km, one encounters our GPS and GNSS constellations. With the knowledge that LAGEOS will stay on orbit for almost 10,000,000 years at a quarter of this altitude, it's safe to conclude that GNSS satellites will remain in orbit for many millions of years. In order for the satellite to deorbit, it's perigee must effectively lower to under 700 km, which could only occur under the influence of perturbations effective over an incredibly long period of time.