How far from a sidereal day's rate the mean motion of a geosynchronous
orbit may be, in revolutions a day: a tenth of it either side, a period
from about 21.8 to 26.6 hours. Wide enough for any orbit that keeps
roughly in step with the turning Earth, however far its figure of eight
has drifted in longitude, and far from the nearest other family, the
navigation orbits Galileo and GPS fly at 1.7 and 2 revolutions a day.
How far from a sidereal day's rate the mean motion of a geosynchronous orbit may be, in revolutions a day: a tenth of it either side, a period from about 21.8 to 26.6 hours. Wide enough for any orbit that keeps roughly in step with the turning Earth, however far its figure of eight has drifted in longitude, and far from the nearest other family, the navigation orbits Galileo and GPS fly at 1.7 and 2 revolutions a day.