The Geostationary Ring
The Slowenian-Austrian engineer Herman Potocnik (1892–1929) has probably never dreamt
that his concept of the geostationary orbit would become a great success in the space age.
In 1929, he published under the pseudonym Hermann Noordung, the book “Das Problem
der Befahrung des Weltraums – Der Raketen Motor”,
where he described a space station in
the geostationary orbit for meteorological observations. In 1945, Arthur C. Clarke, familiar
with the work of H. Potocnik, published the well-known article “Extra-Terrestrial Relays” in
the journal “Wireless World”, where he explained the advantages of geostationary satellites
Currently, about 300 operational spacecraft for telecommunication, navigation, meteorol-
ogy, Earth observation, Earth surveillance and space science take advantage of the properties
of this unique orbit. The ideal geostationary orbit is circular, lies in the plane of the Earth’s
equator and completes one revolution in one sidereal day (1436.1 min). Because of the pres-
ence of various types of perturbations, the ideal geostationary orbit is a ﬁction. In reality, all
geostationary spacecraft have slightly eccentric and inclined orbits and the orbital period
deviates slightly from one sidereal day. We denote the region in space that contains all
operationally used geostationary spacecraft as the geostationary ring. “Operationally used”
signiﬁes here that at least the East–West motion is controlled; however, many operational
spacecraft also maintain more fuel-expensive North–South control.
In total, more than 800 spacecraft and rocket upper stages are in the geostationary ring and
vicinity. Uncontrolled objects in inclined orbits may represent a safety hazard to operational
geostationary spacecraft. Collisions between spacecraft and rocket stages in the geostation-
ary ring can be avoided by transferring these objects, at the end of their operational life, into
a disposal orbit located sufﬁciently high above the geostationary ring. Concerned about the
situation and safety in the geostationary ring, the Inter-Agency Space Debris Coordination
Committee (IADC) has issued a recommendation on the minimum altitude increase of the
disposal orbit. However, this action does not eliminate the possibility of equally damaging
collisions between spacecraft and large fragments from past explosions in and near the
At least two rocket stages and one spacecraft are currently believed to have exploded while
in or near the geostationary orbit. Based on similar explosions in low Earth orbit, these three
events likely produced about 1000 fragments larger than 10 cm. These fragments are too
small to be routinely catalogued and therefore, they are not included in this document.
However, the existence of a large fragment population in the geosynchronous region has
been veriﬁed by statistically sampling the population with large, ground-based telescopes.
Consequently, using only the objects in this report to calculate destructive collision rates in
or near the geosynchronous region may signiﬁcantly underestimate the hazard.
The Problem of Space Travel – the Rocket Engine, Verlag Richard Carl Schmidt & Co., Berlin, 1929.
Space Debris 1, 219–220, 2001.