ROOM
23
Special Report
The trapped objects represent a variety of
ages (~45 years) and sizes (up to a factor of
30 in size difference), as well as a number of
manufacturers and launching states. The trend
has been for fewer objects to become trapped
over the years, as operators follow improved
best practices [8]. However, the trapped objects
will remain in GEO, and constitute a continuing
threat to operational spacecraft.
Besides the larger (greater than a few square
metres in cross sectional area) tracked objects
found in the public domain catalogue [9],
observational campaigns estimate around 500
unknown, un-catalogued debris objects brighter
than 18.5 visual magnitudes, or about 29 cm in size
assuming an albedo of 8%, in the geostationary
ring [10]. This figure does not include high area-
to-mass (HAMR) objects drifting through the
GEO ring, nor does it include large station-kept
satellites not included in the public catalogue.
In addition, there is another class of objects
that is also of concern. These objects have high
area-to-mass ratios and their orbital elements
can change on time-scales of weeks to months
The oblateness of Earth
causes the existence of
two stable gravitation
wells [6] which ‘trap’
non-station-kept objects
in the geostationary ring.
The trapped objects are
mostly old payloads [7].
Below left: The
cumulative growth of the
number of defunct
satellites that orbit about
the western pinch point
(the geo-potential well at
105 W).
Below: The distribution
of objects that can be
correlated (in blue) with
the public catalogue, as
well as a new population
of faint objects that are
not found in the catalogue
(in red). The right-hand
distribution of
uncorrelated objects
contains the high
area-to-mass (HAMR)
objects [15].
weathering, etc.) at long distances that generally
preclude making repairs to orbiting systems. But a
slot at GEO is a valued, finite resource, and there is
competition between countries and companies to
use it. What are the major issues and hazards that
are part of operating in the GEO orbit?
The year 1963 saw the dawn of the commercial
satellite era with the launch of the first GEO
satellite, Syncom 2. Geosynchronous satellite
communications have since brought many benefits
to mankind. But as a result of past activities in
space, a massive amount of space debris - non-
functional and uncontrolled objects - has been left
in Earth orbit which poses a serious challenge to
the sustainability of outer space [1].
One source of larger debris in the GEO ring is
the population of non-functioning payloads and
upper stages that couldn’t be moved to higher
orbits, as is current practice, at their end of life [2].
These objects are trapped in one or both of the
two gravitational wells, or ‘pinch points’, caused
by the gravitational anomalies (more specifically,
perturbations related to the tesseral components
of the spherical harmonic expansion of the Earth
gravitational model) of the Earth at the Equator [3].
Objects trapped in the wells oscillate back and
forth, passing through the wells, the period and
amplitude of the oscillations being dependent on the
specific orbital geometry. The objects thus trapped
are primarily defunct payloads, including the first
commercial GEO communications satellite, Intelsat-1
F1 (‘Early Bird’) [4].
CHARACTERISTIC
75°
EAST WELL
105°
WEST WELL
TRAPPED IN
BOTH WELLS
Payload: Radugas (29), Gorizonts (9), Ekrans (8), etc
83
39
15
Rocket Body: Largely Proton-K fourth stages
17
0
3
Debris: 2006 Feng Yun and 1978 Ekran 2
2
0
0
Total
102
39
18
A slot at GEO is a valued,
finite resource and there is
competition between countries
and companies
