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Special Report
by solar radiation pressure, which causes them to
periodically pass through the GEO belt [11, 12, 13, 14].
Space weathering and satellite aging
A modern communications satellite is a complex
system involving numerous subsystems that have
finite lifetimes due to mechanical wearing (e.g. Sun-
tracking solar panel bearings, momentum wheels,
etc.), limited propulsion resources (gas jets or
similar), and carefully engineered thermal surfaces
which can be subject to degradation due to space
‘weathering’ [17] or collisions with small debris.
Aging can be viewed as a continuous slight
degradation of the performance of some surfaces,
such as weathering of thermal surfaces, or it can
be a discrete event punctuated by ‘anomalies’, such
as failure of a critical component.
Even though satellite subsystems are
instrumented with sensors that provide health and
status, or ‘housekeeping’, data, not everything can
be sensed, and sometimes the housekeeping data
stream is unavailable.
It is important that GEO satellites remain
functional until the end of their useful lives
when they can be re-orbited into the GEO
disposal, or ‘graveyard’ orbit [18], deplete their
stored energy sources and be decommissioned.
A satellite that is not properly disposed of only
becomes a new element of the debris picture,
although it has been speculated that even
satellites in the graveyard orbit may possibly
shed debris that could drift into the protected
GEO zone, or lower [19].
Limited resources
Given the various near-term actions that might
enhance the safety of flights for satellites in GEO,
where should the next dollar be spent and what
could have the biggest impact in the short term?
International cooperation, in this regard,
means multilateral discussions, conferences and
workshops (e.g. UN COPUOS meetings). Certainly
a large COPUOS-style meeting might cost about
US$4 million for a 10-day meeting (estimated by
labour, travel, lodging and per diem costs), which
is much less expensive than the US$50 million
projected price for a Falcon 9 launch (excluding
the cost of the payload) [21].
Talk is often described as ‘cheap’ but, as the ranks
of actors in the space area continues to grow, these
efforts are certainly needed to keep the existing
problem from getting worse. Given the deliberative
nature of such bodies, however, and the need for
consensus, nothing happens very quickly.
If the UN COPUOS were to increase its meeting
schedule by a factor of two, could it increase its output
by a similar factor, or decrease the time needed to get
‘results’ (treaties, guidelines, reports on best practices,
etc.)? Probably not, as time betweenmeetings is used
by delegations to confer with their Capitals, to read,
discuss, and formpositions on issues.
Data sharing is also relatively inexpensive and can
allow information to flow from the ‘best’ sources to
those who need it. All operators would benefit from
exchanging information on their satellites with
the owners and operators of other satellites, along
the lines of the Space Data Association (SDA), and
it is important to have contact information readily
available for emergency situations.
Yet the likelihood of two operational satellites
colliding with each other continues to be low. Of
greater concern are the defunct satellites and
populations of space debris, for which there are no
Trapped objects will remain in GEO,
and constitute a continuing threat to
operational spacecraft
Geostationary satellites
- photograph taken by Bill
Livingston of the National
Solar Observatory on Kitt
Peak in Arizona (lat. 31.95,
long. 248.5). Camera
setting was f/6.3; focal
length80 mm; film:
Ektachrome 100 G.
