Space Security Index

Originally adopted in 1994, the ITU Constitution 89 governs international sharing of the
nite radio spectrum and orbital slots used to communicate with, and house satellites in,
GEO. Article 45 of the Constitution stipulates that “all stations…must be established and
operated in such a manner as not to cause harmful interference to the radio services or
communications of other members.” 90 Military communications are exempt from the ITU
Constitution, though they must observe measures to prevent harmful interference. It is
observed that “interferences from the military communication and tracking systems into
satellite communications is on the rise,” 91 as military demand for bandwidth grows.
While crowded orbits can result in signal interference, new technologies are being developed
to manage the need for greater frequency usage, allowing more satellites to operate in closer
proximity without interference. Frequency hopping, lower power output, digital signal
processing, frequency-agile transceivers, and software-managed spectrum have the potential
to signicantly improve bandwidth use and alleviate conicts over bandwidth allocation.
Current receivers have a higher tolerance for interference than those created decades ago,
reecting the need for increased frequency usage and sharing. 92 Signicant research is also
being conducted on the use of lasers for communications, particularly by the military. Lasers
transmit information at very high bit rates and have very tight beams, which could allow for
tighter placement of satellites, thus alleviating some of the current congestion and concern
about interference.
Today, issues of interference arise primarily when two spacecraft require the same frequencies
at the same time, and their elds of view overlap or they are transmitting in close proximity to
each other. While interference is not epidemic, it is a growing concern for satellite operators,
particularly in crowded space segments. e simplest way to reduce such interference is to
ensure that all actors have access to reasonable and sucient bandwidth. To this end the
U.S. DOD released a portion of the military-reserved spectrum from 1.710-1.755 GHz to
the commercial sector for third-generation wireless communications. 93
Bilateral eorts are also under way to harmonize radio frequency utilization. In 2004, the
U.S. and EU agreed to major principles over frequency allocation and interoperability
between the U.S. GPS and the EU Galileo navigational system; 94 details were nalized in
2007 for a common GPS-Galileo civilian signal, allowing for interoperability of the two
systems while also maintaining the integrity of the U.S. military signal. 95
Orbital slots
Today’s satellites operate mainly in three basic orbital regions: LEO, MEO (Medium
Earth Orbit), and GEO (see Figure 1.1). As of 30 April 2011, there are approximately
966 operating satellites, of which 470 are in LEO, 64 in MEO, 398 in GEO, and 34 in
Highly Elliptical Orbit (HEO). 96 HEO is increasingly being used for specic applications,
such as early warning satellites and polar communications coverage. LEO is often used for
remote sensing and earth observation, and MEO is home to space-based navigation systems
such as the GPS. Most communications and some weather satellites are in GEO, as orbital
movement at this altitude is synchronized with the Earth’s 24-hour rotation, meaning that
a satellite in GEO appears to “hang” over one spot on Earth.
GEO slots are located above or very close to the Earth’s equator. Low inclinations are also
desired to maximize the reliability of the satellite footprint. e orbital arc of interest to the
U.S. lies between 60° and 135° W longitude because satellites in this area can serve the entire
continental U.S.; 97 these desirable slots are also optimal for the rest of the Americas. Similar
desirable spots exist over Africa for Europe and over Indonesia for Asia.
The Space Environment
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