a. Space threats and countermeasures must be examined from two different perspectives.
Threats to U.S. space systems and
Threats to U.S. military forces
from foreign space systems and countermeasures.
b. Space systems are critical to U.S. military forces in all types of operations and at all levels of conflict.
Space systems generally consist of three segments:
The threats to each of these segments is different, therefore each will be discussed separately.
c. The user segment consists of ground, aircraft and ship terminals and user sets.
d. The threats to the systems that comprise the user segment systems are generally the same as the threats
to other systems operated by the owning unit. They are exposed to the same threats as other equipment in
the area because they can be damaged or destroyed by direct fire, indirect fire, ground attack or air attack.
Ground terminals, such as small UHF transceivers and GPS receivers, have very small visual signatures. It
is unlikely that these small terminals would be targeted directly. Some larger components of user segment
equipment and terminals, particularly large satellite antennas, have distinct visual signatures which should
be camouflaged or positioned to make detection by an enemy more difficult. Satellite receivers do not emit
any identifiable electromagnetic signature. Most transmitters which send signals to satellites use directional
antennas so that output power is focused on the satellite. This makes detection by ground and even aircraft
electronic warfare equipment more difficult unless the transmitting antenna is pointed at a low angle to the
horizon and in the direction of the enemy or the enemy detection system is close enough to detect a side lobe
emitted by the antenna.
e. The countermeasures to protect the user segment of a space system are no different than the countermeasures to
protect other similar type equipment.
Minimize exposure of equipment to
direct or indirect fire through terrain selection and ballistic
Minimize detection of transmissions
through proper antenna siting and orientation.
Camouflage large items or equipment
with distinctive signatures
f. The control segment consists of facilities associated with telemetry, tracking and commanding (TT&C) of
satellites and the network control of users accessing the satellite(s) such as mission control stations, tracking
stations, monitoring facilities and facilities designed to communicate commands to the satellite(s). These facilities
are critical to the continued operation of a satellite. In general, these are specialized facilities. Many of the facilities
are located outside the United States. They are often in remote areas which can make physical security of the site
difficult. In some respects these facilities represent the most vulnerable segment of most space systems.
g. Most control segment facilities are susceptible to being damaged or destroyed by enemy ground or air attack.
h. Most mission control facilities for U.S. space systems are located in CONUS. An attack by a foreign military
force would probably be considered as a strategic threat against the United States and would result in escalation
of the level of conflict. Protection against terrorist attack can be accomplished by a reinforced guard force and
increased security measures. Protection of control facilities located overseas is coordinated with the host nation.
i. Survivability of control stations can be increased by increasing their mobility thus making targeting by an enemy
more difficult. Mobility can be achieved by making the stations smaller and lighter. Control stations located in a
combat theater of operations are more susceptible to enemy attack than those located in more secure areas away
from the combat zone. Positioning of control segment terminals is determined by the type of system and the
orbit of the satellites being controlled. In general, satellites in high altitude orbits, particularly in geostationary
orbit, require less control than those in low Earth orbit. In addition, the footprint of a satellite in geostationary
orbit is usually much greater than one in low Earth orbit, therefore the control station could be a great distance
from the user terminals. For example, during DESERT STORM, DSCS user terminals in the Kuwait theater
were provided network control by a control station in Germany. The GPS satellites require precisely located
and aligned monitoring stations. The current system has five fixed monitoring stations around the world.
The destruction of one of these would result in some GPS satellites being out of contact with the Master
Control Station in Colorado for extended periods. A mobile monitoring station would be able to be deployed
to replace any of the fixed monitoring stations, if necessary. Most satellite terminals used by U.S. tactical
military forces are already mobile but some could be made smaller which would enhance their mobility.
Mobile terminals also have the advantage that they can be repositioned when the tactical forces they are
supporting move. In many cases, however, the antennas must be dismantled and reassembled in the new
location thus communication with the satellite or the reception of data from the satellite is not possible
while moving. Most space systems have provisions for another facility to take over mission control should
the primary facility not be able function.
j. The space segment consists of satellites orbiting the Earth. Satellites are not invulnerable to incapacitation,
damage or destruction but they are the least vulnerable segment of most space systems. The satellites are
small targets, travelling at high speed. Nothing is invulnerable and space systems are not an exception. The
primary threat to all operational satellites is the environment in space. It is also possible for a nation to develop
systems capable of damaging or destroying an orbiting spacecraft. Deliberately negating a satellite is not a simple
task. Few nations have the capability to interfere with a satellite. Only the United States and the Soviet Union
have ever demonstrated the ability to destroy an orbiting satellite. Of course, if an enemy is willing to expend
enough time, money, materiel and other resources, any system can be disrupted, damaged or destroyed.
k. The environment in space looks peaceful but it is not benign. As explained in Chapter 5, space is a hostile
environment that is much different than on the surface of the Earth. In spite of the fact that satellites are designed
to operate in space, more satellites have failed due to the effects of the environment than any other cause.
l. Atmospheric drag is a hazard for LEO satellites. Although the density of the atmosphere above 100 miles
is very low, satellites at this altitude must travel at about 17,000 mph. There are enough molecules of
atmospheric gasses at 100 miles altitude to induce low levels of drag. The more paraphernalia
(especially solar arrays) protruding from the basic satellite, the higher the overall drag. Drag results in
a decrease in orbital velocity. As the satellite slows, it drops in altitude, where drag is even greater.
Unless its orbit is raised, the satellite will eventually enter even more dense atmosphere and will burn up.
Above LEO, the atmosphere is not a threat because the satellite's life is shorter than the time it will take
for the orbit to decay. High levels of solar activity cause the atmosphere to expand outward. This can
result is a significant shortening of orbital lifetime.
m. Solar energy in the form of both light and flows of atomic particles combine to influence the orbits of
satellites. Their net effect is the same as atmospheric drag, resulting in accelerating the decay of the orbit.
The amount of energy varies with the activity of the Sun; periods of large prominences and sun spots can
greatly increase the perturbation of orbits. The same rules apply; more surface area on the satellite translates
into higher drag.
n. High energy radiation and charged particles from the Sun and from outside the solar system can damage
microcircuits on satellites. The Earth's magnetic field deflects some types of radiation and charged particles
but there are others upon which a magnetic field has little effect. The intensity of the radiation is greater
when the Sun is more active. All satellites are designed to withstand normal radiation levels or they would
fail soon after achieving orbit. Average radiation levels in space are higher than on the surface of the Earth.
There are regions within the Van Allen radiation belts surrounding the Earth where the concentration of charged
particles is much higher than average. The result is that most satellites have more hardening than ground systems.
o. The thermal environment in space is also hazardous. Parts of satellites in shadow can radiate heat into
space until the temperature is near absolute zero (absolute zero = 0º Kelvin = 273º C = 460º F). Parts
exposed to direct sunlight can rapidly heat to high temperatures. The performance of some components
changes significantly over a range of temperatures. Electronic components can completely fail if the temperature
gets too high. Any failures associated with these thermal management systems may mean failure of the satellite.
p. Outgassing is a problem associated with operating in the high vacuum (referred to as a hard vacuum) found at
LEO. Outgassing is the boiling off, albeit at a low rate, of volatile particles from the materials in the satellite.
Some of these materials, when subjected to a hard vacuum, lose part of their mass to sublimation; that is,
some molecules evaporate slowly into the vacuum of space directly from the solid phase to the gaseous phase.
Examples of these materials include many microelectronic chips and integrated circuits, circuit boards, some
plastics, lubricants, insulation and molded composite materials. Materials that use solvents and adhesives
to bind parts together have residual volatile components of solvents and adhesives in the finished products.
Outgassing may result in deposits of thin films of outgassed materials on other surfaces on or in the satellite.
Should outgassing deposit material on sensors or certain electronics, sensor degradation and even satellite
failure can result. Over time, outgassing can cause physical changes to the properties of some materials.
q. Space debris is a significant and growing hazard to satellites. Space debris is manmade, nonoperational
material in orbit around the Earth. Space debris ranges in size from very small paint chips to complete
rocket boosters. A number of rocket bodies and even satellites have exploded after achieving orbit, thus
adding to the space debris problem. Below about 150 miles in altitude, most space debris is slowed by
atmospheric drag, falls into more dense atmosphere and burns up. Impacting at thousands of miles an hour,
even the smallest of these items can cause disproportionate damage. The U.S. Space Shuttle Challenger
suffered window damage from a .2mm fleck of white paint that impacted at 8,000 mph. The Long Duration
Exposure Facility<$ISatellites;Long Duration Exposure Facility (LDEF)>, a satellite left in orbit for six years
before being recovered, showed marked damage from thousands of collisions.
to the Space
r. There is no way to change the environment in space therefore satellites must be designed to survive the
hostile environment of space. Since the late 1950's much has been learned about conditions in space.
Technology has developed materials that are much more resistant to damage. Reliable thrusters with
sufficient fuel provide thrust to raise a satellite's orbit to counter the effects of atmospheric and solar drag.
Electronics are built to be resistant to many forms of radiation. Thermal management systems provide
heat where needed, reflect sunlight and dissipate concentrations of heat that build up in the satellite into
space. Satellites such as DoD's DMSP weather satellite and others carry sensors to characterize the
environment in space. Shields protect critical components from micrometeorites and small pieces of
space debris. Today most satellite failures occur during launch or shortly after being placed into orbit
due to the mechanical or electronic failure of some component. If they continue to operate after this initial
period, they remain operation for many years unless designed for a shorter operating life.
a. A deliberate attack of a satellite can consist of jamming of signals to the spacecraft, spoofing, or the use of
a weapon to damage or destroy the satellite.
b. Satellites routinely receive commands from the control segment that cause the satellite to change its operation.
This may involve commands to reposition the satellite in its orbit, to adjust power levels, to control the thermal
management subsystem. In addition, the control segment sends signals to the satellite to adjust the operation of
the payload. For example, GPS navigation messages transmitted by the payload are routinely updated.
Communications satellites receive signals transmitted by users, route them through the communications
payload processor on the satellite and retransmit the signal to other users. Jamming of a satellite involves
transmitting signals which interfere with the operation of the satellite or its payload.
c. Susceptibility of a satellite is determined by many factors to include the frequency of the signals, the
directionality of the receiving antennas, the power of the jamming signal compared to the user's signals,
the codes required to access the satellite, and other factors.
UHF vs. SHF
d. In general, UHF communications satellites are more susceptible to jamming than SHF communications
satellites because the UHF signal has a narrower bandwidth and the receiving antenna is designed to receive
signals from a large geographic area. SHF communications satellites are more susceptible than EHF
a. An antisatellite weapon is intended to physically damage or destroy a target satellite. There have
been a variety of antisatellite weapons concepts and designs. Some have even been built and tested.
Direct Ascent, coorbital, and "mines." Warheads of varying types have been demonstrated or
postulated, from nuclear to simple sand and even lightweight plastic balloons.
b. Direct ascent ASAT weapons launch directly at the satellite, intercepting it as it approaches overhead,
in much the same way that an air defense missile intercepts an aircraft. There is no attempt to place the
ASAT weapon into orbit. A typical direct ascent ASAT attacks the target satellite nearly head on,
resulting in closing velocities on the order of 16 kilometers per second. This is similar to hitting a
bullet with a bullet. Accurate tracking of the target satellite is essential and the U.S. has the best and
most comprehensive satellite tracking network in the world. The seeker and processor on the ASAT
weapon must be capable of identifying the target and locking on it. U.S. technology improvements
have demonstrated the ability to intercept a satellite as it passes nearly overhead. At impact velocities
as high as 16 km per second, no explosive is needed when the ASAT strikes the satellite. The kinetic
energy involved destroys the satellite. To date, only the U.S. has successfully demonstrated a direct
ascent ASAT attack. Direct ascent ASAT weapons are restricted to engaging only satellites in low
c. A coorbital ASAT weapon<$IAntiSatellite Weapons> is launched into an orbit similar to the target
satellite, closes in on the target, then destroys it, usually with a warhead exploded at short range. The
USSR developed a coorbital ASAT weapon and tested it about 20 times with less than half the texts
being successful. The ASAT payload was launched on an S11 Tsyklon rocket. The maximum
demonstrated operational altitude was 2000 kilometers. This type of ASAT has a limited amount of
maneuverability, and is expected to achieve the kill on the second orbit. The last operational test was
conducted in 1982.
d. Space mines have not been deployed, however the concept is simple. A satellite with one or more
explosive charges is launched into space and placed into GEO close (1,000 km) to the target satellite,
then placed into a storage mode, perhaps for years, until called upon to make the attack. At that time
the mine is awakened by ground control, "drifted" over to the target satellite, and commanded to destroy
the target. To deploy a space mine, a country requires the ability to build the satellite, launch it into GEO
and to control it from the ground. With the ability to track small objects in space it is unlikely that a
space mine could be deployed without being detected.
a. Lasers generate intense beams of light. A characteristic of lasers is that the light in the beam is coherent,
i.e., the light waves are aligned. The beam does not radiate in all directions, thus beam divergence is a small
angle. The result is that a high percentage of the energy radiate out of the end of the laser can be focused
on a target a considerable distance away. Laser weapons damage or destroy their target by heating them.
Generating the intense laser beam, controlling the output, tracking a fast moving satellite and keeping the
beam focused on the satellite are difficult tasks. No known operational ASAT lasers are deployed but there
are working prototypes which have engaged ground targets. There is no evidence that a laser weapon has
ever been used to destroy an onorbit satellite.
b. Particle beam weapons (either charged particle beams or neutral particle beams) accelerate atomic
particles (neutrons, protons, or electrons) to relativistic velocities (significant fractions of the speed of light)
toward their targets. Depending on beam type, intensity, and dwell time, the results of this beam attack
can vary from cutting metal to overloading internal electronics. Both ground based and spacebased systems
have been proposed. A few ground based prototypes have been demonstrated but no operational particle
beam weapons are currently deployed by any nation. Testing of such a system to insure that it is
operational would be essential and such test would probably be detectable.
c. Like lasers, microwave and other RF weapons are also speedoflight weapons. Like particle beam
weapons, there are no known RF ASAT weapons deployed today. However, the likelihood is that
eventually weapons of this type will be acquired, most likely as both groundbased and spacebased
systems with sufficient flexibility to allow multiple attacks within a short period of time. The RF
weapon principle is to cause a meltdown in the internal communications architectures of the targeted
d. Space systems are not defenseless. There are many countermeasures which can be used to reduce or
eliminate threats and enhance the survivability of satellites.
e. Treaties and agreements between nations are useful as strategic countermeasures to provide protection
and survivability. For example, one of the provisions of the 1967 Outer Space Treaty, ratified by the
space nations of the world, states that nations will not interfere with another nation's space systems.
This agreement serves a useful purpose because it clarifies that any action against another nation's space
system is an act of aggression rather than just nuisance interference. Jamming of radio broadcasts from
ground transmitters is not in violation of any treaty. Jamming of control communications to or from a
satellite would, however, be considered a violation of the Outer Space Treaty. Treaties and agreements
are most effective when they are of some benefit to all the signatories. To be effective, there must be means
to verify compliance with the provisions of the treaty or agreement. Once hostilities begin, treaties and
agreements between combatants may have little relevance.
f. Deterrence has been an effective strategic countermeasure in many different areas to include space systems.
Deterrence involves informing adversaries, in advance, that if actions are taken against friendly space systems,
then corresponding retaliatory action will be taken. Deterrence presumes that the U.S. has the political fortitude
and means to damage, destroy or otherwise negate the enemy's space systems and the enemy values it's space
systems. Effective deterrence presumes a relative parity or balance between potential opponents. Satellites
must include special sensors to detect and confirm that a failure was the direct result of a deliberate enemy
action against the satellite rather than an act of nature or a routine failure of a component. In addition, an enemy
must believe that potential losses exceed possible gains. Measuring the success of deterrence is as difficult as
measuring as the impact of a safety program. If nothing happens, there is nothing to measure.
g. Proliferation results in a more robust system that gives an enemy too many targets to damage or destroy
before there is a significant impact on the effectiveness of a system. An attacker has to expend more resources
before there is any effective degradation of an enemy's system. Proliferation can result from the inherent
design of a system so that if some components are damaged, destroyed or simply fail to operate correctly
the overall system retains its operational effectiveness. For example, the Global Positioning System consists
of 21 satellites and 3 operational, on orbit spares. The system is designed so that the loss of a satellite has
only minor impact on the overall operational effectiveness of the system. The loss of even more GPS
satellites would result in a gradual degradation of capabilities rather than a catastrophic failure. For this
reason, a surprise attack that could destroy the system would be extremely difficult and the likelihood of
detection of preparations of such a large effort would be high. Most satellites are expensive, therefore
building, launching and maintaining extra satellites merely to have excess capability is rarely an affordable
option. Proliferation can also be the result of widespread distribution of components, especially user
terminals. For example, it would be extremely difficult for an enemy to physically destroy enough UHF
SATCOM user terminals in a large force to have a significant impact on military operations. Not only
are the terminals relatively small, but there are thousands of them.
h. Deception makes it more difficult for an enemy to detect, track and engage the real components of a
system. Camouflage of user terminals and ground control terminals to conceal them is a common deception
technique. Positioning terminals where they would not be expected or where the surrounding environment
make them more difficult to detect can be effective ways to improve survivability. Physical and electronic
decoys, especially of larger terminals, can be an effective method in deceiving an enemy as to the location
and number of the actual terminals. Deception techniques and plans are, by their nature, usually classified.
i. The orbit selected for a satellite is based primarily on the mission it is designed to perform. The orbit
also influences the satellite's vulnerability. A satellite in low Earth orbit travels fast but there would be
little reaction time against an attack by a direct ascent ASAT. Satellites in LEO are also more susceptible
to jamming because they are closer to the emitter, however, the jammer must be within the footprint of the
satellite which restricts where it could be positioned on the ground. In addition, the satellite would be within
sight and range of the jammer for relatively short periods. A satellite in geostationary orbit is far enough
away to provide warning time (3-6 hours) if a ground based ASAT were launched against it. An alternative
is for a potential adversary to position a satellite nearby in the same geostationary orbital plane on the pretext
of some valid requirement. Sometime afterward the enemy satellite could maneuver quickly to damage or destroy
the target satellite. Inclining the orbit slightly at geosynchronous altitude enhances survivability but results in a
ground trace of a figure 8 that sacrifices some of the unique advantages of a geostationary orbit. A satellite in a
highly elliptical orbit is still susceptible to interception, however, an enemy's attempt to place another satellite
into the same orbit would be very suspicious since there are an infinite number of other variations.
j. Most satellites have small rocket engines that are used periodically to adjust their orbit and orientation.
Some satellites have larger rockets so that more radical changes to their orbit can be made. Maneuvering a
satellite can reduce its vulnerability to interception. In addition, sufficient warning of imminent attack is
essential. The U.S. Space Surveillance Network is the most comprehensive and capable in the world. It
performs functions that would crucial to detecting attacks by other spacecraft. The most difficult situation
would be the detection and attack assessment by a direct ascent ASAT attacking a satellite in low Earth orbit.
Additional maneuverability of a satellite may require larger rocket engines on the satellite and certainly more
fuel which thus reduces the payload weight that can be put into orbit. Autonomous Operations. Most
satellites require control from ground stations to maintain the system in optimum operating condition.
If some of the functions performed by fixed ground stations and the control segment can be performed on
the satellite, then the system acquires a greater degree of autonomy. Autonomous operation also decreases
reliance on critical, single node, ground stations.
k. There are two basic ways to reconstitute a satellite constellation after attack.
The first is to activate reserve or spare satellites that are maintained in orbit. In many satellite constellations
older satellites have been replaced by newer models. The old satellites are often placed into a standby mode
to conserve energy and fuel. Although they no longer operate at full capacity or do not have all of the
capabilities of the more modern satellites, they are capable of providing some capabilities in emergency
situations. The alternative is to launch replacement satellites. Some programs include the construction
of one or more extra satellites to be used in case of a launch failure or a failure of a satellite once it is in orbit.
In other cases, the satellites on orbit have remained in excellent operating condition far longer than planned.
As a result, replacement satellites were not launched as frequently as originally planned yet the satellites
continued to be built and delivered on schedule. Replacement launches are difficult because of the shortage
of launch vehicles and the considerable time it takes to prepare them for launch.
l. Hardening involves adding or designing components so that they are more resistant to damage or
destruction. Hardening is often associated with increasing the resistance to damage from the effects
of nuclear or directed energy weapons but also includes measures to increase survivability against
physical attack and naturally occurring environmental effects. Equipment can be designed and constructed
to protect from electromagnetic pulse (EMP), lasers, and other weapons. Hardening does not increase the
performance of a satellite but it can make it much more difficult for an enemy to destroy or damage.
Hardening against a variety of threats is difficult, adds expense to system design, parts and construction,
and may result in larger or heavier equipment. The result is a compromise between a device that can be
destroyed easily and one that can survive against any threat yet is too large, too heavy and too expensive.
m. It is not practical to build equipment that is hardened to survive a direct hit by a nuclear weapon. It is
possible, however, to design and build equipment that provides enhanced resistance to damage from
electromagnetic pulse and radiation generated by a nuclear explosion. There is no blast shock wave effect
in space because there is no atmosphere. Due to the nature of the electromagnetic environment in space and
its effect on spacecraft, all satellites have some degree of protection against damage from electromagnetic
effects or they will not survive long even with out being attacked. Satellites can be hardened by including
filters, Faraday cages, surge arrestors, waveguide cutoffs and use fiberoptic components to increase survivability
against upset and surges generated by electromagnetic pulse.
a. Space systems are available around the world. It is expected that an adversary will use space systems
to enhance its military operations. The space system does not have to belong to an enemy nor be a
military system for it to be an asset. It is possible that a space system that is an asset to U.S. military
forces could also be an asset to an enemy, i.e., the U.S. military and an adversary may use weather
data from a METEOSAT satellite. Or, an adversary could access a U.S. owned and operated satellite
such as the GOES weather satellites.
b. The United States military has more ability to use space systems and products provided by space
systems than any other military force in the world, but it is not the only military force that uses space
systems to support its operations. Although it is not expected that the U.S. military will lose it
preeminent position in the near future, it is expected that foreign military forces will increase their
use of space systems, especially civil and commercial systems.
c. As of 1996, the following nations had the ability to launch a satellite into space: United States,
C.I.S., China, European Space Agency, Japan, India, Italy, and Israel. As costs decrease, more
commercial launch systems are expected to become operational.
d. The number of countries with facilities to build satellites is much larger. The United States has
the lead in building sophisticated satellites but there is significant competition from many foreign
companies. It is expected that the capabilities of foreign firms will continue to grow in number and
increase in sophistication of the satellites they can construct. There are many countries and commercial
firms that buy a satellite and pay for its launch to acquire space capabilities. This is especially true for
satellite based communications systems.
e. Many nations and commercial firms operate satellite communications systems. Most of the world
has access to satellite systems through international consortiums such as INTELSAT and INMARSAT.
Because of the large number of participating nations in these systems, it is likely that adversaries in
future conflicts will have access to INTELSAT and INMARSAT, possible even through the same satellite.
Many have already orbited communications systems dedicated to their own uses, or are planning to do so.
Space based communications support access is also available to nonowners who are willing to lease or
otherwise pay for it. Owned or leased, spacebased communications support to civil, commercial, and
military operations is a reality for many countries, and will be for others. Soon, mobile satellite
communications systems are expected to become operational. Most will be able to provide communications
directly between small handheld receivers similar to cellular telephones network.
f. Low resolution systems provide valuable data over large areas and use a variety of spectral and special
sensors to record and report on weather, environment, and terrain conditions. By international agreement
all civil weather satellites transmit data in an unencrypted format. Anyone with a proper receiver can
receive, process and display data from these systems. Examples of these systems include:
Landsat satellites (U.S. commercial
system-terrain imaging.) receiving stations are located around the world.
The number of licensed stations is increasing. Prior to a conflict foreign
governments can purchase Landsat data with little restriction.
SPOT satellites (French system-terrain
imaging.) have data available commercially.
Russia operates multispectral
environmental satellites. Data is commercially available.
Japan and Europe operate environmental
satellites such as JERS and ERS which have visible image and synthetic aperture
radar sensors and the data is available commercially.
National Oceanographic and Atmospheric
Administration (NOAA) polar orbiting weather satellites and Russian Meteor
GOES, METEOSAT and GMS geostationary
weather satellites operated by the U.S., Europe, and Japan,
g. These consist of satellites with sensors that are capable of providing greater detail than low
resolution systems. Most provide data to a central processing facility which then disseminates
processed data and products to users. Some are capable of providing data in near real time that
can be of immediate value to a military commanders. These are exclusively assets of governments
today. In the near future systems with a resolution of less than 5 meters may be commercially.
h. These systems are designed to provide near real time warnings of critical tactical events, such as
ballistic missile attack or nuclear detonation. Other than the United States, only Russia is believed
to have satellites capable of early detection of an ICBM and that is only within a specific geographic
i. The U.S.'s Global Positioning System (GPS) and Russia's GLONASS satellites provide worldwide
position and navigation service. GPS's Standard Positioning Service (SPS) is available to anyone with
a GPS receiver. No classified codes are needed. Normally accuracy is limited to 76 m Spherical Error
Probable (SEP) but can be degraded to much worse accuracy when it is in the national interest. SPS
receivers are available commercially from manufacturers around the world GPS's Precision Positioning
Service (PPS) provides 16 m SEP accuracy but requires a receiver that is capable of loading classified
codes to remove some of the deliberate error in the signal from the GPS satellites. The production of
PPS GPS receivers is controlled by the U.S. military and certain U.S. allies participating in the GPS
program. The classified codes needed for PPS are generated and distributed by the U.S. In many
cases, SPS provides sufficient accuracy to give a military force an advantage.
g. GLONASS is a space based navigation system that is similar to GPS. It was initiated by the
USSR and has been continued by Russia. The accuracy of GLONASS is expected to be better
than GPS's SPS but not as good as PPS. Russia has stated that it does not intend to implement a
degraded position and navigation service. An adversary of the U.S. could use GLONASS if GPS
does not provide the desired accuracy. To date, GLONASS receivers are not widely available.