An animation depicting the orbits of
GPS satellites in medium earth orbit.
In the context of spaceflight
is an object
which has been placed into orbit
objects are sometimes called artificial satellites
to distinguish them from natural
such as the Moon
The first artificial satellite, Sputnik 1
was launched by the Soviet Union in 1957. By 2009 thousands of
satellites had been launched into orbit around the Earth. These
originate from more than 50 countries and have used the satellite
launching capabilities of ten nations. A few hundred satellites are
currently operational, whereas thousands of unused satellites and
satellite fragments orbit the Earth as space debris
. A few space probes
have been placed into orbit around
other bodies and become artificial satellites to the Moon, Venus,
Mars, Jupiter and Saturn.
Satellites are used for a large number of purposes. Common types
include military (spy) and civilian Earth observation satellites,
communication satellites, navigation satellites, weather
satellites, and research satellites. Space
and human spacecraft
orbit are also satellites. Satellite orbits vary greatly, depending
on the purpose of the satellite, and are classified in a number of
ways. Well-known (overlapping) classes include low Earth orbit
, polar orbit
, and geostationary orbit
Satellites are usually semi-independent computer controlled
systems. Satellite subsystems attend many tasks, such as power
generation, thermal control, telemetry, attitude control
and orbit control.
The first fictional depiction of a satellite being launched into
orbit is a short story
by Edward Everett Hale
, The Brick Moon
. The story is serialized
in The Atlantic
, starting in 1869. The idea surfaces again in
's The Begum's Fortune
In 1903 Konstantin
(1857–1935) published The Exploration of Cosmic
Space by Means of Reaction Devices
: Исследование мировых
пространств реактивными приборами
), which is the first
academic treatise on the use of rocketry to launch spacecraft
. He calculated the orbital speed
required for a minimal orbit
around the Earth at 8 km/s, and that a
could be used to
achieve this. He proposed the use of liquid hydrogen
and liquid oxygen
, though other combinations can
In 1935 Slovenian Herman
(1930–1996) published his sole book, The Problem
of Space Travel — The Rocket Motor
: Das Problem der Befahrung des
Weltraums — der Raketen-Motor
), a plan for a breakthrough into
space and a permanent human presence there. He conceived of a space
station in detail and calculated its geostationary orbit
. He described the
use of orbiting spacecraft for detailed peaceful and military
observation of the ground and described how the special conditions
of space could be useful for scientific experiments. The book
described geostationary satellites (first put forward by
Tsiolkovsky) and discussed communication between them and the
ground using radio, but fell short of the idea of using satellites
for mass broadcasting and as telecommunications relays.
In a 1945 Wireless World
article the English science fiction writer Arthur C. Clarke
(1917-2008) described in detail the
possible use of communications
for mass communications. Clarke examined the
logistics of satellite launch, possible orbits
and other aspects of the creation of a network
of world-circling satellites, pointing to the benefits of
high-speed global communications. He also suggested that three
satellites would provide
coverage over the entire planet.
History of artificial satellites
artificial satellite was Sputnik 1,
launched by the Soviet
Union on 4 October 1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer and Kerim Kerimov as his assistant.
turn triggered the Space Race between the
Union and the United States.
Sputnik 1 helped to identify the density of high atmospheric layers
through measurement of its orbital change and provided data on
-signal distribution in the ionosphere
. Because the satellite's body was
filled with pressurized nitrogen
also provided the first opportunity for meteoroid
detection, as a loss of internal
pressure due to meteoroid penetration of the outer surface would
have been evident in the temperature data sent back to Earth.
unanticipated announcement of Sputnik 1's success
precipitated the Sputnik crisis in
States and ignited the so-called Space Race within the Cold
was launched on
November 3, 1957 and carried the first living passenger into orbit,
In May, 1946, Project RAND
Design of a Experimental World-Circling Spaceship
stated, "A satellite vehicle with appropriate instrumentation can
be expected to be one of the most potent scientific tools of the
Twentieth Century.The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy.
The United States Air Force
RAND eventually released the above report, but did not believe that
the satellite was a potential military weapon; rather, they
considered it to be a tool for science, politics, and propaganda.
In 1954, the Secretary of Defense stated, "I know of no American
29, 1955, the White
House announced that the U.S. intended to launch
satellites by the spring of 1958.
This became known as
. On July 31, the
Soviets announced that they intended to launch a satellite by the
fall of 1957.
Following pressure by the American Rocket Society
, and the International Geophysical
, military interest picked up and in early 1955 the Air
Force and Navy were working on Project
, which involved using a Jupiter C rocket
to launch a satellite. The
project succeeded, and Explorer 1
the United States' first satellite on January 31, 1958.
In June 1961, three-and-a-half years after the launch of Sputnik 1,
the Air Force used resources of the United States Space
to catalog 115 Earth-orbiting
The largest artificial satellite currently orbiting the Earth is
the International Space
Space Surveillance Network
States Space Surveillance Network
(SSN) has been tracking space
objects since 1957 when the Soviets opened the space age with the
launch of Sputnik I. Since then, the SSN has tracked more than
26,000 space objects orbiting Earth. The SSN currently tracks more
than 8,000 man-made orbiting objects. The rest have re-entered
Earth's atmosphere and disintegrated, or survived re-entry and
impacted the Earth. The space objects now orbiting Earth range from
satellites weighing several tons to pieces of spent rocket bodies
weighing only 10 pounds. About seven percent of the space objects
are operational satellites (i.e. ~560 satellites), the rest are
is primarily interested in the active
satellites, but also tracks space debris which upon reentry might
otherwise be mistaken for incoming missiles. The SSN tracks space
objects that are 10 centimeters in diameter (baseball size) or
Non-Military Satellite Services
There are three basic categories of non-military satellite
Fixed Satellite Service
Fixed satellite services
handle hundreds of billions of voice, data, and video transmission
tasks across all countries and continents between certain points on
the earth’s surface.
Mobile Satellite Systems
Mobile satellite systems help connect remote regions, vehicles,
ships, people and aircraft to other parts of the world and/or other
mobile or stationary communications units, in addition to serving
as navigation systems.
Scientific Research Satellite (commercial and
Scientific research satellites provide us with meteorological
information, land survey data (e.g., remote sensing), Amateur (HAM)
Radio, and other different scientific research applications such as
earth science, marine science, and atmospheric research.
weapons/"Killer Satellites" are satellites that are
armed, designed to take out enemy warheads, satellites, other space
assets. They may have particle weapons, energy weapons, kinetic
weapons, nuclear and/or conventional missiles and/or a combination
of these weapons.
satellites are satellites used for observation of
distant planets, galaxies, and other outer space objects.
- Biosatellites are
satellites designed to carry living organisms, generally for
satellites are satellites stationed in space for the
purpose of telecommunications.
Modern communications satellites typically use geosynchronous orbits, Molniya orbits or Low Earth orbits.
satellites are satellites of unusually low weights and
small sizes. New classifications are used to categorize these
satellites: minisatellite (500–100 kg), microsatellite (below
100 kg), nanosatellite (below 10 kg).
satellites are satellites which use radio time signals transmitted to enable mobile
receivers on the ground to determine their exact location. The
relatively clear line of sight between the satellites and receivers
on the ground, combined with ever-improving electronics, allows
satellite navigation systems to measure location to accuracies on
the order of a few meters in real time.
satellites are Earth observation satellite or
deployed for military or intelligence applications.Very little is known
about the full power of these satellites, as governments who
operate them usually keep information pertaining to their
reconnaissance satellites classified.
observation satellites are satellites intended for
non-military uses such as environment monitoring, meteorology, map
making etc. (See especially Earth Observing System.)
- Space stations
are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished
from other manned spacecraft by its lack
of major propulsion or
landing facilities — instead, other vehicles
are used as transport to and from the station. Space stations are
designed for medium-term living in orbit, for
periods of weeks, months,
or even years.
satellites are satellites which are connected to
another satellite by a thin cable called a tether.
satellites are primarily used to monitor Earth's weather and climate.
The first satellite, Sputnik 1
, was put
into orbit around Earth
and was therefore in
. By far this is
the most common type of orbit with approximately 2456 artificial
satellites orbiting the Earth
orbits may be further classified by their altitude
The commonly used altitude classifications are Low Earth Orbit
(LEO), Medium Earth Orbit
(MEO) and High Earth Orbit
(HEO). Low Earth orbit is
any orbit below 2000 km, and Medium Earth Orbit is any orbit
higher than that but still below the altitude for geosynchronous orbit
at 35786 km.
High Earth Orbit is any orbit higher than the altitude for
Orbital Altitudes of several
significant satellites of earth.
The satellite’s functional versatility is imbedded within its
technical components and its operations characteristics. Looking at
the “anatomy” of a typical satellite, one discovers two modules.
Note that some novel architectural concepts such as Fractionated Spacecraft
upset this taxonomy.
Spacecraft bus or service module
This bus module
consist of the
- The Structural Subsystems
The structural subsystem provides the mechanical base structure,
shields the satellite from extreme temperature changes and
micro-meteorite damage, and controls the satellite’s spin
- The Telemetry Subsystems (aka Command and Data
The telemetry subsystem monitors the on-board equipment operations,
transmits equipment operation data to the earth control station,
and receives the earth control station’s commands to perform
equipment operation adjustments.
The power subsystem consists of solar panels and backup batteries
that generate power when the satellite passes into the earth’s
shadow. Nuclear power sources (Radioisotope
) have been used in several successful
satellite programs including the Nimbus
- The Thermal Control Subsystems
The thermal control subsystem helps protect electronic equipment
from extreme temperatures due to intense sunlight or the lack of
sun exposure on different sides of the satellite’s body (e.g.
Optical Solar Reflector
- The Attitude and Orbit Controlled Control
The attitude and orbit controlled subsystem consists of small
rocket thrusters that keep the satellite in the correct orbital
position and keep antennas positioning in the right
The second major module is the communication payload, which is made
up of transponders. A transponders is capable of :
- Receiving uplinked radio signals from earth satellite
transmission stations (antennas).
- Amplifying received radio signals
- Sorting the input signals and directing the output signals
through input/output signal multiplexers to the proper downlink
antennas for retransmission to earth satellite receiving stations
End of life
When satellites reach the end of their mission, satellite operators
have the option of de-orbiting the satellite, leaving the satellite
in its current orbit or moving the satellite to a graveyard orbit
. Historically, due to
budgetary constraints at the beginning of satellite missions,
satellites were rarely designed to be de-orbited. One example of
this practice is the satellite Vanguard
. Launched in 1958, Vanguard 1
4th manmade satellite put in Geocentric
, was still in orbit as of August 2009.
Instead of being de-orbited, most satellites are either left in
their current orbit or moved to a graveyard orbit. As of 2002, the
FCC now requires all geostationary satellites to commit to moving
to a graveyard orbit at the end of their operational life prior to
This list includes countries with an independent capability to
place satellites in orbit, including production of the necessary
launch vehicle. Note: many more countries have the capability to
design and build satellites — which relatively speaking, does not
require much economic, scientific and industrial capacity — but are
unable to launch them, instead relying on foreign launch services.
This list does not consider those numerous countries, but only
lists those capable of launching satellites indigenously, and the
date this capability was first demonstrated. Does not include
consortium satellites or multi-national satellites.
- Russia and Ukraine were parts
of the Soviet Union and thus inherited their launch capability
without the need to develop it indigenously. Through Soviet
Union they also are on the number one position in this list of
- France, United Kingdom launched their first satellites by own launchers
from foreign spaceports.
Korea (1998) and Iraq (1989) have
claimed orbital launches (satellite and warhead accordingly), but
these claims are unconfirmed.
addition to the above, countries such as South Africa, Spain, Italy, Germany, Canada, Australia, Argentina, Egypt and private
companies such as OTRAG, have developed their
own launchers, but have not had a successful launch.
- As of
2009, only eight countries from the list above ( Russia and Ukraine instead of
USSR, also USA, Japan, China, India, Israel, and
Iran) and one regional organization (the European
Space Agency, ESA) have independently launched satellites on
their own indigenously developed launch vehicles.
launch capabilities of the United Kingdom and France now fall
under the ESA.)
- Several other countries, including South Korea, Brazil, Pakistan, Romania, Taiwan, Indonesia, Kazakhstan, Australia, Malaysia and Turkey, are at
various stages of development of their own small-scale launcher
- South Korea
launched a KSLV rocket
(created with assistance of Russia) in 25 August 2009, but it
failed to put satellite STSAT-2 into precise
orbit and the satellite did not start to function.
- North Korea claimed a launch in April 2009, but U.S. and
Korean defense officials and weapons experts later
reported that the rocket failed to send a satellite into orbit, if
that was the goal. The United States, Japan and South Korea
believe this was actually a ballistic
missile test, which is a claim also made after North Korea's
1998 satellite launch, and later rejected.
Launch capable private entities
On September 28, 2008, the private aerospace firm SpaceX
successfully launched its Falcon 1 rocket in
to orbit. This marked the first time that a privately built
liquid-fueled booster was able to reach orbit. The rocket carried a
prism shaped 1.5 m (5 ft) long payload mass simulator that was set
into orbit. The dummy satellite, known as Ratsat, will remain in
orbit for between five and ten years before burning up in the
First satellites of countries
Canada was the
third country to build a satellite which was launched into space,
it was launched aboard a U.S. rocket from a U.S. spaceport.
The same goes for Australia
, who launched
on-board a donated Redstone
The first Italian-launched was San Marco
, launched on 15 December 1964 on a U.S. Scout rocket
from Wallops Island (VA,USA) with
an Italian Launch Team trained by NASA. Australia's launch project
) involved a donated U.S. missile and
support staff as well as a joint launch facility with the United Kingdom.
Attacks on satellites
In recent times satellites have been hacked by militant
organizations to broadcast propaganda and to pilfer classified
information from military communication networks.
Satellites in low earth orbit have been destroyed by ballistic
missiles launched from earth. Russia, the
States and China have
demonstrated the ability to eliminate satellites.
the Chinese military shot down an aging weather satellite,
followed by the US Navy shooting down a
defunct spy satellite in February
Due to the low received signal strength of satellite transmissions
they are prone to jamming
land-based transmitters. Such jamming is limited to the
geographical area within the transmitter's range. GPS satellites
are potential targets for jamming, but satellite phone and
television signals have also been subjected to jamming.It is
trivial to transmit a carrier to a geostationary satellite and thus
interfere with any other users of the transponder. It is common on
commercial satellite space for earth stations to transmit at the
wrong time or on the wrong frequency and dual illuminate the
transponder rendering the frequency unusable. Satellite operators
now have sophisticated monitoring that enables them to pin point
the source of any carrier and manage the transponder space
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