How Satellites Work
"Man must rise above the Earth -- to the top of the
atmosphere and beyond -- for only thus will he fully
understand the world in which he lives."
Yerbolat Assylbekov
Batyrbek Ashirbayev
Early Observation
 Socrates made the observation centuries before humans
successfully placed an object in Earth's orbit, even though
he didn't know how to achieve it.
 Isaac Newton published his now-famous cannonball
thought experiment in 1729. His thinking went like this:
Imagine you place a cannon atop a mountain and fire it
horizontally. The cannonball will travel parallel to Earth's
surface for a little while but will eventually succumb to
gravity and fall to the ground. Keep adding gunpowder to
the cannon. With the extra explosives, the cannonball will
travel farther and farther before it falls. Add just the right
amount of powder and impart just the right velocity to the
ball, and it will travel completely around the planet, always
falling in the gravitational field but never reaching the
 In October 1957, the Soviets finally proved Newton
correct when they launched Sputnik 1 -- the first
artificial satellite to orbit Earth.
 Since Sputnik, several nations, led predominantly by
the United States, Russia and China, have sent some
2,500 satellites into space
What is satellite?
 A satellite is any object that moves in a curved path around
a planet. The moon is Earth's original, natural satellite, and
there are many man-made (artificial) satellites, usually
closer to Earth. The path a satellite follows is an orbit,
which sometimes takes the shape of a circle.
 Newton proposed that a force - gravity - exists between
any two objects in the universe. If it weren't for this force,
a satellite in motion near a planet would continue in
motion at the same speed and in the same direction -- a
straight line. This straight-line inertial path of a satellite,
however, is balanced by a strong gravitational attraction
directed toward the center of the planet.
Satellite cont’d
 Sometimes, a satellite's orbit looks like an ellipse, a
squashed circle that moves around two points known
as foci
 As a result, the net force applied to the satellite isn't
uniform all the way around the orbit, and the speed
of the satellite changes constantly. It moves fastest
when it's closest to the planet -- a point known as
perigee -- and slowest when it's farthest from the
planet -- a point known as apogee.
YouTube video explains
Three types of orbits used by satellites:
 Geostationary Orbit: In order to orbit the Earth in
24 hours, a satellite has to be placed in an
orbit 22,237 miles above the Earth.
 Highly-Elliptical Orbit: the satellite appears to slow down as it
moves away from the Earth and speeds up as it
approaches the Earth.
 Low-Earth Orbit: A satellite in LEO travels at altitudes about three
hundred to one thousand two-hundred and fifty miles
above the Earth's surface.
What's Inside a Typical Satellite?
 All of them have a metal or composite frame and body, usually known
as the bus. The bus holds everything together in space and provides
enough strength to survive the launch
 All of them have a source of power (usually solar cells) and batteries for
storage. Arrays of solar cells provide power to charge rechargeable
batteries; also, they have onboard computer to control and monitor the
different systems. Power on most satellites is precious and very limited.
Nuclear power has been used on space probes to other planets.
 All have a radio system and antenna. Most satellites have a radio
transmitter/receiver, so that the ground-control crew can request status
information from the satellite and monitor its health. Many satellites
can be controlled in various ways from the ground to do anything from
change the orbit to reprogram the computer system.
 All of them have an attitude control system. The ACS keeps the satellite
pointed in the right direction.
Difference Between a Satellite and
Space Junk
 A satellite is any object that revolves around a planet
or smaller celestial body: moons as natural satellites,
man-made objects like Sputnik and Expolorer.
 Space Junk: 100m pieces of orbital debris no larger
than 1 centimeter; 500,000 pieces in the 1-10
centimeter range and approximately 21,000 items
larger than 10 centimeters
 Orbital Debris are from: exploding rockets, the slip of
an astronaut’s hand, jettisoned items.
Orbital Velocity and Altitude
 A rocket must accelerate to at least 40,320 kph to completely
escape Earth's gravity and fly off into space
 Orbital velocity is the velocity needed to achieve balance
between gravity's pull on the satellite and the inertia of the
satellite's motion -- the satellite's tendency to keep going.
 This is approximately 27,359 kph at an altitude of 242 kilometers.
 Without gravity, the satellite's inertia would carry it off into
 The orbital velocity of the satellite depends on its altitude above
Earth. At lower altitudes, a satellite runs into traces of Earth's
atmosphere, which creates drag, which causes the orbit to
decay until the satellite falls back into the atmosphere and burns
What are satellites used for?
They often affect our lives without our realizing it: they make us safer,
provide modern conveniences, and broadcast entertainment.
Weather (climate and environmental monitoring).
Land Stewardship
Space Science
What’s new for us, personally
 It helped us to see the real examples of what the gravity is
and it’s used in the modern world. The satellites are acted
upon by the force of gravity and the force does accelerate
it towards the Earth. Thanks to gravity, the satellites don’t
fly away from our planet. Also, the satellites never fall on
the Earth. the projectile will fall around the Earth, always
accelerating towards it under the influence of gravity, yet
never colliding into it since the Earth is constantly curving
at the same rate. Such a projectile is an orbiting satellite.
Brown, G. How Satellite Works. Web. 4 Apr 2014. <
http://www.physicsclassroom.com/mmedia/vectors/sat.cfm >
FCC.gov. How Satellites Work. <
http://transition.fcc.gov/cgb/kidszone/satellite/kidz/leo.html >
The Physics Classroom: Satellite Motion. Web. 4 Apr 2014.
Union of Concerned Scientists website.
YouTube video clip. <
https://www.youtube.com/watch?v=54MSV2B399o >

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