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Feb 12, 2014



WHAT IS A SATELLITE?

NASA has more than a dozen Earth science satellites in orbit. They help NASA
study the oceans, land and atmosphere.
Credits: NASA

The Jason-2 satellite orbits Earth. It carries tools and sensors to help
scientists study the oceans.
Credits: NASA

The Sputnik satellite was about the size of a basketball and weighed 183 pounds.
Credits: NASA


This article is part of the NASA Knows! (Grades 5-8) series.


A satellite is a moon, planet or machine that orbits a planet or star. For
example, Earth is a satellite because it orbits the sun. Likewise, the moon is a
satellite because it orbits Earth. Usually, the word "satellite" refers to a
machine that is launched into space and moves around Earth or another body in
space.

Earth and the moon are examples of natural satellites. Thousands of artificial,
or man-made, satellites orbit Earth. Some take pictures of the planet that help
meteorologists predict weather and track hurricanes. Some take pictures of other
planets, the sun, black holes, dark matter or faraway galaxies. These pictures
help scientists better understand the solar system and universe.

Still other satellites are used mainly for communications, such as beaming TV
signals and phone calls around the world. A group of more than 20 satellites
make up the Global Positioning System, or GPS. If you have a GPS receiver, these
satellites can help figure out your exact location.


Why Are Satellites Important?
The bird's-eye view that satellites have allows them to see large areas of Earth
at one time. This ability means satellites can collect more data, more quickly,
than instruments on the ground.

Satellites also can see into space better than telescopes at Earth's surface.
That's because satellites fly above the clouds, dust and molecules in the
atmosphere that can block the view from ground level.

Before satellites, TV signals didn't go very far. TV signals only travel in
straight lines. So they would quickly trail off into space instead of following
Earth's curve. Sometimes mountains or tall buildings would block them. Phone
calls to faraway places were also a problem. Setting up telephone wires over
long distances or underwater is difficult and costs a lot.

With satellites, TV signals and phone calls are sent upward to a satellite.
Then, almost instantly, the satellite can send them back down to different
locations on Earth.
 

What Are the Parts of a Satellite?
Satellites come in many shapes and sizes. But most have at least two parts in
common - an antenna and a power source. The antenna sends and receives
information, often to and from Earth. The power source can be a solar panel or
battery. Solar panels make power by turning sunlight into electricity.

Many NASA satellites carry cameras and scientific sensors. Sometimes these
instruments point toward Earth to gather information about its land, air and
water. Other times they face toward space to collect data from the solar system
and universe.


How Do Satellites Orbit Earth?
Most satellites are launched into space on rockets. A satellite orbits Earth
when its speed is balanced by the pull of Earth's gravity. Without this balance,
the satellite would fly in a straight line off into space or fall back to Earth.
Satellites orbit Earth at different heights, different speeds and along
different paths. The two most common types of orbit are "geostationary"
(jee-oh-STAY-shun-air-ee) and "polar."

A geostationary satellite travels from west to east over the equator. It moves
in the same direction and at the same rate Earth is spinning. From Earth, a
geostationary satellite looks like it is standing still since it is always above
the same location.

Polar-orbiting satellites travel in a north-south direction from pole to pole.
As Earth spins underneath, these satellites can scan the entire globe, one strip
at a time.


Why Don't Satellites Crash Into Each Other?
Actually, they can. NASA and other U.S. and international organizations keep
track of satellites in space. Collisions are rare because when a satellite is
launched, it is placed into an orbit designed to avoid other satellites. But
orbits can change over time. And the chances of a crash increase as more and
more satellites are launched into space.

In February 2009, two communications satellites - one American and one Russian -
collided in space. This, however, is believed to be the first time two man-made
satellites have collided accidentally.


What Was the First Satellite in Space?
Sputnik 1 was the first satellite in space. The Soviet Union launched it in
1957.


What Is the History of NASA Satellites?
NASA has launched dozens of satellites into space, starting with the Explorer 1
satellite in 1958. Explorer 1 was America's first man-made satellite. The main
instrument aboard was a sensor that measured high-energy particles in space
called cosmic rays.

The first satellite picture of Earth came from NASA's Explorer 6 in 1959.
TIROS-1 followed in 1960 with the first TV picture of Earth from space. These
pictures did not show much detail. But they did show the potential satellites
had to change how people view Earth and space.


How Does NASA Use Satellites Today?
NASA satellites help scientists study Earth and space.

Satellites looking toward Earth provide information about clouds, oceans, land
and ice. They also measure gases in the atmosphere, such as ozone and carbon
dioxide, and the amount of energy that Earth absorbs and emits. And satellites
monitor wildfires, volcanoes and their smoke.

All this information helps scientists predict weather and climate. The
information also helps public health officials track disease and famine; it
helps farmers know what crops to plant; and it helps emergency workers respond
to natural disasters.

Satellites that face toward space have a variety of jobs. Some watch for
dangerous rays coming from the sun. Others explore asteroids and comets, the
history of stars, and the origin of planets. Some satellites fly near or orbit
other planets. These spacecraft may look for evidence of water on Mars or
capture close-up pictures of Saturn's rings.

More About Satellites
Play "Missions to Planet Earth"!
Orbits 'R' Us!
Be Spuzzled! Game 
The Three Little Piggy-back Satellites
Earth Missions Past, Present and Future Satellites
Eyes on Earth 3-D
Space Place Live!: How can a satellite stay put over the same spot on Earth?
     Watch this episode
     Read the transcript



--------------------------------------------------------------------------------

Read What Is a Satellite? (Grades K-4)

Return to NASA Knows! (Grades 5-8)

Return to Students 5-8

Dan Stillman, Institute for Global Environmental Strategies

Last Updated: Aug 7, 2017
Editor: Sandra May



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