How does a television signal get to the other
side of the world in seconds? What tells ships
exactly where they are in the middle of the
ocean? How do we get warning that storms are
coming? Satellites do all these things and more.
WHAT ARE SATELLITES?
Satellites are objects in outer space that fly
around planets in circular paths called orbits.
Artificial satellites are made by people.
Thousands of satellites are zooming around our
planet right now.
The Soviet Union launched the first artificial
satellite, Sputnik 1, in 1957. Sputnik 1
broadcasted a steady signal of beeps. It circled
Earth for three months and then fell back into the
atmosphere and burned up. The atmosphere is
the air that surrounds Earth.
HOW DO SATELLITES GET INTO SPACE?
Satellites need to reach a height of at least 120
miles (200 kilometers) to orbit. They also need to
travel faster than 18,000 miles per hour (29,000
kilometers per hour). A satellite any lower or
slower would soon fall back down to Earth. It
takes a rocket to bring satellites up to that height
Most satellites are launched from the ground.
Some small satellites can be launched from high-
flying planes. This uses less fuel.
Other satellites are launched using a space
shuttle or other piloted rocket. This way,
astronauts on the space shuttle can make sure
the satellite is working and gets into the right
WHAT ARE SATELLITES USED FOR?
Satellites are used for a great many things.
Communications satellites beam TV, radio, and
telephone signals all around the world.
Navigational satellites help people know where
they are and get where they are going. Weather
satellites take pictures of clouds and storms
from above to help make weather forecasts. Spy
satellites look down and snoop on other
countries. Other satellites help scientists to
study Earth and other planets.
HOW DO SATELLITES WORK IN SPACE?
Space is a difficult place to be. You can’t plug in
a cord in outer space, so satellites need to take
a power source with them. It’s hard to get
satellites pointed in the right direction because
there’s nothing to turn them with. Satellites
need to work in the freezing cold of Earth’s
shadow as well as in the blazing heat of the
Sun’s rays. They also need to be tough enough
to survive collisions with tiny asteroids (space
Most satellites use both power from the Sun and
batteries to work. They catch the Sun’s energy
using large flat solar panels. Satellites keep
these panels pointed at the Sun. They use
batteries when the Sun doesn’t shine on them.
Satellites can stay pointed in the right direction
using small rockets called attitude thrusters.
They can also use instruments called
gyroscopes. Sometimes magnets on board the
satellite can push against the magnetic field of
Earth to aim the satellite correctly.
No air flows past satellites to cool them. To keep
from getting too hot in the Sun, satellites have
panels that open and close. This lets heat
escape. Satellites often spin so the Sun doesn’t
make one side so hot that it melts.
Satellites also need to be made from strong
materials in case tiny asteroids hit them. They
need materials that don’t become brittle in the
cold and the harsh radiation of space.
DO WE GET SATELLITES BACK FROM SPACE?
When satellites stop working they are often left
in orbit as so much space junk. Others drift too
low to keep orbiting and burn up as they fall. Still
others are brought back to Earth for repairs.
Nonworking satellites are sometimes sent down
from orbit into the atmosphere to burn up on
purpose. Space is very large, but still scientists
need to be careful that satellites don’t crash
into each other. They try to get rid of the broken
HOW MANY SATELLITES ARE THERE?
Since Sputnik 1, more than 5,000 satellites from
many countries have been launched. Artificial
satellites now orbit the Sun, Mars, Venus, and
other planets and their moons. Most satellites,
however, orbit Earth. High above your head
thousands of satellites circle the planet every