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28 Space

A spacecraft that travels in a steady path,

or orbit, around the Earth is called a satellite.

Satellites receive and send on communication

and navigation signals, watch the weather,

survey the land, and study space.

HOW DO SATELLITES STAY UP IN SPACE?

Satellites stay up in orbit because of their speed. A satellite in orbit about

300 km (190 miles) above Earth must travel at a speed of 28,000 km/h

(17,400 mph) to stay in space. This speed is called its orbital velocity. There

are several types of. SATELLITE ORBIT.

HOW DO ROCKETS WORK?

Rockets burn fuel mixtures called. PROPELLANTS . The burning fuel creates

a stream of hot gases that shoots out of the rocket’s exhaust nozzle. The backward

force of the gas jet gives the rocket a forward force called thrust. The rocket’s

forward thrust propels the spacecraft into space.

Spacecraft are launched into space by rockets – the only

engines powerful enough to overcome Earth’s gravity

and lift objects into space. Most spacecraft use launch

vehicles with several linked rocket units, or stages.

Rocket propellants contain fuel and oxidant. The fuel needs oxygen

to burn, and the oxidant provides the oxygen. Most engines can

take the oxygen they need from the Earth’s atmosphere, but in

airless space a rocket has to carry its own oxygen supply.

WHAT KINDS OF PROPELLANTS DID ROCKETS USE?

Most rockets burn liquid propellants, and some burn

solid propellants. The space shuttle main engines burned

liquid hydrogen and liquid oxygen. Its booster rockets

burned solid propellants. When a shuttle lifted off,

almost 90 per cent of its weight was propellant.

DO SATELLITES EVER RETURN TO EARTH?

Low-flying satellites may fall back to Earth after

only a few months because they pass through traces

of air in the upper atmosphere, which slow them

down. High-flying satellites can stay in space forever.

FIND OUT MORE. Mass Media 298–299 • Telecommunications 192–193 • Weather 50

Satellites travel around Earth in elliptical

(oval) orbits, over the Equator, the poles,

or on paths in between.

FIND OUT MORE. Elements 160–161 • Engines 198–199 • Forces 164 • Space Travel 30

PROPELLANTS

4 INTEGRAL SATELLITE

Launched into orbit in 2002,

Integral is an astronomy satellite

that studies sources of gamma rays

in space. Its elliptical orbit takes it

as far as 150,000 km (93,000 miles)

above Earth.

SATELLITES

Satellites

ROCKETS

Rockets

4 ORBITS

Satellites fly around Earth in

different orbits. In a geostationary

orbit, a satellite hovers over one

fixed place as the Earth rotates.

SATELLITE ORBITS

SOYUZ LIFT-OFF 3

The Russians have used

the same kind of

Soyuz rocket to launch

spacecraft since 1967.

Core stage burns for

about 5 minutes

after ignition

Payload module contains

scientific instruments

Four boosters burn

for about 2 minutes

after ignition

Service module

contains spacecraft

electronics

Solar panels provide

electrical power

Upper stage burns

for about 4 minutes

after ignition

Highly

elliptical orbit Geostationary orbit

Equatorial

orbit

Polar orbit

rockets

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satellites