GPS - eyes in the sky | South China Morning Post
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  • Mar 30, 2015
  • Updated: 11:16pm

GPS - eyes in the sky

PUBLISHED : Tuesday, 03 June, 2008, 12:00am
UPDATED : Tuesday, 03 June, 2008, 12:00am

Quick Facts

Find synonyms for:

locate exactly, put on top, height

In 1978, the United States launched 24 satellites equipped with computers and tools that would set up a global navigation network. This Global Positioning System (GPS) allowed the US military to pinpoint the exact location of their equipment and people.

GPS satellites move in orbit around the Earth at an altitude of about 20,200 kilometres. They transmit signals on a time schedule precisely controlled by atomic clocks.

GPS receivers on the ground automatically select the three satellites nearest to them and relay their signals into a computer. The computer then calculates the exact position of the receiver and sends back a geographic location.

Some GPS tools send back a longitude and latitude. Others display a map and superimpose your location. All sorts of people, including city drivers, explorers and sailors, use GPS tools.

Specialist GPS equipment contacts a fourth satellite so pilots, balloonists and others can calculate altitude as well as the geographic position.

Most GPS tools on the market are accurate to within about 100 metres. But military receivers are accurate to within a metre.

Something else

Choose the correct alternative:

Satellites can be loaded with all sorts of tools.

Corporate satellites receive/transmit television programmes, and give us mobile phone and internet access.

Satellites equipped with cameras give us accurate weather forecasts/sightings, and allow us to make really detailed maps - even of very remote areas.

These eyes in the sky also take daily pictures of polar caps/tips and deserts, allowing us to monitor and study global warming.

Satellite Inventors

The Space Age began on October 4, 1957 when the Soviet Union launched Sputnik 1, the world's first satellite.

The first person to work out exactly what would be needed to launch spacecraft was Konstantin Tsiolkovsky. Although this Russian was a scientist by profession, he also wrote science fiction stories as a hobby.

Tsiolkovsky designed the first rocket fuel made from liquid hydrogen and liquid oxygen. He also calculated that satellites would have to travel around the Earth at a minimum speed of eight kilometres per second.

Although he died in 1935, decades before Sputnik was launched, Tsiolkovsky's work was so important that he is called the Father of Human Spaceflight.

True or False?

The Space Age started about 50 years ago.

Rocket fuel is liquid.

The Father of Human Spaceflight was German.

Space-based Telescopes

Fill in the gaps with the following words:

universe, supernovas, space, galaxies

Satellites carrying powerful telescopes help us explore _______________.

The Hubble Space Telescope that was launched on April 24, 1990 orbits the Earth every 97 minutes at a height of 589km. Hubble sends us wonderful pictures of black holes and _______________, and is now helping us calculate how old the _______________ is.

The Chandra X-ray Observatory that was launched on July 23, 1999, orbits the Earth every 64.3 hours at a height of 140,161km. Chandra has given us images of neutron stars, small galaxies being invaded by bigger _______________ and other exciting phenomena.

A new project, the Spitzer Space Telescope, will be launched in 2009.

You can see these pictures online for free at and

fab fact!

GPS software uses simultaneous algebraic equations to calculate exact location. Simple ones use three to calculate latitude and longitude. Those used by pilots use four calculations to analyse altitude.

fab fact!

Cross-country runners, joggers and other sports enthusiasts train using GPS equipment. Once their workout is over, they download the data to a PC and work out distance, speed and other details that help them calculate how well they are doing.

fab fact!

GPS trackers are useful security devices. Car and truck owners use them to find and recover stolen property. The police use them to keep an eye on the movements of people under house arrest. Some parents use them to keep an eye on their children!


Answer the following questions. To test your memory, try answering without referring to the text. If you can't remember the details, read the piece again.

1 GPS stands for:

a. Global Positioning Satellite

b. Global Placement System

c. Global Positioning System

2 The GPS was launched in:

a. 1935

b. 1958

c. 1978

3 The first satellite was launched by:

a. the US

b. the Soviet Union

c. the UK

4 Which is older?

a. Hubble Space Telescope

b. Chandra X-ray Observatory

c. Spitzer Space Telescope

5 Which has the highest orbit around Earth?

a. Hubble Space Telescope

b. Chandra X-ray Observatory

c. Spitzer Space Telescope

6 Standard GPS tools are accurate to:

a. about 1,000m

b. about 100m

c. about 10m


Synonyms: pinpoint, superimpose, altitude

True or False: T, T, F

Fill in the gaps: space, supernovas, universe, galaxies

Correct alternative: transmit, forecasts, caps

Quiz: 1. c, 2. c, 3. b, 4. a, 5. b, 6. b


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