In
October 1957, the former USSR launched Sputnik 1, the first artificial
satellite, into space in 1957. The following January, Explorer 1 was put
into orbit by the United States. Between the late 1950s and 1976 several
lunar probes were sent to explore the surface of the Moon. Luna 1 was the
first successful lunar probe. It passed within 6,000 km (3,730 miles) of
the Moon. Luna 3 was the first probe to send back pictures to the Earth
of the far side of the Moon. The first to achieve a soft landing was Luna
9 in February 1966. Luna 16 collected soil samples, bringing them back
without any human involvement. The success of these missions forced people
to take space exploration more seriously. Since then artificial satellites
have been circling the Earth. Although most of the hundred or more operational
satellites at present in orbit are for military use, there are many delicated
to peaceful purposes.
Some of the most interesting research satellites include those which are designed to assist in prediction of the weather and to give warning of approaching fronts, depression, cyclones and so on. Many televised weather reports, worldwide, now make use of these satellite pictures to help explain the most likely short and medium term weather patterns. Other types of satellite scan the Earth's surface, pinpointing promising sites of mineral deposits or giving early warning of developing crop diseases.
Astronomical satellites, too, are examining the universe in the infrared and X-ray and gamma ray wavelengths. These satellites produce information unobtainable in any other way. The Earth's atmosphere filters out most or all of such wavelengths emitted by celestial bodies, which means that ground based observers cannot detect them.
A
satellite is sent into an orbit that is most suitable for the kind of work
it do. Space telescope has such as Hubble take the low orbits - 300 km
(186 miles) above the Earth's surface. US spy and surveillance satellites
orbit on a north/ axis to get a view of the Earth, while those belonging
to Russia often follow elliptical orbits that allow them to spend more
time over their own territory. Communications and weather satellites are
positioned above the equator. They take exactly 24 hours 1 to complete
an orbit, and therefore seem to hover above the same point on the Earth's
surface - known as a geostationary orbit, making them ideal vehicles for
efficient long-distance communication.
If you know when to look, and sometimes just by chance, you can see such satellites, usually a little after sunset or just before sunrise. Being so high above the Earth's surface, they reflect back the Sun's light, even though the Sun is below the horizon.
The detailed study of the behaviour of satellites in orbit can be useful. By timing the motion of satellites across the background of fixed stars, vital information can be obtained about the precise shape of the Earth; it also permits more accurate predictions of satellite appearance to be made.
All satellites transmit their information back to Earth by radio signals,
some of which have been picked up by amateur astronomers. Generally speaking,
however, a powerful short-wave receiver and a large aerial system, or antenna,
are required.
Cooperation
in SPACE
