Satellites

JERS-1 Courtesy of NASDA

Introduction

A satellite is an object that orbits another object due to the gravitational attraction between the two. In other words, the Earth is a satellite of the Sun and our Moon is a satellite of the Earth. Mankind has placed many artificial satellites in orbit around the Earth for purposes from Meteorology to Telecommunications, their orbits being calculated with incredible accuracy before they are launched on one of many possible spacecraft.

Earth Observation

There are many satellites currently in orbit designed to observe the Earth. From the data and images obtained, it is possible to monitor the climate, study crops, track vehicles, evaluate environmental damage, predict the weather, and perform many other useful tasks. It is possible to get resolutions of up to about ten metres, although the rapidly orbiting satellites do not usually give greater resolutions of a kilometre. Satellite altimeters have also made it possible to measure the height of land and sea surfaces to within a few centimetres, allowing us to measure changes in sea levels to incredible accuracy. The European Galileo satellite array, consisting of 30 satellites, will greatly improve satellite navigation in conjunction with current Global Positioning Satellites when the project is completed in 2007.

Observational Astronomy

Astronomers must be able to observe right across the electromagnetic spectrum in order to gain the maximum information about phenomena in the universe. However, the Earth's atmosphere acts as a filter and blocks waves of certain frequencies, so astronomers cannot easily observe high energy ultraviolet, X-ray, gamma, long wavelength radio or infrared emitters from the surface.

One solution to this problem is to observe from just above the atmosphere. This can be achieved by sending up detectors on sounding rockets (short flight rockets that spend about five minutes above the atmosphere) or by mounting equipment on satellites. The Hubble Space Telescope was built for this purpose. On board Hubble at the moment are an Advanced Camera for Surveys (observing from ultraviolet to infrared), a Wide Field and Planetary Camera, Near Infrared Camera and Space Telescope Imaging Spectrograph.

Also in orbit is the Chandra X-Ray Observatory, and the Spitzer Space Telescope, observing in the infrared, is trailing the Earth in its orbit around the Sun.

XMM-Newton is a joint NASA/ESA project that observes X-ray emissions from such objects as pulsars and black holes. It was launched into an elliptical Earth orbit in December 1999.

Images, courtesy of NASA: Stellar spire in the Eagle Nebula (top), imaged by the Hubble Space Telescope. Orbiting white dwarf stars RX J0806 (bottom), imaged by the Chandra X-Ray Observatory.

Planck

(2007 - )

Planck is one of ESA's newest satellites. Named in honour of the Nobel Prize-winning German Scientist Max Planck, it is set to launch in 2007 and will image the cosmic microwave background to an unprecedented degree of precision. This will allow testing of cosmological theories about the origins of the universe.

Image courtesy of ESA.