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Space Defence Satellites.

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Space Defence Satellites


Satellites (artificial satellites) are ant object that has been purposely placed into orbit around Earth, other planets, or the Sun. Since the launching of the first satellite in 1957, thousands of these “man-made moons” have been rocketed into Earth orbit. Today, satellites play key roles in the communications industry, in military intelligence, and in the scientific study of both Earth and outer space.

Types of Satellites

Engineers have developed many kinds of satellites; each designed to serve a specific purpose or mission.  For instance the telecommunications and broadcasting industries use communications satellites to carry radio, television, and telephone signals over long distances without the need for cables or microwave relays. Navigational satellites pinpoint the location of objects on Earth, while weather satellites help meteorologists forecast the weather. The United States government uses surveillance satellites to monitor military activities.  Scientific satellites serve as space-based platforms for observation of Earth, the other planets, the Sun, comets, and galaxies, and are useful in a wide variety of other applications.

Satellite Launches

Placing a satellite into orbit requires a tremendous amount of energy, which must come from the launch vehicle, or device that launches the satellite. The satellite needs to reach an altitude of at least 120 miles and a speed of over 18,000 mph to lift into orbit successfully. Satellites receive this combination of potential energy (altitude) and kinetic energy (speed) from multistage rockets burning chemical fuels.

The first stage of a multistage rocket consists of rocket engines that provide a huge amount of force, or thrust. The first stage lifts the entire launch vehicle—with its load of fuel, the rocket body, and the satellite—off the launch pad and into the first part of the flight.

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Cosmic Radiation and Micrometeoroid Protection

Satellites have to endure the effects of radiation and of continuous, damaging micrometeoroid hits, especially during long-term missions. Earth’s atmosphere blocks most cosmic radiation from affecting microprocessors in computers on the ground. A satellite, however, needs shielding for its computers. Radiation from space also causes some materials to become brittle, so parts of satellites break more easily after long exposure to the electromagnetic radiation of space. Solar panels gradually produce less and less power because of damage from radiation effects and from the impact of micrometeoroids.

Military Satellites

Many military satellites are similar to commercial ones, but they send encrypted data that only a special receiver can decipher. Military surveillance satellites take pictures just as other earth-imaging satellites do, but cameras on military satellites usually have a higher resolution.

The U.S. military operates a variety of satellite systems. The Defence Satellite Communications System (DSCS) consists of five spacecraft in geostationary orbit that transmit voice, data, and television signals between military sites. The Defence Support Program (DSP) uses satellites that are intended to give early warning of missile launches. DSP was used during the Persian Gulf War (1991) to warn of Iraqi Scud missile launches.

Some military satellites provide data that is available to the public. For instance, the satellites of the Defence Meteorological Satellite Program (DMSP) collect and disseminate global weather information. The military also maintains the Global Positioning System (GPS), which provides navigation information that anyone with a GPS receiver can use.

The US’s Strategic Defence Initiative (SDI), announced by President Reagan in March 1983, revitalised and harmonised research into active defence means - including ground-based, airborne and spaced based sensor and weapon systems.

The aim to move away from the single option of retaliation and, at the very least.

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Passive sensors (such as infrared detectors) are used for surveillance, and tracking, as well as discrimination, by detecting thermal signature differences between targets and decoy. For example, during mid-course, light balloon decoys will cool off
much more rapidly that heavy warheads, and this temperature difference can be detected. However, offence countermeasures, such as placing small heaters in the empty balloons or surrounding the threat complex with aerosols that will mask the position and signature of re-entry vehicles, have a significant potential to defeat this form of discrimination. Power requirements for such sensors range from a few kilowatts up to 100 kilowatts, depending on the size and complexity of the infrared detector systems.

Active sensors (such as radar or ladar) are used for tracking, and
discrimination of real targets from decoys by emitting a signal that is modified when it reaches the target or decoy, with targets producing different changes in the signal than are produced by decoys. For example, some types of decoys will produce a much
weaker reflection of a radar beam than is produced by a warhead. Power requirements for such large space-based sensor systems can range from 1 MWe for laser radars to 5 MWe for space based microwave radars.

Interactive sensors (such as a neutral particle beam generator of an X-Ray Laser) are used for discrimination by generating emissions that interact with a target or decoy, with targets changing in a fashion that is observably different from the changes in the decoy. For example, a neutral particle beam will penetrate through several centimetres of aluminium before it interacts with aluminium atoms to produce secondary radiation. The NPB will thus produce observable secondary radiation when it strikes a warhead, which is much thicker than this depth, but it will pass through the very thin

skin of a balloon decoy without interacting and producing observable secondary radiation.  

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