<text><span class="style10">pace Exploration (5 of 5)</span><span class="style7"></span><span class="style10">The Uses of Space Technology</span><span class="style7">Many artificial satellites are used for communications. </span><span class="style26">Comsats</span><span class="style7">, as they are sometimes known, are often placed in </span><span class="style26">geostationary </span><span class="style7">orbit, 36900 km (22900 mi) above the equator. Satellites in this orbit travel at the same speed as the Earth rotates and thus appear to remain fixed in the sky.</span><span class="style26">Weather satellites</span><span class="style7"> operate either in geostationary orbit, or polar orbit. A </span><span class="style26">polar orbit </span><span class="style7">carries a satellite over the North and South Poles, passing over a different strip of the Earth on every orbit. Such satellites can survey the entire planet every 24 hours.</span><span class="style26">Earth-resources satellites</span><span class="style7">, such as those in the US Landsat series, can be used to prospect for new mineral resources, check the spread of diseases in crops and monitor pollution.Space provides a good vantage point for astronomers, whose instruments can examine the universe from above the distortions of the atmosphere. The Hubble Space Telescope, launched by space shuttle in 1990, is designed to detect fainter objects than any telescope on the ground, although it has suffered technical problems.The movement of a space station cancels out the effect of gravity, making astronauts and their equipment weightless. These conditions can be used for manufacturing new materials such as perfect crystals.The military also make use of space. Satellites can detect ground detail far more effectively than conventional aircraft. Spy satellites can detect objects as small as individual vehicles andpeople. The US Strategic Defense Initiative (ΓÇÿStar WarsΓÇÖ) program aimed to provide a space-based laser defense system against nuclear weapons. However, many scientists doubted the feasibility and desirability of the project and since the end of the Cold War it has been abandoned.</span></text>
</content>
<content>
<layer>background</layer>
<id>23</id>
<text>ΓÇó THE INNER PLANETSΓÇó THE OUTER PLANETSΓÇó NUCLEAR ARMAMENT AND DISARMAMENTΓÇó ENGINESΓÇó SEEING THE INVISIBLEΓÇó AIRCRAFT</text>
