<text><span class="style10">pace Exploration (3 of 5)</span><span class="style7"></span><span class="style10">Space shuttles</span><span class="style7">Unlike earlier spacecraft, space shuttles are reusable. The main vehicle is winged like an airplane, but is launched into orbit by booster rockets that are then discarded. The main vehicle can subsequently land like a conventional glider. The American space shuttle made its debut on 12 April 1981, with the launch of the orbiter </span><span class="style26">Columbia</span><span class="style7">. The program came to an abrupt halt on 28 January 1986, 73 seconds after the 25th shuttle launch. A leak from a rocket booster caused an explosion that destroyed the </span><span class="style26">Challenger</span><span class="style7"> orbiter and killed its crew of seven. Shuttle operations resumed on 29 September 1988, when </span><span class="style26">Discovery</span><span class="style7"> was launched on the 26th shuttle mission.The Soviet Union's reusable spacecraft is the VKK, which stands for </span><span class="style26">Vosdushno Kosmicheski Korabl</span><span class="style7"> (`airborne space craft'). The first VKK to be launched was Buran (`snowstorm'), which completed two orbits of the Earth on 15 November 1988. Although designed to carry a crew, </span><span class="style26">Buran's</span><span class="style7"> first flight was unmanned.</span><span class="style10">Unmanned probes</span><span class="style7">Much of our knowledge of the Solar System has come from unmanned probes. These have now returned data from every known planet except Pluto. Spacecraft have landed on Venus and Mars and probes are either planned, or on course, to enter orbit around Jupiter and Saturn.</span></text>
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<text><span class="style10">loating in space</span><span class="style7">. On 7 February 1984 Captain Bruce McCandless left the US space shuttle Challenger to make the first untethered `float' in space.</span></text>
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<text>ΓÇó THE INNER PLANETSΓÇó THE OUTER PLANETSΓÇó NUCLEAR ARMAMENT AND DISARMAMENTΓÇó ENGINESΓÇó SEEING THE INVISIBLEΓÇó AIRCRAFT</text>