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The exploration of Jupiter has been conducted via close observations by automated spacecraft. It began with the arrival of ''Pioneer 10'' into the Jovian system in 1973, and, , has continued with seven further spacecraft missions. All of these missions were undertaken by the National Aeronautics and Space Administration (NASA), and all but one have been flybys that take detailed observations without the probe landing or entering orbit. These probes make Jupiter the most visited of the Solar System's outer planets as all missions to the outer Solar System have used Jupiter flybys to reduce fuel requirements and travel time. Plans for more missions to the Jovian system are under development, none of which are scheduled to arrive at the planet before 2016. Sending a craft to Jupiter entails many technical difficulties, especially due to the probes' large fuel requirements and the effects of the planet's harsh radiation environment. The first spacecraft to visit Jupiter was ''Pioneer 10'' in 1973, followed a year later by ''Pioneer 11''. Aside from taking the first close-up pictures of the planet, the probes discovered its magnetosphere and its largely fluid interior. The ''Voyager 1'' and ''Voyager 2'' probes visited the planet in 1979, and studied its moons and the ring system, discovering the volcanic activity of Io and the presence of water ice on the surface of Europa. ''Ulysses'' further studied Jupiter's magnetosphere in 1992 and then again in 2000. The ''Cassini'' probe approached the planet in 2000 and took very detailed images of its atmosphere. The ''New Horizons'' spacecraft passed by Jupiter in 2007 and made improved measurements of its and its satellites' parameters. The ''Galileo'' spacecraft is the only one to have entered orbit around Jupiter, arriving in 1995 and studying the planet until 2003. During this period ''Galileo'' gathered a large amount of information about the Jovian system, making close approaches to all of the four large Galilean moons and finding evidence for thin atmospheres on three of them, as well as the possibility of liquid water beneath their surfaces. It also discovered a magnetic field around Ganymede. As it approached Jupiter, it also witnessed the impact of Comet Shoemaker–Levy 9. In December 1995, it sent an atmospheric probe into the Jovian atmosphere, so far the only craft to do so. Future probes by NASA include the ''Juno'' spacecraft, launched in 2011, which will enter a polar orbit around Jupiter to determine whether it has a rocky core, among other objectives. The European Space Agency selected the L1-class JUICE mission in 2012 as part of its Cosmic Vision programme to explore three of Jupiter's Galilean moons, with a possible Ganymede lander provided by Roscosmos. JUICE is proposed to be launched in 2022. ==Technical requirements== Flights from Earth to other planets in the Solar System have a high energy cost. It requires almost the same amount of energy for a spacecraft to reach Jupiter from Earth's orbit as it does to lift it into orbit in the first place. In astrodynamics, this energy expenditure is defined by the net change in the spacecraft's velocity, or delta-v. The energy needed to reach Jupiter from an Earth orbit requires a delta-v of about 9 km/s, compared to the 9.0–9.5 km/s to reach a low Earth orbit from the ground. Gravity assists through planetary flybys (such as by Earth or Venus) can be used to reduce the energetic requirement (i.e. the fuel) at launch, at the cost of a significantly longer flight duration to reach a target such as Jupiter when compared to the direct trajectory.〔Fischer, 1999, p. 44〕 Ion thrusters capable of a delta-v of more than 10 kilometers/s were used on the Dawn spacecraft. This is more than enough delta-v to do a Jupiter fly-by mission from a solar orbit of the same radius as that of Earth without gravity assist.〔CRC Handbook of Chemistry and Physics, 64th EDITION, (C) 1983, page F-141〕 A major problem in sending space probes to Jupiter is that the planet has no solid surface on which to land, as there is a smooth transition between the planet's atmosphere and its fluid interior. Any probes descending into the atmosphere are eventually crushed by the immense pressures within Jupiter. Another major issue is the amount of radiation to which a space probe is subjected, due to the harsh charged-particle environment around Jupiter (for a detailed explanation see Magnetosphere of Jupiter). For example, when ''Pioneer 11'' made its closest approach to the planet, the level of radiation was ten times more powerful than ''Pioneers designers had predicted, leading to fears that the probes would not survive. With a few minor glitches, the probe managed to pass through the radiation belts, but it lost most of the images of the moon Io, as the radiation had caused ''Pioneer'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Exploration of Jupiter」の詳細全文を読む スポンサード リンク
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