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STEREO (Solar Terrestrial Relations Observatory) is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections. ==Mission profile== The two STEREO spacecraft were launched at 00:52 UTC on October 26, 2006, from Launch Pad 17B at the Cape Canaveral Air Force Station in Florida on a Delta II 7925-10L launcher into highly elliptical geocentric orbits. The apogee reached the Moon's orbit. On December 15, 2006, on the fifth orbit, the pair swung by the Moon for a gravitational slingshot. Because the two spacecraft were in slightly different orbits, the "ahead" (A) spacecraft was ejected to a heliocentric orbit inside Earth's orbit while the "behind" (B) spacecraft remained temporarily in a high Earth orbit. The B spacecraft encountered the Moon again on the same orbital revolution on January 21, 2007, ejecting itself from Earth orbit in the opposite direction from spacecraft A. Spacecraft B entered a heliocentric orbit outside the Earth's orbit. Spacecraft A will take 347 days to complete one revolution of the Sun and Spacecraft B will take 387 days. The A spacecraft/sun/earth angle will increase at 21.650 degree/year. The B spacecraft/sun/earth angle will change −21.999 degrees per year. Their current locations are shown (here ). Over time, the STEREO spacecraft will continue to separate from each other at a combined rate of approximately 44 degrees per year. There are no ''final'' positions for the spacecraft. They achieved 90 degrees separation on January 24, 2009, a condition known as quadrature. This is of interest because the mass ejections seen from the side on the limb by one spacecraft can potentially be observed by the ''in situ'' particle experiments of the other spacecraft. As they passed through Earth's Lagrangian points and , in late 2009, they searched for Lagrangian (trojan) asteroids. On February 6, 2011, the two spacecraft were exactly 180 degrees apart from each other, allowing the entire Sun to be seen at once for the first time.〔(【引用サイトリンク】title=First Ever STEREO Images of the Entire Sun )〕 Even as the angle increases, the addition of an Earth-based view, e.g. from the Solar Dynamics Observatory, will still provide full-Sun observations for several years. In 2015, contact will be lost for several months when the STEREO spacecraft pass behind the Sun. On October 1, 2014, contact was lost with STEREO-B during a planned reset to test the craft's automation, in anticipation of this Solar 'conjunction' period. , contact had not been re-established, but efforts were still underway to regain communication and control. They will then start to approach Earth again, with closest approach sometime in 2023. They will not be recaptured into Earth orbit. 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「STEREO」の詳細全文を読む スポンサード リンク
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