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The James Webb Space Telescope (JWST), previously known as Next Generation Space Telescope (NGST), is a space observatory under construction and scheduled to launch in October 2018. The JWST will offer unprecedented resolution and sensitivity from long-wavelength visible to the mid-infrared, and is a successor instrument to the Hubble Space Telescope and the Spitzer Space Telescope. The telescope features a segmented 6.5-meter (21 ft) diameter primary mirror and will be located near the Earth–Sun L2 point. A large sunshield will keep its mirror and four science instruments below . JWST's capabilities will enable a broad range of investigations across the fields of astronomy and cosmology.〔(【引用サイトリンク】url=http://www.nsf.gov/attachments/106804/public/mather_jwst_science_update.ppt )〕 One particular goal involves observing some of the most distant objects in the Universe, beyond the reach of current ground and space based instruments. This includes the very first stars, the epoch of reionization, and the formation of the first galaxies. Another goal is understanding the formation of stars and planets. This will include imaging molecular clouds and star-forming clusters, studying the debris disks around stars, direct imaging of planets, and spectroscopic examination of planetary transits. In gestation since 1996,〔(【引用サイトリンク】 title=ESA JWST Timeline )〕 the project represents an international collaboration of about 17 countries〔(【引用サイトリンク】 title=NASA – JWST – people )〕 led by NASA, and with significant contributions from the European Space Agency and the Canadian Space Agency. It is named after James E. Webb, the second administrator of NASA, who played an integral role in the Apollo program. The JWST has a history of major cost overruns and delays. The first realistic budget estimates were that the observatory would cost $1.6 billion and launch in 2011. NASA has now scheduled the telescope for a 2018 launch. In 2011, the United States House of Representatives voted to terminate funding, after about $3 billion had been spent and 75 percent of its hardware was in production. Funding was restored in compromise legislation with the US Senate, and spending on the program was capped at $8 billion. , the telescope remained on schedule and within budget, but at risk of further delays. == Overview == The JWST originated in 1996 as the Next Generation Space Telescope (NGST). In 2002 it was renamed after NASA's second administrator (1961–1968) James E. Webb (1906–1992), noted for playing a key role in the Apollo program and establishing scientific research as a core NASA activity.〔(【引用サイトリンク】title=About James Webb )〕 The JWST is a project of the National Aeronautics and Space Administration, the United States space agency, with international collaboration from the European Space Agency and the Canadian Space Agency. The telescope has an expected mass about half of Hubble's, but its primary mirror (a 6.5 meter diameter gold-coated beryllium reflector) will have a collecting area about five times larger (25 m2 vs. 4.5 m2). The JWST is oriented towards near-infrared astronomy, but can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument. The telescope will focus on the near to mid-infrared for three main reasons: high-redshift objects have their visible emissions shifted into the infrared, cold objects such as debris disks and planets emit most strongly in the infrared, and this band is difficult to study from the ground or by existing space telescopes such as Hubble. The JWST will operate near the Earth-Sun L2 Lagrange point, approximately beyond the Earth. Objects near this point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance〔(【引用サイトリンク】title=L2 Orbit )〕 and use a single sunshield to block heat and light from the Sun and Earth. This will keep the temperature of the spacecraft below , necessary for infrared observations.〔(news.nationalgeographic.com 2015-04-23 Hubble Still Wows At 25, But Wait Till You See What's Next )〕 Launch is scheduled for 2018 on an Ariane 5 rocket. Its nominal mission length is five years, with a goal of ten years.〔(【引用サイトリンク】title=About the Webb )〕 The prime contractor is Northrop Grumman. 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「James Webb Space Telescope」の詳細全文を読む スポンサード リンク
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