詹姆斯韦伯天文望远镜James Webb Space Telescope

【机器翻译自wiki】

The James Webb Space Telescope (JWST or “Webb“) is a space telescope that is planned to be the successor to the Hubble Space Telescope.[6][7] The JWST will provide greatly improved resolution and sensitivity over the Hubble, and will enable a broad range of investigations across the fields of astronomy and cosmology, including observing some of the most distant events and objects in the universe, such as the formation of the first galaxies. Other goals include understanding the formation of stars and planets, and direct imaging of exoplanets and novas.[8]

詹姆斯·韦伯太空望远镜(JWST或“韦伯”)是一架太空望远镜,计划作为哈勃太空望远镜的继任者。[6] [7] JWST将极大地改善哈勃望远镜的分辨率和灵敏度,并将在天文学和宇宙学领域进行广泛的研究,包括观察宇宙中一些最遥远的事件和天体,例如第一次形成星系。其他目标包括了解恒星和行星的形成,以及对系外行星和新星的直接成像。[8]

The primary mirror of the JWST, the Optical Telescope Element, is composed of 18 hexagonal mirror segments made of gold-plated beryllium which combine to create a 6.5-meter (21 ft; 260 in) diameter mirror that is much larger than the Hubble’s 2.4-meter (7.9 ft; 94 in) mirror. Unlike the Hubble, which observes in the near ultravioletvisible, and near infrared (0.1 to 1 μm) spectra, the JWST will observe in a lower frequency range, from long-wavelength visible light through mid-infrared (0.6 to 27 μm), which will allow it to observe high redshift objects that are too old and too distant for the Hubble to observe.[9] The telescope must be kept very cold in order to observe in the infrared without interference, so it will be deployed in space near the Earth–Sun L2 Lagrangian point, and a large sunshield made of silicon– and aluminum-coated Kapton will keep its mirror and instruments below 50 K (−220 °C; −370 °F).[10]

JWST的主要反射镜是光学望远镜元件,由18个由镀金铍制成的六边形镜段组成,这些镜段组合起来可形成直径6.5米(21英尺; 260英寸)的镜,该镜的直径远大于哈勃望远镜的2.4倍-米(7.9英尺; 94英寸)镜子。与哈勃望远镜不同,它在近紫外,可见光和近红外(0.1至1μm)光谱中观察,而JWST将在较低的频率范围内观察,从长波可见光到中红外(0.6至27μm) ,这将使其能够观测到高红移物体,而这些物体太旧且距离太远,哈勃望远镜无法观察到。[9]为了使红外线望远镜不受干扰,望远镜必须保持非常冷的状态,因此它将部署在地球–太阳L2拉格朗日点附近的空间中,由硅和铝涂层的Kapton制成的大型遮阳板将保持其镜面和低于50 K(-220°C; -370°F)的仪器。[10]

The JWST is being developed by NASA—with significant contributions from the European Space Agency and the Canadian Space Agency[1]—and is named for James E. Webb, who was the administrator of NASA from 1961 to 1968 and played an integral role in the Apollo program.[11][12] Development began in 1996 for a launch that was initially planned for 2007, but the project has had numerous delays and cost overruns, and underwent a major redesign in 2005. The JWST’s construction was completed in late 2016, after which its extensive testing phase began.[13][14] In March 2018, NASA delayed the launch after the telescope’s sunshield ripped during a practice deployment.[15] Launch was delayed again in June 2018 following recommendations from an independent review board, and is currently scheduled for March 2021.[3][16][17]

JWST由美国国家航空航天局(NASA)开发,并得到了欧洲航天局和加拿大航天局的大力贡献[1],并以詹姆斯·E·韦伯(James E. Webb)的名字命名。韦伯(James E. Webb)曾在1961年至1968年担任美国航天局的局长,阿波罗计划。[11] [12]开发工作于1996年开始,最初计划于2007年启动,但该项目遇到了许多延误和成本超支,并于2005年进行了重大重新设计。JWST的建设于2016年底完成,此后开始了广泛的测试阶段。 [13] [14] 2018年3月,在练习部署期间望远镜的遮阳罩被撕裂后,NASA推迟了发射。[15]根据独立审查委员会的建议,发射工作于2018年6月再次推迟,目前定于2021年3月进行。[3] [16] [17]

Features

Launch configuration of the JWST in an Ariane 5.

在Ariane 5中启动JWST的配置。

The JWST has an expected mass about half of Hubble Space Telescope‘s, but its primary mirror (a 6.5 meter diameter, 21.3-foot gold-coated beryllium reflector) will have a collecting area about five times as large (25 m2 or 270 sq ft vs. 4.5 m2 or 48 sq ft). The JWST is oriented toward near-infrared astronomy, but can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument. The design emphasizes 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. Ground-based telescopes must look through the atmosphere, which is opaque in many infrared bands (see figure of atmospheric transmission).

JWST的预期质量约为哈勃太空望远镜的一半,但其主镜(直径6.5米,21.3英尺镀金铍反射镜)的收集面积约为五倍(25平方米或270平方英尺, 4.5平方米或48平方英尺)。 JWST面向近红外天文学,但也可以看到橙色和红色可见光,以及中红外区域,具体取决于仪器。 该设计强调了近红外至中红外的三个主要原因:高红移物体的可见发射移向红外,碎屑盘和行星等冷物体的红外发射最强,并且很难从该波段进行研究。 地面或现有的太空望远镜,例如哈勃望远镜。 地面望远镜必须透过大气层,在许多红外波段它是不透明的(请参见大气传输图)。

Even where the atmosphere is transparent, many of the target chemical compounds, such as water, carbon dioxide, and methane, also exist in the Earth’s atmosphere, vastly complicating analysis. Existing space telescopes such as Hubble cannot study these bands since their mirrors are not cool enough (the Hubble mirror is maintained at about 15 °C (288 K)) and hence the telescope itself radiates strongly in the infrared bands.[citation needed]

即使在大气透明的地方,地球大气中也存在许多目标化合物,例如水,二氧化碳和甲烷,这使分析变得极为复杂。 现有的太空望远镜(例如哈勃望远镜)无法研究这些波段,因为它们的反射镜不够凉爽(哈勃镜保持在15°C(288 K)左右),因此望远镜本身在红外波段会强烈辐射。

The JWST will operate near the Earth–Sun L2 (Lagrange) point, approximately 1,500,000 km (930,000 mi) beyond Earth’s orbit. By way of comparison, Hubble orbits 550 kilometres (340 mi) above Earth’s surface, and the Moon is roughly 400,000 kilometres (250,000 mi) from Earth. This distance makes post-launch repair or upgrade of the JWST hardware virtually impossible. Objects near this point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance[18] and use a single sunshield to block heat and light from the Sun and Earth. This will keep the temperature of the spacecraft below 50 K (−220 °C; −370 °F), necessary for infrared observations.[10][19] The prime contractor is Northrop Grumman.[20]

JWST将在离地球轨道约1,500,000公里(930,000英里)的地球-太阳L2(拉格朗日)点附近运行。 相比之下,哈勃绕地球表面行进550公里(340英里),而月球距离地球大约40万公里(25万英里)。 这个距离使得JWST硬件的发布后维修或升级几乎不可能。 靠近此点的物体可以与地球同步绕太阳公转,从而使望远镜保持大致恒定的距离[18],并使用单个遮阳板来阻挡来自太阳和地球的热量和光。 这将使航天器的温度保持在50 K以下(−220°C; -370°F),这是红外观测所必需的。[10] [19] 主要承包商是诺斯罗普·格鲁曼公司。[20]

Three-quarter view of the top

Bottom (sun-facing side)

遮阳防护Sunshield protection

Test unit of the sunshield stacked and expanded at the Northrop Grumman facility in California, 2014.Main article: Sunshield (JWST)

2014年,在加利福尼亚州诺斯罗普·格鲁曼公司的诺斯罗普·格鲁曼工厂堆叠并扩展了遮阳板的测试装置。主要文章:遮阳板(JWST)

To make observations in the infrared spectrum, the JWST must be kept very cold (under 50 K (−220 °C; −370 °F)), otherwise infrared radiation from the telescope itself would overwhelm its instruments. Therefore, it uses a large sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Earth–Sun L2 point keeps all three bodies on the same side of the spacecraft at all times.[21] Its halo orbit around L2 avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays.[18] The shielding maintains a stable temperature throughout the structures on the dark side, which is critical to maintaining precise alignment of the primary mirror segments.[citation needed]

为了在红外光谱中进行观察,必须将JWST保持在非常低的温度(低于50 K(-220°C; -370°F)),否则望远镜本身的红外辐射会淹没其仪器。 因此,它使用大型遮阳板来阻挡来自太阳,地球和月球的光和热,并且其位置靠近地球-太阳L2点,使所有三个物体始终保持在航天器的同一侧。[21] 它围绕L2的光晕轨道避开了地球和月球的阴影,为遮阳板和太阳能电池板保持了恒定的环境。[18] 屏蔽层可在整个暗侧结构上保持稳定的温度,这对于维持主镜段的精确对准至关重要。

The five-layer sunshield is constructed from polyimide film, with membranes coated with aluminum on one side and silicon on the other.[22] Accidental tears of the delicate film structure during testing are one factor delaying the project.[23]

五层遮阳板由聚酰亚胺薄膜制成,一侧覆盖有铝膜,另一侧覆盖有硅膜。[22] 在测试过程中,易碎薄膜结构的意外撕裂是延误该项目的因素之一。[23]

The sunshield is designed to be folded twelve times so it will fit within the Ariane 5 rocket’s 4.57 m (5 yards) × 16.19 m (17.7 yards) payload fairing. Once deployed at the L2 point, it will unfold to 21.197 m (23.18 yards) × 14.162 m (15.55 yards). The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama, before it was delivered to Northrop Grumman in Redondo Beach, California, USA for testing.[24]

遮阳罩设计为可折叠十二次,因此将适合Ariane 5火箭的4.57 m(5码)×16.19 m(17.7码)有效载荷整流罩。 一旦部署到L2点,它将展开到21.197 m(23.18码)×14.162 m(15.55码)。 该遮阳板在阿拉巴马州亨茨维尔的ManTech(NeXolve)处手工组装,然后交付给美国加利福尼亚雷东多海滩的诺斯罗普·格鲁曼公司进行测试。[24]

光学特性Optics

Engineers cleaning a test mirror with carbon dioxide snow, 2015

Main mirror assembled at Goddard Space Flight Center, May 2016.Main article: Optical Telescope Element

JWST’s primary mirror is a 6.5-meter-diameter gold-coated beryllium reflector with a collecting area of 25 m2. This is too large for existing launch vehicles, so the mirror is composed of 18 hexagonal segments, which will unfold after the telescope is launched. Image plane wavefront sensing through phase retrieval will be used to position the mirror segments in the correct location using very precise micro-motors. Subsequent to this initial configuration they will only need occasional updates every few days to retain optimal focus.[25] This is unlike terrestrial telescopes like the Keck which continually adjust their mirror segments using active optics to overcome the effects of gravitational and wind loading, though the Webb telescope will use 126 small motors, and is made possible because of the lack of environmental disturbances of a telescope in space.[26]

JWST的主镜是直径为6.5米的镀金铍反射镜,收集面积为25平方米。 这对于现有的运载火箭来说太大了,因此反射镜由18个六角形部分组成,这些六角形部分将在望远镜发射后展开。 通过相位恢复的图像平面波前感测将用于使用非常精确的微型电机将镜段定位在正确的位置。 进行此初始配置后,他们仅需要每隔几天进行一次偶尔更新即可保持最佳焦点。[25] 这与地面望远镜不同,例如凯克(Keck)地面望远镜使用主动光学器件不断调整其镜段,以克服重力和风荷载的影响,尽管韦伯望远镜将使用126台小型电动机,并且由于没有受到环境的干扰而成为可能。 太空望远镜。[26]

JWST’s optical design is a three-mirror anastigmat,[27] which makes use of curved secondary and tertiary mirrors to deliver images that are free of optical aberrations over a wide field. In addition, there is a fast steering mirror, which can adjust its position many times per second to provide image stabilization.

JWST的光学设计是三反射镜,[27]利用弯曲的第二和第三反射镜在宽视场上提供无光学像差的图像。 此外,还有一个快速转向镜,它可以每秒多次调整其位置,以提供图像稳定性。

Ball Aerospace & Technologies Corp. is the principal optical subcontractor for the JWST project, led by prime contractor Northrop Grumman Aerospace Systems, under a contract from the NASA Goddard Space Flight Center, in Greenbelt, Maryland.[2][28] Eighteen primary mirror segments, secondary, tertiary and fine steering mirrors, plus flight spares have been fabricated and polished by Ball Aerospace based on beryllium segment blanks manufactured by several companies including Axsys, Brush Wellman, and Tinsley Laboratories.[citation needed]

鲍尔航空航天技术公司是JWST项目的主要光学分包商,由总承包商诺斯罗普·格鲁曼航空航天系统公司牵头,根据马里兰州格林贝尔特的美国宇航局戈达德航天中心的合同。[2] [28] Ball Aerospace已根据Axsys,Brush Wellman和Tinsley Laboratories等多家公司制造的铍分段毛坯,制造并抛光了18个主反射镜分段,辅助,三级和精细转向镜以及飞行备用零件。[需要引证]

The final segment of the primary mirror was installed on 3 February 2016,[29] and the secondary mirror was installed on 3 March 2016.[30]

主镜像的最后部分是在2016年2月3日安装的,[29]而次镜像是在2016年3月3日,安装的[30]。

科学实验设备Scientific instruments

NIRCam model

NIRSpec model

MIRI 1:3 scale model

The Integrated Science Instrument Module (ISIM) is a framework that provides electrical power, computing resources, cooling capability as well as structural stability to the Webb telescope. It is made with bonded graphite-epoxy composite attached to the underside of Webb’s telescope structure. The ISIM holds the four science instruments and a guide camera.[31]

集成科学仪器模块(ISIM)是一个框架,可为Webb望远镜提供电能,计算资源,冷却能力以及结构稳定性。 它由附着在韦伯望远镜结构底面的石墨-环氧树脂复合材料制成。 ISIM拥有四台科学仪器和一台引导相机。[31]

  • NIRCam (Near InfraRed Camera) is an infrared imager which will have a spectral coverage ranging from the edge of the visible (0.6 micrometers) through the near infrared (5 micrometers).[32][33] NIRCam will also serve as the observatory’s wavefront sensor, which is required for wavefront sensing and control activities. NIRCam was built by a team led by the University of Arizona, with Principal Investigator Marcia J. Rieke. The industrial partner is Lockheed-Martin‘s Advanced Technology Center located in Palo Alto, California.[34]
  • NIRCam(近红外相机)是一种红外成像仪,其光谱覆盖范围从可见光的边缘(0.6微米)到近红外的(5微米)。[32] [33] NIRCam也将用作天文台的波前传感器,这是波前传感和控制活动所必需的。 NIRCam由亚利桑那大学领导的团队和首席研究员Marcia J. Rieke共同建造。 工业合作伙伴是位于加利福尼亚帕洛阿尔托的洛克希德·马丁公司的先进技术中心。[34]
  • NIRSpec (Near InfraRed Spectrograph) will also perform spectroscopy over the same wavelength range. It was built by the European Space Agency at ESTEC in NoordwijkNetherlands. The leading development team is composed of people from Airbus Defence and Space, Ottobrunn and Friedrichshafen, Germany, and the Goddard Space Flight Center; with Pierre Ferruit (École normale supérieure de Lyon) as NIRSpec project scientist. The NIRSpec design provides three observing modes: a low-resolution mode using a prism, an R~1000 multi-object mode and an R~2700 integral field unit or long-slit spectroscopy mode.
  • NIRSpec(近红外光谱仪)还将在相同的波长范围内进行光谱分析。 它是由欧洲航天局在荷兰诺德韦克的ESTEC建造的。 领先的开发团队由来自德国奥托布伦和腓特烈港的空中客车防御与太空公司以及戈达德太空飞行中心的人员组成; Pierre Ferruit(里昂高等师范学校)担任NIRSpec项目科学家。 NIRSpec设计提供了三种观察模式:使用棱镜的低分辨率模式,R〜1000多对象模式和R〜2700积分场单元或长缝光谱模式。
  • [35] Switching of the modes is done by operating a wavelength preselection mechanism called the Filter Wheel Assembly, and selecting a corresponding dispersive element (prism or grating) using the Grating Wheel Assembly mechanism.[35] Both mechanisms are based on the successful ISOPHOT wheel mechanisms of the Infrared Space Observatory. The multi-object mode relies on a complex micro-shutter mechanism to allow for simultaneous observations of hundreds of individual objects anywhere in NIRSpec’s field of view. The mechanisms and their optical elements were designed, integrated and tested by Carl Zeiss Optronics GmbH of Oberkochen, Germany, under contract from Astrium.[35]
  • [35]通过操作称为滤光轮组件的波长预选机制并使用光栅轮组件机制选择相应的色散元件(棱镜或光栅)来完成模式的切换。[35] 两种机制均基于红外空间天文台成功的ISOPHOT滚轮机制。 多对象模式依赖于复杂的微快门机制,可以同时观察NIRSpec视野中任何位置的数百个单个对象。 这些机构及其光学元件是由德国Oberkochen的Carl Zeiss Optronics GmbH根据Astrium的合同设计,集成和测试的。[35]
  • MIRI (Mid-InfraRed Instrument) will measure the mid-to-long-infrared wavelength range from 5 to 27 micrometers.[36][37] It contains both a mid-infrared camera and an imaging spectrometer.[2] MIRI was developed as a collaboration between NASA and a consortium of European countries, and is led by George Rieke (University of Arizona) and Gillian Wright (UK Astronomy Technology Centre, Edinburgh, part of the Science and Technology Facilities Council (STFC)).[34] MIRI features similar wheel mechanisms as NIRSpec which are also developed and built by Carl Zeiss Optronics GmbH under contract from the Max Planck Institute for Astronomy, Heidelberg. The completed Optical Bench Assembly of MIRI was delivered to Goddard in mid-2012 for eventual integration into the ISIM. The temperature of the MIRI must not exceed 6 Kelvin (K): a helium gas mechanical cooler sited on the warm side of the environmental shield provides this cooling.[38]
  • MIRI(中红外仪器)将测量5至27微米的中至长红外波长范围。[36] [37] 它包含一个中红外照相机和一个成像光谱仪。[2] MIRI是NASA与欧洲国家联盟之间的合作开发的,由George Rieke(亚利桑那大学)和Gillian Wright(爱丁堡英国天文学技术中心,科学和技术设施理事会(STFC)的一部分)领导。 [34] MIRI具有与NIRSpec类似的轮机构,该机构也是由卡尔·蔡司光电有限公司根据海德堡马克斯·普朗克天文学研究所的合同开发和制造的。 MIRI的完整光学平台组件已于2012年中期交付给Goddard,最终集成到ISIM中。 MIRI的温度不得超过6开尔文(K):位于环保屏的热侧的氦气机械冷却器可以提供这种冷却。[38]
  • FGS/NIRISS (Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph), led by the Canadian Space Agency under project scientist John Hutchings (Herzberg Institute of AstrophysicsNational Research Council of Canada), is used to stabilize the line-of-sight of the observatory during science observations. Measurements by the FGS are used both to control the overall orientation of the spacecraft and to drive the fine steering mirror for image stabilization. The Canadian Space Agency is also providing a Near Infrared Imager and Slitless Spectrograph (NIRISS) module for astronomical imaging and spectroscopy in the 0.8 to 5 micrometer wavelength range, led by principal investigator René Doyon at the University of Montreal.[34] Because the NIRISS is physically mounted together with the FGS, they are often referred to as a single unit, but they serve entirely different purposes, with one being a scientific instrument and the other being a part of the observatory’s support infrastructure.
  • FGS / NIRISS(精细制导传感器和近红外成像仪和无缝隙光谱仪)由加拿大太空总署领导,由项目科学家John Hutchings(加拿大国家研究委员会赫兹伯格天体物理研究所)领导,用于稳定视线科学观测期间的天文台。 FGS的测量不仅用于控制航天器的总体方向,而且用于驱动精细的转向镜以实现图像稳定。加拿大航天局还提供了一个近红外成像仪和无缝隙光谱仪(NIRISS)模块,用于在0.8至5微米波长范围内的天文成像和光谱学,由蒙特利尔大学的首席研究员RenéDoyon领导。[34]由于NIRISS与FGS物理安装在一起,因此它们通常被称为一个单元,但它们的用途完全不同,一个是科学仪器,另一个是天文台支持基础设施的一部分。

NIRCam and MIRI feature starlight-blocking coronagraphs for observation of faint targets such as extrasolar planets and circumstellar disks very close to bright stars.[37]

NIRCam和MIRI具有阻挡星光的日冕仪,用于观察微弱的目标,例如非常接近明亮恒星的太阳系外行星和绕星盘。[37]

The infrared detectors for the NIRCam, NIRSpec, FGS, and NIRISS modules are being provided by Teledyne Imaging Sensors (formerly Rockwell Scientific Company). The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) and Command and Data Handling (ICDH) engineering team uses SpaceWire to send data between the science instruments and the data-handling equipment.[39]

Teledyne Imaging Sensors(以前的Rockwell Scientific Company)提供了用于NIRCam,NIRSpec,FGS和NIRISS模块的红外探测器。 詹姆斯·韦伯太空望远镜(JWST)综合科学仪器模块(ISIM)和命令与数据处理(ICDH)工程团队使用SpaceWire在科学仪器和数据处理设备之间发送数据。[39]

Spacecraft Bus

Main article: Spacecraft Bus (JWST)

Diagram of the Spacecraft Bus. The solar panel is in green and the light purple flats are radiators shades.

航天飞机的示意图。 太阳能电池板为绿色,浅紫色的平板为散热器阴影。

The Spacecraft Bus is the primary support component of the James Webb Space Telescope, that hosts a multitude of computing, communication, propulsion, and structural parts, bringing the different parts of the telescope together.[40] Along with the Sunshield, it forms the Spacecraft Element of the space telescope.[41] The other two major elements of the JWST are the Integrated Science Instrument Module (ISIM) and the Optical Telescope Element (OTE).[42] Region 3 of ISIM is also inside the Spacecraft Bus; region 3 includes ISIM Command and Data Handling subsystem and the MIRI cryocooler.[42]

 Spacecraft Bus 是詹姆斯·韦伯太空望远镜的主要支持组件,该主机承载着大量的计算,通信,推进和结构性部件,将望远镜的不同部分整合在一起。[40] 它与遮阳罩一起构成了太空望远镜的航天器元素。[41] JWST的其他两个主要要素是综合科学仪器模块(ISIM)和光学望远镜要素(OTE)。[42] ISIM的3区也位于  Spacecraft Bus 内; 区域3包括ISIM命令和数据处理子系统以及MIRI低温冷却器。[42]

The Spacecraft Bus is connected to Optical Telescope Element via the Deployable Tower Assembly, which also connects to the sunshield.[40]

航天器总线通过可展开塔式组件连接到光学望远镜元件,该组件也连接到遮阳板。[40]

The structure of the Spacecraft Bus must support the 6.5-ton space telescope, while it itself weighs 350 kg (about 770 lb).[8] It is made primarily of graphite composite material.[8] It was assembled in California by 2015, and after that it had to be integrated with the rest of the space telescope leading up to its planned 2021 launch. The bus can provide pointing of one-arcsecond and isolates vibration down to two milliarcseconds.[43]

航天器客车的结构必须支持6.5吨的太空望远镜,而它本身的重量为350千克(约770磅)。[8] 它主要由石墨复合材料制成。[8] 它于2015年在加利福尼亚组装完毕,此后必须与其余的太空望远镜整合,直至计划于2021年发射。 总线可以提供一秒的指向性,并且可以将振动隔离到2毫秒。[43]

The Spacecraft Bus is on the Sun-facing “warm” side and operates at a temperature of about 300 K.[41] Everything on the Sun facing side must be able to handle the thermal conditions of JWST’s halo orbit, which has one side in continuous sunlight and the other in the shade of the spacecraft sunshield.[41]

航天器客车位于朝阳的“温暖”侧,其工作温度约为300K。[41] 面向太阳的一面的所有物体都必须能够处理JWST晕圈的热条件,该晕圈的一侧在连续的阳光下,另一侧在航天器遮阳板的阴影下。[41]

Another important aspect of the Spacecraft Bus is the central computing, memory storage, and communications equipment.[40] The processor and software direct data to and from the instruments, to the solid-state memory core, and to the radio system which can send data back to Earth and receive commands.[40] The computer also controls the pointing and moment of the spacecraft, taking in sensor data from the gyroscopes and star tracker, and sending the necessary commands to the reaction wheels or thrusters depending.[40]

航天器总线的另一个重要方面是中央计算,内存存储和通信设备。[40] 处理器和软件将数据与仪器之间,以及与固态存储器核心和无线电系统之间的数据直接传送,后者可以将数据发送回地球并接收命令。[40] 计算机还控制航天器的指向和力矩,从陀螺仪和恒星跟踪器获取传感器数据,并根据需要向反作用轮或推进器发送必要的命令。[40]

Comparison with other telescopes

Comparison with Hubble primary mirror

Calisto architecture for SAFIR would be a successor to Spitzer, requiring even cooler passive cooling than JWST (5 Kelvin).[44]

SAFIR的Calisto体系结构将是Spitzer的后继体系,它需要比JWST(5开尔文)更冷的被动冷却。[44]

The desire for a large infrared space telescope traces back decades; in the United States the Shuttle Infrared Telescope Facility was planned while the Space Shuttle was in development and the potential for infrared astronomy was acknowledged at that time.[45] Compared to ground telescopes, space observatories were free from atmospheric absorption of infrared light; this would be a whole “new sky” for astronomers.[45]

人们对大型红外太空望远镜的渴望可以追溯到几十年前。 在美国,航天飞机正在研制中时,计划进行航天飞机红外望远镜设施建设,当时人们认识到了红外天文学的潜力。[45] 与地面望远镜相比,天文台没有大气吸收红外光。 对于天文学家来说,这将是一个全新的天空。[45]

The tenuous atmosphere above the 400 km nominal flight altitude has no measurable absorption so that detectors operating at all wavelengths from 5 µm to 1000 µm can achieve high radiometric sensitivity.— S. G. McCarthy & G. W. Autio, 1978[45]

在标称飞行高度400 km以上的脆弱大气中没有可测量的吸收,因此在从5 µm至1000 µm的所有波长下运行的探测器都可以实现高辐射敏感性。—— S。G. McCarthy&G. W. Autio,1978年[45]

However, infrared telescopes have a disadvantage—they need to stay extremely cold and the longer the wavelength of infrared, the colder they need to be.[46] If not, the background heat of the device itself overwhelms the detectors, making it effectively blind.[46] This can be overcome by careful spacecraft design, in particular by placing the telescope in a dewar with an extremely cold substance, such as liquid helium.[46] This has meant most infrared telescopes have a lifespan limited by their coolant, as short as a few months, maybe a few years at most.[46]

但是,红外望远镜有一个缺点-它们需要保持极冷,并且红外波长越长,它们就需要越冷。[46] 如果不是这样,则设备本身的背景热量会使检测器不堪重负,从而使其实际上是盲目的。[46] 可以通过精心设计的航天器来克服这一问题,特别是将望远镜置于杜瓦瓶中,杜瓦瓶中应含液态氦等极冷的物质。[46] 这意味着大多数红外望远镜的使用寿命受其冷却剂的限制,短至几个月,最多可能只有几年。[46]

 It has been possible to maintain a temperature low enough through the design of the spacecraft to enable near-infrared observations without a supply of coolant, such as the extended missions of Spitzer and NEOWISE. Another example is Hubble’s NICMOS instrument, which started out using a block of nitrogen ice that depleted after a couple of years, but was then converted to a cryocooler that worked continuously. The James Webb Space Telescope is designed to cool itself without a dewar, using a combination of sunshield and radiators with the mid-infrared instrument using an additional cryocooler.[47]

通过设计航天器,可以将温度保持在足够低的水平,从而无需供应冷却剂即可进行近红外观测,例如Spitzer和NEOWISE的任务扩展。 另一个例子是哈勃(Hubble)的NICMOS仪器,该仪器最初使用一块氮气冰块,该氮气冰块在几年后耗尽了,但随后被转换为可连续工作的低温冷却器。 詹姆斯·韦伯太空望远镜的设计目的是在不产生杜瓦瓶的情况下进行自我冷却,将遮阳板和散热器与中红外仪器结合使用,并使用一个额外的低温冷却器。[47]

The telescope’s delays and cost increases can be compared to the Hubble Space Telescope.[48] When Hubble formally started in 1972, it had an estimated development cost of $300 million (or about $1 billion in 2006 constant dollars),[48] but by the time it was sent into orbit in 1990, the cost was about four times that.[48] In addition new instruments and servicing missions increased the cost to at least $9 billion by 2006.[48]

可以将望远镜的延迟和成本增加与哈勃太空望远镜进行比较。[48] 哈勃望远镜于1972年正式开始使用时,其开发成本估计为3亿美元(按2006年的恒定美元计算,约为10亿美元),[48]但到1990年将其送入轨道时,成本约为这一数字的四倍。 [48] 此外,到2006年,新的仪器和维修任务将成本增加到至少90亿美元。[48]

In contrast to other proposed observatories, most of which have already been canceled or put on hold, including Terrestrial Planet Finder (2011), Space Interferometry Mission (2010), International X-ray Observatory (2011), MAXIM (Microarcsecond X-ray Imaging Mission), SAFIR (Single Aperture Far-Infrared Observatory), SUVO (Space Ultraviolet-Visible Observatory), and the SPECS (Submillimeter Probe of the Evolution of Cosmic Structure), the JWST is the last big NASA astrophysics mission of its generation to be built.[citation needed]

与其他拟议的观测站相反,大多数观测站已被取消或搁置,包括地球行星搜寻器(2011),空间干涉测量任务(2010),国际X射线观测站(2011),MAXIM(微弧X射线成像) 任务),SAFIR(单孔径远红外天文台),SUVO(太空紫外可见天文台)和SPECS(宇宙结构演化的亚毫米探针),JWST是该代航天飞机中最后一个重大的NASA天体物理学任务 内置。[需要引用]

History

Development and construction

YearEvents
1996NGST started.
2002named JWST, 8 to 6 m
2004NEXUS cancelled[52]
2007ESA/NASA MOU
2010MCDR passed
2011Proposed cancel
2021Planned launch

Early development work for a Hubble successor between 1989 and 1994 led to the Hi-Z[53] telescope concept, a fully baffled[Note 1] 4-meter aperture infrared telescope that would recede to an orbit at 3 AU.[54] This distant orbit would have benefited from reduced light noise from zodiacal dust.[54] Other early plans called for a NEXUS precursor telescope mission.[55][56]

在1989年至1994年间为哈勃继任者进行的早期开发工作导致了Hi-Z [53]望远镜的概念,这是一台完全困惑的[注1] 4米孔径红外望远镜,它将在3 AU后退到轨道。[54] 这种遥远的轨道本来会受益于黄道带尘埃所减少的光噪声。[54] 其他早期计划则要求进行NEXUS前驱望远镜任务。[55] [56]

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.[57] 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.

JWST起源于1996年的下一代太空望远镜(NGST)。 2002年,它以NASA的第二任行政长官(1961–1968)James E. Webb(1906–1992)的名字重新命名,以在阿波罗计划中发挥关键作用并将科学研究作为NASA的一项核心活动而闻名。[57] JWST是美国国家航空航天局,美国航天局的项目,欧洲航天局和加拿大航天局进行了国际合作。

In the “faster, better, cheaper” era in the mid-1990s, NASA leaders pushed for a low-cost space telescope.[58] The result was the NGST concept, with an 8-meter aperture and located at L2, roughly estimated to cost $500 million.[58] In 1997, NASA worked with the Goddard Space Flight Center,[59] Ball Aerospace,[60] and TRW[61] to conduct technical requirement and cost studies, and in 1999 selected Lockheed Martin[62] and TRW for preliminary concept studies.[63] Launch was at that time planned for 2007, but the launch date has subsequently been pushed back many times (see table further down).

在1990年代中期的“更快,更好,更便宜”时代,NASA领导人推动了低成本太空望远镜的发展。[58] 结果就是NGST概念,其孔径为8米,位于L2处,估计耗资5亿美元。[58] 1997年,美国国家航空航天局(NASA)与戈达德太空飞行中心,[59] Ball Aerospace [60]和TRW [61]合作进行技术要求和成本研究,并于1999年选择洛克希德·马丁[62]和TRW进行初步概念研究。 [63] 该产品原定于2007年推出,但随后又多次推迟了发布日期(请参见下表)。

A JWST mirror segment, 2010.

In 2003, NASA awarded the $824.8 million prime contract for the NGST, now renamed the James Webb Space Telescope, to TRW. The design called for a descoped 6.1-meter (20 ft) primary mirror and a launch date of 2010.[64] Later that year, TRW was acquired by Northrop Grumman in a hostile bid and became Northrop Grumman Space Technology.[63]

2003年,美国国家航空航天局(NASA)向TRW授予了NGST(现更名为James Webb太空望远镜)的8.248亿美元主要合同。 该设计要求使用镜面开阔的6.1米(20英尺)主镜,发射日期为2010年。[64] 那年晚些时候,TRW被诺斯罗普·格鲁曼公司(Northrop Grumman)恶意收购,并成为诺斯罗普·格鲁曼公司(Northrop Grumman Space Technology)。[63]

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is leading the management of the observatory project. The project scientist for the James Webb Space Telescope is John C. MatherNorthrop Grumman Aerospace Systems serves as the primary contractor for the development and integration of the observatory. They are responsible for developing and building the spacecraft element, which includes both the spacecraft bus and sunshield. Ball Aerospace has been subcontracted to develop and build the Optical Telescope Element (OTE). Northrop Grumman’s Astro Aerospace business unit has been contracted to build the Deployable Tower Assembly (DTA) which connects the OTE to the spacecraft bus and the Mid Boom Assembly (MBA) which helps to deploy the large sunshields on orbit.[65] Goddard Space Flight Center is also responsible for providing the Integrated Science Instrument Module (ISIM).[31]

NASA位于马里兰州格林贝尔特的戈达德太空飞行中心正在领导天文台项目的管理。 詹姆斯·韦伯太空望远镜的项目科学家是约翰·马瑟(John C. Mather)。 诺斯罗普·格鲁曼航空系统公司是天文台开发和集成的主要承包商。 他们负责开发和建造航天器组件,其中包括航天器总线和遮阳罩。 Ball Aerospace已转包给开发和制造光学望远镜元件(OTE)。 诺斯罗普·格鲁曼公司(Northrop Grumman)的Astro航空业务部门已签约建造可展开塔式组件(DTA),该组件将OTE连接到航天飞机的公共汽车和中臂组件(MBA),后者有助于在轨道上部署大型遮阳罩。[65] 戈达德太空飞行中心还负责提供综合科学仪器模块(ISIM)。[31]

Cost growth revealed in spring 2005 led to an August 2005 re-planning.[66] The primary technical outcomes of the re-planning were significant changes in the integration and test plans, a 22-month launch delay (from 2011 to 2013), and elimination of system-level testing for observatory modes at wavelength shorter than 1.7 micrometers. Other major features of the observatory were unchanged. Following the re-planning, the project was independently reviewed in April 2006. The review concluded the project was technically sound, but that funding phasing at NASA needed to be changed. NASA re-phased its JWST budgets accordingly.[citation needed]

2005年春季揭示的成本增长导致2005年8月进行了重新规划。[66] 重新计划的主要技术成果是集成和测试计划发生了重大变化,发射时间推迟了22个月(从2011年到2013年),并且取消了波长小于1.7微米的天文台模式的系统级测试。 天文台的其他主要特征没有改变。 重新规划之后,于2006年4月对该项目进行了独立审核。该审核得出结论,该项目在技术上是合理的,但是需要更改NASA的资金阶段。 NASA相应地重新分配了其JWST预算。[需要引用]2005年春季揭示的成本增长导致2005年8月进行了重新规划。[66] 重新计划的主要技术成果是集成和测试计划发生了重大变化,发射时间推迟了22个月(从2011年到2013年),并且取消了波长小于1.7微米的天文台模式的系统级测试。 天文台的其他主要特征没有改变。 重新规划之后,于2006年4月对该项目进行了独立审核。该审核得出结论,该项目在技术上是合理的,但是需要更改NASA的资金阶段。 NASA相应地重新分配了其JWST预算。[需要引用]

In the 2005 re-plan, the life-cycle cost of the project was estimated at about US$4.5 billion. This comprised approximately US$3.5 billion for design, development, launch and commissioning, and approximately US$1.0 billion for ten years of operations.[66] ESA is contributing about 300 million, including the launch,[67] and the Canadian Space Agency about $39M Canadian.[68]

在2005年的重新计划中,该项目的生命周期成本估计约为45亿美元。 其中包括约35亿美元用于设计,开发,发射和调试,约10亿美元用于十年的运营。[66] ESA出资约3亿欧元,包括发射[67]和加拿大航天局(Canadian Space Agency)出资约3900万加拿大元。[68]

In January 2007, nine of the ten technology development items in the project successfully passed a non-advocate review.[69] These technologies were deemed sufficiently mature to retire significant risks in the project. The remaining technology development item (the MIRI cryocooler) completed its technology maturation milestone in April 2007. This technology review represented the beginning step in the process that ultimately moved the project into its detailed design phase (Phase C). By May 2007, costs were still on target.[70] In March 2008, the project successfully completed its Preliminary Design Review (PDR). In April 2008, the project passed the Non-Advocate Review. Other passed reviews include the Integrated Science Instrument Module review in March 2009, the Optical Telescope Element review completed in October 2009, and the Sunshield review completed in January 2010.[citation needed]

2007年1月,该项目的十个技术开发项目中有九个成功通过了非拥护者审查。[69] 这些技术被认为足够成熟,可以消除项目中的重大风险。 其余的技术开发项目(MIRI低温冷却器)于2007年4月完成了其技术成熟的里程碑。这项技术评审代表了该过程的开始步骤,最终将该项目进入了详细的设计阶段(C期)。 到2007年5月,成本仍然达到目标。[70] 2008年3月,该项目成功完成了初步设计审查(PDR)。 2008年4月,该项目通过了非拥护审查。 其他通过的审查包括2009年3月的综合科学仪器模块审查,2009年10月完成的光学望远镜元件审查以及2010年1月完成的Sunshield审查。[需要引用]

In April 2010, the telescope passed the technical portion of its Mission Critical Design Review (MCDR). Passing the MCDR signified the integrated observatory can meet all science and engineering requirements for its mission.[71] The MCDR encompassed all previous design reviews. The project schedule underwent review during the months following the MCDR, in a process called the Independent Comprehensive Review Panel, which led to a re-plan of the mission aiming for a 2015 launch, but as late as 2018. By 2010, cost over-runs were impacting other projects, though JWST itself remained on schedule.[72]

2010年4月,该望远镜通过了“关键任务设计评审(MCDR)”的技术部分。 通过MCDR表示综合天文台可以满足其任务的所有科学和工程要求。[71] MCDR涵盖了所有以前的设计审查。 在MCDR之后的几个月中,该项目的时间表进行了审核,该过程称为“独立综合审核小组”,该流程重新制定了旨在于2015年启动的任务计划,但直到2018年后期。到2010年,成本超过了 尽管JWST本身仍按计划进行,但运行仍在影响其他项目。[72]

By 2011, the JWST project was in the final design and fabrication phase (Phase C). As is typical for a complex design that cannot be changed once launched, there are detailed reviews of every portion of design, construction, and proposed operation. New technological frontiers have been pioneered by the project, and it has passed its design reviews. In the 1990s it was unknown if a telescope so large and low mass was possible.[73]

到2011年,JWST项目已进入最后的设计和制造阶段(C期)。 正如通常无法启动的复杂设计的典型情况那样,对设计,构造和建议的操作的每个部分都有详细的审查。 该项目开创了新的技术前沿,并通过了设计审查。 在1990年代,尚不清楚是否有可能制造出如此大而轻的望远镜。[73]

Assembly of the hexagonal segments of the primary mirror, which was done via robotic arm, began in November 2015 and was completed in February 2016.[74] Final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began.[75] In March 2018, NASA delayed the JWST’s launch an additional year to May 2020 after the telescope’s sunshield ripped during a practice deployment and the sunshield’s cables did not sufficiently tighten.[15] In June 2018, NASA delayed the JWST’s launch an additional 10 months to March 2021, based on the assessment of the independent review board convened after the failed March 2018 test deployment.[16] In August 2019, the mechanical integration of the telescope was completed, something that was scheduled to be done 12 years ago in 2007. Following this engineers now are working to add a five layer sunshield in place to prevent damage to telescope parts from infra red rays of the sun.[76]

通过机械臂完成的主镜六角形部分的组装于2015年11月开始,并于2016年2月完成。[74] 韦伯望远镜的最终建造工作于2016年11月完成,之后开始了广泛的测试程序。[75] [15]在练习部署期间望远镜的遮阳罩被撕裂并且遮阳罩的电缆没有充分拧紧后,美国宇航局于2018年3月将JWST的发射推迟了一年再到2020年5月。[15] 根据对2018年3月测试部署失败后召集的独立审查委员会的评估,NASA在2018年6月将JWST的发射又推迟了10个月,直到2021年3月。[16] 2019年8月,完成了望远镜的机械集成,计划于12年前的2007年完成此工作。在这名工程师的帮助下,现在他们正努力在其上添加五层遮阳板,以防止红外线对望远镜零件的损坏。 太阳的。[76]

Primary mirror segments made of beryllium

Mirror segments undergoing cryogenic tests at the X-ray & Cryogenic Facility at Marshall Space Flight Center

Mirror segment after being coated with gold

Cost and schedule issues[edit]

YearPlanned
launch
Budget Plan
(Billion USD)
19972007[73]0.5[73]
19982007[77]1[48]
19992007 to 2008[78]1[48]
20002009[36]1.8[48]
20022010[79]2.5[48]
20032011[80]2.5[48]
200520133[81]
200620144.5[82]
2008, Preliminary Design Review
200820145.1[83]
2010, Critical Design Review
20102015 to 20166.5[citation needed]
201120188.7[84]
201320188.8[85]
20172019[86]8.8
20182020[87]≥8.8
20182021[88]9.66

The JWST has a history of major cost overruns and delays which have resulted in part from outside factors such as delays in deciding on a launch vehicle and adding extra funding for contingencies. By 2006, $1 billion had been spent on developing JWST, with the budget at about $4.5 billion at that time. A 2006 article in the journal Nature noted a study in 1984 by the Space Science Board, which estimated that a next generation infrared observatory would cost $4 billion (about $7 billion in 2006 dollars).[48] By October 2019, the estimated cost of the project had reached $10 billion for launch in 2021.[89]

JWST有着重大的成本超支和延迟的历史,部分原因是外部因素,例如延迟确定运载火箭和增加应急费用。 到2006年,已经在开发JWST上花费了10亿美元,当时的预算约为45亿美元。 2006年《自然》杂志上的一篇文章指出,太空科学委员会在1984年进行的一项研究估计,下一代红外天文台将耗资40亿美元(以2006年的美元价值计算,约为70亿美元)。[48] 到2019年10月,该项目的估计成本已达到100亿美元,将于2021年启动。[89]

The telescope was originally estimated to cost $1.6 billion,[90] but the cost estimate grew throughout the early development and had reached about $5 billion by the time the mission was formally confirmed for construction start in 2008. In summer 2010, the mission passed its Critical Design Review with excellent grades on all technical matters, but schedule and cost slips at that time prompted Maryland US Senator Barbara Mikulski to call for an independent review of the project. The Independent Comprehensive Review Panel (ICRP) chaired by J. Casani (JPL) found that the earliest possible launch date was in late 2015 at an extra cost of $1.5bn (for a total of $6.5bn). They also pointed out that this would have required extra funding in FY2011 and FY2012 and that any later launch date would lead to a higher total cost.[91]

最初估计该望远镜的成本为16亿美元,[90]但该成本估计在整个早期开发过程中不断增长,到2008年正式确认该特派团开始建造时,其成本已达到约50亿美元。2010年夏季,该特派团通过了 关键设计评审在所有技术问题上均具有优异的成绩,但当时的进度和成本单据促使马里兰州美国参议员芭芭拉·米库尔斯基(Barbara Mikulski)要求对该项目进行独立评审。 由卡萨尼(J. Casani)(JPL)主持的独立综合审查小组(ICRP)发现,最早的启动日期为2015年底,额外费用为15亿美元(总计65亿美元)。 他们还指出,这将在2011财年和2012财年需要额外的资金,任何较晚的发布日期都将导致更高的总成本。[91]

On 6 July 2011, the United States House of Representatives’ appropriations committee on Commerce, Justice, and Science moved to cancel the James Webb project by proposing an FY2012 budget that removed $1.9bn from NASA’s overall budget, of which roughly one quarter was for JWST.[92][93][94][95] $3 billion had been spent and 75% of its hardware was in production.[96] This budget proposal was approved by subcommittee vote the following day. The committee charged that the project was “billions of dollars over budget and plagued by poor management”.[92] In response, the American Astronomical Society issued a statement in support of JWST,[97] as did Maryland US Senator Barbara Mikulski.[98] A number of editorials supporting JWST appeared in the international press during 2011 as well.[92][99][100] In November 2011, Congress reversed plans to cancel the JWST and instead capped additional funding to complete the project at $8 billion.[101]

2011年7月6日,美国众议院商务,司法与科学拨款委员会提出了取消2012年詹姆斯·韦伯(James Webb)项目的提议,提出了2012财年预算,该预算从NASA的总预算中删除了19亿美元,其中大约四分之一用于JWST 。[92] [93] [94] [95] 已花费30亿美元,其硬件的75%已投入生产。[96] 该预算提案在第二天由小组委员会投票批准。 委员会指控该项目“超出预算数十亿美元,并受到管理不善的困扰”。[92] 作为回应,美国天文学会发表了支持JWST的声明,[97]马里兰州的美国参议员芭芭拉·米库尔斯基也是如此[98]。 2011年,国际新闻界也出现了许多支持JWST的社论。[92] [99] [100] 2011年11月,国会撤消了取消JWST的计划,取而代之的是,将完成该项目的额外资金限制为80亿美元。[101]

Some scientists have expressed concerns about growing costs and schedule delays for the Webb telescope, which competes for scant astronomy budgets and thus threatens funding for other space science programs.[102][85] Because the runaway budget diverted funding from other research, a 2010 Nature article described the JWST as “the telescope that ate astronomy”.[103]

一些科学家已经对韦伯望远镜的成本增加和时间表延误表示担忧,韦伯望远镜竞相争夺很少的天文学预算,从而威胁到其他空间科学计划的资金投入。[102] [85] 由于预算失控挪用了其他研究的资金,2010年《自然》杂志将JWST描述为“吃天文学的望远镜”。[103]

A review of NASA budget records and status reports noted that the JWST is plagued by many of the same problems that have affected other major NASA projects. Repairs and additional testing included underestimates of the telescope’s cost that failed to budget for expected technical glitches, missed budget projections, and evaluation of components to estimate extreme launch conditions, thus extending the schedule and increasing costs further.[85][90][104]

对NASA预算记录和状态报告的审查指出,JWST受到许多影响其他NASA主要项目的相同问题的困扰。 维修和其他测试包括低估了望远镜的成本,这些成本未能为预期的技术故障,预算未达到预期的预算以及评估极端发射条件的组件进行评估,从而无法延长预算并进一步增加成本。

One reason for the early cost growth is that it is difficult to forecast the cost of development, and in general budget predictability improved when initial development milestones were achieved.[85] By the mid-2010s, the U.S. contribution was still expected to cost $8.8 billion.[85] In 2007, the expected ESA contribution was about €350 million.[105] With the U.S. and international funding combined, the overall cost not including extended operations is projected to be over $10 billion when completed.[106] 

早期成本增长的原因之一是难以预测开发成本,总体而言,当达到初始开发里程碑时,预算的可预测性就会提高。[85] 到2010年代中期,美国的捐款仍预计会花费88亿美元。[85] 2007年,欧空局的预期捐助约为3.5亿欧元。[105] 加上美国和国际资金的总和,到完成时,不包括扩展业务在内的总成本预计将超过100亿美元。[106]

On 27 March 2018, NASA officials announced that JWST’s launch would be pushed back to May 2020 or later, and admitted that the project’s costs might exceed the $8.8 billion price tag.[87] In the 27 March press release announcing the latest delay, NASA said that it will release a revised cost estimate after a new launch window is determined in cooperation with the ESA.[107] If this cost estimate exceeds the $8 billion cap Congress put in place in 2011, as is considered unavoidable, NASA will have to have the mission re-authorized by the legislature.[108][109] In February 2019, despite expressing criticism over cost growth, Congress increased the mission’s cost cap by $800 million.[110] In October 2019, the total cost estimate for the project reached $10 billion in US dollars.[111]

2018年3月27日,美国宇航局官员宣布将JWST的发射推迟到2020年5月或更晚,并承认该项目的成本可能超过88亿美元的价格标签。[87] 美国宇航局在3月27日发布的最新新闻稿中宣布了最新的延期,称将与欧空局合作确定新的发射窗口后,将发布经修订的费用估算。[107] 如果这笔费用估计超出了国会在2011年设定的80亿美元的上限(这被认为是不可避免的),那么美国宇航局将不得不让立法机关重新授权该任务。[108] [109] 2019年2月,国会议员尽管对成本增长表示批评,但仍将特派团的成本上限提高了8亿美元。[110] 2019年10月,该项目的总费用估算达到100亿美元。[111]

Partnership

NASAESA and CSA have collaborated on the telescope since 1996. ESA’s participation in construction and launch was approved by its members in 2003 and an agreement was signed between ESA and NASA in 2007. In exchange for full partnership, representation and access to the observatory for its astronomers, ESA is providing the NIRSpec instrument, the Optical Bench Assembly of the MIRI instrument, an Ariane 5 ECA launcher, and manpower to support operations.[67][112] The CSA will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations.[113]Participating countries

自1996年以来,NASA,ESA和加拿大空间探测局就在望远镜上进行了合作。2003年,ESA的成员批准了ESA参与建造和发射,并于2007年签署了ESA与NASA的协议。以换取全面的伙伴关系,代表权和进入天文台的权利 欧洲航天局为其天文学家提供NIRSpec仪器,MIRI仪器的光具座组件,Ariane 5 ECA发射器以及支持作战的人力。[67] [112] CSA将提供精细制导传感器和近红外成像仪无缝光谱仪,以及提供人力以支持行动。[113]参与国

Public displays and outreach

Early full-scale model on display at NASA Goddard (2005).

A large telescope model has been on display at various places since 2005: in the United States at Seattle, WashingtonColorado Springs, ColoradoGreenbelt, MarylandRochester, New YorkManhattan, New York; and Orlando, Florida; and elsewhere at Paris, FranceDublin, IrelandMontreal, CanadaHatfield, United Kingdom; and Munich, Germany. The model was built by the main contractor, Northrop Grumman Aerospace Systems.[114]

自2005年以来,大型望远镜模型已在不同地方展出:美国的华盛顿州西雅图市; 科罗拉多州科罗拉多斯普林斯; 马里兰州格林贝尔特; 纽约州罗切斯特; 纽约曼哈顿; 和佛罗里达的奥兰多; 和法国巴黎的其他地方; 爱尔兰都柏林; 加拿大蒙特利尔; 英国哈特菲尔德; 和德国慕尼黑。 该模型是由主要承包商诺斯罗普·格鲁曼航空系统公司建立的。[114]

In May 2007, a full-scale model of the telescope was assembled for display at the Smithsonian Institution‘s National Air and Space Museum on the National MallWashington D.C. The model was intended to give the viewing public a better understanding of the size, scale and complexity of the satellite, as well as pique the interest of viewers in science and astronomy in general. The model is significantly different from the telescope, as the model must withstand gravity and weather, so is constructed mainly of aluminum and steel measuring approximately 24×12×12 m (79×39×39 ft) and weighs 5.5 tonnes (12,000 lb; 6.1 short tons).[citation needed]

2007年5月,在华盛顿特区国家广场的史密森学会的国家航空博物馆中组装了一个完整比例的望远镜模型,该模型的目的是让观看者更好地了解其尺寸,比例和大小。 卫星的复杂性,以及引起观众对科学和天文学的兴趣。 该模型与望远镜有很大的不同,因为该模型必须承受重力和天气,因此主要由铝和钢制成,尺寸约为24×12×12 m(79×39×39 ft),重5.5吨(12,000磅; 6.1短吨)。[需要引用]

The model was on display in New York City‘s Battery Park during the 2010 World Science Festival, where it served as the backdrop for a panel discussion featuring Nobel Prize laureate John C. Matherastronaut John M. Grunsfeld and astronomer Heidi Hammel. In March 2013, the model was on display in Austin, Texas for SXSW 2013.[115][116]

该模型在2010年世界科学节期间在纽约市炮台公园展出,在此背景下,诺贝尔奖获得者约翰·马瑟(John C. Mather),宇航员约翰·格伦斯菲尔德(John M. Grunsfeld)和天文学家海蒂·哈默尔(Heidi Hammel)参加了小组讨论。 2013年3月,该模型在德克萨斯州奥斯汀的SXSW 2013上展出。[115] [116]

Mission

The JWST’s primary scientific mission has four key goals: to search for light from the first stars and galaxies that formed in the Universe after the Big Bang, to study the formation and evolution of galaxies, to understand the formation of stars and planetary systems, and to study planetary systems and the origins of life.[117] These goals can be accomplished more effectively by observation in near-infrared light rather than light in the visible part of the spectrum. For this reason the JWST’s instruments will not measure visible or ultraviolet light like the Hubble Telescope, but will have a much greater capacity to perform infrared astronomy. The JWST will be sensitive to a range of wavelengths from 0.6 (orange light) to 28 micrometers (deep infrared radiation at about 100 K (−170 °C; −280 °F)).

JWST的主要科学任务有四个主要目标:从大爆炸之后在宇宙中形成的第一批恒星和星系中寻找光,研究星系的形成和演化,了解恒星和行星系统的形成,以及 研究行星系统和生命起源。[117] 通过在近红外光而不是光谱的可见光部分进行观察,可以更有效地实现这些目标。 因此,JWST的仪器不会像哈勃望远镜那样测量可见光或紫外光,但具有更大的执行红外天文学的能力。 JWST将对波长范围从0.6(橙色光)到28微米(约100 K(-170°C; -280°F)的深红外辐射)敏感。

JWST may be used to gather information on the dimming light of star KIC 8462852, which was discovered in 2015, and has some abnormal light-curve properties.[118]

JWST可能被用来收集2015年发现的KIC 8462852星的调光信息,该星具有某些异常的光弯曲特性。[118]

发射和任务时长Launch and mission length

As of October 2019, launch is planned 30 March 2021,[3] on an Ariane 5 rocket from French Guiana.[119] The observatory attaches to the Ariane 5 rocket via a launch vehicle adapter ring which could be used by a future spacecraft to grapple the observatory to attempt to fix gross deployment problems. However, the telescope itself is not serviceable, and astronauts would not be able to perform tasks such as swapping instruments, as with the Hubble Telescope.[2] Its nominal mission time is five years, with a goal of ten years.[120] JWST needs to use propellant to maintain its halo orbit around L2, which provides an upper limit to its designed lifetime, and it is being designed to carry enough for ten years.[121] The planned five year science mission begins after a 6-month commissioning phase.[121] An L2 orbit is only meta-stable so it requires orbital station-keeping or an object will drift away from this orbital configuration.[122]

截至2019年10月,计划于2021年3月30日发射,[3]用法属圭亚那的阿里亚纳5号火箭发射。[119] 该天文台通过运载火箭转接环连接到阿丽亚娜5号火箭,以后的太空飞船可以使用该环对付天文台,以解决总部署问题。 但是,望远镜本身无法维修,宇航员将无法像哈勃望远镜一样执行诸如交换仪器之类的任务。[2] 其名义任务时间为五年,目标是十年。[120] JWST需要使用推进剂来维持其绕L2的光晕轨道,这为其设计寿命提供了上限,并且其设计载有足够的十年时间。[121] 经过六个月的调试阶段,计划中的五年科学任务开始。[121] L2轨道仅是亚稳态的,因此它需要保持轨道静止,否则物体将偏离该轨道配置。[122]

Orbit

JWST will not be exactly at the L2 point, but circle around it in a halo orbit.

Two alternate Hubble Space Telescope views of the Carina Nebula, comparing ultraviolet and visible (top) and infrared (bottom) astronomy. Far more stars are visible in the latter.

哈勃太空望远镜的两个备用哈勃太空望远镜视图,比较了紫外线和可见天文学(上)和红外天文学(下)。 在后者中可以看到更多的恒星。

The JWST will be located near the second Lagrange point (L2) of the Earth-Sun system, which is 1,500,000 kilometers (930,000 mi) from Earth, directly opposite to the Sun. Normally an object circling the Sun farther out than Earth would take longer than one year to complete its orbit, but near the L2 point the combined gravitational pull of the Earth and the Sun allow a spacecraft to orbit the Sun in the same time it takes the Earth. The telescope will circle about the L2 point in a halo orbit, which will be inclined with respect to the ecliptic, have a radius of approximately 800,000 kilometers (500,000 mi), and take about half a year to complete.

JWST将位于地球-太阳系统的第二个拉格朗日点(L2)附近,该点距地球1,500,000公里(930,000英里),与太阳直接相对。 通常情况下,绕太阳旋转的物体比地球绕得更远将需要一年以上的时间才能完成其轨道,但是在L2点附近,地球和太阳的引力共同作用使航天器可以在绕太阳的同时旋转太阳 地球。 望远镜将绕晕轨道绕L2点旋转,该轨道相对于黄道倾斜,半径约为800,000公里(500,000英里),约需半年时间才能完成。

[18] Since L2 is just an equilibrium point with no gravitational pull, a halo orbit is not an orbit in the usual sense: the spacecraft is actually in orbit around the Sun, and the halo orbit can be thought of as controlled drifting to remain in the vicinity of the L2 point.[123] This requires some station-keeping: around 2–4 m/s per year[124] from the total budget of 150 m/s.[125] Two sets of thrusters constitute the observatory’s propulsion system.[126]

[18]由于L2只是一个没有重力引力的平衡点,因此光晕轨道不是通常意义上的轨道:航天器实际上在太阳周围的轨道上,并且光晕轨道可以被认为是受控的漂移而得以保留 在L2点附近。[123] 这需要一些站内维护:每年150 m / s的总预算中大约每年2-4 m / s [124]。[125] 两套推进器构成了天文台的推进系统。[126]

红外天文学Infrared astronomy

Infrared observations can see objects hidden in visible light, such as HUDF-JD2 shown.

JWST is the formal successor to the Hubble Space Telescope (HST), and since its primary emphasis is on infrared observation, it is also a successor to the Spitzer Space Telescope. JWST will far surpass both those telescopes, being able to see many more and much older stars and galaxies.[127] Observing in the infrared is a key technique for achieving this because of cosmological redshift and because it better penetrates obscuring dust and gas. This allows observation of dimmer, cooler objects. Since water vapor and carbon dioxide in the Earth’s atmosphere strongly absorbs most infrared, ground-based infrared astronomy is limited to narrow wavelength ranges where the atmosphere absorbs less strongly. Additionally, the atmosphere itself radiates in the infrared, often overwhelming light from the object being observed. This makes a space telescope preferable for infrared observation.[128]

JWST是哈勃太空望远镜(HST)的正式继任者,并且由于其主要重点是红外观测,因此它也是Spitzer太空望远镜的继任者。 JWST将远远超过这两个望远镜,能够看到越来越多的更古老的恒星和星系。[127] 红外观测是实现这一目标的关键技术,这是因为宇宙学的红移,因为它可以更好地穿透模糊的灰尘和气体。 这样可以观察较暗,较冷的物体。 由于地球大气层中的水蒸气和二氧化碳会强烈吸收大部分红外光,因此基于地面的红外天文学被限制在较窄的波长范围内,而大气层吸收程度较弱。 另外,大气本身在红外辐射中,通常会淹没来自被观察物体的光。 这使得太空望远镜更适合用于红外观察。[128]

The more distant an object is, the younger it appears: its light has taken longer to reach human observers. Because the universe is expanding, as the light travels it becomes red-shifted, and objects at extreme distances are therefore easier to see if viewed in the infrared.[129] JWST’s infrared capabilities are expected to let it see back in time to the first galaxies forming just a few hundred million years after the Big Bang.[130]

一个物体越远,它就会显得越年轻:它的光需要更长的时间才能到达人类观察者。 因为宇宙正在膨胀,所以随着光的传播,它会发生红移,因此,如果在红外光下观察,则更容易看到远距离的物体。[129] 预计JWST的红外能力将使它及时回到大爆炸之后几亿年形成的第一个星系。[130]

Infrared radiation can pass more freely through regions of cosmic dust that scatter visible light. Observations in infrared allow the study of objects and regions of space which would be obscured by gas and dust in the visible spectrum,[129] such as the molecular clouds where stars are born, the circumstellar disks that give rise to planets, and the cores of active galaxies.[129]

红外辐射可以更自由地穿过散射可见光的宇宙尘埃区域。 红外观测可以研究在可见光谱中会被气体和尘埃遮盖的物体和空间区域,[129]例如,诞生恒星的分子云,产生行星的星际圆盘以及核心 活跃星系。[129]

Relatively cool objects (temperatures less than several thousand degrees) emit their radiation primarily in the infrared, as described by Planck’s law. As a result, most objects that are cooler than stars are better studied in the infrared.[129] This includes the clouds of the interstellar mediumbrown dwarfsplanets both in our own and other solar systems, comets and Kuiper belt objects that will be observed with the Mid-Infrared Instrument (MIRI) requiring an additional cryocooler.[36][130]

如普朗克定律所述,相对较凉的物体(温度低于几千度)主要在红外线中发出辐射。 结果,大多数比星冷的物体在红外条件下得到了更好的研究。[129] [36] [130]其中包括星际中云,褐矮星,我们自己的太阳系和其他太阳系中的行星,彗星和柯伊伯带天体,而中红外仪器(MIRI)则需要观察它们。 ]

Some of the missions in infrared astronomy that impacted JWST development were Spitzer and also the WMAP probe.[131] Spitzer showed the importance of mid-infrared, such as in its observing dust disks around stars.[131] Also, the WMAP probe showed the universe was “lit up” at redshift 17, further underscoring the importance of the mid-infrared.[131] Both these missions launched in the early 2000s, in time to influence JWST development.[131]

影响JWST发展的一些红外天文学任务是Spitzer以及WMAP探测器。[131] 斯皮策显示了中红外的重要性,例如观察恒星周围的尘埃盘。[131] 此外,WMAP探测器显示,在红移17时,宇宙“被照亮了”,进一步强调了中红外的重要性。[131] 这两个任务都是在2000年代初发动的,以及时影响JWST的发展。[131]

Ground support and operations

The Space Telescope Science Institute (STScI), located in BaltimoreMaryland on the Homewood campus of Johns Hopkins University, was selected as the Science and Operations Center (S&OC) for JWST with an initial budget of $162.2 million intended to support operations through the first year after launch.[132] In this capacity, STScI will be responsible for the scientific operation of the telescope and delivery of data products to the astronomical community.

位于马里兰州巴尔的摩市约翰·霍普金斯大学霍姆伍德分校的太空望远镜科学研究所(STScI)被选为JWST的科学和运营中心(S&OC),其最初预算为1.622亿美元,旨在通过第一笔预算支持运营 推出后一年。[132] STScI将以这一身份负责望远镜的科学操作,并将数据产品交付给天文界。

Data will be transmitted from JWST to the ground via NASA’s Deep Space Network, processed and calibrated at STScI, and then distributed online to astronomers worldwide. Similar to how Hubble is operated, anyone, anywhere in the world, will be allowed to submit proposals for observations. Each year several committees of astronomers will peer review the submitted proposals to select the projects to observe in the coming year. The authors of the chosen proposals will typically have one year of private access to the new observations, after which the data will become publicly available for download by anyone from the online archive at STScI.

数据将通过NASA的深空网络从JWST传输到地面,在STScI上进行处理和校准,然后在线分发给全世界的天文学家。 与哈勃望远镜的运作方式类似,世界上任何地方的任何人都可以提交观测建议。 每年,几个天文学委员会将对提交的建议进行同行评审,以选择来年要观察的项目。 所选方案的作者通常将有一年的私人访问新观测值的时间,此后,任何人都可以从STScI的在线存档中公开下载数据。

The bandwidth and digital throughput of the satellite is designed to operate at 458 gigabits of data per day for the length of the mission.[133] Most of the data processing on the telescope is done by conventional single-board computers.[134] The conversion of the analog science data to digital form is performed by the custom-built SIDECAR ASIC (System for Image Digitization, Enhancement, Control And Retrieval Application Specific Integrated Circuit). NASA stated that the SIDECAR ASIC will include all the functions of a 9 kg (20 lb) instrument box in a 3 cm package and consume only 11 milliwatts of power.[135] Since this conversion must be done close to the detectors, on the cool side of the telescope, the low power use of this IC will be crucial for maintaining the low temperature required for optimal operation of the JWST.[135]

在任务期限内,卫星的带宽和数字吞吐量被设计为每天以458吉比特数据运行。[133] 望远镜上的大多数数据处理都是由传统的单板计算机完成的。[134] 模拟科学数据到数字形式的转换是由定制的SIDECAR ASIC(图像数字化,增强,控制和检索专用集成电路系统)执行的。 美国国家航空航天局(NASA)表示,SIDECAR ASIC将具有3厘米封装的9千克(20磅)仪器箱的所有功能,并且仅消耗11毫瓦的功率。[135] 由于此转换必须在望远镜的冷侧靠近探测器的地方进行,因此该IC的低功耗对于维持JWST最佳操作所需的低温至关重要。[135]

After-launch deployment

Nearly a month after launch, a trajectory correction will be initiated to place the JWST into a halo orbit at the L2 Lagrangian point.[136]

发射后近一个月,将开始进行轨道校正,以将JWST置于L2拉格朗日点的晕圈。[136]

  • JWST after-launch deployment planned timeline[2]

Animation of James Webb Space Telescope trajectory

詹姆斯·韦伯太空望远镜轨迹的动画

Polar view

Equatorial view

Allocation of observation times

JWST observing time will be allocated through a Director’s Discretionary Early Release Science (DD-ERS) Program, a Guaranteed Time Observations (GTO) Program, and a General Observers (GO) Program.[137] The GTO Program provides guaranteed observing time for scientists who developed hardware and software components for the observatory. The GO Program provides all astronomers the opportunity to apply for observing time. GO programs will be selected through peer review by a Time Allocation Committee (TAC), similar to the proposal review process used for the Hubble Space Telescope. JWST observing time is expected to be highly oversubscribed.

JWST的观测时间将通过主任的自由裁量早期释放科学(DD-ERS)计划,保证时间观测(GTO)计划和普通观察员(GO)计划分配。[137] GTO计划为为天文台开发硬件和软件组件的科学家提供了保证的观察时间。 GO计划为所有天文学家提供了申请观测时间的机会。 GO计划将由时间分配委员会(TAC)通过同行评审来选择,类似于哈勃太空望远镜的提案评审流程。 JWST的观察时间预计将大大超额预定。

Early Release Science Program

Atmospheric windows in the infrared: much of this type of light is blocked when viewed from the Earth’s surface. It would be like looking at a rainbow but only seeing one color.

红外中的大气窗口:从地球表面观察时,大部分此类光被阻挡。 就像看着彩虹,却只看到一种颜色。

In November 2017, the Space Telescope Science Institute announced the selection of 13 Director’s Discretionary Early Release Science (DD-ERS) Programs, chosen through a competitive proposal process.[138] The observations for these programs will be obtained during the first five months of JWST science operations after the end of the commissioning period. A total of 460 hours of observing time was awarded to these 13 programs, which span science topics including the Solar Systemexoplanetsstars and star formation, nearby and distant galaxiesgravitational lenses, and quasars.

2017年11月,太空望远镜科学研究所宣布,通过竞争性提案流程选择了13个主任的酌定早期释放科学(DD-ERS)计划。[138] 这些项目的观测结果将在调试期结束后的JWST科学操作的前五个月内获得。 这13个程序总共获得了460小时的观测时间,涵盖了科学主题,包括太阳系,系外行星,恒星和恒星形成,附近和遥远的星系,引力透镜以及类星体。

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