NASA engineer Ernie Wright looks on as the first six flight ready James Webb Space Telescope’s primary mirror segments are prepped to begin final cryogenic testing at NASA’s Marshall Space Flight Center.
The James Webb Space Telescope (JWST), previously known asNext Generation Space Telescope (NGST), is a major space observatory under construction and scheduled to launch in October 2018. The JWST will offer unprecedented resolution and sensitivity from long-wavelength (orange-red) visible light, through near-infrared to themid-infrared (0.6 to 27 micrometers), and is a successor instrument to the Hubble Space Telescope and the Spitzer Space Telescope. While Hubble has a 2.4-meter (7.9 ft) mirror, the JWST features a larger and 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 50 K (−220 °C; −370 °F).
JWST’s capabilities will enable a broad range of investigations across the fields of astronomy and cosmology. One particular goal involves observing some of the most distant objects in the Universe, beyond the reach of current ground and space-based instruments, such as theformation of the first galaxies. Another goal is understanding theformation of stars and planets. This will include direct imaging ofexoplanets.
In gestation since 1996, the project represents an international collaboration of about 17 countries 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% of its hardware was in production. Funding was restored and capped at $8 billion. As of winter 2015–2016, the telescope remained on schedule for an October 2018 launch and within the 2011 revised budget.
Diagram of James Webb Space Telescope
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. 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 Space Telescope‘s, but its primary mirror (a 6.5 meter diameter gold-coated beryllium reflector) will have a collecting area about five times as large (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 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.
The JWST will operate near the Earth-Sun L2 (Lagrange) point, approximately 1,500,000 km (930,000 mi) beyond the Earth. (By way of comparison, the Moon is roughly 400,000 km or 250,000 miles from Earth.)
Objects near this point can orbit the Sun in synchrony with the Earth, allowing the telescope to remain at a roughly constant distance 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.
Comparison with Hubble primary mirror
The telescope’s delays and cost increases can be compared to the Hubble Space Telescope. When it formally started in 1972, what came to be known as Hubble had a then estimated development cost of $300 million (or about $1 billion in 2006 constant dollars), but by the time it was sent into orbit in 1990, cost about four times that. In addition, new instruments and servicing missions increased the cost to at least $9 billion by 2006.
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), Laser Interferometer Space Antenna(2011), and the International X-ray Observatory (2011), MAXIM (Microarcsecond X-ray Imaging Mission), SAFIR (Single Aperture Far-Infrared Observatory), SUVO (Space Ultraviolet-Visible Observatory), SPECS (Submillimeter Probe of the Evolution of Cosmic Structure), the JWST is the last big NASA astrophysics mission of its generation to be built.
Program status[edit source]
A review of the program released in August 2011 stated that the cost for the telescope and 5 years of operations will be $8.7 billion, with a planned launch in 2018. Of that price, about $800 million is for the five years of operations.
On 17 December 2015 Arianespace and European Space Agency signed a contract for the JWST to be launched on October 2018 using an Ariane 5 ECA with a cryogenic upper stage from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana.
The 18th and final primary mirror segment was installed on February 3, 2016 and technicians will now install the other optics and conduct tests on all the assembled components.
Early development work for a Hubble successor between 1989 and 1994 led to the Hi-Ztelescope concept, a fully baffled[Note 1] 4-meter aperture infrared telescope that would recede to an orbit at 3 AU. This distant orbit would have benefited from reduced light noise fromzodiacal dust. Other early plans called for a NEXUS precursor telescope mission.
In the “faster, better, cheaper” era in the mid-1990s, NASA leaders pushed for a low-cost space telescope. The result was the NGST concept, with an 8-meter aperture and located at L2, estimated to cost $500 million. In 1997, NASA worked with the Goddard Space Flight Center, Ball Aerospace, and TRW to conduct technical requirement and cost studies, and in 1999 selected Lockheed Martin and TRW for preliminary design concepts.
Cost growth revealed in spring 2005 led to an August 2005 re-planning. 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 program was independently reviewed in April 2006. The review concluded the program was technically sound, but that funding phasing at NASA needed to be changed. NASA re-phased its JWST budgets accordingly.
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. ESA is contributing about €300 million, including the launch, and the Canadian Space Agency about $39M Canadian.
In January 2007, nine of the ten technology development items in the program successfully passed a non-advocate review. These technologies were deemed sufficiently mature to retire significant risks in the program. 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 program into its detailed design phase (Phase C). By May 2007, costs were still on target. 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.
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. 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 programs, though JWST itself remained on schedule.
By 2011, the JWST program 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 program, and it has passed its design reviews. In the 1990s it was unknown if a telescope so large and low mass was possible.
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.
Cost and schedule issues[edit source]
|1997||2007||0.5 Billion USD|
|1999||2007 to 2008||1|
|2010||2015 to 2016||6.5|
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). In June 2011, it was reported that the Webb telescope will cost at least four times more than originally proposed, and launch at least seven years late. Initial 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. A 2013 estimate put the cost of development and five years of operation at $8.835 billion.
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. A review of NASA budget records and status reports by journalists noted that the JWST is plagued by many of the same problems that have plagued several other major NASA projects. Mistakes included: underestimates of the telescope’s cost that failed to budget for expected technical glitches, and failure to act on warnings that budgets were being exceeded, thus extending the schedule and increasing costs further.
NASA, ESA 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. The CSA will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations.
- Participating countries
- Czech Republic
- United Kingdom
- United States
Proposed U.S. withdrawal[edit source]
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. This budget proposal was approved by subcommittee vote the following day; however, in November 2011, Congress reversed plans to cancel the JWST and instead capped additional funding to complete the project at $8 billion.
The committee charged that the project was “billions of dollars over budget and plagued by poor management”. The telescope was originally estimated to cost $1.6bn but the cost estimate grew throughout the early development reaching about $5bn 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. Because the runaway budget diverted funding from other research, the science journal Nature described the James Webb as “the telescope that ate astronomy”. However, termination of the project as proposed by the House appropriation committee would not have provided funding to other missions, as the JWST line would have been terminated with the funding leaving astrophysics (and the NASA budget) entirely.
The American Astronomical Society issued a statement in support of JWST in 2011, as did Maryland US Senator Barbara Mikulski. A number of editorials supporting JWST appeared in the international press during 2011 as well.
Public displays and outreach[edit source]
A large telescope model has been on display at various places since 2005: in theUnited States at Seattle, Washington; Colorado Springs, Colorado; Greenbelt, Maryland; Rochester, New York; Manhattan, New York; and Orlando, Florida; and elsewehere at Paris, France; Dublin, Ireland; Montreal, Canada; Hatfield, United Kingdom; and Munich, Germany. The model was built by the main contractor,Northrop Grumman Aerospace Systems.
In May 2007, a full-scale model of the telescope was assembled for display at theSmithsonian Institution‘s National Air and Space Museum on the National Mall,Washington 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).
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. Mather, astronautJohn M. Grunsfeld and astronomer Heidi Hammel. In March 2013, the model was on display in Austin, Texas for SXSW 2013.
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 andplanetary systems and to study planetary systems and the origins of life. 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 28micrometers (deep infrared radiation at about 100 K (−170 °C; −280 °F)).
One of the early and more pressing goals of the JWST will be to gather enough information in order to answer which theory is correct out of the few theories that remain behind the phenomenon of the dimming light of star KIC 8462852.
Infrared astronomy[edit source]
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. Observing in the infrared is a key technique for achieving this, because it better penetrates obscuring dust and gas, allows observation of dim cooler objects, and because of cosmological redshift. 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 space the ideal place for infrared observation.
The distant universe: 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 these objects are therefore easier to see if viewed in the infrared. JWST’s infrared capabilities are expected to let it see all the way to the very first galaxies forming just a few hundred million years after theBig Bang.
Comparison of examples of primary mirrors. JWST is at the lower left.
Comparison of nominal sizes of primary mirrors of notable optical telescopes. Dotted lines show mirrors with equivalent light-gathering ability. Thanks to user at 22.214.171.124 for data on holes in mirrors. en:Yerkes Observatory en:Great Paris Exhibition Telescope of 1900 en:Hooker Telescope en:Hale telescope en:BTA-6 en:Multiple Mirror Telescope en:Large Zenith Telescopeen:Gaia (spacecraft) en:Kepler (spacecraft) en:James Webb Space Telescope en:Hubble Space Telescope en:LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) en:Gran Telescopio Canarias en:Hobby–Eberly Telescope en:Southern African Large Telescope en:Large Binocular Telescope en:Very Large Telescope en:Magellan Telescopes en:Keck Telescopesen:Subaru Telescope en:Gemini Observatory en:Large Synoptic Survey Telescope en:Giant Magellan Telescope en:Thirty Meter Telescope en:European Extremely Large Telescopeen:Overwhelmingly Large Telescope en:Arecibo Observatory en:Tennis court en:Basketball courten:Human height
See also[edit source]
- High-Definition Space Telescope
- Wide Field Infrared Survey Telescope
- List of largest infrared telescopes
- List of largest optical reflecting telescopes
- List of space observatories
- New Worlds Mission (proposed occulter for the JWST)
- Physical cosmology
- “Baffled”, in this context, means enclosed in a tube in a similar manner to a conventional optical telescope, which helps to stop stray light entering the telescope from the side. For an actual example, see the following link: Freniere, E.R. (1981). “First-order design of optical baffles”. Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, First-order design of optical baffles. Radiation Scattering in Optical Systems. pp. 19–28.