Thirty Meter Telescope
Artist's rendering of proposed telescope
|Alternative names||California Extremely Large Telescope|
|Location(s)||(proposed) Mauna Kea Observatory in Hawaii, United States|
|Organization||TMT International Observatory|
|Altitude||4,050 m or 13,290 ft|
|Wavelength||Near UV, visible, and Mid-IR (0.31–28 μm)|
|First light||est. 2027|
|Telescope style||Segmented Ritchey–Chrétien telescope|
|Diameter||30 m or 98 ft|
|Secondary diameter||3.1 m or 10 ft|
|Tertiary diameter||2.5 m × 3.5 m or 8.2 ft × 11.5 ft|
|Collecting area||655 m2 or 7,050 sq ft|
|Focal length||f/15 (450 m):52|
The Thirty Meter Telescope (TMT) is a proposed astronomical observatory with an extremely large telescope (ELT) that has become the source of controversy over its planned location on Mauna Kea on the island of Hawaii in the US state of Hawaii. Construction of the TMT on land which is sacred to Native Hawaiian culture and religion attracted press coverage after October 2014, when construction was temporarily halted due to protests. While construction of the telescope was set to resume on April 2 and later on June 24, 2015, it was blocked by further protests each time. The Board of Land and Natural Resources approved the TMT project, but the Supreme Court of Hawaii invalidated the building permits in December 2015, ruling that the board had not followed due process. On October 30, 2018, the Court approved the resumption of construction. The TMT would become the last area on Mauna Kea on which any telescope will ever be built.
Scientists have been considering ELTs since the mid 1980s. In 2000, astronomers considered the possibility of a telescope with a light-gathering mirror larger than 20 meters in diameter. The technology to build a mirror larger than 8.4 meters does not exist; instead scientists considered using either small segments that create one large mirror, or a grouping of larger 8-meter mirrors working as one unit. The US National Academy of Sciences recommended a 30-meter telescope be the focus of U.S. interests, seeking to see it built within the decade. Scientists at the University of California and Caltech began development of a design that would eventually become the TMT, consisting of 492 segmented mirrors with nine times the power of the Keck telescope. Due to its immense light-gathering power and the optimal observing conditions which exist atop Mauna Kea, the TMT would enable astronomers to conduct research which is infeasible with current instruments. The TMT is designed for near-ultraviolet to mid-infrared (0.31 to 28 μm wavelengths) observations, featuring adaptive optics to assist in correcting image blur. The TMT will be at the highest altitude of all the proposed ELTs. The telescope has government-level support from several nations.
In 2000, astronomers began considering the potential of telescopes larger than 20 meters in diameter. Two technologies were considered; segmented mirrors like that of the Keck Observatory and the use of a group of 8-meter mirrors mounted to form a single unit. The US National Academy of Sciences made a suggestion that a 30-meter telescope should be the focus of US astronomy interests and recommended it to be built within the decade. The University of California, along with Caltech began development of a 30-meter telescope that same year. The California Extremely Large Telescope (CELT) began development along with the Giant Magellan Telescope, the Giant Segmented Mirror Telescope (GSMT) and the Very Large Optical Telescope (VLOT). These studies would eventually become the Thirty Meter Telescope. The TMT would have nine times the collecting area of the older Keck telescope using slightly smaller mirror segments in a vastly larger group. Another telescope of a large diameter in the works is the European Extremely Large Telescope (E-ELT) being built in northern Chile.
The telescope is designed for observations from near-ultraviolet to mid-infrared (0.31 to 28 μm wavelengths). In addition, its adaptive optics system will help correct for image blur caused by the atmosphere of the Earth, helping it to reach the potential of such a large mirror. Among existing and planned ELTs, the TMT will have the highest altitude and will be the second-largest telescope once the E-ELT is built. Both use segments of small 1.44 m hexagonal mirrors—a design vastly different from the large mirrors of the Large Binocular Telescope (LBT) or the Giant Magellan Telescope (GMT). The TMT has government-level support from the following countries: Canada, China, Japan and India. The United States is also contributing some funding, but less than the formal partnership.
In cooperation with AURA, the TMT project completed a multi-year evaluation of five sites:
- Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain
- Cerro Armazones, Antofagasta Region, Republic of Chile
- Cerro Tolanchar, Antofagasta Region, Republic of Chile
- Cerro Tolar, Antofagasta Region, Republic of Chile
- Mauna Kea, Hawaii, United States (This site was chosen and approval granted in April 2013)
- San Pedro Mártir, Baja California, Mexico
- Hanle, Jammu and Kashmir, India
The TMT Observatory Corporation board of directors narrowed the list to two sites, one in each hemisphere, for further consideration: Cerro Armazones in Chile's Atacama Desert, and Mauna Kea on Hawaii Island. On July 21, 2009 the TMT board announced Mauna Kea as the preferred site. The final TMT site selection decision was based on a combination of scientific, financial, and political criteria. Chile is also where the European Southern Observatory is building the E-ELT. If both next-generation telescopes were in the same hemisphere, there would be many astronomical objects that neither could observe. The telescope was given approval by the state Board of Land and Natural Resources in April 2013. There has been opposition to the building of the telescope, based on potential disruption to the fragile alpine environment of Mauna Kea due to construction, traffic and noise, which is a concern for the habitat of several species, and that Mauna Kea is a sacred site for the Native Hawaiian culture. The Hawaii Board of Land and Natural Resources conditionally approved the Mauna Kea site for the TMT in February 2011. The approval has been challenged; however, the Board officially approved the site following a hearing on February 12, 2013.
Partnerships and funding
The Gordon and Betty Moore Foundation has committed US$200 million for construction. Caltech and the University of California have committed an additional US$50 million each. Japan, which has its own large telescope at Mauna Kea, the 8.3-metre Subaru, is also a partner.
In 2008, the National Astronomical Observatory of Japan (NAOJ) joined TMT as a Collaborating Institution. The following year, the telescope cost was estimated to be $970 million to $1.4 billion. That same year, the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) joined TMT as an Observer.
In 2010, a consortium of Indian Astronomy Research Institutes (IIA, IUCAA and ARIES) joined TMT project as an observer. The observer status is the first step in becoming a full partner in the construction of the TMT and participating in the engineering development and scientific use of the observatory (Subject to approval of funding from Indian Government). Two years later, India and China became partners with representatives on the TMT board. Both countries agreed to share the telescope construction costs, expected to top $1 billion.
The continued financial commitment from the Canadian government had been in doubt due to economic pressures. Nevertheless, on April 6, 2015, Prime Minister Stephen Harper announced that Canada would commit $243.5 million over a period of 10 years. The structure will be built by Dynamic Structures Ltd. in British Columbia, and then shipped to Mauna Kea.
In 2008, the TMT corporation selected two semi-finalists for further study, Mauna Kea and Cerro Amazones. In July 2009, Mauna Kea was selected. Once TMT selected Mauna Kea, the project began a regulatory and community process for approval. Mauna Kea is ranked as one of the best sites on Earth for telescope viewing and is home to 13 other telescopes built at the summit of the mountain, within the Mauna Kea Observatories grounds. Telescopes generate money for the big island, with millions of dollars in jobs and subsidies gained by the state. The TMT would be one of the most expensive telescopes ever created.
- In 2010 the Governor of Hawaii signed off on an environmental study after 14 community meetings.
- The BLNR held hearings on December 2 and December 3, 2010 on the application for a permit.
- On February 25, 2011 the board granted the permits after multiple public hearings. This approval had conditions, in particular that a hearing about contesting the approval be heard.
- A contested case hearing was held in August 2011, which led to a judgment by the hearing officer for approval in November 2012. The telescope was given approval by the state Board of Land and Natural Resources in April 2013. This process was challenged in court with a lower court ruling in May 2014. The Intermediate Court of Appeals of the State of Hawaii declined to hear an appeal regarding the permit until the Hawaii Department of Land and Natural Resources first issued a decision from the contested case hearing that could then be appealed to the court.
- The dedication and ground-breaking ceremony was held, but interrupted by protesters on October 7, 2014. The project became the focal point of escalating political conflict, police arrests and continued litigation over the proper use of conservation lands. Native Hawaiian cultural practice and religious rights became central to the opposition, with concerns over the lack of meaningful dialogue during the permitting process.
- On December 2, 2015, the Hawaii State Supreme Court ruled the 2011 permit from the Hawaii Board of Land and Natural Resources was invalid. The high court stated: "BLNR put the cart before the horse when it approved the permit before the contested case hearing". and "Once the permit was granted, Appellants were denied the most basic element of procedural due process – an opportunity to be heard at a meaningful time and in a meaningful manner. Our Constitution demands more". In March 2017, the Board’s hearing officer, retired judge Riki May Amano, finished six months of hearings in Hilo, Hawaii, taking 44 days of testimony from 71 witnesses. On July 26, 2017, Amano filed her recommendation that the Land Board grant the construction permit.
- On September 28, 2017, the State of Hawaii Board of Land and Natural Resources (BLNR), acting on Amano's report, approved, by a vote of 5-2, a Conservation District Use Permit (CDUP) for the TMT. Numerous conditions, including the removal of three existing telescopes and an assertion that the TMT is to be the last telescope on the mountain, were attached to the permit.
- On October 30, 2018, the Supreme Court of Hawaii ruled the CDUP was valid, allowing construction to proceed.
The TMT would be a general-purpose observatory capable of investigating a broad range of astrophysical problems. Total diameter of the dome will be 217 feet with the total dome height at 180 feet (comparable in height to an eighteen-storey building). Total area of the structure is projected to be 1.44 acres within a 5-acre complex.
The centerpiece of the TMT Observatory is to be a Ritchey-Chrétien telescope with a 30-metre (98 ft) diameter primary mirror. This mirror is to be segmented and consist of 492 smaller (1.4 m), individual hexagonal mirrors. The shape of each segment, as well as its position relative to neighboring segments, will be controlled actively.
A 3.6-metre (12 ft) secondary mirror is to produce an unobstructed field-of-view of 20 arcminutes in diameter with a focal ratio of 15. A flat tertiary mirror is to direct the light path to science instruments mounted on large Nasmyth platforms. The telescope is to have an alt-azimuth mount. Target acquisition and system configuration capabilities need to be achieved within 5 minutes, or ten minutes if relocating to a newer device. To achieve these time limitations the TMT will use a software architecture linked by a service based communications system. The moving mass of the telescope, optics, and instruments will be 1430 tonnes. The design of the facility descends from the W. M. Keck Observatory.
Integral to the observatory is a Multi-Conjugate Adaptive Optics (MCAO) system. This MCAO system will measure atmospheric turbulence by observing a combination of natural (real) stars and artificial laser guide stars. Based on these measurements, a pair of deformable mirrors will be adjusted many times per second to correct optical wave-front distortions caused by the intervening turbulence.
This system will produce diffraction-limited images over a 30-arc-second diameter field-of-view, which means that the core of the point spread function will have a size of 0.015 arc-second at a wavelength of 2.2 micrometers, almost ten times better than the Hubble Space Telescope.
Three instruments are planned to be available for scientific observations:
- Wide Field Optical Spectrometer (WFOS)' providing near-ultraviolet and optical (0.3–1.0 μm wavelength) imaging and spectroscopy over a more than 40-square arc-minute field-of-view. Using precision cut focal plane masks, WFOS would enable long-slit observations of single objects as well as short-slit observations of hundreds of objects simultaneously. WFOS would use natural (uncorrected) seeing images.
- Infrared Imaging Spectrometer (IRIS) mounted on the observatory MCAO system, capable of diffraction-limited imaging and integral-field spectroscopy at near-infrared wavelengths (0.8–2.5 μm). Principal investigators are James Larkin of UCLA and Anna Moore of Caltech. Project scientist is Shelley Wright of UC San Diego.
- Infrared Multi-object Spectrometer (IRMS) allowing close to diffraction-limited imaging and slit spectroscopy over a 2 arc-minute diameter field-of-view at near-infrared wavelengths (0.8–2.5 μm).
The proposed construction of the TMT on Mauna Kea sparked protests and demonstrations across the state of Hawaii. Mauna Kea is the most sacred mountain in Hawaiian culture. The mountain is also conservation land held in trust by the state of Hawaii.
On October 7, 2014, the groundbreaking for the TMT was interrupted by demonstrators causing a postponement of construction In late March 2015, demonstrators again halted the construction crews. On April 2, 2015, about 300 protesters gathered on Mauna Kea, some of them trying to block the access road to the summit; 23 arrests were made. Once the access road to the summit was cleared by the police, about 40 to 50 protesters began following the heavily laden and slow-moving construction trucks to the summit construction site.
On April 7, 2015, the construction was halted for one week at the request of Hawaii state governor David Ige, after the protest on Mauna Kea continued. Project manager Gary Sanders stated that TMT agreed to the one-week stop for continued dialogue; Kealoha Pisciotta, president of Mauna Kea Anaina Hou, one of the organizations that have challenged the TMT in court, viewed the development as positive but said opposition to the project would continue. On April 8, 2015, Governor Ige announced that the project was being temporarily postponed until at least April 20, 2015. Construction was set to begin again on June 24, though hundreds of protesters gathered on that day, blocking access to the construction site for the TMT. Some protesters camped on the access road to the site, while others rolled large rocks onto the road. The actions resulted in 11 arrests.
On December 2, 2015, the Supreme Court of Hawaii invalidated the TMT's building permits, ruling that due process was not followed when the Board of Land and Natural Resources approved the permit before the contested case hearing. The TMT company chairman stated: "T.M.T. will follow the process set forth by the state." A revised permit was approved on September 28, 2017 by the Hawaii Board of Land and Natural Resources. On October 30, 2018, the Supreme Court of Hawaii ruled, 4-1, that the revised permit was acceptable and construction may proceed.
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