India to partner giant 30 meter telescope project

A couple of months ago, I had reported about a giant new astronomical telescope that is being set up at Mauna Kea, the highest point in the U.S. state of Hawaii, through international cooperation. This new telescope with a 30 meter diameter mirror is being called as Thirty Meter Telescope (TMT) It is expected that it would enable the user astronomers to gaze 13 billion light years into the universe.

Last week, India officially signed as a partner for the TMT project along with the U.S., Japan, Canada and China. India will contribute about Rs 1.3 Billion over the construction period 2014-23. with 30 percent of it in cash and balance in kind, to be spent on vital components of the telescope to be built in India in partnership with various industries.

A telescope's light gathering power and ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light). The larger the objective, the more light the telescope collects and the finer detail it resolves. The the largest telescope in India has only a 2-metre mirror ( on Mt. Saraswati, Digpa-ratsa Ri, Hanle in south-eastern Ladakh in the eastern Jammu and Kashmir state of India), though India is building one at Devasthal, Nainital, Uttrakhand state, that will have 3.6 meter diameter. Readers can imagine how much more powerful the TMT telescope is likely to be.

Genaral internal arrangement of the telescope

Telescopes can use either lenses or mirrors as objectives. The telescopes using lenses are known as refracting telescopes (dioptrics). The ones that use mirrors are called as reflecting telescopes (catoptrics) and those using a combination of lenses and mirrors are known as Catadioptric telescopes. Any large sized telescope has to be either of the latter two types because of practical difficulties in making optical glass flats of such large size, that would give distortion free images and grinding the same to required convex objective lens shapes. Comparatively, curved mirrors are easier to make and can be given even parabolic or hyperbolic shapes.

The mirror consists of 492 hexagonal segments

However, when we think of making a 30 meter diameter mirror objective, it is impossible to create a single, workable 30-meter diameter mirror. It is bound to be too heavy and will eventually sag from gravity distorting the curve profile. There are other problems in maintaining such a large mirror. At Mauna Kea, there is another large telescope built by Japan and known as Subaru telescope. A mishap happened at this telescope when there was a coolant leak onto the primary mirror in July, 2011. The mishap had a significant impact on functioning of Subaru Telescope and recovery work to put back telescope back in shape including meticulous inspection and cleaning of the affected areas took almost two years and was completed only in the summer of 2013.

To avoid such problems, TMT design has decided to substitute the single objective mirror with 492 mirror segments of hexagonal shape of 1.44 meters size, that will be assembled like a jig-saw puzzle to make on mirror. Position of each of these mirrors, will be precisely controlled along three axises using at least 3 precision actuators to sense and correct any segment displacement even to an extent of a micron ( one hundredth part of a millimeter), so that the entire assembly would behave like a single, gigantic 30 meter-wide surface.

 

A Hexagonal segment with controllers

India has agreed to fabricate, test and supply these 492 mirrors along with 1500 actuators to control the hexagonal mirrors along with the segment support assembly to keep all the mirrors in position so they function as a single mirror of hyperboloid shape. Most of these parts would be fabricated in Bengaluru city in Karnataka state. Bengaluru’s expertise in astrophysics, electronics and software development will be put to test in this project.

Eswar Reddy, programme director of TMT-India and associate professor at the Indian Institue of Astrophysics feels that the “trickiest part” is to get hundreds of segments behave like a gigantic monolithic mirror and this involves developing several new technologies in mechanics, electronics, optics and control software.TMT-India has been formed by coming together of number of research institutions comprising of Indian Institue of Astrophysics, the IIA, Aryabhatta Research Institute for Observational Sciences (Nainital) and the Inter-University Centre for Astronomy and Astrophysics (Pune).

Prof. Eswar Reddy says that The TMT, which is expected to be completed in 2023, will be 150 times more powerful than the Hubble Space Telescope, allowing astronomers to look well beyond our solar system, to the near-beginning of time and will be able to observe the universe when it was very young, just half a million light years.

Henry Yang, Chair of the TMT International Observatory Board and Chancellor of the University of California Santa Barbara says; "The official signing today with India's investment reassures the success of TMT, India's contributions in the areas of software systems, segment production and the production of the very high precision sensors and actuators that make the primary mirror possible are key to the project."

11^th December 2014

A quantum jump in Astrophysics

The highest point in the U.S. state of Hawaii; Mauna Kea is a dormant volcano located on the island of Hawaii. It stands tall at 13,803 ft (4,207 m) above sea level. Because of extremely favourable observing conditions,Mauna Kea's summit is considered as one of the best sites in the world for astronomical observations. The atmosphere here is extremely dry. Since the water vapor in the atmosphere absorbs radiation in submillimeter and infrared region of the electromagnetic spectrum, Mauna Kea is an ideal spot for submillimeter and infrared astronomy. The cloud cover always remains below the summit and keeps the air above the summit free of atmospheric pollution, stable and without any turbulence. The night skies are very dark as it is far away from any city lights. All these factors make Mauna Kea an ideal place to set up astronomical observatories.

In the early 1960s, the Hawaii Island Chamber of Commerce began encouraging astronomical development of Mauna Kea. After 10 long years, a 2.2 meter diameter telescope built by University of Hawaii, UH 88 came up here. It was the seventh largest optical/infrared telescope in the world at that time. Today the Mauna Kea Science Reserve has 13 observation facilities, each funded by as many as 11 countries. The largest facility, commissioned in 1999, has been built by Japan and is known as the Subaru Telescope, considered as one of the world’s biggest, it has a single main mirror that measures 8.2 meters in diameter.

The main function of any telescope is to collect light from a celestial object. Once it is collected, a telescope must focus it into a sharp image. Through careful site selection, enclosure and telescope design, Subaru was built to obtain the highest resolving power possible and has superb Light-Collecting and Light-Resolving Powers. A computer controlled system of support holds the Subaru telescope's single piece primary mirror in shape with a surprisingly small error of 0.012 μm (1/5,000,000 inch). The cylindrical shape enclosure minimizes air turbulence inside, and linear motors drive the solidly built telescope smoothy and accurately.

Subaru telescope is soon likely to have a competitor that would have light-condensing capabilities that would be 13 times greater than the Subaru telescope’s, which means that the telescope can search for stars that are less bright or farther from Earth. It should also help scientists see some 13 billion light years away for a glimpse into the early years of the universe. This new telescope would be able to identify an object as small as a coin from a distance equivalent to 500 Km. What makes this new telescope even more interesting venture for India, is that India is also contributing towards the construction cost expected to top $1.4 billion and will also have a share of the observation time. An agreement was signed by The University of California system, the California Institute of Technology and the Association of Canadian Universities for Research in Astronomy with China, India and Japan as partners to construct this telescope in January 2013.

India will contribute about Rs 1,300 crore over the construction period 2014-23. with 30 percent of it in cash and balance in kind, to be spent on vital components of the telescope to be built in India in partnership with various industries. Indian participation will be funded by the Government of India through the Department of Science and Technology (DST) and the Department of Atomic Energy (DAE). The DST will be the coordinating department for the project.

Initially China had joined the project as an observer in 2009, followed by India the next year. Now both are full fledged partners along with Japan, who already has its own large Subaru telescope at Mauna Kea. The new telescope is scheduled to be completed in 2022 and would have its 30 meter diameter primary mirror composed of 492 segments of 1.44 meter diameter each. These mirror segments will be positioned relative to each other through sophisticated sensors, actuators and control systems, so that the entire assembly behaves like single monolithic mirror. This design perhaps has been adopted in light of a mishap with Subaru telescope wherein there was a coolant leak onto the primary mirror in July, 2011. The mishap had a significant impact on functioning of Subaru Telescope and recovery work to put back telescope back in shape including meticulous inspection and cleaning of the affected areas took almost two years and was completed only in the summer of 2013. India would set up a facility to polish about 100 mirror segments and provide sophisticated components, like actuators, edge sensors and segment support assembly for the active optics, which helps in maintaining accurately the shape of the primary mirror. India will also contribute significantly to the complex software necessary for the operation of the telescope, including the telescope control systems and various components of the observatory software.The Inter-University Centre for Astronomy and Astrophysics (IUCAA) jointly with the Indian Institute of Astrophysics in Bangalore and the Aryabhatta Research Institute of Observational Sciences in Nainital will execute India's contribution to this project

The project was launched with a groundbreaking and blessing ceremony to mark the start of construction, in presence of 100 astronomers and officials from the five countries on October 7 at a location 4,012 meters high on Mount Mauna Kea. For India, beginning of this project is particularly of great significance as the largest telescope in India has only a 2-metre mirror ( on Mt. Saraswati, Digpa-ratsa Ri, Hanle in south-eastern Ladakh in the eastern Jammu and Kashmir state of India), though India is building one at Devasthal, Nainital, Uttrakhand state, that will have 3.6 meter diameter. The new telescope is likely to be a great boon for Indian astrophysicists and is surely a quantum jump for study of Astrophysics in India.

9^th October 2014