Pasadena, CA – February 6, 2019 – The Indian Institute of Astrophysics (IIA), on behalf of India TMT, recently signed a contract with Larsen & Toubro (L&T) to manufacture 100 Segment Support Assemblies (SSA) for the TMT. L&T is one of the largest leading construction engineering companies in India.
The 30-meter diameter primary mirror, which will be made of 492 individual hexagonal segments each measuring 1.44 meters across corners, will be one of the largest ever made for an optical telescope. The telescope will integrate the 492 segments into a single light-gathering surface that is 30-meters wide.
The SSA is a system of complex optomechanical sub-assemblies on which each hexagonal mirror is mounted. SSAs also provide precise real-time 3-D positioning and alignment of each segment to deliver the best possible imaging capability.
The design of the segment support for TMT is based on a moving frame concept: A fixed frame is attached to the mirror while a moving frame provides the base for the axial and lateral support assemblies. Each segment is supported axially by a 27-point “whiffletree,” which is a network of thin rods attached to the back of the mirror and providing a mechanical support structure designed to evenly distribute the weight of the glass. The lateral support of each segment, a critical requirement when the telescope points toward low elevations, is provided by a central metallic diaphragm recessed into the glass.
The SSAs include active mechanisms and sensors, notably the segment warping harnesses and their actuators. Each segment has 21 warping harness assemblies comprising 21 actuators. Each segment support assembly hosts a total of 537 precision mechanical components, sensors and actuators and weighs nearly 58kg. Each individual glass-ceramic segment weighs 153kg.
Representatives from L&T and the TMT project offices in Pasadena and India met on 30 January 2019 to answer final questions before the start of work. They discussed technical details and set up a process of regular meetings going forward to keep the teams informed of work updates. The meeting took place in L&T’s Coimbatore facility, which is dedicated to precision and heavy engineering business supply and equipment to defense, nuclear power and aerospace.
Professor Eswar Reddy, the Programme Director of India-TMT, expressed his delight with the current progress of the SSAs: “L&T is starting to manufacture complex SSA pieces and key subsystems for the TMT main mirror. L&T shall be responsible for the procurement of raw materials, manufacturing, inspection and assembly of the SSA components, as per TMT prescribed requirements.” [From this year, India set to manufacture key components for largest ground-based observatory. The IndianExpress February 9, 2019 - https://indianexpress.com]
Initially, there will be a production qualification phase of the SSAs, over which tests will be performed to evaluate the quality of the fabrication procedures and method of assembling. The first qualification units from L&T are expected at the end of 2020.
After production, the manufactured SSAs will be shipped to the newly built India TMT Optics Fabricating Facility (ITOFF) at the IIA Centre for Research and Education in Science and Technology (CREST) campus near Bengaluru. SSAs will also be dispatched throughout China, Japan and USA, where polished mirror segments will be mounted to proceed to final optical precision testing. All SSAs, sensors and actuators for the TMT primary mirror are key instrumentation components and will be developed and manufactured in India.
Production hardware and SSA prototype for the telescope are featured in the TMT technical laboratory in California [TMT Monrovia Lab Overview, 2018, 00:50 sec].