Tmt comp background



India TMT Coordination Center (ITCC), Larsen & Toubro (L&T) and TMT-Project Office (TMTPO) participants at the Segment Support Assembly (SSA) pre-build meeting at L&T facility, Coimbatore, in India – 22 May 2019 - Image credit: TMT International Observatory / Nikhil Naik

Segment Support Assembly (SSA) Pre-Construction Meeting at Larsen & Toubro in India

Pasadena, CA (June 06, 2019) – A Segment Support Assembly (SSA) “pre-build” meeting at the Coimbatore facility of Larsen & Toubro (L&T) was successfully completed on May 22, 2019. The meeting was aimed at assessing the readiness of the L&T team to start manufacturing their first SSAs. Participants included India TMT Coordination Centre (ITCC) and the TMT Project Office team.

The teams at ITCC and L&T worked diligently to put together a successful plan to manufacture SSAs in India. The project management plan and role of all project team members were reviewed. All documentation and information regarding the SSA design plans, the list of all custom materials, and their status for procurement and delivery were laid out and evaluated. Similarly, the final drawings and process routing sheets for the SSA components were revised and updated. 


The SSA  system is designed to effectively reduce the deformation of the TMT primary mirror segments induced by gravity and thermal distortion. Each mirror segment will be mounted on an SSA, and supported in translation and rotation while maintaining the optimal shape of its optical surface.

The SSA uses a combination of mechanical whiffletrees for axial support, a central diaphragm for lateral support, and a whiffletree-based remote-controlled warping harness for surface figure corrections. Each SSA will be tuned independently for the 82 types of segments, each containing 537 precision mechanical components, sensors and actuators that are to be manufactured prior to their integration within the support assembly.

In short, SSAs will hold the mirror segments in place and let each segment be positioned in real time to allow the 492 segments to perform as a single 30-meter diameter mirror.


The meeting established a formal and clear starting point for the construction of the first 100 contracted SSAs in India. (For more information, see previous article “Contract Signed for TMT Primary Mirror Segment Support Production”)

Moving forward, additional on-site meetings will be regularly scheduled. Mr. Rajakumar, project coordinator at L&T, and ITCC, will coordinate inspections of manufactured components and parts, as well as their testing. SSA assembly will be done at L&T, in an area that is climate controlled with respect to temperature and humidity level. Rounds of inspection will be carried out by ITCC before enabling production to continue into the assembly process.  


Robert Anderson, TMT Lead Quality Assurance Engineer and SSA work package manager, said “I am delighted to see an efficient collaboration between the teams. All participants for SSA construction in India were present. They prepared very hard to ensure the project will achieve the best construction results. The TMT project office and ITCC are fully supporting L&T progress. With the aim of strengthening the partnership and supporting cooperation, we will share knowledge and lessons learned on the SSA assembly process that has been accomplished in the U.S. In this respect, it is planned that L&T and ITCC engineers will come to the TMT lab near Pasadena in the fall of 2019 to get training on SSA assembly”.


The L&T team has now ordered most of raw materials needed. L&T management is fully committed to the TMT project and the production of the SSAs components, which is expected to start around mid-July 2019. Once manufactured at L&T, the SSAs will be shipped to the India TMT Optical Fabrication Facility (ITOFF) where the mirror segments will be accurately polished and shaped into hexagons.


TMT Segment Support Assembly Module

TMT Segment Support Assembly Module - Segment Support Assemblies will hold in place each of the 492 TMT primary mirrors, letting them be positioned in real time to provide the best possible imaging capability - Image credit: TMT International Observatory



TMT M1 Segment

TMT Primary Mirror Segment - The TMT primary mirror includes 492 hexagonal glass ceramic segments, each of them held in position by a support system called Segment Support Assembly (SSA) - Image credit: TMT International Observatory / Fred Kamphues


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