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Integration of TMT Segment Support Assembly (SSA) and part of SSA Module Acceptance Test Tool, August 2022 - TMT SSA system is installed for the first time on top of the aluminum segment test plate at Westend facility in the Netherlands. From left, TNO engineer Rik van den Hoeven- (Integration Test Engineer), Alan Tubb (TMT), Scott Page (TMT) and Nico van der Heiden- (TNO Project Manager) - Image credit: TMT International Observatory

TMT Segment Mount Undergoes Tests in the Netherlands

Pasadena, CA -  A few months ago, TMT Optical engineers traveled to the Netherlands to support the Dutch company TNO install a TMT Segment Support Assembly (SSA) onto an SSA Module Acceptance Test Tool (SMATT). This is an important step in the design and construction of the M1 optics system, a 492-segment primary mirror for the TMT. 

The SSA modules are complex electromechanical systems used to mount the glass segments onto the M1 mirror cell. The SSAs actively warp the surface of the mirror segments to optimize M1 figure and optical performance. Each SSA consists of three mechanical precision structures called whiffletrees, each of them providing nine axial support points. Thus, each mirror segment is supported by 27 flexure points bonded to the back of the segment.
The SMATT will be used to measure the mechanical loads on TMT’s primary mirror support points. The SMATT consists of a force field test plate made from aluminum, simulating an actual glass mirror segment with the same weight and center of gravity, equipped with 27 sensors to measure the loads between the mirror and the SSA.
The SMATT unit is critical because it will be used to verify all TMT’s segment support structures.
Over the last few months, TNO has been designing and manufacturing components of the SMATT system with S&T working on the control and software and Technolution working on the Warping Harness Control electronics.
This was the first time that a TMT production SSA was mounted onto the test tool. After integration, the TMT optics team and TNO research staff were able to start testing the SMATT automated system.
“It has been rewarding to be involved in a work environment with our TNO colleagues who have gained such valuable expertise on a similar tool they designed for the ESO European Extremely Large Telescope,” said Bryan Smith, TMT mechanical engineer managing the SSA work. “We have a nice collaboration on-going with this team, including lead engineer experts who not only have experience with the manufacturing of the tool but the intricate tests that are needed in order to validate that the SSAs are acceptable to be installed in the telescope.”
TMT SSA Module Acceptance Test Tool (SMATT)

TMT SSA Module Acceptance Test Tool (SMATT) The tool will be used to check each TMT primary mirror segment support - Front view of the SMATT force field test plate after assembly of SMATT and SSA. The hardware combination is mounted on top of a tiltable trolley and electrical cables are connected to the control units, August 2022 - Image credit: TMT International Observatory

A tilt trolley was designed to rotate the assembly and allow testing the SSA with SMATT at variable altitude angles. This testing procedure will help verify the behavior of the segment structure and measure with high precision the force distribution over the 27 load cells while simulating changes in telescope elevation.
“It was a successful series of tests, and also very exciting to get the first data from the new tool,” said Ben Gallagher, TMT telescope optics group leader. “We could change the gravity orientations several times and were able to make comparisons between varying interface loads. The tests showed that we have a repeatable and good quality segment mount system.”
TMT SSA Module Acceptance Test Tool (SMATT)

TMT SSA Module Acceptance Test Tool (SMATT) - Side views of the tilt trolley supporting the fully assembled Segment Support Assembly SSA and SMATT tool developed by TNO research organization, August 2022 - Image credit: TMT International Observatory

The TMT quality assurance team also worked with TNO to ensure that the SMATT will fully meet requirements, and the next step will be to organize a final acceptance test of the tool later this year. Once TMT has accepted the SMATT, it will be used in India and California to verify the quality of all manufactured SSAs and ensure that the interface loads meet TMT specifications.

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