Primary mirror segment shape correction via Warping Harness (WH) control adjustment is key to obtaining the required image performance of the Thirty Meter Telescope (TMT). We analyzed two separate experimental activities to better predict the segment WH performance. First, we took measurements of WH influence functions and Singular Value Decomposition (SVD) modes on a prototype TMT segment and compared these to model predictions. Second, we applied the TMT control algorithm on-sky at the Keck Observatory during their segment exchange and warping activities. We then used these measurements to improve our WH control simulations to include the observed effects. Altogether, the prototype segment measurements, on-sky TMT control algorithm measurements, and detailed simulation helped to better predict segment correction performance for TMT.
ScotchWeld 2216 is the selected epoxy for the Thirty Meter Telescope primary. The Invar interface components are adhered to the Clearceram segments with this epoxy. The work presented quantifies the bond strength sensitivities for TMT and validates the design. Coupons were subjected to numerous tensile and shear destructive tests. The bond preparation parameters were perturbed, and the sensitivities were evaluated. An attempt at artificial aging of the epoxy bonds was made using cyclical loads and environments. Non-destructive creep testing was evaluated interferometrically with 200mm test articles. Strength was enhanced (33%) by “conditioning” or an elevated cure (100C for 1 hour). The epoxy is strengthened (54%) at the site temperature of 2C. We measured reduced cohesive strengths for thick primer (36% weaker) and for Invar oxide (70% weaker), among other process-related degradations. For artificial aging, cyclical stresses had a minimal impact on strength, but cyclical temperature-humidity tests did significantly reduce strengths (36% weaker). 2216 epoxy exhibits visco-elastic creep in shear. For structural applications, this is unimportant, but for the TMT original design, it resulted in a surface figure degradation (2 nm P-V) over a 9-hour observation window. With alternate epoxies, with much higher Tg’s glass transition temperatures, we saw similar creep responses. 2216 epoxy provides for good strength margins for the TMT design as long as attention to the preparation details is strictly adhered to, and its properties are understood in the context of the overall design performance.
Large flat mirrors play important roles in large aperture telescopes. However, they also introduce unpredictable problems. The surface errors created during manufacturing, testing, and supporting are all combined during measurement, thus making understanding difficult for diagnosis and treatment. Examining a high diameter-to-thickness ratio flat mirror, TMT M3MP, and its unexpected deformation during processing, we proposed a strain model of subsurface damage to explain the observed phenomenon. We designed a set of experiment, and checked the validity of our diagnosis. On that basis, we theoretical predicted the trend of this strain and its scale effect on Zerodur®, and checked the validity on another piece experimentally. This work guided the grinding-polishing process of M3MP, and will be used as reference for M3M processing as well.
For polishing the ultra-thin TMT M3MP, a polishing support system with 18 hydraulic supports (HS) is introduced. This
work focuses on the designing and testing of these HSs. Firstly the design concept of HS system is discussed; then
mechanical implementation of the HS structure is carried out, with special consideration of fluid cycling, work
pressurization and the weight component. Afterward the piping installation and the de-gas process for the working fluid
are implemented. Pressurization and stiffness are well checked before system integration for the single HS unit. Finally
the support system is integrated for the polishing process.
The PSS (pentaprism scanning system) has advantages of simple structure, needless of reference flat, be able of on-site testing, etc, it plays an important role in large flat reflective mirror’s manufacturing, especially the high accuracy testing of low order aberrations. The PSS system measures directly the slope information of the tested flat surface. Aimed at the unique requirement of M3MP, which is the prototype mirror of the tertiary mirror in TMT (Thirty Meter Telescope) project, this paper analyzed the slope distribution of low order aberrations, power and astigmatism, which is very important in the manufacturing process of M3MP. Then the sample route lines of PSS are reorganized and new data process algorism is implemented. All this work is done to improve PSS’s measure sensitivity of power and astigmatism, for guiding the manufacturing process of M3MP.
M3M (Mirror 3 Mirror) of TMT (Thirty Meter Telescope) project is a 3.5m×2.5m×0.1m solid flat elliptical mirror. M3MP is a 1/4 prototype of M3M serving as a pathfinder for M3M. Fabrication and testing of M3MP were carried out based on planned sketch for M3M established in the past 2 years. Technology including polishing strategy, on site vertical Fizeau sub-aperture interfere test, scanning pentaprism system and dual-supporting system were tested in the fabrication of M3MP. This paper give a brief introduction of the work on M3MP and some of results.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will enter the preliminary design phase in 2016. The GSSM is the tertiary mirror of TMT and consists of the world’s largest flat telescope mirror (approximately 3.4m X 2.4 m X 100mm thick) having an elliptical perimeter positioned with an extremely smooth tracking and pointing mechanism in a gravity-varying environment. In order to prepare for developing this unique mirror system, CIOMP has been developing a 1/4 scale, functionally accurate version of the GSSM prototype during the pre-construction phase of GSSM. The prototype will incorporate the same optomechanical system and servo control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with an elliptical perimeter. The mirror will be supported axially by an 18 point whiffletree and laterally with a 12 point whiffletree. The main objective of the preconstruction phase includes requirement validation and risk reduction for GSSM and to increase confidence that the challenge of developing the GSSM can be met. The precision mechanism system and the optical mirror polishing and testing have made good progress. CIOMP has completed polishing the mirror, the prototype mechanism is nearly assembled, some testing has been performed, and additional testing is being planned and prepared. A dummy mirror is being integrated into the cell assembly prototype to verify the design, analysis and interface and will be used when testing the prototype positioner tilt and rotation motions. The prototype positioner tilt and rotator structures have been assembled and tested to measure each subsystem’s jitter and dynamic motion. The mirror prototype has been polished and tested to verify the polishing specification requirement and the mirror manufacturing process. The complete assembly, integration and verification of the prototype will be soon finished. Final testing will verify the prototype requirements including mounted mirror surface figure accuracy in 5 different orientations; rotation and tilt motion calibration and pointing precision; motion jitter; and internally generated vibrations. CIOMP has scheduled to complete the prototype by the end of July 2016. CIOMP will get the sufficient test results during the pre-construction phase to prepare to enter the preliminary design for GSSM.