The Thirty Meter Telescope (TMT) International Observatory (TIO) successfully completed a design review for a critical component of the primary mirror segment control system. On August 14–15, 2024, the Preliminary Design Review (PDR) for the Primary Mirror Control System (M1CS) Segment Controller & Cabling, along with the embedded software, was successfully conducted at the TIO Pasadena office, with some remote participation via Zoom.
The review included contributions from experts at the W.M. Keck Observatory in Hawaiʻi and the Dominion Radio Astrophysical Observatory of Canada's Herzberg Institute of Astrophysics. External observers were present from The India TMT Coordination Centre and the National Astronomical Observatory of Japan. Dr. Gelys Trancho, TIO Project Systems Engineer, chaired the review.
The design team consisted of TIO staff, led by Jimmy Johnson, TIO Controls Group Lead, alongside the M1CS team led by Dr. Mark M. Colavita from the Jet Propulsion Laboratory (JPL). This work was carried out under a contract between TIO and Caltech.
The design team, reviewers and observers during the session of the M1CS Segment Controller & Cabling and Embedded Software Preliminary Design Review held at the TIO Pasadena office.
The Thirty Meter Telescope International Observatory is designed with a segmented 30-meter primary mirror composed of 492 hexagonal segments, each measuring 1.44 meters. Each segment is precisely controlled in piston, tip, and tilt by a system of sensors and actuators. The M1CS is crucial in managing the real-time control of these segments, ensuring they function as a single, unified 30-meter mirror. This sophisticated control system, developed using the proven strategies from the Keck Telescopes, ensures the mirror maintains its optimal shape in the face of temperature changes, gravitational forces, and wind disturbances.
The Segment Controller and Cabling (SCC) and the associated embedded software (GLCE) are integral components of the M1CS, along with the actuator and edge sensor subsystems.
M1CS Segment Controller and Cabling (SCC) and the associated embedded software (GLCE).
During the review, the team focused on the M1CS SCC electronics, including those for the actuators, edge sensors (both analog and digital), the warping harness, and the lower and upper segment electronic boxes (LSEB and USEB). Electronics also included the local area network design, including the deployment of the network across the mirror cell, the construction and propagation of hard clock signals for distributed synchronization, and lab test results demonstrating that all timing requirements are met. Except for the network components, which are mostly custom off the shelf, all SCC components reside on the mirror segments. The review verified the hardware prototypes met stringent requirements for power, heat, weight, latency, and jitter.
On the embedded software side, the review detailed the software running on the mirror segment controllers, including the actuator software on the Actuator Controllers (3 times per segment, totaling 1,476 units), the Lower Segment control software on the LSEB controllers (492 units), and the Upper Segment control software on the USEB controllers (1,476 units). The team reviewed architecture, design, interfaces, protocols, and code samples.
The reviewers found the design, grounded in prototyping and refinement processes, significantly reduces risk. A full presentation was given on these extensive activities, illustrating how the iterative approach produced robust solutions capable of meeting the M1CS requirements while eliminating key technical risks. Significant reuse is expected from both the hardware and software prototyping, which will minimize the effort required for the final design.
The PDR also evaluated the core design, requirements, interfaces, hazard analysis, risk assessment, failure mode analysis, and risk reduction activities, such as prototyping.
The review panel expressed appreciation for the exceptional quality of work demonstrated throughout the prototyping process. The dedication and expertise of the JPL team have not only met but exceeded expectations in several areas, laying a strong foundation for the project's success.
The PDR marks a significant progression in the M1CS development, reinforcing our commitment to developing this critical subsystem of the TMT International Observatory. Funding for this work was awarded to TIO through the National Science Foundation design and development funding.
We extend our gratitude to all participants and look forward to continued success as we advance towards the next phase of the M1CS development.
This material is based upon work supported by the National Science Foundation under Cooperative Agreement No. 2331108. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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