Work is moving forward on TMT’s Telescope Control System (TCS), which is responsible for the coordination and control of the various telescope subsystems, responding to commands received from the observatory control system and from expert user interfaces. A part of TMT’s India work-share, the TCS is technically challenging due to the large number of external interfaces and the need for efficient communication with many distributed teams from USA, Japan, Canada, China and India.
A critical component of TMT, the TCS has four main functions:
Sequencing of the commands that control, synchronize, and monitor the telescope subsystems,
Converting target positions into coordinates relevant to each subsystem,
Providing wavefront control software for all seeing-limited instruments, and blending offloads commands for the Adaptive Optics system,
Ensuring the optimal precision for the telescope pointing.
Following the completion of the TCS Conceptual Design Review phase, a Request for Proposal (RfP) was issued to identify Indian vendors capable of carrying out the TCS design and development. OACES, a Pune-based business division of Honeywell Automation India, was selected to work on the TCS Preliminary Design.
The TCS team, which comprises members of the TMT project office in Pasadena, the developers from OACES, and staff from IUCAA (also from Pune, India), meet weekly via teleconference to discuss technical matters and monthly for program management updates. Face-to-face meetings are also organized four times a year to review the previous three months’ work and plan ahead for the next quarter. These meetings are crucial to strengthening the team cohesion, and improving coordination and communication among geographically dispersed groups.
This past April, a third of the way through the Preliminary Design (PD), the team met at the TMT Project Office in Pasadena to review the completed work to date. During that week, an entire day was dedicated to Quality Assurance sessions, and project status presentations were attended by members of the TMT system engineering group, management, the observatory software group and members of the TMT controls group. This meeting included discussions about the TCS software architecture, the TCS requirements and schedule, and covered areas as diverse as the interface definition and design details for the pointing kernel, the corrections module, the interfacing to the enclosure, the telescope structure and the M3 mirror. After a full week of discussion, it was clear that, although a considerable amount of work remains to be done, the OACES team is performing well and is on track to a successful Preliminary Design Review (PDR).
Jimmy Johnson, TMT lead software engineer at the project office, said, “I am delighted to see that, since the TCS kick-off workshop a year and a half ago, OACES has developed a strong partnership to deliver the telescope control system. We are making important progress toward Preliminary Design Review.” A second interim status update and peer-review meeting is planned for early next year, before the full 2019 PDR.
About the TCS
The telescope control system consists of a sequencer and status/alarm monitor, a pointing kernel, a corrections module, and several interface components for subsystems that are not directly compliant with the TMT common software (CSW). These interfaces are realized as CSW assemblies and hardware control daemons that abstract the protocols for communication with the mount, segment handling system, enclosure and the M2 and M3 mirrors.
The sequencer and status/alarm monitor provide high-level control of the pointing and tracking of the mount structure, the primary, secondary and tertiary mirrors, and the enclosure, including its cap, base, shutter and vents. The telescope enclosure has a “calotte” design, which is made up of a fixed based, a horizontally-rotating structure, a cap structure mounted on an inclined track, and a circular aperture with its cap cover, giving the observatory its distinctive appearance. TCS has direct control over the mount structure, the enclosure and the M2 and M3 systems.
TCS will provide extremely accurate and sophisticated algorithms for controlling the telescope pointing and tracking. TMT pointing kernel converts target positions (right ascension and declination) into pointing and tracking demands in the appropriate coordinate systems for the telescope mount, instrument rotators, atmospheric dispersion correctors, instrument and adaptive optics system wavefront sensor probes, and the enclosure cap and base.
The corrections module on the TMT is responsible for the creation and management of the look-up tables that control the position and shape of the primary, secondary and tertiary mirrors as a function of zenith angle and temperature. It will also process data from the telescope global metrology system and provide appropriate position information to the other control systems. While the telescope is pointing, TCS will also provide information on the quality of correction and makes adjustment to the primary, secondary and tertiary mirrors. Any position error detected will be passed to the Telescope Control System (TCS) for correction.
All India-TMT activities are coordinated by the India TMT Coordination Center (ITCC) at the Indian Institute of Astrophysics in Bengaluru, set up by the Department of Science & Technology (DST) of India. The Inter-University Center for Astronomy and Astrophysics (IUCAA) at Pune leads the Telescope Control System (TCS) work and is responsible for delivering TCS developed by the industrial contractor OACES.
