AITC Update
Published in the RSAA Lunations
Vol1 Issue32 1–30 September 2022
Adaptive Optics Real-Time Control program
While the first proposal for the Adaptive Optics (AO) concept dates back to the 1950’s, the implementation of the first AO systems had to wait for deformable mirror technologies to mature sufficiently and only happened by the beginning of the 1970’s. At the time of these pioneering instruments (RTAC in 1974 and then CIS in 1981) developed for the USAF, the system design and in particular the proposed wavefront sensing strategies, allowed the early AO engineers to use now obsolete analog computers to drive the deformable mirrors. While the AO technology was slowly emerging, the first generation of digital processors appeared on the market. The first AO system for astronomy COME-ON, developed in Europe, relied on Shack-Hartmann wavefront sensors and required the use of digital processors (Motorola DSP running at 33 MHz and delivering the required 150kMAC/s -- Multiply Accumulate / second to run the AO loop at 200Hz). When the first AO system on the VLT was commissioned (NaCo), by 2000, it was equipped with a staggering cluster of 12 of these DSP chips to drive what was at the time the most complex AO loop designed for astronomy. Today, a cluster of 168 similar DSPs is powering the LBT AO RTCs.
Soon after NaCo first light, and concurrently to the development of more AO systems for 8-10m telescopes, a significant effort has been invested at ESO to fit the need for a standard platform, serving all AO projects foreseen for the VLT instrumentation, by using common components and COTS hardware. SPARTA, the Standard Platform for Adaptive optics Real Time Applications, has provided a generic decomposition in functional blocks for AO real-time control that has been applied, unchanged, to a variety of different AO systems, ranging from very small single conjugate AO with less than 100 actuators (e.g. MACAO) to much larger and faster systems (e.g. SPHERE). The design went from a cluster of specialized CPU boards not delivering the required performance and showing high data communication latency between CPUs, to a cluster of hybrid boards hosting 2 CPUs (PPC) and 2 FPGAs facing issues linked to a costly development cycle or strictly integer computations. To address these technical limits, and deliver the required deterministic performance, the final SPARTA standard architecture hosts additional DSP modules to perform floating point operations and operations which require significant memory capacity. Additionally, FPGAs are used for input/output processing and operations which are largely integer based and highly parallel (wavefront processing) and CPUs are used for operations which require significant algorithmic complexity. Today, several core components of the RTC box have become obsolete and cannot be reused in the long term. The platform does not scale anymore due to current performance trends of AO requirements and is now discontinued at ESO.
Today, AITC is jointly developing COSMIC, a RTC platform for AO, together with CNRS - Observatoire de Paris - PSL. COSMIC fulfils the need of all currently foreseen instruments at ESO and other observatories, while maximizing efficiency and minimizing cost and complexity, with long term maintainability and scalability as the core drivers of the development cycle. The hardware concept relies on dense clusters of GPUs and many-cores, integrating optimised hardware interfaces based on either FPGA boards or emerging technologies such as NVidia’s DPUs or Intel’s IPUs. The software platform relies on off-the-shelf libraries and a both optimised and modular approach to build a variety of pipelines able to cope with various AO flavors, from single conjugate to multi-conjugate and multi-object AO. The comprehensive software stack includes the hard real-time pipeline as well as a supervisory software and a middleware solution, based on abstraction layers to adapt to various observatories frameworks.
The Paris node, where this R&D was originally initiated back in 2015, is now entering the construction phase for MICADO SCAO RTC (ELT first light instrument) while starting the design study for the SPHERE+ RTC upgrade. The AITC node partnered with Microgate and CAS at Swinburne to successfully deliver the new AO RTCs (2 units) for the Keck telescopes (now fully in operation) and is working hard on producing documentation for the Preliminary Design Review of MAVIS. The AITC team is also currently delivering a lab RTC to ESO for the GHOST demonstrator and working with other teams worldwide on potential future collaborations. Beyond these instruments projects, the team is also engaged in top ranked R&D collaborations worldwide with both vendors (e.g. NVidia) and academia (e.g. KAUST, BSC) to establish these technologies as the unchallenged standard for all future AO instruments and facilities and institute the COSMIC teams as the go-to providers for all future demanding RTC applications.
The COSMIC AITC node consists of Julien Bernard and Nicolas Doucet, with help from Hao Zheng, Jesse Cranney, François Rigaut and Damien Gratadour.
Damien Gratadour
