Adaptive Secondary Mirror
The MMT336 is the first adaptive secondary ever installed on a telescope.
An industrial team formed by , Microgate, ADS and Media Lario with the fundamental scientific support of Osservatorio Astrofisico di Arcetri and Dipartimento di Ingegneria Aerospaziale - Politecnico di Milano was committed in 1998 by Steward Observatory to building the adaptive secondary unit for the new MMT. The thin shell has been manufactured by the Mirror Lab in Tucson, AZ, that also conceived and realized the optical setup used for optical and performance calibration of the system.
The integration and dynamic tests on the unit were completed at Microgate premises in July 2000. In 2002, after accurate optical testing a Mirror Lab, the unit was installed on the telescope, where it is currently being used for science.
Within the industrial team, Microgate was responsible for design, development and manufacture of the adaptive mirror control system. The adaptive mirror control system is based on totally customized electronics.
Special control boards have been developed for this purpose, each controlling eight channels by means of four DSPs, for a grand total of 168 DSPs working in parallel, achieving a computing power of 7 billion operations per second.
The position commands are transferred from the Real Time Reconstructor by means of a high speed fiber optic link.
MMT336 Facts:
- Mirror diameter: 640mm
- Thin mirror thickness: 2mm
- Number of actuators: 336
- Capacitive sensors reading noise: 5 nm rms
- Control loop frequency: 40 KHz
- Typical response time (any mode): 1.3 ms
- Number of control electronics crates: 3
- Number of DSP control boards: 42
- Number of DSPs: 168
- Computational power: 7 billions MACs/s (multiply and accumulate per second, integer 16x16 -> 40 bit)
- Real time communication speed: 160 Mbit/s
- Data transfer and computational latency: 115µs (from RTR output ready to commands applied to the mirror)