2GDSM: 2nd Generation Deformable Secondary Mirror
The M2-Unit with Deformable Secondary Mirror (DSM) installed on the VLT unit telescope UT4 as part of the VLT Adaptive Optics Facility has proven to be a very successful system, being an integral part of the highly requested instruments MUSE and ERIS with their AO-assisted modes. With the arrival of MAVIS on UT4 in 2031, it is expected that the very high request on UT4 will see very high ranked observations not being allocated time.
The second generation deformable secondary mirror (2GDSM) is an ESO led project aiming at upgrading UT3 to a second adaptive telescope, like UT4. The project builds on the upgrade already implemented by the GRAVITY+ project, with laser guides stars (LGS) now available on all UTs. The 2GDSM will be procured from AdOptica, taking advantage of synergies with the ELT-M4 for technology developments and leveraging on a common pool of spares to be shared with the AOF-DSM.
| Builders |
ESO (in house) |
| Industrial partner | AdOptica |
| Project Manager | Senol Yazici |
| Project Scientist | Amelia Bayo |
| Project Engineer | Pierre Haguenauer |
| Project Status | Design phase |
| Destination | VLT UT3 |
Status and provisional timeline
- Kick Off Meeting (KOM) -- February 2026
- Final Design Review (FDR) -- August 2027
- Preliminary Acceptance Europe -- Q3 2029
Technical Details
| Modes | passive mode (equal performance as current M2), SCAO, MCAO, GLAO, LTAO |
| Number of actuators | 1170 |
| Stroke compatible with achieving max WFE residuals of, in AO close loop: | < 80nm RMS for 0.9arcsec seeing (@30deg from zenith) < 150nm RMS for 1.5arcsec seeing |
| Micro roughness: | < 2nm RMS |
| Stability: | surface stability < 20nm RMS WFE over 8hours (without optical feedback from AO) |
| Coating reflectivity: | 97% in [450-600nm] 98% in [600-13000nm] |
Instrument Description
The 2GDSM consists (in a nutshell) of:
An M2 Hub compatible with the spider interface of VLT UT3, an hexapod linking the hub to the mirror’s optical surface, a deformable Secondary Mirror assembly with 1170 force actuators operating in closed loop on a set of 1170 co-located capacitive sensors deforming a 2mm thick Zerodur shell, and a coated science grade thin shell (with integrated magnets) compatible with the AOF-DSM shell and its spare.
The 2GDSM will have the same number of actuators (1170) and the same geometry as the existing AOF-DSM to ensure perfect compatibility from mechanics to operations and performance. The 2GDSM will provide the potential for different modes of AO correction (and noAO mode) for the various instruments installed at the five UT3 foci. Its features and specifications will not hinder the implementation of known adaptive correction modes such as: SCAO, MCAO, GLAO, LTAO using natural or artificial guide stars. The time overhead for acquisition when observing with the 2GDSM is required to be less than 2 minutes.
