project TMT Tertiary Mirror Support System and Positioner Assembly

The TMT International Observatory LLC (TIO) recently awarded a contract to AMOS for designing and manufacturing the tertiary mirror support system and positioner assembly (M3SSPA) of the future extremely large TMT telescope. Once constructed, the TMT telescope will have a 30-meter primary mirror and be the largest ground-based, optical telescope in the Northern hemisphere.

With its preferred site located on Maunakea in Hawaii, TMT is one of three extremely large telescopes under construction in the world. Building such a telescope is a major challenge. Engineers must design and build large moving structures capable of holding the telescope’s different mirrors in place with nanometric precision.

After being chosen to design the secondary mirror support system and positioner, AMOS is now selected to develop another critical part of the telescope: the tertiary mirror support system and positioner assembly, known as the “M3SSPA.” This system consists of a large mount that carries and orients the M3 mirror. Located on a tower emerging from the center of the 30-meter primary mirror support structure, the tertiary mirror captures the light reflected by the secondary mirror at the top of the telescope, and transmits it towards one of the two Nasmyth platforms on the side of the telescope, where the scientific instruments are located.

The M3SSPA system is composed of two elements:

• A system to support the 3.6×2.5-meter elliptic flat tertiary mirror and ensure that the mirror’s surface keeps its optimal shape with a precision in the order of a fraction of a micrometer
• A positioning mechanism allowing the mirror to direct the beam with a high precision towards the telescope instruments and to flip 180° so as to illuminate the instruments on one or the other side of the telescope, depending on the observations to be made.