The Workhorse

The Medium-Sized Telescope (MST) is called the CTAO’s “workhorse” because it will be responsible for covering a large portion of the Observatory’s energy range by detecting the mid-range energy gamma rays that are relatively more frequent and easier to capture than the lower and higher end of the CTAO’s energy range. That’s one of the reasons they will be located on both sites.

The Design

The MST is a modified version of the Davies-Cotton design. This design, which was originally created to collect solar radiation, has been used by CTAO predecessors HEGRA, H.E.S.S. and VERITAS.

The Reflector

The MST will have 86 hexagonal-shaped mirrors that are aligned with an active mirror control assembly to create a uniform reflector of about 12 metres in diameter. A reflective surface of 88 m2 collects and focuses the Cherenkov light into the camera, where the light can be digitised and processed. 

The Cameras

Two camera designs will be used for the MSTs: NectarCAM for the CTAO-North site and FlashCam for the CTAO-South site. The MST cameras will use Photomultiplier Tubes (PMTs) and have a large field of view of about 8 degrees, enabling observation of gamma-ray sources that may be concentrated in one area of the sky or widely spread apart.

MST Rendering (Credit: Gabriel Pérez Díaz, IAC)

The MST Prototype

An MST prototype operated in Berlin between 2012 and 2020 to validate the design of the individual components, test the interfaces between the mating assemblies and to define the assembly process of the product. Extended test campaigns with FlashCam and NectarCAM prototypes were performed on the telescope during this period in order to verify their interfaces and overall integrity. 

The MST Collaboration

The Medium-Sized Telescope (MST) is being built by an international collaboration of institutes and universities from Austria, Brazil, France, Germany, Italy, Poland, Spain and Switzerland. 


A dual-mirrored version of the MST, the Schwarzschild-Couder Telescope (SCT), is proposed as an alternative type of medium telescope. The SCT’s two-mirror optical system is designed to better focus the light for greater imaging detail and improved detection of faint sources. In collaboration with the SST and MST groups and institutes in Germany, Italy, Japan and Mexico, institutes in the United States have been the pioneers of the SCT design since 2006.

Credit: Deivid Ribeiro, Columbia University

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