Small-Sized Telescope

»The SSTs will outnumber all the other telescopes with 70 planned to be spread out over several square kilometers in the southern hemisphere array.«

The Small-Sized Telescopes (SSTs) will outnumber all the other telescopes with 37 planned to be spread out over several square kilometers in the southern hemisphere array only. This is because very high-energy gamma-ray showers produce a large amount of Cherenkov light over a large area, and the SST’s smaller mirror is sensitive to the highest energy gamma rays (between a few TeV and 300 TeV). The SSTs’ wide coverage and high sensitivity improve CTA’s chances of detecting the highest energy gamma rays.


Three different SST implementations were proposed for the final SST design: ASTRI-Horn, GCT and SST-1M. A harmonization process was initiated in 2018 and, in its June 2019 meeting and following the CTAO Management proposal, the Council decided that “the CTA-SST design should be based on the ASTRI/CHEC design, taking into account the experience gained from all designs.” A rendering of the current proposed SST design is below.

Credit: G. Pérez, IAC, SMM

Further Reading

Looking for a simpler explanation of how CTA telescopes work? Download the SST in “simple words” fact sheet.

The SST design is a dual-mirror Schwarzschild-Couder aplanatic configuration and, thanks to its small plate scale, uses a novel compact camera based on SiPM sensors. The 4.3 m diameter primary mirror is segmented into hexagonal facets and the 1.8 m secondary mirror is monolithic.

(Last Updated: Dec 2019)

SST Camera


CHEC-S prototype camera. Credit: Christian Foehr (MPIK)

The SST’s camera, also known as the CHEC camera, uses custom peak-hold application-specific integrated circuits (ASICs) for signal capture. The dual-mirror design allows us to maintain the same angular resolution and collecting area across a wide field of view with a short focal length. The camera consists of 2048 silicon photo-multiplier pixels forming approximately a 9o x 9o field of view. The CHEC is unique as an SST dual-mirror camera in its ability to capture Cherenkov light not as fixed images, but as movies consisting of hundreds of frames each lasting one billionth of a second.


SST Collaboration


The joint SST collaboration benefits from the research and development work previously carried out within the ASTRI, CHEC and GCT projects aimed at the development of end-to-end SST dual-mirror telescopes. The ASTRI project ( led by the Italian National Institute of Astrophysics (INAF) with the collaboration of a number of Italian universities, the Italian National Institute of Nuclear Physics (INFN)Universidade de São Paulo in Brazil and North-West University in South Africa, the CHEC project, led by MPIK, is an international collaboration between the University of Adelaide, the University of Amsterdam, DESY Zeuthen, Durham University, the Erlangen Centre for Astroparticle Physics (ECAP), the University of Leicester, the University of Liverpool, Nagoya University, and the University of Oxford. The GCT telescope project is carried out by the Observatoire de Paris-Meudon.

SST Contacts:

SST Coordinator: Gianpiero Tagliaferri
ASTRI: Salvo Scuderi, Giovanni Pareschi

CHEC: Richard White