The SiTian project, designed to utilize 60 telescopes distributed across multiple sites in China, is a next-generation time-domain survey initiative. As a pathfinder for the SiTian project, the Mini-SiTian (MST) has been proposed and implemented to test the SiTian’s brain and data pipeline, and to evaluate the feasibility of its technology and science cases. Mounted at the Xinglong Observatory, the MST project comprises three 30 cm telescopes and has been operated since 2022 November. Each telescope of the MST possesses a large field of view, covering 2 . ° 29 × 1 . ° 53 FOV, and is equipped with g ′ , r ′ and i ′ filters, respectively. Acting as the pioneer of the forthcoming SiTian project, the MST is dedicated to the discovery of variable stars, transients, and outburst events, and has already obtained some interesting scientific results. In this paper, we will summarize the first-two-year operation of the MST project.

Time-domain astronomy is one of the most important areas. Large sky area, deep-field, and short timescale are the priority of time-domain observations. SiTian is an ambitious ground-based project processing all sky optical monitoring, aiming for a sky-survey timescale of less than 1 day. It is developed by the Chinese Academy of Sciences, an integrated network of dozens of 1 m class telescopes deployed worldwide. The Mini-SiTian Telescope Array is being carried out for demonstrations on optical design, group scheduling, and software pipeline developments, to overcome the high technical and financial difficulties of the SiTian project. One array contains three 300 mm F/3 telescopes, with an FOV of 5° over the 400–1000 nm wavelength range. The Mini-SiTian Telescope Array is now under commissioning in Xinglong Observatory, and a perfect platform for technical research and educational purposes.

The SiTian project is mainly aimed at a photometric survey of the 10,000 square degrees sky within 30 min in three bands. The telescopes for the SiTian array must have a super-wide field-of-view (FOV). For the optical system discussed in this paper, we have investigated four types of wide-field telescope optics: Cassegrain with correctors, three-mirror anastigmatic, prime focus, and modified Schmidt types. Weighing up the pros and cons, the catadioptric system, transformed from a modified Schmidt telescope, was adapted for the prototype of the SiTian array. The optics of the SiTian array is a 1 m/1.27 m modified Schmidt optical system, with an aperture of 1 m, an FOV of 7°(25 square degrees), and a focal ratio of 2.06, and is capable of imaging from 400 to 1000 nm. The image scale is 1 arcsec per 10 µm, and the optimal optical performance is 2 arcsec (80% of the encircled energy diameter less than 20 µm), which is suitable for the photometric survey.

The third Antarctic Survey Telescope array instrument at Dome A in Antarctica, the AST3-3 telescope, has been in commissioning from March 2021. We deployed AST3-3 at the Yaoan astronomical station in Yunnan Province for an automatic time-domain survey and follow-up observations with an optimised observation and protection system. The telescope system of AST3-3 is similar to that of AST3-1 and AST3-2, except that it is equipped with a 14 K × 10 K QHY411 CMOS camera. AST3-3 has a field of view of $1.{65}^{\circ }\times 1.{23}^{\circ }$ and is currently using the g band filter. During commissioning at Yaoan, AST3-3 aims to conduct an extragalactic transient survey, coupled with prompt follow-ups of opportunity targets. In this paper, we present the architecture of the AST3-3 automatic observation system. We demonstrate the data processing of observations by representatives SN 2022eyw and GRB 210420B.

The Multi-Channel Photometric Survey Telescope (Mephisto) is a wide-field ground-based telescope with a 1.6 m primary mirror and 2◦ field of view (FOV). The telescope is capable of synchronous photometric imaging in blue, yellow, and red channels covering a wavelength range from 320 nm to 1000 nm by using large cubic splitters with dichroic coatings. A high-accuracy photometric survey requires higher requirements for the transmittance and reflectance of dichroic coatings. However, the light ray incident angle on the cubic splitter surface is 45°±6°, and the refractive index difference between the p-component and s-component of incident light causes an obvious p/s efficiency difference of both the reflection and transmission through the cubic, which will introduce extra error on the photometric accuracy. This paper proposes an effective method to calculate the uniformity of the imaging efficiency of the Mephisto. By sampling on the pupil plane with each FOV, the efficiency of each light ray can be calculated by the curve fitting method. The efficiency difference over the full focal plane is less than 2.5%, 1.5%, and 0.5% for the blue channel, yellow channel, and red channel respectively, introduced by the cube dichroic coatings and the filters, which can be used for the calibration. The method paves the way to solve coating uniformity for large aperture telescopes.