The Challan instrument is a solar full-disk imaging spectroscopic telescope planned to be installed at three sites with a 120-degree longitudinal difference, enabling continuous 24-hour observations of the Sun. It will take data every 2.5 min with a spatial resolution of 2–3′′ and a spectral resolving power (R) of >43,000 in Hα and Ca ii 8542 Å bands simultaneously. Challan is composed of two modules, each dedicated to a specific waveband. This modular design is beneficial in minimizing the scattered light and simplifying the structure and engineering. The primary scientific goal of Challan is to investigate solar flares and filament eruptions. It is also expected to detect small-scale events in the solar chromosphere. In 2025, Challan will be installed at the Big Bear Solar Observatory for test observational runs, followed by scientific runs in 2026.

Introduction
Scientific Objectives and System Requirements
Concepts of Design
    Technique and Specification
    Modular Design
    Optical Design and Mechanisms
Optical Alignment
Control Software & Automation
Data Acquisition and Processing
Summary and Conclusion
Acknowledgments
References

• Heesu Yang(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea) Corresponding author
• Eun-Kyung Lim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Sujin Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Su-Chan Bong(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Yeon-Han Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Seonghwan Choi(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Maria S. Madjarska(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Max Planck Institute for Solar System Research, 37077 Göttingen, Germany, Space Research and Technology Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria)
• Donguk Song(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan)
• Hannah Kwak(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Research Institute of Natural Sciences, Chungnam National University, Daejeon 34134, Republic of Korea)
• Sung-Hong Park(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Department of Astronomy and Space Science, University of Science and Technology, Daejeon 34113, Republic of Korea)