CROMIS – The case for an orbital H-alpha solar telescope

Monitoring of the Sun and space weather is becoming increasingly important, with applications ranging from satellite and astronaut safety to GNSS reliability and power grid operations. The chromosphere, a complex and dynamic layer of the Sun’s atmosphere best visible in the H-alpha spectral line, holds significant information for resolving open questions like coronal heating and improving space weather forecasting. Ground-based telescopes are severely limited by weather, geographical distribution, schedule, or insufficient spatial or temporal resolution, while existing space observatories often lack high cadence or full-disk coverage of the chromosphere. The CROMIS (ChROmosphere Monitoring InStrument) project, funded by ESA and optimized for a SmallSat platform, addresses this critical data gap by providing near 24/7 full-disk monitoring of the Sun in H-alpha.

The core technical challenges and focus areas of CROMIS include instrument design to achieve high-resolution, high-cadence imaging within a compact form factor; robust systems design and integration to embed a sensitive, high-data-rate instrument into a cost-effective small satellite bus; and the development of mission operations and ground architecture for constant monitoring and rapid data access. We present the CROMIS mission concept, highlighting architectural decisions made to balance demanding scientific performance requirements with the constraints of a SmallSat platform. As the first Croatian astrophysical space science instrument, this initiative also serves as a capacity-building project and a valuable case study in designing a space science mission within the collaborative framework of the broader SmallSat community.