Abstract: This article investigates the combination of magnetic data from the MSS-1 and Swarm satellites for improved investigations of Earth’s magnetic field and Geospace. The study highlights the complementary nature of polar-orbiting (Swarm) and low-inclination (MSS-1) satellites in geomagnetic modelling and monitoring large-scale magnetospheric contributions. Data from close encounters between MSS-1 and Swarm (intersatellite distance < 100 km) confirm the excellent data quality of the two satellite missions (< 1 nT median difference in scalar intensity F) and allow for data calibration and validation and investigations of in-situ ionospheric currents. The reason for a small but consistent difference (F as measured by MSS-1 is 0.5 to 1.0 nT larger than that measured by Swarm) is unknown. Combining MSS-1’s low-inclination data with Swarm’s near-polar observations significantly enhances the spatial−temporal resolution of Earth’s magnetic field models, allowing for new opportunities for studying both rapid core field variations at low latitudes and the local-time dependence of large-scale magnetospheric current systems. A joint analysis of magnetic data from six satellites during the May 2024 geomagnetic storm reveals a clear dawn−dusk asymmetry, with equatorial magnetic disturbances during dusk being approximately 150 nT more negative than during dawn.