Overview
ISO 17520:2024 provides a standardized method for determining the effective vertical cut-off rigidity (EVCR) of charged particles (cosmic rays and solar energetic particles) penetrating inward through the Earth's magnetosphere. The standard defines principal requirements and calculation techniques based on models of the geomagnetic field to assess particle access to near‑Earth space for rigidities above 0.2 GV. It is the second edition (revising ISO 17520:2016) and adds basic tables for IGRF epochs including 2015 and 2020.
Key topics and requirements
- Definition of key terms: particle magnetic rigidity, lower/upper cut-off rigidity, penumbra, effective cut-off rigidity, and EVCR (vertical direction).
- Trajectory tracing method: numerical integration of charged‑particle trajectories in combined internal (IGRF) and external (e.g., Tsyganenko) geomagnetic field models to determine allowed/forbidden access.
- Model parameterization: EVCR depends on geographic latitude/longitude, altitude (250 km to 20 000 km), geomagnetic disturbance level (e.g., K-index), and local time.
- Accuracy and validation: calculation techniques should achieve better than 2% accuracy; example results and world grids are provided (Tables B.1–B.4).
- Data generalization and libraries: guidance for building EVCR databases (world grids) and analytic generalization methods to interpolate across disturbance levels, local time and altitude, avoiding infeasibly large tabulations.
- Boundary and acceptance criteria: atmospheric boundary at 20 km (WGS‑84) treated as forbidden; trajectories reaching 15 Earth radii are considered to escape the magnetosphere (allowed).
- Applicability range: for galactic, solar and anomalous charged particle components with rigidity > 0.2 GV.
Applications and users
ISO 17520:2024 is practical for:
- Spacecraft designers and satellite systems engineers assessing radiation penetration and shielding requirements.
- Space weather analysts and mission planners modelling particle access to orbits and manned stations.
- Radiation effects specialists conducting single‑event effect and dose assessments for electronics and materials.
- Researchers building or using cut-off rigidity databases and interpolation software for orbit radiation environment estimation.
- Operators of LEO, MEO and high‑altitude missions requiring standardized input for radiation risk and instrument background analysis.
Benefits include repeatable, validated EVCR calculations that reflect geomagnetic disturbance and local time, enabling consistent assessments of particle penetration and impact on space systems.
Related standards and models
- References to the International Geomagnetic Reference Field (IGRF) and external field models (e.g., Tsyganenko) are integral to ISO 17520:2024.
- The document aligns with work from ISO/TC 20 (Aircraft and space vehicles), SC 14 (Space systems and operations).
- ISO 16695 is cited for internal magnetic field terminology.