Determining Ionizing Doses in Medium Earth Orbits Using Long-Term GPS Particle Measurements

TL;DR

This study uses long-term GPS satellite measurements to assess ionizing radiation doses in medium Earth orbits, comparing real data with models to evaluate their accuracy and reliability.

Contribution

It provides the first comprehensive comparison of in-situ measurements with empirical radiation models in MEOs, highlighting discrepancies and model reliability.

Findings

Electron TID exceeds model median/mean predictions

Proton TID contributions are minor in MEOs

Model fluences align with measurements at high percentiles

Abstract

We use long-term electron and proton in-situ measurements made by the CXD particle instruments, developed by Los Alamos National Laboratory and carried on board GPS satellites, to determine total ionizing dose (TID) values and daily/yearly dose rate (DR) values in medium Earth orbits (MEOs) caused by the natural space radiation environment. Here measurement-based TID and DR values on a simplified sample geometry--a small (with a radius of 0.1 mm) Silicon detector within an Aluminum shielding sphere with a thickness of 100 mil--are compared to those calculated from empirical radiation models. Results over the solar cycle 24 show that electron TID from measurements in GPS orbit is well above the values calculated from the median/mean fluences from AE8 and AE9 models, but close to model fluences at high percentiles. Also, it is confirmed that in MEOs proton contributions to TID are minor and mainly dominated by solar energetic protons. Several factors affecting those dose calculations are discussed and evaluated. Results from this study provide us another out-of-sample test on the reliability of existing empirical space radiation models, and also help estimate the margin factors on calculated dose values in MEOs that pass through the heart of the Earth's outer radiation belt.