Satellite Radiation Dose vs. Shielding

Trapped-electron + bremsstrahlung + proton dose vs. aluminum depth, tuned to SHIELDOSE-2 reference points. A first-order screen for shielding trades and part-tolerance selection - run AE9/AP9 + SHIELDOSE-2 in SPENVIS for the design value.

This calculator estimates the dose-depth curve - total ionizing dose (TID) versus aluminum shielding thickness - for any orbit from low Earth orbit (LEO) to geostationary (GEO), summing trapped electrons, the bremsstrahlung X-rays they generate in the shield, and trapped-plus-solar protons. It is a parametric analytic model tuned to reproduce published SHIELDOSE-2 reference points (Seltzer 1994), with belt geometry vs. altitude and geomagnetic screening vs. inclination built in - a first-order screen for shielding trades and part-tolerance selection. The design value still comes from AE9/AP9 + SHIELDOSE-2 run in SPENVIS.

Every electronic part has a total-ionizing-dose (TID) tolerance, measured in krad(Si) - the accumulated dose at which it stops working reliably. The mission's job is to keep the dose behind the shielding below that number. The relationship between shield thickness and dose is the dose-depth curve, and it is the first thing a radiation engineer builds for a new orbit. This tool estimates it.

The dominant driver is altitude, because it sets which radiation belt you sit in. LEO below ~800 km sees only the inner-belt tail and South Atlantic Anomaly passes - a benign few krad/yr behind a couple of millimetres. The MEO region around 20,000 km (the GPS / O3b belt) is the worst place to be: it sits in the heart of the outer electron belt and can exceed 100 krad/yr thin-shielded. GEO at 35,786 km is electron-dominated at tens of krad/yr. Inclination matters too: Earth's magnetic field deflects charged particles, so a low-inclination orbit is better screened than a polar one that runs through the belt horns and polar cusps.

The dose-depth curve has a characteristic shape driven by three sources. Trapped electrons dominate at thin shielding and attenuate steeply (short range in aluminum), so the curve falls fast over the first few millimetres. Protons - trapped plus solar - attenuate more slowly and take over at depth. Bremsstrahlung - penetrating X-rays generated when electrons stop in the shield - barely attenuates at all and forms the deep-shield floor. The practical consequence is diminishing returns: in an electron-dominated orbit the first 2-4 mm of aluminum buys most of the reduction, and beyond ~5-10 mm you are fighting protons and the bremsstrahlung floor. That is why spot-shielding a few sensitive parts usually beats shielding the whole box.

What this tool does not do: it is a parametric analytic model, tuned to reproduce published SHIELDOSE-2 reference points, not a physics-first transport code. Real design uses AE9/AP9-IRENE for the trapped-particle environment and SHIELDOSE-2 (in SPENVIS) for the dose-depth integral, followed by a geometry-specific 3D sector-shielding analysis of the actual spacecraft - a slab model like this one assumes uniform shielding in all directions. It also does not model displacement damage (a separate failure mode from TID), single-event effects (see the companion single-event-effect rate tool), or solar-particle-event worst-case transients. Treat the numbers as a first-order screen for shielding trades and part-tolerance selection.