Monday

Electric propulsion technology now enables satellite operators to achieve geostationary orbit without the use of chemical propellant via electric orbit raising. This enables lower cost access to space by reducing mass, but necessitates a longer (~200 day) raising period, during which satellites pass through the hazardous radiation environment of the Van Allen belts.

Increased radiation exposure during electric orbit raising must be accounted for by mission planners through the use of environment models such as NASA’s AP9/AE9. However, case studies such as the CRRES mission show that our predictive capability is limited by the drastic changes to the proton (inner) belt and slot region that can occur in a large solar energetic particle trapping event. Such changes raise the risk for shielding to be under-designed.

We show the accumulation of damage calculated by a range of models in terms of non-ionising dose for a variety of electric orbit raising scenarios that have been used to date, and discuss how varying key parameters affects the result. We use the reduction in solar cell performance as a measure of degradation, with the dominant contribution coming from 3 – 10MeV trapped protons.

In particular, we show that the trajectory, solar cell coverglass thickness and state of the proton belt can affect solar cell degradation accrued during electric orbit raising and before the beginning of service by up to ~10%. We conclude that more real-time information is required on the transient nature of the proton belt’s outer region to help assess radiation damage.