Eclipse-Free-Time Assessment Tool for IRIS

can be used to perform an Eclipse-Free-Time (EFT) assessment of IRIS (Infrared Imaging Surveyor) mission orbits. EFT is defined to be those time intervals longer than one day during which the IRIS spacecraft is not in the Earth’s shadow. Program IRIS_EFT implements a special perturbation of orbital motion to numerically integrate Cowell’s form of the system of differential equations. Shadow conditions are predicted by embedding this integrator within Brent’s method for finding the root of a nonlinear equation. The IRIS_EFT software models the effects of the following types of orbit perturbations on the long-term evolution and shadow characteristics of IRIS mission orbits: