The Long-Term Orbit Predictor (LOP) trajectory propagation program is a useful tool in lifetime analysis of orbiting spacecraft. LOP is suitable for studying planetary orbit missions with exploratory (mapping) trajectories. Sample data is included for a geosynchronous station drift cycle study, a Venus radar mapping strategy, a frozen orbit about Mars, and a repeat ground trace orbit.
LOP uses the variation-of-parameters method in formulating the equations of motion. Terms involving the mean anomaly are removed from numerical integrations so that large step sizes, on the order of days, are possible. Consequently, LOP executes much faster than programs based on Cowell's method, such as the companion program ASAP (the Artificial Satellite Analysis Program, NPO-17522, also available through COSMIC). The program uses a force model with a gravity field of up to 21 by 21, lunisolar perturbation, drag, and solar radiation pressure.
The input includes classical orbital elements (either mean or oscillating), orbital elements of the sun relative to the planet, reference time and dates, drag coefficients, gravitational constants, planet radius, rotation rate. The printed output contains the classical elements for each time step or event step, and additional orbital data such as true anomaly, eccentric anomaly, latitude, longitude, periapsis altitude, and the rate of change per day of certain elements. Selected output is additionally written to a plot file for postprocessing by the user.
LOP carries the NASA case number NPO-17052. It was originally released as part of the Cosmic collection.