Real-Time Modeling of Albedo Pressure on Spacecraft and Applications for Improving Trajectory Estimation and Earth’s Energy Imbalance Measurements

Albedo is the electromagnetic energy from the Sun that is received and either reflected or radiated from the Earth. This energy is similar to Solar Radiation Pressure received directly from the sun but is less in magnitude and results in a near radial pressure vector from the direction of the Earth. Thermal radiation is produced continuously, even during shadowed portions of the orbit. Although it is a relatively small pressure force, proper modelling of this disturbance can better help in modeling the trajectory of spacecraft. This paper examines a method to model both short and longwave radiation from the Earth and determine the net force vector applied to the spacecraft at any point in time. The resultant force can be integrated over each orbit to examine the effect of Earth radiation on the spacecraft trajectory. Models for the Earth and orbits are simulated using the JPL MONTE tool. Results for the expected Earth radiation pressure are presented for a spherical spacecraft that is being designed to more accurately measure the Earth’s Energy Imbalance (EEI) or net radiative flux at the top of the atmosphere. By accounting for near-real time variations in earth radiation pressure, more accurate simulations can be made of the net radiative flux (incoming solar minus Earth outgoing radiation) experienced by the Earth orbiting spacecraft. Such a direct measurement of EEI is envisioned to help answer the question of how fast our planet is warming over time.