Modeling and Control for Distributed Measurements of the Earth's Energy Imbalance
This paper presents a modeling and control framework for distributed systems in low Earth orbit, with the scientific objective of obtaining high accuracy estimates of the Earth's Energy Imbalance (EEI). This metric robustly quantifies the difference between the absorbed solar radiation, and the infrared radiation emitted into space. Formally, the EEI represents the globally and annually integrated net radiative flux at the top of the atmosphere. The EEI is directly correlated with physical variations in the Earth system. Obtaining accurate measurements hereof poses a major technological challenge, attributed to calibration errors of current spaceborn radiometers. This work presents a modeling and control framework for in-orbit EEI monitoring and mapping with high precision, using a distributed array of spherical spacecraft. Perturbations and their effects on orbit and attitude are modeled, accounting for spacecraft shape and thermo-optical properties, and are subsequently used to derive optimal control for maintaining an appropriate spin rate. This enables each spacecraft to align closely with the orbital normal with coordinated attitudes across the formation, leading to improved spatiotemporal resolution in EEI estimation.