Goddard Enhanced Onboard Navigation System (GEONS) 3.1 Mathematical Specifications

This document details the mathematical algorithms implemented in the Goddard Enhanced Onboard Navigation System (GEONS). GEONS is an enterprise, multi-mission, flight software library for onboard, autonomous spacecraft navigation in real-time. GEONS includes tools for simulation and analysis of navigation systems on the ground. GEONS does not include any data or features that are specific to any particular mission. The user must configure GEONS, at compile time and at run time, for the specific application. This configurability enables GEONS to be used for a wide variety of mission types and allows the user to optimally balance computation time, memory, and navigation accuracy for the considered application. For flight applications, the GEONS flight software can be integrated either within a GPS receiver, a communications receiver, or an onboard computer.

GEONS is written in ANSI standard C with object-oriented techniques, and it uses a UD-factorized extended Kalman filter (EKF) architecture. GEONS can process measurement data from GPS receivers, ground stations, spacecraft crosslinks, cameras, LiDAR, accelerometers, and attitude sensors to provide high-accuracy solutions for spacecraft position, velocity, and time. The software has high-fidelity dynamics models, including non-spherical gravity, third body gravitational perturbations, solar radiation pressure, atmospheric drag, process noise models, and clock error models. Additional capabilities include fault detection, time and coordinate transformations, consider covariance parameters, and estimation of measurement biases and force model parameters.

The core GEONS algorithms and software have over 20 years of flight heritage. Previous versions of GEONS have successfully flown on the following NASA missions: Magnetospheric Multiscale (MMS), Global Precipitation Measurement (GPM), Neutron Star Interior Composition Explorer (NICER), and Starling. Additionally, GEONS has been baselined to provide onboard navigation for multiple upcoming missions. Although GEONS has only flown on Earth orbiting missions to date, it can support a wide range of orbit regimes including cislunar space and beyond.