The Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) mission is a high-priority mission under the Copernicus Sentinel Expansion program. It is designed to monitor global atmospheric carbon dioxide (CO?), methane (CH4) and nitrogen dioxide (NO2) emissions specifically from human activities. The constellation is composed of three spacecraft (CO2M-A, CO2M-B & CO2M-C) flying in a sun-synchronous low Earth orbit with an 11-day cycle comprising 159 revolutions, and a local time at the descending node (LTDN) of 11:30 UTC. The spacecraft are injected into the same orbit with certain in-plane phasing between them. At the time of writing, the launch of CO2M-A is planned for mid-2027.
 
The main observation modes for the CO2M mission are Nadir with Yaw Steering and Sun-Glint. These modes define the attitude profiles the spacecraft adopts to acquire scientific data. The Nadir profile is designed for observations performed when flying over land, whereas the Sun-Glint profile is employed for observations performed when flying over ocean surfaces.
 
Whereas the Nadir Yaw steering profile is an attitude profile flown by several missions operated by EUMETSAT, the Sun-Glint profile introduces a novel operational concept. The goal of the Sun-Glint observation mode is to maximize the radiance in the sensors. This is achieved with pitch angle values optimized by the Cox-Munk model (with 7 m/s wind speed). Illumination conditions are driven by the beta angle. Its variability introduces a seasonal shift of the profile with boundary conditions the summer and winter solstices.
 
Based on the above, a reference pitch profile is defined and stored on-board as Chebyshev polynomials. This profile can be applied year-round by introducing the appropriate seasonal offset, which is maintained on-board as a look-up table. To account for maximum angular accelerations, this reference profile has been smoothed. Additionally, upper and lower plateaus have been introduced to maximise radiance at high and low altitudes, while a central plateau to minimises transition times between Sun-Glint and Nadir modes. Finally, a yaw steering computed on-board is applied.
 
In addition to the main observation modes, the spacecraft supports an Extended Sun-Glint profile and attitude-guided profiles. The Extended Sun-Glint profile features increased pitch bounds to meet the constraints required for the MAP Sun calibration. Attitude-guided profiles are designed for slews associated with payload calibrations. These profiles are commanded as Chebyshev polynomials computed on ground.
 
As stated above, the Sun-Glint and Attitude Guided profiles introduce a new paradigm in attitude modelling at EUMETSAT. Limitations imposed by the NAPEOS software currently in operation have driven the adoption of modern technologies and libraries to enable the implementation of these advanced attitude profiles.
 
GODOT is an astrodynamics library developed by ESA/ESOC for mission analysis and in-flight operations. Its implementation combines both C++ and Python, introducing a new paradigm through the concept of the “Universe,” which consists of modular plugins (e.g., the frame plugin). The library’s architecture is highly extensible and incorporates the concept of “evaluables” (such as TimeEvaluables and ScalarEvaluables), eliminating the need for file-based precomputations typically required as inputs for other tools.
 
The first part of this paper outlines the objectives of the CO?M mission and its requirement to support multiple attitude modes. The second part details how the modelling of these attitude profiles has been implemented by EUMETSAT Flight Dynamics as an extension to the GODOT library’s frame plugin.