BIOMASS is ESA’s Earth Explorer mission dedicated to global forest biomass mapping using a Large Deployable Reflector (LDR) P-band SAR from a dawn–dusk sun-synchronous orbit at approximately 670 km altitude in a quasi-repeat orbit of 3 days and 44 orbits. BIOMASS was launched on the 29th of April of 2025 from Kourou, and the mission spans a 6-month commissioning phase (COM, completed in November 2025), followed by a tomographic phase of about 16 months (TOM, to April 2027) and an interferometric phase of about 42 months (INT, to September 2031). BIOMASS introduces a novel concept to improve coverage by using three different roll profiles phases, reducing the need for frequent repositioning. These three roll profile phases are eventually followed by repositioning maneuvers.

The Launch and Early Operations Phase (LEOP) was longer than usual, with an initial 2-day period for platform operations and a subsequent 6-day phase for LDR deployment. During this time, the Flight Dynamics team at ESOC performed orbit determinations to characterise the injection dispersions and initialise the operational reference orbit; as well as monitored the deployment of the LDR via the evolution of the spacecraft angular momentum. The reference orbit acquisition was relatively straightforward, requiring a total Δv of 4.7 m/s, executed over six manoeuvres to achieve the target sun-synchronous configuration.

During the imaging phase, the scientific requirements for the SAR measurements impose relatively mild constraints on the ground-track absolute control (of 2km) but very tight performance needs on ground-track repeatability of a 3-day cycle in relation to the previous 3-day cycle, with targets of 100 m during TOM and 200 m during INT. This relative ground-track control added complexity beyond the one with a more typical ground-track absolute orbit control. Additionally, an altitude constraint of 500m relative to the reference orbit -previously analysed in a paper for the 29th ISSFD- had to be maintained. These requirements were addressed through a novel orbit control concept involving manoeuvres exactly every 3 days, ensuring optional cycle-to-cycle repeatability but increasing operational complexity.

Pre-launch analysis focused on orbit control for ground-track and eccentricity, as well as the high level of automation required to support the planned 3-day maneuver pattern.

During COM, manoeuvres were prepared to achieve repeated overflights of the ground calibration station under varying drift conditions. Emphasis shifted to refining the orbit control strategy to improve the 3-day repeatability performance and increase automation in the flight dynamics chain. The complexity of the orbit control algorithm and operations required fine-tuning, and an unexpected limitation was identified: manoeuvres with commanded durations below 3.1875 s could not be executed. This prompted a change in the commanding approach, enabling effective manoeuvres with equivalent durations down to about 0.5 s.

In preparation for the imaging phases, where relative ground-track control becomes particularly stringent, the commanding concept was further adapted. Manoeuvre planning was moved from a 2-day to a 1-day lead time to reduce uncertainty from the drag model, and strategies were developed to perform collision-avoidance manoeuvres without interrupting science acquisitions.

This paper reports on the flight dynamics operations from LEOP through commissioning and the preparation and initial months of the imaging phase.