Since its arrival at Europe’s Spaceport in French Guiana three weeks ago, ESA’s Biomass satellite has been under the scrutiny of satellite engineers who have been carefully executing the long list of tasks on the ‘to do’ list to make this new Earth Explorer mission ready for liftoff on 29 April. The latest milestone passed, is that Biomass’ propulsion subsystem has been prepared for fuelling and has undergone thorough system checks.
The check-out process was carried out by the OHB-Sweden team, who impressively managed to complete their tasks a full day ahead of schedule.
For those interested, here’s some engineering details
The propulsion subsystem consists of several metres of tubing, ensuring that the hydrazine propellant, stored in the 177-liter tank, reaches all eight thrusters. These thrusters are arranged in pairs at the four corners of the satellite.
To regulate propellant flow and facilitate fuelling and pressurisation, the system incorporates multiple valves, including flow control valves, latching valves, and service valves.
Each thruster is safeguarded by two flow control valves positioned in series—both of which must be opened when the thruster is firing. For safety, these valves remain closed by default; unless powered, internal magnets keep them shut.
The system is further divided into two thruster branches, each containing four thrusters, isolated from the main tank by latching valves. These bistable valves maintain their state—either open or closed—until actively switched, allowing controlled isolation or activation of an entire thruster branch.
At this stage, all valves have been rigorously checked for leaks. The leak testing process involves pressurising one side of a closed valve with helium while creating a vacuum on the downstream side. A helium detector then measures any traces of gas that pass through. Given the internal volume and surface area involved, these tests require considerable time and precision.
With the propulsion system successfully passing all checks, the satellite is now safeguarded against propellant loss once loaded, ensuring its readiness for propellant fuelling.
While testing the propulsion subsystem is a meticulous and time-intensive task, it remains a crucial step in preparing for liftoff on a Vega-C rocket on 29 April.
And back to the general stuff
Once in orbit and commissioned, Biomass mission will play a key role in delivering novel information about the state of our forests, how they are changing over time, and advance our knowledge of the carbon cycle. It is the first satellite to carry a fully polarimetric P-band synthetic aperture radar for interferometric imaging. Thanks to the long wavelength of P-band, around 70 cm, the radar signal can slice through the whole forest layer to measure the ‘biomass’, meaning the woody trunks, branches and stems, which is where trees store most of their carbon.
