European Space Agency

Ultrasonic Flow Meter (UFM)


The objective of the project was to design, manufacture and qualify a high accuracy flow meter for a liquid propulsion system. The flow meter should be non-intrusive in essence and should be able to measure the flowrate of propellants feeding the thrusters with a target accuracy better than 0.1%FS during the Liquid Apogee Engine Firing (LAEF).

On geostationary telecommunications satellites, the use of accurate flow metering during the main engine firing would considerably improve the knowledge on remaining propellant at beginning of life and thus improve the on-orbit propellant monitoring. Flow meters are already being embarked on the U.S. satellite TELSTAR-4 (Pitot design) and on the Japanese satellite ETS-VI (Turbine flow meter).

The advantages of the ultrasonic solution are its non-intrusive nature and potential accuracy. The typical flow meter package comprises an ultrasonic sensors assembly with the associated control electronics.


Main challenge of the project was to upgrade commercial UFM equipment for space applications, thereby improving the signal processing electronics to comply with the stringent accuracy requirements.


As LAEF consumes more than two thirds of the propellant masses, a direct mass flow measurement during geostationary transfer represents a gain in the global end accuracy. More accurate predictions on the remaining propellant means that de-orbiting of the satellite can be accurately forecasted, hence replacement planning becomes far more efficient and might lead to a reduction of the amount of SpaceCraft. The demonstrated uniquely high mass flow measurement accuracy of the design (representing a gain in propellant mass), combined with its low power consumption (<1 Watt) and weight make the equipment highly attractive as an add-on for propellant gauging on telecom satellites.

In addition, flexibility of the design has been aimed at a minimization of re-current unit costs.


Under ESA contract, an Ultrasonic Flowmeter (UFM) has been developed that provides a highly accurate direct measurement of the propellant mass flowrate consumption in a bi-propellant propulsion system with negligible pressure losses.

The UFM equipment was successfully qualified against all functional and environmental requirements, with a demonstrated end-accuracy of £ ±0.05% Full Scale, for both Liquid Apogee Engine (LAE) Firing (range 40 to 170 g/s) and Reaction Control Thruster (RCT) Firing (range 1 to 10 g/s). Life propellant tests have demonstrated its abilities to measure the actual range of satellite propellants used in bi-propellant propulsion systems.

The UFM design can be directly welded in the propulsion tubing system and is flexible for adaptation to customer specific interfaces. The QM model design uses all Titanium wetted parts, yielding into a mass for the unit (excluding electronics) of less than 200 grams.  


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During the programme, a Development Model (DM) was manufacturing and tested, followed by the manufacturing and qualification testing of a Qualification Model (QM). The qualification tests have taken into account typical telecommunications satellites requirements and encompassed a life propellant test to verify the ability of the equipment to measure actual satellite propellants.

Current status

Under the contract, qualification has been successfully closed and all objectives of the development program have been met. The design can be directly implemented as is for use on geostationary telecommunication satellites.

Status date

Tuesday, May 26, 2009 - 12:15