The objective of the project was to upgrade to space level requirements an existing commercial pressure transducer design providing a desired accuracy below 0.05%FS and to qualify it for space usage.
In order not to degrade the performances through a poor resolution in the data handling system for telemetry a digital interface was required.
To be competitive on the international space market, the pressure transducer should have low power consumption, low weight, small size and low cost.
Main challenge of the project was to upgrade a commercial pressure transducer for space applications, thereby improving the measurement technology to comply with the stringent accuracy requirements.
With the overall satellite lifetime increase of requirements, next generation platforms desirable highly accurate predictions on the remaining propellant, such 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 Bradford High Accuracy Pressure Transducer can be used a key element for the widely used PVT methodology, thereby strongly improving the gauging accuracy of this technology.
Apart from the commercially attractive feature of two gauging parameters in one unit, the design is generic for a variety of pressure ranges and is flexible for adaptation to customer specific requirements. This makes it a highly qualified cost-effective off-the-shelf component.
Under ESA contract, Bradford Engineering has developed a Pressure Transducer with measurement accuracy that is two orders of magnitude better than most common designs and is compatible with the full range of satellite propellants.
The PT was successfully qualified against all applicable functional and environmental requirements, with a demonstrated end-accuracy of £ ±0.01% Full Scale. An additional feature is the possibility of providing a temperature output with accuracy £ ±0.5°C, from the available data.
The design utilizes a piezo-resistive sensing element. In order to obtain the desired accuracy, innovative low cost signal processing electronics have been developed. In order to create an accurate and reliable electronics system, most of offset/drift and common mode effects of the electronics are eliminated internally by taking multiple measurements. The sensing element is digitally compensated by a 7x5th order polynomial approximation to take into account temperature drift and non-linearities of the sensor. The polynomial coefficients are obtained through an accurate calibration, which aims at a pressure error band level of ± 0.005% FS.
The QM design provides a weldable Titanium interface to the propellant tubing, where sealing of the propellant is provided by a fully welded design. Dedicated compatibility tests have shown compatibility with all major satellite propellants.
Baseline dimensions are 125x Ø39mm and the mass budget is maximum 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 propellant compatibility test to verify compatibility of the design with satellite propellants.
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 and pressure gauging applications in general.
From the High Accuracy Pressure Transducer (HAPT) design, a cost attractive Standard Accuracy Pressure Transducer (SAPT) has been derived, which uses simplified (analogue) electronics and has a demonstrated accuracy of £ ±0.1% Full Scale pressure output.
Heritage of the Bradford PT design is in the meantime available for multiple space programs.