Sherborne Sensors’ inclinometers support RUAG Space

Custom servo inclinometers deliver precision performance throughout testing of new Thruster Orientation Mechanism for satellite platforms

Sherborne Sensors, a global leader in the design, development and manufacture of sensors for military, aerospace and industrial applications, has helped RUAG Space, Europe’s largest independent supplier of space technology, to complete life test qualification of its innovative satellite Thruster Orientation Mechanism (TOM). Sherborne Sensors supplied a special variant of its LSI Servo Inclinometer to deliver precision performance throughout three months of rigorous testing under extreme temperature and thermal vacuum conditions.

Pointing mechanisms and electrical propulsion (EP) thrusters are used by commercial satellites for moving from launch orbit into their real orbit and to perform micro-positioning manoeuvres. RUAG’s new TOM simplifies the overall design of a satellite by having two TOMs instead of the eight stationary thrusters units employed in conventional designs. Sherborne Sensors’ LSI Servo Inclinometer was mounted on the TOM qualification model in order to perform three key tests – mechanical pointing accuracy, potentiometer verification and motor margin – in a large vacuum chamber, where an extremely low pressure of 10-7 mbar (known as a ‘hard vacuum’) is achieved to simulate the in-orbit environment.

“Finding measurement devices capable of operating at this very low pressure is not easy to do,” says Andrew Skulicz, AIT Engineer at RUAG Space. “The most important aspect was that they were able to operate between -40°Fand +104°F under hard vacuum conditions. Sherborne Sensors was the only company that could provide us with inclinometers that covered the range that we wanted, together with accuracy of better than +/-0.05°. The inclinometers on the TOM not only successfully operated throughout a sequence of thermal vacuum cycles, but also sustained that operation for nearly three months while the mechanism was undergoing its life test.”

Sherborne Sensors was careful to ensure the inclinometers did not contain any compounds that would suffer the outgassing of organic compounds such as adhesives and rubber, while providing the case of the inclinometer with a vent to counter the effect of differential pressure between the sealed case of the inclinometer and the vacuum conditions it was used in. With the test results demonstrating and verifying the TOM’s performance against everything it can reasonably expect to experience from manufacture through mission to end-of-life, RUAG’s TOM programme represents the cutting edge of the European scientific community and is approved by the European Space Agency (ESA).

“Our customisations ensured that there was no danger of any minor leaks destroying the high vacuum conditions over time, as well as relieving any mechanical stresses that could occur during de-pressurisation,” adds Mike Baker, managing director at Sherborne Sensors. “The LSI was also characterised for performance over the applications operable temperature range to give a high degree of accuracy. We also provided RUAG with a ‘look-up’ chart listing the individual temperature errors over the complete range of environmental temperatures expected to be met in the application. This enabled RUAG to correct in real time for the effects of temperature and deliver more accurate results.”

About
RUAG Space has developed a new type of thruster orientation mechanism (TOM) that simplifies the overall design of a satellite by having two TOMs instead of the eight stationary thrusters units employed in conventional designs. Each TOM features one or two thrusters mounted on a gimbal structure and is powered by actuators. Able to support the largest range of thruster combinations and thruster mass in the market today, RUAG’s TOM means only a quarter of the normal amount of Xenon tubing is required to supply fuel to the electrical propulsion thrusters.

The nature of RUAG’s TOM design means it has to accommodate the environmental loads induced during launch and spacecraft separation from the launch vehicle, as well as the extreme of temperature experienced in space. It has therefore been subjected to a design qualification test programme that entailed a series of rigorous functional and performance tests in order to demonstrate and verify its performance against everything it can reasonably expect to experience from manufacture through mission to end-of-life, which could be ten years or more.

Sherborne Sensors’ LSI Servo Inclinometers were used to measure the pointing vector of RUAG’s TOM with respect to a reference frame, with accuracy to higher than 0.05° being essential. The performance of the potentiometers was also checked under different thermal conditions to ensure they could return accurate telemetry back to the spacecraft, while motor margin tests were conducted to verify the performance of the on-board stepper motors did not degrade. The inclinometers were used to verify the performance of the potentiometers over the full angular range of -14°/+34° and to detect if the motor looses steps with an accuracy of at least 0.01°.

About RUAG Space
As the largest independent supplier of space technology in Europe, RUAG Space develops, manufactures and tests subsystems and equipment for satellites and launch vehicles. From our locations in Switzerland, Sweden and Austria RUAG's space division offers a comprehensive portfolio of products and services for institutional and commercial space missions. Heritage and flexibility as well as outstanding reliability have made RUAG Space a long lasting partner of choice for satellite and launcher primes worldwide. Visit: www.ruag.com/space

About Sherborne Sensors
Sherborne Sensors is a global leader in the design, development, manufacture and supply of high‐precision inclinometers, accelerometers, force transducers and load cells, instrumentation and accessories for industrial, military and aerospace customers. Products are supplied under the AS9100B Quality Accreditation and are renowned for their ultra‐reliability and long‐life precision within critical applications. Sherborne Sensors can customise any of its wide range of products to conform to specific customer requirements. All Sherborne Sensors’ products are thoroughly tested and calibrated to international standards at the factory prior to shipment and are accompanied by an industry exclusive two‐year comprehensive warranty and Guaranteed On‐Time Delivery programme. For further information go to www.sherbornesensors.com