27 March 2012
UK inclinometers used for satellite thruster orientation mechanism
London based Sherborne Sensors' inclinometers are being used by Europe's largest independent suppliers of space technology, to complete life test qualification of a satellite thruster orientation mechanism (TOM).
Sherborne supplied a special variant of its LSI Servo Inclinometer to RUAG Space, in a bid to provide precision performance throughout three months of rigorous testing under extreme temperature and thermal vacuum conditions.
Pointing mechanisms and electrical propulsion thrusters are used by commercial satellites for moving from launch orbit into their real orbit and to perform micro positioning manoeuvres. RUAG's TOM is designed to simplify the overall design of a satellite by having two TOMs instead of the eight stationary thrusters units employed in conventional designs. Sherborne's 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 and 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 needed 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. According to RUAG, its TOM programme represents the cutting edge of the European scientific community and is approved by the European Space Agency.
"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 depressurisation," added 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."