The objective of this activity is to assess the feasibility of a high-resolution accelerometer in order to increase the station keeping autonomy in relation with the electric engine of the @BUS platform.
The accelerometer would be used to measure the East/West drift of the satellite during the North/South thrusts. It would permit to define in real-time the maximum North/South thrust time in order to obtain an acceptable East/West drift while not requiring control from ground stations.
The key issues of the study are:
- The compatibility of the mechanical concept with the launch vibration,
- The compatibility of the accelerometer servo-control with the flight micro-vibration environment,
- The design of a concept that matches the requirements of compactness in terms of mass, volume and power consumption.
The current project will lead to the implementation of a versatile and high-performance accelerometer exhibiting nano-g resolution.
- Acceleration sensed along 3 translation axes,
- An operating range covering 5 orders of magnitude from 2Ã—109 g to 5Ã—104g The accelerometers will fit in a compact packaging:
- Small volume of 1.5dm3, 15cmÃ—10cmÃ—10cm,
- A total mass lower than 2kg,
- A total power consumption of 6W including the DC/DC converters, with a ready-to-use integrated MIL-STD-1553B interface.
The accelerometers will be manufactured with space-qualified parts and in accordance with the ESA procedures to achieve a high-reliability instrument with a life duration compatible with the telecom requirements.
The instrument is delivered after series of tests and calibrations.
The accelerometer is servo-controlled and electrostatic.
It is based on the electrostatic levitation of a 20g proof-mass inside an electrode cage. Capacitive position sensors detect the displacements of the proof-mass, deliver the information to the servo-control which in turn maintains the proof-mass at the centre of the cage by applying the appropriate potentials on the electrodes.
The mechanical core is mounted on a reference sole plate and enclosed in a hermetic housing. The front-end electronics surrounds the housing: it consists of 6 capacitive sensors and 6 analog correcting networks for controlling the motion of the proof-mass along the 6 degrees of freedom.
The acceleration analog estimate is digitised and transmitted to the satellite through a MIL-STD1553B bus.
The activity focuses on the concept definition and performance model of the accelerometer including:
- Preliminary global architecture (with respect to the mechanical and electronic parts),
- Sensor dimensioning (with respect to the mechanical and thermal environment),
- Demonstration of the launch mechanical loads withstanding without locking device,
- Definition of operational environmental envelope (mechanical, EMC/ESD, magnetic, thermal),
- Establishment of a mathematical model for system analysis (including noise PSD, bias and scale factor, stability and non linearity).
The first phase of the activity has been successfully completed, showing the feasibility of a new concept using accelerometers for increased on-orbit autonomy. For Alphabus an alternative option has been chosen to achieve on-orbit autonomy, and it has therefore been decided not to pursue the activity.