Case studies

Micro-vibration test device introduced for ESA satellites

The need

Satellites experience vibrations while they are in space, which can reduce the resolution of images and the accuracy of measurements made over great distances. This is a similar effect to taking a photo with a zoom lens and an unsteady hand. The vibrations can be caused by common elements or procedures, such as spinning reaction wheels, solar array drives and rotating cryocoolers. ESA needs to be able to test and correct for these jitters and vibrations to improve the accuracy of its Earth observations.

The solution

To make such testing possible, NPL has developed a micro-vibration platform for ESA that can measure vibrations made by subsystems, or small satellites, to an unprecedented degree of accuracy. It is about 0.7 m diameter and is so sensitive it can measure the force of a single dropped feather. The platform also generates small, controlled forces and torques to shake satellite instruments and components in six degrees of freedom (6DoF). Components and sub-systems can be mounted on the platform and tested before the satellite is assembled and launched into space.

The micro-vibration platform is built as a structure of two main levels: a lower isolation platform and an upper measurement platform. The vibration isolation platform is actively controlled and uses highly sensitive seismometers to sense ground vibrations coming into the system. This controls the actuators which remove the effects of the vibration coming from sources such as footsteps and even waves from the nearby North Sea. This ensures a quiet measurement environment for the measurement platform that is mated on top.

The measurement platform allows two modes of operation:

  • it can measure the forces and torques exerted by a specimen mounted on the test table to micronewton scale

  • it actively produces and directs a pre-defined micro vibration disturbance in multiple axes simultaneously onto a specimen, to test its susceptibility to such disturbances.

The system is housed in a tent to limit perturbations caused by airflow, and can also be used in a vacuum. The instrument will be used to measure and correct for internal vibrations, and to test satellite components under a range of controlled vibration conditions to ensure that they can operate correctly in a satellite environment without affecting other sensitive systems.

The impact

The European Space Agency (ESA) has added a micro-vibration test instrument developed by the National Physical Laboratory (NPL) to its satellite testing facilities. The instrument measures vibrations caused by satellite subsystems, to limit their effects on measurements made from space. This facility is the result of five years of collaboration between NPL and ESA, and demonstrates NPL's capability to design and commission commercial-grade instruments. It helps give confidence to ESA and the European space community in their assessment of the critical area of micro-vibration measurement.

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