Vibration Testing – CyanoSat Engineering Model

Vibration testing is an important step in the development of any payload design for space operation. The objective of the test is to prove that the payload would survive operational and launch loads. It is a reliable and time-tested method with carefully defined standards for different types of payloads being tested.

The test simulates the real-life conditions of the launch, and cycles through various test methods and conditions to gather information related to the resonant frequency of various components of the payload to assist in the identification and evaluation of possible mechanical, design or performance flaws.

CyanoSat Engineering Model was tested at CSIRO’s Infrastructure Technologies vibration test facility at CSIRO’s Clayton North campus. This facility is operated by the CSIRO Fire Systems Laboratory, which is NATA-accredited for a range of vibration tests. The facility can conduct many of the standard space/launch related test methods. We thank Christopher Preston and Dung Ngo, of CSIRO Services – Infrastructure Technologies, for helping the team setting up and running the test.

The test facility operates an LDS V824 electrodynamic shaker powered by a 32 kW amplifier. The shaker may be rotated and connected to a 900×900 mm magnesium plate slip table, allowing vibration to be applied in the vertical or horizonal direction. The shaker can deliver up to 26 kN of force, at accelerations of up to 100 g, or at velocities of nearly 2000 mm/s. Maximum static loads of up to approximately 300 kg (vertical) or 1000 kg (horizontal) are able to be accommodated. The shaker and trunnion holding the slip table are fitted with pneumatic isolation units, isolating the reaction forces developed by the 5 tonne combination from the surrounding laboratory floor.

Vibration tests were performed in each of the three orthogonal axes (X, Y, and Z). A control accelerometer was placed on the shaker platform near to the test item, with additional accelerometers placed on the backs of each mirror to record the motion of mirrors themselves.

The test program included a series of tests in each of the three axes including:

• low-level (sine) resonance search (LLRS), in which the shaker varies the applied sinusoidal vibration between 20 and 2000 Hz at a fixed sweep rate (specified in octaves/minte) at a low amplitude (acceleration),
• random intermediate and full qualification random vibration, simulating launch conditions.

During each of the LLRS tests, transmissibility signals – the ratio between the control and response (i.e. mirror-mounted) accelerometers, were collected. Comparisons of these LLRS spectra before and after random vibration tests permitted identification of potential changes or damage to the test item.

The test plan was prepared by Nick Carter, based on space-industry standards, including specifications for environment, setup, instrumentation, test levels, test runs, and safety protocols.

The team is satisfied with the results. The observations were matching expected values and provided enough information to drive confidence and improvements in the current design.

The test unit was probed both before and after the test using a Coordinate Measuring Machine, at Clayton CBIS, to assess and quantify any test damage and design or manufacturing flaws. It was found that the mirrors have an offset of a few hundred microns to the designed position, possibly resulting from the combination of indentations that were observed after the vibration test at the point load joints and some manufacturing flaws.

The team looks forward to analysing these CMM results and implementing necessary modification to the current design to improve upon the already excellent results so far measured using the CyanoSat imager.

For more information on this capability and services, please contact Christopher Preston at Christopher.Preston@csiro.au.