Failure detection and analysis is a very important aspect of unmanned and therefore remotely operated spaceflight missions. A dedicated failure detection system for every mechanical part would significantly increase the weight and complexity of a spacecraft. The goal of the SOMID experiment was to develop, build and flight test a failure detection system which monitors multiple components onboard
a spacecraft regarding its correct function or causes of a possible malfunction. As every kind of mechanical event on a spacecraft induces micro-vibrations into its structure, solid-borne sound was chosen as the source of information for SOMID. Accelerometers on the supporting structure and outer hull of the rocket measured generated specific and well-defined events. Those events were created by two valves and a servomechanism which were mounted on the bulkhead of the experiment module. The piezo-based accelerometers were operational during the entire mission, which allowed recording of data from the valves and the servomechanism as well as every other kind of vibration caused during the different phases of flight. The measured data was stored on a flash data storage for post flight numeric evaluation. Laboratory experiments conducted before the launch of the rocket had already shown that every event has its specific frequency spectrum. This spectrum can be used as a method of failure detection on space vehicles. Using the system as an source of information about impacts of micro-meteorites and space debris is also possible. The SOMID experiment was flight tested on the REXUS-12 sounding rocket on the 19th of March 2012. From the scientific point of view the flight of the SOMID experiment was a success. All recorded data from T-570s until the payload impact could be recovered from the onboard data storage. All events in the experiment timeline were triggered at the right time during flight. A first look at the data with a prepared evaluation routine showed, that the quality of the measurements is as expected. In the following months further evaluation will be undertaken to meet the primary scientific goal of the experiment of monitoring all predefined mechanical events on the rocket. Due to the failure of the recovery system it is now a secondary goal to identify, isolate and analyze further, non-nominal events that potentially caused the failure. Upon impact the experiment itself was heavily damaged, although critical components such as the power supply and Microcontroller board are still operational. After the examination of the actual flight experiment is finished, work on the design and construction of a more compact and lightweight monitoring system for mechanical events on spacecraft will begin. If data evaluation shows, that non-nominal events can also be detected by this system, the next steps will be further development and integration into existing systems for the purpose of failure detection.
