LIFE TEST OF THE SCARAB INSTRUMENT SLIPRING UNITS

The SCARAB instrument was designed by the Laboratoire de Meteorologie Dynamique in the late 80’s to study the radiation budget of the Earth from space. As part of the French-Soviet research program, the FM1 instrument was put into orbit, in February 1994, onboard a Russian platform for a 2-year mission. Unfortunately, the radiometer failed one year later. The CNES investigated the potential causes of the mission loss. This work was very difficult mainly because the onboard observable parameters were poor. However, the failure assumptions were all related to slipring units’ performances. This is why a number of slipring changes were defined and implemented. A new qualification program was mandatory including vibration loads and a lifespan test. An optical head model was used in order to faithfully reproduce the flight environments and apply them to the sliprings. The life test was performed at the rated speed, that is to say a 3-year test, which included qualification margin. Meanwhile, the FM2 model was launched. It delivered only one year in-flight measurement data. The mission was stopped in April 1999 when the satellite data transmitters broke down. However, the FM2 instrument is still normaly working today. The life qualification test closed up in August 2000. The results recorded during the test showed the sliprings successfully performed except for the line electrical resistance increase over life and the end of life (EOL) noise level. The hardware inspection revealed no serious damage, but a normal material wear in the sliprings and the bearings. The life test has permitted us to build an engineering database that will be at designers and users disposal for future projects using this electrical contact technology.