340 Two further minor anomalies were recorded for the cooler system . On Dec ember  13, 2002 there  appeared to be a transient transition to the ‘door -bell’ mode of the cooler (when the displacer B  piston  repeatedly strikes the end- stop of the body) . The displacer being driven by the pressure wave was very  near to full stroke and a small change in the amplitude resulted in this behavior . This could have been  initiated by ambient temperature changes or small changes in fill pressure, etc . Telemetry was triggered  by the displacer B amplitude which automatically turned off the coolers . The cooler was restarted after  some testing and has continued to operate successfully.  

A third cooler anomaly was similar to the previous one,  having occurred on July 28, 2009. In this case , it  was not possible to reactivate the cooler at the same unbalanced pre- anomaly setting (amplitude ratio of  82.5%) . A slight modification was made to allow the cooler to continue to run with t he B side compressor  at 77.5% of normal amplitude; avoiding end -stop contacts (with ~0.5- mm margin) with the side B  detectors heating at a slightly higher  rate. The cooling rate on the working side (A) was unchanged. This  mode of cooler operation induces a little more vibration but with a negligible impa ct on the spacecraft .  Only the MISR instrument has reported a  vibration induced effect and this was at a very low level .   Over the past  16 years , the Kistler AG piezoelectric accelerometers have recorded vibration  outliers as  short, high intensity signals , strongly  correlated with the high energy  radiation environment. Previously  noted by Nichitiu [ 8], the accelerometers integrated into the cooler system have been demonstrated to  provide a bonus measurement of space radiation. As a multi- component force transducer, the tri -axial  accelerometers consist  of a stack of quartz discs or plates and electrodes , with quartz disc s cut in an  appropriate axis . The orientation of the sensitive axes coincides with the axes of force components to be  measured. An internal charge- to-voltage converter provides a low impedance output.  During normal  operation, there are short fluctuations (spikes lasting for only one telemetry sample), which appear as an  increase in the level of vibration exceeding 4 sigma [8]. The sensor typica lly records  a normal level within   8 seconds  afterwards , the time between two consecutive telemetry samples.  These spikes, or accelerator  outliers, occur mo st often for the z -direction  compressor vibrations . Outliers occur for other directions and  for the displacer  accelerometer, but their rate is very low.    The occurrence of the z -direction compressor  transducer outliers is well described by a decreasing  power -law as a function of  magnitude. The spatial distribution of these observations is provided in Fi gure  13, showing accelerometer readings correlating significantly with the South Atlantic Anomaly (SAA) [8] .

The high energy  particles - the source of anomalous accelerometer signals  - are localized mainly in the  SAA region, while  the polar regions, partic ularly the southern pole, are associated with a higher risk  for  satellites during intense solar proton events .  

Figure 13.  Accelerometers Anomalies Due to S pace Radiation (I ncl. SAA)