Double Star Active Archive - STAFF-DWP Data errors and reprocessing Keith Yearby and Hugo Alleyne University of Sheffield Nicole Cornilleau-Wehrlin LPP

Boom deployment failure + Resets The STAFF antenna boom failed to deploy which means interference is very high, particularly below 100Hz. The worst affected datasets (10Hz waveform data and spectral matrix data) will not be archived in calibrated form, but could be accessed from the raw data. Power spectral density data is processed to synthesise a single axis measurement aligned for minimum interference. This is then integrated over 4 seconds (about one spin) to provide a reasonably isotropic measurement. Particle correlator data is not affected by the interference. Single event upsets (SEU) occur at a rate between one every ~500 hours above L=2.5, increasing to about one per hour at L=1.5. These are corrected by the watchdog, and normal operation restored in less than one second. Very little impact on data quality.

Spacecraft telemetry errors The Double Star raw telemetry data is released to instrument teams even when it contains uncorrected transmission errors. There are no flags or check bits to indicate that uncorrected errors may be present. –It would be extremely useful if an ‘uncorrected errors’ flag could be provided in the raw data header during reprocessing. This should be available as an output from the Reed Solomon decoder. The best we can do at present is to check that the data is correctly formatted and within the bounds of what the instrument can physically measure. Data containing transmission errors can occasionally fall through these checks. Errors will typically appear in the PSD or ACF data as individual points with much higher values than those around them. These errors are mostly rare and less of a problem than the high level of interference due to the failure to deploy the STAFF antenna boom.

Housekeeping data filter A simple software tool has been developed to remove HK frames containing transmission errors from the data stream. It is controlled by a parameter database so could be used by other instruments. The database defines which parameters have values that are static or change in a predictable way during normal operation. Provided such parameters in the current frame match either the frame before or the frame after, then the current frame is considered valid. Limitations: –More than one unexpected, but real, change in a parameter could cause valid frames to be rejected. –Cannot detect errors in parameters that are not static or predictable. However, as errors tend to occur in bursts, it is quite effective in practice. Example - counter parameter - should increment by 1 each frame: –123, 124, 125, 126, 127, 255, 129, 130, 131, 0, 1, 2, 3, 4, 5, 6 –Frame containing 255 is rejected because it matches neither value before or after. –Transition from 131 to 0 is OK because each matches a value on one side.

Science data errors It is difficult to check the science data itself for transmission errors as almost all binary values are valid. However, each science packet has a 48 bit header which is checked for self consistency (eg. packet size corresponds to commanded mode). This will catch any error burst which includes the header. It would also be possible to reject a packet if the header of the immediately following packet is bad (error burst likely to include end of current packet), but this is not currently implemented. Raw data has one second time resolution - identified bad data is not included in 4 second averaged data for archive.

(Re)processing With the exception of the combined plots which already exist, none of the data has yet been processed to create DAA products. All other STAFF-DWP datasets will be processed for the first time when re-processed raw data is available. Software tools to do this are in place, with the exception of the caveat datasets. It is not planned to systematically reprocess the combined plots, though individual days might be reprocessed if substantially improved raw data became available. Problem - no space left on RAID storage at Sheffield used for Cluster / Double Star raw data. Cannot currently import any reprocessed raw data. In short term can move older Cluster data to alternative storage.