Double Star Active Archive - DWP/STAFF 1 Double Star Active Archive STAFF/DWP Keith Yearby and Hugo Alleyne University of Sheffield Nicole Cornilleau-Wehrlin LPP

Double Star Active Archive - DWP/STAFF 2 Introduction The wave experiment onboard the TC1 satellite of the Double Star Program consists of a three-axis search coil antenna, three pre-amplifiers, and a Magnetic Wave Form unit provided by LPP (formerly CETP) and the Digital Wave Processor provided by the University of Sheffield. The three first elements are spares of the Cluster STAFF experiment. The search coil aims to measure magnetic fluctuations in the frequency range 0.1 Hz - 4 kHz to characterise waves and turbulence. The Magnetic Wave Form unit digitises the waveform continuously in the frequency range Hz, with snapshots up to 180 Hz. The Digital Wave Processor is based on the Cluster DWP experiment, but it has been modified to perform an onboard spectral analysis in the 10Hz to 4kHz range, similar to the Cluster STAFF spectrum analyser. DWP also contains a particle correlator experiment which computes the auto-correlation (ACF) of electron counts received by the PEACE HEEA sensor. The correlator detects modulations and short time particle bursts in the electron population as an indicator of wave-particle interactions.

Double Star Active Archive - DWP/STAFF 3 Numerical Data products D1_CP_STA_DWP_PSD - Magnetic field power spectral density –Based on the Cluster STAFF power spectral density data product, but measured along single axis aligned for minimum interference. –Frequency resolution: 27 channels, approximately logarithmically spaced 10Hz to 4 kHz. –Time resolution: 4 seconds. –~1.6MB per day (gzipped). D1_CP_STA_DWP_COR_* - Particle correlator data. –On board auto-correlations of the electron counts measured by PEACE. –Auto-correlation product similar to the Cluster particle correlator data. –In addition, raw particle count time series data. Prime and summary parameter data from Double Star Data Centre –STAFF magnetic wave power in 3 channels. Waveform and spectral matrix data –Due to the high level of interference it is not planned to archive these products, except as part of the raw data.

Double Star Active Archive - DWP/STAFF 4 Graphical Datasets D1_CG_STA_DWP_PSD –Power spectral density plots, made directly from the power spectral density numerical dataset. 10Hz to 4kHz range, 4s time resolution, ~330kB per day (gzipped PostScript). D1_CG_STA_DWP_COMBI –Spectrum plots combining spectra produced on the ground from the 10Hz bandwidth waveform data with the 20Hz to 4kHz onboard analysis. 2Hz to 4kHz range, 1 minute time resolution.

Double Star Active Archive - DWP/STAFF 5 Example STAFF/DWP PSD dataset

Double Star Active Archive - DWP/STAFF 6 Example STAFF/DWP Combined plot

Double Star Active Archive - DWP/STAFF 7 Example STAFF/DWP Combined plot

Double Star Active Archive - DWP/STAFF 8 Caveats 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 one spin to provide a reasonably isotropic measurement. –Particle correlator data is not affected by the interference. 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. –The best we can do then is 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.

Double Star Active Archive - DWP/STAFF 9 Technical Status It is proposed that STAFF/DWP DAA data production will be performed by the University of Sheffield, except for the combined plots which already exist at LPP. The ICD and User guide are written. Production software and procedures in place. Minor changes needed for new data product naming convention (DP to CP, etc.). Header files defined. Just waiting for final approval of data formats before starting production.

Double Star Active Archive - DWP/STAFF 10 Funding status There has never been any formal UK national agency (PPARC/STFC) funding for Double Star, only an agreement that staff funded for Cluster operations may work on Double Star as well. Preliminary work on Double Star archiving has been done by Keith Yearby, now the only STFC funded person for DWP operations. We estimate that 6 months FTE is required to complete the Double Star archiving, and request that this be included in any extension to the ESA funding for Cluster DWP archiving.