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According to MRD (461-SYS-RQMT-0019L) RMRD_1307 & RMRD_1363: each spacecraft clock will be kept within 500 microsec with respect to GPS time (1 PPS < 500 microsec of GPS time).

CIDP to IDPU ICD (10160.17-CIDP_FPI_IDPU_ICD-01) RC@IDPU_0180 allocates 50 microsec for the delay from CIPD receipt of the 1 PPS and its issuance of the triple-pulse time-at-tone (TaT)

According to MRD (461-SYS-RQMT-0019L) FPI was granted a waiver (MMS_DW-0233) to exceed the 100 microsec time-tagging requirement.

  • The greatest error observed was 119.5 microsec and we generally allocate 120 microsec for conversatism
  • Pre-launch testing report (FPI-SYS-RPT-0403) explains the exceedances as a limitation of the testing procedure
  • The results show variability by instrument suite bay (Table 2-4 in FPI-SYS-RPT-0403)
  • No adjustment of the received Time Tags is done to account for these delays.

In General:  FPI time tag difference < 670 microsec with respect to GPS time

 

Assignment of Time Tags to Measurements of Individual FPI Spectrometers and/or Energy

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Observations

Please note that the timing of individual energy and deflection step combinations is NOT directly inferrable from simple linear spacing.

  • The time tag for separate observations (say energy step 25, deflection state 0 and energy step 25, deflection state 1) are NOT derivable by dividing 30ms up into 128 evening spaced intervals.
  • Integration times of 195 microsec/1 millisec for DES/DIS are separated by variable settling times
  • Settling time values van vary from ~20 microsec to ~250 microsec depending on the instrument type (DES or DIS), low vs high range in the power supply electronics, and upward versus downward sweep in the energy steps.
     

SPEDAS Notes for FPI Time Tagging

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