HESSI SCIENCE OPERATIONS

Telemetry to CD production:

Start with telemetry files: vc1 and vc3 per contact. (vc1 = instrument State of Health, vc3 = Science)

hsi_contact2fits combines vc1 and vc3 packets, splits files into files per each orbit, named hsi_yyyymmdd_hhmm_nnn.fits. The date and time, yyyymmdd_hhmm, corresponds to the start of the orbit. For this, we need access to the ehpemeris data, to be provided by the GDS in ASCII files.

The "nnn" is a version number, for instances in which a file is generated that has the same yyyymmdd_hhmm as a previous file.

The catalog data will be generated as part of hsi_contact2fits, and appended to the hsi_yyyymmdd_hhmm_nnn.fits files.

These files are then written to CD. SOC Data Flow Diagram

Contents of the various files:

Inputs to hsi_contact2fits:

  • contact files contain telemetry frames:
    • vc1 files contain stored instrument/state of health packets
    • vc3 files contain stored science data
  • ephemeris files contain:
    • position and velocity of spacecraft at 10 sec intervals
    • times of spacecraft day and night, and SAA pasage

Outputs from hsi_contact2fits:

  • FITS file contains (as binary table extensions):
    • vc1 & vc3 packets
    • Catalog for the given time interval
    • Catalog contains (in binary table extensions):
      • Observing Summary: (Implemented)
        • spin-averaged count rates in 8 energy bands, summed over detectors
        • monitor rates
        • modulation variance, 2 Coarsest collimators
        • data gap start and end times
        • S/C position
      • Instrument Log: (Not Implemented)
        • Housekeeping, State of Health data for the Imager, Spectrometer, Particle Monitor, etc...
      • Flare List: (Partially Implemented)
        • Id number
        • Start, peak and end times, in energy range [3.0, 20.0] keV
        • peak count rate
        • total counts
        • Highest energy of observed photons
        • Flare position, arcsec from Sun center
        • Flags for flares that start/end in Eclipse or SAA
      • Spectral catalog: (Not Implemented)
        • count and photon spectra as a function of time
        • Thermal + double power law photon spectra,
        • dE = E/2 energy resolution.
      • Image catalog: (Not Implemented)
        • Images in the 8 energy bands given by the Observing Summary, If possible, Cadence determined by Count Rate

Other database files needed by hsi_contact2fits:

  • The Calibration database contains the data needed for spectral response matrices. From /ssw/hessi/dbase
  • The Grid response database contains the data needed for grid response matrices. From /ssw/hessi/dbase
  • The Stellar position database contains the position of stars used by the RAS/SAS SW to determine the aspect solution. From /ssw/hessi/dbase
  • The Solar ephemeris database contains the position, size, and orientation of the Sun.

Other data to be generated after contact:

  • Real-time Science data catalog: Generated by hsi_contact2fits from vc2 packets for each contact. Posted on the HESSI ftp site for quick access.
  • Whole-Mission HESSI catalog: During catalog generation by hsi_contact2fits, the catalog extensions are saved in separate files (hsicat_yyyymmdd....etc) and are appended to form weekly files (or possibly monthly:TBD). These will be accessible for web-based browsing.
  • Contact2fits file database: A list of each FITS file generated including the filename the start and end times for the file, and the contact from which it came.

Distribution:

  • The FITS files are hopefully sent via internet to SDAC and ETH. CDs are mailed. The data is stored locally on a RAID system.

16-Oct-1999, jmm