Jitter Files

• are accurate
  • Absolute accuracy: 0.5^" ÷ 2^"
    • Relative error in Guide Stars Coordinates: 0.3^" ÷ 0.4^"
    • FGSs Alignment uncertainty: < 50 mas
    • Thermal breathing of the telescope: ~15 mas

  • Relative Accuracy within the same HST visit: < 10 mas !
    • Entry or exit of Earth shadow: 5 ÷ 8 mas

    Caution! A zero point drift has been discovered by comparing jitter offsets and cross-correlation offsets.

  
  

• are produced by:
  • the Observatory Monitoring System (OMS) at STScI since October 1994:
    • The missing jitter files for the first ten months of WFPC2 operations have been built by ST-ECF (Dolensky et al., 1998) in collaboration with STScI.
      By mid 1998 the complete set of jitter files is available to the community.

  
  

• to study:
  • Telescope Pointing Stability

  • Trends in the telescope/instruments performance
    with the orbital environment

  
  

• are built:
  • Correlating time-tagged engineering telemetry stream with the Mission Schedule (event list driver of all HST activities)

  
  

• contain:
  • Measurements, averaged over 0.05 to 3 seconds, of:
    • pointing information (RA, DEC, ROLL)

    • environment information (Magnetometers read outs, etc.)

  
  

See some graphical examples (Jitter Balls).