PATH Reference

PATH data information:

• The binary PATH Files are named: ADPOUT01 ... ADPOUT22.

• The PATH Segment Definitions for each file are:
  • ADPOUT01: GMT start - 253/00:30:00 to GMT end - 253/12:29:59
  • ADPOUT02: GMT start - 253/12:30:00 to GMT end - 254/00:29:59
  • ADPOUT03: GMT start - 254/00:30:00 to GMT end - 254/12:29:59
  • ADPOUT04: GMT start - 254/12:30:00 to GMT end - 255/00:29:59
  • ADPOUT05: GMT start - 255/00:30:00 to GMT end - 255/12:29:59
  • ADPOUT06: GMT start - 255/12:30:00 to GMT end - 256/00:29:59
  • ADPOUT07: GMT start - 256/00:30:00 to GMT end - 256/12:29:59
  • ADPOUT08: GMT start - 256/12:30:00 to GMT end - 257/00:29:59
  • ADPOUT09: GMT start - 257/00:30:00 to GMT end - 257/12:29:59
  • ADPOUT10: GMT start - 257/12:30:00 to GMT end - 258/00:29:59
  • ADPOUT11: GMT start - 258/00:30:00 to GMT end - 258/12:29:59
  • ADPOUT12: GMT start - 258/12:30:00 to GMT end - 259/00:29:59
  • ADPOUT13: GMT start - 259/00:30:00 to GMT end - 259/12:29:59
  • ADPOUT14: GMT start - 259/12:30:00 to GMT end - 260/00:29:59
  • ADPOUT15: GMT start - 260/00:30:00 to GMT end - 260/12:29:59
  • ADPOUT16: GMT start - 260/12:30:00 to GMT end - 261/00:29:59
  • ADPOUT17: GMT start - 261/00:30:00 to GMT end - 261/12:29:59
  • ADPOUT18: GMT start - 261/12:30:00 to GMT end - 262/00:29:59
  • ADPOUT19: GMT start - 262/00:30:00 to GMT end - 262/12:29:59
  • ADPOUT20: GMT start - 262/12:30:00 to GMT end - 263/00:29:59
  • ADPOUT21: GMT start - 263/00:30:00 to GMT end - 263/12:29:59
  • ADPOUT22: GMT start - 263/12:30:00 to GMT end - 263/23:00:00

• The PATH ephemeris data are recorded at one second intervals.

Notes from Kathy Powell, May 14, 1997.

Estimate of errors in PATH data.

Errors in the altitudes assigned to LITE profiles depend on the accuracy of the Space Shuttle Postflight Attitude and Trajectory History (PATH) ephemeris data. The accuracy of the ephemeris data is described in the PATH Product Interface Control Document (ICD), ICD-I-TOP-002A, May 27, 1992, and the STS-64 PATH Final Report.

The quality of the PATH ephemeris is measured from the accuracy of the Shuttle attitude measurements and trajectory determination. Trajectory information comes from a smoothed Kalman filter estimate based on Shuttle tracking data. The STS-64 PATH Final Report states that the trajectory information generally agreed with real-time navigation processing to within about 250 meters in position during the entire mission. The report did not quantify the accuracy of the Shuttle attitude measurements. The PATH Product ICD provides a general description of the accuracy for all Space Shuttle ephemeris data and states that a 3 sigma uncertainty in body-axis attitude could nominally be about 0.2 degrees per axis, and can be as high as 2 degrees (3 sigma) due to spacecraft elasticity and thermal expansion.

An error of about 250 m in position can lead to an error in altitude of approximately +-260 m. If one considers attitude errors of approximately 0.2 sigma per axis, this could lead to an additional altitude error of approximately +-65 m.

I was able to confirm that there were times when this magnitude of error in altitude occurred by computing the altitudes of LITE surface returns over the oceans.