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Perigee Times and Spin Axis Orientation(includes updated ISEE-2 values for 80-82


Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Time span: 1977-10-22 to 1977-10-25


This data set contains the updated spin axis orientations issued by the project to correct for the values on the original ISEE 2 Multi-Coordinate Ephemeris (MCE) tapes for the period 01Jan80 to 09Oct82. The original ISEE-2 MCE data tapes had incorrect values for this period. For completeness, parameters from launch to re-entry for both ISEE 1 and ISEE 2 are included. There is one file of spin axis data for each spacecraft. Each file has some header lines followed by the date, Universal Time, ecliptic latitude, and ecliptic longitude (both in degrees) of the spacecraft spin axis for that particular time. The ecliptic longitude is defined as the angle in the ecliptic plane relative to the sun's direction as seen from the earth, i.e., 0 degrees pointing toward the sun, +90 degrees toward dusk, 180 degrees away from the sun, and 270 degrees toward dawn (in the direction of the earth's orbital motion around the sun. The ecliptic latitude is the angle of the spin axis out of the ecliptic plane, +90 degrees pointing toward the north ecliptic pole, -90 degrees toward the south ecliptic pole. For most of the mission, the spin axis of both spacecraft were pointing close to +90 degrees. (From launch until 01Nov77, the ISEE 1 spin axis latitude was close to 0 degrees). The spin axis orientation was updated whenever the instantaneous orientation had drifted 0.05 degrees from the last recorded value. Under normal circumstances there is one record per day. Occasionally, spacecraft maneuvers led to more frequent updates. The 0.05-degree figure was chosen because the project could not establish the spin axis orientation to a greater accuracy than 0.1 degree. A third file in the data set contains a table of the orbit numbers and perigee times for both spacecraft from launch to re-entry. The parameters are orbit number; perigee time for ISEE 1 orbit [year, day of year (January 1 = Day 1), Universal Time (HHMM)]; and perigee time for ISEE 2 orbit [same format as ISEE 1 data]. The number in the last column should be ignored. The uncertainty in the separation vector between ISEE 1 and ISEE 2 is approximately 1 km or 1%, whichever is greater, and to within 1 degree in direction relative to the earth-sun line. The uncertainty in orbital position is less than or equal to 1 km in the overlap comparison. Further details of the separation strategy are given in the documentation. All of these data are in ASCII format. This data set is also archived as data set 77-102A-00L. The original MCE data are archived as data sets 77-102A-00K and 77-102B-00I.

Alternate Names

  • Perigee Times and Spin Axis Orien


  • Space Physics: Zodiacal Light/Interplanet Dust


  • 77-102A-00L
  • 77-102B-00J

Additional Information


Questions and comments about this data collection can be directed to: Dr. H. Kent Hills



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