https://spdf.gsfc.nasa.gov/pub/data/pioneer/pioneer10/particle/gtt/ip_15min_ascii/aareadme.txt

This directory contains half-year files of 15-min count rates and 
related parameters from the the Geiger Tube Telescope (GTT) flown 
on Pioneer 10.  The data were initially provided to NSSDC by the 
GTT team at U. Iowa in VMS binary format on magnetic tapes.  They 
have been converted to ASCII format at GSFC/SPDF, with an almost 
complete retention of the original sequence of words in the data 
records.  (Only unused words were dropped, and the spacecraft ID 
was moved.)  The data, and their binary format, are extensively 
discussed at
https://spdf.gsfc.nasa.gov/pub/data/pioneer/pioneer10/particle/gtt/aavoldesc.sfd.

The format of the ASCII data contained in this directory follows:
  Length of record =1445bytes + LF

       Item number       Format         Function
 
            1            A24            ASCII timecode format of start
                                        time (in spacecraft event time)
            2 Note 1     I5             Year of Data  72,73 ...(ERT)
            3 Note 1     I4             Day of Data            (ERT)
            4 Note 2     F11.8          Beginning Day Fraction (ERT)
            5            F11.8          Ending Day Fraction    (ERT)
            6            I3             Spacecraft ID (10 or 11)
            7 Note 3     I4             Length of Period in Minutes
            8 Note 4     I4             Period Type
            9            I4             Number of samples this interval
           10-21 Note 5  12E13.5,1x        Effective Counts
                          
           22-33         12E13.5,1x        (Sum of Raw Counts)/.09375
           34-45         12E13.5,1x        Counting Rate Ave in Counts/sec
           46-57         12E13.5,1x        Sigma (Standard Deviation)
           58-69 Note 6  12E13.5,1x        M     Fourier Coefficients
           70-81         12E13.5,1x        K        "         " 
           82-93         12E13.5,1x        D        "         "
           94-105        12E13.5        Sum of Raw Counts
          106            I5             Number of Errors this Interval
          107 Note 7     F11.3          Day and Day Fraction since 1950.0
          108            F11.3          Radius to SC from earth in AU
          109            F9.3           Earth-Sun distance in AU
          110            F9.3           Radius to SC from the Sun in AU
          111 Note 8     F9.3           Celestial Longitude of Earth
          112 Note 8     F9.3           Celestial Longitude of SC
          113 Note 9     F9.3           Longitude of Solar Equator + 270
          114 Note 8     F15.11         Celestial Latitude of Earth
          115 Note 8     F11.7          Celestial Latitude of SC
          116 Note 9     F11.7          Heliographic Latitude of SC
          117 Note 9     F11.7          Heliographic Latitude of Earth


        Note 1:  Earth received time  (ERT) for the data.

        Note 2:  Beginning time is the time of the first data point
                 found in the interval.  The Ending time is the
                 time of the last data point in the interval.

        Note 3:  This number will be the number of minutes in the
                 interval since these are quarter hour averages
                 the number will be 15.

        Note 4:  This is a number assigned to describe the 
                 accumulation period; for quarter hour averages 
                 it will be 1.

        Note 5:  Items 10 through 105 represent 8 sets of values.  The
                 order of the detectors are as follows: 	 

                       Position        Detector
                           1               G
                           2               A
                           3               B
                           4               G
                           5               AB
                           6               ABC
                           7               C
                           8               D
                           9               ABC
                          10               DEF
                          11               G + G
                          12               ABC + ABC

        Note 6:  The Fourier Coefficients are used in the following 
                 formula.
                 F(phi) = M ( 1 + K Cos ( phi - D ) )
  
        Note 7:  This time is spacecraft event time for the center
                 time of the data used in the sum.

        Note 8:  The celestial latitude and longitude are measured in
                 a reference system using the Sun as the reference body
                 body and the true ecliptic of date as the reference 
                 plane.
                 This plane contains the vernal equinox and the 
                 longitudes are measured eastward from the line 
                 between the vernal equinox and the Sun. The latitudes
                 are measured from the plane. Northward being positive.

        Note 9:  Calculated quantities.
                 Inclination of solar equator to ecliptic, I=7.25 
                 degrees.  Longitude of the ascending node of the 
                 solar equator on the ecliptic 
                 Omega=73 degrees+40 minutes +50.25*t seconds
                 where t is the time in years reckoned from 1850.0 .
                 Reference: Explanatory Supplement to the Astronomical
                 Ephemeris and the American Ephemeris and Nautical
                 Almanac, 1961, page 307.
	
        Note 10: All positional coordinates are referred to the
                 equinox/ecliptic of date.