This is the README file for D2OALAPI

D2OALAPI contains the Dynamics Explorer-2 (D2) Orbit and Attitude (OA) data 
that was included with the LAPI VAX binary data.  The D2OALAPI CDF files were
generated by converting the VAX binary format stored at the Space Physics
Data Facility (SPDF).  The VAX binary format was converted from the original
Sigma-9 machine that was used to collect and process Dynamics Explorer
telemetry.  The following are the extracted OA elements included within the
DE-2 LAPI Orbit/Attitude CDF files:

 Sensor  OA Parameter           Unit            valid Range
   0     Invariant Latitude     deg             0 to 90
   1     Magnetic Local Time    hr              0 to 24
   2     Altitude               km              300 to 1100
   3     Latitude               deg             -90 to 90
   4     Longitude              deg             0 to 360
   5     Local Solar Time       hr              0 to 24
   6     L-Shell                unitless ratio  0 to 100
   7     Orbit Number           unitless number 0 to 9000
   8     Satellite Speed (GEI)  km/sec          6 to 10
   9     Solar Zenith Angle     radians         0 to pi
  10     Light/Dark Indicator   unitless flag   0 = dark, 1 = light

The following items were also converted and included in the CDF files:

 Sensor  OA Parameter           Unit            Range
   9     Solar Zenith Angle     deg             0 to 180

All variables are stored as 4 byte real numbers where -3.4e+38 is used to
indicate a fill value.  A special note on the L-Shell.  The L-Shell was 
determined by an iteration process which was terminated after 100 
iterations with no solution, and thus are filled.

A status byte is included in the CDFs and indicates the status of 
processing achieved at Goddard Space Flight Center (GSFC).
  
    Status  Meaning                        Number of Bits
      0     SPDF Status Flag - All               8

Each bit which makes up the status byte was extracted so that each bit
could be individually examined.  These were labeled starting at bit 0
as follows:

    Status  Meaning                        Number of Bits
      1     SPDF StatusFlag - Bit 7              1
      2     SPDF StatusFlag - Bit 6              1
      3     SPDF StatusFlag - Bit 5              1
      4     SPDF StatusFlag - Bit 4              1
      6     SPDF StatusFlag - Bit 3              1
      7     SPDF StatusFlag - Bit 2              1
      8     SPDF StatusFlag - Bit 1              1
      9     SPDF StatusFlag - Bit 0              1

The SPDF status byte defines the processing undergone when converting 
the original DE LAPI telemetry from its Sigma-9 format to its VAX binary 
format.  The SPDF status byte was meant to describe the values that were 
encountered when reading the Sigma-9 magnetic tape.  Bits 3, 6, and 7 are 
contained within status 0.  Bit 3 indicates that the SPDF encountered a 
Bad Sensor ID, bit 6 when the SPDF Previous Sensors Differ from the current 
sensors, and bit 7 when the SPDF detected a Time Gap in telemetry.  The 
remainder of the bits were not defined in the SPDF documentation.  These 
SPDF flags are specific to LAPI sensor data and telemetry.  They do not 
refer to these OA sensors, but the are related because the OA data is 
contained within the same VAX binary file to coincide with the LAPI data.
These processing status bits may give a clue to missing OA data in the
CDF data file.

Orbit and Attitude values are considered instantaneous measurements.  They 
have no accumulation period, only data latency between measurements.