An  example of a record in an eci  (`earth-centered  inertial')  file is

08 1993 03 30 11 59 52.00 -17409.92089 -11220.03748  16714.65641  -.46716519 -2.89933902 -2.51410869    GPS08  123.0  NM

This is a free-formated line with many of the fields optional.
The first field  (integer)  contains  the  satellite's id (SVN for GPS 
satellites and an agreed-upon ID for other satellites). The next six fields
record the UTC time: year (int),  month (int),  day of month (int),  hour (int),
and  second (float).  Fields  eight through ten contain the inertial  Cartesian
coordinates: x (float), y (float) and z (float) in km. They can either
represent the center of mass position or phase center position.
All subsequent fields are optional but their order should be kept as follows:
Three velocity components: u (float), v (float), w (float) in km/sec,
the satellite name (character*(*)), the yaw angle (float) in degrees and
the eclipse status (character*2).

Some more details about the yaw angle and the eclipse status:
The yaw angle is defined as the angle between the s/c X axis and the
W vector, measured counter clockwise as you look down the Z axis toward
Earth. The W vector is defined to be the normalized projection of the
velocity vector on a plane perpendicular to the spacecraft position vector.
The eclipse status relates the following information: 
NE for Not Eclipsing (Nominal)
SH for SHadow crossing
PS for Post Shadow maneuver
NN for NooN turn
NM for NoMinal but in eclipse season