• J2000GPS is distinct from the epoch J2000.0, which the IAU 1994 Resolution C7 recommends be defined at the geocenter and at the date 2000 January 1.5 Terrestrial Time(TT), where TT = TDT.
• J2000GPS is also distinct from the date 2000 January 1.5 UTC time, which we can refer to as J2000UTC. Exactly 13 leap seconds separate these epochs, i.e.: J2000GPS = J2000UTC - 13 = 2000-01-01 11:59:47.000 UTC
• Times before and after J2000GPS are descrived in GPS seconds around this epoch, i.e., continuous time.

E GPS23 403261200 0.000000000000000E+00 4.213090921042242E-02 
1.449777480113355E-01 7.188055942732944E-01 -6.786198911851030E-01

FIELD NUMBERS AND DESCRIPTIONS
------------------------------
Fields 0-7 are REQUIRED.

0   Typically E for Earth-Fixed, I for Inertial, B for body-fixed.
    Note that nothing inherently limits this to a single character
    in order to allow for more descriptive or exact coordinate systems.
1   Name of object (satellite, station, ??? ); white-space is not
    allowed in the name.
2   Integer (t_i) seconds past J2000GPS. To get GPS seconds past GPS
    week 0 second 0, ( 6-JAN-1980 00:00:00.0000), add 630763200; we
    assume this is a signed int in C++.
3   Float seconds (t_f) past t_i, double for C++.
4   Unit attitude quaternion, scalar component
5   Unit attitude quaternion vector, i component
6   Unit attitude quaternion vector, j component
7   Unit attitude quaternion vector, k component