SP3Parser supposes time scale is GPS
When parsing position and velocity epochs of a SP3 file, the SP3Parser
supposes that the time system is GPS (See line 281 of the parser).
280 hasVelocityEntries = false;
281 timeScale = timeScales.getGPS();
282 maxSatellites = 0;
However, according to SP3-c and SP3-d standards, the time system can be different from GPS. It is specified in line thirteen for SP3-c and twenty one for SP3-d. For SP3-a, the time system is GPS.