imap_processing.spice.time.ttj2000ns_to_met

imap_processing.spice.time.ttj2000ns_to_met(tt_ns: ArrayLike) → NDArray[float]

Convert terrestrial time nanoseconds since J2000 to mission elapsed time (MET).

This is the inverse of met_to_ttj2000ns. The conversion process is: TTJ2000ns -> ET -> MET

Parameters:

tt_ns (float, numpy.ndarray) – Number of nanoseconds since the J2000 epoch in the TT timescale.

Returns:

The mission elapsed time in seconds.

Return type:

numpy.ndarray[float]