It is disclosed a system and method for drilling rock cores, and in particular to determine their orientation in the subsurface. The core drilling system includes a drill string with a drill bit at an end thereof, a core sampling arrangement mounted inside the drill string at said end thereof, the core sampling arrangement including a core tube ( 100) for holding a core sample, the core tube having a first end located near the drill bit and a second end distant from the drill bit, a core catcher ( 101) fixed at the first end of the core tube ( 100), a core tube head (102) fixed to the second end of the core tube ( 100), the system further including a rotational joint (104) connecting the core tube head to a latching unit (105) adapted to releasable lock to the drill string, wherein said rotational joint (104) allows the latching unit (105) to rotate independently from the core tube (100). The system further includes an orientation unit (103) that is rotationally free from the core tube through being located at the opposite side of the rotational joint ( 104) relative to the core tube, fixed at or integrated into the latching unit ( 103) or placed as a separate freely rotational section between the rotational joint (104) and a second rotational joint fixed to the latching unit.
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