OPM metadata block. ref_frame_epoch is the REF_FRAME_EPOCH text, kept as written.
ref_frame_epoch
REF_FRAME_EPOCH
@type t() :: %Sidereon.CCSDS.OPM.Metadata{ center_name: String.t(), comments: [String.t()], object_id: String.t(), object_name: String.t(), ref_frame: String.t(), ref_frame_epoch: String.t() | nil, time_system: String.t() }