Complex sentence: They are approached by another member of the Special Forces of the CDF, adapted to live in space, who had attached himself to the exterior of their craft, who informs them they have no option but to land and begin the colony anyway.
Split into simpler sentences: They are approached by another member of the Special Forces of the CDF, adapted to live in space, who had attached himself to the exterior of their craft. He informs them they have no option but to land and begin the colony anyway.