Pyramidology reached its peak by the early 1980s. Interest revived when in 1992 and 1993 Rudolf Gantenbrink sent a miniature remote-controlled robot rover, known as Upuaut, up one of the "air shafts" in the Queen's Chamber of the Great Pyramid of Giza. Upuaut discovered the shaft closed off by a stone block with decaying copper hooks attached to the outside. In 1994 Robert Bauval published the book "The Orion Mystery", attempting to prove that the pyramids on the Giza plateau were built to mimic the stars in the belt of the constellation Orion, a claim that came to be known as the Orion correlation theory.