(Reuters) - The detailed manual used by U.S. astronauts Neil Armstrong and Buzz Aldrin to land on the moon in 1969 is going up for auction in July and could fetch up to $9 million, New York auctioneers Christie’s said on Wednesday.

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The 44-page ring-bound Apollo 11 lunar module timeline book details every procedure that was needed to undock, land and rendezvous the Eagle with its Columbia command module when Armstrong and Aldrin became the first men to walk on the moon.

“These are step-by-step instructions that cover the entire portion of the Eagle flight. It is a series of instructions on everything from ‘don your helmets’ to ‘check your power system,’” Christina Geiger, head of books and manuscripts at Christie’s, told Reuters.

Along with technical data, the book, which was carried aboard the Eagle, contains drawings and almost 150 check marks and annotations written in real time by Armstrong and Aldrin.

Since there was no audio or video recording of what happened in the cockpit of the Eagle, the manual is regarded as a unique witness to space history. It also marks the first writing by a human being on another celestial body.

It is being sold by a private collector who purchased it previously from Aldrin, Christie’s said.

Collectors pay huge sums for space exploration artifacts. In 2017, Sotheby’s sold a zippered bag used by Armstrong and laced with moondust for $1.8 million.

“Everybody wants something that has flown to space or to the moon. It’s so cool to be able to gaze up at the moon and think: ‘I’ve got an object in my pocket that was there,’” said Geiger.

The last manned mission to the moon took place in 1972.

Christie’s has placed a $7 million to $9 million estimate on the timeline book, which will go on public view in New York from May 3 to 17 ahead of a global tour before the auction on July 18.

The book is the star item in a 150-lot auction marking the 50th anniversary of the moon landing called One Giant Leap: Celebrating Space Exploration 50 years after Apollo 11.