It’s one not-so-small sale for RR Auction, one giant opportunity for Omega enthusiasts.

Two Speedmasters originally given to NASA astronauts Richard “Dick” Gordon Jr. and Edgar “Ed” Mitchell are being auctioned off in the auction house’s Space Exploration sale this month. Running from now until October 16, the online auction includes more than 600 lots that run the gamut, from astronaut equipment to museum-worthy relics.

The stars of the sale are, of course, the two Speedmasters. Astronaut Walter Schirra took the first Speedy to space in 1962, before NASA greenlit the model for all manned space missions in 1965. Astronaut Buzz Aldrin famously wore a Speedmaster as he walked the moon’s surface in 1969, leading it to become the official “moonwatch.”

Omega didn’t just issue Speedys for missions, though: The Swiss watchmaker also made special, solid-gold versions to commemorate NASA’s Apollo triumphs. These personalized pieces are exceedingly rare and highly coveted: Neil Armstrong’s commemorative chronograph recently sold for a record $2.1 million at RR Auction, for example.

Mitchell’s Speedmaster Professional (Ref. BA 145.022) is one of 1,014 that Omega created to celebrate the Apollo moon landings. For the first time, the watchmaker presented the model in 18-karat gold rather than steel. The reference also features a solid-gold “OM” (Or Massif) dial with black accents and a burgundy “dot over ninety” bezel. Inside lies the manual caliber 861 movement.

Mitchell’s example, numbered 1002, was engraved with his name, his mission, and the iconic line: “To mark man’s conquest of space with time, through time, on time.” It was presented to Mitchell following the successful Apollo 14 moon landing in 1971, during which he became the sixth person to walk on the lunar surface. Accompanied by a letter of authenticity from his daughter, Karlyn Mitchell, the watch is expected to fetch in excess of $100,000.

Gordon’s example, also expected to sell for over $100,000, was one of 26 Speedmasters created as part of Omega’s first “Tribute to Astronauts” series. These gold timepieces—practically the same as the commemorative Apollo Speedys—were handed out at a special gala dinner in Houston on November 25, 1969. Two were presented to President Richard Nixon and Vice President Spiro Agnew, with the remaining 26 given to America’s pioneering astronauts. Gordon was still in quarantine from the Apollo 12 mission at the time, but received his personalized example shortly afterward. The engraving contains a small error—“R” instead of “F” for his middle initial—adding another interesting layer to the watch’s backstory. It comes with a signed letter from Gordon himself.

You can explore the full catalog and register to bid online on the RR Auction website.