The aerospace vehicle revered as the fastest machine within Earth’s atmosphere will be offered for sale by RM Auctions at its annual London auction on September 8. During its first flight in 1991, the Hypersonic Flying Laboratory, known as Kholod—an experimental collaborative project between NASA and the Soviet Central Institute of Aviation Motors—achieved a speed of 4,925 mph (or about Mach 7.5), which set a still-unbroken record. The 5-ton, 39-foot-long craft cost more than $10 million to produce. RM is offe…