Such zippers are usually very stiff and difficult to open and close. Nasa first used them during the Mercury and Gemini space programs, and later made an even stronger version for the Apollo space program. The zippers were placed on the main opening and sealing of both pilots’ pressure suits and spacesuits, extending from the neck ring that connected to the helmet, either from the front or back to the crotch to allow the pilot or astronaut easy access to put on the suit. “Zippers were ideal to use, because they were lightweight and easily integrated into soft, cloth-based suits and allowed the wearer flexibility while they were wearing them,” says Cathy Lewis, curator at the National Air and Space Museum in Washington DC.

Modern spacesuits no longer have zippers, though. The type of zipper that was used relied on two heavy-duty, brass zippers that compressed a rubber gasket sandwiched between them when the suit was pressurised. While this seal was reliable, says Lewis, it did require frequent retesting throughout the production and flight test cycle. “The seal, while reliable for short-term use, was not so for long-term use,” she explains.

The chemical interaction between the copper in the brass zippers and the rubber gasket caused quick deterioration of the rubber, but as long as missions were less than a few weeks and required only a handful of re-pressurisations without retesting, then there was little concern. However, as modern astronauts stay on the International Space Station for weeks and months, the current Extravehicular Space Activity (EVA) spacesuits rely on a hard seal instead – with two metal pieces (usually aluminium, but in some cases steel) joined together to compress a rubber gasket or O-ring. “This demands that the suits are much heavier, but the seal can be inspected frequently and the O-ring replaced when necessary,” says Lewis.