SpaceX’s [1] futuristic Starship interplanetary craft may embody the golden age of sci-fi in more ways than one: in addition to (theoretically) taking passengers from planet to planet, it may sport a shiny stainless steel skin that makes it look like the pulp covers of old.

Founder and CEO Elon Musk [2] teased the possibility in a picture posted to Twitter, captioned simply “Stainless Steel Starship.” To be clear, this isn’t a full-on spacecraft, just part of a test vehicle that the company plans to use during the short “hopper” flights in 2019 to evaluate various systems.

As with most Musk tweets, this kicked off a storm of speculation and argument in the Twitterverse.

The choice surprised many because for years, modern spaceflight has been dependent on advanced composite materials like carbon fiber, which combine desirable physical properties with low weight. When metal has been required, aluminum or titanium are much more common. While some launch components, like the upper stage of the Atlas 5 rocket, have liberally used steel, it’s definitely not an obvious choice for a craft like the Starship, which will have to deal with both deep space and repeated reentry.

As Musk pointed out in subsequent comments, however, stainless steel has some advantages versus other materials when at extremely hot or cold temperatures.

Usable strength/weight of full hard stainless at cryo is slightly better than carbon fiber, room temp is worse, high temp is vastly better

— Elon Musk (@elonmusk) December 24, 2018[3]

This is a special full-hardness steel alloy mentioned as being among the 300 series of high-strength, heat-resistant alloys — not the plentiful, pliable stuff we all have in our kitchens and buildings. Musk...

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