SpaceX's The futuristic interplanetary spacecraft can incorporate the golden age of science fiction in more than one way: in addition to (theoretically) taking passengers from one planet to another, it may have a shiny stainless steel skin that makes it look like a cellulose wrapper old .
Founder and CEO Elon Musk He joked with the possibility in a photo posted on Twitter, simply captioned as "Stainless Steel Starship". To be clear, this is not a complete spacecraft, just part of a test vehicle that the company plans to use during the short funnel. flights in 2019 to evaluate several systems.
As with most Musk tweets, this triggered a storm of speculation and discussion on the Twitterverse.
The choice surprised many because for years, modern spaceflight has been dependent on advanced composite materials, such as carbon fiber, that combine desirable low weight physical properties. When metal is needed, aluminum or titanium are much more common. While some launch components, such as the Atlas 5 rocket's upper stage, have generously used steel, it's definitely not an obvious choice for a vehicle like Starship, which will have to deal with both deep space and repeated re-entry.
As Musk pointed out in subsequent comments, however, stainless steel has some advantages over other materials when in extremely hot or cold temperatures.
It is a special alloy steel of total hardness mentioned as being among the 300 series of heat resistant and high strength alloys – not the plentiful and pliable material we all have in our kitchens and buildings. Musk also mentioned another super-so-called SX500 that SpaceX metallurgists have developed for use in Raptor engines that will power the vehicle.
So why stainless? It's all about re-entry.
Many craft and reusable stages that need to cope with the heat of entering the atmosphere at high speed use an "ablative" heat shield that disintegrates or breaks in a controlled manner, driving heat away from the vehicle.
This is unlikely to be a possibility for Starship, however, replacing and repairing this material would require downtime and crews where and when the aircraft lands, and the spacecraft must be (possibly) a fast-return ship with maximum re-use. The heat shield that reflects and survives is a better bet for this – but a huge engineering problem.
Scott Manley put together a beautiful video illustrating some of these ideas and speculations in detail:
Musk said before the Starship (then still called BFR) that "almost all the time he's reentering, he's just trying to brake, as he distributes that force in the largest possible area." Reentry will probably look more like a Space Shuttle-esque planar than the ballistic descent of the first stage of Falcon 9 and the braking of the engine.
The move to stainless steel has the nice side effect of making the craft look really cool – more in keeping with science fiction books and comics than your readers might have expected. The painting works would burn immediately, Musk said:
You can not expect it to keep shining for long; it may be stainless, but like a pan you left on the stove, the stainless steel can still burn and the bottom of the ship will probably look pretty rough after a while. It's all right – the spaceship that develops a patina is an enchanting development.
The details are still few, and for all of us we know that SpaceX could redesign the craft again based on how the tests go. Next year will see the first landing gear flights to the Starship rig and possibly the lower stage of the Super Heavy, which will raise its large bright volume of the lower atmosphere.
The technical documentation promised by Musk is expected to arrive in March or April, but whether it refers only to the test vehicle or take a look at the spacecraft that SpaceX intends to send around the Moon is unknown. Either way, you should expect more information to be revealed spontaneously earlier, at Musk's discretion – or lack thereof.