Why SpaceX's Starship mega-rocket looks unlike anything the company has ever built before
- SpaceX's Starship rocket is predominantly silver instead of the conventional white.
- The silver color comes from noncorrosive stainless steel that SpaceX used to build the rocket.
Nestled on the very southern tip of Texas, near the small village of Boca Chica, sits a not-so-small space rocket: SpaceX's Starship mega-rocket.
Not only is Starship the world's largest, most powerful rocket, it also looks unlike anything SpaceX has ever built. In fact, it doesn't really resemble any other rocket in the world.
As shown below, the mega-rocket consists of two stages. The first stage rocket booster, called Super Heavy (on the far left), is completely silver, while the second stage spacecraft, dubbed Starship, is half silver, half black.
This silver-black color scheme is a vast change from SpaceX's white Falcon 9 rockets or NASA's orange and white Space Launch System.
So why the flashy specs, SpaceX?
SpaceX's silver rocket made of steel
Starship's mostly-silver appearance comes from a type of non-corrosive alloy called 300-series stainless steel. It's the first time someone has made a rocket from this material since the 1950s.
The reason why most rocket companies avoid steel is because it's heavy, and the heavier your actual rocket, the less payload you can carry to space on the same fuel tanks.
Instead, the outer frame of most rockets is built of durable but lightweight metals like aluminum and titanium. Titanium is great for keeping a rocket lightweight but it can cost up to 15 to 20 times more than steel.
That's why, in 2019, SpaceX replaced its Falcon 9 rockets' titanium grid fins with welded steel fins. However, cost is not the only reason SpaceX now prefers steel over titanium in its rockets.
According to material science experts, steel works better in extreme temperature conditions than titanium. That means both under extreme heat, like during launch and atmospheric re-entry, but also extreme cold, like in deep space.
And that's important since Starship's mission is to eventually shuttle humans to the moon and Mars, exposing the spacecraft to temperatures as cold as -455 degrees Fahrenheit (-270 degrees Celsius), which could make most rocket material weak, brittle, and prone to cracks or breaks.
Stainless steel, on the other hand, actually increases in strength at these cryogenic temperatures, making it ideal for deep space travel.
Moreover, Mike Gruntman, a professor of astronautics at the University of Southern California, told Insider, "It is essential to use stainless steel to prevent corrosion. The vehicle skin is subjected to dynamic loads during the powered ascent through the atmosphere - so structural strength of the materials is also important. Plus, price also plays a role."
SpaceX's black-studded Starship spacecraft
Starship has a black underbelly, similar to NASA's Space Shuttles, and for similar reasons, too.
The black is a series of heat-resistant hexagonal tiles made of silica, designed to protect the spacecraft from scorching temperatures as it re-enters Earth's atmosphere.
You can see a close-up of these tiles in action from multiple flamethrowers in this video that SpaceX founder and CEO Elon Musk posted on Twitter in March 2019:
—Elon Musk (@elonmusk) March 17, 2019
One difference between Starship's tiles and the Space Shuttles' is their hexagonal shape. The Shuttles' tiles were square.
When a Twitter user asked about the tile's unusual shape, Musk responded that hexagonal-shaped tiles leave "no straight path for hot gas to accelerate through the gaps."
In other words, it's an extra measure to prevent the spacecraft from overheating and blowing up upon re-entry.
Why are most rockets white?
The reason is simple: cost.
White absorbs the least amount of heat among all the colors in the visible spectrum, which helps keep the rocket as cool as possible. And that's important since rocket fuel typically needs to be kept at temperatures between -297 degrees Fahrenheit and -432 degrees Fahrenheit.
So, if your rocket is baking in the bright sun on the launchpad for hours, or days, it's going to be cheaper to keep it cool if it's white. This may also be the case for silver, according to research that found silver cars had cooler cabins than black cars.
SpaceX wouldn't comment on whether, or not, that's the reasoning for their silver Starship rocket. But it makes sense that if they don't have to paint the rocket white, and keep its natural steel color, then they not only save money on paint, but also end up with a lighter rocket, since paint is heavy.
"Absorptive and emissive properties, including color, will always play a role for passive thermal control," Gruntman said. Although when it comes to heat management, white is even better than silver.
Despite a clear explanation from SpaceX for Starship's silver and black visage, chances are it's to keep the rocket light and safe, and isn't just for show.
Recently, during a conference in Washington, DC, SpaceX president and COO Gwynne Shotwell said, "The real goal is to not blow up the launch pad. That is success."
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