Rocket Engines, Fireworks, and Chemistry...

...and why we can thank ancient Chinese alchemists for global satellite internet.

SpaceX recently completed another hot fire test of Starship’s Raptor engine in anticipation of another orbital test of the vehicle later this year. The engine is a beast, with over 3000 kilonewtons of thrust (at sea level) and a chamber pressure of over 300 bar.¹

Any rocket engine is really just a controlled explosion. That controlled explosion is the core technology that enables us to launch spy satellites, deploy integrated broadband communication networks, and explore the solar system.

But this Fourth of July holiday I got thinking about the original controlled explosion…the firework!

The core ingredient of any firework is explosive black powder (75% potassium nitrate, 15% charcoal and 10% sulfur). It was first discovered by Chinese alchemists over a thousand years ago during the Tang Dynasty.² When one puts black powder in a contained space with a small hole and lights it, the release of energy through the hole blasts it in a given direction.

But where do the colors come from? Mix it with other chemicals! “Strontium makes red. Barium produces green. Copper burns blue, and so on.” And if we add metals (like aluminum, magnesium, and titanium), we get the sparkles and flashes! And sound? Vary the size of the hole for the gas and energy to escape, or contain the explosion altogether! A small hole with a lot of gas makes a high-pitched whistle, and a large explosion with no hole makes a loud, deep “boom”.³

So in short, technical feasibility aside, I’m advocating for Elon and SpaceX to mix some barium and aluminum into Raptor’s controlled explosion for Starship’s next orbital test :). It’s likely the only thing that would make what is an already incredibly inspirational thing that much more exciting.

Happy Fourth of July everyone!

-Mike

1. https://spaceflight101.com/spx/spacex-raptor/

2. https://interestingengineering.com/culture/the-history-of-fireworks-from-ancient-china-to-today

3. https://phys.org/news/2021-12-fireworks-pyrotechnics-chemist-science-brilliant.html