Why do SpaceX rockets take off white and come back black and white?

If you’ve ever seen footage of a SpaceX rocket launch, perhaps you’ve noticed a strange phenomenon… When the rocket leaves the launch pad, it’s white…

But when it comes back down from space all of a sudden it’s half black and white… and it has these really well defined sections of black and white.

What is happening? What causes this?

Today we’re going to take a deep dive into the subject of cryogenic rocket propellants and THEN we’re going to play with fire, because SCIENCE!!! In our very first “do not try this at home” demonstration, to help teach you just what exactly is going on during these launches!

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[m.zahranaditiyawan]

No, its black because some of space stuck to the booster

[minhtrungle]

Obviously because space is black, so when you dip a rocket in it it turns black.

[hzpc]

Appreciation for the use of the metric system you fine sir!

[MrMediator]

"Space changes a rocket"
"Oh yeah, in what way?"
"I used to be white" - Falcon 9

[thejesuschrist]

Glorious video! Loved the science project, thanks for enlightening us. 😇

[rulerofmonkeys]

I thought those binoculars were real for the first half of the video.

[mayankshrivastava]

I honestly believe every person interested in rockets is a pyromaniac in disguise! Loved the experiment. Love your work man!!

[robalox]

I watch all of your videos, no exception. I came to this one as I saw the notification and told myself "nothing new, i know this alread". NO I DIDNT. I wasnt expecting all the technical stuff you just said. Well done, I learned today <3

[river]

My friend and I provided the footage of the old truck pouring black smoke :)

It was a pleasure to help with this video Tim :)

[chadritenour]

Excellent video in both concept and execution. I'd advise considering more similar such content from a conceptual standpoint. Spacecraft design and associated physics is incrededibly interesting and not always apparent. Content such as this potentially provides answers to questions many of your viewers would not otherwise consider asking. Well-done!

[FrenchSpaceGuy]

I just would like to add some nuance one point: at 3:32 you claim that rockets remain pristine on ascent. But once first stages are jettisoned, they are already blackened, covered with soot because of recirculation and stream detachment. My latest video explains this effects in detail if someone's interested.
Otherwise: good job Tim, very interesting video.

[zzanzare]

I've been wondering about this for a looong time before I met a guy who worked at spacex and explained it to me. I never understood why nobody was curious about such an obvious thing.

[leonardsimmers]

Very nice video Tim! Great explanation for those who might be wondering about the white and black. Having been a fabrication engineer. I already knew about the soot from the RP1 as the Falcon 9 re-enter's the atmosphere, and the landing burn. Loved the little experiment with the aluminium, dry ice and candle. Showing the effects of the soot on the frozen section of the tube. Top marks my man. Great stuff.

[canadianstudentspaceinitia]

Wow! This type of presentation is great. You are not only a great educator, you make more and more people fall in love with space exploration!

[scottpayne]

Great video Tim! You have one of these most informative and purposeful channels on YouTube!

[AJMartorano]

I’m glad you covered this it had me confused

[ananthasainakkala]

1:02 Cat's reaction: OMFG what's wrong with these humans 🤭

[christiantrevino]

I LOVE THIS CHANNEL, as an aerospace engineer in the making this is the coolest stuff to me👍🏼

[b-lt]

Great video, two tiny corrections, kerosene is jet fuel. Same thing. RP-1 is a more highly refined form of petroleum than kerosene and eliminates many impurities like sulfur which would be bad for the engines. Both are basically diesel but higher grades. All of them are made from petroleum however the distillation temperature will yield diesel, kerosene, RP-1 or any number of products.
And the soot actually doesn't come from the exhaust plume of the engines. Those burn extremely clean. Because it's combusted at high pressures with pure oxygen there is almost no soot left, even if the engine runs fuel rich, most of that will burn up once it leaves the nozzle. You can observe this very well with the high speed footage of Saturn V. A black band of material exits the engines with a flame front climbing up towards the engines, never reaching them.

The soot comes from the gas generators that drives the turbopump. Here the combustion is extremely fuel rich and only partial leaving a lot of soot. It's the small flame vents next to the engine nozzles where a slow moving flame can be observed. It's easily observable on the BFR announcement where he stands in front of booster. This is what provides the soot. If they where staged combustion kerosene engines like RD-180 there wouldn't be much soot. That's why BFR will be pretty shiny after reentry, no major soot because of different fuel, and staged combustion engines that will burn the bit of soot that methane could make.

[macronencer]

Great explanation, and a fun experiment too. I look forward to your video about the environmental impact of rockets! I've often wondered what the numbers are on that.