r/Damnthatsinteresting • u/Moooses20 • Mar 06 '25

GIF RemoveDEBRIS satellite harpoons space junk in a plan to clean Earth's orbit

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u/KPSWZG Mar 06 '25

I needed to do math. The starlink satelite weights around 250kg, AGU Aplications said that of 250kg of Aluminium can produce 30kg of aluminium oxide. So in total we have one metric tone of aluminium oxide released. Thats extreamly low number. Starlink alone would need to fire those satelites for thousand of years to make significant impact. But at the same time. The increase of launches in total might contribute to steady rise of falling satelites and if something is not a problem today but might be tomorow the we shoild start working on it now to fix it.

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u/Clothedinclothes Mar 06 '25 edited Mar 06 '25

AGU Aplications said that of 250kg of Aluminium can produce 30kg of aluminium oxide

NO.

Not unless you're also doing some kind of Star Trek level of nuclear physics that is converting the other 220kg mass of Aluminium into pure energy. 

...chemical reactions don't make products with more or less mass than the total reactants.

I don't know what it's trying to calculate there, but whatever is it's not chemical conversion of Aluminium into Aluminium Oxide. 

Here's the maths: 

The molar mass of Al is 26.98g, while the molar mass of Al2O3 (Aluminium Oxide) is 101.96g i.e. 26.46% Aluminium by mass. 

If you fully oxidise 250kg of Aluminium it will make 944.77kg of Al2O3. 

Multiplied by 120 satellites, that's 113.37 metric tonnes of Al2O3.*

Correction, I forgot to double the Al percent by mass because its AL x2 in Al2O3.

Which makes it 52.92% by mass = 472kg of oxide per satellite. Making a total of 57 metric tonnes of Aluminium Oxide.

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u/Bettlejuic3 Mar 06 '25

No. 250kg aluminum produce 472kg Al2O3

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u/Clothedinclothes Mar 06 '25 edited Mar 06 '25

Yes my calculation was wrong as I forgot to double for the 2 Al per mole. Rather than 26.46% by mass it's 52.92% by mass.

Which for 120 satellite with 250kg Aluminium each burning up works out to about 57 metric tonnes of Al2O3.

Either way all that Aluminium doesn't disappear up its own butthole.