Friday, July 17, 2009

Amount of carbon dioxide emitted by an Apollo launch

Looking at the size of the Saturn V, the most powerful machine ever created, one cannot help but wonder how much atmospheric CO2 would have been generated by a single Apollo launch. Intuitively, one would say it would have to be enormous. However intuition is often wrong as I will show below. This is an easy calculation to make. Only the first stage of this rocket used a carbon containing fuel: RP-1. The tank contained 770,000 liters of the stuff, which corresponds to about 700,000 kg. Since RP-1 is mostly aliphatic carbohydrates, one can assume the ratio of carbon to hydrogen to be about that of CH2, leading to the realization that burning all that fuel leads to the creation of 50 megamoles of CO2 - wow! or about 1.1 million cubic meters, about the volume of a cube 100 meters on all sides. In weight this is about 2.2 million kilograms, or in the parlance used to compare CO2 emissions, 2.2 kilotonnes.

Now we should place that in perspective. The US generates 5.9 gigatonnes of CO2 each year which comes down to about 20 tonnes per person per year. So a single Apollo launch generated about 1/3 of 1 millionth of the current annual production of CO2 by the US or the total yearly emission associated with 110 people. Much more of course in 1969 units. In the calculation, I neglected to mention the CO2 generated to produce the liquid hydrogen for the second and third stages. This would maybe double the amount of CO2 produced depending on the process used to make LH2 but I'll ignore it for now as it doesn't significantly change the conclusion. In other units, the 2.2 kilotonnes is about the CO2 production of 400 typical US cars/year (or about 1000 Priuses ;-) ). In more modern units, it is the amount of CO2 produced to charge about 360 million iPods - close to the total number of iPods ever produced. So if we get every iPod/iPhone/iPod touch owner to not charge their iPod(s) a few times where they normally would have, we'll have made up for the CO2 produced by firing the rockets for the Apollo missions.

I hope I didn't make too many order of magnitude errors here ;-) I just wrote it out on the back of an envelope. I wonder whether the firing of the rockets actually weighed up against all the other activity around the program such as flying the astronauts around the world for training and all the buildings and other stuff they did to make the missions possible. Perhaps not.

The image above came from wikipedia where you can find a much larger version.

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