Let's Calculate The Carbon Footprint of the SpaceX BFR

The SpaceX Big Falcon Rocket is a proposed two-stage commercial intercontinental transport system. Get on the BFR in New York at 6 pm and you are in Tokyo at 7 pm (New York time) which is 8 am Tokyo time for that important business meeting.

Pretty nifty and futuristic right?

Well, let's stop for a second and try to figure out the carbon footprint for this trip.

Conventional Plane Trip

To be fair we need to figure out the carbon footprint for a conventional jetliner trip from New York USA to Tokyo Japan first.

Conveniently there is a website that will do that for you called Carbon Footprint Calculator

Using this site we get 0.79 metric tons (790 kg) of CO₂ emitted for an economy class passenger, 2.3 metric tons (2300 kg) of CO₂ emitted for a business class passenger and 3.2 metric tons (3200 kg) of CO₂ emitted for a first class passenger.

This is for a one way trip from JFK airport in New York to HND airport in Tokyo (13 time zones or roughly one-half way around the world).

BFR Trip

The fuel for the BFR is claimed to be methane (CH₄) and the fuel load is estimated to be 240,000 kg (240,000,000 g).

The atomic mass number for carbon is 12 and for hydrogen it is 1. Therefore the molar mass number for methane is 12 + 4 x 1 = 16. In other words, an Avogadro's number (6.022 x 10²³) of methane molecules will have a mass of 16 g.

The number of moles of methane aboard a BFR is therefore 240,000,000 grams divided by 16 = 15,000,000 moles of methane.

Each carbon in the CH₄ will be swapped over to a carbon in a CO₂ molecule. This is a one-to-one translation so we therefore know that each BFR trip will generate 15,000,000 moles of CO₂.

The atomic number for oxygen is 16 so the molar mass number for CO₂ is 12 + 2 x 16 = 44. This means that an Avogadro's number of carbon dioxide (i.e. one mole) has a mass of 44 grams.

From above we determined that 15,000,000 moles of carbon dioxide will be generated. This means that a single BFR trip will generate 15,000,000 moles x 44 grams/mole = 660,000,000 g = 660,000 kg of carbon dioxide.

It is hard to find a reference for the number of passengers that will be aboard this BFR intercontinental rocket so as a first guess I will assume it will be 100 people.

That means each passenger's carbon footprint will be 660,000 kg / 100 people = 6600 kg of carbon dioxide per passenger.

Let's compare that to a first class passenger aboard a jetliner which we found to be 3200 kg of carbon dioxide.

If the BFR carried 200 passengers per trip then the carbon footprint would come down to being roughly equivalent to the carbon footprint of a first class passenger.

To get the carbon footprint of a jetliner economy class passenger (i.e. a guy like me) then the BFR will need to carry at least 835 passengers. That does not seem realistic.

Closing Words

Elon Musk has been quoted as saying:

"Climate change is the biggest threat that humanity faces this century, except for AI, I keep telling people this. I hate to be Cassandra here, but it’s all fun and games until somebody here loses a fucking eye. This view of [climate change] is shared by almost everyone who’s not crazy in the scientific community.”

So it would seem to be ironic that Mr. Musk uses the fear of climate change to lobby for government subsidies for his Tesla automobile and trucking company while seemingly ignoring the impact of his proposed rocket on climate change.

In general, the theme these days is to try to reduce your carbon footprint to help mitigate the impact of this grand experiment called fossil fuel burning.

It seems to me that pandering to the rich so that they can get to their international business meeting in one hour is not the direction we want to be going.

Post Sources

<sub>1. Carbon Footprint Calculator. link
2. Big Falcon Rocket. link
3. Avogadro's constant. link
4. Elon Musk: 'Climate Change Is All Fun and Games Until Someone Loses a Fucking Eye', Newsweek November 15 2017.</sub>

Image Credit

The globe icon in the image was created by Mlevy2207 and sourced from https://commons.wikimedia.org/wiki/ File:America-globe.jpg (CC BY-SA 4.0 license.) and modified by Procrastilearner. CC BY-SA 4.0 license.