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What is the carbon footprint of space tourism?

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Amazon founder Jeff Bezos does not appear best pleased with Richard Branson stealing some of his thunder with the Virgin Galactic launch: Branson went 53 miles (85 kilometers) into suborbital space on Sunday while Bezos has a self-funded trip to space planned for July 20. Bezos published a document comparing his Blue Origin to Branson’s Virgin Galactic, including its impact on the ozone layer.

Source: Blue Origin

The fine print at the bottom notes that “a liquid hydrogen/liquid oxygen rocket engine (which Blue Origin uses) has 100X less ozone loss and 750X less climate forcing magnitude than an air-launched hybrid engine (which Virgin Galactic uses).”

But what is the carbon impact of a flight? Neither Blue Origin nor Virgin Galactic has been particularly transparent about the carbon footprints of their ventures, and all we can do is guess.

 

Virgin Galactic

Virgin Galactic has only said that it is equivalent to a business class return ticket on a transatlantic flight, which the Financial Times calculates to be 1,238 kilograms of carbon dioxide per person.

 

Source: Virgin Galactic

 

A much earlier article in the Wall Street Journal suggests that it is higher:

“According to the U.S. Federal Aviation Administration’s environmental assessment of the launch and re-entry of Virgin Galactic’s spacecraft, one launch-land cycle emits about 30 tons of carbon dioxide, or about five tons per passenger. That is about five times the carbon footprint of a flight from Singapore to London.”

 

For something that isn’t going to happen very often, that isn’t such a big deal, even if it is nothing more than an expensive joyride. But as in everything else these days, you have to go beyond just the fuel burn.

The Virgin Galactic plane burns HTPB (Hydroxyl-terminated polybutadiene) and nitrous oxide, sometimes referred to as rubber cement and laughing gas. HTPB is the main ingredient of polyurethane and is made from butadiene, a hydrocarbon extracted during the steam cracking process used to make ethylene. The heat needed to make the 900 degrees Celcius steam comes from natural gas, and one study estimated there is about a metric ton of CO2 emitted for every metric ton of ethylene, so it probably is about the same for butadiene.1 So that would mean that emissions including upstream manufacturing emissions of the fuel are double, or about 60 metric tons of CO2.

This doesn’t include the fuel used for the big plane that carried the craft up, and of course, it doesn’t include the embodied carbon from building the whole operation.

 

Blue Origin

Bezos’ New Shepard is a rocket, not a space plane, and needs a little more oomph to get off the ground, so it is running on liquid hydrogen and liquid oxygen. The products of combustion are water and a tiny bit of nitrogen oxide.

 

Launch of New Shepard. Source: NASA

 

However, hydrogen has a big carbon footprint of its own. Most of it is “grey” hydrogen made by steam reformation of natural gas, a process that releases 7 kilograms of CO2 per kilogram of hydrogen. Compressing it and cooling it into liquid hydrogen is also energy-intensive; in an earlier post, the company making it said it took 15 kilowatt-hours of electricity per kilogram of hydrogen. A lot of liquid hydrogen is made in Texas, where according to the U.S. Energy Information Administration, the electricity emits 991 pounds of CO2 per megawatt-hour, or 0.449 kilograms per kilowatt-hour, or 6.74 kilograms per kilogram of hydrogen.2 That totals roughly 14 kilograms of CO2 per kilogram of liquid hydrogen.

Compressing and liquifying oxygen is energy intensive too: according to engineer John Armstrong, to produce one metric ton of liquid oxygen (LOX) you need about 3.6 megawatt-hours of electricity. Applying Texas electricity, you get 1.61 kilograms of CO2 making 1 kilogram of LOX.

 

Source: Reddit

 

Bezos hasn’t released any details on the amount of fuel it takes to launch his rocket, but a Redditor did some estimates and came up with 24,000 kilograms of fuel. At a 5.5 mix ratio (hydrogen is really light, 1/16 the weight of oxygen) you get:

  • 4363 kilograms of hydrogen X 14 kilograms of CO2 = 61 metric tons of CO2
  • 19637 kilograms of oxygen x 1.61 kilograms of CO2= 31.6 metric tons of CO2
  • Totalling 93 metric tons of CO2 per launch

 

None of this includes the incalculable upfront carbon emitted making all the prototypes and infrastructure and the rockets and planes themselves, a Life Cycle Analysis of the whole enterprise would be mind-boggling, but that is another story.

 

So What’s the Big Deal?

In the larger scheme of things, it’s not much, with Virgin Galactic at 60 metric tons of CO2, Blue Origin at 93 metric tons. After all, a full 777-200 going from Chicago to Hong Kong pumps out 351 metric tons and that kind of flight happens many times per day. It’s carrying many more people many more miles, but the total CO2 emissions from flying dwarf that of these rockets.

It looks even less dramatic when you compare it to the average footprint of the billionaire who could afford a $250,000 ticket; he probably already has a carbon footprint of 60 to 80 metric tons per year flying private between multiple residences.

In the end one can probably conclude that we don’t need fewer rockets and less space tourism, we need fewer billionaires.

 

 

Source Treehugger

July 22, 2021

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