Thinking about space today, one wonders- what is the carbon footprint of the space program? At first glance, not that bad; one source says 28 Tons of CO2 per launch. Other aspects are worse, like the 23 tons of particulates from the ammonium perchlorate and aluminum solid rocket boosters, and the 13 tons of hydrochloric acid.
Others say that the liquid fuel rocket is the cleanest thing going, burning liquid hydrogen as fuel and just producing water vapour. What could be bad about that?
For one thing, it takes a lot of energy to make liquid hydrogen; Praxair, a big producer, says it takes 15 Kilowatt-hours of electricity to make a kilogram of the stuff. The shuttle is carrying 113 tons of it. That works out to 1,360,770 kWh of electricity, about the same as 128 average American homes use in a year.
The plants that make the liquid hydrogen are near the refineries in the southern states; I cannot find out where they get their electricity, but will assume that it is the same mix as the rest of the country, about 50% coal fired. Coal produces 2460 kWh per ton, so if half the energy used to make the liquid hydrogen is from coal, that means it took 270 tons of coal to produce it.
The energy information administration reports that bituminous and sub-bituminous coal, the main kinds used in electricity production, produce 4,931 pounds and 3,716 pounds of CO2 per ton of coal burned respectively.
So lurking behind the modest 28 tons of CO2 produced by the launch is 672 tons of CO2 produced in squeezing and chilling that hydrogen into a liquid. That doesn't account for the footprint of the trucks driving it to Florida or the losses that boil off along the way. Or, of course, the manufacture of the one-shot external fuel tank.
Praxair is building a liquid hydrogen plant near Buffalo to take advantage of the cheap green power of Niagara Falls, at at which point the overall carbon footprint of the stuff will be reduced. But right now, liquid hydrogen can hardly be called a green fuel.