The recent private recreational spaceflights undertaken by Richard Branson and Jeff Bezos have sparked much debate and considerable outrage. One argument against these endeavours is the colossal waste of energy for what is essentially a glorified joyride.
But we take joyrides everyday; vacations and excursions in planes, trains, and automobiles, collectively expelling many orders of magnitude more greenhouse gases into the atmosphere. I was curious as to how spaceflight compared, and how a carbon tax might apply. A few quick searches show that a Falcon 9 (RP-1 fuel) vehicle emits 425 metric tons of CO2, about what 100 passenger vehicles emit in one year.
So, should a carbon tax on spaceflight be public policy, inline with terrestrial transportation? A simple analysis for CO2, assuming something like $100/MT, determines an F9 launch would be taxed $42,500 per flight.
Other fuels and concomitant impacts would be taxed accordingly; hydrogen and methane based fuels would pay less and more as appropriate, and other emissions (NOx, chlorine, alumina, etc.) considered per their environmental impact.
Is this a reasonable policy, and do the numbers look about right if so?
I realise these are simple calculations, but don’t want to get lost in the weeds on the policy question. I’m sure our esteemed rocket scientists can weigh-in to correct and augment the analysis.
If we were to implement a carbon tax of some form, then of course it should apply equally to rockets. And we should implement a carbon tax. But it would make no sense whatsoever to implement a special carbon tax just for rockets.
Yes, a Falcon 9 emits in the ballpark of 4-500 tons of CO2 per flight.
Blue Origin’s New Shepard vehicle burns hydrogen, which ends up as water. So, no direct CO2 emissions. However, almost hydrogen is produced by steam reformation of natural gas, and the resulting CO2 is just as bad as if it were burned. Actual mass figures are hard to come by, but the entire thing weighs less than 50 tons, so probably on that order for equivalent CO2 use.
I’m not sure about SpaceShipTwo. The numbers could be worked out, it’s just that its rocket uses an unusual chemistry and we can only make rough estimates about the fuel use of its carrier plane. Probably tens of tons rather than hundreds, though.
Either carbon taxes or carbon markets are reasonable policy (I prefer the latter, but don’t have a problem with either). And around $100/ton is about right for now, though one could argue for higher numbers.
So overall, I’m in agreement. All carbon emitters should be taxed or forced to buy credits, including anyone launching rockets. Arguably they should pay a multiplier since the emissions are farther up in the atmosphere where they tend to do more damage, but I don’t know how well characterized that is.
Correct. See the 4th paragraph in the OP. I’m not sure why this is a problem; the idea behind a carbon tax is to offset the environmental impact. Cleaner fuels result in lower taxes.
ETA: Excellent addition by @Dr.Strangelove re: considering the impacts of fuel production. I think those are reasonable to consider (although not the construction of the vehicles themselves – that is a separate issue IMO).
There are questions about when a carbon tax would be applied. For the most part, it makes sense to charge the emitters. So the party burning hydrogen would not pay a tax, but the hydrogen supplier would (and pass on the costs).
On the other hand, that’s kinda impractical for road vehicles. No one wants to keep track of their emissions. But you know that the gasoline is going to be burned as fuel and can tax that. Alternatively, tax the refinery. These things can be worked out but they require some thought.
Incidentally, the SpaceX Starship has around 4600 t of propellant, at a oxidizer:fuel ratio of ~3.6:1. So 1000 t of CH4, and 750 t of carbon. That carbon then burns to 2750 t of CO2, which at $100/t tax is $275,000.
Musk wants to fly the thing for a few million per flight, so the carbon tax isn’t an insignificant part of the cost. He also wants to switch to carbon-neutral generation of the methane, though I’m not sure how cost effective that’ll be.
Even if Starship costs $20M/launch, it’ll still be an incredible savings over the current state. A 1.5% cost increase over that due to the carbon tax isn’t a big deal.
One reason I prefer a carbon market over a tax is that it allows carbon emitters and carbon capture tech to come to an equilibrium. Eventually we need to have net zero CO2 emissions. But some emissions will be very costly to cut, and it’ll make sense to capture those instead. The right price is difficult to predict though since it changes with new technology. A market system is more responsive to changing conditions.
Obviously, CO2 and water dominate the exhaust. But CO and O2 are not insignificant (and even H2 is higher than I’d expect). However, it goes on to say this:
The one-dimensional kinetics modeling of the after-burning characteristics of the exhaust plume was performed assuming a piecemeal constant pressure (13.3-14.7 psia) and entrainment of ambient temperature air. The small concentration of unburnt methane is rapidly oxidized, surviving less than 1 msec. The model predicted that nearly complete CO oxidation occurs, with concentrations reduced to 3 ppm within 100 msec. The plume exit concentration is approximately 1 ppm. There is no significant thermal NO formation, with just 1 ppm formed during the early part of the entrainment process.
So even the remaining CO (and CH4) end up oxidizing almost completely. The approximation of just looking at the input carbon is valid.
Methane is the cheapest propellant there is. Plain kerosene is pretty cheap, but gets more expensive when refined into RP-1. Methane is just natural gas, though. I don’t know if SpaceX plans on using a specially pure grade of it, but even if so the purification step is trivial once it’s liquified.
Hydrogen is very expensive, partly due to the extreme cold. In spaceflight, usually if you hear of “cryogenic propellant”, they mean hydrogen. Liquid oxygen and such is still cryogenic, but hydrogen is… extra cryogenic, so only it gets the label. Plus hydrogen causes embrittlement and a bunch of other issues.
If SpaceX can drive down the non-propellant costs to negligible levels, then they can launch for <$1M. That’s super optimistic but that’s the limit they’re driving toward. Might need a Starship 2, once they start learning which mistakes they made on the first.
Another reason methane is cheap is because it has a high oxygen ratio. Almost 4 units of oxygen per 1 of methane. And oxygen is really cheap… like <$100/ton.
Yeah, that’s in the ballpark. I don’t actually know the net efficiency of steam reformation off the top of my head, but it’s probably not too much worse than 50%. Might depend on where the excess energy comes from (i.e., electrical, etc.).
Long run you can generate it with wind/solar/nuclear and electrolysis. It’s just not done now since the cost is higher. A carbon tax might change the winner.
