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Calculating Environmental Damage From Space Tourism Rockets
MithrandirAgain writes "A new study from several scientists at the Aerospace Corporation claims spaceships that rely on rubber-based fuel could help cause climate change. The fuel apparently expels a black carbon soot into the stratosphere when burned with nitrous oxide, which could be contributing to global climate changes, like shrinking the icecaps. However, the authors are careful about their work being an end-all study and are 'inviting others to take a look.' Virgin Galactic, whose SpaceShipTwo just made its first solo flight (and uses the type of fuel discussed in the study), is listening to the scientists' concerns. CEO George Whitesides said, 'I think we and others in the industry welcome the opportunity to talk about all of these issues.' SpaceShipTwo does use a hybrid engine 'because of its significantly lower environmental impact than other designs,' and Whitesides stresses, 'I think as we look at this more, we'll find the impact will be far smaller than that set out in the paper. In any case, I welcome the conversation.'"
What I find interesting is that they're claiming that injecting soot into the stratosphere would cause global warming (at least according to the summary, didn't RTFA.) When blasts of particulate matter from other sources have reached those heights (for example, when Krakatoa went postal) it resulted in global cooling instead. I'm assuming there's a different mechanism involved.
The higher the technology, the sharper that two-edged sword.
The reason they went with this motor design was simplicity of construction, low chance of explosions and other nasty failure modes, reliability and price. Yet another is that this motor type can be shut off before the burn is complete (unlike the SpaceShuttle side boosters which use a thermite-like mixture (with a rubber-like binder) which provides its own oxidizer.
The Rutan design uses nitrous oxide as an oxidizer to be able to better control the burn.
I don't recall environmental factors being discussed when Rutan and co. were publicizing the motor design.
The engineering reasons are perfectly good, though, and research into figuring out a blend which spews out less soot would probably be good from all standpoints (possibly even upping the specific energy content of the motor/fuel)
Careful now: FUD as we typically use it on Slashdot is doubt raised by pure rhetoric, in the absence of facts. These guys have actual *data*. You can question their assumptions, but they're not just using scary words.
The obvious question that comes to my mind is why do think that any significant amount of soot from the 1000 rockets launched this year would still be in the atmosphere in 40 years? Do they have any reason to suspect that it stays around that long?
I've found the original Geophysical Research Letter article (it's behind a paywall unless you're at an institution that subscribes to GRL, which I am).
They do *not* assume that the soot sticks around for 40 years: they include a settling time for the soot particles of a couple of years (details more complicated). But they run the model for 40 years to give the ocean and cryosphere time to adjust.
They use a detailed model of the interaction of sunlight with soot particles: this model was developed for studying nuclear holocaust scenarios. They make some assumptions here about the size and properties of rocket soot particles, but I don't see any red flags.
Finally, again comparing to volcano's, the best data I can find for a volcanic eruption that changed the climate (1991 Pinatubo) suggests that it dumped 17 million tons of CO2. I know this is talking about rubber particulates and not CO2, but there's a big difference in magnitude between 17 million tons in a few days and 1.3 million tons over 40 years.
Soot particles have a *very* different climate effect than CO2, it's apples and oranges.
Based on what I read in their article and on my personal experience as a climate modeling scientist, I can tell you that they're using the right computer model for the job, and their assumptions about soot input seem reasonable, and they're including all the relevant physics.
It should also be mentioned that the climate change effects they're predicting (1 polar temperature rise, 5-15% northern polar sea ice loss) are observable, but *much* smaller than the predicted changes from anthropogenic greenhouse gas emissions (up to 8C polar temperature rise, possible total loss of summer sea ice). But still, no joke.
Then you come along with some volcano analogy, despite the fact the entire study is based on the *high altitude* generation of soot particles and I haven't seen any flying volcanos recently.
The GP is absolutely correct though. The article was talking about stratospheric effects. As it happens, vulcanism is perfectly capable of ejecting all sorts of substances that can have profound effects on weather into the stratosphere. How do you think eruptions like Krakatoa and Pinatubo had globe-spanning effects?
The higher the technology, the sharper that two-edged sword.