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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)
Seriously! We can use the N2O to send six people into space, or use the same amount to make, like, a million people think they're in outer space - for about thirty seconds anyway.
While the Wired story doesn't show blatant bias unlike the Nature story, "Space tourism to accelerate climate change", it still remains that no mechanism for the claimed climate changes has been described. It's just, "These guys ran their computer model and this is what they got." That's extremely unhelpful.
This offends your worldview so you dismiss it.
For a better analysis, lets review the story so far:
1. A group of highly qualified academics publish research showing that hybrid rocket engines *may* have a polluting effect far out of proportion to the emissions they have on paper. The researchers are careful to stress the word *may*
2. They find another expert in the field who says "This is interesting, but not a definitive conclusion" i.e. agrees with the assessment of the original team.
3. Spokespeople for corporations who want to make profits from the use of hybrid rockets say its all bullshit, despite these spokespeople having no real qualifications.
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.
When science says things you don't like, and you decide to dismiss the academic structures on which science is based just because you don't like the new (possible) reality, that is a bit of a dick move.
Here is the real bitch though; nobody is going anywhere significant in N20/rubber hybrid rockets. They are good for quick-and-easy sub-orbital rides because they are safe and simple to build, but to get into orbit you need more powerful fuels which likely do not have the soot problem - so if space tourism does take off and get some non-pathetic technology, they will have moved on from producing soot-rich exhausts anyhow.
If we can put a man on the moon, why can't we shoot people for Apollo-related non-sequiturs?
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.
A very important distinction: planes, ships, and buses are designed to run clean, with little or no soot output. They also operate in the troposphere, where rainfall "washes" the atmosphere and cleans out the soot and other particles regularly. This is a very different thing than NO+rubber rockets (which are literally as clean-burning as a burning tire) in the stratosphere, where small particles tend to linger for years.