It Adds Up

Virgin Galactic SpaceshipTwo

Virgin Galactic is planning several flights per day for the next decade!  This is fantastic and would no doubt lead to orbital operations.  But I am wondering: What does the rocket do the stratosphere?  I am not even sure that VG has spelled out , exactly,  the propellants.  We know it is a nitrous oxide based hybrid but perhaps the fuel has aluminium?  Something else? 

 

So the propellant is, let's guess, 10 tons per flight.  All of it emitted into the stratosphere.  Now VG is talking on the order of 1000 flights per year.   Now lets assume an ODP of 0.5 - about like old fashioned SRMs.  Thus we have 5000 ODP-tons per year.   Is that a lot?  I think it is. 

Are Space Planes Really Environmentally Friendly?

A recent article in the New York Times reports on Virgin Galactic's (VG) efforts to offer " 'a trip of a lifetime' that won't harm the planet." Sounds great, and I'd sure like to ride with Jim Lovelock, one of the early influential scientists on my career in stratospheric ozone measurements (he invented the electron capture detector that remains the most sensitive way to detect chlorofluorocarbons). Sir Richard Branson (SRB) is quoted in the article as saying "The [carbon] cost of us putting someone into space will be less than flying to London and back on a commercial plane." Note the qualifier 'carbon', which was added by the author of that article.

It wouldn't be hard to calculate the carbon footprint of a VG spaceflight - say from New Mexico to Sydney, Australia, and to compare that on a per-passenger basis to the carbon footprint of a flight to the same destination on a 747. Now I don't doubt VG's claims that I have seen elsewhere that the carbon footprint would be smaller. However, what is missing in this comparison are the impacts on the stratosphere and mesosphere, which are minuscule in the case of the 747 (most of the ozone-harming emissions of subsonic aircraft remain in the lower atmosphere, where they are removed by photochemical processes). The impacts of emissions in the stratosphere and mesosphere, however, are usually all very harmful to ozone. So without a doubt, the impacts of VG spaceflights on the environment will be significant on a per passenger basis.

The recent paper in Astropolitics by Ross et al., of which I am a coauthor, points out that large numbers of such flights (in the case of space tourism or frequent launches of small payloads for climate change mitigation) could be the next major ozone depletion problem - perhaps as soon as the 2030s. the culprit? Emissions of soot, NOx, water vapor, and hydrocarbons. The stratospheric and mesospheric impacts of some of these emissions (e.g., H2O and NOx) are reasonably well understood, whereas the impacts of others (soot, HCs) are not. And the by-products of the "hybrid" rocket engines that VG will employ are a complete unknown - until we have measurements in the plumes of those rockets to confirm combustion models.

It would certainly be a shame if billions of dollars are spent between now and then to develop capabilities that reduce our global warming impacts, only to be shown to cause major damage to Earth's protective ozone layer, especially after the hugely successful efforts to limit other ozone depleting substances (ODS).

I don't doubt SRB's and VG's good intentions - after all, they are activively seeking ways to reduce their fossil carbon footprint and even offering a $25 milllion prize for demonstrating the ability to remove 10 billion tons of CO2 from the atmosphere in 10 years. It would seem that in this case, however, they need to take a broader view of the environmental impacts of their space launch activities. At the very least, it would be bad PR if Jim Lovelock's ride into space were to deplete more ozone than a year's worth of Virgin Atlantic flights from London to Sydney.

Now, it would be great PR if VG were to propose to use that flight with Jim Lovelock to actually measure their impacts on ozone. Perhaps someone will be able to blog about that issue in the not-too-distant future!

Parabolic Arc Gets it!

This is typical of sort of helpful - but sort of unclear - stuff on the web. Actually the story is not new but the writer sort of "gets it" about rockets and ozone with the tagline:

"Space tourism threat: less carbon emissions than ozone depletion?"

I interpret this as:

"Risk to space tourism profits is from ozone depletion, not global warming!"

which is pretty much on the mark. Nice going Doug Messier! Doug is one of the few spacetravel bloggers who understand that ODSs and GHGs are different. Coupled but different. Doug understands that rocket emissions are not a big deal from a GHG perspective but might well be a big deal from an ODS perspective. Eventually.

Anyway, its good to see somebody understand these two points. Is Virgin Galactic reading this?

Finally Solar Power Satellites?

Not a lot of details. This would be a pretty big satellite. The idea is to use "existing rockets" which does not narrow things down much. From an emissions perspective, the interesting factors are:

1. which launch vehicle

2. what launch rate

3. what period of time

But here is an interesting quote from the CEO: "These space launch vehicles primarily use natural fuels (H2, O2) and have an emissions profile similar to a fuel cell."

So he means Delta IV Heavy I guess. But this notion of "natural fuels" - the word natural is not defined and is usually a marketing ploy - leaves me wondering if this is serious at all.

Also I wonder what PG&E's exposure is. The risk is all Solaren's? I could not even find a website for Solaren. Anyway it looks very cool.

Disruptive Technology

This is an excellent overview of hypersonic propulsion. It is interesting that Director calls this "disruptive technology". He also touches briefly on scaling up X-51 by 100X and how hypersonic propulsion can be used for launch with "aircraft like" operations. The charts, while pretty cool, do not mention anything about the possible stratospheric effects of burning hydrocarbon fuel at 25 km altitude.

As you can see from the plot 25 km is right in the middle of the ozone layer. But ozone chemistry is tricky and sometimes adding one ozone destroying molecule just chemically ties up another and results in a decrease in ozone destruction. This is how subsonic aircraft cause an ozone increase.

Will hypersonic propulsion do that too? Or will they cause ozone loss? How much gain or loss?

Space Shuttle Reentry "Emission"

Space Shuttle and trailing hot gas plume during entry

If you add molecules of nitric oxide (one oxygen and one nitrogen, chemical symbol = NO) in the stratosphere at altitudes greater than about 20 km, the result is ozone depletion. One way to generate NO molecules to air is to heat it to about 2500 deg centigrade at which point nitrogen and in the air react to form nitric oxide (that is, NO).

Air can be heated to this temperature by the friction around a Space Shuttle during entry (or reentry). (BTW it is not really "friction" heating, but that is another post.) That is why the Space Shuttle has those tiles, to protect it from the very hot air that surrounds the vehicle during reentry and forms the glowing plume behind it. So the Shuttle for practical purposes the Shuttle is an "NO emitter" during reentry.

Almost three decades ago two guys Park and Raish (1980) did a quick calculation and estimated that the Space Shuttle generates approximately 0.02 kilotons of NO in the upper stratosphere during each entry as air heats up in the hot tail (see picture above) behind the Shuttle.

This is interesting of course because this NO will react with and destroy some ozone. This is also bad because ozone destruction, in general, is bad. So it is interesting that simply by returning to earth, the Space Shuttle causes ozone depletion.

Very roughly this is equivalent to the mass of total NO emitted by the jet engines of a Concorde supersonic transport during half a dozen or so transatlantic flights. (The Concorde does not fly anymore by the way.) I point this out so that you can put the Space Shuttle reentry NO production during reentry into some context by comparing it to another source of NO molecules that scientists worry about, supersonic transports. Park and Raish did not calculate the ozone destruction caused by a Shuttle reentry. A different model would be needed to do that.

I wonder a few things here:

1. The Park and Raish work was done over a quarter of century ago. Would the result be different using up to date calculations and models?

2. How does the ozone depletion from Shuttle entry compare to the depletion from Shuttle launch? The emissions from the big solid rockets likely cause more ozone depletion but I wonder how much more?

Where Is the White House going on HFCs?

This is interesting.  EPA and State Department want to phase-out HFCs using the levers and buttons of the Montreal Protocol.  In the process, the Montreal Protocol would become the de facto international legal mechanism for greenhouse gas regulation.  But the President is not going that way despite hard lobbying by EPA and State..

What is the White House policy here?   The big plan is not obvious. 

Advecting and Mixing Space Shuttle Plume at Sunset

Note the inset detail showing where ice particles have grown large enough to fall from the cloud layer.  This phenomenon, called virga, indicates that ice particles in the plume are growing to a critical size.  This might be removing ozone destroying nitrogen compounds (called denitrifying) the tropopause region since we know that the solid rocket motor alumina particles carry HNO3.   

Rocket Emissions and the Montreal Protocol

One of the most interesting comments in response to Ross et al. (2009) was from David Fahey of NOAA's Chemical Science Division.  David in a key figure involved with the many and varied scientific aspects of ozone layer protection.  See here for a nice review by David. 

Here his comment: "There's a number of exemptions to the protocol," he said. "Each one by itself is small, but if you go too far, it could be death by a thousand cuts."

 

Often it is difficult to make reccomendations without falling to the "Cassandra Complex" but the space industry should take an interest in not being one of the thousand cuts.  

A World that Might Come About

Here is an interesting paper that shows how large space systems might cause so much ozone loss that a few decades down the road rocket launches could be regulated.   That is to say - limited or capped.  That paper is not definitive in any sense but that is the point.  There are factors of 10 uncertainty in:

1. How much global ozone loss rockets actually cause - especially liquids

 

2. How much ozone loss would be "too much"?

 

As the Iridium - Kosmos collision showed it is most unwise to allow multiple factors of ten to run around your space policy and space ops spreadsheets and white boards.  Before that collision, certain "Cassandras" were hinting that such a collision was likely to happen in the next few years. 

 

Ross et al. (2009) play the same hand.  There are factors of ten running around the science and policy that will cause a collision at some point if ignored. 

A World Avoided

This is interesting.  A model by Newman et al. (2009) that explores how the stratosphere, and so the solar UV intensity at the earth's surface, would have evolved sans the Montreal Protocol.  The idea of actually running through these numbers and publishing them is pretty clever.  We take the Protocol for granted but it has been around for so long (1985) that it is also beginning to seem like a 20th century idea.  The players have changed.  The substances have changed.  So the paper has large poltical value. 

The paper also shows that there is technical value in modeling what will never be.  You can learn new things about a system by watching how a numerical model evolves and responds to changed assumptions and runs off into new parameter spaces.  Still this is not a "science" paper in the strict sense.  It is a political science paper in that Newman et al. (2009) do two things there:

1. Wave a big stick regarding the model.  They say "Our model can deep dive into nonlinear territory and provide consistent results."  This is important. 

2. The Montreal Protocol is a powerful and successful policy apparatus to control industrial emissions that affect the atmosphere. 

One might read into this something like "the Montreal Protocol is successful and the Tokyo Protocol is not." 

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