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!