July 11, Branson ascended 80 km (49 miles) to reach the edge of space in his piloted Virgin Galactic VSS Unity spaceplane, while Bezos’ autonomous Blue Origin rocket launched today on July 20, coinciding with the anniversary of the Apollo 11 Moon landing. Although Bezos launched later than Branson, he set out to reach higher altitudes — about 120 km, or 74 miles.
The launch demonstrates a new type of offering to very wealthy tourists: The opportunity to truly reach outer space. Tour packages will provide passengers with a brief 10-minute frolic in zero gravity and glimpses of Earth from space. Not to be outdone, later in 2021, Elon Musk’s SpaceX will provide four to five days of orbital travel with its Crew Dragon capsule.
What are the environmental consequences of a space tourism industry likely to be? Bezos boasts that his Blue Origin rockets are greener than Branson’s VSS Unity. The Blue Engine 3 (BE-3) launched Bezos, his brother and two guests into space using liquid hydrogen and liquid oxygen propellants.
VSS Unity, on the other hand, used a hybrid propellant comprised of a solid carbon-based fuel, hydroxyl-terminated polybutadiene (HTPB), and nitrous oxide (or laughing gas), while the SpaceX Falcon series of reusable rockets will propel the Crew Dragon into orbit using liquid kerosene and liquid oxygen.
Burning these propellants provides the energy needed to launch rockets into space — but it simultaneously generates greenhouse gases and air pollutants. Large quantities of water vapor are also produced by burning the BE-3 propellant, while combustion of both the VSS Unity and Falcon fuels produces CO2, soot and some water vapor. The nitrogen-based oxidant used by VSS Unity also generates nitrogen oxides, compounds that contribute to air pollution closer to Earth. Roughly two-thirds of this propellant exhaust is released into the stratosphere (12 km-50 km) and mesosphere (50 km-85 km), where it can persist for at least two to three years.
The very high temperatures during launch and re-entry (which is when the protective heat shields of the returning crafts burn up) also convert stable nitrogen in the air into reactive nitrogen oxides. These gases and particles have many negative effects on the atmosphere. In the stratosphere, nitrogen oxides and chemicals formed from the breakdown of water vapor convert ozone into oxygen and deplete the ozone layer which guards life on Earth against harmful UV radiation.
Water vapor also produces stratospheric clouds that provide a surface for this reaction to occur at a faster pace than it otherwise would.
Space tourism and climate change
What’s more, CO2 exhaust emissions and soot trap heat in the atmosphere, contributing to global warming. Cooling of the atmosphere can also occur, as clouds formed from the emitted water vapor reflect incoming sunlight back to space. A depleted ozone layer would also absorb less incoming sunlight, and so heat the stratosphere less.
Figuring out the overall effect of rocket launches on the atmosphere will require detailed modeling, in order to account for these complex processes and the persistence of these pollutants in the upper atmosphere. Equally important is a clear understanding of how the space tourism industry will develop.
Virgin Galactic anticipates it will offer 400 spaceflights each year to the privileged few who can afford them. Blue Origin and SpaceX have yet to announce their plans. But globally, rocket launches wouldn’t need to increase by much from the current 100 or so performed each year to induce harmful effects that are competitive with other sources, like ozone-depleting chlorofluorocarbons (CFCs), and CO2 from aircraft.
During launch, rockets can emit between 4 and 10 times more nitrogen oxides than Drax, the largest thermal power plant in the UK, over the same time period. CO2 emissions for the four or so tourists on a space flight will be between 50 and 100 times more than the one to three tonnes of emissions that are generated per passenger on a long-haul airplane flight.
In order for international regulators to keep up with this nascent industry and control its carbon pollution, scientists need a better understanding of the effect space tourism will have on our planet’s atmosphere.