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) launch Bezos, his brother and two guests in space using liquid hydrogen and liquid oxygen thrusters. VSS unit used a hybrid thruster composed of a solid carbon-based fuel, hydroxyl-terminated polybutadiene (HTPB), and a liquid oxidant, nitrous oxide (laughing gas). The SpaceX Falcon series of reusable rockets will propel the Crew Dragon into orbit using liquid kerosene and liquid oxygen.
Our first human flight on Tuesday will be the 16th flight in #NewShepard‘s story. Discover the meticulous and rigorous launch program that brought us to this first step. Follow the launch live on https://t.co/7Y4TherpLrfrom 6:30 a.m. CDT / 11:30 a.m. UTC. #NSFirstHumanFlight pic.twitter.com/xWQRYLikZd
— Blue Origin (@blueorigin) July 18, 2021
Burning these propellants provides the energy needed to launch rockets into space while generating greenhouse gases and air pollutants. Large amounts of water vapor are produced by the combustion of the BE-3 propellant, while the combustion of VSS Unity and Falcon fuels produces CO₂, soot, and water vapor. The nitrogen-based oxidizer used by VSS Unity also generates nitrogen oxides, compounds that contribute to air pollution closer to Earth.
Nearly two-thirds of propellant exhaust is released into the stratosphere (12 km-50 km) and mesosphere (50 km-85 km), where it can persist for at least 2–3 years. The very high temperatures during launch and reentry (when the protective heat shields of the returning craft burn out) 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 to oxygen, depleting the ozone layer that protects life on Earth from harmful UV rays. Water vapor also produces stratospheric clouds which provide a surface for this reaction to occur at a faster rate than it would otherwise.
Space tourism and climate change
Exhaust CO₂ emissions and soot trap heat in the atmosphere, contributing to global warming. Cooling of the atmosphere can also occur, as clouds formed from emitted water vapor reflect incoming sunlight back into space. A depleted ozone layer would also absorb less incoming sunlight and therefore heat the stratosphere less.
Determining the overall effect of rocket launches on the atmosphere will require detailed modeling 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 plans to offer 400 space flights each year to the privileged few who can afford it. Blue Origin and SpaceX have yet to announce their plans. But globally, rocket launches would not need to increase much from the current around 100 made each year induce harmful effects which are competitive with other sourcessuch as ozone-depleting chlorofluorocarbons (CFCs) and CO₂ from airplanes.
During launch, rockets can emit between 4 and 10 times more nitrogen oxides than Drax, the largest thermal power station in the UK, during the same period. The CO₂ emissions of the approximately four tourists taking a space flight will be between 50 and 100 times greater than those one to three tons per passenger on a long-haul flight.
For international regulators to track this fledgling industry and properly control its pollution, scientists need to better understand the effect these billionaire astronauts will have on our planet’s atmosphere.