The commercial competition to take tourists to space is intensifying between two of the world’s biggest billionaires, Virgin Group founder Sir Richard Branson and former Amazon CEO Jeff Bezos. On Sunday 11 July, Branson flew 80 km to reach the edge of space in his Virgin Galactic VSS Unity spaceplane. Bezos’ autonomous Blue Origin rocket was launched into space on July 20, marking the anniversary of Apollo 11’s moon landing.
These flights provided an opportunity to the very wealthy to reach outer space. On both trips, passengers enjoyed a brief ten-minute flight with zero gravity and a glimpse of Earth from space. Going a step further, Elon Musk’s SpaceX will conduct four to five days of orbital travel with its Crew Dragon capsule later in 2021. Bezos claims that his Blue Origin rocket is better environmentally than Branson’s VSS Unity. Blue Engine 3 (BE-3) used liquid hydrogen and liquid oxygen propellants.
‘Greenhouse gases and air pollutants are also produced’
VSS Unity used a hybrid propellant consisting 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 use liquid kerosene and liquid oxygen to propel Crew Dragon into orbit. Burning these propellants provides the energy needed to launch rockets into space while also producing greenhouse gases and air pollutants. The burning of the BE-3 propellant generates large amounts of water vapor, while the combustion of both the VSS Unity and Falcon fuel 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 near Earth. Roughly two-thirds of the propellant exhaust is released into the stratosphere (12 km–50 km) and the 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 (when the protective cover of the returning vehicle burns) also converts the fixed nitrogen in the air to reactive nitrogen oxide.
These gases and particles have many negative effects on the atmosphere. In the stratosphere, nitrogen oxides and chemicals formed by the breakdown of water vapor convert ozone into oxygen, depleting the ozone layer that protects life on Earth against harmful UV radiation. Water vapor forms stratospheric clouds, which form a surface, causing this reaction to occur at a faster rate than under normal conditions. Space tourism and climate change release heat in the atmosphere due to CO2 and soot emissions, which contribute to global warming.
Clouds made of emitted water vapor reflect light
The atmosphere may also cool, as clouds made of emitted water vapor reflect sunlight back into space. A depleted ozone layer will also absorb less incoming sunlight, and therefore warm the stratosphere less. Detailing the overall impact of rocket launches on the atmosphere would require detailed studies, to ascertain the impact of these complex processes and the presence of these pollutants in the upper atmosphere. It is equally important to understand how the space tourism industry will develop.
Virgin Galactic estimates that it will arrange 400 space flights each year for the privileged few who can afford it. Blue Origin and SpaceX have yet to announce their plans. But globally, rocket launches should not need to exceed the current number of 100 each year to avoid its harmful effects. During launch, the rockets could emit four to ten times more nitrogen oxides than Drax, the UK’s largest thermal power plant, in the same period.
A better understanding of the impact of billionaire astronauts needed
CO2 emissions for four or so tourists in a space flight would be 50 to 100 times higher than for one to three tons per passenger on a long-haul flight. As international regulators need to keep up with this nascent industry and properly control its pollution, scientists need a better understanding of the impact these billionaire astronauts have on our planet’s atmosphere.
Author- Alois Marais, Associate Professor in Physical Geography, UCL