Elon Musk’s Starlink satellites are falling back to Earth: Is ozone layer at risk? | Technology News
The Satellites are Re-Entering the Earth’s Atmosphere, and the Environment is at Risk
The world is eagerly watching Elon Musk’s Starlink satellite constellation, a project that has been making headlines with its rapid expansion. However, a recent phenomenon has raised concerns about the environmental impact of these satellites. In January 2023, about 120 Starlink satellites re-entered the Earth’s atmosphere, creating a spectacular display of artificial meteor showers that could be spotted by people around the world. While this might seem harmless, scientists are sounding the alarm about the serious threat these re-entries pose to the environment.
The Re-Entry of Satellites: A Threat to the Ozone Layer?
When satellites re-enter the Earth’s atmosphere, they burn up, releasing metals like aluminium, which is abundant in low Earth orbit (LEO) satellites like Starlink. The concern is that these metals, specifically aluminium, could damage the ozone layer. According to the European Space Agency (ESA), there are over 28,000 objects in space, with most of them in LEO. The increasing demand for internet coverage is accelerating the rapid launch of small communication satellite constellations, including Starlink’s plan to launch 12,000 more satellites.
What Happens during the Re-Entry of Satellites?
During re-entry, the aluminium in these satellites creates aluminium oxide, which is a threat to the ozone layer. The LEO satellites usually orbit between 550 and 1,200 km above the Earth. Once their operational period comes to an end, they are decommissioned and allowed to fall back on Earth, a mechanism designed to prevent space debris from accumulating.
As satellites re-enter the atmosphere, they travel at about 27,000 km per hour, generating extreme heat through aerodynamic friction. The satellite disintegrates almost instantly, and most of its components vaporize. Most satellites are designed to burn up entirely before reaching the Earth’s surface to avoid posing a danger to people or property. However, the burning-up process is not environmentally neutral, as the metals in the satellite undergo chemical transformations, including aluminium, which usually comprises about 40% of a satellite’s mass.
Why is Aluminium Oxide a Concern?
The re-entries usually occur in the mesosphere, around 50 to 80 km above the Earth’s surface. The aluminium oxide nanoparticles emitted during the burn-up remain suspended in this region for extended periods before descending into lower altitudes. The scientific concern is about what happens when these particles eventually reach the stratosphere, which is home to the ozone layer that protects all life from harmful ultraviolet radiation.
According to researchers from the University of Southern California’s Department of Astronautical Engineering, aluminium oxide can act as a catalyst for chemical reactions involving chlorine, similar to the process that led to ozone depletion caused by chlorofluorocarbons (CFCs) in the past. CBFs can destroy ozone molecules.
What Do Scientists Say?
Recent studies have suggested a significant increase in aluminium oxide in the atmosphere related to the re-entry of satellites. In February 2023, NASA conducted high-altitude test flights over Alaska, collecting aerosols that revealed the presence of 10% stratospheric sulphuric acid particles containing aluminium and other metals emitted from satellite and rocket re-entries. These tests confirmed that space hardware is leaving a detectable chemical signature in the atmosphere.
Challenges and Potential Solutions
Experts point to the absence of a comprehensive regulatory framework that addresses the atmospheric impact of re-entries. The US Federal Communications Commission (FCC) provides licenses to satellite mega-constellations, but it does not consider re-entry debris or ozone depletion in its assessments. Commercial satellites have been excluded from environmental review under the National Environmental Policy Act (NEPA).
From a global perspective, the UN Committee on the Peaceful Uses of Outer Space (COPUOS) has begun discussions around guidelines for space sustainability, but progress has been slow. There is no binding international agreement regarding pollution from satellite re-entries.
Experts say coordinated action from various stakeholders will help address the challenge. They suggest satellite manufacturers could come up with alternatives to aluminium or design spacecraft that can be boosted into higher graveyard orbits rather than allowed to re-enter. A graveyard orbit is an orbit where decommissioned satellites are placed to reduce the risk of collisions between operational satellites and space debris. This, however, may require additional onboard propellant and may only delay the problem for some more years.
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