Space Debris
In addition to potential impact with meteoroids, spacecraft are also at risk from the nearly 130 million pieces of man-made space debris. There are some 128 million pieces <1 cm, approximately 900,000 from 1–10 cm, and 34,000 pieces >10 cm. The larger pieces are tracked by radar and lasers to assist in spacecraft deployment and to detect potential collisions with satellites and larger platforms such as the International Space Station (ISS). Traveling at greater than 7.5 kms–1, this space debris can pose a greater threat to spacecraft than that posed by meteoroids. Even a piece of 1-millimeter small debris can create an impact crater 10 times its size. For example, in 1983 the shuttle Challenger’s windscreen was struck by a paint flake less than 0.3-mm in diameter, causing a large crater in the 20-mm thick windscreen. A 1-cm piece of debris could create the equivalent amount of energy as a hand grenade explosion. A 1-kg 10-cm Cubesat in LEO has the equivalent kinetic energy of a bowling ball at 2,000 mph. Even a 1-mm piece of debris can create an impact crater 10 times its size.
On 15 November 2021, Russia destroyed one of its own satellites—Cosmos 1408—creating over 1,500 pieces of space debris that passed within a few hundred meters of China's Tsinghua Science satellite. The ISS and the Chinese space station were threatened since the debris was in orbit at a similar height—occupants had to take cover several times. On 26 June 2024 the ~6,000-kg Russian-owned decommissioned satellite, called RESURS-P1, in a nearly circular orbit at ~355 km disintegrated (seemingly accidentally), resulting in more than 100 pieces of trackable debris, again forcing ISS occupants to take shelter in their spacecraft (coincidentally two astronauts from Boeing’s Starliner were docked at the ISS and had to take shelter in their spacecraft). In August 2024, Chinese Long March 6A rocket’s upper stage broke up in orbit, resulting in over 300 pieces of trackable debris. SpaceX has reported that its Starlink satellites performed approximately 50,000 collision-avoidance maneuvers between 1 December 2023, and 31 May 2024.
Space junk doesn’t just cause a problem in space. In March 2024 part of a pallet from a discarded ISS battery fell to Earth, smashing through the roof of a Florida home. In 2020 an Ivory Coast village recovered a 12-m-long pipe fallen from a Chinese rocket that cast off its empty core after launch.
Orbital debris collisions cost satellite operators an estimated USD$86 to USD$103 million in losses a year, a figure that will grow as each operator and each collision generate more debris. The Space Sustainable Rating (SSR) initiative has been developed in conjunction with the World Economic Forum and is set to operate by 2022. SSR will rate spacecraft in terms of their risk associated with causing physical damage in space, based on factors such as the orbit selected, the availability of measures that can be taken to avoid collisions, and the ability to detect spacecraft from Earth. Launch providers and satellite operators will be incentivised to reduce space debris by receiving a good rating which will lead to lower insurance costs and less difficulty in obtaining financial backing.
As an example of other initiatives to clean up space, on 12 July 21 the British-based Skyrora activity began its ‘Finding Prospero’ mission to retrieve a 66-kilogram Prospero satellite from orbit after 50 years having been launched from a British rocket in 1971 from Woomera, South Australia. In May 2023, Arianespace and ClearSpace signed a launch contract for ClearSpace-1, the first active debris removal mission planned for launch in the second half of 2026. The mission, based on a Vega C light launcher, will launch the spacecraft into LEO and use robotic arms to capture and deorbit a piece of derelict space debris with a mass of some 112 kg. Space MAITRI is a joint Australian-Indian mission to show progress toward space debris management and a sustainable space environment.
In late 2023, the US Senate has passed the Orbits Act that, should it become law, would direct NASA to create a special program to reduce the amount of space junk in orbit. The bill would also direct the US Department of Commerce’s Office of Space Commerce (OSC) to publish a list of debris that poses the greatest risk to orbiting spacecraft.
Alumina produced by satellite re-entry
When satellites re-enter Earth’s atmosphere and burn up, they release significant quantities of aluminum oxide (Al₂O₃) particles, or alumina—a single 250 kg satellite may release around 30 kg of alumina nanoparticles. Studies estimate that in 2022, approximately 17 metric tons of aluminum oxide were introduced into the atmosphere due to satellite re-entries. That amount is expected to increase dramatically with the rapid expansion of satellite megaconstellations such as Starlink.
Alumina particles may remain in the upper atmosphere (the mesosphere) for up to 30 years before descending into the stratosphere, where they could catalyse reactions between ozone and chlorine, accelerating the depletion of the ozone layer. The concern is that alumina nanoparticles could act as surfaces for these ozone-depleting reactions, potentially reversing progress made in restoring the ozone layer since the banning of ozone-depleting chemicals through the Montreal Protocol.