Large networks of satellites in low-Earth orbit (below about 2,000 kilometres) built to provide internet and other services. In 2018 there were around 2,000 satellites in orbit in total. By late 2025 there were more than 9,000 of SpaceX's Starlink internet satellites alone, and the company has filed regulatory paperwork for as many as 42,000. Other operators building mega-constellations include OneWeb, Amazon, and the Chinese networks Qianfan and Guowang.
A paper published in Nature by Alejandro Borlaff and colleagues at NASA's Ames Research Centre estimated that there could be around half a million satellites in low orbits by 2040.
The growing number of satellites is already causing problems for ground-based telescopes, whose images are contaminated by streaks of reflected sunlight. The Nature paper found the problem could soon extend to space telescopes as well. A simulation modelling dozens of planned mega-constellations showed that around a third of Hubble Space Telescope images could be affected. Around 96% of exposures from SPHEREx (a NASA mission already in orbit), ESA's ARRAKIHS instrument (slated for launch by 2030) and China's Xuntian space telescope (due to launch in 2026) could be contaminated.
SpaceX has tried to make its satellites less reflective, with limited success. Business pressures push in the opposite direction: Starlink's satellites have grown in size over time, in order to serve more customers and offer higher connection speeds. Bigger satellites are usually brighter ones.
Astronomers can time observations to minimise interference if they have details of a constellation's orbits, but this approach does not scale as the sky grows more crowded. The James Webb Space Telescope, at 1.5m kilometres from Earth, is far too distant for low-flying satellites to pose a problem, but flying low offers advantages—Earth's magnetic field shields against cosmic rays and data downloads are easier.
In 2022 the International Astronomical Union set up the Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference to broker compromises between astronomers and mega-constellation operators—limiting satellite numbers or orbits, for example.
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