Satellite 'constellations' could hamper night sky observations, astronomers raise concerns

Astronomers are raising concerns around groups of large satellites orbiting the Earth, which could disrupt their ability to observe stars in the night sky and perform radio astronomy.

The international team of scientists, including those from Imperial College London, have published a paper in Nature journal, detailing the impact of the prototype BlueWalker 3 satellite on astronomy.

The BlueWalker 3 is a prototype satellite, part of a satellite constellation planned by its owner AST SpaceMobile, intended to deliver mobile or broadband services anywhere in the world.

Observations of the BlueWalker 3 showed it was one of the brightest objects in the night sky, outshining all but the brightest stars, the researchers said.

Several companies around the world have envisaged such satellite constellations.

However, owing to their closer-to-Earth location and relatively large size, their potential to disrupt night sky observations is high, which is why astronomers are raising concerns around these constellations, or groups of satellites.

"The night sky is a unique laboratory that allows scientists to conduct experiments that cannot be done in terrestrial laboratories.

"The pristine night sky is also an important part of humanity's shared cultural heritage and should be protected for society at large and for future generations," said Dave Clements, from the Department of Physics at Imperial.

Observations taken within weeks of the BlueWalker 3's launch in September 2022 showed that the satellite was among the brightest objects in the sky.

These observations were supported by data from professionals and amateurs from sites across the world, including those in Chile, the US, Mexico and Aotearoa New Zealand.

The data was also used to calculate the satellite's trajectory over time, that could help astronomers to try and avoid them or at least know where they will be in the data.

However, mitigating against the brightness is difficult beyond masking their position and losing data for that portion of the sky, the researchers said.

Further, because the BlueWalker 3 uses wavelengths close to those that radio telescopes observe in, the satellite could also hamper radio astronomy.

"BlueWalker 3 actively transmits at radio frequencies that are close to bands reserved for radio astronomy, and existing observatory protection from radio interference may not be sufficient.

"Further research is therefore required to develop strategies for protecting existing and upcoming telescopes from the numerous satellites planned for launch over the next decade," said Mike Peel, co-lead of CPS's Sathub, which was envisaged as "a new comprehensive, worldwide, coordinated, and public observing initiative". One of its components include astronomical data repositories.

While the researchers recognised that the satellite constellations are important for improving worldwide communications, they say that their interference with astronomical observations could severely hamper their progress in understanding of the cosmos.

Their deployment should therefore be conducted with due consideration of their side effects and with efforts made to minimise their impact on astronomy, they said in their paper.