The explosive growth in the number of low-Earth orbit (LEO) satellites, from providers like Elon Musk’s Starlink, poses a direct threat to astronomical research facilities the world over, including those in South Africa.
The department of science, technology & innovation has already taken measures to protect South African radio astronomy facilities from terrestrial interference, including declaring the region of the Karoo in the Northern Cape where the South African portion of the Square Kilometre Array (SKA) is being built as a radio quiet zone where limited radio activity is permitted.
According to Adrian Tiplady, MD for strategy and partnerships at the South African Radio Astronomy Observatory (Sarao), the regulations were not designed with interference from satellites in mind, so other steps must be taken to protect astronomy in South Africa because, he told TechCentral, it is one of the country’s most valuable contributions to the world.
“As the technology of astronomical facilities progresses and scientists begin to push the boundaries of this scientific endeavour, our instruments get more and more sensitive, and we try to identify locations on the surface of the planet that would maximise the scientific return of those facilities,” he said. “It just so happens that South Africa exhibits characteristics that support next-generation astronomical facilities.”
South Africa’s location makes it an important location for the global astronomy community for two reasons.
The first is that the bulk of astronomical research investment has historically gone to facilities in the northern hemisphere. South Africa’s position in the southern hemisphere, with the view to the centre of the Milky Way galaxy directly overhead, presents much better opportunities for new discoveries, said Tiplady.
VLBI research
The second reason making South Africa an important astronomical location is its participation in very long baseline interferometry (VLBI) research. VLBI is a radioastronomy technique that combines the telescopic power of multiple facilities across the world to form “one giant telescope”, allowing for the collection of data from a larger portion of the sky than individual facilities can do on their own.
According to Tiplady, South Africa’s distance from other telescopes in the VLBI network aides in collecting data samples that are of very good quality.
Read: SA scientists want Musk’s Starlink out of their space
LEO satellites can interfere with radioastronomy ground stations to varying degrees. The signals radio astronomy equipment aim to observe are exceptionally faint as they have travelled for millions or even billions of years before reaching Earth. Any low-level frequencies from man-made objects could mimic cosmic signals and pollute the data collected for astronomy, potentially leading to false results that could support false theories. If detected, these signals can be masked out, but that has the disadvantage of reducing the quality of the data, said Tiplady.
Strong disruptive signals, which typically occur in a narrow band, have the potential to saturate the sensitive receivers used for astronomy in the same way that too high a volume distorts the sound coming out of a speaker. These type of signals render the spectrum used for astronomy unusable.
Signals that are even stronger pose a physical threat to radioastronomy equipment as they can cause permanent damage to the amplifiers and receivers used.
The threat of interference from satellite sources is nothing new. In the past, however, satellite activity has been limited to a few geostationary satellites and an even smaller contingent of LEO spacecraft. “They were typically one or two, so you could undertake operational avoidance actions,” said Tiplady.
Modern LEO mega-constellations are much, much larger, having at least a thousand satellites in the sky by definition. SpaceX subsidiary Starlink, by far the largest constellation, already has more than 7 600 satellites in orbit. Starlink already has permission from the US Federal Communications Commission to launch up to 12 000 satellites into orbit. In October 2024, SpaceX filed documents with the International Telecommunication Union, an agency of the United Nations, requesting permission to launch another 30 000 satellites, which could see its constellation grow to around 47 000 in next five years.
Others are in the works (or have already started deploying LEO satellites), including OneWeb; Amazon’s Project Kuiper; Starshield; China’s Xingwang, Qianfan and Yinhe; Lynk Global; and E-space. Qianfan alone plans to have 14 000 satellites in its constellation, while Kuiper’s will be smaller, but significant, at around 3 200.
“With the advent of mega constellations, it becomes practically impossible to constantly move dishes around to avoid those satellites, so there’s a significant amount more collaboration that needs to be undertaken with satellite operators to jointly develop and implement mitigation actions,” Tiplady explained.
He said various technologies have been tested to try and minimise interference from LEO satellites. The most promising involves directing the beam, or signal, away from known radio astronomy sites until it has passed over. Having the satellite shift its frequency to spectrum not used by astronomy observatories is an additional measure that could be taken. According to Tiplady, satellite beam redirection stipulations can be included in the licensing agreement an operator agrees to before they are allowed to provide their services in the country.
Regulation
However, communications regulator Icasa’s hands are for the moment tied because LEO satellites are regulated internationally by the ITU, with the upcoming World Radiocommunication Conference in 2027 earmarked as the stage where LEO interference will be looked at in detail.
Read: Low-frequency network gets around SKA’s need for radio silence
“What is important is that Icasa ensures that any kind of licensing processes for satellite service providers takes note of and considers the various mechanisms coming out of those ITU study groups – in South Africa through the astronomy authority and Sarao, and the broader international community for dealing with satellite interference. South Africa has a critical, strategic and important asset with respect to radioastronomy for the global community and we need to protect that,” said Tiplady. – © 2025 NewsCentral Media
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