Radio telescopes observing the cosmos face growing challenges because of electromagnetic interference from thousands of satellites in low Earth orbit. Now, experiments involving SpaceX鈥檚 Starlink satellites have shown how to virtually eliminate one form of this problem.
As these kind of satellites hurtle around the planet, they send so-called downlink signals to Earth to provide internet and communication services. When they pass through areas of the sky where radio telescopes are observing, the temporary blips from those strong signals can potentially impact hours of data collected by instruments that cost millions or even billions of dollars to build and run.
In 2023 and 2024, SpaceX worked with the US National Science Foundation鈥檚 National Radio Astronomy Observatory (NRAO) to demonstrate a potential solution: Starlink satellites could temporarily redirect or switch off their downlink transmissions while moving through the line of sight of an active radio telescope.
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This represents 鈥渙ne of many possible solutions for a pressing problem鈥�, says at the NRAO. 鈥淭he number of satellites is going to increase exponentially in the coming years, which would mean radio astronomers will see more interference more often.鈥�
Avoiding this is particularly important when radio telescopes are doing what are known as calibration scans, lasting a few minutes. Interference then could negatively affect hours-long observation runs, says Nhan. He also warns that extreme interference could potentially damage some radio telescopes鈥� electronic components.
Nhan and his NRAO colleagues coordinated tests with SpaceX that involved the Green Bank Observatory in West Virginia pointing its radio telescope, one of the largest in the world, towards parts of the sky crisscrossed by dozens of Starlink satellites. SpaceX set these satellites to redirect their downlink signals to avoid the observatory site. Satellites passing near the telescope鈥檚 line of sight temporarily disabled these signals entirely.
The beam avoidance demonstrations seem to have achieved a 鈥渘oticeable impact鈥� in reducing interference, says at the International Astronomical Union鈥檚 Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference. 鈥淚f the method is implemented in all telescopes, this would be a huge step forward,鈥� he says.
Follow-up tests of the beam avoidance measure have shown similar success at the Very Large Array radio telescope in New Mexico, says Nhan. SpaceX voluntarily activated the protective measure for VLA starting in August and is coordinating with NRAO to do the same for the Green Bank Observatory, once the latter returns to full operation after months of maintenance.
But this measure only helps radio astronomers avoid one type of potential interference. Other problems arise when downlink transmissions leak into frequency bands that are protected for radio astronomy or satellite signals fill up parts of the radio spectrum that are passively observed by these telescopes, says Di Vruno. His has even shown how unintentional radiation from electronic devices on Starlink satellites can produce additional interference.
The work so far is still helpful, however. Other radio observatories such as the Square Kilometre Array, under construction in Australia and South Africa, are also working with SpaceX to offset potential interference, says Di Vruno. He and Nhan hope that such measures can also be implemented by other satellite companies too 鈥� even though none are legally required to do so.
The Astrophysical Journal Letters
