The 197 radio astronomy antennas of the Square Kilometer Array (SKA) in South Africa will be located in a radio-silent area the size of Pennsylvania, where even a cell phone is banned, to preserve the array’s view of the sky. Yet this precaution will not save the telescope, which is due to be completed in the late 1920s, from what may soon be overloaded: tens of thousands of communications satellites that transmit radio signals directly. from heaven. “The sky will be full of these things,” says SKA general manager Phil Diamond.
SpaceX has already launched hundreds of Starlink satellites, the first “megaconstellation” to provide Internet services to remote areas. The satellites have aroused the ire of optical astronomers because of the light streaks they leave across the fields of view of telescopes. Now even radio astronomers are concerned. This week, SKA released an analysis of the impact Starlink and other constellations would have on the array. He discovers that they would interfere with one of the radio channels that SKA intends to use, hampering searches for organic molecules in space and for water molecules used as key markers in cosmology.
SpaceX promises to address the concern. But radio astronomers are also looking for regulations. The United Nations Office for Outer Space Affairs (UNOOSA), which discussed the SKA analysis at a seminar this week, is evaluating ways to prevent satellites from polluting the night sky with light and radio signals, not only. for astronomy, but also for wildlife and the public. The astronomers also hope that the International Telecommunication Union (ITU), a United Nations organization, will intervene. “Spectrum is a resource that is consumed by private companies that generally have no regard for science,” says radio astronomer Michael Garrett, director of the Jodrell Bank Center for Astrophysics in the UK. “It is only government intervention that can stop this state of affairs, in my opinion.”
So far, SpaceX has launched more than 700 Starlinks on an initial target of 1440 and has gained approval for 12,000. Other operators, like Amazon’s OneWeb and Project Kuiper, have similar ambitions. Studies suggest that wide-field optical surveys will be most affected, with satellite tracks spoiling most images. The team that builds the Vera C. Rubin Observatory, a sensing telescope in Chile that will see its first light next year, has worked with SpaceX to reduce the impact. The company changed the orientation of the satellites as they move towards their final orbit, painted them a less reflective color, and fitted “visors” to reduce reflections. Since August, all Starlink satellites launched have visors, Patricia Cooper, vice president of government affairs for SpaceX satellites, said at the UNOOSA seminar this week. “We are trying to find a path where we can coexist,” he said.
The SKA’s analysis, which when completed will be the largest radio observatory in the world, highlights the new concern. The band that Starlink uses to transmit Internet signals occupies a considerable portion of frequencies from 10.7 to 12.7 gigahertz, within a range known as the 5b band which is one of the seven bands that SKA’s South African dishes will be targeted. The SKA analysis calculated the impact of 6400 satellites, taking into account both direct signals and losses called “sidelobes”.
The team calculated that satellite broadcasts will lead to a 70% loss of sensitivity in the downlink band. If the number of satellites in megaconstellations reaches 100,000, as many predicted, the entire 5b band would be unusable. SKA would lose its sensitivity to molecules such as the simplest amino acid, glycine, a component of DNA. “If it were detected in a forming planetary system, it would be very interesting information,” says Diamond. “This is a new area that SKA is opening up.” The band could also contain the fingerprints of water molecules in distant galaxies, a tracer that cosmologists use to study how dark energy is accelerating the expansion of the universe.
Since 1959, the ITU has protected a number of narrow frequency bands for astronomy. But in the past few decades, digital receivers have allowed telescopes to “operate across the spectrum,” Diamond says. “We have learned to coexist with transmitters,” typically by excluding them from a silent radio zone or by placing telescopes in remote areas. But they have no control over the transmitters that fly high.
Radio astronomers want satellite operators to turn off their transmitters, switch to other bands or point them far away when flying over a radio observatory. Tony Beasley, director of the US National Radio Astronomy Observatory, says he has discussed these options with SpaceX. “In the next year or two, we will do tests where we will try to coordinate in real time, technically, with them.” Beasley says this is a reflection of SpaceX’s corporate culture: “They want to do cool things; they don’t want to do any harm.”
Other astronomers don’t want to rely on corporate goodwill. At the UNOOSA seminar, they pushed for two recommendations: that all future satellites in low earth orbit be designed to avoid the beam of radio telescopes and in quiet areas, and that they control leakage from their side lobes. Those recommendations, along with others discussed this week for the protection of optical observers, will be discussed in a number of UN subcommittees next year before going to UNOOSA and ultimately the UN General Assembly for the approval.
Beasley is philosophical about the situation. “SpaceX legally broadcasts within one of their bands and there will be impacts for anyone trying to do radio astronomy,” he says. “These spectrum allocations represent the company’s goals and intentions. Let’s make [them] to enable trade and to enable defense and all kinds of activities. We need to come up with a solution that satisfies all of these to some extent. “