Radio astronomy began in the 1930s when Karl Jansky, an engineer at Bell Telephone Laboratories, accidentally discovered radio waves coming from the Milky Way. He was investigating sources of interference in transatlantic radio communications, no-one expected this to be the birth of radio astronomy. The finding opened an entirely new window on the universe, one that could peer through clouds, dust and observe phenomena invisible to optical telescopes. The field really took off after World War II when surplus military radar equipment became available to scientists with major discoveries following rapidly from pulsars to quasars, the cosmic microwave background radiation and the detailed structure of galaxies. Today’s radio telescopes, from giant single dishes like the 500 metre FAST telescope in China to vast interferometer arrays like the Square Kilometre Array, continue to revolutionise our understanding of the universe.
500m Aperture Spherical Radio Telescope located in Guizhou Province, China (Credit : SCJiang)
But there is a problem. Until recently, the sky has been relatively “radio quiet” but astronomers using the Low Frequency Array radio telescope (LOFAR) made an unexpected discovery. They detected radio signals from 47 out of 68 satellites that were observed, including signals within frequency bands specifically protected for radio astronomy by international regulations. This wasn’t the planned communication signals that satellites use to transmit internet to Earth. Instead, the detected emission is coming from onboard electronics, and hence distinct from intended communications transmissions. These “unintended electromagnetic radiation” (UEMR) emissions leak from satellites’ internal electronics across wide frequency ranges.
“Radio telescopes like LOFAR are designed to detect the faintest traces of radiation from the Universe. But measurements increasingly reveal interference from satellites that were not meant to be transmitting in those frequencies” – Dr Emma van der Wateren from the Netherlands Institute for Radio Astronomy.
Unfortunately, the problem is rapidly worsening too. One satellite alone is not the problem, but with thousands of satellites being launched in great clusters, together they can fundamentally change the radio environment of the sky. With companies like SpaceX, Amazon, and others planning to launch even more satellites for global internet coverage, the radio noise could soon become overwhelming. The cumulative effect of unintended emissions from thousands upon thousands of low Earth orbit satellites could have a significant and even profound impact on radio astronomy, not only on LOFAR observations but other radio telescopes as well, introducing unwanted noise at frequencies reserved for the exploration of deep space.
The interference is particularly problematic because UEMR is much more intense, or brighter, than naturally occurring radio emitting objects. Just as light pollution from towns and cities drowns out the light from faint galaxies and nebulae, so this radiation can potentially drown out the faint signals from deep space. Perhaps frustratingly though, the likes of SpaceX are not actually breaking any rules since these kinds of signals are not covered by any international regulation. While electronics on Earth must meet strict standards to prevent interference, the same standards are not applied to satellites in orbit.
Starlink satellites waiting to be deployed into Earth orbit (Credit : SpaceX)
The move to include The Committee on Radio Astronomy Frequencies (CRAF) in the International Special Committee on Radio Interference (CISPR) is a very positive step that gives hope. The CISPR are the international body that sets standards to prevent electronic devices from interfering with each other and, CRAF membership gives astronomers a voice in setting future policy
I always liken astronomy to listening to an orchestra. It’s no good just tuning into the double bass or the cymbals, you have to listen to all the instruments to fully appreciate the music. In astronomy, we have to study the universe across all wavelengths of the electromagnetic spectrum to learn about the nature of objects in space. If we lose the ability to study the cosmos in radio frequencies we limit our ability to explore and learn. With new telescopes like the Square Kilometre Array (SKA) and other new facilities coming online the timing couldn’t be better.
Source : Radio astronomers join global standards body seeking to address satellite interference