Radio interference from satellites threatens astronomy—zone proposed for testing new technologies

by Christopher Gordon De Pree, Christopher R. Anderson and Mariya Zheleva, The Conversation


Radio observatories like the Green Bank Telescope are located in radio-quiet zones that protect them from interference. Credit: NRAO/AUI/NSF, CC BY

Visible light is only one part of the electromagnetic spectrum that astronomers use to study the universe. The James Webb Space Telescope was built to see infrared light, other space telescopes capture X-ray images, and observatories such as the Green Bank Telescope, the Very Large Array, the Atacama Large Millimeter Array, and dozens of other observatories around the world operate in radio wavelengths .

Radio telescopes are in trouble. All satellites, whatever their function, use radio waves to transmit information to the Earth’s surface. Just as light pollution can obscure a starry night sky, radio emissions can overwhelm the radio waves that astronomers use to learn about black holes, newly forming stars, and the evolution of galaxies.

We are three scientists working in astronomy and wireless technology. With tens of thousands of satellites expected to enter orbit in the coming years and with increasing use on the ground, the radio spectrum is filling up. Radio quiet zones—areas, usually in remote areas, where terrestrial radio transmissions are limited or prohibited—protected radio astronomy in the past.

As the problem of radio pollution continues to grow, scientists, engineers and policy makers will need to figure out how everyone can efficiently share the limited radio frequency range. One solution we’ve been working on in recent years is to create a facility where astronomers and engineers can test new technologies to prevent radio interference from blocking the night sky.

Astronomy with radio waves

Radio waves are the longest-wavelength emissions in the electromagnetic spectrum, meaning that the distance between two peaks of the wave is relatively far. Radio telescopes collect radio waves at wavelengths from millimeter to meter wavelengths.

Even if you’re not familiar with radio telescopes, you’ve probably heard of some of the research they do. The fantastic first images of accretion discs around black holes were both produced by the Event Horizon Telescope. This telescope is a global network of eight radio telescopes, and each of the individual telescopes that make up the Event Horizon telescope is located in a place with very little radio frequency interference: a radio quiet zone.

A radio quiet zone is an area where terrestrial transmitters, such as cell phone towers, are required to reduce their power levels so as not to affect sensitive radio equipment. The US has two such zones. The largest is the National Radio Quiet Zone, which covers 13,000 square miles (34,000 square kilometers) mostly in West Virginia and Virginia. Contains the Green Bank Observatory. The other, the Table Mountain Field Site and Radio Quiet Zone, in Colorado, supports research by a number of federal agencies.

Similar radio quiet zones are home to telescopes in Australia, South Africa and China.

A satellite explosion

On October 4, 1957, the Soviet Union launched Sputnik into orbit. As the small satellite circled the globe, radio amateurs around the world were able to receive the radio signals beamed back to Earth. Since that historic flight, wireless signals have become part of nearly every aspect of modern life—from aircraft navigation to Wi-Fi—and the number of satellites has grown exponentially.

The more radio broadcasts there are, the more difficult it becomes to deal with interference in radio quiet zones. Current laws do not protect these bands from satellite transmitters, which can have disastrous consequences. In one example, emissions from an Iridium satellite completely obscured observations of a faint star made in a protected zone reserved for radio astronomy.

Internet satellite networks like Starlink, OneWeb and others will eventually fly over every location on Earth and transmit radio waves to the surface. Soon, no location will be truly quiet for radio astronomy.

Large satellite constellations, such as those of Starlink, can be seen streaking across the night sky and marring both visible and radio astronomy.

Interventions in the sky and on the ground

The problem of radio interference is not new.

In the 1980s, the Russian Global Navigation Satellite System – essentially the Soviet Union’s version of GPS – began broadcasting on a frequency officially reserved for radio astronomy. The researchers recommended a number of fixes for this interference. When the operators of the Russian navigation system agreed to change the transmission frequency of the satellites, a great deal of damage had already been done due to the lack of testing and communication.

Many satellites look down on Earth using parts of the radio spectrum to monitor features such as surface soil moisture that are important for weather forecasting and climate research. The frequencies they rely on are protected under international agreements, but are also threatened by radio interference.

A recent study showed that a large portion of NASA’s soil moisture measurements face interference from ground-based radar systems and consumer electronics. There are systems in place to monitor and deal with interference, but avoiding the problem entirely through international communication and pre-launch testing would be a better option for astronomy.

Solutions in a crowded radio spectrum

As radio spectrum continues to fill up more, users will have to share. This could include time, space or frequency sharing. Regardless of the specifics, solutions should be tested in a controlled environment. There are early signs of cooperation. The National Science Foundation and SpaceX recently announced an astronomy coordination agreement to benefit radio astronomy.


Radio interference from satellites threatens astronomy—zone proposed for testing new technologies

Two images from the Very Large Array in New Mexico show what a faint star looks like in a radio telescope without satellite interference, left, and with satellite interference, right. Credit: G. Taylor, UNM, CC BY-ND

Working with astronomers, engineers, software and wireless experts, and with support from the National Science Foundation, we’ve led a series of workshops to develop what a national radio belt could deliver. This zone will be similar to existing radio quiet zones, covering a large area with restrictions on radio transmissions at close range. Unlike a quiet zone, the facility will be equipped with sensitive spectrum monitors that will allow astronomers, satellite companies and technology developers to test receivers and transmitters together on a large scale. The aim would be to support creative and collaborative uses of radio spectrum. For example, a zone established near a radio telescope could test plans to provide wider access bandwidth for both active uses, such as cell towers, and passive uses, such as radio telescopes.

For a new paper just published by our team, we spoke to radio spectrum users and regulators, ranging from radio astronomers to satellite operators. We found that most agreed that a radio dynamic belt could help solve and potentially avoid many critical interference issues in the coming decades.

Such a band doesn’t exist yet, but our team and many people in the US are working to refine the idea so that radio astronomy, earth sensing satellites, and government and commercial wireless systems can find ways to share the precious natural resource which is the radio spectrum.

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