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Visible light is only 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-rays, and observatories such as the Green Bank Telescope, Very Large Array, Atacama Large Millimeter Array and dozens of other observatories around the world work at radio wavelengths.
Radio telescopes face a problem. All satellites, regardless of function, use radio waves to transmit information to the Earth’s surface. Just as light pollution can obscure a starry night sky, radio transmissions can flood the radio waves astronomers use to learn about black holes, newly forming stars, and the evolution of galaxies.
We are three researchers who work in astronomy and wireless technology. With tens of thousands of satellites expected to enter orbit in the next few years and increasing use on the ground, the radio spectrum is becoming crowded. Radio quiet zones – regions, usually located in remote areas, where ground-based radio transmissions are restricted or prohibited – have previously protected radio astronomy.
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 range of radio frequencies. One solution that we have 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
EHT cooperation
Radio waves are the longest wavelength emissions on the electromagnetic spectrum, meaning that the distance between two peaks of the wave is relatively far apart. Radio telescopes collect radio waves in wavelengths from about one millimeter to one meter.
Even if you’re not familiar with radio telescopes, you’ve probably heard of some of the research they do. The stunning 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 location with very little radio frequency interference: a radio quiet zone.
A radio quiet zone is a region where ground-based transmitters, such as cell phone towers, are required to lower 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) mainly in West Virginia and Virginia. It 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.
Large satellite constellations, such as those of Starlink, can be seen marching in lines across the night sky, damaging both visible and radio astronomy.
A satellite bomb
On October 4, 1957, the Soviet Union launched Sputnik into orbit. As the small satellite circled the globe, amateur radio enthusiasts around the world were able to pick up the radio signals it sent back to Earth. Since that historic flight, wireless signals have become part of almost every aspect of modern life—from airplane navigation to Wi-Fi—and the number of satellites has grown exponentially.
The more radio transmissions there are, the more challenging it becomes to deal with interference in radio silent zones. Existing laws do not protect these zones from satellite transmitters, which can have devastating effects. In one example, transmissions from an Iridium satellite obscured the observations of a faint star made in a protected band assigned to radio astronomy.
Satellite networks such as Starlink, OneWeb and others will eventually fly over every location on Earth and send radio waves down to the surface. Soon, nowhere will be truly quiet for radio astronomy.
Interference 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 transmitting on a frequency officially protected for radio astronomy. Researchers recommended a number of fixes for this disruption. By the time the operators of the Russian navigation system agreed to change the transmission frequency of the satellites, much 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 properties such as surface soil moisture that are important for weather prediction and climate research. The frequencies they depend on are protected under international agreements, but are also threatened by radio interference.
A recent study showed that a large part of NASA’s measurements of soil moisture experience interference from ground-based radar systems and consumer electronics. There are systems in place to monitor and account for the interference, but avoiding the problem entirely through international communications and pre-launch testing would be a better option for astronomy.
ALMA (ESO/NAOJ/NRAO), J. Guarda (CC BY 4.0)
Solutions to a crowded radio spectrum
As the radio spectrum continues to become more crowded, users will have to share. This may involve sharing in time, in space or in frequency. Regardless of the specifications, solutions must 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.
Working with astronomers, engineers, software and wireless specialists, and with support from the National Science Foundation, we have led a series of workshops to develop what a National Radiodynamic Zone can provide. This zone will be similar to existing radio quiet zones, covering a large area with restrictions on radio transmissions nearby. Unlike a quiet zone, the facility would be equipped with sensitive spectrum monitors that would 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 use of the radio spectrum. For example, a zone established near a radio telescope could test schemes to provide wider bandwidth access for both active uses, such as cell towers, and passive uses, such as radio telescopes.
For a new paper our team just published, we spoke to users and regulators of the radio spectrum, from radio astronomers to satellite operators. We found that most agreed that a radiodynamic zone could help resolve, and potentially avoid, many critical disruptions in the coming decades.
Such a zone does not yet exist, but our team and many people across the United States are working to refine the concept so that radio astronomy, Earth-sensing satellites, and public and commercial wireless systems can find ways to share the precious natural resource that is the radio spectrum.
Christopher Gordon De Pree is Deputy Director of Electromagnetic Spectrum, National Radio Astronomy Observatory; Christopher R. Anderson is Associate Professor of Electrical Engineering, United States Naval Academy; and Mariya Zheleva is Assistant Professor of Computer Science, University at Albany, State University of New York.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
