Square Kilometre Array project frets about satellite interference

The SKA will consist of thousands of radio receivers. Construction work will begin next year
The project to build the largest telescope facility on earth has now also expressed concern about the coming era of satellite mega-constellations.
The Square Kilometer Array (SKA) will connect radio antennas across South Africa and Australia to explore the vastness of the cosmos.
However, the government organization says that the science of the telescope would be severely affected if thousands of telecommunications spacecraft were to fly overhead regardless of the radio interference they could cause.
A number of companies - including US entrepreneur Elon Musk's SpaceX outfit and UK / India-based OneWeb - are planning large networks in the sky to route broadband internet.
The Square Kilometer Array Organization (SKAO) says it is imperative that these companies work with radio astronomy to minimize their impact on the South African and Australian antennas.
Scientists observing the universe in visible / optical light have already complained about the brightness of some spacecraft and how this can leave streaks in celestial images.
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Frequencies
The problem for radio astronomers is slightly different - it concerns the potential of the satellites' downlink communications to flood the signals that the SKA is trying to detect from space.
The particular concern is the spectrum in band 5b - a range of frequencies that range from 8.3 to 15.4 GHz.
Some of it is dedicated to satellite use, but astronomers also like to use it because there are some interesting features to see here. This includes atoms and molecules that are involved in life processes on earth.
So far, satellites and astronomers have lived relatively happily side by side in Volume 5b, mainly because the existing spaceships for telecommunications were either not operated via radio systems or, as they passed by, ensured that they did not transmit.
However, that scenario could change radically with the introduction of thousands of high-speed, broadband, low-orbit satellites, the SKAO warns.
Astronomers working in visible light have complained about satellite brightness
The organization has just completed a pilot study describing the impact of a sample of the population of 6,400 broadband spacecraft on the SKA mid-telescope segment of the project, which will soon be built in South Africa and will consist of a series of 197 shells.
The investigation showed that - without any mitigation measures - the loss of sensitivity in band 5b due to frequency interference means that observations take 70% longer.
As the observation sessions last longer, fewer astronomers are given the opportunity to use the SKA - and this reduces their scientific return on investment.
"There is tremendous scientific and public interest in identifying the origins of life beyond those found on Earth. One of the most promising ways to find it elsewhere in our galaxy is to detect complex prebiotic molecules whose spectral signatures are between these are concentrated around 10 and 15 GHz ", explained SKA Science Director Dr. Robert Braun.
"This is just one of many exciting scientific goals that depend on sensitive access to this frequency range. The prospect of losing sensitivity in this key frequency band is extremely worrying."
With damage control, satellite operators would either direct their transmissions away from the SKA antennas or turn them off completely when moving overhead.
The SKA is to be built in sparsely populated areas in order to avoid interference from telephone, television, WLAN and other ground-based radio links. This means that there shouldn't be many customers around the "SKA-Mid-Telescope" for the broadband services that the new players in satellite communications will provide.
"We pointed out a few problems, but we also pointed out the solutions," said Tim Stevenson, SKAO's head of insurance.
"We know the limitations associated with these satellite systems. After all, some of us are actually spacecraft engineers.
"What we need is a pragmatic approach because we also see the value of what they do. This is the modern world and access to the Internet is critical to development. Indeed, some of our Member States are in developing countries, so we are very sensitive to such issues, "he told BBC News.
Graphics: SpaceX has promised to work with astronomers to avoid possible impact
Elon Musk's SpaceX company is committed to eliminating the astronomy impact of its new Starlink broadband constellation. OneWeb is in the process of pulling out of bankruptcy proceedings but made similar commitments earlier this year.
The SKA is one of the major scientific projects of the 21st century.
The goal is to produce a radio telescope with a collecting area of ​​one million square meters (one square kilometer) - the equivalent of about 200 soccer fields.
The SKA will examine radio sources in the sky that emit wavelengths from centimeters to meters - but achieve sensitivities that are far beyond the range of current radio telescopes.
This should enable him to see the hydrogen in the first stars and galaxies to form after the Big Bang.
The SKA will also pinpoint the positions of the next 100 million galaxies. Scientists hope this map will reveal new details about "dark energy," the mysterious negative pressure that seems to be pushing the cosmos apart at ever increasing speed.
Construction of the SKA is slated to begin next year. Routine scientific observations are expected to be conducted in the late 2020s.
The implementation of the project will cost the 14 member states of the SKAO almost EUR 2 billion.
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
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