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Forecasting the occupancy of satellite megaconstellations in SKA observations

This paper forecasts that the rapid increase in satellite megaconstellations will lead to significant radio frequency interference for the Square Kilometre Array (SKA), potentially affecting observations for up to 100% of the time at low frequencies and necessitating advanced mitigation techniques.

Original authors: Nicolas Cerardi, Emma Tolley, Federico di Vruno

Published 2026-04-27

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CC BY 4.0

Original authors: Nicolas Cerardi, Emma Tolley, Federico di Vruno

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Cosmic "Mosquito" Problem: Why the World’s Biggest Radio Telescope is in Trouble

Imagine you are trying to listen to a single, tiny whisper from a friend standing a mile away in a quiet forest. To hear them, you use the most sensitive, high-tech hearing aid ever invented. You are focused, your ears are tuned, and the world is silent.

Suddenly, a swarm of thousands of mosquitoes begins buzzing right next to your ear. They aren't screaming, but their constant, high-pitched zzzzzz makes it impossible to hear that distant whisper. Even if you try to ignore them, the sheer volume of the buzzing drowns out the very thing you came to hear.

This is the problem facing the Square Kilometre Array (SKA), the world’s most powerful upcoming radio telescope.

The Players

The SKA (The Super-Ear): This is a massive project building a giant "ear" in Australia and South Africa. It’s designed to listen to the "whispers" of the universe—the faint radio signals from the birth of the first stars and the echoes of the Big Bang.
Satellite Megaconstellations (The Mosquitoes): Companies like SpaceX (Starlink) are launching tens of thousands of small satellites into orbit to provide global internet. While great for your Wi-Fi, these satellites are "noisy" in the radio spectrum. They emit signals (intentional) and electronic "humming" (unintentional) that act like cosmic mosquitoes.

The Study: What did the scientists find?

A group of researchers just released a "forecast" (a weather report for space noise). They wanted to know: How much of the time will these satellites be "buzzing" in the telescope's ear?

They used math to simulate the orbits of over 50,000 satellites and compared them to the "field of view" (the area the telescope is looking at). Here is their "bad news" report:

The Low-Frequency Nightmare (SKA-Low): This part of the telescope looks at very low frequencies (the "deep bass" of the universe). The researchers found that for these observations, the satellites are almost impossible to avoid. In some cases, satellites will be in the telescope's direct line of sight 100% of the time. It’s like trying to listen to a whisper while standing in the middle of a swarm of mosquitoes.
The Mid-Frequency Headache (SKA-Mid): This part looks at higher frequencies. It’s a bit better—at high frequencies, the "buzzing" is rare. But as the telescope tries to listen to lower frequencies (the "mid-range"), the interference jumps up significantly, potentially ruining 30% to 80% of the observation time.

Why does this matter?

If the telescope is constantly "hearing" satellites, scientists can't tell the difference between a signal from a galaxy billions of light-years away and the electronic hum of a satellite passing by.

If we aren't careful, we might spend billions of dollars building the world's best ear, only to find we can't hear anything because the sky is too "loud."

Is there hope?

The scientists aren't saying we should stop the satellites or stop the telescope. Instead, they are calling for a "peace treaty" and better "noise-canceling headphones."

They suggest:

Better Tech: Developing new ways to "subtract" the satellite noise from the data (like modern noise-canceling headphones).
Cooperation: Asking satellite companies to "steer" their signals away from the telescopes or share their location data so the telescopes know when a "mosquito" is coming.

In short: The universe is whispering beautiful secrets to us, but we need to make sure we don't drown them out with our own technology.

Technical Summary: Forecasting the Occupancy of Satellite Megaconstellations in SKA Observations

Paper Reference: Cerardi, N., Tolley, E., & di Vruno, F. (2026). Forecasting the occupancy of satellite megaconstellations in SKA observations. Astronomy & Astrophysics.

1. The Problem: Growing RFI from Megaconstellations

The Square Kilometre Array (SKA), scheduled for science operations in 2030, faces a significant threat from Radio Frequency Interference (RFI) generated by the rapid expansion of satellite megaconstellations (e.g., Starlink, OneWeb, GuoWang). Unlike traditional RFI, satellite interference stems from three distinct sources:

Intentional transmissions within ITU-R allocated bands.
Unintended Electromagnetic Radiation (UEMR) from spacecraft electronics (noted as particularly problematic due to its broadband nature).
Reflections from bright terrestrial sources.

The core challenge is that the number of satellites in Earth's orbit is projected to increase by an order of magnitude by 2030, potentially contaminating the sensitive frequency ranges required for studying the Epoch of Reionization and the Cosmic Dawn.

2. Methodology: Analytical Statistical Modeling

To avoid the computational complexity of propagating tens of thousands of individual satellite orbits with sub-second resolution, the authors developed an analytical model based on the framework established by Bassa et al. (2022).

Satellite Modeling: The model utilizes the Walker pattern to characterize orbital shells based on inclination ( $i$ ), altitude ( $h$ ), and the number of satellites ( $n$ ). It incorporates data from major planned/active fleets (Starlink Phase 1 & 2, OneWeb, GuoWang, QianFan, and Leo).
Effective Beam Definition: The authors define two exposure scenarios to account for the fact that bright RFI can impact observations even if the satellite is not in the center of the telescope's view:
1. Main Beam (MB) only: Exposure limited to the primary beam (until the first null).
2. Main Beam + 1st Sidelobe: Exposure including the first sidelobe (until the second null).
Statistical Approach: The model calculates the expected number of satellite counts in the Field of View (FoV) and uses a Poisson distribution to generate mock catalogs of satellite crossings. They estimate $f_{N_{sat} \geq 1}$ , which represents the fraction of observing time during which at least one satellite is present within the effective beam.

3. Key Contributions

First Radio-Specific Forecast: While previous work focused on optical satellite trails, this is the first study to provide quantitative occupancy forecasts specifically for radio interferometers like the SKA.
Frequency-Dependent Analysis: The study provides a comprehensive mapping of satellite exposure across the entire operational bandwidth of both SKA-Low (50–350 MHz) and SKA-Mid (0.35–15.4 GHz).
Open Science: The authors have made their forecasting code publicly available to allow other observatories to assess their own RFI risks.

4. Key Results

The study reveals that satellite interference will be a pervasive and unavoidable factor in SKA operations:

SKA-Low (50–350 MHz):
- High Exposure: Even considering only the main beam, satellites will be present for at least 30% of the time across half the frequency range, rising to 90% below 150 MHz.
- Sidelobe Impact: When including the first sidelobe, exposure reaches 100% below 100 MHz.
- Spatial Variation: Exposure is not uniform; it increases as observations point toward the South Celestial Pole due to the density of Starlink shells.
SKA-Mid (0.35–15.4 GHz):
- Frequency Split: High-frequency observations (>5 GHz) are relatively safe (exposure <5%).
- Low-Frequency Vulnerability: Below 1 GHz, the impact is severe. Including the first sidelobe, up to 80% of observations below 500 MHz could be impacted by satellites.
- Science Impact: The authors specifically highlight that 21cm cosmology science (crucial for understanding the early universe) will be severely affected across all relevant redshifts.

5. Significance and Implications

The paper concludes that traditional RFI mitigation—such as "flagging" (deleting) data segments when a satellite is detected—will be insufficient and highly detrimental to the SKA's sensitivity, as it would result in the loss of a massive fraction of observing time.

The authors call for three critical shifts in the field:

Advanced Mitigation: Development of "less data-destructive" techniques, such as RFI subtraction or boresight avoidance.
Improved Characterization: More rigorous measurements of UEMR and the cumulative effect of many incoherent satellite signals.
Industry Cooperation: A necessity for constructive relationships between astronomers and private satellite operators to facilitate the sharing of orbital data and the steering of satellite emissions.