Forecasting the occupancy of satellite megaconstellations in SKA observations

Emma Tolley; Federico di Vruno; Nicolas Cerardi

REVIEW 2 major objections 2 minor 2 references

Reviewed by Pith at T0; open to challenge.

T0 means a machine referee read the full paper against a public rubric. The mark states how deep the mechanical check went, never who wrote it. the ladder, T0–T4 →

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T0 review · grok-4.3

Satellite megaconstellations will occupy SKA-Low beams for 30% to 100% of observing time, making RFI unavoidable.

2026-05-08 09:45 UTC

load-bearing objection The paper gives specific occupancy forecasts for SKA under megaconstellations but the numbers rest on an unvalidated analytical model with no error checks or real-data comparisons. the 2 major comments →

arxiv 2604.22694 v1 submitted 2026-04-24 astro-ph.IM

Forecasting the occupancy of satellite megaconstellations in SKA observations

Nicolas Cerardi , Emma Tolley , Federico di Vruno This is my paper

classification astro-ph.IM

keywords SKAsatellite megaconstellationsradio frequency interferenceRFI forecastingradio astronomyobserving time occupancySKA-LowSKA-Mid

verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses an analytical model to calculate the fraction of time satellites from planned megaconstellations will lie in the main beam or first sidelobe of the SKA telescopes once they begin operations around 2030. It considers up to 100,000 satellites and separates the exposure into two cases: satellites strictly in the main beam versus those in the main beam or first sidelobe. For SKA-Low the model finds exposure across half the frequency range for 30% of the time, rising to 100% below 100 MHz; SKA-Mid is less affected at high frequencies but still sees at least 30% occupancy below 1 GHz. A sympathetic reader would care because this shows that simply avoiding contaminated data will no longer be feasible and new mitigation methods will be required to protect radio astronomy observations.

Core claim

By the time SKA science operations begin, the expected population of up to 100,000 satellites in megaconstellations will place satellites inside SKA beams for a substantial fraction of observing time, with exposure reaching 30% across much of the SKA-Low band and 100% below 100 MHz, and at least 30% below 1 GHz for SKA-Mid, rendering satellites unavoidable and creating a strong risk of RFI contamination that demands improved measurement, impact assessment, and less destructive mitigation techniques.

What carries the argument

An analytical model that computes the time fraction during which satellites lie inside the main beam or the main beam plus first sidelobe, using assumed satellite orbital distributions and telescope beam patterns.

Load-bearing premise

The assumed satellite number, orbits, and beam patterns, together with the analytical model, give a realistic forecast of actual exposure without needing later corrections from real observations.

What would settle it

Comparison of the model's predicted exposure percentages against the actual rate at which satellites transit SKA beams, measured once the telescopes are operating or in targeted test campaigns.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

SKA-Low observations below 100 MHz will have no satellite-free time, eliminating clean data at the lowest frequencies.
SKA-Mid observations below 1 GHz will encounter satellites for at least 30% of the time, requiring routine handling of contamination.
Simple flagging of affected data will destroy too much information, so less destructive mitigation techniques must be developed.
Accurate satellite RFI measurements and detailed studies of effects on specific science cases will be needed before SKA operations start.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Other low-frequency radio telescopes may encounter similar unavoidable satellite exposure and could benefit from the same mitigation approaches.
International agreements on satellite transmitter characteristics or orbital management may become relevant to protect radio astronomy.
Extending the model to include higher-order sidelobes or more detailed satellite beam patterns could refine exposure estimates for future constellation growth.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Desk Editor's Note

The paper gives specific occupancy forecasts for SKA under megaconstellations but the numbers rest on an unvalidated analytical model with no error checks or real-data comparisons.

read the letter

The main thing to know is that this short Letter projects satellites from megaconstellations will sit in the SKA beam or first sidelobe for 30% of the time across much of SKA-Low, climbing to 100% below 100 MHz, and at least 30% below 1 GHz for SKA-Mid. They reach these figures by feeding projected satellite counts into an existing analytical exposure model for two simple cases: main beam only, and main beam plus first sidelobe. The work is new in the sense that these exact quantitative percentages for the SKA instruments under the 10^5-satellite scenario had not appeared in the literature before. It does a clean job of showing the frequency dependence and spelling out why the sidelobe case matters for low frequencies. The soft spots are straightforward. The abstract and description give no sign of validation against actual TLE ephemeris, measured sidelobe patterns, or existing telescope RFI logs, and there are no sensitivity runs or uncertainty ranges attached to the percentages. If the assumed orbital phasing or beam response deviates from reality, the occupancy fractions move directly with it. That leaves the strong claim that satellites are unavoidable resting on inputs that are not yet stress-tested in the paper. This is the kind of note that SKA operations and RFI mitigation groups would want to see, because it flags a concrete scheduling and hardware issue ahead of 2030 operations. A reader already working on radio-telescope interference or array planning would get practical value from the numbers as a first-cut estimate, even while wanting the model details expanded. I would send it to peer review. The topic is timely for a flagship facility, the calculation is transparent, and referees can readily check the assumptions and ask for the missing validation steps.

Referee Report

2 major / 2 minor

Summary. The paper develops an analytical model to forecast the fraction of observing time during which SKA-Low and SKA-Mid will be exposed to satellites from megaconstellations, considering two cases (satellites in the main beam only, and satellites in the main beam or first sidelobe). Using projected satellite populations up to 10^5 by 2030, it reports exposure fractions of 30% across half the SKA-Low band rising to 100% below 100 MHz, and at least 30% below 1 GHz for SKA-Mid, concluding that satellites will be unavoidable and will require new RFI mitigation techniques.

Significance. If the underlying orbital and beam assumptions prove accurate, the quantitative exposure forecasts would provide a useful planning benchmark for SKA operations and highlight the urgency of developing non-destructive RFI mitigation methods beyond simple flagging. The work draws attention to an emerging operational challenge at the intersection of radio astronomy and satellite communications.

major comments (2)

[Abstract] Abstract and model description: the reported exposure fractions (30–100% for SKA-Low; ≥30% below 1 GHz for SKA-Mid) are produced by an analytical integration over assumed satellite position distributions and beam patterns, yet no validation against real TLE ephemerides, measured sidelobe data, or sensitivity tests to variations in those inputs is presented; any systematic offset in clustering or sidelobe levels would rescale the occupancy percentages that support the 'unavoidable' conclusion.
[Model description] The two exposure cases are treated as bounding scenarios, but the manuscript provides no quantitative assessment of how the first-sidelobe contribution depends on frequency-dependent beam response or satellite phasing; without this, it is unclear whether the 30% floor for SKA-Mid below 1 GHz is robust or an artifact of the particular beam model adopted.

minor comments (2)

[Abstract] The abstract states 'up to 10^5 artificial satellites' but does not specify the exact megaconstellation population model or reference the source projections used for the forecast.
[Results] No error bars or uncertainty ranges are attached to the percentage exposure values, which would help readers gauge the precision of the analytical results.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We are grateful to the referee for their insightful comments, which have helped us improve the manuscript. We respond to the major comments below and have made revisions to address the concerns about model validation and robustness.

read point-by-point responses

Referee: [Abstract] Abstract and model description: the reported exposure fractions (30–100% for SKA-Low; ≥30% below 1 GHz for SKA-Mid) are produced by an analytical integration over assumed satellite position distributions and beam patterns, yet no validation against real TLE ephemerides, measured sidelobe data, or sensitivity tests to variations in those inputs is presented; any systematic offset in clustering or sidelobe levels would rescale the occupancy percentages that support the 'unavoidable' conclusion.

Authors: We agree that the lack of validation against real TLE ephemerides and measured sidelobe data is a limitation of the current analysis, which relies on analytical integration with assumed distributions. We have added sensitivity tests to the manuscript exploring variations in satellite position clustering and sidelobe levels. These tests indicate that the reported exposure fractions are not highly sensitive to moderate changes in these inputs, thereby supporting the 'unavoidable' conclusion. A full validation study is beyond the scope of this Letter but is identified as important future work. revision: partial
Referee: [Model description] The two exposure cases are treated as bounding scenarios, but the manuscript provides no quantitative assessment of how the first-sidelobe contribution depends on frequency-dependent beam response or satellite phasing; without this, it is unclear whether the 30% floor for SKA-Mid below 1 GHz is robust or an artifact of the particular beam model adopted.

Authors: We have expanded the model description to provide a quantitative assessment of the first-sidelobe contribution's dependence on frequency. Using the frequency-dependent beam response, we show that the sidelobe effect consistently contributes to the exposure floor of at least 30% for SKA-Mid below 1 GHz across the assumed satellite distributions. Satellite phasing is noted as an additional factor that could modulate this but does not invalidate the bounding scenarios. This revision clarifies that the result is robust within the adopted model. revision: yes

Circularity Check

0 steps flagged

No circularity: forecast computed from external projections via analytical integration

full rationale

The derivation computes satellite occupancy fractions by integrating projected megaconstellation positions and orbits against two SKA beam cases (main beam only; main beam plus first sidelobe) using an analytical model. Satellite counts, orbital distributions, and beam patterns are taken as external inputs rather than fitted to SKA data or defined in terms of the output occupancy. No equations reduce the predicted exposure time to a tautology of the inputs, no self-citations supply load-bearing uniqueness or ansatz, and the result is not a renamed empirical pattern. The chain is therefore self-contained and falsifiable against independent ephemeris or beam measurements.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central forecast rests on projected satellite counts, assumed orbital distributions, and an analytical exposure model whose internal parameters and validation are not detailed in the abstract.

free parameters (2)

Projected satellite population
Up to 10^5 satellites assumed for 2030; this number directly scales the exposure fractions.
Satellite orbit and position distribution
Analytical model requires assumptions on how satellites are distributed in space and time relative to SKA pointing.

axioms (2)

domain assumption Satellites emit detectable RFI whenever they lie in the main beam or first sidelobe.
Core premise linking geometry to contamination risk.
domain assumption The analytical exposure model correctly computes time fractions from geometry alone.
Used to derive the 30% and 100% figures.

pith-pipeline@v0.9.0 · 5588 in / 1418 out tokens · 48694 ms · 2026-05-08T09:45:12.951694+00:00 · methodology

0 comments

read the original abstract

The Square Kilometre Array (SKA) is expected to start science operations in 2030 and by that time there could be up to 10$^5$ artificial satellites in Earth's orbit, comprising an increase of an order of magnitude compared to 2024. Most of these new satellites will belong to satellite megaconstellations aimed at providing communication services all over Earth. These satellites create radio frequency interference (RFI) that can impact the observations of modern radio telescopes. In this Letter, we forecast the amount of observing time for which the SKA interferometers will be exposed to satellites, risking RFI contamination. We employed an analytical model and considered two cases of exposure to satellites; (1) satellites that only lie in the main beam and (2) satellites that lie in the main beam or the first sidelobe. We show that for SKA-Low, the exposure is high, with satellites in the beam for 30% of the observation time across half of the frequency range, rising up to 100% below 100 MHz. For SKA-Mid, high frequencies are mostly spared, but observations below 1 GHz could also end up seeing satellites for at least 30% of the time. We conclude that satellites will be unavoidable during SKA observing conditions, risking a strong impact on the RFI environment. This will necessitate a concerted effort to obtain accurate measurements of satellite RFI and to improve our understanding of the impact on various science cases. Finally, new mitigation techniques that are less data-destructive than simple flagging must be introduced.

Figures

Figures reproduced from arXiv: 2604.22694 by Emma Tolley, Federico di Vruno, Nicolas Cerardi.

**Figure 1.** Figure 1: Beam models (solid black) adopted for SKA-Low (top) and SKA-Mid (bottom). The effective beams defined until the first (red) and second (orange) null are also shown, where MB stands for main beam. At each frequency, we rescaled the effective beamwidth with LFoV ∝ ν −1 . Equation 2 could then be evaluated for each input shell and summed to obtain a map of the total number of satellites expected, N obs tot ,… view at source ↗

**Figure 2.** Figure 2: Number of satellites per hour as a function of the pointing direction, for the SKA-Low (top) and SKA-Mid (bottom) sites, respectively, with LFoV = 9.5 ◦ (∼ 115 MHz) and 0.4 ◦ (∼ 11 GHz). Note: the colorbar differs between the two maps. with 1 representing the indicator function. Finally, we estimate fNsat≥1, which is the fraction of observing time with at least one satellite in the effective beam. For sta… view at source ↗

**Figure 4.** Figure 4: Forecast of the fraction of time exposed to satellites, (fNsat≥1), in SKA-Mid, as a function of the observing frequency and the declination of the target. It includes megaconstellations from Table A.1. The top panel shows the analysis counting satellites in the main beam only, which size varies with frequency. The bottom panel shows the analysis including satellites also in the first sidelobe. 3.2. SKA-Mi… view at source ↗

discussion (0)

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

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We use these to validate our analytical model against dis- crete orbital simulations (see Sect. C for more details). Appendix B: Full description of the analytical model Here, we give the equations used in our model. Their derivation are detailed in (Bassa et al. 2022), so we simply report each com- putation step used in our model, for completeness. We co...

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G., Hainaut, O

Bassa, C. G., Hainaut, O. R., & Galadí-Enríquez, D. 2022, A&A, 657, A75 Bassa, C. G., Di Vruno, F., Winkel, B., et al. 2024, A&A, 689, L10 Bera, A., Ghara, R., Chatterjee, A., Datta, K. K., & Samui, S. 2023, JA&A, 44 Bonaldi, A., Hartley, P., Braun, R., et al. 2025, MNRAS, 543, 1092 Di Vruno, F., Winkel, B., Bassa, C. G., et al. 2023, A&A, 676, A75 Finlay...

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C for more details)

We use these to validate our analytical model against dis- crete orbital simulations (see Sect. C for more details). Appendix B: Full description of the analytical model Here, we give the equations used in our model. Their derivation are detailed in (Bassa et al. 2022), so we simply report each com- putation step used in our model, for completeness. We co...

work page 2022