Starlink signal leaks are keeping radio astronomers from catching echoes of the early Universe

Radio astronomers spent decades designing the Square Kilometre Array Low (SKA-Low) to hear one of the faintest signals in the observable Universe — the emission of neutral hydrogen from the “cosmic dawn” epoch, when the first stars ignited some 13 billion years ago. Instead, the instruments are increasingly catching electronic “junk” from SpaceX satellites.

This is not about the directed broadband beams that Starlink transmits deliberately. The problem is the stray emission from onboard electronics, which leaks through the satellite's structure and spreads across frequencies never allocated for it.

What the study found

A team from Curtin University used the Engineering Development Array 2 — a prototype SKA-Low station in Australia — and over 29 days analyzed about 76 million radio images. The results, published in the journal Astronomy & Astrophysics, were discouraging: 112,534 individual emissions were recorded from 1,806 unique Starlink satellites in the 73–235 MHz band — exactly where SKA-Low operates.

Some of the craft put out periodic signals 13 kHz wide near 137 MHz once every 100 seconds. These are not scheduled communication sessions that operators could work around, but unpredictable hardware leaks. Researchers cannot model such a signal and subtract it from the data.

The scale of the problem is illustrated by the numbers. The power of the leaks reaches 10⁶ Jy/beam, whereas detecting hydrogen from the early Universe requires a sensitivity on the order of 10⁻⁵ Jy — the interference itself is roughly 10,000 times stronger than the cosmic signals being sought. On some frequencies Starlink interference was present in 30% of the images, including inside the ITU-protected bands 73–74.6 MHz and 150.05–153 MHz, where there should be no signals at all. According to Steven Tingay of Curtin University, in brightness the emission is comparable to the most powerful natural radio sources in the sky.

Formally, no one is breaking the rules

The main difficulty is regulatory. The International Telecommunication Union (ITU) protects a number of astronomical bands only against intentional transmissions. Unintended emission from equipment remains in a gray area and is legally “invisible,” even when it falls within protected spectrum. The authors compare this to quiet-hours rules that ban deliberate noise but ignore a neighbor's air conditioner droning all night.

SpaceX has already met science halfway: the satellites got sunshades against optical glare, and an agreement with the NSF settled some of the high-frequency radio bands. But beam management does not solve the problem of low-frequency leaks. The ITU is reportedly discussing the issue, but discussion is not regulation, and the constellation already exceeds 6,000 craft. The company is aware of the scientists' findings and open to dialogue about future changes to the “hardware.”

Algorithmic filtering of the interference is still, by the researchers' own admission, in its infancy and may require computing power comparable to processing the science data itself. The real solution remains engineering fixes — as already happened with optical brightness. The only question is whether they will manage to agree on who protects the radio sky, and how, before the window of opportunity closes.

Source: Hacker News