The hole in the law above the Karoo

The legal shield around South Africa’s most valuable scientific instrument does not reach the objects most likely to interfere with it.

The Karoo Central Astronomy Advantage Area (KCAAA), established under the country’s Astronomy Geographic Advantage Act, protects MeerKAT and the Square Kilometre Array-Mid (SKA-Mid) telescope now under construction from ground-based interference. Satellites sit outside it.

“Satellites are physically geographically located outside the KCAAA while their transmissions enter the protected area,” the South African Radio Astronomy Observatory (Sarao) said in a written response to questions from TechCentral.

The act does allow the minister to act against spectrum users that “transmit or broadcast into” the zone, including forcing a move to another frequency. But large moving constellations were not what those rules were written for.

In submissions to the communications regulator’s public hearings this month on the draft radio frequency spectrum regulations, it called for enforceable coordination between satellite operators and radio astronomy facilities, and for compatibility assessments covering aggregate interference from whole constellations rather than single satellites.

“A single satellite transmitting into the main beam can overwhelm faint cosmic signals,” Sarao said. Interference can be orders of magnitude stronger than the signal astronomers are trying to detect. The larger worry is cumulative: thousands of satellites transmitting at once, compounded by unintended electromagnetic radiation leaking from satellite electronics.

There is no satellite headcount at which radio astronomy tips over, Sarao said, because it depends on frequencies, orbits, power and beam configurations. It pointed to ITU-R studies of the 2 690-2 700MHz band that “demonstrated potentially severe interference to radio astronomy” from constellations far smaller than those now proposed.

South Africa is not yet routinely measuring satellite interference at MeerKAT. Monitoring “has primarily focused on terrestrial services” and is being extended to space-based sources. The clearest evidence so far comes from elsewhere: SKA Obversatory-supported observations by the Lofar telescope detected unintended emissions from Starlink satellites between 110MHz and 188MHz, inside a protected radio-astronomy band.

One mitigation under international discussion stops short of switching satellites off across the whole reserve. Through the International Telecommunication Union, the international community is “engaging with operators to develop technical and regulatory mitigation measures,”, said Adrian Tiplady, Sarao deputy MD for strategy and partnerships. “One of the options is to create nulls (holes) in their coverage around radio telescopes.” Those holes would be far smaller than the protected area, focused on the dishes rather than the Karoo as a whole.

The window is now, Sarao said, because satellites have long operational lives and their numbers are climbing.