Elon Musk’s constellation of Starlink satellites could have dire consequences for the operations of the world’s largest radio telescope – the Square Kilometre Array (SKA).
SpaceX has already launched more than 900 Starlink satellites into space and continues to ramp up its orbiting network of small satellites to deliver global high-speed Internet across the world.
The company, which was founded by CEO Elon Musk, has also stated that its planned network of up to 42,000 satellites will not interfere with sensitive astronomy hardware based on Earth.
It has even begun outfitting its satellites with visors that make them 31% as bright as the previously unvisored versions.
Despite this, these satellites are still 2.5-times brighter than SpaceX’s goal, which does not mitigate their impact on telescopes around the world.
This is especially bad news for the SKA, the world’s largest radio telescope system based in South Africa.
The SKA project is an intergovernmental collaboration between 15 countries to build the world’s largest radio observatory comprising two telescopes located in Australia and South Africa.
In an impact analysis published last year, the SKA Organisation (SKAO) found that it would be almost impossible for the South African SKA telescope to remain unaffected by Musk’s Starlink system.
Furthermore, if the current configuration of the Starlink satellites remains unchanged and continues to roll out, the SKA telescope’s operations could be crippled severely.
The source of the problem lies in the spectrum used by the Starlink satellites and the SKA telescope in the Northern Cape.
As the SKA is a radio telescope installation, it functions within a defined radiofrequency spectrum band. Unfortunately for the scientists of the SKAO, this is the same spectrum band used by Musk’s Starlink satellites.
The SKA telescope requires minimal interference from radio signals, which is why it is built within a legally-protected Radio Quiet Zone that protects it from ground-generated radio signals such as cellphones or Wi-Fi.
Unfortunately, the Radio Quiet Zone does not hold jurisdiction over tens of thousands of small satellites rapidly orbiting and beaming signals back to Earth.
“Radio transmissions from satellite constellations use a frequency range which has been in use by the satellite industry for many years,” the SKA band said in its analysis.
“It sits within the range of frequency observed by the SKA-Mid’s band 5b receivers, and is immediately adjacent to an internationally protected radio astronomy band.”
Despite this, radio telescopes have been able to conduct observations in all these frequency ranges due to the small number of visible satellites and their mostly geostationary orbit.
“The deployment of thousands of satellites in low earth orbit (LEO) will inevitably change the situation as astronomers now face a much larger number of fast-moving radio sources in the sky,” the SKAO said.
Blinded by satellites
The SKAO said that while the radio signals beamed to the telescope by the Starlink satellites will not damage the equipment, they will essentially blind it periodically.
In its analysis, the organisation said that strong interfering signals can “saturate” the receiver signals and drown out all other signals seen by the Band 5b receivers.
“As a consequence, all data in that frequency band would be lost, rendering these receivers useless for a portion of the time,” the SKAO said.
This saturation is predicted to occur for a small percentage of the operation time for the initial phase of the Starlink constellation deployment (around 6,400 satellites), provided the satellites do not reflect light directly onto the SKA dishes.
However, if there were to be around 100,000 of these satellites in orbit, the saturation would be continuous and would render the installation essentially useless.
“There is tremendous scientific and public interest in identifying the origins of life beyond that found on Earth and one of the most promising methods of tracking it down elsewhere in our galaxy is the detection of complex pre-biotic molecules, whose spectral signatures are concentrated between about 10 and 15 GHz,” said SKA Science Director Dr Robert Braun.
“This is only one of many exciting science goals that depend on sensitive access to this frequency range. The prospect of losing sensitivity in this key frequency band is extremely worrying.”
The analysis found that one impact of the lost sensitivity would be a 70% increase in the required integration time – the time astronomers need to look at a particular object in order to observe it clearly – in the satellite transmission range.
“A loss of observing efficiency on top of the expected large oversubscription on the telescope will translate directly into lost science and it is quite possible that the most challenging experiments that might otherwise have been undertaken will no longer be viable at all in these circumstances,” Dr Braun said.
A simple software fix
While the outlook is bleak with the satellite constellation in its current configuration, the SKAO said the most effective resolution would be a software update to the Starlink satellites.
This would be pushed to the hardware with the simple goal of ensuring that the satellites did not point their beams near the SKA dishes.
“SKAO would require operators to steer their satellites’ beams away from the telescope site, a measure which would require a simple software modification with no repercussion on the constellation’s deployment, positioning or hardware,” the SKAO said.
“While a cost-effective implementation of this solution does depend on the hardware and software deployed on the satellites, operators already use this technique to comply with international regulations when their satellites cross the path between geostationary satellites in higher orbit and their receiving ground stations, for example, to avoid affecting telecommunications and TV transmissions.”
This would reduce the impact of the Starlink constellation on the SKA by a factor of 10, resulting in a 7% increase in integration time instead of the aforementioned 70%.
The loss of sensitivity is inevitable, however, and every Starlink satellite launched will contribute towards the reduced efficiency of the world’s biggest radio telescope.
“While any loss of sensitivity is regrettable, SKAO recognises the need for compromise between the competing scientific and commercial drivers,” the SKAO said.