170 spacecraft in the classified constellation are emitting odd signals. It's unclear why.
An amateur astronomer monitoring satellites as a hobby has
discovered a strange signal being emitted by SpaceX's classified network of
satellites known as "Starshield".
In 2021, Elon Musk's space firm SpaceX signed a $1.8 billion
classified contract with an unknown US government agency, as reported by the
Wall Street Journal. In 2024, Reuters reported that the contract SpaceX signed
is with the National Reconnaissance Office (NRO), the government agency
responsible for managing spy satellites. According to sources who spoke to the
news agency, Musk's firm is creating a network of hundreds of satellites that
can operate as a swarm in low-Earth orbit, capable of imaging the Earth below.
"The National Reconnaissance Office is developing the
most capable, diverse, and resilient space-based intelligence, surveillance,
and reconnaissance system the world has ever seen," the NRO said in a
statement seen by Reuters.
The specific capabilities of the satellite network are
unknown, with both SpaceX and the NRO declining to comment on the specifics of
the project. However, a source told Reuters that "no one can hide"
from the system's reach.
Cut to amateur satellite tracker Scott Tilley, tracking
satellites from his home in British Columbia. Tilley was working on one of his
projects, when he accidentally began a search of radio frequencies which are
usually not used by satellites to send data back to Earth.
"It was just a clumsy move at the keyboard,"
Tilley told NPR. "I was resetting some stuff and then all of a sudden I'm
looking at the wrong antenna, the wrong band."
There in the 2,025-2,110 MHz range, where there should be
nothing but silence, he found a spacecraft emitting a signal back down to
Earth. Comparing his observations to those from other amateur satellite
trackers around the world, he found the culprit.
"Bang, up came an unusual identification that I wasn't
expecting at all," he added. "Starshield."
It is unusual to see satellites emitting in this range for a
good reason. That band is not allocated for sending data down from satellites
to Earth, but is reserved for "uplinking" to satellites.
"Strong wideband S-band emissions have been detected
from satellites associated with the Starshield constellation. These emissions,
centred within the 2025–2110 MHz band allocated internationally for
Earth-to-space and space-to-space links, exhibit Doppler characteristics and
power levels consistent with direct space-to-Earth transmissions," Tilley
explained in a paper detailing these observations.
"In plain terms, this band is reserved primarily for
uplinks (Earth-to-space) and, to a limited extent, space-to-space crosslinks
between authorized spacecraft. There is no provision in the ITU regulations for
space-to-Earth downlink transmissions within 2,025–2,110 MHz," he added.
In total, 193 separate satellites have been catalogued in
this constellation, with Tilley finding that 170 are emitting on S-band.
Without notifying the proper authorities and gaining permission to use this
band, which SpaceX does not appear to have done, the firm could be in breach of
national licensing requirements.
It is not clear why the satellites are sending data in this
band, particularly as transmission speeds would be around those achieved by 3G.
Tilley suggested that it could be a deliberate tactic to hide Starshield away
from observers below, while Kevin Gifford, a computer science professor at the
University of Colorado and specialist in spacecraft radio interference, told
NPR that it could just be that SpaceX is simply taking advantage of the quiet
band, and worrying about permissions later.
"From a regulatory perspective, the apparent downlink
operation within the 2025–2110 MHz band raises questions regarding compliance
with ITU Radio Regulation Footnote 5.392, which reserves this spectrum
primarily for Earth-to-space and space-to-space links in the Space Operation,
Space Research, and Earth Exploration-Satellite Services," Tilley adds.
"To date, no public record exists in the ITU Master
International Frequency Register (MIFR) authorizing Starshield downlink
transmissions in this range. If confirmed, this would highlight a gap between
the practical deployment of modern large constellations and the international
coordination mechanisms intended to prevent harmful interference."
The study is posted to open research repository Zenodo.