Classified satellite network emits mysterious signal: NPR

A constellation of classified defense satellites built by the commercial company SpaceX is emitting a mysterious signal that could violate international standards, NPR has learned.

Satellites associated with the Starshield satellite network appear to be transmitting toward the Earth’s surface on frequencies normally used to do just the opposite: send commands from Earth to satellites in space. Using these frequencies to “transmit” data goes against standards set by the International Telecommunications Union, a United Nations agency that seeks to coordinate the use of radio spectrum globally.

Starshield’s unusual transmissions can potentially interfere with other scientific and commercial satellites, warns Scott Tilley, an amateur satellite tracker in Canada who was the first to spot the signals.

“Nearby satellites could receive radio interference and may not respond properly to commands — or ignore commands — from Earth,” he told NPR.

Outside experts agree there is a risk of radio interference. “I think this is definitely happening,” said Kevin Gifford, a computer science professor at the University of Colorado Boulder who specializes in radio interference from spacecraft. But he added that the question of whether this interference was truly disruptive remained unresolved.

SpaceX and the U.S. National Reconnaissance Office, which operates the satellites for the government, did not respond to NPR’s request for comment.

Caught by the wrong antenna

The discovery of the signal happened purely by chance.

Tilley regularly monitors satellites from his home in British Columbia as a hobby. He was working on another project when he accidentally triggered a sweep of normally silent radio frequencies.

“It was just a clumsy keyboard move,” he said. “I was resetting some things and all of a sudden I’m looking at the wrong antenna, the wrong band.”

The band of radio spectrum he found himself examining, between 2,025 and 2,110 MHz, is reserved for “uplinking” data to orbiting satellites. This means that there should be no signals from space in this range.

But Tilley’s experienced eye noticed that there seemed to be a signal coming from the sky. It was in a part of the group “that shouldn’t have anything there,” he said. “I grabbed my mouse, hit the record button, and let it record for a few minutes.”

Tilley then took the data and compared it to a catalog of observations made by other amateur satellite trackers. These amateurs, located around the world, use telescopes to track satellites as they move across the sky, then share their positions in a database.

“Bang, an unusual identification happened that I didn’t expect at all,” he said. “Star shield.”

Starshield is a classified version of SpaceX’s Starlink satellites, which provide internet service around the world. The United States has already reportedly paid more than $1.8 billion for the network, although little is known about it. According to SpaceX, Starshield conducts both Earth observation and communications missions.

Since May 2024, the National Reconnaissance Office has conducted 11 Starshield satellite launches in what it describes as its “proliferated system.”

So far, the National Reconnaissance Office says it has launched more than 200 satellites under its “proliferated architecture” system to facilitate military Earth observation and communications missions.

Document from the National Reconnaissance Office

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Document from the National Reconnaissance Office

“The NRO’s proliferated system will increase speed of access, diversify communication channels, and improve resiliency,” the agency says of the system. “With hundreds of small satellites in orbit, data will be delivered in minutes or even seconds.”

Tilley says he has detected signals from 170 Starshield satellites so far. All appear in the 2025-2110 MHz range, although the precise frequencies of the signals vary.

The purpose of Signal in question

It’s unclear exactly what the satellite constellation does. Starlink, SpaceX’s public satellite Internet network, operates at much higher frequencies to enable broadband data transmission. Starshield, on the other hand, uses a much lower frequency range that likely only allows data transmission at rates closer to those of 3G cellular, Tilley says.

Tilley says he thinks the decision to downlink in a band typically reserved for uplink data could also be designed to hide Starshield’s operations. Frequently changing the specific frequencies used could prevent outsiders from finding the signal.

Gifford says another possibility is that SpaceX was simply taking advantage of a quiet part of the radio spectrum. Uplink transmissions from Earth to satellites are typically rare and brief, so these frequencies likely remain dark most of the time.

“SpaceX is smart and savvy,” he says. It’s possible that they just decided to “do it and ask for forgiveness later.”

He notes that it is unlikely that Starshield’s signals have caused significant disruption so far, otherwise other satellite operators would have complained.

Tilley told NPR that he decided to make his discovery public because satellite operators around the world should be aware of what’s going on.

“These are objects in classified orbits, which could potentially disrupt other legitimate uses of space,” he said.