NASA issues a warning about SpaceX Starlink satellites

At the moment, NASA — in cooperation with the Department of Defense — keeps tabs on 25,000 such objects, including the International Space Station, the Hubble Space Telescope, thousands of satellites pointed back toward Earth and out into space, and all kinds of debris leftover from decades of launches.

The Gen2 constellation would more than double that figure. And that’s before any crashes.

“An increase [of the number of satellites] of this magnitude... brings additional risk of debris-generating collision events based on the number of objects alone,” NASA warns in the letter.

Without the addition of any new satellites, the amount of space junk is already past "a "tipping point" where debris would continue to increase even if all launches were stopped," retired NASA scientist Donald Kessler told Scientific American last year. 

Collisions aren’t totally avoidable

NASA disputes SpaceX's claim that its satellites’ automated collision-avoidance systems eliminate the possibility of crashing into large objects, arguing that skies filled with constellations such as Starlink will be so crowded that “close encounters” will be unavoidable. Under those conditions, the idea that the risk of collision can be engineered away “lacks statistical substantiation,” the letter says.

In a well-publicized series of tweets last year, astronautics research Hugh Lewis revealed that there were some 1,630 close passes (with a kilometer) between Starlink internet satellites and other objects (including other Starlink satellites) in June 2021.

NASA's letter also notes that the satellites would sit at an altitude of 328-360 kilometers, just below the orbit of the International Space Station. When spacecraft visit the ISS to deliver supplies or bring new crewmembers, for example, they often spend time at that altitude to align with the ISS and prepare for docking, in what are called phasing maneuvers.

“The proposed volume of autonomously maneuvering satellites directly parked in common phasing altitudes could result in potential loss of launch/entry opportunities,” interrupting operations aboard the space station, the agency said.

In December, the Chinese government said that two Starlink satellites nearly collided with its space station, which was orbiting at 555 kilometers.

The thicket of satellites would also shorten the windows for safe launches, NASA said. Such launch windows are the moments — often fleeting — when everything from Earth's position in space to local weather conditions align. The agency specifically named the 2024 Europa Clipper mission as an example of the type of launch that could be put at risk.

In a sign of SpaceX's central role in the space industry, NASA announced last year it would pay SpaceX $178 million to launch that probe.

The satellites could block views of space and Earth

Finally, NASA says the Starlink constellation could block views important to space exploration, Earth science, and even planetary safety.

Roughly one-third of the proposed satellites would orbit Earth above the Hubble Space Telescope, which sits 535 kilometers above sea level. Satellites already photobomb eight percent of the composite images Hubble takes, according to the letter. The addition of 10,000 satellites in orbit beyond the telescope “could more than double the fraction of Hubble images degraded,” NASA said.

All 30,000 satellites stand to obscure the views of several satellites that sit in much higher orbits, where they use “lidar and radar instruments spanning both the radio and optical electromagnetic spectrum” to monitor Earth’s climate. The agency says “sun-glint and reflections from the Starlink spacecraft” could render those measurements inaccurate.

The constellation could also keep telescopes on the ground from getting a clear view of what’s out there — and of what’s headed our way.

“NASA estimates that there would be a Starlink in every single asteroid survey image taken for planetary defense against hazardous asteroid impacts, decreasing asteroid survey effectiveness by rendering portions of images unusable,” the agency writes, saying the satellites would threaten “our planet’s ability to detect and possibly redirect a potentially catastrophic impact.”

It's not just SpaceX

This isn't the first time NASA has raised concerns about a satellite constellation. In 2020, the agency expressed "substantial concerns" about a network of 243 satellites that Texas company AST & Science wanted to place in orbit. Those satellites are still on the ground.

While Starlink has faced plenty of criticism from astronomers who say the satellites obscure their view of the night sky, the constellation has also been used to enable communication with areas that have suffered natural disasters. Earlier this week, Starlink satellites helped restore the connection to Tonga after a devastating volcano.

SpaceX has yet to issue a response to NASA's objections.