WASHINGTON — SpaceX passed the threshold of more than 2,000 Starlink satellites launched after a Falcon 9 placed another set of broadband internet spacecraft into orbit Jan. 18.

The Falcon 9 lifted off from Launch Complex 39A the Kennedy Space Center at 9:02 p.m. Eastern. The launch was originally scheduled for 7:04 p.m. Eastern, but SpaceX postponed the launch to the second of two opportunities that evening. The company did not disclose the reason for the delay.

The Falcon 9 second stage released its payload of 49 Starlink satellites into low Earth orbit 15 and a half minutes after liftoff. However, the deployment took place in a part of the orbit without ground station coverage, so confirmation did not come until the stage passed over a ground station in Alaska about an hour later.

The rocket’s first stage landed on a droneship in the Atlantic eight and a half minutes after liftoff. The stage made its 10th flight, after previously launching a GPS 3 satellite, the Turksat 5A communications satellite, the Transporter-2 rideshare mission, and six other Starlink missions. This is the fourth Falcon 9 booster to have completed at least 10 missions, including one that has launched and landed 11 times.

The 49 satellites on this mission, called Starlink 4-6 by SpaceX, bring the total number of Starlink satellites launched by the company to 2,042, according to statistics kept by astrophysicist and spaceflight analyst Jonathan McDowell. That figure includes two prototype “Tintin” satellites launched in February 2018 and the series of Starlink launches, carrying up to 60 satellites at a time, that started in May 2019.

Not all those 2,042 satellites are operational or even still in orbit. McDowell counts 1,879 satellites in orbit, counting this latest set of satellites, with 1,495 satellites in operational orbits. SpaceX Chief Executive Elon Musk, in a Jan. 15 tweet, said there were 1,469 satellites active, with 272 moving to operational orbits.

SpaceX’s current Starlink constellation is authorized for 4,408 satellites, all in orbits at around 550 kilometers. The company is seeking a Federal Communications Commission license for a second-generation system of approximately 30,000 satellites that it says would launch using its Starship vehicle under development.

The growth of satellite megaconstellations in general, and Starlink in particular, has worried astronomers, who fear that the satellites will interfere with observations of the night sky. Those concerns prompted a series of workshops as well as discussions with SpaceX, which has taken steps to reduce the brightness of its satellites.

In a paper published Jan. 17 in The Astrophysical Journal Letters, astronomers assess the effect that Starlink had on one observatory, the Zwicky Transient Facility (ZTF) at Palomar Observatory in California. The research found a sharp increase in the number of images taken near dawn and dusk that had streaks from satellites.

“In 2019, 0.5% of twilight images were affected, and now almost 20 percent are affected,” said Przemek Mróz, lead author of the study, in a Caltech news release about the research.

However, the same study found little evidence that the satellite streaks were interfering with the science being done by the observatory, which tracks near Earth asteroids as well as phenomena like supernova explosions. “There is a small chance that we would miss an asteroid or another event hidden behind a satellite streak, but compared to the impact of weather, such as a cloudy sky, these are rather small effects for ZTF,” said Tom Prince, a Caltech professor emeritus of physics and a co-author of the study, in the release.

The study, though, found that SpaceX was falling short of a goal set by astronomers in reducing the brightness of the Starlink satellites. The ZTF measurements found that the Starlink satellites equipped with visors had an average magnitude of 6.8, slightly brighter than the threshold of magnitude 7 set by astronomers to minimize effects on sensitive instruments, like the camera that will be used with the Vera Rubin Observatory under development in Chile.

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