Organisers of an American Astronomical Society conference in Hawaii held a special session to discuss the ways in which satellite megaconstellations, such as the one currently being built by SpaceX, are poised to disrupt telescopic observations. The astronomers also proposed potential solutions to this emerging problem.
The special session, titled “Challenges to Astronomy from Satellites,” was held yesterday at the 235th Meeting of the American Astronomical Society (AAS) currently being held in Honolulu, Hawaii.
The session, chaired by Connie Walker from the National Science Foundation’s Optical-Infrared Astronomy Research Laboratory in Tucson, Arizona, was prompted by recent developments relating to the construction of the SpaceX Starlink megaconstellation, but the point of the meeting was to discuss the prospect in general, as several other firms are planning to build substantial satellite constellations of their own.
That Starlink was a focal point of the meeting barely registers as a surprise. SpaceX has now launched three batches of its small-sats, which places the total number at around 180. Each launch has been accompanied by a light show, in which an orderly procession of Starlink satellites have been seen zipping across the night sky. This train-like effect lasts for a week or more until the satellites disperse to their higher service orbits, but even then they are still visible to the naked eye. Perhaps unsurprisingly, Starlink trains have already disrupted astronomical observations.
That’s certainly one problem, but another has to do with the sheer volume of satellites expected to enter into orbit over the coming years. SpaceX ultimately wants its Starlink constellation to consist of tens of thousands of satellites, while other companies, such as OneWeb, Telsat, and Amazon, are hoping to build their own multi-satellite constellations. The private sector is set to increase the number of objects in space by an order of magnitude, and this unprecedented experiment—without any apparent thought to the consequences—could disrupt astronomical observations to an alarming degree.
Jonathan McDowell, an astronomer at Harvard-Smithsonian Centre for Astrophysics and an expert on satellites, attended this special AAS session and talked to his peers about the subject. He also met with SpaceX reps.
“I do believe SpaceX is making a good-faith effort to fix the problem,” McDowell told Gizmodo in an email. “I think they can get the satellites fainter than what the naked eye can see, which is a minimal thing to not spoil the night sky for non-astronomers.”
As for professional astronomers, he fears there will be times of the year when these satellites will pose “at minimum a big problem,” saying he worries there will be issues astronomers have not even thought of yet.
During yesterday’s session, Patricia Cooper, the vice president of satellite government affairs for SpaceX, said the “level of brightness and visibility was a surprise to us,” reported SpaceNews.
This unexpected luminosity, said Cooper, is a consequence of the satellites having to be deposited in a low orbit as well as the way in which their large solar arrays are initially oriented. Once in their intended orbits, some 550 kilometres above Earth, their brightness is vastly diminished, but they can still be seen from the ground.
SpaceX has responded to this problem. For the most recent deployment—in which SpaceX became the largest commercial satellite operator in the world—one Starlink satellite was treated with a special dark coating intended to diminish its reflectivity. We won’t know if this solution will work until February, when the satellites go into service.
In addition, the private space company is making the coordinates of each Starlink satellite available to astronomers, who can use this information when planning their observations, according to the Washington Post.
“We don’t know yet if these mitigations are useful and effective,” said Cooper. “We tend to work very quickly. We tend to test, learn and iterate.”
The session also addressed megaconstellations in general, discussing the ways in which these satellite arrays could influence scientific observations, whether these satellites are used for telecommunications, as is the case for Starlink, or sweeping surveys of the Earth’s surface, such as the proposed ICEYE constellation, which would involve fleets of satellites equipped with synthetic-aperture radar (SAR).
Speaking at the session, astronomer Patrick Seitzer from the University of Michigan warned of the deleterious effects, such as multiple streaks on images, ghost-like artifacts, the saturation of detectors with light, and interference with electronic devices, the BBC reported.
“Mega-constellations in Low Earth Orbit are coming and they are coming fast,” Seitzer was quoted as saying in the BBC. “The new satellites are brighter than 99% of objects in orbit,” adding that the initial batch of Starlink sats is “just the start.”
Seitzer recommended that SpaceX make it so that its Starlink satellites are not visible to the naked eye even when in their service orbits and that the company work to reduce the brightness of these objects to prevent the over-saturation of large professional telescopes, the BCC reported. Upsettingly, he said the Vera C. Rubin Observatory, previously known as the Large Synoptic Survey Telescope, will be badly affected by megaconstellations, as this observatory, with its highly sensitive equipment, will map the entire sky once every three days.
Another problem mentioned at the conference is the threat of excessive radio interference coming from some of these satellites, such as the aforementioned ICEYE. Speaking to reporters at the conference, Harvey Liszt from the National Radio Astronomy Observatory (NRAO), said if SAR is pointed at a radio telescope that’s looking directly back at it, SAR “will burn out the radio astronomy receiver,” reported the BBC.
Hopefully these discussions will further compel the private sector to adopt sensible practices prior to lobbing their products into space. It’s deeply disappointing that we’re having these conversations so late into the game. Being able to predict that tens of thousands—or possibly even hundreds of thousands—of satellites in low Earth orbit will affect our view of the cosmos isn’t exactly rocket science.