HONOLULU — SpaceX says it’s committed to working with the astronomy community to address the brightness of its Starlink satellites, but some astronomers remain concerned about the deleterious effect that system and other megaconstellations will have on their field.
One of the 60 satellites in the latest Starlink launch Jan. 6 featured an experimental coating intended to reduce its brightness. SpaceX said it will see in the coming weeks how well those coatings work, as well as study any effects they have on the performance of the satellite itself, before deciding how to move forward.
“Our level of brightness and visibility was a surprise to us,” said Patricia Cooper, vice president of satellite government affairs for SpaceX, during a Jan. 8 special session on the topic of megaconstellation effects on astronomy during the 235th Meeting of the American Astronomical Society (AAS) here. SpaceX President Gwynne Shotwell also said last month that SpaceX was surprised by the brightness of the satellites.
Cooper said that brightness is affected by several issues. The Starlink satellites initially appear bright when released in a lower parking orbit, and the configuration of each satellites’ single large solar array when raising its orbit can also influence its brightness. Once in a final operating orbit of 550 kilometers, the spacecraft brightness decreases to a visual magnitude of about five, making them visible to the naked eye only in darker night skies.
One challenge, she said, is the unique design of the satellite made it difficult to determine exactly what causes the spacecraft to reflect so much light. “It turns out, we think, that surfaces that scatter light, or reflect light diffusely, are also significant contributors,” she said. That led to the testing of surfaces on the experimental satellite, nicknamed “DarkSat” by some, to reduce that reflectivity.
While DarkSat is now in orbit, it will take some time to see how effective it is. Patrick Seitzer, an astronomer at the University of Michigan who is studying the effect of satellite constellations on optical astronomy, said at a later press conference that the satellite likely won’t reach its operational orbit until late February. “Then serious measurements can begin,” he said.
Cooper said that SpaceX would work quickly to reduce the brightness of its satellites, but didn’t give a specific timetable or state if other experimental satellites are in the works. In the meantime, the company will continue to launch the original design of Starlink satellites that are designed to be operational for five years, a plan that some astronomers at the meeting criticized.
“We don’t know yet if these mitigations are useful and effective,” she said. “We tend to work very quickly. We tend to test, learn and iterate.”
SpaceX has been meeting with a committee of the AAS to discuss the astronomy community’s concerns about Starlink and to examine ways to mitigate them. That work has included a half-dozen teleconferences and an in-person meeting during this AAS conference, said Jeff Hall, director of Lowell Observatory and chair of the AAS committee.
“We have not had to cajole SpaceX in any way. They’ve been very receptive and very proactive,” he said. Those discussions, he said, initially focused on SpaceX’s Starlink deployment plans, but more recently have been more just “keeping in touch” as SpaceX prepared to launch its experimental DarkSat.
Hall added that it was premature to discuss regulations regarding satellite brightness. “Regulation of the Wild West up there is necessary, but that is going to take a great deal of time to implement,” he said, while the problem posed by Starlink and other constellations is a near-term issue that needs to be addressed now.
Hall and other astronomers said that, like SpaceX, they were surprised by how bright the Starlink satellites appeared. “What surprised everyone — the astronomy community and SpaceX — was how bright their satellites are,” Seitzer said. “We knew these tens of thousands of megaconstellations were coming, but based on the sizes and shapes of things currently in orbit, I thought they’d be maybe eighth or ninth magnitude. We were not expecting second or third magnitude.”
Both astronomers and SpaceX said they hope, as an initial step to get the Starlink satellites dim enough to not be visible to the naked eye even in the darkest skies. The next step will be to figure out what else can be done to mitigate their effects on major observatories, specifically the Vera Rubin Observatory (formerly Large Synoptic Survey Telescope) under construction in Chile. Astronomers said that wide-field telescope was particularly threatened by Starlink and other megaconstellation satellites.
Hall said his AAS committee plans to start discussions with OneWeb later this month, shortly before the company begins full-scale deployment of its constellation. Six OneWeb demonstration satellites are currently in orbit, at altitudes higher than SpaceX. Seitzer said the satellites, at about eighth magnitude, are too dim to be seen by the naked eye, but pose in some cases greater concerns to professional astronomers than Starlink satellites because, at their altitudes, they may be visible all night during the summer, rather than just around sunset and sunrise.
With SpaceX seeking to deploy up to 1,500 Starlink satellites in 2020 alone, and with OneWeb and other constellations under development, astronomers warned this was a major issue to them. “The issue of megaconstellations and astronomy is a serious issue,” Seitzer said. “We have a very short time to deal with this issue.”