Rocket builder SpaceX is rapidly becoming the world's foremost satellite operator, having launched 420 of its own satellites in the past year – with plans for thousands more.
However, the unprecedented scale of SpaceX's satellite internet project, known as Starlink, has caused a public outcry from astronomers around the globe. The network represents SpaceX's plan to build a network of about 12,000 small satellites to provide high-speed internet to anywhere in the world.
Starlink satellites have appeared as bright streaks across images taken by telescopes, ever since SpaceX launched the first mission almost a year ago.
The satellites are visible enough at times that an astronaut on board the International Space Station even spotted Starlink earlier this month.
SpaceX in recent months has taken to addressing astronomer's concerns directly. The American Astronomical Society (AAS) in December noted that "the response from our community was loud enough that SpaceX reached out to the AAS looking to establish a line of communication."
On Monday, SpaceX CEO Elon Musk and members of his Starlink division gave a presentation before the National Academy of Sciences, Engineering, and Medicine. The company's leadership gave updates on the changes SpaceX has made to the design of its Starlink satellites, as well as changes to how the satellites move in space, to help reduce the brightness and damage to astronomer's images.
"SpaceX is committed to making future satellite designs as dark as possible," the company said in a press release on Tuesday about the presentation.
"We also firmly believe in the importance of a natural night sky for all of us to enjoy, which is why we have been working with leading astronomers around the world to better understand the specifics of their observations and engineering changes we can make to reduce satellite brightness," SpaceX added.
"With the benefit of hindsight, the changes seem quite simple," Musk said during Monday's presentation. "We'll feel a bit silly in hindsight, as it's not that hard."
The company emphasized that it continues to work with AAS to address the Starlink astronomy issue, as well as with the Vera C. Rubin Observatory in Chile.
"The Vera C. Rubin Observatory was repeatedly flagged as the most difficult case to solve, so we've spent the last few months working very closely with a technical team there to do just that," SpaceX said. "Among other useful thoughts and discussions, the Vera Rubin team has provided a target brightness reduction which we are using to guide our engineering efforts as we iterate on brightness solutions."
The company is testing Starlink brightness solutions even as its continues to rapidly build the "constellation" of satellites. The company said it has begun to make public "predictive data prior to launch at the request of astronomers," to help them know when and where the satellites will be.
SpaceX told AAS in December that the company plans to have as many as 1,584 Starlink satellites in space by the end of this year. Additionally, with SpaceX currently launching a new Starlink mission about once a month, the company's director of satellite policy David Goldman wrote in a letter to the FCC on Monday that the company "anticipates that before the end of 2020 it will begin offering commercial service in the northern United States and southern Canada, and then will rapidly expand to near global coverage of the populated world in 2021."
As Starlink satellites move across the sky, the reflection of sunlight at dawn and dusk makes them especially visible from the ground.
"This happens because the satellites are illuminated by the Sun but people or telescopes on the ground are in the dark," SpaceX explained.
The company outlined for astronomers its goals in reducing the brightness of the satellites. While Starlink satellites are visible to the naked eye while in orbit, SpaceX said its first goal is for the spacecraft to be "generally invisible to the naked eye within a week of launch," as well as "for almost all phases of their mission." Its second goal is to minimize Starlink's impact on astronomy, "by darkening satellites so they do not saturate observatory detectors."
SpaceX noted a big contributor to Starlink brightness "are the white diffuse phased array antennas on the bottom of the satellite, the white diffuse parabolic antennas on the sides (not shown below), and the white diffuse back side of the solar array. These surfaces are all white to keep temperatures down so components do not overheat."
So far it has experimented with one way of reducing brightness. One of the satellites in a batch of 60 launched in January was given a darkening treatment. Nicknamed "DarkSat," the Starlink satellite saw its brightness reduced "by about 55%," the company said.
Although the "DarkSat" approach did reduce the satellite's brightness, dark surfaces get hot and can damage the satellites, while still reflecting some light. Instead, SpaceX plans to to launch a different method next month: "A sun visor solution."
This design is nicknamed "VisorSat." SpaceX said one of the Starlink satellites will have "a deployable visor," pictured below, that is intended "to block sunlight from hitting the brightest parts of the spacecraft." During launch the visor is flat against the body of the satellite but, after its deployed in orbit, the visor extends.
"The visor prevents light from reflecting off of the diffuse antennas by blocking the light from reaching the antennas altogether," SpaceX said. "Not only does this approach avoid the thermal impacts from surface darkening the antennas, but it should also have a larger impact on brightness reduction."
The company appears to be confident in the VisorSat design, as SpaceX said that by "June all future Starlink satellites will have sun visors." The Starlink satellites already in space without these darkening design changes will be taken out of orbit in a few years.
SpaceX emphasized that, overall, "it will not be possible to create satellites that are invisible to the most advanced optical equipment on Earth." But the company's attempts to reduce Starlink's brightness will help astronomers mitigate the damage to imagery.
The company also hinted at a "next generation" Starlink satellite that will be built to take advantage of the company's massive Starship rocket, which SpaceX is developing now. SpaceX president Gwynne Shotwell said in October that Starship will be able to "take 400 satellites at a time." While the company didn't specify what those next generation changes will be, SpaceX said those Starlink satellites "will be specifically designed to minimize brightness while also increasing the number of consumers that it can serve with high speed internet access."
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