SpaceX has placed more than 1,000 Starlinks in orbit, and other companies are following suit. Here’s the latest on what’s being done to protect astronomy.

On January 20th, SpaceX sent yet another volley of satellites into low-Earth orbit. This latest launch continues to build the company’s Starlink network, which aims to provide broadband internet in hard-to-reach places around the world. Despite recent developments, the growing number of satellites still deeply troubles astronomers.

Falcon 9 launch
A batch of Starlinks launches on a SpaceX Falcon 9 rocket.
BaloSurf / S&T Online Photo Gallery

Starlink now has 952 satellites in operational orbit (out of 1,015 launched), according to spaceflight observer Jonathan McDowell, which makes it the leader of a growing pack when it comes to large satellite constellations. At the same time, Starlink has also led the way in engaging with astronomers and voluntarily reducing the satellites’ impact on astronomy.

At the 237th meeting of the American Astronomical Society (AAS), SpaceX representative Patricia Cooper presented improvements to the original Starlink design, reducing the brightness of all satellites launched since July 2020 using a sunshade. SpaceX also implemented changes to all of the operational satellites’ orientations to minimize reflection.

Astronomer Patrick Seitzer (University of Michigan, Ann Arbor) confirmed these mitigations have dimmed the so-called “VisorSats” to about a third the brightness of the original satellites, a significant improvement. As Cooper put it, “What a difference a year makes.”

To read more about the VisorSat implementation and subsequent brightness measurements, see article by amateur astronomer Anthony Mallama: “Starlink Satellites Are Fainter Now — But Still Visible

Artist's conception of VisorSat, where a Starlink satellite will be equipped with a deployable visor that shades the antennas from sunlight. The visor will be transparent to radio frequencies.

Even with the VisorSat design, though, the Starlink satellites are still brighter than the recommended 7th-magnitude limit, which would put all satellites out of range of unaided eyes. “The 7th-magnitude brightness target is enormously helpful,” Cooper said. “Now we have something to drive toward.”

At the same time, Cooper suggested there might be a limit to what the company can do. “We’re going to come to a point of — not the end of creative brainstorming, but some lead prospects that we want to put more effort and emphasis on,” she said.

Even if SpaceX manages to dim its satellites to 7th magnitude, though, chief scientist Tony Tyson of the Vera Rubin Observatory pointed out that a Starlink streaking across a single exposure taken by the observatory’s sensitive, wide-field camera would still be 40 million times brighter than the typical galaxy in the image.

“There’s an impact there that is impossible to remove,” Tyson said. When a telescope reaches down to 25th magnitude, simple rejection algorithms, such as those that suffice to clean most amateur astrophotos, don't work.

New Guidelines

The 7th-magnitude recommendation came as part of SATCON1, a conference that took place from June 29 to July 2, 2020. The conference recognized that SpaceX, while a leader, is far from the only player in the game: Other participants included OneWeb and Amazon’s Project Kuiper, both of whom also had representatives at the AAS panel event, as well as professional and amateur astronomers and dark-sky advocates.

Participants assembled guidelines for both satellite and telescope operators to mitigate the threat that numerous, bright satellites would pose to astronomy, wide-field astrophotography, and stargazers.

For satellite operators, in addition to the blanket 7th-magnitude limit, the group also proposed an altitude-dependent brightness limit, and it recommends satellites fly no higherthan 600 km.

OneWeb’s 74 satellites are above that limit, at 1,200 km. They’re correspondingly fainter than Starlinks at first glance, with a median magnitude of 7.9. But due to their greater distance, OneWeb satellites travel at slower speeds and appear more in focus to telescopes. According to Tyson, the surface brightness of a 7.9-magnitude, 1,200-km OneWeb satellite streaking across an image is actually the same as a 7th-magnitude Starlink satellite at 500 km.

What’s more, OneWeb’s higher altitude means these bright objects will remain visible throughout the entire night during summer months.

Satellite night-long visbility depends on altitude
At the recent American Astronomical Society's panel event, astronomer Patrick Seitzer presented this plot showing the visibility of satellites throughout the night depending on altitude. The calculations are for elevations greater than 30°, and assume 10,000 satellites at each altitude divided amongst 100 orbital planes with an orbital inclination of 53°. The red lines mark astronomical twilight, so the space between the red lines is the darkest time of night.
Patrick Seitzer (University of Michigan, Ann Arbor)

Despite the recommendation, OneWeb is unlikely to change altitude; it already has approval from the Federal Communications Commission (FCC) to fly there. And while it has recently streamlined its constellation plans (in part due to new ownership following a Chapter 11 reorganization), the company still ultimately plans to put 6,372 satellites in the sky.

OneWeb satellite
An artist's impression of the OneWeb satellite in orbit.
OneWeb Satellites

Project Kuiper also has FCC approval for 6,236 satellites, though at the lower altitude of 600 km. Combined with the 12,000 in Starlink’s final constellation (which could go up to 42,000, if a 2019 filing wins approval), that’s more than 24,000 satellites and possibly up to 54,000 satellites from just three companies. And there are smaller companies looking to edge in, too. So it’s not surprising that astronomers and even satellite operators agreed that depending on the goodwill of individual companies would not suffice in the long-term.

“We have dealt primarily with the big three constellations,” Seitzer said. “But sliding under the telescope cover, so to speak, there are many smaller constellations of 30 to 50 satellites. My concern is that we will get blindsided by them as their numbers grow and grow and grow.”

International regulation will be key, they agreed — in part to prevent companies from simply moving to countries with more lax restrictions.

Next Steps

To that end, Connie Walker (NSF’s NOIRLab) and colleagues have recently written up a report to be submitted the United Nations Committee on the Peaceful Uses of Outer Space outlining recommendations to protect dark skies, including guidelines for satellite operators. The UN is not a regulatory body, so if the plan is ultimately approved, it would then go to member nations for policy and enforcement.

While academia, federal agencies, and international bodies move along at an “Entish” pace, as panel participant Aparna Venkatesan (University of San Francisco) put it for the Tolkien fans, the satellite-constellation industry continues to develop on a fast clip. SpaceX aims to provide global service by the end of the year; meanwhile, OneWeb plans to have its first-generation network of 648 satellites aloft by mid-2022.

Rubin Observatory construction at sunset
The Vera C. Rubin Observatory is under construction in Chile and is expected to see first light this year, with operations starting in 2022.
LSST Corporation

Also in 2022, the Rubin Observatory is due to start operations, beginning full-sky observations intended to generate a decade-long movie of the night sky. But it will have to do so while dealing with satellites too numerous to dodge and too bright as yet to completely remove from observations.

“This notion of future-proofing is a charming idea,” Tyson said, referring to the idea that observatories can take actions now to protect themselves as near-Earth space becomes more crowded. “But very frankly, we did a lot of simulations and found that there is no combination of mitigations that we know of that can correct for the lost science — particularly the discovery of the unexpected.”

Editorial note: This article has been updated to note that the dark-sky report to the United Nations Committee on the Peaceful Uses of Outer Space is in preparation but has not yet been submitted.




Image of Brocke


January 22, 2021 at 5:04 pm

Is all the knowledge and wisdom out there not able to stop a handful of insane maniacs?

It is not decisive whether they act out of greed or because they consider themselves to be the saviors of humanity, what is decisive is what damage they cause and then leave it to the general public to put it back in order. I am so angry.

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Andrew James

January 22, 2021 at 9:50 pm

Astronomy is a world-wide endeavour whose whole benefit brings countries together. All the vast monies spent on accumulated ground-based assets to investigate the heavens satiates our collective intellectual curiosity to learn and understand where we fit in the scheme of things. It is not profit based nor jingoistic but loudly speaks volumes about all humanity - past, present and future.

Yet these artless neophytes and philistines lack any constraints and use compulsion to inflict their nefarious deeds. Worst, the don't speak for anything altruistic but instead shove everything valuable into their pockets, then walk away and leave the mess for others to clean up. (Clearly the FCC could not careless about the international implications.)

Our skies are the last vestige of unspoiled Nature. It truly sickens me that no matter what I say or do I cannot stop this horrible stinking madness. I also have zero faith in the United Nations Committee on the Peaceful Uses of Outer Space, because after all the pontificating and pottering, the damage will be already irreversible. Pity.

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Anthony Barreiro

January 22, 2021 at 11:00 pm

It is encouraging that even the major satellite companies recognize the necessity of international regulation. I'm grateful to the members of the astronomy community who are communicating the problems and setting parameters for meaningful mitigations, and the people from SpaceX who are trying to find workable engineering solutions. While I'm as concerned as anybody about the harmful effects of these satellites, I'm also aware that I'm posting this comment *over the internet*. 65 years ago there wasn't a single artificial satellite in Earth orbit. We are still a young spacefaring species. I hope we figure out how to use satellites without obliterating our view of the rest of the universe.

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Andrew James

January 22, 2021 at 11:29 pm

For decades, my community has been slowly persuade to take light pollution seriously. It is done for cultural, environmental, educational and scientific reasons. This is being replicated almost everywhere throughout the world. So why are we doing it? IMO, it is because of the growing awareness of the fragility of the Earth, with people wanting to participate in little way to its maintenance. We've reached the stage where we pruned the tree too much, and from the lack of leaves, we are killing the plant. Sensible people see this. Yet hen some desultory democracy making up 5% of the world's population happily thinks it's perfectly OK to affect the other 95% environment, then we have a problem. If one issue causes such distrust and anger, then this is it.
People and lovers of astronomers are palpable and utterly furious. I think few Americans quite understand how much this is damaging your country's reputation and how it smacks of unfettered imperialism. You say "International regulation will be key", but it is the US FCC that is the one making these decisions. On 21 Jan 2021, Biden named Jessica Rosenworcel as Acting Chairperson. If you want change lobby her!!!!

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January 23, 2021 at 3:21 pm

Thank goodness I'm primarily a planetary observer. But I did take one 75 min total of M51 which had two satellite crossings. Exact orbital plane. Maybe Starlink.

Very few people care about dark skies and satellite tracks. Going to be an uphill battle.

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Image of Carl


January 25, 2021 at 8:01 am

The article says "when a telescope reaches down to 25th magnitude, simple rejection algorithms (...) don't work". In case the satellites (when in final orbit) stay at a fixed position relative to a certain location on earth, the movement of the satellite relative to the sky should be very fast, so rejection algorithms should work. Is my assumption right, or did I miss something?

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Monica Young

January 25, 2021 at 8:34 am

Hi Carl, Rejection algorithms work by rejecting individual pixels in stacked images. The other images in the stack provide the information in the missing pixels. However, very sensitive telescopes such as Vera Rubin Observatory are taking single exposures to create a mosaic of the whole sky. Rejecting pixels becomes complicated, all the more so because the satellite streaks are so bright that attempting to remove them actually creates cross-talk in the electronics, resulting in ghost images across the image. You can read more about the particulars in the March 2020 issue of Sky & Telescope.

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Yaron Sheffer

February 3, 2021 at 5:01 pm

If by "fixed position" you mean geosynchronous, then this is not the case here because the satellites described in this articles are in much lower, non-synchronous orbits. Pushing these pests 100 times higher into geosynch orbits would sure make them much much fainter!

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Tomasz Kokowski

February 1, 2021 at 5:19 am

Global Internet from land and Space sounds fantastic, isn't it?
It's a kind of stories how bright the future is going to be.

However, business model of providing Internet from sats seems very familiar to ugly one we find nearly every "new digital/sharing economy": privatize benefits, socialize costs.

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Andrew James

February 1, 2021 at 5:03 pm

"Global Internet from land and Space sounds fantastic, isn't it?
It's a kind of stories how bright the future is going to be."

Yet. Who is allowed controls the 'Global Internet' then? Users with still be geoblocked, governments will impose censorship, more individuals will be tracked or monitored, etc.

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