Credit: SpaceX/Starlink

I wanna see it painted, painted black

Black as night, black as coal

I wanna see the sun blotted out from the sky

I wanna see it painted, painted, painted, painted black

— “Paint It Black” by the Rolling Stones

Last month, the SpaceX launch of the first group of sixty Starlink satellites signaled the intent of connecting the entire Earth via a cocoon of internet service. Clearly that’s a laudable goal, one that will rely on lots more follow-on spacecraft circuiting our planet.

Prior to going operational, Starlink has already produced a global shout-out – in interconnecting the ire of the astronomical community.

An image of the NGC 5353/4 galaxy group made with a telescope at Lowell Observatory in Arizona, USA on the night of Saturday 25 May 2019. The diagonal lines running across the image are trails of reflected light left by more than 25 of the 60 recently launched Starlink satellites as they passed through the telescope’s field of view. Although this image serves as an illustration of the impact of reflections from satellite constellations, please note that the density of these satellites is significantly higher in the days after launch (as seen here) and also that the satellites will diminish in brightness as they reach their final orbital altitude.
Credit: Victoria Girgis/Lowell Observatory

Due to the reflective solar panels and other metal surfaces on Starlink satellites they have been observable to the naked eye at night. The visibility of the satellites, combined with a rapid increase in the number of satellites in low Earth orbit has caused anxiety in astronomical and stargazing circles.

On the receiving end of their anger, SpaceX lead rocketeer and space entrepreneur, Elon Musk responded by tweet: “There are already 4900 satellites in orbit, which people notice ~0% of the time. Starlink won’t be seen by anyone unless looking very carefully & will have ~0% impact on advancements in astronomy. We need to move telescopes to orbit anyway. Atmospheric attenuation is terrible.”

“We care a great deal about science,” Musk also tweeted, saying he has sent a note to the Starlink team to decrease spacecraft albedo – the amount of light the satellites reflect.

Eye contact

“While I am concerned about the potential implications for these large constellations on ground-based astronomy, I’m trying to get some analysis put together to better assess the impact,” explains T.S. Kelso, operator of CelesTrak that keeps a disciplined eye on satellites and orbital debris.

Kelso said he’s had eye contact with the Starlink train of satellites, “even though the sky still wasn’t fully dark and I was looking through thin clouds,” he told Inside Outer Space.

Falcon 9 booster topped with sixty Starlink satellites.
Credit: SpaceX

“But I’ve gone out twice since looking under clear skies and not been able to see anything. I’m sure the visibility is directly related to the Sun-satellite-observer angle where the panels are tracking the Sun and the sunlight is reflecting toward the observer – much like the Iridium flares. So, it may only affect a small part of the sky,” Kelso adds.

“I suspect the result was unexpected for SpaceX, given that they had to consider a lot of other things in the design and never considered the implications,” Kelso says. “They would have had to ask some astronomers for feedback to understand. At least Musk seems to be considering what can be done now to minimize the impact.”

Trade-offs

“The Starlink debate has certainly caught my interest,” says orbital debris expert, Hugh Lewis, a Professor of Astronautics and Head of the Astronautics Research Group at the U.K’s University of Southampton.

For Lewis the debate about astronomy versus space-enabled connectivity is representative of a broader debate about trade-off: To do a lot of good — connecting the world — we might have to do a little harm – increase debris concerns, affect astronomy, others.

“At the moment, our technology is not good enough to avoid all harm, so we have to figure out how much harm we are willing to accept; clearly, different people and different communities have different thresholds. I’m encouraged by the signals coming from SpaceX and Musk about ambitions to address the albedo issue,” Lewis said.

“But it’s frustrating because this issue wasn’t already on their agenda, and they hadn’t already engaged with the astronomy community. Had these conversations happened at an early enough stage, then the satellite design might have been changed – although given the publicity Starlink has received since launch, the slight cynic in me also suspects that nothing would have changed.”

Acceptable risk/harm

Lewis told Inside Outer Space: “For me, it’s definitely not about putting up roadblocks to progress. I’m a big fan of connecting the world! It should be about enabling companies like SpaceX to meet their ambitions whilst also respecting the thresholds related to acceptable risk/harm.

There is a huge collective of support, knowledge and wisdom that could get behind these ambitions, but this collective is seemingly being ignored, or only thought about after the fact, for reasons that I understand, if not fully support. The silver lining is that SpaceX/Musk seems willing to listen now, at least, on Twitter! Perhaps there is still an opportunity to enable,” Lewis concludes.

Credit: AURA

Nuisance or real problem?

Meanwhile, the Association of Universities for Research in Astronomy (AURA) has issued a statement on the Starlink constellation of satellites. AURA is the managing organization for many ground-based telescopes for the National Science Foundation (NSF). They note that the launch of the Starlink system may have impacts on the observational capabilities of these facilities.

For example, one facility is the Large Synoptic Survey Telescope (LSST), under construction by NSF in Chile and slated to begin wide-field imaging of the sky in 2021.

“LSST will create an astronomical survey that depends on dark skies for its core science,” AURA says. “LSST’s frequent imaging of the same region of sky will be a mitigating factor for Starlink interference, providing enough uncontaminated images to reject the images that contain satellite trails or other anomalies.

Credit: LSST Project/NSF/AURA

In the case of the full constellation of Starlink satellites, initial calculations show that LSST images would, on average, contain about one satellite trail per visit for an hour or two after sunset and before sunrise. A very conservative upper limit on the number of LSST pixels affected by Starlink satellites is about 0.01%, and quite likely smaller. Therefore, for LSST, even a constellation of about 10,000 Starlink satellites would be a nuisance rather than a real problem.

That said, AURA emphasizes, however, that the impact of satellite constellations on other AURA telescopes that have wider fields, longer exposures, and/or less sophisticated data processing pipelines may be much more significant.

“Furthermore, Starlink may be only the first in a series of new technologies that could impact LSST and other ground-based astronomy facilities,” AURA says. “We believe that the design and implementation of these constellations should be undertaken in consultation with the astronomical community to minimize their impact.”

Understanding the impact

Another organization, the International Astronomical Union (IAU), is also concerned about these satellite constellations.

“Until this year, the number of such satellites was below 200, but that number is now increasing rapidly, with plans to deploy potentially tens of thousands of them. In that event, satellite constellations will soon outnumber all previously launched satellites,” an IAU statement points out.

“We do not yet understand the impact of thousands of these visible satellites scattered across the night sky,” adds the IAU. Despite their good intentions, these satellite constellations may threaten both the principle of a dark and radio-quiet sky but also as a resource for all humanity and for the protection of nocturnal wildlife.

“Satellite constellations can pose a significant or debilitating threat to important existing and future astronomical infrastructures,” the IAU observes, “and we urge their designers and deployers as well as policy-makers to work with the astronomical community in a concerted effort to analyze and understand the impact of satellite constellations. We also urge appropriate agencies to devise a regulatory framework to mitigate or eliminate the detrimental impacts on scientific exploration as soon as practical.”

For more information on Starlink, go to:

https://www.starlink.com/

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