Starlink satellite trains - is this the future of the night sky?
Almost 15 years later, seeing the aurora borealis is a bit like a drug, says photographer Ronn Murray.
"Once you get a taste for it . . . you're always trying to see it again because you get this kind of spiritual high from it."
The lakes by Delta Junction in Alaska weren't frozen over yet when it was just dark enough to see the magical halation over the night's sky and another phenomenon Murray instantly knew - a moving train of lights.
Guide and part-owner of the Aurora Chasers, an Alaska based tour group, Murray had seen the lineup of satellites a few days prior. He recognized it from other people's accounts but had never seen it himself. Literally the stars aligned, and the night sky opened up on a drive 150 miles outside of Fairbanks. The footage shows what looks like stars trailing one another amid the emerald glow of the northern lights.
"We were a bit baffled at first then realized, 'Wait, that must be Starlink,'" he said. "Then my wife got her star tracker app out, and it showed that's what we had seen."
The view, as mesmerizing as it is surprising, has astronomers wondering, is there any way to dim the lights on these satellites, or are we doomed to a mega-constellation future?
Murray captured the 46 objects launched on Aug. 31 by SpaceX clumped together, reflecting the sun back to observers on Earth. These satellites are part of the growing Starlink constellation aimed at providing broadband internet around the globe, much in the manner GPS provides location data to cellphones around the planet.
But unlike GPS, the task requires tens of thousands of satellites for service to work without drops in coverage. In three years, the aerospace company SpaceX, owned by Elon Musk, has gone from 60 satellites to launching over 3,500 Starlinks to date. Nearly half of all active satellites are from SpaceX, according to data from the nonprofit satellite tracker CelesTrak. A recent Federal Communications Commission authorization approved the launch of 7,500 more satellites and a nodding sentiment in the company's plan to launch 30,000 orbiting internet boxes - a feat, that at this rate, it could achieve before 2050.
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Why are Starlink satellite trains visible?
Most satellites are visible. Timing is everything.
The most famous satellite, our moon, is visible as it traverses our sky. We see the lunar surface because one half of it is pointed at our sun at all times. It's easier to see the moon at night when we are in the shadow of the sun.
These principles hold up for smaller orbiting bodies as well. If you time it right, you can see the International Space Station at night. You can see it pass in front of a full moon.
Starlink satellites are also quite luminous, something they've been working on dimming with the astronomical community since they started launching satellites.
The most distinct factor in creating Starlink trains has to do with physics:
A satellite rides along a launch vehicle into low Earth orbit (LEO).
The satellite is released into space where, barring any interruption, it will spin in orbit around Earth.
As a Starlink satellite orbits, it will unfold its solar panels and lay flat in a low drag position to resist gravity's pull back to Earth.
When ready, it will point its panels directly "up" and its antennas directly down toward Earth to communicate data for customers.
SpaceX doesn't just launch one satellite. Any given launch contains 50 to 60 satellites; on Dec. 28, SpaceX put 54 into orbit.
Moving at the same altitude and speed, these satellites initially spin around the globe clumped together. This is what is seen on land as the "train." When the timing is right, each satellite uses its ion thruster to ascend into higher altitude and operational orbit.
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How does the theory hold up in practice?
Jonathan McDowell, an astrophysicist working at the Harvard-Smithsonian Center for Astrophysics, has been tracking orbital data from every Starlink launch. He's observed that batches of satellites will ascend to operational orbits in groups, taking advantage of what's known as plane drift, to cover different parts of the globe with a single launch.
Rising to operational orbit in phases might improve global coverage, but it means a non-trivial part of these satellites' life is sitting parked where they are more visible. McDowell notes, "Instead of taking one month from launch to operational, in some cases it takes three months from launch because they're in this intermediate orbit for a while."
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SpaceX wants to shorten Starlink trains
To a certain extent, it is in the company's best interest to limit how visible their constellation is. Seeing them at night is a byproduct of them not achieving operational orbit. For however long they are parked or navigating past the ISS and Tiangong altitudes, it is that much longer they are not providing internet to customers and not making money for SpaceX.
Satellites we depend on for GPS faced similar infrastructure issues. It took decades of failed launches and cut federal budgets until the constellation of 24 GPS satellites we rely on today was finished in 1994. Early applications required timing usage with the availability of enough satellites to triangulate a position. Nowadays, there are a handful of GPS-like constellations offering 16 feet (4.9 meter) accuracy for users around the world.
SpaceX's gambit is to also meet that goal with its planned 30,000-satellite constellation. While this mega-constellation sounds like a lot, OneWeb and Amazon's Project Kuiper are vying for similar fleets. By some estimates, the combined satellites may number over 100,000 by 2030.
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How will this affect terrestrial astronomy?
Visibility of these satellites affect critical scientific work from our planet. As SpaceX works to limit its visibility, astronomers are worried about the big picture. A study simulating the effects of 65,000 proposed satellites published in the Astronomical Journal found that 1 in 5 observations of the night sky will be streaked by the passing of satellites. The level of disruption depends on whether operators are able to reduce brightness enough for astronomers.
SpaceX's operating altitude, less reflective materials and angle toward the sun all contribute to how much scientific data is obstructed. One of the research's authors, Meredith Rawls at the University of Washington, is cited in SpaceX's FCC filings that these mitigation efforts are "voluntary, insufficient, and in the case of Starlink Gen2, untested." SpaceX did not reply to a request for comment for this report.
Astronomer Patrick Seitzer from the University of Michigan said that there are other issues beyond what we can see, since satellites will also emit thermally. Even when there is "no shadow," he said, "they're always going to be visible."
A final concern is that mega-constellations interfere with radio communication. These satellites use high-frequency bands to transmit data to customers. It is the main reason the FCC is the compliance agency approving the launch of Starlink's next batch of devices. Unlike light interference, obstruction is difficult to pinpoint, said radio astronomer Harvey Liszt from the University of Virginia, so responsibility becomes diffused across the many companies now vying for the skies.
Currently, Starlink communication stays within its allocated frequency, bands but the airwaves are getting crowded. In the past, astronomers could avoid noise from commercial radio bands by moving to remote locations such as the Atacama mountains in Chile or the desert of New Mexico. As satellite companies communicate among higher-frequency bands, however, there is no mountain high enough to avoid their emissions. Scientists must adapt.
Broadcasting in remote regions is also a market target for SpaceX. It's company webpage lists maritime, aviation and RVs among its applications.
Ashley VanderLey of the National Science Foundation radio astronomy facilities said that the NSF has been able to coordinate with SpaceX with its constellation and that generally companies in the United States have shown a good-faith effort to work with astronomers to try to resolve issues.
For Murray, the Starlink constellation may give his company a competitive edge. Some tours can take them 200 miles from their home base of Fairbanks, where you are guaranteed no cell service. Without it, it is hard to track where a cloud-free view might be for his clients.
"It's not the aurora we're chasing - it's the clear skies," Murray said. "We're like storm chasers, but we're trying to get out of the storm."
Starlink-based internet would allow Murray to locate open skies. Whether the vantage above is clear from satellites will depend on the stewardship of space from the ground.
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