8.01.2023
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 light emerald glow of the northern lights.
Diagram of a Starlink satellite
Ion thrusters
4.3 ft
(1.3 m)
9.1 ft (2.8 m)
A loaf of bread
Solar panels unfold after launch
extending to over 26 ft (8 m)
“We were a bit baffled at first then realized, ‘wait that must be Starlink.’ Then my wife got her star tracker app out, and it showed that’s what we had seen.”
The view, while equal parts 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 across the globe, much in the manner Global Positioning System (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 FCC 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, they could achieve before 2050.
Why do we see Starlink satellite trains?
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, also known as nighttime.
These principles hold up for smaller orbiting bodies as well. If you time it right, you can see the International Space Station (ISS) 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.
From parked trains to operational Starlinks
Once launched into orbit, Starlinks take months to go from objects in the night sky to internet providers, 550 km away from a computer on Earth. Of all satellites, 80–85 percent are in an operational orbit. Five to 10 percent fail to operate as designed.
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.”
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.
This is a look at the company’s current capacity across the globe. Each Starlink is able to broadcast within a footprint around 2.9 million square miles (7.5 million km²), which is roughly the area of Australia.
The most distinct factor in creating Starlink trains has to do with physics.
A global Starlink network
Each dot represents one of the 3,336 satellites in the SpaceX constellation. Most of these objects are hard to spot in the nights sky. The highlighted satellites are from the most recent launches and most visible. They are likely to be bunched up as they move into an operational orbit.
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, it’s nothing when you consider that OneWeb and Amazon’s Project Kuiper are vying for similar fleets. By some estimates, the combined satellites may number over 100,000 by 2030.
How will this impact terrestrial astronomy?
Visibility of these satellites impact critical scientific work from our planet. As SpaceX works to limit its visibility, astronomers are worried about the big picture. A studysimulating 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 comment on this story.
Astronomer Patrick Seitzer from the University of Michigan explainsthat there are other issues beyond what we can see, since satellites will also emit thermally, “[when] there is no shadow — 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’s difficult to pinpoint, radio astronomer Harvey Liszt from the University of Virginia says, 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 like 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 as its company’s page lists maritime, aviation and RVs among its applications.
Ashley VanderLey from the National Science Foundation radio astronomy facilities says 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. We’re like storm chasers, but we’re trying to get out of the storm,” says Murray.
Starlink-based internet would allow Murray to locate open skies. Whether the vantage above is clear from satellites will depend on how we steward space.
Quelle: The Washington Post