It has been three years since SpaceX launched its first Starlink Internet communication satellites to draw Astronomers' attention to the stripes left by these satellites in the night sky photos. Since then, many other starlinks have been launched: more than 2300 star chains now orbit the earth, accounting for nearly half of all operational satellites.
Scientists have made some progress in coping with this shock. For example, in recent days, the International Astronomical Union (IAU) will launch a website for the first time, which includes tools to help telescope operators predict satellite positions so that they can point instruments to other places.
However, accumulating evidence shows that these "giant constellations" of satellites will cause considerable interference to astronomical observatories and other sky watchers around the world. But the satellite company has not found a solution yet. SpaceX has been trying to solve this problem by installing sunshades on starlinks to darken its appearance in the night sky. However, nature learned that the company has stopped doing so.
Tens of thousands of new satellites may be launched in the next few years. Meredith Rawls, an astronomer at the University of Washington in Seattle, said: "this is an unsustainable track. At present, our science is very good. But when will we miss a discovery?"
The cost of giant constellations
Since the launch of the first Starlink, astronomers have gone from panicking about the scientific observation of satellite light damage to organizing a global response. After a series of international seminars in 2020 and 2021, the International Astronomical Union established a center to protect the dark and quiet sky from the interference of satellite constellations. Its upcoming website aims to serve as a center for astronomers, policy makers, satellite operators and the public to coordinate how to reduce the impact of satellites shining in the sky.
A recent study shows that the future satellite constellations will be most obvious in the summer nights around 50 degrees south latitude and 50 degrees north latitude, where many European and Canadian astronomical facilities are located. The research report points out that if SpaceX and other companies launch their proposed 65000 satellites, the sky at these latitudes will have bright spots all night around the summer solstice. In the hours before and after sunrise and sunset, about one of every 14 stars visible to the naked eye is actually a satellite.
"It's really terrible," said Samantha Lawler, an astronomer at the University of Regina in Canada who led the work
Astronomical Observatories that study broad skies rather than focusing on individual celestial bodies will be most affected. The zweiji transient facility (ztf) used the 1.2m Telescope in Palomar mountain, California to measure the broad sky. 18% of the satellite stripes were observed in the images taken at dusk in August 20213. Astronomer przemek Mr ó Z of the University of Warsaw pointed out that this number will rise with the increase of the number of satellites. He made a preliminary analysis of the ztf data in April 2022, and found that the satellite stripes affected about 20-25% of the twilight images.
Mr ó Z said that so far, many measurement results of ztf have not been damaged by satellite fringes, partly because its image processing method can detect and mask the trajectory of satellites. But other observatories face greater challenges -- especially the vera-c-rubin Observatory, an 8.4-meter-wide telescope funded by the United States and built in Chile. Because it will photograph the entire visible sky every three days, it will be particularly vulnerable to satellite fringes in its images. Rawls and other astronomers are working on ways to mitigate damage, such as algorithms that can identify and eliminate satellite fringes in the data. But repairing data requires a lot of time and effort.
Busy sky
The increase in the number of satellites may also have a negative impact on the field of radio astronomy and increase the number of space debris. Other broader impacts could affect life around the world: the presence of satellites has led to a bright background in the sky, which may disorient animals that rely on celestial navigation. In addition, the stripes of satellites will also interfere with human knowledge systems, such as the indigenous knowledge system that relies on the information of the dark sky to mark important events throughout the year.
Karlie noon, an astronomy doctoral student and Aboriginal research assistant at the Australian National University in Canberra, pointed out that the growing threat of satellite constellations has increased other degradation of the night sky, such as light pollution. "Just like our land was colonized, our sky is now colonized. And it's not just about indigenous people," she pointed out that the company does not necessarily consult the scientific community when launching satellites.
Some satellite operators have been trying to alleviate this problem. Companies including SpaceX, oneweb in London and Amazon Kuiper project in Seattle, Washington have met regularly with the International Astronomical Union and the National Astronomical Society to discuss how to reduce the impact of satellites. SpaceX has tested ways to dim its starlinks, including the installation of sun visors. Sunshades do reduce the brightness of satellites, but they seem to be excluded from the latest generation of Starlink. The satellites launched since September use lasers instead of radios to communicate with each other, and the sun visors interfere with these communications.
David Goldstein, an engineer of SpaceX, said in a speech at a webinar hosted by the Federation of British Astronomical Societies (FAS) earlier this month that SpaceX is studying other mitigation measures, such as adding stickers or other materials to the satellite mirror to reflect light lines far away from the earth.
At present, the company is still sorting out how good this may be. An unpublished analysis of the brightness of 102 observed galaxies shows that the new generation of galaxies appears to be brighter than those known to have sunshades. Anthony mallama, a retired astronomer in charge of the analysis, pointed out that, however, they were not as bright as the original starships without sunshades.
Meanwhile, oneweb has launched 428 of the original 648 satellites planned. Their orbital height is much higher than starlinks - 1200 kilometers instead of 550 kilometers. These satellites are usually darker than Starlink simply because they are farther away, but their brightness can vary considerably depending on how they capture and reflect sunlight.
Jeremy tregloan reed, an astronomer at Atacama University in Copiapo, Chile, said that a preliminary study on 50 oneweb satellites during 2021 found that nearly half of them were brighter than the "safety" limit set by astronomers. Oneweb says it is committed to reducing the visibility of its satellites. It uses a telescope in Sicily to measure its brightness and is using this information to design darker satellites in the future.
Amazon's Kuiper project will add more than 3200 satellites, and it plans to launch its first two prototype satellites before the end of this year. One of them will contain a sun visor so that the company can compare its ability to turn down the brightness of the satellite.
Although the International Astronomical Society and other astronomical organizations have been pushing the United Nations to recognize this problem, there is no law on how bright satellites should appear in the night sky. Representatives of many countries will discuss the issue of sky protection at the meeting of the United Nations Committee on the peaceful uses of outer space to be held in Vienna on June 1.