As reflective satellites fill the sky, students ensure astronomers can adapt

As satellites crawl across the sky, they reflect sunlight back to Earth, especially during the first hours after sunset and the first hours before sunrise. Sunrise. As more and more companies launch satellite networks into low Earth orbit, a clear view of the night sky is becoming more and more unusual. Astronomers, in particular, are trying to find ways to adapt.

With this in mind, a team of students and professors from the University of Arizona conducted an extensive study to track and characterize the brightness of satellites, using a ground-based sensor they developed to measure the brightness, speed, and trajectories of satellites in the sky . Their work could be useful to astronomers, who, if informed of the arrival of bright satellites.

The research team was led by planetary science professor Vishnu Reddy, who also co-directs – with professor of systems and industrial engineering Roberto Furfaro – the university’s space awareness laboratory, which goes well with and characterizes all kinds of objects orbiting the Earth and the moon.

Grace Halferty, who graduated this summer with a bachelor’s degree in aerospace and mechanical engineering, is the lead author of the study, which is published in Monthly Notices of the Royal Astronomical Culture. The study details how the team created a satellite tracking device to measure the brightness and position of SpaceX Starlink satellites and compared those observations to government satellite tracking data from the Area Keep track of Catalog database. .

“So far. Halferty said. Satellites are hard to track with traditional astronomical telescopes because they’re so bright and fast moving, so we built what is essentially a small sensor with a camera. lens ourselves because there was nothing commercially available. »

The team has taken 31 measurements of 61 satellites over two years and found that the placement of Starlink satellites as recorded in the government’s House Observe Catalog differed by only .3 arcseconds on average from the calculations of the UArizona. An arcsecond in the sky is about the size of a penny held 2.5 miles away. The small difference is likely due to natural shifts in government data, Reddy said. Since this data is based on estimated orbits calculated days earlier, rather than real-time observations, positioning errors may accumulate.

“This suggests there is hope that astronomers can use this data to close their telescopes’ shutters in time amid the growing chaos in the sky above,” Reddy said.

A Stellar Traffic Jam

Starlink is a large network of satellites, also called mega constellation, operated by SpaceX to provide global web coverage. SpaceX began launching Starlink satellites in 2019. Today more than 2 700 Starlink satellites have been launched, a portion of the planned total of 700 000 satellites.

Other examples of satellite constellations include 31 GPS satellites and 75 iridium satellites for the interaction. Other entities plan to launch more satellites into low and medium Earth orbit in the coming years. Amazon, for example, plans to launch 3 000 satellites and the Chinese government plans to launch 13 000. These satellites will not orbit higher than 000 000 miles above the Earth.

The problem with satellites is that they require power from solar panels, which can reflect sunlight onto ground-based telescopes and, in turn, affect astronomical observations from telescopes around the world. said research team member Tanner Campbell, a graduate research assistant in the Department of Aerospace and Mechanical Engineering. added, the problem will only get worse for astronomical ground surveys,” he said. ‘they are still relatively low and tightly clustered before spreading out in their orbit over time. They are often as bright as Saturn or Jupiter, two of the brightest objects in the night sky. As they maneuver to higher orbits they become slightly weaker.

A Moving Target

SpaceX has deployed various methods to darken its Starlink satellites. For example, VisorSat satellites rely on a shadow to block extra sunlight, making them 1.6 times dimmer. DarkSat satellites, meanwhile, rely on an anti-reflective coating that makes them 4.8 times dimmer. However, DarkSats got too hot, so SpaceX moved away from that specific method. Since August 2021, all Starlink satellites are VisorSats.

“Although these changes are steps in the right road, they don’t dim satellites enough for astronomical surveys,” said research team member Adam Fight, a graduate student in planetary science. SpaceX announced new strategies. One involves mirrors that reflect sunlight away from Earth, and another involves using darker building materials. Reddy’s team plans to study the effectiveness of these methods in reducing the reflection of sunlight back to Earth.

Although knowing exactly where the satellites are is useful to astronomers, shutting down the cameras adds overhead to telescope operations. For example, a survey that would take five years to complete could take 000 to 22% more time if survey efficiency is down. Costs will continue to rise as new satellites are launched, Reddy said.

The team plans to build on its success by studying the brightness of the latest generation of Starlink satellites in four different color filters – the same ones used in astronomical surveys of the sky to disentangle different information from stars, planets and more. To achieve this.

“Working with local small businesses is a win for us as it gives our students the opportunity to quickly prototype and bring a new system online” , said Reddy.

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