A recent study showed that satellites such as Blue Walker 3 are affecting night sky observations, highlighting the conflict between bright satellites and astronomy. Being able to get online or use a mobile phone anywhere in the world is increasingly taken for granted, but the brightness of the internet and telecommunications satellites that support global communications networks could cause problems for ground-based astronomy. An international study coordinated by Siegfried Eggl, an aerospace engineer at the University of Illinois at Urbana-Champaign, confirmed that recently deployed satellites are as bright as stars seen with the naked eye.
"Through observations, we learned that AST Space Mobility's BlueWalker 3 satellite - a constellation prototype satellite with an approximately 700-square-foot phased array antenna - achieved a peak brightness of magnitude 0.4, making it one of the brightest objects in the night sky," Eggl said. "While this is record-breaking, the satellite itself is not our only concern." The untracked launch vehicle adapter has an apparent magnitude of 5.5, which is also brighter than the 7 recommended by the International Astronomical Union.
For comparison, the brightness of stars we see with the naked eye ranges between minus 1 and magnitude 6, with minus 1 being the brightest. Sirius is the brightest star, with a brightness of minus 1 magnitude. Planets such as Venus are sometimes brighter, approaching minus 4th magnitude, but the faintest stars we can see are around 6th magnitude.
"One might think that if there are bright stars, a few more bright satellites wouldn't make a difference. But there are several companies planning to launch constellations," Eggl said. "For example, Starlink has received permission to launch thousands of satellites, but they may end up getting the full request to launch tens of thousands of satellites."
"This is just a constellation of satellites. Europe and China also want to form their own constellations, and so does Russia. Those satellites that the United States is negotiating with the Federal Communications Commission alone are equivalent to launching 400,000 satellites in the near future. There are only 1,000 stars that can be seen with the naked eye. If you add 400,000 moving bright satellites, it will completely change the night sky."
Eggl is a member of the International Astronomical Union's Center for the Protection of Dark and Quiet Skies from Satellite Constellations. He said: "Blue Walker 3 is so bright that most large telescopes such as the Rubin Observatory believe that it may obscure a large part of the exposure area. They already have to avoid observing Mars and Venus for the same reason, but we know the positions of the planets, so we can avoid them. We cannot accurately predict the positions of all satellites years in advance. Just accepting the frequent data loss of a multi-billion dollar observatory is not an option."
While satellites won't necessarily damage the telescope's CCD, or charge-coupled device, they can still cause streak data to be lost, he said. Extremely bright satellites can disrupt the entire field of view, much like stargazing if someone shines a flashlight into your eyes from time to time.
Egger said several ways to address this issue are currently being explored in collaboration with the Illinois Advanced Space Systems Laboratory and satellite operators such as SpaceX.
Starlink is studying how to make satellite surfaces darker so they absorb more visible light and reflect less. But this absorption generates heat. The satellite then has to emit infrared light, which means observations at optical wavelengths won't be much of a problem, but infrared observations may be. And heat is one of the biggest engineering problems encountered in space. So painting everything black has the same impact.
Another SpaceX idea is to use dielectric mirrors to make the satellite's solar panels more reflective. These mirrors allow satellites to redirect reflections so they are not pointed directly at Earth.
"If SpaceX could point their solar panels in different directions to avoid flicker, or use these mirror tricks, they might solve a lot of the problems we have with optical flicker on Starlink satellites," Eggl said. "It's not so easy for other vendors. AST has huge satellites with hundreds of square feet of electronic phased arrays on them that need to communicate with cell phones on the ground. If they make the satellites smaller, more radio signals will leak out through what are called side lobes, which could affect radio astronomy observatories."
The National Astronomical Observatory also prefers to keep satellites pointed toward the Earth's surface for maximum efficiency. Starlink solutions may not be easily translated to AST satellites, so new mitigation strategies are required.
"We're trying to work with the space industry where possible. We want to work on this together and get everyone involved because that's the fastest way to get the mission done," he said.
Compiled source: ScitechDaily