When astronomers first envisioned the Vera Rubin Observatory in the 1990s, the skies above Chile's Cerro Pachón were a pristine canvas filled with millions of stars, galaxies, and nebulas. However, the landscape changed dramatically just before the observatory's expected inauguration, as the era of megaconstellations emerged. Astronomers began racing to devise solutions to protect their precious observations from the looming threat of satellite contamination.
Construction of the $680 million Vera Rubin Observatory commenced in 2015, and initially, all plans were proceeding smoothly. However, the launch of SpaceX's first batch of Starlink satellites in 2019 marked the beginning of a new challenge for astronomers. With these satellites orbiting Earth at a mere 340 miles (550 kilometers) above the surface, their brightness became a significant concern for telescope observations. According to Meredith Rawls, a research scientist for the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) and an astronomer at the University of Washington, "All the characteristics that make Vera Rubin Observatory exceptional for surveying the southern sky also mean it will capture a significant number of these satellites."
The Vera Rubin telescope, set to begin its operations later this month, features an impressive 26-foot-wide (8.4 meters) mirror, making it one of the largest mirrors in the world. It is equipped with the largest camera ever constructed for an astronomical telescope—a 5.4-foot-wide (1.65 m), 3,200-megapixel device containing 189 CCD detectors. This advanced technology allows the telescope to tilt its mirror and change its view of the sky each night, enabling a complete sky survey every three days.
In each survey, the Vera Rubin Observatory will capture not only the countless stars and galaxies invisible to the naked eye but also the overwhelming number of satellites that are millions of times brighter than these celestial treasures. This situation is expected to worsen over time. SpaceX initially proposed a constellation of 12,000 satellites but has now increased its plans to 42,000. Other broadband operations, including Amazon's Kuiper network and various Chinese projects, aim to launch tens of thousands of satellites, potentially increasing the total number of satellites in orbit from about 10,000 to 100,000 within the next decade.
Meredith Rawls expressed her frustration regarding the timing of this satellite explosion, stating, "It's existentially frustrating that we are putting a bunch of stuff in orbit that is interfering with our views of the cosmos." Since 2016, Rawls has worked on the Vera Rubin Observatory project, initially focusing on image processing algorithms to detect unexpected celestial events like supernovae. However, the emergence of satellites forced her to shift her focus to developing techniques for identifying and flagging satellite presence in images, distinguishing them from genuine astronomical phenomena.
Despite the challenges posed by satellite streaks, Rawls believes that they are not a death knell for the scientific mission of the Vera Rubin Observatory. She describes satellite streaks as akin to "bugs on a windshield on a summer night," obscuring views at times but not completely ruining them. While a significant portion of the exposures may contain satellite streaks, the vast field of view means that the actual number of affected pixels is relatively small. Each detector has 4,000 pixels, and with 189 CCD detectors tracking the sky, the impact can be mitigated.
Noelia Noël, a professor of astrophysics at the University of Surrey, estimates that up to 40% of the images captured by the Vera Rubin telescope over its decade-long mission could feature satellite streaks. "If you take 10 million images, over 4 million of them could be degraded," Noël remarked, emphasizing the financial implications, as one night of observations costs approximately £60,000 (around $81,000). The potential for wasted resources due to image degradation is concerning for taxpayers supporting the project.
In 2021, an incident highlighted the risk of misidentifying satellite streaks as astronomical phenomena. Scientists initially believed they had observed a star explosion in the oldest known galaxy, only to discover that a piece of debris had passed in front of their telescope, reflecting sunlight. Rawls stated, "We don't want to give people a catalog of data where each pixel is supposed to be an actual star, and then surprise, a third of them are just bright detections where it happened to be in the satellite trail."
To counteract the challenges posed by satellites, Rawls and her team are developing algorithms that utilize a stacking method to compare multiple images of the same sky area. This technique helps to identify outliers, allowing them to differentiate between passing satellites and genuine astronomical events. If a bright object appears in one image and disappears in another, it's more likely to be a satellite rather than a stellar event.
Megaconstellations like Starlink are just one aspect of the satellite dilemma. In 2022, AST SpaceMobile began deploying its BlueBird satellites, massive antenna arrays designed to provide 5G service directly to smartphone users. These satellites are exceptionally bright, requiring the Vera Rubin Telescope to plan its observations around their passes to prevent wasted observation time.
The future of the Vera Rubin Observatory's sky observations remains uncertain as the number of satellites continues to grow. Rawls hopes that initiatives to darken satellites, already attempted by SpaceX with limited success, will eventually yield results, minimizing light contamination. The International Astronomical Union (IAU) has urged satellite manufacturers to make their satellites less visible, aiming for a brightness equivalent of magnitude 7 on the scale used to measure celestial objects. Currently, Starlink satellites fall between magnitudes 3 and 5, indicating a significant gap in achieving the ideal brightness level.
In conclusion, as the Vera Rubin Observatory prepares to open its eyes to the cosmos, the interplay between satellite technology and astronomical research will be crucial. The ongoing challenges and innovative solutions developed by astronomers like Meredith Rawls will shape the future of ground-based astronomy amidst an increasingly crowded sky.
