SpaceX Tests Lower Satellite Orbits to Stop Starlink From Ruining Telescope Images

SpaceX is working to make its satellites less of a nuisance to astronomers by testing ways to prevent Starlink from appearing in images of space. The company recently lowered the altitude of a number of its Internet satellites to reduce their brightness when viewed from Earth.

IN letter SpaceX said it has begun operating 300 of its satellites at lower orbital altitudes as part of the company’s efforts to reduce Starlink’s impact on optical astronomy, the Federal Communications Commission (FCC) said. The company says the new method was successful, resulting in a nearly 60 percent reduction in the number of sunlit satellites appearing in images taken by the Vera Rubin Observatory, a telescope in Chile.

Low Earth orbit is becoming increasingly cluttered with satellites, most of which belong to SpaceX. There are currently 6,912 Starlink satellites in orbit, located approximately 342 miles (550 kilometers) above the Earth’s surface. Orbiting satellites add unwanted noise to observations of the night sky by reflecting sunlight and appearing as streaks in images taken by ground-based observatories. The first Starlink satellites were very bright, making them visible to the naked eye and saturating the lenses of telescopes pointed in their direction.

In December 2022, the FCC granted SpaceX permission to launch up to 7,500 next generation Starlink satelliteswhich are larger and brighter than their predecessors. First-generation Starlinks weigh about 573 pounds (260 kg), but future versions are much larger at 2,755 pounds (1,250 kg) and therefore are estimated to be about a full magnitude brighter than the OG satellites.

SpaceX is collaborating with the National Science Foundation (NSF) to reduce the impact of its next generation of satellites on optical astronomy. The company recently lowered the altitude of its Starlink demonstration satellites to 217 miles (350 km) above Earth’s surface, reducing their ability to catch and reflect sunlight.

“SpaceX’s analysis also shows that peak brightness from nadir surfaces increases only slightly when operating at a distance of 350 km. [217 miles]due to higher eclipse fraction and angular velocity,” the company wrote in its letter. In other words, SpaceX argues that the reflective brightness of satellites, when viewed directly from below, does not increase much at lower altitudes because they spend more time in Earth’s shadow and move faster across the sky.

The NSF agrees that this strategy can help. Lower orbits could “be beneficial for ground-based optical and infrared astronomy because satellites move faster through the telescope’s focal plane and are more out of focus, reducing overall brightness per pixel,” an NSF spokesperson told Gizmodo via email. “At lower altitudes, satellites are also blocked from sunlight by the Earth for longer periods of the night without being reflected from the Earth.” This allows the satellites to remain fainter than about 7th magnitude—the threshold for naked-eye visibility—for most of the night, the spokesman explained.

Previous attempts have been made to reduce the impact of Starlink on astronomical observations. SpaceX is working with the International Astronomical Union and its Center for the Protection of Dark and Quiet Skies from Satellite Constellation Interference to find the underlying source of its satellites’ reflectivity and develop strategies to mitigate it. As a result, the company changed the orientation of the satellites and their solar panels, and installed visors to reduce their brightness.

This recent change in satellite orbits is still being assessed as it may have some disadvantages. “There are trade-offs: Satellites at lower altitudes may be brighter at twilight, and impact science requires observations at twilight, such as near-Earth object studies,” NSF added. The foundation will continue to work with SpaceX over the next year to test whether mitigation measures are working as intended.

It’s not just that SpaceX is launching satellites into orbit, but the growing amount of equipment cluttering Earth’s orbit could further complicate our understanding of space unless more companies commit to reducing their involvement in astronomy.