Scientists, SpaceX debate Starlink satellites’ impact on night sky

Laurel Kornfeld

SpaceX’s launch of the first 60 of its Starlink satellites, designed to provide internet service to under served areas, is generating controversy about their potential impact on night sky observation and radio astronomy.

The first of what is to be a mega constellation of 12,000 Starlink satellites were visible as a train of bright lights passing overhead in the sky during the nights immediately following launch. While the view excited some observers, it generated concern over the satellites’ long-term impact on the night sky.

Planetary astronomer Alex Parker of the Southwest Research Institute (SwRI) expressed concern that the 12,000 satellites could be brighter and more numerous than stars visible to the naked eye.

The International Dark Sky Association (IDA) pointed out that the satellites’ reflective solar panels and metal surfaces make them visible at night. They were observed worldwide in the nights following their launch.

“The rapid increase in the number of satellite groups poses an emerging threat to the natural nighttime environment and our heritage of dark skies, which the International Dark Sky Association (IDA) has worked to protect since 1988,” the organization said in a statement responding to the satellites’ launch. “We do not yet understand the impact of thousands of these visible satellites scattered across the night sky on nocturnal wildlife, human heritage, or our collective ability to study the cosmos.”

A summer astronomy project for Smith College undergraduates in New Hampshire was already impacted adversely when students looking through a telescope suddenly saw the bright satellites stream across the sky, the IDA statement notes.

SpaceX CEO Elon Musk said the satellites are being raised to a higher orbit, from 273 miles (440 kilometers) over Earth’s surface after launch to 342 miles (550 kilometers), where they are expected to be less visible.

“If we need to tweak sat orientation to minimize solar reflection during critical astronomical experiments, that’s easily done,” Musk said on Twitter. “There are already 4,900 satellites in orbit, which people notice ~0 percent of the time. Starlink won’t be seen by anyone unless looking very carefully and will have ~0 impact on advancements in astronomy.”

The satellites would have no impact on radio astronomy because they do not use the lower Ku frequencies used in radio astronomy, Musk added.

Claiming SpaceX is dedicated to science, Musk said he has instructed the company’s engineers to reduce future Starlink satellites’ reflectivity by making them less shiny.

“We’ll get a better sense of value of this when satellites have raised orbits, and arrays are tracking to the Sun,” Musk said on Twitter.

His initial claim that the satellites would not be visible at night when the stars are out was challenged by several astronomers. Cees Bassa of the Netherlands Institute for Radio Astronomy did his own calculations of the satellites’ visibility and determined they would be visible after sunset. Being above the Earth’s surface, they would continue to be illuminated by sunlight after the Sun sets on Earth.

“My aim was to show people these satellites were going to be more visible than people said they would — among them Elon Musk,” Bassa said. Between 70 and 100 satellites would be visible on summer nights once all 12,000 are launched, he said.

Even if the satellites are fainter than the brightest 500 stars in the sky, they would adversely affect astronomers in dark sky areas, where 1,000 to 2,000 stars are visible on a typical clear night, according to Darren Baskill of the University of Sussex.

Astronomers already have to correct images impacted by passing satellites, said Nestor Espinoza of the Max Planck Institute for Astronomy in Heidelberg.

SpaceX is monitoring the progress of the 60 launched satellites, which have successfully deployed their solar panels, generated power, and communicated with mission controllers on Earth.

Using their onboard propulsion systems, the satellites are expected to take between three and four weeks to reach their designated orbit and are programmed to avoid one another and other objects in orbit.

According to a SpaceX statement released on May 31, “the observability of the Starlink satellites is dramatically reduced as they raise orbit to greater distance and orient themselves with the phased array antennas toward Earth and their solar arrays behind the body of the satellite.”

A total of nine companies plan on launching satellites for the purpose of providing broadband internet service to underserved parts of the world. OneWeb is working on a network of 648 satellites, six of which have already launched. Telesat aims to launch 292, and Amazon is planning a constellation of 3,236.

Video courtesy of Movie Vertigo