25.04.2023

Since their initial launch in 2019, SpaceX’s Starlink internet satellites have become infamous for photobombing observations from ground-based telescopes. While Starlink — along with other satellite “megaconstellations” — has been a primary concern for ground-based telescope observations, a new issue has begun to pop up; the satellites are now occasionally obstructing images from one of NASA’s flagship space telescopes, the Hubble Space Telescope. These “photobombings” point to a concerning future for astronomy in low Earth orbit (LEO), as telescopes in LEO may begin to face the same problems ground-based telescopes face today — especially as these satellite megaconstellations grow.

To learn more about this growing issue, NSF sat down with astrophysicist Dr. Jonathan McDowell from the Harvard-Smithsonian Center for Astrophysics to discuss the topic.

Satellites have long been an issue for astronomy, but due to the relatively low amount of satellites in orbit during the first several decades of spaceflight, the issue was not an extreme concern. The environment in LEO has been rapidly changing over the past few years, however, as more private companies (i.e. SpaceX and Amazon) and nations express interest in and launch so-called satellite “megaconstellations.” The most well-known, and arguably the most controversial, megaconstellation today is Starlink — SpaceX’s publicly-available internet satellites — and OneWeb, a company aiming to provide commercial internet service worldwide.

Starlink and OneWeb are not the only two megaconstellations, though, as there are several megaconstellations currently in development. This includes Project Kuiper, Amazon’s competitor to Starlink, which is set to begin demo launches later this year.

Due to Starlink being one of the first true satellite megaconstellations — and planned to be larger than any other megaconstellation currently in development — the program has garnered much attention from the public and astronomers alike.

Leading up to the maiden Starlink launch, astronomers were not immensely concerned about their effect. While astronomers knew the size of Starlink’s constellation would likely threaten ground-based astronomy, they would soon find that Starlink’s impact on their observations and research would be far more serious than previously thought. Dr. McDowell explained, “[Astronomers] had greatly underestimated how bright these satellites were going to be. We hadn’t paid it a lot of attention, and we didn’t realize how enormous the satellites were going to be because they hadn’t told us. [W]e didn’t appreciate the impact they were going to have.”

Fortunately, SpaceX has been working closely with astronomers to mitigate the effects of Starlink’s size and brightness on astronomical observations. The company has tested multiple designs to reduce the brightness of the satellites, such as dark paint and sunshades. However, due to thermal issues and the fact that sunshades would block the laser links on newer satellites, these mitigations were only flown on a limited number of older satellites.

While SpaceX is investigating newer forms of dark coatings for the satellites, the current primary brightness mitigation technique is aligning the satellites so that their large and extremely reflective solar arrays face away from Earth.

These mitigation techniques were all designed to limit the impacts of Starlink on ground-based astronomy. However, the techniques do little to lessen the impact of Starlink on LEO-based observation, which was previously thought to have been a safe haven from the negative effects of Starlink.

Dr. McDowell explained that around 3% of Hubble’s observations prior to Starlink were obstructed by satellite trails. Thankfully, this did not always mean the data was useless, as he explained, “Most of that was not ‘Throw away the science,’ it was ‘Okay, we can’t use that image for this purpose’… but more and more you are getting to the point where [you say] ‘Okay, that data is useless for the purpose we took it.'”

Hubble currently orbits around 10km below the operational orbit of most Starlink satellites. This, combined with its narrow field of view, means it should be safer than other telescopes — but will still be heavily affected as more and more megaconstellations begin to grow in LEO.

Wide field-of-view space telescopes in LEO, such as China’s upcoming Xuntian telescope, will be more severely affected. Xuntian will feature a field of view that is over 300 times larger than that of Hubble, allowing it to image a very large swath of sky at once. Wide field-of-view telescopes can be used to survey the sky, noting changes in areas over time. NASA’s upcoming Nancy Grace Roman Space Telescope will serve a similar purpose.

While Roman – alongside the joint NASA/ESA/CSA James Webb Space Telescope — will never need to worry about Starlink satellite streaks thanks to its position at the Earth-Sun Lagrange point 2 (L2), Xuntian — in a 390 kilometer LEO — will be faced with a tough challenge. While its wide field of view will be excellent for capturing large areas of space, it also drastically increases the chances of satellites passing through the telescope’s line of sight.

With the negative effects of satellite megaconstellations becoming more and more clear, it raises a question: will future LEO telescopes need to take these satellite constellations into account?

Dr. McDowell replied simply, “Absolutely.”

He continued, “The solution for, say, most American missions is going to be ‘Let’s put them high up.’ But, if you’re a developing country, like if India wanted to launch another space telescope … maybe they don’t have the rockets to put it higher up. And so I think it’s going to be a real challenge for future low Earth orbit observatories … particularly for ones that have a wide field of view that are searching for new things.”

“We have the ‘scalpels’ which look at a known object with a big magnification, and then we have the surveys, which look at a bunch of sky at once, trying to find things that haven’t been seen before – and those [survey telescopes] are the ones [that will be affected].”

He then added one final thought: “…I think that low Earth orbit astronomy is going to be problematic every bit as much as ground-based astronomy.”

But thankfully, this increase in satellite counts should not be problematic for every type of astronomy. He explained, “There may be missions where you do the calculation, and you go ‘Yeah, that’s a 1% effect, we’re not going to worry about it,’ and other missions where you go ‘No, you know what, you’ve got to go high because we’ve just lost LEO for this purpose.'”

X-ray telescopes in LEO, such as Japan’s upcoming XRISM mission, should be minimally affected as Starlink is not bright in the X-ray spectrum.

As megaconstellations continue to develop and grow, astronomers will need to adjust how they study the cosmos. LEO is no longer a safe haven for astronomy — telescopes will need to be launched into higher orbits if they want to limit the effects of satellite transits. Distant locations like L2 may end up being a truly safe haven, as astronomers reach for an unobstructed view of the heavens.

(Lead image: The Hubble Space Telescope seen from the Space Shuttle’s crew cabin during a servicing mission. Credit: NASA)

Quelle: NSF