Researchers at the Zwicky Transient Facility in California have analyzed the extent to which SpaceX's Starlink satellite constellation affects terrestrial astronomical observations. The results are mixed.
The new paper, published in The Astrophysical Journal Letters and led by former Caltech postdoctoral fellow Przemek Mróz, offers some good news and some bad news. The good news is that Starlink does not currently cause problems for researchers at the Zwicky Transient Facility (ZTF), which operates from Caltech's Palomar Observatory near San Diego. ZTF, which uses both optical and infrared wavelengths, scans the entire night sky once every two days in an attempt to detect sudden changes in space, such as previously unseen asteroids and comets, stars that suddenly fade, or colliding neutron stars.
But that does not mean that Starlink satellites, which provide low-bandwidth broadband Internet around the Earth, have no influence. The recently completed study, which reviewed archival data from November 2019 to September 2021, found 5,301 satellite streaks directly attributable to Starlink. Not surprisingly, "the number of affected images increases over time as SpaceX implements more satellites," but, until now, scientific operations on the ZTF "have not yet been severely affected by satellite stripes, despite the increase in their number observed during the analyzed period," the astronomers write in their study.
The bad news has to do with the future situation and how satellite mega-constellations, whether Starlink or another fleet, will affect astronomical observations in the coming years, especially observations made in twilight. In fact, images most influenced by Starlink were those taken at dawn or dusk. In 2019, it meant satellite streaks in less than 0.5% of all twilight images, but by August 2019, this had escalated to 18%. Starlink satellites orbit at a low altitude of about 324 miles (550 km), which makes them reflect more sunlight during sunset and sunrise, creating a problem for observatories in the twilight.
Astronomers make observations at dawn and dusk as they search for terrestrial asteroids that may appear next to the Sun from our perspective.. Two years ago, ZTF astronomers used this technique to discover 2020 AV2 - the first asteroid completely in Venus' orbit. One concern expressed in the new paper is that when Starlink reaches 10,000 satellites - which SpaceX expects to achieve in 2027 - all ZTF images taken in the twilight will contain at least one satellite strip. After yesterday's launch of a Falcon 9 rocket, the Starlink mega constellation consists of over 2,000 satellites.
In a Caltech Press release, Mróz, now at the University of Warsaw in Poland, said he does not "expect Starlink satellites to affect non-twilight images, but if the satellite constellation of other companies enters higher orbits, this could cause problems for non-twilight observations. " A pending satellite constellation managed by OneWeb, a UK-based telecommunications company, will orbit a operational height at 745 miles (1,200 km), for example.
The researchers also estimated the proportion of pixels lost as a result of a single satellite stripe and found that it was not large.” By "not large" they mean 0.1% of all pixels in a single ZTF image.
That said, "simply counting pixels affected by satellite streaks does not capture the whole problem, for example, resources needed to identify and mask satellite streaks or the chance of missing an initial detection of an object, "write the researchers. . As Thomas Prince, an astronomer at Caltech and a co-author of the study pointed out in the press release, there is actually a "small chance" that "we would miss an asteroid or other event hidden behind a satellite strip, but compared to the impact of The weather, such as a cloudy sky, these are rather small effects for ZTF. "
SpaceX has not responded to our request for comment.
The researchers also examined the measures taken by SpaceX to reduce the brightness of Starlink satellites. Implemented in 2020, these measures include visors that prevent sunlight from illuminating too much of the satellite's surface. These measures have served to reduce the brightness of Starlink satellites by a factor of 4.6, which means that they are now on the order of 6.8 (f. reference, the brightest stars shine with an order of magnitude of 1, and human eyes can not see objects much weaker than 6.0). This marks a major improvement, but it's still not great, as members of the 2020 Satellite Constellations 1 workshop asked for satellites in LEO to have sizes over 7.
The current study only considered the effects of Starlink on the Zwicky Transient Facility. Each observatory will be affected differently by Starlink and other satellites, including the upcoming Vera C. Rubin Observatory, which is expected to be hit hard by mega constellations. Observatories are too expected to experience problems due to radio interference, the appearance of ghost-like artifacts, among other potential problems.
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