EVAN GOUGH, UNIVERSE TODAY, 16 FEB 2020
(SpaceX)
Picture the space around Earth filled with tens of thousands of communications satellites. That scenario is slowly coming into being, and it has astronomers concerned.
Now a group of astronomers have
written a paper outlining their detailed concerns, and how all of these satellites could have a severe, negative impact on ground-based astronomy.
SpaceX and other companies are casting their keen capitalist eyes on the space around Earth. SpaceX and OneWeb are the only companies - so far - to launch any portions of their
satellite constellations.
But a number of other companies have plans to do the same, and eventually all of those satellites will number in the tens of thousands.
The astronomy community has raised some concerns about these satellite constellations. The
Royal Astronomical Society and the
American Astronomical Society have both released statements expressing their concern and desire to work with companies in the satellite constellation business.
Those statements are polite, cautious in their criticism, and written in the spirit of cooperation.
But this new paper lays out all of the astronomical community's concerns, backed up with data, and presses their point more insistently.
The first 240 Starlink satellites in Celestrak. (Gallozzi et al., 2020/Celestrak.)
"For centuries ground based astronomical observations have led to exceptional progresses in our scientific understanding of the Laws of Nature."
A satellite constellation is a group of artificial satellites that work together to provide global or near-global communications coverage. They have the potential to make high-speed internet available almost anywhere. Obviously, there are a lot of benefits to that.
But there are criticisms, too, and three astronomers from Italy's INAF–Osservatorio Astronomico di Roma, have presented these criticisms in detail. The three are Stefano Gallozzi, Marco Scardia, and Michele Maris.
Their paper is titled "
Concerns about ground based astronomical observations: A step to Safeguard the Astronomical Sky".
When you add up all the satellites that companies want to launch as part of their constellations, you get somewhere around 50,000 satellites. The question is, what effect will of those satellites have on ground-based astronomy?
The authors of the report claim that all of these satellites will inevitably damage astronomical observing.
A note to readers: English is not the first language of the authors of the paper, so some of the quotes contain small inconsistencies, but the meaning is clear.
"Depending on their altitude and surface reflectivity, their contribution to the sky brightness is not negligible for professional ground based observations," the report says in the introduction.
"With the huge amount of about 50,000 new artificial satellites for telecommunications planned to be launched in Medium and Low Earth Orbit, the mean density of artificial objects will be of >1 satellite for square sky degree; this will inevitably harm professional astronomical images."
(Gallozzi et al., 2020)
TABLE: There are only 172 stars in the whole sky exceeding the expected brightness of Starlink satellites. Higher altitude LEO satellites (e.g. over 1000 km-altitude) will be visible all the night reaching approximately the 8th magnitude.
Since SpaceX is the furthest along in deploying their constellation, their name pops up frequently in the paper. SpaceX's Starlink system has already launched almost 250 of their satellites, and they plan to deploy up to 42,000 satellites in total.
According to
the paper, these satellites "will shine from the 3rd to the 7th magnitude in sky after sunset and before sun dawn."
The authors say that all of those satellites will inevitably leave trails in astronomical images, and may inhibit the search for Near Earth Objects. There's some degree of risk that we might not spot a potential impact because of all these satellites.
But it's not just images that will be negatively affected, according to the report.
"Serious concerns are common also to other wavelengths eligible for ground based investigation, in particular for radio-astronomy, whose detectors are already saturated by the ubiquitous irradiation of satellites communication from space stations as well as from the ground."
Back in May 2019, Elon Musk tried to dismiss any astronomical concerns about Starlink. Among his rather brusque dismissal of criticisms was his statement that "We need to move telelscopes (sic) to orbit anyway. Atmospheric attenuation is terrible."
Musk has a huge profile in the space community, so his words might have convinced some that there are no problems between Starlink and astronomy. But Musk is an entrepreneur, not a scientist.
For all his accomplishments, Musk is not an expert in astronomy or astronomical observing. Is his statement that Starlink "will have ~0 percent impact on advancements in astronomy," accurate and informed?
The three authors of
the new paper don't seem to think so. They outline the risks that satellite constellations pose to astronomy, and it's not all about whether they're visible in optical light.
They point out that there are "dangerous effects arising from such changes in the population of small satellites. A dedicated strategy for urgent intervention to safeguard and protect each astronomical band observable from the ground is outlined."
"Without ground based observations most of current space based astronomy would be useless or impossible."
The authors start at the beginning, by pointing out the enormous advances in understanding made by ground-based observations. "For centuries ground based astronomical observations have led to exceptional progresses in our scientific understanding of the Laws of Nature." That's hard to argue with.
In
the paper's first section, they talk about how space-based astronomy, or space telescopes, have contributed to knowledge. But they point out that ground-based and space-based astronomy need each other and produce the best science when they work together.
"Without ground based observations most of current space based astronomy would be useless or impossible."
It's safe to say that the authors don't agree with Musk's glib assertion that "We need to move telelscopes (sic) to orbit anyway. Atmospheric attenuation is terrible."
Maybe Musk has never heard of
adaptive optics. Adaptive optics allow modern ground-based telescopes to overcome the effect of the atmosphere on observations. Upcoming telescopes like the European Extremely Large Telescope and the Thirty Meter Telescope feature adaptive optics at the heart of their designs.
The authors also point out what should be clear to anyone who thinks about it for very long: compared to ground-based astronomy, space-based telescopes are enormously expensive. And risky.
Advances in telescope technology are made here on Earth. Their deployment is the risky part, but the technologies have already been tested and developed here on Earth. As the authors of the paper point out, testing and developing new telescope technologies is not feasible in space.
"A major limitation of space based telescopes is that they can not be maintained, refurbished or repaired after launch." The Hubble is an exception, and other space telescopes have not been maintained. Once they're done, they're done.
Continue reading this very long article at:
https://www.sciencealert.com/astonomers-have-serious-concerns-about-satellite-constellations-like-starlink
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