Trading The Night Sky For WiFi? Satellite Mega-Constellations Have Serious Consequences For Astronomy
Broadband satellite mega-constellations are set to number in the tens of thousands in the future. That will change the night sky forever and impede progress in scientific research.
Astronomers have to increasingly contend with a problem that they wish would go away but never will — satellite mega-constellations. If plans of private space companies are to materialise, there will likely be satellites in the tens of thousands swarming around Earth within this decade.
This has the astronomy community worried — several premier international organisations have already released numerous polite statements of caution since 2019. Of late, the tone has turned urgent.
Here’s the problem: astronomers rely on gathering the light, or signal, faithfully transmitted from the universe for their study, analysis, and discovery. They decode the universe with light. Dark and radio-quiet skies are prerequisites for this work — the presence of stray bright light or radio noise in the foreground obscures optical images or radio data yielded by meticulous observations.
Imagine taking a picture of a friend standing across the street and noticing the bright headlights of a nearby car splashed over the photograph later. The friend would not be pleased. Astronomers, more so. Except, astronomers want the photographs to be “perfect” so that they can make sense of the universe.
Streaks of light across the sky on astronomical images, as seen a few times on account of SpaceX satellites, complicate research matters by obscuring finer and fainter objects and details and potentially spoiling the chance of discovery.
The broadband communication satellites, which are the source of worry, will circle the planet in “low-Earth orbits” or altitudes between 160 km and 2,000 km from the Earth’s surface. They are going up in large numbers as “constellations” in order to provide fast and reliable internet access to most of the world, especially to parts that don’t have it yet.
As an unintended consequence, they will mar the view of the sky.
“For thousands of years, only celestial objects were in the sky. Then came a few satellites which were seen in some observations but not many. If we increase the number by orders of magnitudes, these satellites will impinge on every observation,” says Dr Jayant Murthy, a senior professor at the Indian Institute of Astrophysics, Bengaluru.
This rise by orders of magnitude is waiting to happen. Elon Musk’s SpaceX, which has been shipping its internet satellites to space in batches of about 60, has gone from zero to 590 “Starklink” satellites in a year. According to the plan, this number will rise to 12,000 eventually.
For perspective, the total number of satellites in orbit until last year was just over 2,000.
In that context, SpaceX's planned fleet may seem like plenty. But that’s not all. SpaceX is exploring the possibility of adding 30,000 additional satellites over time.
Besides, SpaceX is not the only company with plans to provide internet from space.
The United Kingdom-based communications company OneWeb has plans to launch 648 internet-beaming satellites. They have launched over 70 of them in a couple of batches so far, but insufficient funding sent them spiralling towards bankruptcy earlier this year.
Timely resuscitation by the United Kingdom government, which was anyway looking to part with the European Union's satellite-based navigation system “Galileo”, has given OneWeb a new lease of life. The company plans to put 48,000 broadband satellites in orbit someday.
More recently, Amazon entered the satellite internet space. Its “Project Kuiper” got the approval of the United States Federal Communications Commission at the end of July to deploy its planned constellation of 3,236 satellites.
A mere addition of the planned and existing satellite numbers across several of these “internet from space” projects indicates the magnitude of the problem facing astronomers.
Principally, these broadband satellite constellations will pose problems in three electromagnetic bands — visible light, infrared, and radio wavelengths. Other parts of the spectrum will remain relatively undisturbed.
The major hurdle is the light reflected and emitted by the satellite. The metallic plating on the spacecraft absorbs and reflects the sunlight falling on it to prevent overheating, but it also causes the satellite to become visible to astronomers and astrophotographers. They appear as streaks or dots of light.
Light is the astronomer’s chief currency. Professionals rely on light to obtain and construct the full picture of the universe. The more light they can capture, the more they can learn about their object of observation, be it a distant galaxy or a planet in a different solar system.
“The objects that we try to observe now are faint and we deliberately go to dark regions to observe. If you have bright streaks in every exposure, it is hard to extract the faint objects which we want to observe,” says Dr Murthy.
Some of the celestial objects that may get harder to observe include near-Earth asteroids, exoplanets, gravitational wave sources, such as black holes and neutron stars, detected independently by gravitational signatures, and distant stars and galaxies.
Astronomers typically start looking for near-Earth asteroids in the twilight hours, either between sunset and dusk or between dawn and sunrise. These objects give the scientific community vital information about the state of the early solar system. At the same time, they help identify potential collision threats, in case asteroids are headed straight to Earth.
However, it is during the twilight hours that the satellite constellations are the brightest in the sky, at least those residing in orbits under 600 km. They also remain visible for a few hours.
Gravitational waves, an important component in multi-messenger astronomy, are detected by laboratories like the Laser Interferometer Gravitational-wave Observatory or LIGO. These centres notice the slightest of changes caused by incoming gravitational waves.
Once this detection is made, telescopes in the electromagnetic spectrum are turned to the sky to capture the source of that wave. This search has to be mounted quickly. Or else, the object risks fading away.
Here again, the presence of illuminated satellites in the sky could eat away at the little window that astronomers have to confirm gravitational-wave detection in the electromagnetic spectrum.
Similarly, astronomers could lose sight of a transiting exoplanet momentarily and it could affect their knowledge of key orbital data.
Recognising this wide variety of difficulties imposed by satellite constellations, the astronomy community and the space companies are working together to identify a way forward that benefits both parties.
Recently, more than 250 astronomers and satellite operators, the latter mostly from SpaceX, gathered for the SATCON1 (“Satellite Constellations 1”) workshop, held virtually from 29 June to 2 July this year. Research papers, based on computer modelling of different satellite configurations, were presented and discussed.
Some useful findings and recommendations have emerged. Satellites were reckoned to better off in orbits below 600 km. At that height, they would be visible for a period of time at night including the twilight, but the rest of the night would be open for undisturbed observation.
If this 600 km mark was breached, however, it would lead to light contamination all night long during the summer months and for most of the night in other seasons.
Although SpaceX has its eyes set on lower orbits of around 600 km, OneWeb is thinking of having its network higher up at about 1,200 km.
Design, development, and operational changes for satellites have also been suggested. Chiefly, the reflectivity of the satellites — and therefore, the brightness — has to be lowered.
Experiments in this area are underway as companies are testing out various spacecraft coatings with the aim of dimming the satellites. One of the SpaceX satellites that went up in January had a different coating and is being monitored by observatories for its apparent brightness.
But this is easier said than done. “It is not easy to lower the reflectivity. It will require new developments in materials science and engineering. Plus, the coatings will have to be tested and made space grade,” says Dr Shashi Bhushan Pandey, a senior scientist at the Aryabhatta Research Institute of Observational Sciences, Nainital.
Complementing the design changes, the satellites in orbit would have to be oriented in such a way that they reflect less light. In technical parlance, this aspect is called the spacecraft “attitude”.
Astronomical observatories will have to support the development of a range of software tools. Applications would have to identify and strike off satellite trails from the analysis, a process called "masking".
Other applications would have to aid in predicting key parameters pertaining to when satellites will become visible in the sky, how bright they will be, and what impact they would have on the data.
Dr Pandey expressed doubt over the possibilities of masking. “It isn’t easy to do that even for ordinary photographs we take in our daily lives,” he said.
It appears that the idea behind some of the SATCON1 suggestions is to equip astronomers with adequate information beforehand so that they can plan their observations accordingly.
If only celestial objects could be told when to appear!
But beyond the concrete steps, some broader questions arise that could nudge astronomers in other directions.
For instance, would the rise of satellite mega-constellations compel a greater movement towards space-based observatories?
“It would be nice if there was a surge in space telescopes, but it will not happen,” says Dr Murthy. “The first reason is cost. Any space mission is expensive and limited in lifespan. No one will give that much money for large space missions. The second is feasibility. If we look at TMT, which is a 30 m telescope, and try to launch that with the instruments — it just cannot be done. Any instrument on the ground will be technically superior to one in space.”
Or, perhaps, these satellites could carry instruments that help out with astronomical observations?
Unfortunately, the satellites may be too small — SpaceX satellites are generally described as “mini-fridge-sized” — to carry a meaningful science payload. Dr Murthy says, “In a several tonne satellite, a few extra kilograms makes no difference. If you have a 10 kg satellite, it will be hard to put any reasonable science payload on them.”
Taking an even broader view, it could also be asked: how will space work in the future?
It was easier to manage when the number of satellites going up in space were limited and largely came from government agencies. Now all the stuff up there, including the space debris that is accumulating in orbits, is ballooning. Who decides what to do about it? What if two satellites are on a collision course — who would have to move their satellite? Will there be regulations that dictate what can and cannot go up there, or will market forces decide that?
Our connection with the skies is ancient and natural. Looking up at the sky in wonder is a sacred act that we share with our ancestors. However, it increasingly feels like access to a pristine night sky is going to be harder to come by.
“The stars we see are the same stars that the first people saw. Already those of us in cities have lost this connection to ourselves and our past. Now, these people are planning to change the sky for everyone, with no discussion. We have understood that the environment is important and must be protected but, somehow, we have accepted that the sky can be defaced by a small number of billionaires with no discussion,” says Dr Murthy.
There may be no going back from this position, but, at the least, genuine collaboration between astronomers and satellite operators will have to be forged for mutual benefit. This seems to be happening already, but remaining committed to saving the night sky for as long as necessary and making compromises in favour of space will be crucial.
Otherwise, what we see when we look up may be changed forever.
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