On October 30th, the Star Walk app on my phone let me know that if I saw a bright train of lights moving across the sky, I was probably seeing the 200th batch of Starlinks passing overhead. While I didn’t see that particular Starlink train, I’ve caught other groups going by, and these low-orbiting satellites put on one heck of a show as they reflect sunlight from orbit back toward our planet. We can only see them in the hours before sunrise and after sunset, but they are there all night long, and when we can’t see them by reflected light, they are still causing problems by eclipsing streaks of sky as they fly by.
Credit Night Sky on Youtube: Very bright flight of a Starlink train over Poland/
The Starlink mega constellation of telecommunications satellites isn’t the only constellation being built – it was just the first to sneak up on astronomers and make us aware a new problem we were going to need to plan around. Five years of Starlink launches later, we’re going to take a moment to reflect on the reflected light, radio pollution, and atmospheric concerns being raised with mega-constellations.
High-speed demands Small Orbits
In old-timey science fiction, communications satellites were placed in geosynchronous orbits where they could relay signals to a set region on our world and to other satellites in space. From their altitude of 36 thousand km, these could be giant stations and still only appear as a faint stationary point of light in our sky. In reality, this works, but the connections are too slow for easy conversations, and as internet speeds increase, the lag introduced by the speed of light is actually getting noticeable. A round trip signal to geostationary orbit and back takes 0.02 seconds. (And the system has additional latency from handling all the things it has to handle.)
To improve internet communications, companies like SpaceX have been bringing telecommunications satellites closer to Earth and placing them in orbits 340 to 640 km up. By putting them more than 50 times closer to Earth, they can reduce light speed-induced lag by that same factor of more than 50.
To be clear – Large, High power, low-impact on astronomy satellites aren’t being used for satellite internet because of our need for speed. What is being done with 10,000s of low earth orbit satellites could be accomplished by tens of geostationary and other high orbit satellites that can provide service to polar regions.
While one geostationary satellite can serve the needs of people on a large region of our planet as they sit still in the sky, it takes myriad satellites, that streak by in minutes, to provide service to those same humans. Starlink alone plans to deploy 12,000 satellites in their network, and they have discussed expanding to 34,000 satellites.
And Starlink is just one of the myriad constellations planned by megacorporations and countries around the world.
Each of these networks is designed somewhat differently, and creates its own unique problem to people on Earth trying to enjoy or study the universe beyond. While ultimately fewer in number, the new AST Space Mobile BlueBird Satellites are giant disks of solar panels and antennae that outshine everything in the sky. Orbiting 500 km up, the 168 spacecraft planned for this constellation can saturate a quarter degree of the sky.
High-Bandwidth requires larger size
Back in January 2020, at the American Astronomical Society meeting in Hawaii, many of us listened in as astronomers talked about plans to work with SpaceX to create darker satellites that would impact our ability to see the sky a little bit less. The idea was to work together to make it possible for humans on Earth to go out and enjoy the a meteor shower or take observations of far off galaxies without satellites wrecking their plans.
The International Astronomical Union even worked with astronomers and satellite companies to create international standards for the brightness of satellites and their radio frequency usage so we could protect our dark and radio quiet skies for science.
In 2022 I tried to observe a meteor shower and the constant interruption of satellites kept tricking me into thinking I was seeing a shooting star instead of orbiting hardware.
Today, the latest generation of Starlinks are the brightest ever. Those BlueBird satellites I mentioned are 900 times brighter than the IAU standard.
It is now estimated that every 30-second exposure of 1 degree of the sky will have 1 or more satellites if the observatory is between + or – 50 degrees latitude.
The streaks generated by these satellites could cause observing programs to take order of 10% longer to complete, which doesn’t sound like a lot, but in our highly competitive environment, this will mean entire research questions that can’t be studied. … and more people like me who get frustrated trying to observe meteor showers or other night sky phenomena.
And before you say, “Just use space telescopes” I want to remind you that an 8 meter telescope costs millions to build on earth and billions to build in space. We simply can’t afford to replace all our ground based systems with space telescopes.
Satellites louder than the Universe
Human beings see our universe in optical light. This makes it easy for us to understand how satellites can pollute our astronomical images with reflected sunlight as they pass overhead.
The thing is, this is a passive problem – we have a star that shines, they are shiny, and thus we see reflected light.
In the radio sky we also have problems, but these are more actively created. While Starlink and other telecommunications satellites are supposed to be using specific radio bands that are controlled under international agreements, they often stray into other segments of the spectrum. In 2023, the European LOFAR radio array found unintended radio emissions in the wavelengths of radio generally reserved for science. Those were first generation Starlinks. Now, in 2024, they are finding the 2nd generation satellites are 32 times brighter, and potentially exceed thresholds set by international regulations.
An article on this problem in the journal Science reads “Worst nightmare”: Elon Musk’s Starlink satellites could blind radio telescopes.”
While we have many different telescopes in space, studying wavelengths from the infrared to the ultraviolet, radio astronomy is largely done from Earth because it requires massive dishes and geometries that are easier to attain on a planet’s surface than in space. We can’t move our planet’s radio astronomy capabilities into orbit with current technology.
What goes up, Often comes down
In addition to optical and radio light pollution, we also need to be aware that objects that we put up in low-Earth orbit end up falling back to Earth through our atmosphere. When we put things up in geostationary orbit, they will stay put until moved or hit by something else.
The reason for this difference has to do with the Earth’s atmosphere creating drag up to several 100km above the Earth. This means that everything we put in low Earth orbit either will need to expend energy to stay in orbit regularly or will need to be replaced every few years. Currently, it appears that both these things will happen, and we’re going to see near-daily launches of new bundles of satellites and the regular decay of satellites back through the atmosphere.
This causes two problems. On the way up, rockets release particles into the atmosphere that can eat away at the ozone layer, and on the way down, spacecraft become particulates that can increase global warming. The issues with the ozone layer are particularly troubling as models show a 10 fold increase in launches by rockets burning hydrocarbons – like solid rocket engines – will increase UV radiation in the Northern Hemisphere, increase upper atmospheric temperatures as much as 2 degrees and change atmospheric wind patterns by several percent.
The full impact on the climate isn’t well understood, and many researchers have been demanding that research be funded before things hit an irreversible point. Calls have been made to slow the rate of launch and delay the licensing of new batches of satellites until we understand what we’re doing to our world’s environment. As it stands… the income companies can make off of high-speed satellite internet and cell phone service is dominating the conversation, and the needs of capitalism are dominating over the needs of conservation.
I can report on what is happening. I can report on what science tells us will happen if we continue building out the megaconstellations currently being planned.
And I can tell you I don’t want to experience that future first hand … but it is going to take more than just the words of a reporter to keep our skies dark, our radio telescopes able to do science, and our atmosphere safe from rocket exhaust and spacecraft debris.
I’d like to leave you with one question: Is this worth 0.02 seconds of internet latency due to the speed of light?
Resources:
- Starlink Satellites leaky radio waves obscure the cosmos (ScienceNews)
- Bassa, C. G., Di Vruno, F., Winkel, B., Józsa, G. I. G., Brentjens, M. A., & Zhang, X. (2024). Bright unintended electromagnetic radiation from second-generation Starlink satellites. Astronomy & Astrophysics, 689, L10.
https://doi.org/10.1051/0004-6361/202451856 - Mike Peel on behalf of the IAU CPS (2024). The IAU CPS SatHub: Updates on observation campaigns, services and software to mitigate satellite constellation interference.
- Ryan, R. G., Marais, E. A., Balhatchet, C. J., & Eastham, S. D. (2022). Impact of rocket launch and space debris air pollutant emissions on stratospheric ozone and global climate. Earth’s Future, 10, e2021EF002612. https://doi.org/10.1029/2021EF002612