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In the news there was an article about Starlink beaming 42 million GB of Data per day. Also it states that the lasers form a global mesh network of 9000+ lasers. There are 260.000 acquisistions per day. Connections can stay on for weeks at a time and the lowest connection before breakup was ca 30km, 100.000 ft.

Brashears also said Starlink’s laser system was able to connect two satellites over 5,400 kilometers (3,355 miles) apart. The link was so long “it cut down through the atmosphere, all the way down to 30 kilometers above the surface of the Earth,” he said, before the connection broke.

I derive that link quality is constantly measured and can be used to get some pretty usefull science from the network.

On earth, fiber optics can measure the awakening of cicades, trains, seismic events, etc.

I am not a scientist. So I am asking what kind of science can or is already being done with this system? And what kind of knowledge might be derived from that science?

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  • $\begingroup$ Gravitational wave astronomy perhaps? along the lines of LISA en.wikipedia.org/wiki/… $\endgroup$ Feb 4 at 14:48
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    $\begingroup$ Quickly reading the wiki. To measure you need to split and mirror the signal with a minimal of 3 satellites. I am guessing the laser system are simply not equiped with those. But only direct links are used. $\endgroup$
    – twildeman
    Feb 7 at 14:31

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On earth, fiber optics can measure the awakening of cicadas, trains, seismic events, etc.

I didn't know about the awakening of cicadas (Wired, November 30, 2023, Cicadas Are So Loud, Fiber Optic Cables Can ‘Hear’ Them hat tip to Jacob Krall) but certainly optical fiber seismology is a well-developed concept for both naturally and artificially-induced vibrations and movements. But all of those technologies depend upon imperfections in the silica fibers that cause polarization mode dispersion and micro-reflections (or other more complex phenomenon, especially right after the amplifiers when the light intensities are strongest and the multiplexed wavelengths most susceptible to nonlinear effects in the fiber).

But here you're asking about "free-space" optical communication which really means there's no artificial guiding of the waves (waveguides) but it doesn't mean that the space is necessarily empty and not full of birds, air, gases, clouds, dust, water droplets, etc. ALL OF THOSE should be able to induce detectible shifts if you go out of your way to make your system sensitive to it.

Lasers certainly are used in a surprisingly wide range of atmospheric characterization techniques. (I think "how are lasers used in a "surprisingly wide range of atmospheric characterization techniques?" would make for an excellent Earth Science SE question!)

So I would look for meteorological applications first. However, I would make sure that whatever you are measuring isn't sufficiently covered by the wide range of Earth observation satellites already placed in LEO, GEO and Sun-Earth L2 which image over a very wide range of wavelengths and shoot lots of lasers already!

Another thing; all of the commercial electro-optics and electronics developed for the fiber and free-space optical communications industries are designed to ignore and push through various phenomena (those birds, etc) and deliver the best data possible. They will have some separate data stream for reporting "link-health" for diagnostics and preventative maintenance scheduling, but there won't be the same level of sophistication, because unlike fiber with all its inherent distortions and dispersions and static micro-reflections, free-space is "a breeze". Mostly you are just looking at intensity drop-outs when it rains.

One of the biggest challenges to satellite technology giving us accurate GNSS positions is the electron content of the ionosphere and the precipitable water vapor content (i.e. the gas, not the drops) in the lower atmosphere. In fact GPS signals are used all the time to monitor water in various parts of the upper atmosphere.

The link was so long “it cut down through the atmosphere, all the way down to 30 kilometers above the surface of the Earth,” he said, before the connection broke.

So if the electronics was set up right, it could possibly be able to measure the delay of the signal, and measure deviations in the delay from what the geometrical distances would indicate and that could measure something like the integrated density of air using some model for index of refraction as a function of density, temperature and water content. I don't know if that would be sensitive-enough to be useful, nor if the Starlinks are set up to continuously record path-length induced delays to sufficient precision to later-on recover useful atmospheric-induced effects.

I would suspect that that 30 km path was a special test, and that they may not be using those longest, extreme links continuously. Your article goes on to say (near the end):

“Another really fun fact is that we held a link all the way down to 122 kilometers while we were de-orbiting a satellite,” he said. “And we were able to downstream the video.”

enter image description here

Source (Credit: PCMag/Michael Kan)

But for all the links outside the atmosphere, the interaction of near IR with the ionosphere should be very, very weak.

Maybe short breaks in the links or the received intensity can be linked to space junk passing through the beam... occasionally?

Related:

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    $\begingroup$ Not the lasers per se, but using Starlink to locate position like GPS has been happening for a while. technologyreview.com/2022/10/21/1062001/… $\endgroup$
    – geoffc
    Feb 1 at 14:48
  • $\begingroup$ @geoffc that is very cool, thanks! It also links to the original preprint Signal Structure of the Starlink Ku-Band Downlink $\endgroup$
    – uhoh
    Feb 1 at 23:24
  • $\begingroup$ I think measuring space junk would be a great application and seems very doable to me. Also, they could measure the meteor flux which might be considered more "sciencey". $\endgroup$
    – phil1008
    Feb 2 at 7:51
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    $\begingroup$ @uhoh Yes, I think you're right. The signal to noise ratio from beam transits would probably be too low. Space junk and dust meteors probably could not be tallied more accurately than the Space Surveillance Network (SSN) operated by the U. S. Air Force already does. But, you just gave me an idea... $\endgroup$
    – phil1008
    Feb 3 at 5:10
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    $\begingroup$ cicadas: wired.com/story/… $\endgroup$ Feb 4 at 1:39
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Assuming that the satellite laser links are half-duplex then, when they switch from transmit to receive, there might be an opportunity to do some useful space science.

The outgoing beam will sometimes illuminate particles (e.g. shards of space debris or micrometeoroids). Reflected light from those particles might be detectable by the receiver, immediately after switching from transmit mode to receive mode, due to the round-trip light speed delay - if the particles are large enough, close enough, and slow moving enough.

enter image description here

While the Space Surveillance Network (SSN) operated by the U. S. Air Force already detects and tracks objects 10cm and larger (ref), the signals received immediately after the laser links switch direction might be useful for studying and characterizing the distribution and density of smaller objects and particles in this region of space.

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