Here's a paper (from July 2025) on previous steps in this program, getting up the initial testing in flight. Maximum uplink laser power of 20W, though they got good performance all the way down to 2W. The sat has a laser pointing down that was used to help lock on, but it's not clear if it has any meaningful downlink capability, all discussions are about uplink capability. Lots a nerdy details here.
This tells us that the laser terminals have a FOV of +/-2.5mrad in acquisition mode (so before lock on), and +/-0.5mrad in communication/tracking mode. This corresponds ~100km and ~20km radius FOV from GEO to surface.
> "low-latency links", says the article. I wonder if they consider 500 ms ping to be low, or if they want to replace Geostationary with Low Earth Orbit.
Directional laser beams are orders of magnitude to jam compared to radio wave. That alone makes it of big interest for military applications, even with 500 ms latency.
There is several known cases where jamming caused the loss of costly military drones.
> Directional laser beams are orders of magnitude to jam compared to radio wave. That alone makes it of big interest for military applications, even with 500 ms latency.
2. Jam-Resistant Land Mobile Communications
This system uses a highly redundant optical communication technique
to achieve ultra-low, ultra-robust transmission. The basic unit is
the M1A1 tank. Each tank is labelled with the number 0 or 1 painted
four feet high on the tank turret in yellow, day-glo luminescent
paint. Several detection methods are under consideration:
Black box data doesn't need that crazy throughput either though. Traditional RF is much easier to get right, and works even when the aircraft starts losing track of where it is and stops being able to track the satellite with its laser
> These developments entail a future where travellers could enjoy reliable, high‑speed internet while flying, and where people on ships or in vehicles crossing remote regions can stay connected without interruption.
How reliable/feasible would this be on the ground? From what I understand, shining non-trivial lasers in the sky is a massive liability because of the potential to interfere with aircraft. I don't see anything about the wavelength used, but even if it's outside the visible spectrum, it would still be subject to interference from aircraft when used on the ground or at sea.
I'm really curious how the tracking works in such a system, and how "bad" the beam spread is (my impression is that from the diffraction limit alone the beam has to be spread over at least a ~10m radius after travelling 36000km).
Some info on the laser itself would also be very interesting (power? wavelength?).
Perhaps a little, however. Different paths through the atmosphere will perturb the phase of the signal; depending on conditions not all of that ~10m beam width is going to decode with an acceptable bit error rate.
Tracking and actuation is nothing new or particularly challenging, IMHO. It's the laser/optical part combined with throughput at that distance that is the main area of R&D, I think.
There's a patent (2017/0280211 A1) for using this as a data storage method, and there was a company called Lyteloop trying to leverage the idea for data storage with estimations for petabytes across constellation.
The article says 2.6 gigabits/second which is 2,600,000,000 bits/second, 2,600,000,000b/s * 0.5s / 8 is 162,500,000 bytes, 162,500,000 / 1,000,000 is 162.5 megabytes
These beams are much harder to detect and eavesdrop upon. You increase the difficulty for a remote attacker. I wouldn't stop encrypting the data, however:
The Alphasat TDP‑1 has a telescope with an 135mm aperture. The beam diameter is likely to be at least 700m wide according to the diffraction limit.
It's worth it as another layer of security. The beam width being so narrow means even intercepting it becomes harder. This is more relevant for down-to-earth links where the spot hitting the earth is so narrow it could be confined withing a geographically controlled area, rather than hitting an entire continent like longer wavelengths do.
https://www.spiedigitallibrary.org/conference-proceedings-of...
In addition, here's a random paper on the testing performed on the space borne laser terminals - https://icsos2012.nict.go.jp/pdf/1569586689.pdf
This tells us that the laser terminals have a FOV of +/-2.5mrad in acquisition mode (so before lock on), and +/-0.5mrad in communication/tracking mode. This corresponds ~100km and ~20km radius FOV from GEO to surface.
Directional laser beams are orders of magnitude to jam compared to radio wave. That alone makes it of big interest for military applications, even with 500 ms latency.
There is several known cases where jamming caused the loss of costly military drones.
https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid...
Laser comms could prevent that entirely.
I am reminded of RFC 1217 - Memo from the Consortium for Slow Commotion Research (CSCR) https://www.rfc-editor.org/rfc/rfc1217
OTOH the number of engineers that focus on throughput over latency is quite staggering.
The huge buffers are at the two endpoints (:->
That's where I imagine all my deleted data goes.
Here's an article from 2017 about (then) recent installation of what were almost certainly satellite communication antenna.
https://www.twz.com/10470/air-force-one-jet-reemerges-with-u...
How reliable/feasible would this be on the ground? From what I understand, shining non-trivial lasers in the sky is a massive liability because of the potential to interfere with aircraft. I don't see anything about the wavelength used, but even if it's outside the visible spectrum, it would still be subject to interference from aircraft when used on the ground or at sea.
https://www.techbriefs.com/component/content/article/47300-u...
https://news.ycombinator.com/item?id=46709548 - Discussion from a month ago with several links for a recent example.
https://en.wikipedia.org/wiki/Time-division_multiple_access
https://cga.anu.edu.au/research/activities/laser-beam-steeri...
https://www.darpa.mil/research/programs/excalibur
I guess in some ways even the fancy multi diode fiber lasers are phased arrays, just with the single goal of higher output power.
Some info on the laser itself would also be very interesting (power? wavelength?).
Really cool project though!
The spread makes the tracking easier, I suppose.
Basing your security on laser diffusion seems sus.