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Hey, I worked on this. Glad to see it getting a lot of press :).
by rumdonut 4y ago
Hey, I worked on this. Glad to see it getting a lot of press :).
- tiffanyh 4y agoAnything you can share on latency? (congrats on the achievement)
- Rebelgecko 4y agoIsn't it just "distance/c"? (or something like 0.999c since light is a bit slower in the atmosphere)
- tiffanyh 4y agoThat's why I actually ask. E.g. "light travels approximately 1.5x slower through optical fiber than in a vacuum" https://www.commscope.com/globalassets/digizuite/2799-latency-in-optical-fiber-systems-wp-111432-en.pdf?r=1 https://www.commscope.com/globalassets/digizuite/2799-latenc...
- bloggie 4y agoFun and somewhat related fact - this is one of the main advantages of hollow-core transmission fibers! As far as I know, currently only used to extend the range of HFT orgs...
- ccakes 4y agoTerrestrial radio links are similar in that they can be lower latency than fibre though spectrum concerns can come into play.
- brianwawok 4y agoRadio links can also often be straighter. Easier to go over someone’s house then ask permission to dig a trench.
- itishappy 4y agoHollow core fiber? Total internal reflection requires the core to be a higher index of refraction than the cladding, so I wonder how that works! Turns out, it functions differently. Instead of total internal refraction it has to rely on weird physics like photonic crystals. The pictures are absolutely wild. https://www.rp-photonics.com/hollow_core_fibers.html https://www.rp-photonics.com/hollow_core_fibers.html https://www.google.com/search?q=hollow+core+fiber&tbm=isch https://www.google.com/search?q=hollow+core+fiber&tbm=isch
- aaronax 4y agoFascinating; thanks for the links. I wonder how the splicing process works for that.
- Arnavion 4y ago("1.5x slower" == "its speed in optical fiber is 1/1.5 = 2/3 of the speed in vacuum")
- discordance 4y agoIt's all relative.
- Kye 4y agoAre you able to talk about what kind of hardware is on the satellite? I'm curious if it's commodity like the Mars helicopter or something made for the purpose.
- Aromasin 4y agoNot OP, so I'm guessing purely on my knowledge of how most of the industry works, but there's likely some sort of FPGA with custom IP at the center, connected to a powerful optical transmitter/receiver. Associated reading can be found here: https://www.esa.int/Enabling_Support/Space_Engineering_Technology/Microelectronics/The_use_of_reprogrammable_FPGAs_in_space https://www.esa.int/Enabling_Support/Space_Engineering_Techn... https://ntrs.nasa.gov/api/citations/20150009433/downloads/20150009433.pdf https://ntrs.nasa.gov/api/citations/20150009433/downloads/20... https://www.fierceelectronics.com/electronics/fpga-enables-high-bandwidth-space-systems-lower-system-cost https://www.fierceelectronics.com/electronics/fpga-enables-h...
- error503 4y agoThe main paper seems to be behind a paywall (rolleyes), but I did find this synopsis that covers the basic approach and hardware: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4406&context=smallsat https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4... It sounds like this test payload was part of a larger CubeSet built by NASA, but the actual datacom components seem pretty much off the shelf (besides the optics). 100Gbps transceivers, an optical mux, and an EDFA - all common in terrestrial telecom - and some IR optics to collimate the beam.
- iwillbenice 4y ago
- wmlavender 4y agoIs this likely to work at Lunar distances anytime soon? I saw that the James Webb telescope people were unhappy about losing much of their communication time on the Deep Space Network to the Artemis 1 mission. Could this be more cost effective than an major upgrade to the Deep Space Network? How about at Earth-Sun L1 and L2 distances?
- elihu 4y agoI would expect L1-to-earth communication to be problematic because you'd have to distinguish the signal from the background radiation of the sun. It'd be interesting to know what the technical limits are in terms of output power and aim/focus. Generally, doubling distance means the signal power drops to 1/4th, and maximum data capacity of a communication link is proportional to the signal/noise ratio. So that would mean a 100 Gbps link might drop to 25 Gbps. You might be able to bring the signal/noise ratio back up by using a better detector or a more powerful laser, or aiming better. Or maybe the 100 Gbps data rate is limited by the transceiver, and there's actually plenty of S/N ratio margin that can be traded for range without affecting data rate at all.
- wmlavender 4y agoIf L1 is a problem, then L2 would be a problem as well. After all, at L2 the spacecraft is receiving its commands from the direction of the sun. However, the problem is not quite as bad as it seems. Spacecraft at L1 and L2 Lagrange points actually are in a halo orbit that "orbits" around the Lagrange point. Attempting to stay at exactly the L1 or L2 point is unstable, since gravitational forces tend to knock you away from that point. The halo orbits are much more stable. And for a spacecraft in a halo orbit, you never have to point your antenna directly at the sun. The problem is solvable for radio communication at least. There are currently 4 spacecraft orbiting the Earth-Sun L1 point (ACE, DSCOVR, SOHO, and WIND) as well as 3 spacecraft at the L2 point (Gaia, James Webb, and Spektr-RG).
- cycomanic 4y agoThe issue is not so much background radiation (you'd have similar issues with RF), and your SNR is going to be reduced because of diffraction (as you rightfully point out goes at r^2). However the SNR would still be much better for optics because diffraction scales as 1/lambda. The reason why JWST did get an optical link is that people developing these things are rightfully conservative and optical links in space are really still under heavy development.
- sizzle 4y agoSo nice to hear from you, thank you and your teammates for advancing the state of science and space exploration.