100 Gbps achieved from space to Earth
news.mit.edu
news.mit.edu
Imagine looking at a shell on the bottom of a swimming pool while there are ripples in the water....
Usually the shell is a bit distorted. But at some points in time, you see two shells... And other points in time, none.
If the water represents the atmospheres shimmering due to changing density, and the shell represents the satellite you're trying to receive data from, then at some points in time, you won't be able to receive any data at all, because the receiver cannot see the satellite.
Network links that are up and down every few milliseconds aren't very useful for much apart from bulk science data download. Perhaps that's why this is marketed for science missions rather than space internet?
That said the first rollout of optical comms is to intersatellite links. There the only issue is loss due to diffraction (and pointing etc., but that's a different discussion). Optics has a big advantage because diffraction is proportional to the inverse of wavelength, and the wavelength of light is several orders of magnitude smaller. This determines the size of the transmit and receive antennas/apertures needed, or the loss for a given size. For realistic parameters optics would have 30-50dB less loss which is translates directly to SNR and thus allows the much higher rates.
Source: Doing research in this area
in addition to tracking/telemetry/control low data rate radios in the L/S-bands.
If biased properly an APD can be used for single photon counting and they only cost $70-250, I’m just not sure if they hold up in space without modification.
The cryogenics allow using cryogenic-level bandgaps/carrier-energies, so each optical photon turns into many carriers which then flow out the wire in both directions, the delay between the pulse on both ends localizes the impact along the wire.
The deep space optical demonstrations I know of all work in the near infrared (e.g. 1550 nm), just like most of terrestrial fiber optics used for communication. Probably because there's lots of infrastructure at that wavelength already, and it's a good passband through earth's atmosphere.
I have had to live off a personal satellite in the middle of uncivilized nowhere for a year (literally). Packet loss is the true regulator of speed irrespective of bandwidth numbers.
How about at Earth-Sun L1 and L2 distances?
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.
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).
When the Psyche spacecraft launches and heads to the asteroid belt (was supposed to launch in august) it will do the farthest (by far) lasercomm demo. I work in the group that made the SNSPD ground receiver. As my boss says, with a distance 1000x farther than previous space laser comm demos, closing the link is 1 million times harder...
Fun fact: when the Phyche comm laser is pointed at earth, the size of the spot will be roughly as large as California. Even with the largest optical telescopes, the loss in this link will be insane. That's why you need single photon detectors.
As you get to farther and father distances, one thing you can do is shift from on/off keying to large-M Pulse Position Modulation. This way you can save up the power on your satellite to send fewer but higher power laser pulses, each of which carries more bits of data. I believe the DSOC mission will go up to M=256. Meaning each pulse of photons received on earth will carry 8 bits of information based on when it arrives within an alphabet of 256 time bins.
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.
Associated reading can be found here: https://www.esa.int/Enabling_Support/Space_Engineering_Techn...
https://ntrs.nasa.gov/api/citations/20150009433/downloads/20...
https://www.fierceelectronics.com/electronics/fpga-enables-h...
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.
(congrats on the achievement)
E.g. "light travels approximately 1.5x slower through optical fiber than in a vacuum"
https://www.commscope.com/globalassets/digizuite/2799-latenc...
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.
It takes about 3 days with the Apollo launch system to get from the Earth to the Moon. So if you load roughly 800 4TB portable hard drives into one of these and fly it to the Moon, this will result in an average transmission speed of 100Gbps, if my math is correct.
At that point, what advantage is there in sending a rocket to receive the transmission and then carry the data back when you can just use the exact same link to send the data straight to Earth?
Theoretically, they could carry some number of disks into orbit, fill them, and then drop them back on parachutes. Something like that is actually what the earliest surveillance satellites did. They dropped film from orbit that the military retrieved and developed.
"Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway."
Was surprised to see that Amazon Snowball also exists and serves the same purpose :)
https://www.dlr.de/content/en/articles/news/2016/20161103_wo...
It all depends on the kind of corruption. Periodic spikes, white noise, blackouts - different problems need different solutions
Fun factoid: Reed and Solomon were working at MIT Lincoln Laboratory (ie where the OP result is from) when they invented RS codes. ISTR they were also working on satellite comm, in which Lincoln has a long history.
[Source: I spent a decade there myself and drank the kool aid.]
802.11 data frames also have an acknowledgement at the MAC layer. The radios dynamically ramp up the MCS rate until packets start dropping, then ramp the rate back down.
I'm assuming most of what this would be used for is imagery collected from space. For whatever reason, other commenters seem to think this is for holding conversations, but it clearly says it's for data from science missions. Even if you were trying to talk to someone on the other end, though, it's rarely that big a deal if part of a word cuts out. That happens all the time with existing ground-based calls or even just two people in a loud room and the human brain knows how to handle it.
I moved from NZ where we'd done probably one of the best fiber rollouts of any country; I had 1Gbps into an apartment from about 2016 or so. Before that I'd had 200ish mbps into a house in the suburbs in about 2014 thanks to the previous tenants having run a business from the place and paid for a line in.
Now I live in the UK I can see why it's hard - too much history/housing here is just built up far too much/not built up in a modern way either. Also I think when obtaining permissions from property owners in the case of flats, Kiwis are generally more likely to approve of something like that than people here.
Wake me when telecommunications industry gets their shit together.
I know the laser links themselves might not be new, and while it hasn't been done like this, we knew that it would be possible considering we've done a ton of variants (sat-to-sat, station-to-station, over fiber, over glass, in open air, in a vacuum), even just hitting the beacons on the moon and measuring the reflection somewhat shows that long-distance links could be done. Maybe the new-ness in the laser aspect is the small satellite and energy package compared to high-powered lasers you might expect?
So maaaaaybe you could have a really painful conversation with someone the moon, but not Mars.
edit: This is WITHOUT any latency introduced by the link/protocol, or if you have to then route the message from one side of the earth to the other, just time-of-flight distance calculations, so the absolute minimum possible latency.
You'd be continually talking over the other person.
Well, the Moon's semi-major axis is about 380000 km, which means latency is lower-bounded to about 1 s.
Similarly, Mars' closest approach is 54.6 million km. That means a latency lower bound of 3 minutes.
1. speed of light through atmosphere, so basically c 2. line-of-sight is required, likely stationary base stations. Probably also subject to atmospheric and weather conditions
Seems like they are miles ahead of the MIT team which is still in the demo stage.
But as the FSO link is point to point, you would need something like a high-altitude platform station (HAPS) like a blimp, UAVs with RF or a RF tower on the ground to receive the FSO signal, and then broadcast it to many users.
[1]https://www.nctatechnicalpapers.com/Paper/2018/2018-analysis...
https://www.six-group.com/en/products-services/the-swiss-sto...
Low earth orbit is 3,000 km or so, meaning that's only 10 ms each way.
Odds are good that if you had a mesh network of low earth orbit satellites (like Starlink) you could actually get an antipodal point-to-point video call with less latency than with terrestrial fiber. That's not a function of bad terrestrial switching/routing: it's the fact that light travels faster through vacuum.
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A gaming computer can use 1000W. Google says spacecraft radiators reject 350W/m^2.
If my math is correct (no guarantees) you'd need a king-sized-bed-sized panel just to cool your rig.
Not to rain on your back of the napkin math. Although I think your sentiment is right, the cooling systems for computers in space would need to be bigger since you can use convection to move the heat away.
Computing isn't doing work in the physical sense. An HDD of ordered data doesn't have more potential energy than an HDD of data in a different order.
c / (2/3) = ~1.5
For almost all other applications the factor 1.5 you gain from free-space vs fibre is not worth it. A trip around the equator in an optical fibre takes 200ms. That is acceptable for almost everything. Moreover, the latency of using any something free-space would likely not be much better, because one would need to regenerate at least 3 times (which might add ~10ms or so for each regeneration)
Air barely refracts light, and glass refracts it heavily.
BTW laser links are prone to work worse in bad weather. Microwave links are often used instead.
Overall, services across the board seem to be worse than they were 10 years ago. And yet the tech is certainly more advanced. Really disappointed as a whole with the telecommunications industry. Maybe that's the field I should have focused more on, as they seem to be struggling to improve things even with technological breakthroughs such as this.
Just a shame.
I don't see how this relates to the use-case of millions of broadband users that you are talking about where you are routing fiber cables all over the place. We do have 800-gigabit fiber in core networks, we just don't route it to every home b/c why would we. And 5G radiates to 1000s of users simultaneously.. regularly getting multi-gigabit speeds on mmWave as a regular user is pretty amazing to me.
Do you live in the US? The pathetic state of telecoms in the US is a US problem, not a global problem. In many other places, our internet and cellular service is fast and cheap. But you guys don't like regulation or competition, so this is what you get.
You might find a better experience doing the same. I've found 5G to be truly awful and I live in one of the biggest cities in America where you would expect better infrastructure.