You want your Moon landings in HDTV? So does NASA. Here’s how it’s happening.
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The last few years have made me more and more cynical about the US space program. Despite this, the thought of being able to watch a human moon landing in HD still manages to excite me. And they are using space lasers!
Also, high-speed single photon detector - those got to be useful for more than streaming videos.
Also, high-speed single photon detector - those got to be useful for more than streaming videos.
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It would seem to me that launching a few receivers in LEO (above the clouds) where they could receive the data and then transmit it back either through integrating with Starlink's distribution system or directly to ground stations would be a reasonable investment, if laser communications is the future.
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There's probably a reason, but if space-to-space is feasible and SpaceX has already done it for satellites, why cant they do space-to-space optically then normal satellite-to-ground using whatever SpaceX/DirectTV use to send bandwidth to Earth?
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For people curious about how the detectors work, here's an explainer from the quantum networking group at NIST. The basic idea is that you have a small bit of superconducting material held at the cusp of the transition to a normal metal. Photon hits, deposits a tiny amount of heat, but because the slope of the resistance curve dR/dT is enormous, that tiny amount of heat means a relatively large and easily measured change in resistance. You have single-photon sensitivity, and fast recovery so you can count with very little dead time.
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Ars Legatus Legionis
We are living in science fiction. That sounds like something a Star Trek crewman would suggest to solve the problem of the week.
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I know it won't be available in time for Artemis IV but the plans is to have a constellation around the moon so it would make sense for NASA to extend that to one around the Earth as well. Radio works fine going Earth to orbit. Laser communication backbone between Earth constellation and Lunar constellation. Spacecraft and ground elements talking to lunar constellation. Earth constellation talking to the ground. 24/7 zero downtime ultra high bandwidth deep space comms.
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Ars Legatus Legionis
I think longterm that will be part of the plan. NASA wants to build a lunar constellation with optical backhaul capability. Linking that to a small constellation in Earth orbit would provide flexibility and high uptime.
They don't even need to be LEO sats or all that numerous. Three GEO sats would provide continual relay coverage. Maybe a fourth would be a good idea to provide some redundancy and better near sun avoidance. From there you have lots of options for the last mile (well last thousand miles). From there you could extend the network to Mars and supporting individual deep space vehicles. However even the lunar constellation isn't going to be in place before 2032 and full capability NET 2035.
For the lunar landing they absolutely need some interim solution for 4K video so I am glad they are working on things. It probably even makes sense to schedule the EVA to align with primetime viewing and ideal optical ground station alignment.
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If you want to read more about RealTOR (the COTS Superconducting Nanowire Single-Photon Detectors (SNSPDs)), you can read it here.
https://www.nasa.gov/glenn/glenn-ex...tion/scan/real-time-optical-receiver-project/
https://www.nasa.gov/glenn/glenn-ex...tion/scan/real-time-optical-receiver-project/
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And more about LCOT (Low Cost Optical Terminal) testing, it's here.
https://www.nasa.gov/technology/spa...s-first-laser-communications-uplink-to-space/
https://www.nasa.gov/technology/spa...s-first-laser-communications-uplink-to-space/
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It's interesting that they went with liquid helium cooling for detection at 1550nm rather than more conventional telcom detectors based on ingaas at non-cryogenic temperatures. I suspect that long term they can probably improve the hardware enough that cryogenic cooling isn't needed.
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Quantum Opus:
"turnkey nanowire systems, superconducting single-photon detectors, and bias/readout electronics"
H-ly C--p!
"turnkey nanowire systems, superconducting single-photon detectors, and bias/readout electronics"
H-ly C--p!
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Is this comparing the optical amplifier power to a modem + amplifier (s-band transmitter)? I don't think this is correct as an apples to apples comparison, typically optical systems are 10's to 100's of W for the full chain. The actual final gain amp may be on that order but its far from the only part you need to make the system work.
On a per bit transmitted basis optical does win (because you get so many bits) but the power is not substantially better than RF, you just get more for the money.
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It's likely that SpaceX has built their kit to look for other objects in orbit rather than out into the general void. Though I'm sure they'd enjoy the cash if they were contracted to put stuff up to do it.
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Hi Eric, please correct the errors with the bitrates in the article. B's and b's are mixed up all over the place, which of course denote drastically different values
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260Mbps is correct also according to the post by Quantum Opus' co-founder, so definitely not "260MB per second".
For further reading… here's the research paper about Orion's optical comms architecture.
https://ntrs.nasa.gov/api/citations/20250010065/downloads/R3O2O ArchTestSyst_Impl_Rossoni.pdf
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260Mbps is correct also according to the post by Quantum Opus' co-founder, so definitely not "260MB per second".
All this also likely needs to be corrected to Mbps.
I didn't find hard data, but most likely this was the rated RF output power. The way it's phrased can make people think this was the power consumption of the transmission equipment — which in reality is about twice as much. I'm sure some engineers here can chime in.
For further reading… here's the research paper about Orion's optical comms architecture.
https://ntrs.nasa.gov/api/citations/20250010065/downloads/R3O2O ArchTestSyst_Impl_Rossoni.pdf
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"260 Mbps. At those speeds, the crew could have transmitted a full high-definition movie to Earth in seconds."
Really? Because either your figure is off by a few orders of magnitude or your math is just plain wrong...
Really? Because either your figure is off by a few orders of magnitude or your math is just plain wrong...
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Eh? If they’re using an efficient codec like HEVC this is probably achievable at acceptable bit rates. 700 MB isn’t a huge output size for a 2h video in this regard, so about 25-30 seconds to transmit at 260 Mbps?
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Thinking back to a previous article about phased-array antennas - would the Northwood solution only work in near-earth orbit?
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Surely not -- there wasn't a single mention of reversing the polarity of anything!
Most likely it requires a decent telescope at the receiving end to achieve decent bandwidth. Nothing Hubble-grade, but on the order of a high-end hobbyist telescope -- 8-12" primary aperture, say. I'm basing that on some foggy memories of presentations at various conventions over the years from people working on interplanetary laser comms.
The nanowire detectors allow high speed and getting away with smaller, cruder optics, but one of the key tensions in such a system is always going to be the pressure to achieve maximum data rate with minimum power at the remote end, because that's where the power budget will always be tightest.
Rather than a LEO constellation with all the associated issues of target tracking, my assumption would be some sort of low-count constellation in MEO or maybe GEO (slower orbit, less tracking hassle, handoffs less often), of lasercomm units pointed outwards, and using TDRSS/DSS for the "last mile" to Earth's surface. Starlink probably wouldn't work unmodified (pointing the wrong way, for one thing), but a future-gen Starlink or a Starshield variant optimized for NASA usage seems entirely possible. Not to mention the various Starlink competitors coming down the pipe.
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Ars Legatus Legionis
25 to 30 seconds is not what most people think of as seconds. If it had said in less than a minute that would have been more clear. 260 Mbps is ~ 2GB per minute.
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Agreed. This is one area where higher is probably better. Laser free space optics don't play nice with the sun. There were times Artemis had to turn off the optical experiment because the angle between the sun and the ground station was too low. By putting your sats (ideally at least 4) in GEO ideally you would always have at least one with reasonable angular separation from the sun when viewed from lunar orbit. You would also gain redundancy in that at least two should have line of sight at all times.
Going to HEO would also be an option but GEO has the advantage of nice simple static ground stations. TRDSS is reaching end of life and DSN has limited throughput but GEO to Earth comms at the hundred Mbps level is a solved problem. You could use have Starlink relays but even GEO direct to the ground works. It isn't like latency on the final link really matters when the moon is >1 light second away.
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I suppose I just gave Eric the benefit of the doubt on this one since it didn’t strike me as a major blunder.
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For those curious, photon counting isn't all that new. Photomultiplier tubes (PMT's) have been doing this for a long while. However, what is new with these superconducting nanowire doodads is the quantum efficiencies involved. PMT's might peak at 0.4% of photons converting to electrons whereas these nanowire things can just about reach 98% under ideal lab conditions.
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The logical answer to cloud-cover issues that popped into MY head was to not try to beam the data all the way to the ground, but to a satellite that would convert the laser back to a radio wave and beam the data to wherever it needs to go on Earth.
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theradicalmoderate
Ars Tribunus Militum
By and large, the Starlink inter-satellite laser links are focused on targets that don't move very much. Each bird has a link ahead of and behind it, to satellites in the same orbital plane, so they're effectively stationary to its own flight path, and a link to the satellites to the right and left of them, in different orbital planes. These move very slowly most of the time, but they do cross from right to left and left to right when the birds in question reach their maximum latitude.
In all of these cases, the angular slew that the laser has to deal with is very slow, and the targets are no more than a few hundred km distant. So it's fairly easy to lock onto the target and maintain the lock via a feedback loop.
When you're sending stuff from the Moon, the target's a lot farther away, and it's moving at a fairly high angular rate. Both of those make maintaining the lock more difficult. The good news is the beam is quite a bit wider at the target, so as long as the target is adequately sensitive (wider beam = lower flux of photons hitting the detector), somewhat greater pointing errors are allowed.
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If they've proved the feasibility of a low-cost ground laser terminal, I wonder if multipath protocols through dispersed ground stations would work.
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So a fun fact about Apollo communications. The provider was initially not on contract to provide video, just audio and they would develop the film when they returned. The engineers looked into it, and went back to NASA and said, you know, we could also do video. NASA's response was OK, but if it causes a schedule slip, it gets axed. It didn't.
Source: I talked to some old-timers who worked on it when I wasn't an old-timer.
Source: I talked to some old-timers who worked on it when I wasn't an old-timer.
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Would it be feasible for at least some Starlink satellites to have a space-facing laser sensor?
If so, they cover all the globe and could be used as a kind of "last mile" relay, at least for reception.
Two way would be a different beast though.
If so, they cover all the globe and could be used as a kind of "last mile" relay, at least for reception.
Two way would be a different beast though.
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Sending signals is trivial. We aren't limited to a single watt for transmission. You can massively up the intensity of the signal and then you don't have to rely on nearly perfect superconducting photon sensors. One can also make larger focusing mirrors so that you can focus to a very tight spot where your orbiter is.
As to a distributed array, I don't know how much benefit that is for receiving. NASA says they need 40 ground-based, world-wide sensors to ensure cloudless access. I suspect the transmission beam isn't that large such that you could detect the emissions from opposite sides of the earth. Instead, the emitter aims at southern Australia (e.g.) or possibly even a tighter spot than that. As such, if you only had 3 or 4 satellites in polar orbit, you're pretty likely to have one in visual range that isn't being blinded by the sun.
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I am curious about targeting, and this isn't mentioned in the article. How precise does targeting need to be? I imagine that one of the reasons that single-photon counting is required is because of the dispersion of the laser beam. Which, I presume is different for a ground based station compared to a earth orbiting one. So, maybe, a ground based station has the drawback of intermittent coverage but the advantage of not requiring extremely precise tracking from the transmitter side?
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In one paragraph they said: "50KB per second... 3MB to 5MB per second... 260 Mbps" - so three different units! Could you please cut that down to just two? It's even possible to say "50KB/s, 3,000-5,000 KB/s, and 32,500 KB/s" which gets that down to one unit, but two units would be acceptable.
Later they said "bandwidth about 100 times greater" which implies 260 MB/s instead of Mb/s, and then they explicitly said "maximum rate of 260MB per second", but apparently that is wrong!
The more I read the less certain I was about any of the transmission speed numbers.
Later they said "bandwidth about 100 times greater" which implies 260 MB/s instead of Mb/s, and then they explicitly said "maximum rate of 260MB per second", but apparently that is wrong!
The more I read the less certain I was about any of the transmission speed numbers.
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So space X can stream live 4K video through a full re-entry sequence on the starship, even through the fabled plasma comms blackout.
NASA cant even get high data throughput, 4K or anything even close on SLS or orion etc etc.
It just shows how poor NASA values imagary Quality and openness.
Orion could or rather the service module fire the laser directly to Starlink V2's in LEO and then they can down link the data via normal comms links.
With the contracts for MoonNet out there for tender it seems stupid that for the moon and mars, that Starlink V2's are just not sent out there i a 100+ constallation. Its known unltra reliable and have already proved laser links, with some refining it wold be faster, cheaper and more relaible to make a moon and Mars Net version as the majority of thew work is completed already.
NASA cant even get high data throughput, 4K or anything even close on SLS or orion etc etc.
It just shows how poor NASA values imagary Quality and openness.
Orion could or rather the service module fire the laser directly to Starlink V2's in LEO and then they can down link the data via normal comms links.
With the contracts for MoonNet out there for tender it seems stupid that for the moon and mars, that Starlink V2's are just not sent out there i a 100+ constallation. Its known unltra reliable and have already proved laser links, with some refining it wold be faster, cheaper and more relaible to make a moon and Mars Net version as the majority of thew work is completed already.
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Scotty: "Activate the superconducting nanowire single-photon detectors?!? I can't change the law of physics! I've got to have 30 mintues!"
Geordi: "My visor is picking up superconducting nanowire single-photon detectors in the warp coil."
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I don't know the physics of it, but why not put receivers in orbit that could retransmit the signal to receivers on the ground? Put enough of them in orbit and there will always be some place on earth that can get a bounced signal. Or maybe translate it into a signal that can get through the clouds and send it down. Either way, I would think there are other solutions possible.
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For anyone not familiar with the difference between lower case bits and upper case Bytes, these numbers could be a little misleading. I know most folks reading ars would be aware, but maybe not all.
As written, the jump goes from 3-5MB/s to 35.5MB/s, still an oder of magnitude increase, but not two.
Beyond that, a fascinating article
As written, the jump goes from 3-5MB/s to 35.5MB/s, still an oder of magnitude increase, but not two.
Beyond that, a fascinating article
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yeah, but maintenance and servicing and upgrade is a whole lot easier for 40 ground based 1 meter telescopes than 4 in GEO. As I recall, an off the shelf 1 meter telescope with all the positioning, etc. is less than $1M. $5M for the complete ground station is pretty easy to imagine, esp if we’re not doing fancy cryogenic receivers, so $200M for the whole network (which could be used for other things, too). And if one breaks, putting in a new station is easy.
I’ve seen concept pictures of this class of optical ground terminal in a standard shipping container.
And you can build out the network over a few years, and learn from the experience.
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