Video from Artemis II flyby of the Moon will not initially look spectacular
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It's a telescope being made for Orion. Why wouldn't it be specifically designed to not melt?
Presumably, one can put a front optic on the receiver primary that's either a narrow bandpass filter or just a long-pass filter if you're working at 2 um or thereabouts. The filter absorbs the rest of the sunlight. This is basic, basic optics and I'm sure the people at NASA know this. The star tracking could be side-looking.
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Additional article from ANU.
https://www.anu.edu.au/news/all-new...port-for-nasas-artemis-ii-crewed-moon-mission
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You forgot the classic LaForge maneuver to invert the polarity. Phase changes fix small problems when you're really stuck inverse polarity solves it.
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Optical To Orion (O2O) is essentially a technology demonstrator project. I've had the privilege of working with those folks, including visiting some of the optical ground stations. Suffice it to say that, from my observations, they aren't exactly rolling in cash.
Side note: O2O involves some of the same people who were involved in the Deep Space Optical Communications cat-video-from-deep-space hijinks back in 2023. Not that long ago when I was in a meeting with one of them getting an overview of how their stuff worked, I remarked something along the lines of "That's a lot of effort to download a UHD cat video from deep space." I couldn't argue with his reply: "Hey, man. It won a Webbie."
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I guess they were able to test during the high earth orbit, but that's still quite close compared to lunar distances. It might be an Orion demonstrator, but if it can't be used at all for either leg of the lunar transit, it's hardly a lunar demonstrator.
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The optical comm community isn't huge, and has a lot of overlap. And many of the missions work together and build off previous work.
O2O is a terminal that had a nearly identical partner on the ISS. That was ILLUMA-T. ILLUMA-T communicated with LCRD.
OCTL (https://tmf.jpl.nasa.gov/about/octl.php) at JPL is an optical ground station that has supported LLCD, LCRD, TBIRD, DSOC and now O2O.
And these are lasers in the sky, so obviously cat videos are the way to go.
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That's a big part of the equation. Another is that for a given size, you get higher gain from the antenna at higher frequencies. That means that more of your power is going in the direction you want it to - a tighter beam. (Fun fact - every bit of information transferred requires a minimum energy, so more power means more bits per second possible.) With Radio Frequency, that's a big difference, but we can readily see how that works w/ lasers.
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It has been used multiple times after TLI, but depends on capsule orientation, line of site with one of the three optical ground stations, time of day, and weather. Not continuous, but certainly not only in HEO.
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Especially if they start talking about fucking crypto.
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Wave propagation and media speed are two different things. Radio waves and light are the same speed, but due to the wavelength differences, light can carry more data in the same time frame.
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fellow human
Ars Praefectus
Not true, the IR laser can do the Kessel Run in 12 parsecs.I'm pretty sure that the IR laser and the radio waves travel at the same speed.
The data transmission rate is higher for IR because IR photons have a much shorter wavelength than radio wave photons.
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Lasers as carriers of information have very narrow bandwidths. Their information throughput is very high because the frequency is high (short wavelengths) and can be modulated at high rates.
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Per-bandwidth, the information rate is the same. It's just that one can achieve higher bandwidths for modulation of higher-frequency sources.
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Because they didn't have enough room for the NVIDA GPUs to render the images?
/s because you folks are too nerdy to know sarcasm.
/s because you folks are too nerdy to know sarcasm.
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fellow human
Ars Praefectus
yeaaaaaah
Speaking of that though, I do wonder why NASA’s spacecraft visualizer runs at like 2 fps.
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We know the TPE isn't working. If it was, we'd already have seen the video of the flypast.
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Why does "made for Orion" necessarily mean "able to point near the Sun"? There are many possible reasons this may not be a design requirement for this specific piece of hardware.
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The original moon landing was going to be faked, but the studios contracted found it cheaper to film on location?
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You think NASA has enough budget to buy enough GPUs? Have you seen recent prices?
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Because space hardware always runs a couple of generations behind. Partly because of the amount of time it takes for anything to get approved and built and partly because when you spend $100 million on a capsule, you want hardware that has been proven to work in seriously adverse conditions.
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I was bemoaning that NASA had not designed it to operate from lunar space in a transmit-only sort of manner if it was going to have its receiver swamped by solar light. The argument against being able to do that was that it's a telescope so it would melt ... if it weren't designed for that. So I guess my counter is that, a melting telescope isn't a show-stopped to NASA having prioritized that mode of operation. They didn't, so it can't. But that wasn't the discussion.
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A bit surprised that China, given it's plans for the moon, is not making a similar infrastructure investment.
Perhaps they just aren't publicizing it.
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I think a lot of people here aren't versed in communications. Let me clarify your statement to say that lasers have very narrow relative bandwidths. That is, the bandwidth divided by the carrier frequency is a small fraction. However, the absolute bandwidth is potentially high compared to a radio wave communication system. In fact, the absolute bandwidth of an optical signal can be higher than the carrier frequency of a low-frequency radio wave system.
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Bandwidth, resolution? Fair enough; we're still doing comms on the cheap. But dad-gum it, why can't the aperture of the SAW cameras be adjusted? Instead of the Moon we see an over-exposed blob. It's annoying.
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I have a question about this mission. Sorry if it's not directly related to the data transmission, but for the past few days I have been hearing that it will be the first time a human directly sees the far side of the moon.
But during the Apollo missions, there was a module in orbit around the moon with an astronaut inside, while the other two astronauts descended to the moon.
Could the astronaut in orbit not see the far side of the moon?
But during the Apollo missions, there was a module in orbit around the moon with an astronaut inside, while the other two astronauts descended to the moon.
Could the astronaut in orbit not see the far side of the moon?
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Well, they hired Stanley Kubrick, but being the perfectionist he was, he demanded production in location.
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I think the issue is that this mission is further from a full moon than any of the Apollo missions so they'll see at least a limb of the far side illuminated.
Edit: But no, even in the shadow of the moon, eyes won't really see much of anything. The surface would be illuminated with less light than you can imagine on the darkest, new moon night. There's no atmospheric reflection to work with and starlight just isn't all that bright. And lunar regolith is pretty dark as I recall (like an albedo of 0.1 or 0.2?).
If you have sunlight in your eyes, you really don't have a chance.
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The more accurate news people are saying this is the first time areas of the far side are being seen by human eyes.
In other words, the Apollo missions were flying in different orbits and didn’t fly over certain areas. Also, Apollo lunar missions were timed to optimize light on the potential landing sites; even Apollo 8 was IIRC doing a more thorough look at sites surveyed by Lunar Orbiter. And if the timing was optimized for lighting on the near-side landing sites, it would obviously not be good on the far side.
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My understanding might be flawed but I didn't think that the bandwidth of an optical communication system was related to its throughput. In fact, for fiber optics, narrow channels get you greater throughput as the primary way to increase throughput on a single fiber is to cram as many different carriers onto the fiber as possible (wave division multiplexing). I'm not that familiar with free-space optical communications, given that they aren't super practical inside of the atmosphere, but I would imagine it's similar. I don't imagine that WDM is very practical for free-space optics, though I could be wrong.
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That's kind of a cynical take. The kinder reading is that it was named aspirationally. "Please maintain your Integrity, pretty please..."
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I do too! Though it's just a comm outage, or bandwidth wasn't available.
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Even if you're not using amplitude or frequency modulation, you're still limited in information content by the bandwidth of what you're using as your encoding scheme. There's just a different coefficient in front of it. The Wikipedia article on optical fiber transmission has some good background on the bandwidth, bits/Hz, etc. of the various schemes.*
It it theoretically possible to use a high switching speed along a low switching speed at the same frequency. However, it's worked out better to use all that bandwidth per color and multiplex different colors instead.
* and take a look at some of those modern bandwidth numbers! For the IR light being used the frequencies are probably in the 150-300 THz range and they're using almost 40 THz. That is not the norm for optical systems!
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Voix des Airs
Ars Praefectus
I actually asked someone here (where I am) who knows about such things the other day and the answer I got was that the Apollo lunar orbits were very low, on the order of 100 miles above the lunar surface. Artemis will be much, much higher - like 4000 miles or something. So Artemis will be able to see a lot more of the far side of the moon than Apollo orbiters could.
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Melting if it pointed to the Moon is just one of the examples I picked for why it's not a trivial thing to do. And it only applies to this specific flight, because the current phase of the Moon places Earth close to the Sun as seen from this lunar orbit.
I'm not sure what your overall point is. Are you asking why the O2O's requirement doesn't call for continuous communication throughout the flight for any possible trans-lunar trajectory? I would guess it's because the O2O is a supplemental system, and not a mission-critical communications link.
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My entire point was to quote myself from earlier "[h]owever, I am quite disappointed that NASA didn't put the emitter on the earth-facing side of the capsule during the approach."
I realize it's a non-critical system. But if it worked, people would really rather see high-definition video of the flyby than a slideshow. It's like the launch. There was apparently awesome high-def footage looking down the launch tower that was released only after the mission was progressing. Why on earth wouldn't NASA have prioritized that? NASA needs public support. Good livestream quality would have been a way to accomplish that. Is it mission critical? No - not if one narrowly defines the mission as being the objectives of the Artemis II launch. However, that sort of thing IS mission critical for NASA as a whole.
And it's not mission critical. So if NASA had tried their best to send high-def video and it cut out, so be it. It's just a massive oversight on NASA's part (and I'm not overstating that) to miss the PR opportunity.
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