Video from Artemis II flyby of the Moon will not initially look spectacular
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For those wanting more juicy technical details (aka every reader of ars), the laser communications program is called Optical To Orion (O2O), and details and be had all over the internet, starting with the program source
nasa.gov/goddard/esc/o2o
nasa.gov/goddard/esc/o2o
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I can appreciate that the space-craft side receiver can be blinded by the sun. And when you're visiting the sun near a full moon, there is no nighttime except when you're behind the moon. However, I am quite disappointed that NASA didn't put the emitter on the earth-facing side of the capsule during the approach. There's absolutely no reason the transmission part of the comms package can't just be set to 'send.' There's no need for real-time packet acknowledgement, etc. If you need some sort of feedback to maintain aiming, you can send corrections over radio and/or have a near-zero-bandwidth laser signal that's able to overcome the solar overload.
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Just as long as the public isn't watching video from a camera pointed at a monitor in Australia.
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I have a gut feeling it's more sort of 'sitting' on something around the far side of the dish support, which we can't see in the photo. I wonder if there are pictures from other angles? It does look odd, but lots of things that aren't meant to be constantly filled with people but still people accessible are probably also odd (and scary, like changing the aircraft warning lightbulb at the top of a transmission tower, or climbing up inside the nacelle of a wind turbine)
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The caption from the top image:
Edit: caption has been fixed.
Is it just me having a hard time parsing that?
Edit: caption has been fixed.
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Actually he might have said boobs on the moon, we're not 100% sure...
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The laser comm system is a telescope mounted on a gimbal. I believe it has a star tracker on the gimbal for aiming the telescope, so it wouldn't be able to point very close to the Sun. Also, pointing a telescope anywhere close to the Sun is problematic - the telescope tends to focus sunlight somewhere inside the telescope and melt it. Unless the telescope is specifically designed to avoid this.
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I think that there is a missing clause. It was probably meant to read something like:"the pixellation simulates the low-res video feed that will be available before the hi-res can be distributed."
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We call that carrier bandwidth.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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It's awkward because the dish has to both tilt and rotate. You can see the tilt counterbalance arm on the front side. The walk-way part way up from the base provides access regardless of rotation. I also suspect that there's not a whole lot of people up in the cabin at the top at any time, unless something is going wrong and needs attention.
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Pretty sure he meant higher throughput not the wave itself physically traveling faster or at least I hope he did.
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This is a continual stream from Orion (not just fly-by). Times when there are high res video, it's an optical link stream.
View: https://www.youtube.com/live/6RwfNBtepa4
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No, it looks about that same from both sides - only supported by its connection to the main tower building.
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You can have enough bandwidth for excessively high data rates with either type, since they're bound to be using multi-GHz microwaves and in terrestrial data links you can get many gigabits per second out of only a few hundred megahertz of bandwidth with those. But you need enough signal strength, and that's not happening at these distances without very large antennas and such. A well-aimed laser gets you good signal strength with a much more modest setup, because the beam angle is easy to get very small, so you don't waste most of your transmit power as long as you can maintain aim. I guess you could argue that it's easier to aim because of its different wavelength, but arguably since a laser is on the optical side of the radio vs optics discontinuity, this is a somewhat misleading thing to say. I hadn't expected they couldn't filter out the sun's light well enough to use it more of the time, but I never did the calculations for their setup so hey.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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I would add that O2O is an experimental system. It isn't part of the baseline Orion spacecraft and thus the only spot for it is in the modular experimental bay which is space reserved for mission specific payloads.
In the future it would probably good to have two such optical transceivers and a 3+ sat constellation around the moon and another 3+ sat constellation around the Earth. A comprehensive optical to optical communication network. If you put relays at the EML as well then you could always route around the location of the sun relative to the spacecraft and Earth.
However like all engineering it is crawl-walk-run. The crawl level worked largely as expected and provided tangible benefits. There should be future budgets to expand that concept into a more comprehensive system. Lunar ground assets are unlikely to carry optical comm gear but if they can relay data to a sat overhead using a high throughput radio link and the sat then send it to the optical network they don't need one.
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So random fun... There is a laser receive terminal at Australian National University. (ANU)
https://www.nasa.gov/humans-in-spac...r-artemis-ii-lunar-laser-communications-test/
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It's less awkward than a lot of old windmills. Annoyingly when I do an image search to try to come up with an example all I get are photos of pretty windmills, but there are/were plenty that prioritized function over form.
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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.
The sentence could be clearer but by "quicker" I believe he means a 1 GB file can be transmitted in less time at 200 Mbps compared to 10 Mbps.
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I thought that one was down but it seems to just not be working in the Roku YouTube app. On my laptop it's fine. Very odd.
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Those never work right. You're constantly having to adjust the phase.
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This is the old latency vs bandwidth discussion - the speed at which a signal travels across space (whether through wires/fiber cables, or through space itself as radio or lasers) is distinct from bandwidth. So far as we know, the upper bound of latency is the inverse of the speed of light - that is the best you can do for latency is (distance/C) (EDIT: I accidentally had the numerator and denominator flipped; was re-reading and spotted my mistake), which will give you an answer in a unit of time (usually seconds, but you could use a derived unit like, milliseconds, microseconds, etc - in space, the units might be minutes, hours, or days, because the distances are so vast).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.
But bandwidth is how much data you can transmit PER second. With EMR (ElectroMagnetic Radiation), such as radio, infrared, visible light, ultraviolet, x-rays, etc, you get ever increasing bandwidth as you increase frequency bands.
This is just a function of frequencies, essentially.
For example, in the radio band between 100Mhz and 200Mhz, you have only 100Mhz of total available bandwidth - also, this band is already allocated for other uses, such as terrestrial FM Radio (going from roughly 88Mhz to 108Mhz, Amateur Radio, going from 144-148Mhz, and many other users who've been given slices).
But regulatory allocation aside, the main point remains.
Now consider that from 1Ghz to 2Ghz, again, allocations aside, you have a full Ghz of available bandwidth.
Now, infrared goes from 300Ghz all the way up to 400TerraHertz - that is a giant, giant bandwidth. I don't know if they are using all of that - I doubt it, I doubt they have anywhere near the amount of data needed to saturate such a link.
So the speed the IR waves travel through space is the same as radio, but the bandwidth is much larger.
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You can monitor NASA's deep space network here. It's always cool when they are talking w/ the Voyagers. Voyager 1 is approaching 1 light day distance away(!)
There's a great 60 Symbols youtube video on the challenges of deep space communications.
Also relaying from the surface via an orbiter is how much of the communications w/ Mars rovers works
There's a great 60 Symbols youtube video on the challenges of deep space communications.
Also relaying from the surface via an orbiter is how much of the communications w/ Mars rovers works
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Well, since they are travelling through time, you're trying to get them to time travel to exactly the right time in the past to account for their travel time - they still travel through space at the speed of light, but they can also travel through time, so you can arrange for them to "arrive" at the same instant they were transmitted for real-time communication. It's just super tricky to get that phase right though.
So, like if you are one light year away from earth, you transmit them to a year ago then they travel across that light year for a year and arrive at Earth at the same time you generated them.
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You can ignore the phase, you just need to reverse the polarity.
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Anomalies? Like this?Low-res makes obfuscating/explaining away anomalies that much easier.
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Exactly the end goal would be for individual elements using the shortest link possible. Surface elements talking to overheads sats means the sat is a few hundred km away not 250,000 km away.
A step beyond that is NASA is planning cellular towers on the surface of the moon. So now your surface elements (astronaut on EVA, rover, or remote experiment site) can communication at hundred Mbps or more using <1W of power. Cellular isn't hyperbole or simplification for the masses. NASA intended to use off the shelf 3GPP (i.e. LTE) radios. Why reinvent the wheel. If LTE allows high speed robust communication at a range of up to 10 km on Earth why not use it on the moon.
Now the cellular towers will then need to relay it to overhead sats but they are larger and have larger power budget. The overheads sats will need to relay it to Earth but they combined have constant line of sight, can use optical, and also have higher power budgets. In the diagram gateway was the relay but with the likely death of gateway presumably NASA future lunar constellation would be the relay instead.
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