161–170 of 469 posts
My understanding of the state of the art of inter-satellite optical links is that they have only been used between satellites that are basically in the same orbital plane and in more or less the same orbit. That is, the angle from one satellite to the other changes very very slowly, so that the optics don't have to do much tracking -- and consequently satellites can only form an optical link with other satellites tha…
Earlier quoted context omitted.
How do you spot a satellite? I've never seen one.
1. The satellite needs to be passing overhead at an angle where you can see it, and clear skies etc. 2. The sky needs to be dark enough to see it (so twilight or night) 3. The satellite needs to be illuminated by the sun. 4. The satellite needs to reflect enough light that you can see it. Basically this happens just before sunrise, and just after sunset. So the ground and sky are dark (allowing you to see through the…
I've seen plenty of satellites in the middle of the night, from very dark areas (wilderness). They look like stars, only they move more quickly. These observations go back a decade, at least.
Random thought I just had: What are the odds of a rocket launch crossing through one of these laser links on its way to a higher orbit and disrupting traffic for a fraction of a second? I know space is really big and so the odds of a rocket hitting a satellite on its way up are incredibly low, but now we're talking about lots of lines between each satellite rather than just the satellites themselves. Are the odds sti…
I sit in my hot tub at night and see 1-2+ satellites go over every single time I'm out there. Which also makes me wonder how many of the shooting stars I've seen recently are just old starlinks burning up.
How do you spot a satellite? I've never seen one.
My understanding of the state of the art of inter-satellite optical links is that they have only been used between satellites that are basically in the same orbital plane and in more or less the same orbit. That is, the angle from one satellite to the other changes very very slowly, so that the optics don't have to do much tracking -- and consequently satellites can only form an optical link with other satellites tha…
Take a look at the slides from the presentation, I think the geometry clearly shows cross-plane links in the mesh. Having worked on these types of systems, I've had more difficulty with the lookahead angles (rx from where the target was, tx to where it will be due to speed of light) than the tracking -- fine tracking performance was required for all modes, and it largely became a GNC and acquisition time issue (since…
Sounds very cool that cross-plane links are doable, even if they have predictable complications compared to in-plane.
I would have thought that someone would make a big deal (have a press release, e.g.) out of successfully establishing cross-plane links, but maybe it just doesn't seem that impressive to people who already have good enough precise predictive ephemerides or satellite states to make those links in the first place.
[flagged]
I'm immensely interested in people commenting how they are disinterested in X thing. Please go on! I'd love to know the motivation of posting, it makes no sense to me. Seems to be a self-fulfilled prophecy.
Earlier quoted context omitted.
Phased array antennas probably have a lot to do with this. You can aim the signal more accurately and faster than any mechanical system ever could.
Laser links are not using phased array antennas. It's a physically moving "turret" with a laser and another with a receiver. And they need to be separate units, because the speeds and distances involved are long enough that you are not receiving from the same direction as you are sending.
It's a thrill to think about that. Starlink is really out there.
I bet this is lost on a lot of people. Not to patronize anyone, but what Tuna-Fish is pointing out is that due to the speed of light, the distance between satellites and their relatives velocities, when one satellite is beaming data to another satellite it must aim where the receiving satellite will be, as opposed to where it is now, when the light arrives. Further, the receiver must be looking at where the transmitter was back when the signal was sent, as opposed to where the transmitter is now. And because this is all bidirectional, each satellite must send and receive in different, continuously changing directions at the same time.
My understanding of the state of the art of inter-satellite optical links is that they have only been used between satellites that are basically in the same orbital plane and in more or less the same orbit. That is, the angle from one satellite to the other changes very very slowly, so that the optics don't have to do much tracking -- and consequently satellites can only form an optical link with other satellites tha…
Tracking is an issue, but doppler can also be a thing. At orbital speed (actually up to 2x orbital speeds) the doppler effect between two satellites can change the frequency enough to cause interference. Moving a scope to track a moving target is one problem, allowing the algorithms to adapt at the frequency shifts on the fly another.
Random thought I just had: What are the odds of a rocket launch crossing through one of these laser links on its way to a higher orbit and disrupting traffic for a fraction of a second? I know space is really big and so the odds of a rocket hitting a satellite on its way up are incredibly low, but now we're talking about lots of lines between each satellite rather than just the satellites themselves. Are the odds sti…
I think you could take the time a rocket would be in the way and compare it to the time it would take any given satellite link pair to make an orbit to form an estimate of the chance of a single interference. Then multiply by rockets and satellite pairs to form an overall estimate.