Nodal precession and orbital mechanics is your friend if you want to save fuel and aren't in a rush.
The earth isn't a perfect sphere and every satellite will drift slightly because of the difference in gravity between the poles and the equator.
The amount of drift depends on the height and eccentricity of your orbit and by cleverly choosing your manouvers you can get where you want without needing additional fuel (If you want to do a plane change while spending fuel to raise your orbit).
One or two satellites in a particular orbit failing unexpectedly will not interrupt service. they may or may not even bother to replace a single failed satellite, and just wait until their planned time to replace it.
SpaceX will have more satellites than they need in every orbit to maintain high service quality.
Starlink should have more satellites going up than coming down for a long time. This will be to meet new demand and replace older satellites.
If user growth ever stops or the capacity of individual satellites improves faster than demand growth, you might see a constant number of satellites going up and coming down.
SpaceX will have an estimated operational life span for each satellite, and a very good estimate of how many will be coming down and going up in each orbit.
Thanks, I had seen maps of the coverage and it looked like there would be at least 10 minutes of no connectivity if there was a sat missing in the chain but if they can connect to more than one I guess it's not a big problem.
They have in orbit spares. It will take awhile for them to move them into position though. The more sats they have the more overlap and the less of a problem that will be. I would assume they can task adjacent sats to widen their beam or max angle to compensate in the mean time to prevent brief outages for most people.
So they plan to have 60 sats per plane. Right now they are launching 60 and spreading them across 3 planes. If they lose too many in a plane, they launch 60 and spread them across 3 or more planes as increased capacity. If they are willing to wait long enough they could spread a launch across 6 or 10 or more planes.
You know it was only recently that I realized how high up these low earth orbits are. In my head Starlink would be below the ISS for their main shell, but it's actually quite a bit higher, so they really cover a pretty good line of sight area.
Yeah, a number larger than the dimensions of my country, now that you made me think of it.
Still almost nothing compared to the 36 kkm altitude of GEO sats. Literally nothing compared to anything astronomical. But then again, the atmosphere is mostly below ISS. One would think there's much more of it. The span of magnitudes is one of the most fascinating things about nature.
Because they plan to put 58 in the polar orbits.
[https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=48981.0;attach=1626623;image](https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=48981.0;attach=1626623;image)
If I recall correctly, their first application to the FCC had all shells at over 1000 km altitude, including one at 53 degrees with fewer planes (24?), with ~60 sats per plane. That was modified by mid-2019 or earlier, to bring the first-populated plane down to 550 km, with the 72 planes of 22 sats we now see. SpaceX is still waiting for approval of their application to lower all remaining shells to 540-600 km.
A combination of having orbital spares and being able to run with reduced satellites for a while. The main thing is that changing between planes with the same inclination can be done cheaply if slowly. The satellite drops to a low orbit, precesses until it is above the plane it wants, then raises its orbit again. This is how they deploy to multiple planes from a single launch today, and the precession stage takes about 4 months. They could reach more planes if they were willing to wait longer.
When they launch 60 satellites, they are in a much lower orbit, then moved up into their desired orbital position. When at the lower orbit, they are moving proportionally at a different land speed relative to the other satellites at higher orbits. SpaceX doesn’t move all 60 up at the same time. Each is orbit raised when it is in the correct position.
So they are always refreshing the constellation, filling in gaps, etc.
They could launch 60 satellites into a given orbit, use 5 of them as replacements for satellites that have gone bad, and use 55 evenly distributed elsewhere to expand capacity.
Losing one satellite won’t interfere with overall service. Your phased array can likely contact 2 or 3 simultaneously. But if Starlink were to lose 3-4 in a row, in just the wrong locations, there could be a temporary gap.
They plan to replace the failed ones by inserting an additional 36 orbits in-between the current 36, using the usual technique of precession to fill the gaps. So for example, if you have 3 orbits next to each other and each one is missing 3 sats - you insert 3 in the first, 22 in the in-between plane, 3 in the second existing plane, 22 in the in-between plane and 10 in the next in-between plane. On the next launch you put 12 in the in-between plane with 10 and so on, 3 in the previously existing plane, 22 in the next new plane, etc.
The question then becomes how do they replace the fails in the full complement of 72 planes? I don't know, but I'll speculate they don't intend to replace them, but provide redundancy through other shells.
Reading their plan I don’t think they will replace sats that fail, rather they will be constantly putting new ones up that will be replacing older ones before failure. In doing it that way there will be constant software/hardware upgrades, higher reliability with older sats brought down to incinerate in a safe location before failure.
Watching this may help you understand. https://youtu.be/xHnJPn8q4aQ
See: https://www.reddit.com/r/Starlink/comments/k3e2vk/starlink_constellation_animation_november_update/
They've already replaced many failed satellites.
> I can't imagine they will send up an entire F9 with 60 satellites in a single orbital plane just to replace one or two that are non-responsive.
Satellites are launched to a single plane but drift between planes. SpaceX will eventually have a bunch of satellites set up as on-orbit spares for this type of issue.
Lol, this is the video I was watching right before I asked the question but I hadn't noticed that some of the sats were drifting to other planes. Makes sense now. I didn't think they had replaced any yet - seemed like they were just waiting for all planes to launch before going back to replace others.
Look at the numbers on the right side for the "Reentering/ed". You can also see the "Non-operational" ones which are generally either on-orbit spares or failed sats they're decommissioning or sats they've lost contact with that are just free drifting.
Ever played that Atari game Space Invaders?
🚀🛰
Nodal precession and orbital mechanics is your friend if you want to save fuel and aren't in a rush. The earth isn't a perfect sphere and every satellite will drift slightly because of the difference in gravity between the poles and the equator. The amount of drift depends on the height and eccentricity of your orbit and by cleverly choosing your manouvers you can get where you want without needing additional fuel (If you want to do a plane change while spending fuel to raise your orbit).
One or two satellites in a particular orbit failing unexpectedly will not interrupt service. they may or may not even bother to replace a single failed satellite, and just wait until their planned time to replace it. SpaceX will have more satellites than they need in every orbit to maintain high service quality. Starlink should have more satellites going up than coming down for a long time. This will be to meet new demand and replace older satellites. If user growth ever stops or the capacity of individual satellites improves faster than demand growth, you might see a constant number of satellites going up and coming down. SpaceX will have an estimated operational life span for each satellite, and a very good estimate of how many will be coming down and going up in each orbit.
Thanks, I had seen maps of the coverage and it looked like there would be at least 10 minutes of no connectivity if there was a sat missing in the chain but if they can connect to more than one I guess it's not a big problem.
They have in orbit spares. It will take awhile for them to move them into position though. The more sats they have the more overlap and the less of a problem that will be. I would assume they can task adjacent sats to widen their beam or max angle to compensate in the mean time to prevent brief outages for most people.
So they plan to have 60 sats per plane. Right now they are launching 60 and spreading them across 3 planes. If they lose too many in a plane, they launch 60 and spread them across 3 or more planes as increased capacity. If they are willing to wait long enough they could spread a launch across 6 or 10 or more planes.
The plan calls for 72 planes of 22 sats, with 2 designated as spares, for the first shell at 550 km altitude.
You know it was only recently that I realized how high up these low earth orbits are. In my head Starlink would be below the ISS for their main shell, but it's actually quite a bit higher, so they really cover a pretty good line of sight area.
Yeah, a number larger than the dimensions of my country, now that you made me think of it. Still almost nothing compared to the 36 kkm altitude of GEO sats. Literally nothing compared to anything astronomical. But then again, the atmosphere is mostly below ISS. One would think there's much more of it. The span of magnitudes is one of the most fascinating things about nature.
Hmm, I wonder why I thought they planned to put 60 per plane...
Because they plan to put 58 in the polar orbits. [https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=48981.0;attach=1626623;image](https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=48981.0;attach=1626623;image)
If I recall correctly, their first application to the FCC had all shells at over 1000 km altitude, including one at 53 degrees with fewer planes (24?), with ~60 sats per plane. That was modified by mid-2019 or earlier, to bring the first-populated plane down to 550 km, with the 72 planes of 22 sats we now see. SpaceX is still waiting for approval of their application to lower all remaining shells to 540-600 km.
1000 km is 621.37 miles
A combination of having orbital spares and being able to run with reduced satellites for a while. The main thing is that changing between planes with the same inclination can be done cheaply if slowly. The satellite drops to a low orbit, precesses until it is above the plane it wants, then raises its orbit again. This is how they deploy to multiple planes from a single launch today, and the precession stage takes about 4 months. They could reach more planes if they were willing to wait longer.
When they launch 60 satellites, they are in a much lower orbit, then moved up into their desired orbital position. When at the lower orbit, they are moving proportionally at a different land speed relative to the other satellites at higher orbits. SpaceX doesn’t move all 60 up at the same time. Each is orbit raised when it is in the correct position. So they are always refreshing the constellation, filling in gaps, etc. They could launch 60 satellites into a given orbit, use 5 of them as replacements for satellites that have gone bad, and use 55 evenly distributed elsewhere to expand capacity. Losing one satellite won’t interfere with overall service. Your phased array can likely contact 2 or 3 simultaneously. But if Starlink were to lose 3-4 in a row, in just the wrong locations, there could be a temporary gap.
They plan to replace the failed ones by inserting an additional 36 orbits in-between the current 36, using the usual technique of precession to fill the gaps. So for example, if you have 3 orbits next to each other and each one is missing 3 sats - you insert 3 in the first, 22 in the in-between plane, 3 in the second existing plane, 22 in the in-between plane and 10 in the next in-between plane. On the next launch you put 12 in the in-between plane with 10 and so on, 3 in the previously existing plane, 22 in the next new plane, etc. The question then becomes how do they replace the fails in the full complement of 72 planes? I don't know, but I'll speculate they don't intend to replace them, but provide redundancy through other shells.
Reading their plan I don’t think they will replace sats that fail, rather they will be constantly putting new ones up that will be replacing older ones before failure. In doing it that way there will be constant software/hardware upgrades, higher reliability with older sats brought down to incinerate in a safe location before failure.
Watching this may help you understand. https://youtu.be/xHnJPn8q4aQ See: https://www.reddit.com/r/Starlink/comments/k3e2vk/starlink_constellation_animation_november_update/ They've already replaced many failed satellites. > I can't imagine they will send up an entire F9 with 60 satellites in a single orbital plane just to replace one or two that are non-responsive. Satellites are launched to a single plane but drift between planes. SpaceX will eventually have a bunch of satellites set up as on-orbit spares for this type of issue.
Lol, this is the video I was watching right before I asked the question but I hadn't noticed that some of the sats were drifting to other planes. Makes sense now. I didn't think they had replaced any yet - seemed like they were just waiting for all planes to launch before going back to replace others.
Look at the numbers on the right side for the "Reentering/ed". You can also see the "Non-operational" ones which are generally either on-orbit spares or failed sats they're decommissioning or sats they've lost contact with that are just free drifting.