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It's popular to point out how satellite visualizations exaggerate the size, but we never seem to notice how satellite visualizations shrink the duration of time

It's popular to point out how satellite visualizations exaggerate the size, but we never seem to notice how satellite visualizations shrink the duration of time. You only look at a visualization for maybe a minute, whereas these objects are actually out there whizzing around 24/7 for decades or even millennia. Both effects are misleading dataviz artifacts, but at least they're in opposite directions! A great ESA video, linked from Don Kessler's website, shows a time-lapse simulation that better captures the seriousness of space junk. In the simulation @5:25, realize that each of those flashes represents an Iridium-Cosmos magnitude collision event: http://www.youtube.com/watch?v=RvZ3Lr-Tj6A http://www.youtube.com/watch?v=RvZ3Lr-Tj6A

bryanlarsen 2y ago
The third & fourth factor are whether the satellites are actively avoiding collisions and whether the satellites are in a self-clearing orbit. Depending on the assumptions you make, we could have billions or even trillions of Starlink satellites without triggering Kessler simply because - Starlink satellites are actively controlled and steer to avoid collisions. Yes there are sometimes a couple of failed Starlinks in orbit, but since the active ones avoid the dead ones, you have to calculate the risk of one dead satellite hitting another dead satellite. And that's less than random because they quickly decay out of their crowded orbital plane to a different less crowded one. - dead Starlinks are in a self-clearing orbit, deorbiting in under 5 years. As the article indicates Kessler is a decades-long process. Which can't happen if the satellites don't stay in orbit that long. - most dead Starlinks aren't completely dead, or give alerts before they die, allowing SpaceX to actively deorbit them safely and quickly - the vast majority of particles from a collision in a self-clearing orbit result in immediate clearing. If the original dead Starlink that would take 5 years to clear suddenly fragments, most fragments de-orbit within a single orbit (90 minutes). Elastic deformation reduces their velocity, lowering the orbit. Half of fragments are toward a lower orbit. The other half only boost apogee and either lower perigee or leave it unchanged. Being smaller, their surface area / mass ratio increases, reducing deorbit times. Basically, Kessler is not a concern at VLEO altitudes. Unfortunately most proposed Starlink competitors cannot afford to launch the thousands of satellites necessary for a viable VLEO constellation and instead are launching dozens or hundreds into LEO orbits which aren't self-clearing and do pose a Kessler concern.
- nordsieck 2y ago
  > Half of fragments are toward a lower orbit. The other half only boost apogee and either lower perigee or leave it unchanged. I think this is something that's not intuitive to othe average person. Basically: a collision can change an object that's in a circular orbit into an elliptical orbit with a higher apogee. But it can't circularize the new orbit higher without a 2nd "burn"[1]. Which means that if a satellite that would passively deorbit in a short amount of time is in a collision, it is necessarily true that all of the fragments will also deorbit in a small multiple of that time. > Basically, Kessler is not a concern at VLEO altitudes. Unfortunately most proposed Starlink competitors cannot afford to launch the thousands of satellites necessary for a viable VLEO constellation and instead are launching dozens or hundreds into LEO orbits which aren't self-clearing and do pose a Kessler concern. Thankfully, Kuiper will be just above Starlink. From what I understand, their passive deorbit times are ~10-20 years. The real problem is with OneWeb and the upcoming Telesat Lightspeed which are both at 1000km+. It sounds like OneWeb was planning on a greatly expanded next generation constellation, but they've since scaled their plans back and are incorporating bandwidth from geostationary satellites into their offerings. --- 1. https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
  - bryanlarsen 2y ago
    Even the FCC doesn't appear to understand this correctly. They denied a SpaceX application to put satellites into lower & safer orbits. https://spectrum.ieee.org/starlink-vleo-below-iss https://spectrum.ieee.org/starlink-vleo-below-iss
    - admax88qqq 2y ago
      Absurd if you consider the utility to the average person of the ISS vs Starlink.
      - bryanlarsen 2y ago
        Putting Starlink satellites at an orbit below the ISS would be safer for the ISS than their current altitude above the ISS.
jerf 2y ago
That more-or-less cancels; yes, the satellites are traveling through a 4D space and aren't just at one point in one time, but then that's still sparse in the full 4D space. If anything it makes it more sparse, not less. It's not like crossing paths, but separated by a year, matters at all, to the extent that such a thing can even be defined.
- denton-scratch 2y ago
  > are traveling through a 4D space Huh? My standard interpretation of "4D" in this kind of context is spacetime. But one doesn't "travel" through spacetime; one's entire journey "just is". https://en.wikipedia.org/wiki/Slaughterhouse-Five#Tralfamadorian_philosophy https://en.wikipedia.org/wiki/Slaughterhouse-Five#Tralfamado...
  - denton-scratch 2y ago
    Hey, vote me down to oblivion if you want; I don't care. But I think it's nice to say why. What have I misunderstood? Is this a 4D space in a 5D spacetime? Is "block spacetime" discredited? I thought the parent comment sounded weird, as if I'd missed some important context.
    - dsabanin 2y ago
      To me the main problem with “traveling through 4D” is the fact that “traveling” is happening in the 4-th dimension.
      - merely-unlikely 2y ago
        Isn’t traveling happening in all 4 dimensions?
        lazide 2y ago
        Well, one of them (time) is moving forward at a steady yet unchanging rate. It’s rare to call that ‘traveling’ since it isn’t meaningfully in control of the traveler. More like ‘bring drug along in’
Gravityloss 2y ago
This is a very informative video. Even if no more satellites were launched, the amount of objects would increase over time as collisions would occur. I think it could be submitted on its own. (Btw I checked and ERA-2 re-entered in February 2024. Great work ESA!)

bryanlarsen 2y ago

The third & fourth factor are whether the satellites are actively avoiding collisions and whether the satellites are in a self-clearing orbit. Depending on the assumptions you make, we could have billions or even trillions of Starlink satellites without triggering Kessler simply because - Starlink satellites are actively controlled and steer to avoid collisions. Yes there are sometimes a couple of failed Starlinks in orbit, but since the active ones avoid the dead ones, you have to calculate the risk of one dead satellite hitting another dead satellite. And that's less than random because they quickly decay out of their crowded orbital plane to a different less crowded one. - dead Starlinks are in a self-clearing orbit, deorbiting in under 5 years. As the article indicates Kessler is a decades-long process. Which can't happen if the satellites don't stay in orbit that long. - most dead Starlinks aren't completely dead, or give alerts before they die, allowing SpaceX to actively deorbit them safely and quickly - the vast majority of particles from a collision in a self-clearing orbit result in immediate clearing. If the original dead Starlink that would take 5 years to clear suddenly fragments, most fragments de-orbit within a single orbit (90 minutes). Elastic deformation reduces their velocity, lowering the orbit. Half of fragments are toward a lower orbit. The other half only boost apogee and either lower perigee or leave it unchanged. Being smaller, their surface area / mass ratio increases, reducing deorbit times. Basically, Kessler is not a concern at VLEO altitudes. Unfortunately most proposed Starlink competitors cannot afford to launch the thousands of satellites necessary for a viable VLEO constellation and instead are launching dozens or hundreds into LEO orbits which aren't self-clearing and do pose a Kessler concern.

nordsieck 2y ago
> Half of fragments are toward a lower orbit. The other half only boost apogee and either lower perigee or leave it unchanged. I think this is something that's not intuitive to othe average person. Basically: a collision can change an object that's in a circular orbit into an elliptical orbit with a higher apogee. But it can't circularize the new orbit higher without a 2nd "burn"[1]. Which means that if a satellite that would passively deorbit in a short amount of time is in a collision, it is necessarily true that all of the fragments will also deorbit in a small multiple of that time. > Basically, Kessler is not a concern at VLEO altitudes. Unfortunately most proposed Starlink competitors cannot afford to launch the thousands of satellites necessary for a viable VLEO constellation and instead are launching dozens or hundreds into LEO orbits which aren't self-clearing and do pose a Kessler concern. Thankfully, Kuiper will be just above Starlink. From what I understand, their passive deorbit times are ~10-20 years. The real problem is with OneWeb and the upcoming Telesat Lightspeed which are both at 1000km+. It sounds like OneWeb was planning on a greatly expanded next generation constellation, but they've since scaled their plans back and are incorporating bandwidth from geostationary satellites into their offerings. --- 1. https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
- bryanlarsen 2y ago
  Even the FCC doesn't appear to understand this correctly. They denied a SpaceX application to put satellites into lower & safer orbits. https://spectrum.ieee.org/starlink-vleo-below-iss https://spectrum.ieee.org/starlink-vleo-below-iss
  - admax88qqq 2y ago
    Absurd if you consider the utility to the average person of the ISS vs Starlink.
    - bryanlarsen 2y ago
      Putting Starlink satellites at an orbit below the ISS would be safer for the ISS than their current altitude above the ISS.

jerf 2y ago

That more-or-less cancels; yes, the satellites are traveling through a 4D space and aren't just at one point in one time, but then that's still sparse in the full 4D space. If anything it makes it more sparse, not less. It's not like crossing paths, but separated by a year, matters at all, to the extent that such a thing can even be defined.

denton-scratch 2y ago
> are traveling through a 4D space Huh? My standard interpretation of "4D" in this kind of context is spacetime. But one doesn't "travel" through spacetime; one's entire journey "just is". https://en.wikipedia.org/wiki/Slaughterhouse-Five#Tralfamadorian_philosophy https://en.wikipedia.org/wiki/Slaughterhouse-Five#Tralfamado...
- denton-scratch 2y ago
  Hey, vote me down to oblivion if you want; I don't care. But I think it's nice to say why. What have I misunderstood? Is this a 4D space in a 5D spacetime? Is "block spacetime" discredited? I thought the parent comment sounded weird, as if I'd missed some important context.
  - dsabanin 2y ago
    To me the main problem with “traveling through 4D” is the fact that “traveling” is happening in the 4-th dimension.
    - merely-unlikely 2y ago
      Isn’t traveling happening in all 4 dimensions?
      - lazide 2y ago
        Well, one of them (time) is moving forward at a steady yet unchanging rate. It’s rare to call that ‘traveling’ since it isn’t meaningfully in control of the traveler. More like ‘bring drug along in’

Gravityloss 2y ago

This is a very informative video. Even if no more satellites were launched, the amount of objects would increase over time as collisions would occur. I think it could be submitted on its own. (Btw I checked and ERA-2 re-entered in February 2024. Great work ESA!)