Already it’s getting hard to avoid noticing satellite trains when stargazing with the naked eye. If mega-constellations really scale into the hundreds of thousands, it feels like we’re on track to permanently degrade the night sky, even in places without much light pollution.
With mega-constellation launches accelerating, the sci‑fi premise of imprisoning ourselves behind a debris field feels less fictional. This is essentially the collision-cascade risk described by Kessler Syndrome
Kurzgesagt has a good explainer. Hopefully we never trigger it.
In summer I was lying on a beach in Thailand and used an app on my phone to look at things in the sky. Pretty much every moving glistening object I could see was a Starlink satellite. I know nothing about how their constellation works but I wonder why so many are needed. Surely you only need one or two in line of sight for it to work? I was seeing many more than that.
They're in LEO which means approximately 15 minutes of visibility (horizon-to-horizon). The specific time will vary based on the orbital elements but 15 minutes is a good rule of thumb. To maintain coverage you need there to be some overlap in their visibility for a location. There's also a limit to how many connections each satellite can support.
Not all the satellites that you can see will be "looking" in your direction for a signal. They support some number of cells (specific, small, geographic regions on the ground). No one satellite can cover the entire ground visible to it while overhead so more satellites are needed.
And to add to the above, Starlink is using laser crosslinks to connect their satellites to each other for routing. This crosslink network is improved with more satellites visible to each other.
That would still only require a couple dozens or few hundreds of satellites. For example, Iridium has 60-70, and Globalstar has less than 50 or so.
The actual reason for these new megaconstellations having so many is spatial frequency reuse through directional transmission/reception beams: More satellites means less users competing for each satellite's spectrum-limited bandwidth.
Iridium offers lower bandwidth and much larger cells than Starlink. But yes, the number of customers within a cell is also key to why there are so many Starlink satellites. Suburban (let alone urban) population density can easily consume the bandwidth available through one satellite.
Smaller spot beams are still technically possible for an Iridium-like constellation with fewer satellites. That's what e.g. ASTS is doing.
In fact, more than one (or maybe two, for geometric reasons near the equator where polar orbits are sparse etc.) satellite concurrently visible is pointless if the ground station/mobile device isn't also heavily directional, which is not the case for small, quickly moving handheld devices at least.
One other reason for wanting more satellites splitting footprint coverage between them would be if the satellite transmitters were transmit power limited.
> I wonder why so many are needed. Surely you only need one or two in line of sight for it to work?
Only if you're not bandwidth limited. Having more satellites per steradian of sky allows reusing the same frequency via (physically or electronically) aiming at a particular satellite.
> the sci‑fi premise of imprisoning ourselves behind a debris field feels less fictional
Yeah, no, the numbers don't work for this. The Kessler syndrome is bad, and worth avoiding, but you aren't trapped.
The trick is that you're not staying. Suppose a comms satellite in LEO would, as a result of a hypothetical cascade like this, be destroyed on average in six months but your space vehicle to somewhere else passes through the debris field in like 5 minutes. So your risk is like one in 50 000. That's not good but it wouldn't stop us from leaving.
The reason humans won't leave is more boring and less SF, there is nowhere to go. Nowhere else is anywhere close to habitable, this damp rock is where we were born and it's where we will die, we should take better care of it.
yeah, all this about inhabiting mars, even when earths ecology and economies crash as they're looking to do it will still be orders of magnitude more survivable than mars lol
I don't think anyone is seriously arguing that Mars will be more habitable than Earth. The argument is about the possibility of humans on Earth being wiped out due to freak events like a huge asteroid impact or global thermonuclear war. Earth would still be more habitable than Mars, but the probability that human survivors would be equipped with Mars-level survival tools is tiny, and any facility equipped like this would have to be hardened against desperate survivors trying to take it over and bringing it over capacity. Meanwhile if we had a self-sufficient Mars colony they could resettle any Earth that is more habitable than Mars.
Now I'm not saying it's necessarily a smart allocation of resources. But it does follow the popular IT saying "one is none, two is one. If you care about something make sure you have a backup"
Hence "if we had a self-sufficient Mars colony". Any initial mars colony would not be self-sufficient, but even just by economics alone that would change as the colony grows.
Even if we get stuck in the "initial colony" stage (which is not the plan of any Mars-colonization proponent) with precautions comparable to the ISS you'd still have a colony capable of surviving a minimum of four years (two launch windows, in case one delivery goes wrong) and the capability to return to Earth.
I was on a trip to the mountains recently. Get out into nature, get away from it all, etc. I look up into the sky and see a satellite. I remember when this was a novelty, it was so rare to see them. But I saw at least 10 of them in the time I spent stargazing.
It's just so bleak. We did this for what? To have _more_ internet?! Is that really what we need?
With mega-constellation launches accelerating, the sci‑fi premise of imprisoning ourselves behind a debris field feels less fictional. This is essentially the collision-cascade risk described by Kessler Syndrome
Kurzgesagt has a good explainer. Hopefully we never trigger it.
https://youtu.be/yS1ibDImAYU?si=vbs-PY5VEA9xv_gS