Assuming Starlink is similar, are there any risks of "imprisonment" on Earth having ~8k low-orbit satellites flying around? In that they gravely affect efforts to fly Humans to the Moon/Mars?
So just from a "unusable space" point of view, it's on the order of 10000x less of a problem than airplanes. The caveats here are the satellites are moving much, much faster than airplanes, and they stay in the sky much, much longer.
But it's not really a huge problem unless stuff goes wrong and you get Kessler Syndrome. This is more of a risk with the higher constellations like Amazon's and OneWeb's than it is with SpaceX Starlink (which is in a low enough orbit to de-orbit all debris within a few years, rather than centuries).
This doesn't feel right. Shouldn't the right frame of reference be the distance to the center of the earth, not the sea level? Then it is not a 100x difference, but more like a 10% one.
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Area of sphere: 4πr^2
Airplane cruising height: ~10km
Satellite orbit height: ~550km
Radius of earth: 6371km
thus, relative increase: (6371+550)/(6371+10) = 1.084 = 8.4% increase
Squared (because of first formula) that corresponds with a 1.084^2 = 1.175 = 17.5% increase in area.
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Still, a few caveats:
1. Earth is huge. 510.1 million km² is a lot of space (+20% at 550km altitude). We could have a million sats with each having more than 1km^2 to themselves.
2. Satellites orbit at different heights. Amazon's and SpaceX's satellites will not be on the same orbit.
3. Starlink satellites are at a sufficiently low altitude that Kessler Syndrom is not a problem; even if they all simultaneously turned into millions of pieces of dead debris at the same time, the atmospheric drag would make them lower their orbits and burn up in just a few months.
Thought experiment:
You are standing in a field.
There is a 10x10 meter plate hovering 10 meters above you. There is a 1 square meter target on it. You fire a gun upwards at a random location on the plate. There is a 1 in 100 probability you hit the target.
Now imagine there is a 20x20 meter plate hovering 20 meters above you. It is perfectly occluded by the original 10x10 meter plate. It also has a 1 square meter target on it. When you fire at a random location on the original plate, the bullet passes through it and continues on to the higher plate. What is the probability you hit the target on the higher plate? I believe it is 1 in 400.
From this thought experiment it seems that altitude from launch point is what counts.
If I am launching a rocket, and there is a 1x1 meter satellite orbiting 1000km above me. What is the probability that my rocket hits that satellite compared to an identical satellite at 2000km above me? The area of the angular sector of the sky that the 2000km altitude satellite is 1/4 of the 1000km altitude satellite.
That is, you 2x the height of the target which results in the probability of hitting being 4x less.
Clearly the 10x10 plates are lining up (modulo curvature). But the 20x20 plates are not, they're overlapping. So when I shoot through a random location of my own 10x10 plate, there's a chance that I'll hit a target from somebody else's 20x20 plate. Sum up those additional chances, and they'll cancel out the 4x difference you found.
This feels like it would make a nice puzzle, your phrasing makes for a great misdirect / sleight of hand.
When talking about the area of the spherical shells, it conflates what is above me as equally relevant to things that are on the other side of the planet from me.
That is, satellite X and Y may be over me at 500km and 1000km distance, respectively. Later, they may be directly through the earth from me at distance 13200km and 13700km distance.
In the first case, if I shine a laser straight up, my probability of hitting X is 4 times higher than my probability of hitting Y.
In the second case, (if I could somehow shine a laser straight through the earth), the probabilities are nearly equal.
But my intuition is that for the purpose of escaping earth, this second case does not matter, because we are just dealing with what is above us, not the entire spherical shell.
This is also true for satellites.
Every satellite is in a very deterministic orbit which requires energy to change (enormous amounts of energy for a significant change) so they don't change their orbit significantly nor often.
Ref: https://sos.noaa.gov/catalog/datasets/space-trash-and-satell...
Do you think they don't know where their satellites are?
We really don't. We mostly know for commercial flights, but not so much for general aviation. What aviation does is have zones around airports with restricted airspace that is well-controlled.
* Those 20k planes don't all fly at the same time.
* Retired / Broken planes don't fly, satellites may still be on orbit for decades.
* There are no debris flying in the sky at 11000 km/h
* Planes can adjust their path at will instantly for avoidance.
* Planes can be grounded instantly if we need to.
Orbital space is a limited resource that gets depleted very fast and recovers very slowly. We are talking about launching in the next ten years 5x the total number of satellites that were ever launched so far. I am sure humans in 50 years would still be able to launch a thing or two in space as well.
This is an actual problem, and unlike for planes, once the problem is apparent, you can't just take some of them out of the sky while you figure out a solution.
They absolutely do. Check out https://www.flightradar24.com, there are currently 15,673 planes in the air worldwide at the moment I am typing this comment.
The main reason is that the Starlink satellites fly in a very low altitude, such that even if they lose all control, they will deorbit in a few years. Which means, if something went horrifically wrong, the Starlink system debris would clear itself within a short period of time.
It looks like the Amazon Project Kuiper satellites will be slightly higher up, but still have a natural orbital decay time of between 5-7 years. https://spacenews.com/amazon-lays-out-constellation-service-...
So, the long term risks from these kinds of low-orbit mega constellations is fairly low. If anything goes catastrophically wrong we wait a decade and it's gone.
I think personally, the longer term risks we should be wary of are medium altitude and geostationary orbits that won't naturally clear themselves for decades or centuries if something goes wrong.
SpaceX satellites are around 550km attitude. If someone puts satellites higher than that, collision debris will last longer, the satellites' fuel will last longer so the satellites won't have to be replaced as often, but network latencies will be higher. Seems like 500-600km is the optimal zone for the primary constellations of internet satellites.
Video showing decay of debris vs. its altitude. The "X" shape is because each debris is plotted twice, once at it's perigee and again at its apogee (describing the ellipse of the orbit as they generally are not perfectly circular)
https://www.youtube.com/watch?v=mQT5aMa_7iI
Higher altitude satellites would be a bigger concern but these aren't a big deal.
In general the question of collision risk and debris is something evaluated for every launch/constellation. Starlink, for example, mostly avoids it being an issue by flying so low that debris quickly falls to earth and burns up in the atmosphere (they also design their satellites to fully burn up in the atmosphere). On the flip sides Starlink is planning on an order of magnitude more satellites than this.
Even the worst case though doesn't really impact humans ability to fly to the moon/mars. You can make low earth orbit relatively unusable because there is a high collision risk if you hang out there for a year, but you should basically always be able to fly through low earth orbit to a higher orbit with negligible collision risk.
Space junk is an issue, but it's not anywhere near crisis level yet.
I think it's sometimes hard to reason about the vastness of space, but imagine if the planet Earth had exactly 20,000 cars on it's surface. Even if you crossed the street without looking, your odds of getting hit by a car would be incredibly low. And ofc in reality low earth orbit is bigger than the surface of the earth AND we know where every obstacle is located. If humanity ever gets to the point where we decide it's too crowded, most of these constellations are low enough that they'd naturally deorbit in less than a decade.
Yet, SpaceX already launched 1730 satellites, 1630 of which are active, with a planned constellation of 12,000 satellites.[1]
Amazon's Kuiper Systems hadn't even launched yet, and they're going with ULA for their first launch, which AFAIK, is much more expensive than SpaceX, with only 9 satellites as opposed to 60 satellites at a time.[2]
Also, they've submitted authorization for up to 42,000 total starlink satellites: https://spacenews.com/spacex-submits-paperwork-for-30000-mor...
These low earth orbit constellations will naturally experience orbital decay and at the end of their useful life will simply burn up on re-entry. They're explicitly designed to prevent Kessler Syndrome:
a) debris damaging other satellites or space stations. There currently is no proper liability currently and different monitoring systems are still in development
b) astronomy from earth will see problems.
As long as they are on their orbits there is enough space (haha) and if they don't cause conflict with radio frequencies they also don't cause issues
https://www.esa.int/Safety_Security/Space_Debris/About_space...
Starlink operates at 550km altitude:
They do this thing called "COLA", Collision On Launch Assessment, an analysis of launch trajectory to ensure they it won't hit known objects.
Most launches are timed for minimizing fuel to achieve the desired orbit, and there's only a few seconds of wiggle room for a launch window. So, a particular launch window may be preferred over another depending on the relative probability of a collision. Nobody is explicitly timing their launches or ascent profile with regard to other satellites other than for space stations and other explicit destinations. Most launches the rocket just gets the satellites up into roughly the right orbit, and then the satellites use their own propulsion systems to maneuver into precise orbits over several months.