[ks1723]

But apart from all the other stuff you mention, you’re missing an important point: these things move. And unless all objects are synchronized (which they are not) they occupy a whole orbit, not only their actual volume. If two orbits intersect, the objects occupying those will eventually collide.

Therefore, they occupy much more volume.

[seanhunter]

Yes. This is the idea behind Kessler Syndrome - that the accumulation of clutter in Earth orbit could lead to an "ablation cascade" as more and more things collide and more and more debris is created from those collisions leading to Earth orbit becoming too hazardous to traverse.

"A 1 kg object impacting at 10 km/s, for example, is probably capable of catastrophically breaking up a 1,000 kg spacecraft if it strikes a high-density element in the spacecraft. In such a breakup, numerous fragments larger than 1 kg would be created." https://orbitaldebris.jsc.nasa.gov/library/a-technical-asses...

[HPsquared]

The dimensionality of usable orbits is much less than 3.

For example all the GEO satellites are positioned along a 1D line.

[southernplaces7]

I believe I described it badly or you misunderstood me then. What I was referring to in my mention of three-dimensionality is that the area in which all of them orbit isn't a single flat plane over a sphere shape. It's actually several flat planes layered on top of each other, with an obviously ever greater surface area the higher you go. Thus you have LEO, MEO and GEO satellites all sharing orbital space but at different heights so to speak. I'm aware that any given satellite generally flies along a fixed altitude (though as far as I know their latitude along that altitude can shift enormously)

[HPsquared]

I suppose each satellite has its orbit defined by the elliptical path (4 parameters). Like for GEO you can have many satellites in a single elliptical path.

You can also probably have different satellites on different ellipses whose paths intersect with each other, but the timing is such that they never collide.

I suppose it's quite complex in reality!

[southernplaces7]

What you say is important of course, and it's what makes me less than sure in my assessment. It was after all more of a mental exercise in appreciating just how vast an area of space this relatively tiny quantity of objects is spread across.

To give one further perspective example here: a single large bulk container ship can carry up to 8,500 car-sized units.

This means that even if every single one of the maybe 15,000 satellites in orbit were the size of a car (most of them are much smaller actually), all together, they'd fill no more than the storage spaces of two bulk container ships with lots of room to spare at that.

This, spread over a multi-layered area as vast as our orbital space, means that even with their constantly moving at incredible speeds, and all the junk out there scattered between the satellites themselves, there's an enormous amount of emptiness between it all mitigating against impacts being very likely or frequent at all.

After all, of the 8,070 or so Starlink satellites in orbit right now, there's little mention of more than a few having been knocked out by debris in orbit. It seems that solar storms are their much bigger worry and cause of mishaps.

As the saying goes, space is huge, sometimes more than our brains can easily comprehend. This applies even in the comparatively tiny orbital regions of it that we use daily.

[notahacker]

The mental exercise is fine for realising that satellites don't look as big as pictures of satellites in graphics, it's just missing the point that if you don't want to hit a 20cm x 20cm x 20cm cube that moves at 17,500 mph and has slow and limited capability to adjust that movement you need to allow it quite a bit more space, and be able to predict its movement accurately relative to yours. Especially if any collision means thousands of pieces of shrapnel that continue to move at 17500mph for decades or more, whilst potentially being too small to track but large enough to do a lot of damage.

Trains take up a negligible fraction of the mileage of the lines they operate on and rarely cross other lines, but signalling is still critical.

[southernplaces7]

All of these are useful things to keep in mind of course, and they're why I put forth my consideration as a thought experiment for perspective, not so much as an absolute assertion. Orbital space is complicated, and the the ramifications of accidents are extremely unique compared to those that apply in a terrestrial context, but I still stand by my point about it being absurdly big enough that a sense of proportion is needed in worrying about something like Kessler syndrome.