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Comment by panarky | Hacker News Reader

Probability of collision between 1% and 20%.

These are extraordinarily high numbers.

https://en.wikipedia.org/wiki/Kessler_syndrome

Given SpaceX's (and Amazon's) plans to deploy upwards of 12000 LEO satellites, how do they factor for avoiding these debris (given Kessler Syndrome's premise that this avoidance is only going to get exponentially harder as time goes on and not easier, especially what seems to my untrained eye one satellite too many)?

Also, how do Rockets and other launch vehicles avoid these (I am guessing the debris are extensively tracked or are the launch vehicles built to withstand hits)? Excuse my naivety but it seems like a future where humanity locks itself out from Space altogether isn't a distant possibility at all but one that could happen in our lifetimes?

Their satellites are mostly in low orbits that deorbit naturally after a few years. That doesn’t reduce the risk of collisions, but it does reduce the risk of being locked out of space for a long time.

Still, I find it troubling that a single private US company is basically “using up” a particular orbital elevation without other countries getting a say in it.

> Still, I find it troubling that a single private US company is basically “using up” a particular orbital elevation without other countries getting a say in it.

Space is big enough. They aren't using it up. They create some minor burden for space objects tracking and mission planning, but you could still fit the same orbital band with many more constellations, and other nations/companies will be able to do so if they so choose.

They create a minor burden currently, thus distributing that burden without paying for it themselves, at what point does that burden get to be bad enough we can say they are using it up.

AIUI there are already regulations requiring that satellites be able to de-orbit themselves at EOL, and have some maneuvering capability in order to actively avoid collisions. This is directly paid for by the owners of these satellites as part of the development cost. Most of the objects at high risk of collision are either very old satellites, or debris from collisions of old satellites, from before these requirements existed.

Tracking space debris and other objects in orbit of the earth is something we'd probably want to do anyway, and it makes no sense to duplicate that effort, so of course that burden will be distributed. If that burden becomes too high I'm sure some tax or licensing fee will be introduced to pay for it (assuming such a thing doesn't already exist) but in the grand scheme of things those costs are irrelevant compared to the cost of launching something into space to begin with... Especially when the satellite is still functioning, and generally aware of its own position anyway.

The SpaceX satellites are in such a low orbit that anything that is not actively being pushed back up (well given more speed in reality but whatever) by engines will come down in a couple years due to drag from the atmosphere. Most of the Starlink satellites from the first patch have already come down on their own as planned (as have the 2 tintin proto ones)

This applies for ISS even more (it is huge and thus a lot of drag) and thus it has one of the Progress spacecraft docked or the Russian service module use its engines to boost it back into proper orbit so that it wont crash down on earth.

> This applies for ISS even more (it is huge and thus a lot of drag)

Wouldn't drag be proportional to the surface area, hence the square of the length scale, whereas orbital energy is proportional to the mass, which is cubic in the length scale. I would expect the orbital lifetime to be roughly proportional to their quotient and thus for larger objects to stay up longer.

On the other hand, ISS has a lot more empty (well, air-filled) space inside of it, so it might be a lot less dense than a SpaceX satellite.

Drag is enough of an issue for the ISS that they actually rotate the solar panels to reduce drag when they're not in sunlight, which saves them ~1000kg of propellant per year.

https://en.wikipedia.org/wiki/Night_Glider_mode

> Wouldn't drag be proportional to the surface area, hence the square of the length scale, whereas orbital energy is proportional to the mass, which is cubic in the length scale.

Are you assuming the ISS has a similar surface-to-volume ratio as other orbiting objects?

If the ISS were built like a scaled-up satellite, you'd be right. But as you say,

> ISS has a lot more empty (well, air-filled) space

and this dominates.

It does have a lot of empty space. But I would presume it also has a lot of heavy metal structure to keep that space pressurized to a human-breathable pressure and allow entry and exit. Satellites don't need to keep much under pressure except maybe their maneuvering fuel in a small perfectly-shaped container with a single small hole.

The ISS solar panels are quite large

The ISS has a lot of doohickeys hanging off it, so the cross section is going to be much larger than if the ISS was condensed into a sphere or cube. The ISS is also a lot less dense than most satellites, so even if the drag were the same it would have more of an impact

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