Comment by mcguire | Hacker News Reader

Comment by mcguire | Hacker News Reader

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Objects in orbit are primarily cleared by atmospheric drag, with two major variables: height of perigee (lower causes more drag) and object mass (lighter objects are slowed more). Following an impact, some of the debris will be cleared quickly, but some will not.

"On 11 January 2007, China conducted an anti-satellite missile test in which one of their FY-1C weather satellites was chosen as the target. The collision occurred at an altitude of 865 kilometres, when the satellite with a mass of 750 kilograms was struck in a head-on-collision by a kinetic payload traveling with a speed of 8 km/s (18,000 mph) in the opposite direction. The resulting debris orbits the Earth with a mean altitude above 850 kilometres, and will likely remain in orbit for decades or centuries.[18]" (https://en.wikipedia.org/wiki/Kessler_syndrome#Anti-satellit...)

Kessler syndrome requires the rate of debris creation be greater than the rate of clearing and the rate of clearing in higher orbits is very slow.

https://amostech.com/TechnicalPapers/2012/Orbital_Debris/NIK...

It's not the object's mass that you care about, but its ballistic coefficient [1]. An object which is very heavy, but also very big, will deorbit just as quickly.

[1] https://en.wikipedia.org/wiki/Ballistic_coefficient

> will likely remain in orbit for decades or centuries

How much debris though? If I put orange juice in my coffee mug, after a few runs through the dishwasher there may technically be a few particles of orange juice left, but my taste buds probably won't collide with it.

I'm not sure the analogy holds - again, most of this debris would be occupying a relatively narrow region of space surrounding Earth, and it wouldn't simply decay after a few orbits. Thinking of kessler syndrome as some impenetrable shell of bullets misses the forest for the trees, i think. It doesn't take much debris to render a region of space unsafe for humans or multi-million dollar satellites.

To attempt extend your analogy: you might be confident that most of the juice was washed out of the mug after a few cycles set to scour, but if you are deathly allergic to any exposure to oranges, what's your risk tolerance?

Make sure you clean the dishwasher trap, as well. :)

> what's your risk tolerance?

That's the key question the whole matter hangs on, but there's no objective answer for it. Neil Armstrong privately estimated his chance for successfully returning to earth at 90%. That's alarmingly low! That's barely safer than Russian roulette.

Determining how much risk can be tolerated means figuring out how badly you want the thing. The more you want something, the more risk you can tolerate. Satellites are extremely important to our society, so governments would continue launching the satellites they value most, even if the expected lifespan of the satellite due to space debris was very short.

Of course, superfluous and casual use of space would grind to a halt. One of many casualties of war.

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