Is that right? Scientific American seemed to think it could be a problem in 2019[1]. Space.com says Starlink satellites orbit at an altitude of about 342 miles (550 kilometers)[2]. And the Wikipedia article on Kessler Syndrome[3] (which is a chain reaction of satellite debris) mentions an incident at 555km that was problematic:
"In 1985, the first anti-satellite (ASAT) missile was used in the destruction of a satellite. The American 1985 ASM-135 ASAT test was carried out, in which the Solwind P78-1 satellite flying at an altitude of 555 kilometres was struck by the 14-kilogram payload at a velocity of 24,000 kilometres per hour (15,000 mph; 6.7 km/s). When NASA learned of U.S. Air Force plans for the Solwind ASAT test, they modeled the effects of the test and determined that debris produced by the collision would still be in orbit late into the 1990s. It would force NASA to enhance debris shielding for its planned space station."
[1] https://www.scientificamerican.com/article/spacexs-starlink-...
The real concern for meaningful space debris issues is in the regions where decay requires 100+ of years.
The articles mentions the ASAT because that's what they used to study orbital behavior and decay.
Also generally, Space.com is universally agree to be the single worst 'space news' page known. I would never use it as a source for anything.
waste -> vast
But for anyone who's not 100% comfortable with English, "the vast majority" is not simply a case of a descriptive adjective modifying the noun "majority," but it's actually a common phrase. People don't say "the big majority" or "the large majority," it's specifically "the vast majority."
If you wanted to use a different adjective, you could say "a large majority," and that would mean something like "most but not all and the 'but not all' is kind of significant" where as "the vast majority" means "nearly all of them, and the 'not all' is insignificant."
The real danger is space junk that's at much higher altitudes. OneWeb and Telesat Lightspeed (in planning) operate at 1000+ km, where space junk will take 1000+ years to deorbit on its own. And OneWeb has already had a satellite failure where it can't deorbit the satellite.
Compared to that, anti-satellite missile bust a satellite into pieces and carry indeed the danger of creating a Kessler syndrome. In case these would be used on a large scale, WW III would be imminent anyways. Apart from that, missiles are too expensive to knock out Starlink satellites, and the latter are comparatively easy to replace.
Mind you I'm not the one who came up with the TERRIBLE analogy with cars. Millions of people a year die in car accidents, and this was somehow the example that's supposed to convince us that if "cars are safe" then satellites travelling 100x faster than a car over our heads (and 10x faster than an airplane) are also safe. The whole construct betrays extremely sketchy thought process.
Cars, for the most part, follow the road and the direction they're already going. They (usually) signal if they're about to make changes. And to be safe, we've built an arrangement that they only travel on these specific paths at specific speeds, modifying their speed to match the other cars they might hit.
The challenge with satellites is that steering is hard and very limited. And they don't have brakes they can slam to come to a stop if they need to suddenly avoid a collision.
> And to be safe
Tell that to the 40k people killed and the millions hurt by cars in the US alone.
Cars constantly turn and intersect routes with other cars without any planning, even if perfectly handled and most of time they are not.
> The challenge with satellites is that steering is hard and very limited. And they don't have brakes they can slam to come to a stop if they need to suddenly avoid a collision.
They don't need to break, they just need to know the position of speed of other objects and correct position ahead of time.
The only reason why this is even a program at all is because only the US has even minimally invested in monitoring. If each nation just did the same our accuracy would be far, far higher and things would be way better.
So, as of now, we have minimally invested in solving this problem and it isn't a big issue. Slightly more investment (that is justified if we 10-100-1000x the amount of sats) is required eventually.
But compared to what it takes to make cars not crash into each other its nothing.
(Unless its like US infrastructure design that seems to want to make cars crash into things, but I hope in Space we can avoid that)
Collision avoidance in LEO is quite elegant. When two satellites are predicted to pass uncomfortably close to one another, one satellite will fire its station keeping thrusters to raise its orbit above the other. No brakes or swerving needed, just a slight push well ahead of time. Starlink sats do this over 1000 times per week.
Even better, energy used for avoidance reduces energy needed for station keeping on a 1:1 basis. Avoidance maneuvers are effectively free.
Starlink initially used Krypton for its thrusters. But they have now switched to Argon since its incredibly cheap and available. Xenon for a long time was the standard, but its to expensive and rare.
Some sats also have chemical power, often a Hypergolic propellant, like dinitrogen tetroxide plus hydrazine. Specially for larger sats this is the case.
- https://en.wikipedia.org/wiki/Ion_thruster
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Debris in a crowded orbit will eventually collide, no matter how synchronized it all was initially.
> Debris between 1 cm and 10 cm (approximately 500,000), referred to as the “lethal” population, are the most concerning as they cannot be tracked or cataloged and can cause catastrophic damage when colliding with a satellite. Objects smaller than 1 cm (approximately 135 million measuring from 1mm to 1cm, and many more smaller than 1 mm) that could disable a satellite upon impact are termed the “risk” population
And the Starlink sats are so low that they dont really turn very meaningful debris ever.
And in general, yes LEO can handle millions of sats.
We have like 150k cars in a single tiny country on earth right now.