If there are many satellites orbiting earth, how do space launches not bump into any of them?
In: 2066
You have to think of geometry, and the equation for a volume of a sphere. V=4/3piR^2, and as you see every time you move further from Earth the radius of the sphere increases, and the volume or amount of space increases exponentially. So there is a lot more room in space than on the surface of Earth. There are over 7,000 satellites, smaller than planes and in a larger area. They move way faster, but relatively based on the space they’re not much different than the 7-9k planes flying around. So the likelihood of a rocket launch crashing into a plane is probably just as likely. We make planes avoid rocket launches, but we probably don’t have to, the chance they would collide is tiny (we still track them to be safe). Planes only collide because they share airports and all group up at the same tiny few locations. So the only reason planes hit is because they’re both told to go occupy the same spot of sky.
Space is deeper too, so the kilometers from Earth that satellites can exist in is deeper than Earth to space. Like all the planets can fit in between Earth and the Moon, and the Moon is a satellite. It was very very hard to hit the moon.
On a similar note there may be millions of objects in the asteroid belt but the odds of hitting something while flying through are neglible, no matter what C-3PO says.
Satellites and debris are closely tracked and, when possible, maneuvered to avoid each other. Recently, Starlink satellites have had to alter course at a rate of 50,000 times per year to avoid collisions, and the rate is growing rapidly (perhaps exponentially).
[https://www.space.com/starlink-satellite-conjunction-increase-threatens-space-sustainability](https://www.space.com/starlink-satellite-conjunction-increase-threatens-space-sustainability)
Space is really big. It’s not a perfect analogy but imagine standing in the middle of a city and shooting a gun straight up randomly. When the bullet comes back down, it’s pretty unlikely to hit anyone. Now since we can track where any operational satellite is, and have a good idea of where most dangerous space debris is, imagine you could point the gun straight up but be able to calculate its trajectory and avoid it coming down on any sidewalks, plazas, or any other areas where there’s likely to be people to get hit. Sure if you aim for say the lake in the middle of the park and there just happens to be a person randomly swimming there, but the odds are astronomically low
The problem is that your definition of “big” is not big enough. When Douglas Adams says, “space is big,” he really means it. Imagine throwing a dart at the screen of your monitor and hitting one exact particular pixel to cause a collision. Space, even just the volume of low-Earth orbit, is much bigger than that.
Having said that, SpaceX recently disclosed that their giant sat network performed over 20000 evasion maneuvers in the past year.
Just coming close to another satellite is dangerous because you can imagine each satellite existing within a small cloud of paint chips and dust, all of which is going 17000 mph. Touch it and you don’t just die, you make a bigger cloud of debris. The runaway result of that is called, “Kessler Syndrome” and all the evasions are, in part, an effort to avoid that.
Edit: Or here’s another way to look at it. The volume of LEO is considerably larger than all the lakes and oceans of the world. How do submarines not bump into each other?
I work in this field! Launches (from US allied nations, at least) are always screened using a process called Launch Conjunction Assessment.
As others have said, satellite orbits are carefully tracked and predicted – the planned trajectory of the launch vehicle is compared to all those predicted trajectories to predict any close approaches and associated risk over a given launch window. The mission director can then select an appropriate launch time with minimal risk of collision with any satellite or debris already in orbit.
Space IS big, as others have said, but if you just randomly select a launch time into a crowded orbit regime, existing satellites and especially debris ARE a huge problem – since satellites are amazingly expensive, you want to minimize risk as much as possible.
Imagine you fell from space and landed in the ocean.
Now imagine the odds of randomly landing on a boat.
tens of thousands of them sailing around, and yet the odds are infinitesimally low.
The odds of hitting a satellite in orbit around earth are orders of magnitude even less likely than that example because the volume of space around Earth is unfathomably vast.
A little bit of distance which is e.g. 100kms on earth will be around 10000kms in Space, because space is huge. The satellites you’re talking about are barely a few 100 meters in length. In a area where a small distance that may seem to us, is actually a very large distance.
There’s a game, universe sandbox, you may wanna try out the Satellite tracking function on it. And you can also see how huge distances are between these satellites.
You’re underestimating just how large space is. Consider this, roughly 2% of Earth’s surface is covered by the United States (just using the US as an example because automobile stats are readily available). Each day, roughly 115 *million* cars drive on roads in the US each day. Earth’s surface is also effectively 2 dimensional for things like cars (i.e., cars don’t fly over or under each other, and yes, bridges and tunnels can change that, but for the most part, it’s true). Yet despite the fact that over 115 million vehicles operate in an area less than 2% of the Earth’s surface (even less considering cars only use roads, not the entire continent), we don’t have many major issues. We can operate our vehicles just fine and get things done that need to be done.
Now consider space. Low Earth Orbit (where most satellites operate) is not limited to just 2% of the surface area. Theoretically, they can make use of 100% of the sky and travel anywhere we want them to (practically though, it depends on the purpose of the satellite on what orbit they take). Space is also 3 dimensional, unlike Earth’s surface, so we can put some satellites higher or lower than others. Sometimes, this is only slightly higher or lower than others, maybe a mile or less. Other times, it’s vastly different. The James Webb Space Telescope, for example, orbits over 1 million miles away from the Earth. This means there is **FAR** more space (many orders of magnitude more) to keep satellites in than there is for cars to drive in the US. Yet, there’s only roughly 7,700 satellites in orbit compared to 115 million cars in the US. Quite frankly, considering these numbers, it’d be a miracle if satellites somehow *did* manage to collide.
But those are just the raw numbers on the scale of space. In practice, not only is space insanely large (even just Low Earth Orbit) but every satellite, and even significantly large random pieces of orbiting debris, are being tracked by space agencies to make sure no collisions happen regardless.
Despite the above, there is still a worry that space could eventually become so cluttered (especially if there’s an accident that causes a vast number of very small pieces of debris to scatter into orbit) that no new space craft could be launched without getting torn apart by orbiting debris. This phenomenon is called [The Kessler Syndrome](https://en.m.wikipedia.org/wiki/Kessler_syndrome) and would be detrimental not just to space exploration, but space based communication and systems like GPS. For that reason, space traffic is heavily monitored and regulated to prevent it. There’s also ongoing research on how to “clean up” space if the worst happens, and it *does* become a mess that prevents space travel. Many ideas simply boil down to a big space net that catches the debris and deorbits it.
Most satellites are low Earth orbit, from about 300-2,000 km. Just at 300 km there’s about 560 million square kilometers for them to float around in. But then there’s higher orbit, go up to 400 km and there’s another 580 million square kilometers of area, and so on and so on. That’s an awful lot of room for a few thousand satellites, making the odds of hitting anything pretty low.
But then they also track satellites and account for their positions when launching.
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