Wait, how does launching stuff to low orbits reduce space junk?
Edit: I think I now understand your comment. I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right?
Edit: I think I now understand your comment. I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right?
Objects in low orbit don't stay there. They're slowed down by the atmosphere, and re-enter in a few months or a few years. Only if they're healthy enough to orient themselves, and have the fuel to do it, can they perform the re-boost maneuvers necessary to overcome atmospheric drag and stay up for longer.
So, a satellite which loses control, or gets smashed into bits which can't individually control themselves, just becomes fodder for the drag. It gets swept out of orbit by the wisps of atmosphere out there. Low orbit is very "clean" in terms of junk, because junk simply can't linger there. Just like there aren't a lot of ancient ruins on the beach.
The exact degree of drag is unpredictable because the exosphere is subject to a lot of variables, hence the "months to years" ambiguity. But they don't stay out there for decades or millennia, like junk in higher orbits.
That is a fantastic analogy.
Anything re-entering the atmosphere is subjected to temperatures around 8000 deg. Most things are just totally incinerated, unless they are well-enough insulated to withstand that temperature until they slow down from orbital velocity.
https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag
Is that a thing that can happen?
My intuition is it would be possible if a rocket currently boosting to a higher orbit were to collide with something on its way there, but two objects in the same orbit colliding couldn't get enough delta-v to actually get to a higher orbit. They could maybe get "higher", but not at orbital speeds and so would rapidly decay.
I know next to nothing about orbital mechanics, so maybe someone who does can provide some better insight here.
Apparently not as such. See sibling comment here:https://news.ycombinator.com/item?id=26809297
Basically, just based on impulse and energy conservation, and some assumptions on the size and number of fragments, a head-on collision of two satellites going opposite directions at the same orbit should send some pieces of debris into much higher orbit.
How likely this is to happen in reality, and thus how big a problem this could be is a subject of modeling and much more complex calculations.
See "can you throw a baseball from the ISS and hit the earth" (No, you can't.)
If it helps, start by imagining two satellite-like machines colliding in interstellar space (i.e. not in orbit), where they were initially moving at 1m/s in opposite directions. Even ignoring the possibility of an explosion (unspent fuel, pressurized areas, I dunno), it's still very easy for interactions to violently fling individual parts outward at speeds higher than 1m/s.
Of course, my guess is that the possible amounts of additional delta-v are pretty low, like 100 m/s, and as such the resulting orbit would not be much higher than the original orbit. But that's just wild conjecture.
Fragments that are launched down obviously hit the Earth. But an orbit is a closed ellipse, so the fragments that are launched up will _also_ hit the Earth -- they'll just go up steeply, turn around, and come down. The only fragments that won't initially hit the Earth are the ones that are ejected tangentially, parallel to the Earth's surface. Those will go into an elliptical orbit with a high apogee and perigee at the altitude of the collision. Which means they will _still _come down to that altitude and gradually lose energy.
However.
The grandparent post claimed that "Fragments that are ejected from the collision cannot have more than energy than they had originally, nor can they change direction very much", which I think is clearly what I addressed in my comment, and I stand by my correction of that, and your reply doesn't address this at all.
Also, with respect to "you _cannot_ launch them into a higher orbit", you just agreed that you can have a higher apogee than the collision. If the input satellites had perigees lower than the altitude of collision, you can also have a lower perigee. More velocity at this point on the orbit, higher apogee, higher perigee.... So how do you figure you cannot have a higher orbit?
But more generally, how does this justify your claim that "Fragments that are ejected from the collision cannot have more than energy than they had originally"? Or were you conceding that point and making a different point?
See also my more-detailed cousin of this comment.
Likewise, if the particle is slowed down, the highest point of the new orbit cannot be any lower than than the altitude of the collision.
An interesting feature of orbital mechanics is that a change in velocity at a given point in orbit will change the altitude of the orbit at every point except where the change took place.
Debris from an explosion/collision can have an unlimited apoapsis, but the periapsis is at most the altitude of the incident.
So if it started in low orbit, it will still drop down regularly, and drag will still remove it over time.
The orbits will be elliptical: exactly how elliptical depends on the directions of the two objects hitting each other and the dispersion of the fragments (how much the fragments have sped up or slowed down compared with original objects, and change of direction).
The fragments the stay in orbit the longest should be those that remain closest to a circular orbit?
Sure, but that's not really the point. Using biodegradable plastic is much better than traditional plastic that stays in landfills forever. "Just don't generate trash" isn't an option.
Eg if it is $10m to LEO and $15m to HEO you will pay the extra to get to HEO and put a satellite designed for long life - but if it is $1m to LEO you can build a cheaper satellite and launch it 5 times over the following decades.
I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk.
No. First, The whole reason they need to maintain a fleet, rather then just having it sit there for decades, is that they're so low. The vast majority of planned Starlink satellites from that number are from Phase 2, and are V-band VLEO sats with orbits around 340 km, which is really low. At that altitude, natural decay time is measured in weeks at best. To work they'll need both active thrusters providing regular boost and aerodynamic low drag design (and maintaining orientation for that will itself require fuel). Should they actually lose all control through malfunction or a collision, they and resulting debris will deorbit very rapidly (they'll both have no boost and be less aerodynamic).
And second, "through malfunction or collision", because it's not as if SpaceX (and other LEO satellite operators) doesn't have, and indeed are required to have, plans for controlled deorbit at EOL. Most of the satellites can be expected to get deorbited in a controlled way as planned. Making sure everything burns up has been one of the things slowing Starlink development, it took some work to ensure the optical links would properly go for example.
SpaceX is not interested in leaving them up there. I mean, FFS people, who would be hurt more than SpaceX by Kessler Syndrome!?
>I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk.
Your dismissiveness towards hundreds of millions of underserved people and challenging use cases and ignorance of orbital dynamics does you no favors here.
This is pompous and elitist nonsense of the highest order. People have other more pressing concerns than fast internet. You know...like water, food and cheap power.
Also it's worth noting that communications networks is but one application for LEO satellite constellation technology.
With some gyroscopes, I think they only need electricity for it, not actual reaction mass.
Imagine thinking that a product that costs $500 up-front and $99/mo thereafter and uses ~100 W constantly is designed for "hundreds of millions of underserved people".
LEO sats will probably produce more space junk by mass but junk in LEO will be gone in a few years, no matter how much or little of it their is.
On the other hand Geostationary satellites produce much less junk in terms of mass, but once it's up there it's not coming down for centuries.
That said, an impact at this level can still spew debris into higher orbits, as the chaos of the collision can impart enough energy to some collision ejecta to change their orbit significantly. So you still don't want things bumping into each other.