[johnklos]

Scott Manley, unsurprisingly, did a nice video showing what it'd look like if you could see all the satellites and debris in space from the surface of Earth. It's scary how much stuff there is up there.

https://www.youtube.com/watch?v=dJNGi-bt9NM

[WastingMyTime89]

Not really. Even low Earth orbit is absolutely gigantic. It’s considerably larger than the surface of the Earth after all. Scott Manley has the same issue that this website: for things to be seen, you need to magnify them extremely.

Each dot here represents things at most meters large. Most are centimetres large especially if you look at debris. Yet each dot is the size of a large urban area on Earth. Do the same thing with planes or boats and the Earth will be close to painted a solid colour.

Obviously, to size, you would see nothing from this distance which would be a lot less impressive, a lot less useful but a lot less scary.

[schiffern]

>Obviously, to size would be less scary.

I was expecting this, since it's probably the most common criticism of this type of visualization.

Problem is, that analysis only looks at half the dataviz fidelity coin. It recognizes the (unavoidable) loss of fidelity in size, but it ignores the (also unavoidable) loss of fidelity in time.

In the real world these objects do not remain orbiting Earth for a few minutes (ie the interval you're likely to look at this visualization). Instead, objects above ~800 km remain in Earth orbit for hundreds to thousands of years.[1]

Mathematically this second inaccuracy tends to cancel out the first inaccuracy, therefore (presumably) making this "a lot more scary/impressive."

Strangely I always see the criticism about size, but I never see the countervailing criticism about time. I suppose it's just like you said: the size factor is "obvious", but the time factor much less so.

Eta: For some great visualizations of the space debris problem, I can heartily recommend this (slightly older) ESA video.[2] It's basically a full-length documentary crammed into 15 minutes.

[1] https://commons.wikimedia.org/wiki/File:Orbital_Debris_Lifet...

[2] https://www.youtube.com/watch?t=13s&v=9cd0-4qOvb0

[WastingMyTime89]

> I was expecting this, since it's probably the most common criticism of this type of visualization. Problem is, that analysis only looks at half the dataviz fidelity coin. It recognizes the (unavoidable) loss of fidelity in size, but it ignores the (also unavoidable) loss of fidelity in time.

It’s a real time visualisation. There is no loss of fidelity in time.

Noticing the important distortion in size is legitimate. It’s not really a criticism by the way. It’s simply that the impression of fullness inherent to this visualisation is misleading. Space is obviously mostly empty.

> Instead, objects above ~800 km remain in Earth orbit for hundreds to thousands of years.[1]

And satellites bellow 600km are only there for a couple of years and those bellow 500km a year top. Let’s not forget that area scales with the square of radius.

> Mathematically this second inaccuracy tends to cancel out the first inaccuracy, therefore (presumably) making this "a lot more scary/impressive."

I’m guessing you mean we have to take into account the fact these objects orbit a long time when considering collisions but that’s a separate issue entirely. The two don’t cancel out at all mathematically in any meaningful way.

Don’t get me wrong, I’m not saying debris are not an issue. The new deorbiting rules are definitely a good thing.

[schiffern]

>It’s a real time visualisation. There is no loss of fidelity in time.

Unless you're going to spend multiple lifetimes watching it in "real time," there is unavoidable loss of fidelity here.

I don't mean fidelity in rate-of-time, but in duration-of-time. The total time available limits the duration fidelity, just as our eyeballs and screens limit the size fidelity.

Again it's less obvious (hence this confusion), but it's no less unavoidable.

>Noticing the important distortion in size is legitimate. It’s not really a criticism by the way. It’s simply... misleading.

Extrapolating real-time events into long stretches of time is also demonstrably misleading to humans. See: the history of scientific discoveries in geology.

Your point about "legitimacy" is right on. In data visualization the goal is finding the most useful (least misleading) transform of the data, not raw fidelity.

It's just that, for the purposes of lifetime collision probability estimation, rate-of-time fidelity is more misleading than duration-of-time fidelity (since you can't have both!).

>the fact these objects orbit a long time when considering collisions

Bingo. The "scariness" comes from (where else?) the collision probability, and our estimate thereof.

>The two don’t cancel out at all mathematically in any meaningful way.

I don't claim perfect cancellation with nothing left, just that it "tends" to cancel out (ie it pushes in the opposite direction), and that this factor was being ignored.

[WastingMyTime89]

> Your point about "legitimacy" is right on. In data visualization the goal is finding the most useful (least misleading) transform of the data, not raw fidelity.

I made no point about legitimacy. The fact remains. It is a real time visualisation. It’s interesting to consider what’s currently flying above. It’s not a collision estimation tool.

> Bingo. The "scariness" comes from (where else?) the collision probability, and our estimate thereof.

There is nothing scary about the probability of collision however. Even when you take the very large safety margin the monitoring organisations like to take probability is very low.

[schiffern]

>It’s not a collision estimation tool.

Agreed, but then why did you say it gets less "scary" when you realize the size is exaggerated here?

What else could you be scared of, if you're not (implicitly) using the visualization to estimate collision probability?

Some sort of thalassephobia for giant space objects, perhaps?

>probability is very low

Now keep rolling those dice every day for hundreds or thousands of years. Thousands of dice, for thousands of objects.

People are historically bad at imagining that (just like we're bad at large distances), which is why compressing the duration is misleading.

Risk = probability * cost. The cost of collisions (both the immediate cost and the long-term cost from additional debris generation) is very high.

>There is nothing scary about the probability of collision

If you watch the video I linked earlier, it explains how we're already past the "tipping point." Even if all launches cease (spoiler: they won't), the debris problem would continue to get worse.

Maybe that isn't a scary situation to you, but it is to me.

[tshaddox]

> Unless you're going to spend multiple lifetimes watching it in "real time," there is unavoidable loss of fidelity here.

I don’t understand this argument at all. As stated previously, it’s a real time visualization, thus there is trivially no loss of fidelity in time. To claim that is like claiming that a live web cam of a city street has a loss in fidelity because it doesn’t show what the street will look like in 100 years.

[schiffern]

Not fidelity in rate of time. Fidelity in total duration of time.

Just like humans have trouble imagining/seeing large spans of space (hence the necessity of size enlargement), humans also have trouble extrapolating to long spans of time (hence the necessity of using actual collisional evolution simulations, not "guesstimating" based on pictures or animations).

The size enlargement effect makes the "guesstimate" tend to overestimate, and the time duration compression effect makes it tend to underestimate. From the start the whole thing is fundamentally a bad method of "guesstimation," but for some reason people tend to quickly raise the former issue and completely overlook the latter.

[rlt]

Maybe I’m optimistic, but I believe within a decade full and rapid reusability of launch vehicles, i.e. Starship (if successful), will radically change what is economical in space, to the point of collecting/deorbiting space debris.

[spoonfeeder006]

Maybe better to show a probability density instead?

I.e. the likelihood of hitting an object using a LEO view that is facing parallel to the earth's surface below the viewer

The idea is that in every direction is a color map indicating probability of hitting an object if going straight in that direction to infinity, or till reaching earth's surface (for downward angles), assuming all the objects are frozen in time

Not sure how to represent earth's surface though without fudging the color map colors, so maybe scratch that or use outlines to represent continents instead of surface color

Its an idea maybe?

[mickdeek86]

Does this mean the concerns about a Kessler event are greatly exaggerated?

[mlindner]

I'm not an expert but I would say I've spent a lot of time looking at this.

I'd say the risk is exaggerated in some ways and not in other ways. Kessler syndrome is a real effect but it's also not something that happens suddenly when some threshold is reached. It comes from statistics and generally assumes that no preventative action is taken when satellites are destined to collide with each other. It also assumes no attempts to clean up debris happens. Both of which are not the case in general. Many countries have rules that say that satellites cannot be left in orbit after end of mission (in the US for example that is currently 25 years, and there is effort right now to reduce that to 5 years). This kind of cuts the effects of kessler syndrome short.

Further, Kessler syndrome is different for different altitudes. People keep talking about it with respect to Starlink, but at the altitudes where the Starlink satellites orbit, because of atmospheric drag, debris don't last longer than a decade or so so. This means there isn't enough time for that statistical effect to build up and destroy most satellites, at least at current satellite densities.

There's also the argument that kessler syndrome has in fact already begun. As mentioned, it's a statistical effect that happens over time. Imagine the slowest burning smoldering campfire that takes decades or centuries to burn through it's fuel.

In short, I feel like current plans to reduce the allowed maximum debris lifetimes by some countries (as long as we can get all major space launch countries to agree) will largely make the kessler syndrome not really a risk.

[cwillu]

You're kinda asking if a number is too big, without saying which number you're asking about.

[mickdeek86]

I'm asking whether Kessler syndrome is something we should be worried about

[ghufran_syed]

No, not until the density of objects in LEO is much higher IMO

[simias]

Note that you have an option for a "Ground view" in TFA which lets you get a similar view, but real time and interactive.

[perilunar]

> It's scary how much stuff there is up there

No more scary than the number of airplanes in the air at any given time, which is a similar order of magnitude. flightradar24 tracks around 200k flights per day — there's probably ~10k–20k aircraft in the air at any time.

[jen_h]

True, but they can be methodically grounded if need be, and we’ve done it successfully before. We don’t have any good playbooks for clearing space debris.