The risk of orbital debris and one cheap way to mitigate it | Hacker News Reader

The risk of orbital debris and one cheap way to mitigate it

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It's unclear to me how improving one's ability to pick out satellite reentry events from weather radar data either "mitigates the risk of orbital debris" or (as the article's title claims) "saves billions". Satellites (and space debris) large enough to show up on these radars are certainly large enough to be regularly tracked by the US SSN (https://en.wikipedia.org/wiki/United_States_Space_Surveillan...) (which also provides reentry predictions and estimates), so this is largely a correlation exercise.

It's interesting work (IMO), but the post isn't clear about how the work fits in to the broader space situational awareness/space traffic management ecosystem.

There are probably way more NEXRAD sites than there are SSN radar sites. Also this is using infrastructure that already exists.

This is a good point, and I definitely did a poor job addressing the fit for the flashiness of the title. The understanding that I have is that the SSN does a pretty poor job cataloguing re-entry phenomena and current models for predicting re-entry are pretty unskilled. The idea for something like this is to simply use existing infrastructure to vastly expand the body of knowledge on re-entry events which will allow for a more complete and robust understanding of what's going on above.

That sounds like a really interesting article ;) Seriously, what you've done is interesting enough, you don't need to spice it up with a misleading title.

I did not find a way how to get rid of orbital debris in the article.

Me neither, so I'm reasonably disappointed. Can I propose a method?

We should shoot something really sticky up there, creating a snowball effect. When it becomes to heavy it will fall and disintegrate. We will have some collateral damage, but you cant make an omelet without breaking an egg.

I think it needs a certain density of debris to get into that Katamari Kessler Syndrome.

Also you might want something with a low aerodynamic profile to help with reentry

I worked as a researcher on orbital debris during university and now work full time on this and adjacent problems. My full write-up on the approach for using cheap radar data to assess orbital debris is here on my blog.

Cool research and an interesting article!

I didn't see how the hn title fits though, as your article is on how to identify debris in re-entry phenomenon (super super cool that our doppler radar networks are catching debris re-entry events!). I did not understand the connection between re-entry event detection and mapping debris to prevent collisions before re-entry.

Here are my “back of a napkin” odds. Please correct!

Let’s consider a perfect sphere the size of the earth (500 trillion m^2). On that sphere, there are 10 racecars (each 10 m^2) going lethally fast. What are the chances they will hit each other?

Well, this depends a lot on initial conditions, but if we simply randomize their placement, it should be something on the order of the area of all the cars divided by the area of the sphere. Safe!

Now, let’s assume there are 10000 lethally fast racecars zooming around this earth-sized sphere. Now it is a bit more nerve wracking, but earth is big. And, we can assume they have good initial conditions— all in different lanes (and, IRL, mostly on different spheres!).

So, let’s make things harder. Say I have a gun that shoots 100,000 bullets in all directions on this empty earth, and those bullets keep flying around forever—how long will it take before they hit one of my 10,000 racecars? This is harder to estimate, but it should still be on the order of a 1 in 10 billion chance per orbital cycle (say, of 1 hour each?). So, in 10000 hours (~400 days), you have a chance of 1 in 1 million chance that one of the racecars will be hit by the bullets. So, it will be about a thousand years before you get to a 1 in 1000 chance. Is that about right? Don’t trust my math.

In contrast, the lifetime odds of dying in a car crash are about 1 in 100 (See cite) https://injuryfacts.nsc.org/all-injuries/preventable-death-o...

haven't done the math, but two things come to mind.

1) the distribution is not random. Satelites are more densely distributed in certain diserable orbits, than in others.

2) you can not compare indivdual risks with societal-wide risks.

1. While the orbits might be bunched up, the orbital surface area is bigger than the earth — and satellites are in many different orbital altitudes. So, I wanted to simplify in order to get an order of magnitude estimate.

2. The risk of an individual dying in a car crash is being compared to the risk of any satellite being hit. Of course, people die every day in car crashes and satellites don’t get hit often. The point was to give a sense of the magnitude of acceptable risk.

Because that’s what I’m struggling with — how big of a problem is this at the moment?

The ISS (which always has 3+ humans on it) pretty regularly has to maneuver to avoid debris nowadays (NASA is conservative and will do so if a big window has a ~.01% chance of seeing debris). You can count on your hands the number of times a major collision has occurred since the 90s, but that's probably partly because now more than ever we actively track and avoid debris.

Satellites can also be multi-million to multi-billion dollar assets. They're less like cars and more like oil-rigs.

>it will be about a thousand years before you get to a 1 in 1000 chance. Is that about right? Don't trust my math.

The ESA's long-term collisional evolution simulations, as visualized in this video[0], seem to disagree with that result.

[0] https://youtu.be/9cd0-4qOvb0

Your math gets you within an order of magnitude or so, check out NASA's work on ORDEM to predict this with Monte Carlos.

Two things: 1) The probability is very sensitive to # of objects and size assumptions. If you decrease the area of the bullets by an order of magnitude, the probability that it you will hit one 10 m^2 satellite in a year goes to 10%+ 2) satellite orbits are not randomly distributed. Within 700-900 km altitude, the probabilities are ~2-3 orders of magnitude higher (1/1000/m^2/y)

https://ntrs.nasa.gov/api/citations/20150003495/downloads/20...

Yay for napkins!

I don’t actually see in the presentation where risk estimates are given. Only spatial densities.

And why would decreasing the area of the bullets increase the probability of hitting a satellite?

This is great research and very useful (if sometimes mundane and math heavy!) work. It’s a public good and the author has made important contributions.

I kind of chuckle that many of the comments here are complaining that the article didn’t say the one “quick way” to clean up orbital debris. Is it lasers? Space tugs? Robotic deorbit devices? No! The author did answer it - it’s tracking! Knowing where all the debris objects are and calling out debris offenders/enforcing existing regulations is really enough. This kind of work - not the hundreds of millions spent on space tug demos, harpoons, and exotic nonsense - is actually useful. Everything else is an excuse for rich VCs and armchair aficionados to yell “have you heard about Kessler syndrome?!?”

In broader context: Corporations need to pay for the waste they leave behind. The price would be the cost to recover and cleanup the junk.

I believe creating space junk would be rather expensive to clean up. Same thing for ocean waste. if corporations put cheap non bio degradable plastic in the ocean they will have to pay cleanup cost.

I always wondered why no one doesn't put up deorbit or retrieval bounties on all abandoned/dead debris in orbit. If you can prove you deorbited it then you get the money, if not then someone else has a shot at it. Obviously, it needs more planning than that but the overall concept I think is a good starting point.

If you'd like some good science fiction about this issue and Kessler Syndrome, Makoto Yukimura's Planetes is just an amazing read.

I've watched the animated series.

This seems like a good way to get fluorescent men in suits knocking at your door. Orbital tracking is still rather strategic pursuit, no? There are several rather large radar installations trying very hard at it.

A magnet?

Don't be ridiculous. We need tractor beams.

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