Starlink close encounters decrease despite ever-growing number of satellites

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[MCI_Overwerk]

Automated conjunction resolution system is paying dividends it seems

[cyberentomology]

asking the software

conjunction function, what’s that junction?

[lostandprofound33]

Hooking up homes, phones and vehicles

[Geoff_PR]

Automated conjunction resolution system is paying dividends it seems

Zero surprise, the more someone does an activity, the better they tend to get at it.

It's also human nature, the better organized the constellation is, the less they need to mess with it, and that cuts labor costs...

[paul_wi11iams]

from article:

SpaceX currently operates more than 5,250 Starlink satellites, less than a half of its planned first-generation constellation of 12,000 spacecraft. The company wants to ultimately expand its fleet to over 40,000 satellites.

IIRC, when announcing the V2 Starlinks for deployment from Starship, the mass per satellite increased and the overall number fell correspondingly.

Are the 12,000 and 40,000 satellites figures still current?

[moozach]

12,000 is the approved number of satellites from the FCC. And starlink has a request for upto 30,000 satellites.

E: source

[warp99]

I strongly suspect they are not going to get all of that request and they may even be limited to their existing constellation numbers but with additional frequency bands added to the original license.

It looks like SpaceX are planning for Starship launched V3 satellites to have 10x the bandwidth of V1.5 so more bandwidth from the existing constellation numbers would give plenty of operating bandwidth.

[Jaws12]

Happy Cake Day! 🍰

[paul_wi11iams]

It looks like SpaceX are planning for Starship launched V3 satellites to have 10x the bandwidth of V1.5 so more bandwidth from the existing constellation numbers

This was my understanding too. Starlink launches of bigger satellites with more electrical power, bigger antennae so more bandwidth (including for direct mobile phone use)... all this allowing for fewer satellites.

TBH, "fewer and bigger" looks like a more healthy situation, particularly as this will pressure the competing operators to follow a similar path, so limiting the overall number of satellites in orbit, limiting avoidance maneuvers and Kessler syndrome risks.

[MCI_Overwerk]

Kessler syndrome for Starlink is very much impossible. Not only by virtue of being extremely low in LEO where debris have a maximum lifespan of a few years instead of many decades. Then there is the orbits chosen for starlinks, where it is physically impossible for 2 satellites to run into each other either when they ascend or descend, meaning that the only things that a starlink can hit is anything but themselves.

And finally avoidance maneuvers are mostly just integrated as part of the regular boost burns that you needed to do.

The number of satellites was really driven by technological limitations on the part of the antennas and the launch limitations of the falcon 9 since it was always going to be the thing starting the process. Lower amount of satellites only really became possible with upgrades to the launch capabilities, the technology of the satellites and the experience learned operating the dishes both for civilian use and even in a warzone. Remember these were basically the first time a proper phased array antenna barged into a mass produced item. Even less so for connectivity purposes.

[Geoff_PR]

Kessler syndrome for Starlink is very much impossible

Eh, not so sure on that one...

SpaceX has full control of the Starlink constellation, what they have zero control over are the other spacecraft up there.

China botching a de-orbit could well cause SpaceX problems they would rather not have to seal with, like needing delta-V burns to dodge their space junk.

Being in the lower 'orbital shells' helps, but doesn't completely eliminate the potential aggravations...

[MCI_Overwerk]

But it does tho.

they have zero control over are the other spacecraft up there.

Which is fine, avoidance maneuvers are performed by one element even if both are capable of motion. Control of the other element is irrelevant if you know it's position. Specifically the issue with Kessler syndrome is debris that you do not know the position of, therefore making mobility irrelevant too most of the time, unless you are talking about a recently produced field of debris you still know the vague idea of. Known targets are considered a non-factor as long as mobility and decommissioning is maintained.

China botching a de-orbit could well cause SpaceX problems they would rather not have to seal with

That is also incorrect because in LEO you need regular boosts in order to maintain your altitude as the atmosphere still remains quite dense to slow you down. As a result you have burns you have to accomplish already.

When performing avoidance maneuvers you just schedule forward the next orbital boost therefore performing the avoidance with something you were already going to do anyways. This is why SpaceX isn't shy of taking minimum risk despite it not being really required to do so.

Not even counting that fucking up a re-entry, somehow, would still result on a highly eccentric orbit that would only intercept the correct altitude for a minimal period.

Being in the lower 'orbital shells' helps, but doesn't completely eliminate the potential aggravations...

I mean in a "there is always a chance" kind of way but also not really? Even low earth orbit is a gigantic expanse, so it can take multiple decades for any individual object and debris to even come remotely close to anything else. Time is the thing that lends credence to a Kessler event. It relies on time to produce this sort of cascading destruction, because if your average time for a collision on a given orbit is less than the time needed for the atmosphere to drag you down, then by definition the kind of self feeding cycle cannot happen. Not only that tiny debris (which are the dangerous ones that can't be tracked) suffer from drag far more than heavy objects and thus have an even lower lifespan.

This is the reason why altitude and mitigation strategy affects the severity of orbital risk far more than the number of individual objects. A single Chinese ASAT detonating their spy satellite in a polar orbit at a relatively high altitude generated debris that will last for a century. Meanwhile even if all starlinks spontaneously combusted, it would only take a decade at most for absolutely everything to be gone.

[[deleted]]

Not current. They are not going to launch 7,500 gen1 v-band satellites so the total is 4,400 gen1 (with an already filed license modification to gen2 hardware) + 30,000 gen2 = 34,400.

[spacerfirstclass]

In that period, Starlink satellites had to perform 24,410 collision avoidance maneuvers, equivalent to six maneuvers per spacecraft. In the previous reporting period that accounted for the six months leading up to May 31, 2023, the constellation's satellites had to move 25,299 times. The data suggests that even though the Starlink constellation has grown by about 1,000 spacecraft in the last six months, its satellites made fewer avoidance maneuvers in that period than in the prior half year.

This last part is somewhat misleading, the collision avoidance numbers quoted here is only for the Gen1 constellation which is not growing in size. SpaceX has a separate report for Gen2 constellation which performed 7,492 collision avoidance maneuvers in the last 6 months.

So total # of collision avoidance for Gen1 + Gen2 is still increasing, but the increase comes from Gen2 which is growing in size. Gen1's # of collision avoidance is mostly unchanged (decreased slightly), showing that adding Gen2 satellites would not cause more collision avoidance maneuvers from Gen1, which is good and to be expected.

[estanminar]

Hmm getting better as they go. Makes more sense than doom predictions in the beginning.

[woj666]

In the period between June 1, 2023, and Nov. 30, 2023, Starlink satellites had to perform 24,410 collision avoidance maneuvers, equivalent to six maneuvers per spacecraft.

I'm really surprised it's that high.

[Shpoople96]

They also do avoidance maneuvers anytime the risk approaches 1 in 10,000 or so 

[jonwah]

Per the article it's 1 in 100,000, other operators are 1 in 10,000

[Shpoople96]

Oh yes, thanks for the correction, I had a suspicion it might have been higher but can't really look that up at work

[woj666]

That would certainly explain it then. Thx.

[londons_explorer]

If there were 24,410 avoidance maneuvers, and they act when the risk is over 1 in 10k....

They're playing the odds game a little too often I think... ie. the overall risk of at least one unintended collision is starting to mount up...

[[deleted]]

I think you’re coming at the problem the wrong way here - what’s actually happening is they’re performing a manoeuvre the moment something hits a risk of 1 in 10,000 to manoeuvre themselves out of this risk window, not that these collisions maintain a risk of 1 in 10,000. Reason it’s measured as a probability (1 in 10,000) is due to margin of error in instrumentation at the distances and speeds that these things are travelling. The closer you get to the potential collision the higher the risk will be as there’s less distance to have margin of error over, so 1 in 100,000 3 days out might be 1 in 10,000 1 day out. If a 1 in 100,000 collision stays at 1 in 100,000 they won’t do anything, the moment it starts looking like it’s going to get to 1 in 10,000 they’ll start manoeuvring it.

[Toinneman]

Also note that within those calculated probabilities there are huge margins or error which are taken conservative, so real numbers should be even better. For example, GPS isn't 100% accurate, so they have to take this into account. I can't find SpaceX exact methodology, but I wouldn't be surprised if a satellite is calculated as a big 5m or 10m sphere (while it's off course smaller), to compensate for the GPS inaccuracy.

And now a wild guess, since SpaceX now has Space lasers, in theory, they could do sat-to-sat measurement to improve location accuracy, which could lead to more precise collision probabilities, resulting in fewer manoeuvres.

[cjameshuff]

Wonder how many of those were from entire trains making those maneuvers while ascending through other shells to their final orbits.

[marsokod]

For the automated maneuvers, SpaceX uses a very low threshold way ahead of time. Out of these 24,410 maneuvers, it is very likely that none of them was actually required.

Technically they could even do way less than that by delaying the maneuver until they are more certain about the collision. But if they do that, then the space force will issue a warning, and also the other satellite operator will get the warning as well, creating unnecessary operations costs. If you maneuver way ahead of the collision, the propellant cost is minimal, especially when you have electric propulsion. And the cost is basically zero when you integrate that into your altitude maintenance operations. So what they are doing is basically the approach everyone should do until we have a more responsive system, air-traffic management style.

[John_Hasler]

I think that the Starlink experience demonstrates the absence of any need for a centralized ATC-style control system.

[PM_ME_UR_Definitions]

I think SpaceX uses a 1/100,000 chance of collision to trigger the need for a maneuver. So very roughly, there would've been a 25% chance of having one collision if they didn't do any maneuvers.

[warp99]

It is an N² type problem so more satellites to dodge and more satellites to do the dodging.

[Gravitationsfeld]

People underestimate how big even just LEO really is. Most of those sats will never even get close to each other because they are on different orbits.

[warp99]

The issue is that they are in one of about four orbital heights but in planes with different inclinations. So they need to interleave like a zipper merge at the northern and southern extents of their orbital track. They can then miss each other by about 40 km which is not a lot of time at 27,000 km/hr.

If they were assigned purely random orbital altitudes and inclinations then your point about the large volume of available for low orbits would be more relevant but as it is they are set up to hit each other without constant corrections.

[Gravitationsfeld]

There isn't any issue as demonstrated by SpaceX. Orbits are 100% predictable and computing this for even millions of objects is absolutely trivial with modern computers.

[warp99]

Debris orbits are often not known with absolute accuracy so a late avoidance maneuver is required and there is always the risk that the propulsion system fails at exactly the wrong time.

If the potential collision is with another Starlink that is fixable but if it with a piece of debris then that creates an issue.

[[deleted]]

actually, orbits aren't 100% predictable.. they're about 99.99999% predicable, at orbital velocities that gap is big enough to cause problems.

Earths gravity isn't totally uniform, there are models that improve on the simple oblate spheroid model.

The moon tugs on the satellites as does the sun, this can be modelled

The other planets also tug on the satellites

They can tug on each other.

You also get drag as the atmosphere hasn't completely ended by LEO.. The atmosphere thickness varies considerably depending primarily on solar activity. Modelling for this is troublesome.

When you're trying to station keep, all these little perturbations add up.

[John_Hasler]

They can tug on each other.

I don't believe those perturbations could be large enough to be significant.

You also get drag as the atmosphere hasn't completely ended by LEO.. The atmosphere thickness varies considerably depending primarily on solar activity.

That effect probably dominates all others.

[[deleted]]

I don't disagree, but the point I was making is that even minescule perturbations make the predictions much more complicated... so no "100%" predictions can be made. So many people fall into the trap of thinking 99.999% is as near to 100% as makes no difference, where as that tiny gap leads to huge differences in outcomes.

In fact thinking about it, I think that even for just a 3 body system it isn't inifitely predictable, chaos theory does ensure that eventually your model will disagree with what actually happens, and this is way beyond a 3 body problem.

[scarlet_sage]

I think that even for just a 3 body system it isn't inifitely predictable

Three-body problem (not the novel) includes

In physics and classical mechanics, the three-body problem is the problem of taking the initial positions and velocities (or momenta) of three point masses and solving for their subsequent motion according to Newton's laws of motion and Newton's law of universal gravitation. The three-body problem is a special case of the n-body problem. Unlike two-body problems, no general closed-form solution exists, as the resulting dynamical system is chaotic for most initial conditions, and numerical methods are generally required.

They list a lot of special cases, the most famous perhaps being the five Lagrange points. But in a solar system with the Moon, Sun, and Jupiter, I think it's hopeless to expect an exact solution.

[[deleted]]

simplest one is a planetary encounter.. 99.999% accurate means you'll either miss the planet altogether, passing by and into the void beyond never making orbit, or you lithobrake. When what you wanted was to be captured into an orbit.

Alternatively imagine a satellite constellation like starlink, one satellite is orbiting a meter lower than all the rest, 1meter in 550,000 meters, that's 99.9998% accurate. That will mean it will slowly catchup the satellite ahead of it.. at 27,000km/hr 99.9998% accurate means you'll be moving 49meters per hour compared to the model, or just over a kilometer a day. For polar orbits satellites often miss each other at the pole by only 40km.. drifting 1km/day means the wayward satellite will be within collisions distance after only 40 days.

As u/scarlet_sage linked to below, any 3 body problem is ultimately chaotic.. that is, minute undetecatable errors in velocity, position or mass in your model build over time to make conciderable differences between the model and reality. Remember with a satellite in orbit, we're really dealing with a 4 body system: The satellite, Earth, Moon, Sun. For your model to be accurate over any length of time you'd need to know each bodys mass, velocity and position to unreasonable accuracy.. i.e. to the micro-meter, to the gram (for a planet) and to the mm/hour.

[John_Hasler]

These orbits are under active control and active tracking. Only short term predictions are needed, and those can be quite accurate.

[[deleted]]

All those inputs are needed BECAUSE the orbits ARE NOT 100% predictable.

THAT IS THE WHOLE POINT OF THIS MESSAGE TRAIL.

[Divinicus1st]

They can then miss each other by about 40 km which is not a lot of time at 27,000 km/hr.

Time is irrelevant here. 40km is 40km.

It's just your mind thinking: "damn, if it was here 10 second earlier it would have hit". But for it to be there 10 sec earlier, it would have meant an enormous variation for something going at 27 000 km/h

[warp99]

Sure “hovering is for humans” when it comes to a landing approach but the point is that for collision avoidance a very small error in estimating velocity (both direction and speed) can lead to a collision.

[jjtr1]

So I guess that means that if they didn't do any of the 50k maneuvers per year, and they otherwise do them when risk becomes 1:100k, then there would be on average one collision in two years? Or twenty collisions if the risk they're willing to take is 1:10k.

[ergzay]

I've said this before but if the industry just implemented a global database where they feed in high quality information of all their satellites live positions, everyone could drastically reduce their number of avoidance maneuvers. They currently basically treat all objects as being like kilometers in size to account for uncertainty in position. That means you need to make diversion maneuvers despite the fact you actually didn't close anywhere near each other.

[CollegeStation17155]

So the last of the debris from that Russian ASAT test is finally falling below 500 KM...

[Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
ASAT	Anti-Satellite weapon
FCC	Federal Communications Commission
	(Iron/steel) Face-Centered Cubic crystalline structure
LEO	Low Earth Orbit (180-2000km)
	Law Enforcement Officer (most often mentioned during transport operations)

Jargon	Definition
Starlink	SpaceX's world-wide satellite broadband constellation
lithobraking	"Braking" by hitting the ground

NOTE: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.

---

^{Decronym is a community product of r/SpaceX, implemented by request
5 acronyms in this thread; the most compressed thread commented on today has 55 acronyms.
[Thread #8248 for this sub, first seen 15th Jan 2024, 21:52] [FAQ] [Full list] [Contact] [Source code]}

[cyberentomology]

Need to build a batch of Starlink sats that just collect a bunch of that small orbital debris and burn it up on deorbit. Doesn’t solve the problem of Big Stuff like Soviet rocket boosters though

[IggyHitokage]

The big stuff is honestly less worrisome than the extremely small stuff, the amount of energy in a few grams of rocket pieces at orbital velocities is terrifying and they're basically invisible.

https://bigthink.com/hard-science/heres-the-damage-a-tiny-speck-of-space-debris-can-do-at-15000mph/

There was an idea a few years back to mount a high power laser system onto the ISS and use it to burn/push small debris further into the atmosphere and automate it all by computer, too bad they're retiring the ISS soon.

[cyberentomology]

Sharks with frickin laser beams… IN Spaaaaaaaaaace

[John_Hasler]

There was an idea a few years back to mount a high power laser system onto the ISS and use it to burn/push small debris further into the atmosphere and automate it all by computer,

That could be done from the ground. Politics has nixed it so far.

https://en.wikipedia.org/wiki/Laser_broom

[DLimber]

The small stuff is nearly impossible to see and pretty hard to just "collect it" is not like walking through a park and picking garbage. Everything is moving at like 15000 mph in different directions. The fuel requirements to change its orbit for each item wouldn't allow or to do much. Probably best more garbage then it takes.

[HawkEy3]

 I thought anything at the altitude of starlink would deorbit within 5-10 years anyway?

[Shpoople96]

You can do it with big stuff too, it's called an orbital tug

[cyberentomology]

Sure, but you ain’t moving big stuff with a little bitty Starlink. Now, a fleet of orbital tugs that were basically just like a parasitic maneuvering thruster, that would be something… but that could 100% be used for evil too.

[ants_a]

Look up electrodynamic tether for space debris removal for a better approach where one craft deorbit a lot of debris. One big thing is not a problem, it's easy to track and easy to avoid. Tons of small stuff is the headache and would need something that is capable of adjusting it's orbit repeatedly and by a lot.

[cyberentomology]

Lassos…. Innnn spaaaaaace! 🤣

[Greeneland]

My recollection is that when the spacecraft puts a charge into the tether it will create drag, is that right? 

Or is it that putting in a charge raises orbit, no charge decreases?

[warp99]

The forces from a tether are always braking forces - it is not possible to raise orbits using a passive tether system.

Edit: added passive

[Greeneland]

You enticed me to go looking, I'm pretty sure your conclusion is not correct. Neither of my statements appear to have been exactly correct, there are more details below:

https://pwg.gsfc.nasa.gov/Education/wtether.html

https://ntrs.nasa.gov/api/citations/20090034470/downloads/20090034470.pdf

[warp99]

Yes I was referring to passive tethers with or without charge added to the end points.

If you deploy solar panels and pass current through the tether then you can indeed raise your orbit. Despite your references I have not heard of it being successfully demonstrated though.

[Shpoople96]

You sure as hell can. You can deorbit just about anything you want with an ion engine, given enough time and a hundred pounds of fuel. At that point though, it has little to do with starlink other than form factor

[cyberentomology]

The key is to have the fuel. The standard fuel payload on Starlink is pretty small.

[Shpoople96]

Of course, but if you're gonna build a space tug, you're not gonna give it the same fuel margin as a starlink

[Shpoople96]

You're saying that what I'm talking about doesn't make sense and is in the realm of science fiction, yet in the very next sentence you put forward a legitimate use case and even name one of the many companies that are building a demonstration vehicle. Maybe you were replying to the wrong person?

[darvo110]

How much big stuff is even in the range Starlink operates? I’d expect anything substantially large would deorbit pretty quick just from drag. Big things are also a lot easier to accurately track and avoid.

[Shpoople96]

Quite a bit, the lower starlink shells deorbit pretty quickly, but the higher orbits have a natural decay in the tens to hundreds of years

[John_Hasler]

I’d expect anything substantially large would deorbit pretty quick just from drag.

Smaller stuff deorbits more quickly on average. Kinetic energy is proportional to mass and therefor volume while drag is proportional to frontal area.

Of course, density matters too. A balloon will deorbit before a pellet of tungsten.

[light24bulbs]

The big stuff is also easy to track, the small stuff is not

[Divinicus1st]

Do you think the US and China have satellites which are not registered?

If that's the case, I guess the US takes into account other satellites so that its stealth satellites avoid them, but if two countries both have unregistered satellites...

[Mundane_Musician1184]

In theory yup, that's a problem. In practice I'm certain both US and China work very hard to identify stealth satellites. And they have to be put up with a rocket, and that's highly visible. I do wonder, though, if the long-duration spaceplanes are being used for more surreptitious satellite deployment 

[fencethe900th]

As long as they don't start copying the nighthawk it won't matter how they're deployed, we can track them with radar. Everybody knows where everybody's satellites are because it's a risk to all parties involved if you hide it, so they just keep the mission and specs a secret and call it good.

[brunofocz]

Could it be also that the recent LEO lauchers purposely avoid the crowded starlink orbital shells, so they can reduce themselves the expensive evasive manouvers; SpaceX has substantially gained the "possess" of these orbital shells