zlacker

Actually the person you replied to somewhat incorrectly. They're not targeted re-entries because the on-board propulsion of Starlink is too low to precisely control the re-entry location. However instead the satellites are designed to be intentionally "demisable" meaning that every portion of the satellite should vaporize/turn to char/dust during re-entry.

Put another way, every kilogram of Starlink spacecraft has as much energy "stored" in it's motion as around 4-5 tons of TNT.

>>mlindn+(OP)
You mean 4-5 kg of TNT. Starlink is not relativistic yet.

>>mlindn+(OP)
> Actually the person you replied to somewhat incorrectly. They're not targeted re-entries because the on-board propulsion of Starlink is too low to precisely control the re-entry location.

SpaceX says otherwise, see [1]

   SpaceX spokesman James Gleeson, when asked about the 10 satellites, said SpaceX is “performing a controlled de-orbit of several first iteration Starlink satellites,” using onboard propulsion.  

There's a difference between unscheduled deorbiting (as happened to about 40 satellites after a solar storm in February 2022) and a scheduled deorbiting manoeuvre trigged by ground control. Starlink satellites use electric on-board propulsion (Krypton powered Hall thrusters) that doesn't run out as quickly as chemical or cold gas gas thrusters. There's also not much precision needed to avoid major population centres - Earth is pretty big after all.

[1] https://spacenews.com/spacex-launches-fourth-batch-of-starli...

>>weregi+Gf
I mistyped the comment. It should be 4-5 tons of TNT for the entire satellite.

>>qayxc+nR1
And I'm telling you that the statement is incorrect. Starlink is not equipped with propulsion capable of doing that. They use electric propulsion, which means they can't target a re-entry. They can de-orbit it on a time scale, but they cannot do what is conventionally described as a controlled de-orbit. Meaning they cannot precisely target a general area of the Earth. They can target re-entry within a couple hours to days, but that's still all over the world.

Now, none of this is an actual problem as they're entirely demisable, but the statement that they can achieve controlled de-orbit is false.

>>mlindn+bq3
I think there's a major misunderstanding on what "precision" and controlled de-orbit means here. Precision doesn't mean a targeted landing. It simply means aiming for a certain latitude by adjusting the orbit accordingly, which is sufficient to make the difference between deorbiting over a desert or ocean and potentially densely populated coastlines or other population centres (central Europe comes to mind). Controlled means that it's the operator who decides how exactly and when that happens, i.e. they remain in control of the spacecraft and its orbital parameters throughout the process.

So if you control the orbit, you control the zone of re-entry. It's not a point or an oval in this case, but a "strip" a couple of kilometres wide. This is all that's required if the goal is to avoid major population centres.

This also means that the target is not "all over the world" as you put it - it's a very narrow, well defined stripe/trace (remember the scale we're talking about here!) and that's exactly what a controlled de-orbit is about.

>>qayxc+Mv3
Here's a blog post by ESA that talks about what controlled reentry means. https://blogs.esa.int/cleanspace/2018/11/16/basics-about-con... Controlled requires precise aiming towards a targeted location. Not just the operator deciding to do something. By ESA's definition Starlink de-orbits aren't even "semi-controlled".

This generally involves landing at a precise location of the Earth. It goes by a nickname, Point Nemo. A patch of ocean in the south pacific farthest away from any land. It's also far from standard shipping lanes. If you can't achieve this type of targeting it, definitionally, is not a controlled re-entry.

> It simply means aiming for a certain latitude by adjusting the orbit accordingly

You cannot aim a satellite for a "certain latitude" as orbits cannot follow lines of latitude. That's not how orbital dynamics work. I'm not quite sure what you meant to convey here.

> This also means that the target is not "all over the world" as you put it - it's a very narrow, well defined stripe/trace (remember the scale we're talking about here!) and that's exactly what a controlled de-orbit is about.

No it's all over the world, definitionally, because low earth orbits cross the entire planet as the Earth rotates. The possible locations the satellite can re-enter span a large portion of the globe from the negative to the positive latitude equivalent to the spacecraft's inclination.

I think you have a major misunderstanding yourself. If there's some term I'm using that you don't understand please let me know so I can help you.

>>qayxc+nR1
Not quite. The spokesman is a talking about controlled deorbit, where propulsion is used to actively lower altitude rather than coasting down due to atmospheric drag. This is in contrast to controlled reentry, which targets an ellipse on the ground where any debris would fall. The latter requires either much more thrust than their electric thrusters have, or a much steeper reentry angle than Starlink's circular orbits.

Starlink satellites are pretty well aerodynamically balanced when in their "ducked" orientation, but are not going to be able to overcome aerodynamic torques below 200 km or so, meaning they will be unable to point their thrusters in target directions. At that point, there are still 1-2 days before reentry will occur. Hour-to-hour variability in tropospheric atmospheric density due to solar flux levels and geomagnetic activity means that the precise reentry time will be unpredictable to within a few hours (which equates to anywhere along the ground track of a few orbits).