Comment by aetherspawn

1 year ago

If someone makes a mistake and the satellite deorbits in the wrong place, am I likely to be impaled by a satellite screw or something travelling at terminal velocity?

13 comments

aetherspawn

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oconnor663  1 year ago

No, they burn up. You can think of how much work goes into the heat shields on spacecraft that are supposed to survive reentry. Satellites have none of that.

  • m4rtink  1 year ago

    Starlinks are actually built so that nothing sizeable remains at all after reentry. This even delayed the laser coms a bit, as the original laser mirrors were too sturdy & so pieces of them could theoretically make it through.

  • scottlamb  1 year ago

    I also think a screw at terminal velocity might not be particularly dangerous, similar to the popular "will a penny dropped off the empire skyscraper kill you?" question.

    ...which I suppose is closely related. The deorbiting satellite burns up because all that potential energy goes into heat because of the ~friction~ [edit: compression, thanks for the correction] that limits it to that low terminal velocity.

mlindner  1 year ago

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.

  • qayxc  1 year ago

    > 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...

    • themeiguoren  1 year ago

      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).

    • mlindner  1 year ago

      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.

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