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ESA's GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite is receiving a lot of attention these days, ever since it was announced it ran out of Xenon propellant used by its ion thrusters to keep it in orbit, and it will inevitably reenter the lower atmosphere and parts of it might survive all the way to the surface, with no way to predict over which area it will partially disintegrate.

My main quarrel with that is, that GOCE is an aerodynamically streamlined 1 ton (2,200 lb) Low Earth Orbit (LEO) satellite that doesn't seem to have any flight termination system onboard to help it disintegrate into small enough pieces on reentry to completely burn up in atmosphere due to heat generated from friction. GOCE, as of writing this question, didn't yet fall to Earth, so it is still impossible to say how well that turned out, but European Space Agency (ESA) seems to be sending another set of aerodynamically streamlined satellites into LEO in two weeks time (22 November 2013) on its Swarm constellation mission studying the Earth's magnetic field:

    ESA's Swarm Constellation

    Artist's view of the three Swarm spacecrafts being deployed in Low Earth Orbit by a Breeze M upper stage (Source: ESA Blog)

Eventually, these three 468 kilograms (1,032 lb) streamlined beauties will run out of propellant for orbital maneuvering too, and will just as inevitably reenter the atmosphere and fall back on Earth. And we will again be wondering if any of their pieces will ruin our hairstyle. Or worse.

So my question here is, is ESA really launching another set of potential planetary penetrators into LEO? Or do these spacecraft have some self-destruct range safety / flight termination system installed, or are they otherwise designed to disintegrate easier on reentry than GOCE, the "Ferrari of space", seems to be with computer model predicted up to one quarter of its total mass impacting the Earth on reentry? Any other threat mitigation procedures, like assuring reentry over the middle of an ocean perhaps?

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    $\begingroup$ When you grew up in an urban area it is often hard to imagine how much of the earths surface area is not densely populated at all. You can perform a little experiment yourself. Go to Google Earth, zoom out so you see the whole earth, and zoom into a random point. See how often you land on the roof of a building. $\endgroup$
    – Philipp
    Mar 13, 2014 at 12:38
  • $\begingroup$ Thanks @Philipp I realize that, but that's hardly the point of my question. Plus, it's a really dangerous mindset dismissing it with what are the chances? If they are not zero, and with more and more hardware in LEO, eventually, you'd hit something. Unless they've made sure that can't happen. And that's what my question is about. ;) $\endgroup$
    – TildalWave
    Mar 13, 2014 at 13:59

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Streamlining is not the problem: those fancy-looking outer shells will burn up early on in the re-entry process. The pieces of a satellite that hit the ground are the high-density ones: things like pressurized fuel tanks, thick structural members, and radiothermal generators. If a satellite uses unpressurized maneuvering fuel, has lightweight structural members, and is solar powered, it is unlikely that any dangerously large pieces will hit the ground.

A "potential planetary penetrator" looks more like a telephone pole than a Ferrari.

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  • $\begingroup$ Yes, that planetary penetrators remark was more a tongue-in-cheek one, and I do include a link to one example of how they look like. You otherwise make valid points in your answer, but I'm specifically asking about ESA's Swarm and if their disintegration on reentry was one of the design requirements, or if they assured that by some other means. They do look structurally quite tough with not many weak points that I can see (here's one photo from one of our fun, end of the year posts on Space Exploration Meta). $\endgroup$
    – TildalWave
    Mar 16, 2014 at 4:17

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