In "What are the conditions for re-entry of an object in a (highly) elliptical orbit?" Eerie asks about orbital mechanics of orbital decay of decommissioned satellite: starting with extremely elliptical orbit (apogee 7767 km, perigee at 99 km) the satellite's orbit gradually decays until it's nearly circular, when the satellite finally spirals down burning in the atmosphere.

But a fraction of m/s burn at the apogee would be able to drop the perigee into ~30km range, and then the satellite would rapidly burn up, traveling through the atmosphere at way more than 8km/s instead of risking debris surviving the final reentry and causing damage on the ground.

There's no point saving fuel, because the satellite is going to burn up anyway. The maneuver is really minuscule comparing to what is needed to get the satellite to start aerobraking at all. And the higher reentry speed into the thick atmosphere the less chance any debris will reach the ground. Never mind after so many aerobraking passes the landing point becomes completely unpredictable.

So why is the slowly decaying orbit through edges of Karman line used, instead of one that would make sure the satellite turns into a cloud of hot plasma over Pacific? Any rationale for keeping the perigee so high?

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    $\begingroup$ You are assuming the satellite still has a working propulsion system. That is very often not the case at all. $\endgroup$ – SE - stop firing the good guys Apr 23 '17 at 22:56
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    $\begingroup$ I suspect a steeper reentry might make it more likely that an object will reach the ground before burning up, because the entry time will be much shorter, even though the peak heating and g-force will be a lot higher. $\endgroup$ – Russell Borogove Apr 24 '17 at 6:26

Why are deorbited satellites allowed a slow orbit decay instead of burning them up rapidly?

The ultimate reason is simple: There are no international rules or regulations placing limitations on orbital debris. The only thing that comes close is the Space Liability Convention. That convention is akin to having no speed limits on roadways, including school zones, but retaining the ability to sue the responsible part of an accident for damages.

That said, one of the two vehicles in the related question was launched in 1976. Orbital debris was not yet a concern in 1976. The other vehicle was launched in 2013, when orbital debris was an unregulated concern. Apparently something happened to one of that vehicle's fuel tanks; 2013-062C is denoted as "debris (tank)." This kind of debris is hard to address even now that debris is a concern.


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