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China and the US have reportedly both used kinetic kill vehicles to destroy satellites. This strikes me as rather inefficient, however.

It's well known that micrometeoroids pose a risk to satellites, so satellites are generally hardened against such impacts. There's a limit to how well they can be hardened, though; it seems like an object with a diameter of 10 to 20 cm impacting the core of a satellite should be enough to destroy it. An artificial sphere of this size made out of steel would weigh about 30 kg.

By contrast, a kinetic kill vehicle must have the same kinetic energy as the satellite it intends to destroy. If my understanding of orbital mechanics is correct, the speeds of the two objects is likely to be equal, so the kinetic kill vehicle must have a similar mass to the satellite it intends to destroy. In the case of the semi-recent Chinese launch, that's about 750 kg.

I understand that kinetic kill vehicles are able to tear apart the satellites they impact, and a tiny object putting a hole through a satellite would at best disable it, and could not accomplish the stated goals of either the American or Chinese weapons. That being said, have such small weapons ever been seriously considered? It seems like the significantly lower mass of such a system would be significantly cheaper and easier to launch.

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    $\begingroup$ The concept you describe has been proposed before: Brilliant Pebbles. $\endgroup$ – Deer Hunter Mar 14 '15 at 20:45
  • $\begingroup$ @DeerHunter yeah, although that system was focused on targeting missiles, not satellites. Do you wanna write that up as an answer? $\endgroup$ – raptortech97 Mar 14 '15 at 23:04
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    $\begingroup$ Those kinetic kill vehicles usually follow a buckshot approach - disintegrating into numerous smaller particles in close proximity of the target. The reason for this is precisely what you have surmised - to increase the probability of striking. $\endgroup$ – Everyone Mar 18 '15 at 10:28
  • $\begingroup$ Comparing kinetic energy of two objects is problematic because if you change reference frame, the apparent energy changes. There's no difference between the 1000 kg satellite smashing into a "stationary" 1 kg impactor at 7000 m/s and vice versa. $\endgroup$ – Nick T May 18 '16 at 22:52
  • $\begingroup$ If we're talking about best anti-sat weapons, lasers or other beam weapons would probably come out on top. A laser could potentially be fired from Earth, requires no ammo, and is difficult to dodge. Today's satellites also aren't extensively armored or anything and even if the laser doesn't destroy it, heating on the solar panels could rapidly overcome the thermal management system of the sat $\endgroup$ – Dragongeek Sep 28 at 17:55
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Your question contains a couple of misconceptions:

a kinetic kill vehicle must have the same kinetic energy as the satellite it intends to destroy

No, it doesn't. It just needs enough kinetic energy to break critical parts inside the satellite. The same goes for micrometeoroids.

If my understanding of orbital mechanics is correct, the speeds of the two objects is likely to be equal, so the kinetic kill vehicle must have a similar mass to the satellite it intends to destroy.

That would be the least efficient way to destroy a satellite. You'd launch the kinetic kill vehicle on a trajectory that gives it the highest speed relative to the satellite. A head-on collision would be perfect: both objects traveling at the same speed but in opposite directions.

At the speeds involved, the KKV likely disintegrates on impact, creating a nice big cloud of debris tearing through the satellite. The Vought ASM-135 ASAT used its third stage as its KKV. No need to have a separate impactor.

Using micrometeoroids sounds nice and efficient, but you'd need to accelerate and guide all of them. Much easier to accelerate and guide one larger object.

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