Spacecraft are generally not constructed to be able to penetrate deeply into an atmosphere at high velocity—reentry vehicles do, but witness what happened when the Hayabusa spacecraft and its small sample-return capsule hit the atmosphere together. The bit meant to reach the ground keeps going, everything else shatters into lots of tiny fragments immediately.
As such I can’t help but think that anything human-constructed will tend to fall apart very high up, and dump its energy many kilometers from the ground and in many pieces. Consider the recent meteor in Russia—that was probably a solid lump 15+ meters wide weighing in at 10,000 ish tons, and it lost integrity and fell apart 30 kilometers up. Not to mention that that object was 50-100 times as massive as a 747 and carried ~200 times as much kinetic energy as the total chemical energy of the best rocket ever built. You need some truly epic spacecraft before they become dangerous as anything but (potentially radioactive depending on contents) litter downrange of where they smack the air.
Redirecting small already-earth-crossing rocks by a quarter meter per second such that their path coincides with the Earth ten years later could be another matter all together. But that would be patently obvious as something with enough delta V approached a known object. And if something unofficial can move it, something official can doubtlessly move it back...
The point is not that the spaceship itself is a significant danger, but that at its distant position it could slightly nudge an asteroid on a trajectory strait to earth.
Spacecraft are generally not constructed to be able to penetrate deeply into an atmosphere at high velocity—reentry vehicles do, but witness what happened when the Hayabusa spacecraft and its small sample-return capsule hit the atmosphere together. The bit meant to reach the ground keeps going, everything else shatters into lots of tiny fragments immediately.
As such I can’t help but think that anything human-constructed will tend to fall apart very high up, and dump its energy many kilometers from the ground and in many pieces. Consider the recent meteor in Russia—that was probably a solid lump 15+ meters wide weighing in at 10,000 ish tons, and it lost integrity and fell apart 30 kilometers up. Not to mention that that object was 50-100 times as massive as a 747 and carried ~200 times as much kinetic energy as the total chemical energy of the best rocket ever built. You need some truly epic spacecraft before they become dangerous as anything but (potentially radioactive depending on contents) litter downrange of where they smack the air.
Redirecting small already-earth-crossing rocks by a quarter meter per second such that their path coincides with the Earth ten years later could be another matter all together. But that would be patently obvious as something with enough delta V approached a known object. And if something unofficial can move it, something official can doubtlessly move it back...
The point is not that the spaceship itself is a significant danger, but that at its distant position it could slightly nudge an asteroid on a trajectory strait to earth.