This is Slashdot, so I understand that you didn't read the linked articles. Here is a more general summation from the articles I posted above.
An entry into anotherâ(TM)s airspace is a trespass even if the trespasser doesnâ(TM)t touch the surface of the earth. Airplanes may trespass by flying low over a personâ(TM)s property, for example. An airplane trespasses by flying low enough over the surface to interfere with the ownerâ(TM)s reasonable use and enjoyment of her surface.
The only way to guarantee that you are not trespassing is to be in public airspace which is determined to be 500ft.
And no, you do not have to cause damage to be trespassing.