How many rocket launches are needed to change the axial tilt of the Earth so much that it is noticeable with instruments available today?
We can assume that we are talking about the heaviest rocket ever launched and that all launches are done from the same place, in the same season and at the same hour, all chosen for the biggest effect on the axial tilt.
(I know that the axial tilt is already changing due to natural reasons, my question regards an additional change attributable only to space launches)
Later edit: I'm looking for an answer that involves the kinetic energy derived from the mass and speed of the rocket at launch (and possibly later in the atmosphere). An explosion or an earthquake is usually not directed and much of the energy would be lost.