I've been curious about this subject (increasing or decreasing the planet's mass) & wanting a real fact based explanation. The fact that man has built structures that had a measureable impact to Earth's tilt indicate that there is a calcuable figure that represents the effect that the cumulative mass being removed from close to Earth's core/surface & shifted into orbit or pushed out of the planet's gravitational field has/will have. I've got no idea ehat the impact would be, but at some point reducing the mass of a spinning object has to result in changes. How many non-returning ships sent off-planet does it take to reduce the gravitational field of Earth? Does it impact Earth's orbit around the Sun? And inversely, how much off-planet mined materials brought here before ...idk - Earth's gravity is increased? Assuming the # is "real", shouldn't we be determining how much can be mined on the moon & brought here? Better now than waiting until the next environmental crisis headlines read "Moon weight loss has lead to extreme ellipse-ing of it's orbit: expect even more monumental tidal extremes!". Again, I don't know what the real impact would be, I made this last bit up for dramatic effect/illustrate my question.