# Math Question: Space Travel

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#### plutocrass

##### Guest
Dear Astrophyicsist:<br /><br />Ok, so we're gonna be traveling and putting things in orbit, and/or taking resources from asteroids and building things from stuff we get in outerspace, and generally changing the mass of the earth over time.<br /><br />So what I want to know is this: <br /><font color="yellow">What is the mass of the earth, how much do we expect it to change during a "2001 Space Odyssey/Star Trek/Star Wars" time period when we have outerspace superhighways/space hotels, etc.?</font><br /><br />And for the math question: I read this article about the precision of the Moon's mass/distance with the earth, and if you changed any factor, the earth would be significantly affected such that Life itself would not appear. So I would like to ask, with respect to this line of reasoning, what if it is the earth, and not the moon which changes these factors: <br /><br /><font color="yellow">What percentage change (gain or loss) can the earth suffer before either its tilt, rotational speed, orbiting velocity, and gravitational field from the sun/moon are affected significantly?</font><br /><br />thanks, sorry if this is rambling or unclear, but i hope you math geniouses can read between the lines to understand what it is i'm asking!

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#### h9c2

##### Guest
Earths mass increases every year by about 1.5*10^8 kg through infalling material. Earths mass is about 6*10^24 kg. <br /><br />The article linked to below does some calculations to show a different point, but you'll see how difficult it will be to change the earths mass by a significant fraction on a timescale that is short for human standards.<br /><br />http://www.talkorigins.org/faqs/moon-dust.html<br /><br />

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#### nexium

##### Guest
Matter gained and lost by natural processes is mostly guess work so it could in error by ten or more times. 1.5*10^8 kg = 150 million kilograms = 150,000 metric tons.<br />With Space elevators, we could increase the loss to 6 billion kg per year = 6,000,000 trillion kg in one billion years. 6,000,000 trillion is 6*10^18 which is a loss of one millionth of Earth's mass per billion years, so it would take a million times a billion years to remove all of Earth's mass. A million times a billion is 1*10^15 years Neil

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