Why the Space Elevator’s Center of Mass is not at GEO

So I’m working on the ISEC Press Kit.  We’re getting ready to announce our Pearson and Artsutanov prizes next week and I’m thinking (hoping) that we’ll get some flurry of activity at the ISEC web site.  We want to have some documents on the website readily available to the Press so that when they report about us, they have a fighting chance to get the basic facts straight.

One of my own misconceptions about the Space Elevator was that center of mass would have to be at Geosynchronous orbit (actually a bit above it as we want to have a net upward force on the ribbon so that attaching an Elevator Car to it would not cause the system to fall down).  However, it appears that we need to have the center of mass of the system above GEO even during deployment because “the increase in gravity for the low mass is greater than the decrease for the high mass“.  When you think about it, that makes perfect sense.

I took this quote from Blaise Gassend’s most excellent summary of this issue which you can find here.

And my thanks to Ben Shelef (CEO of the Spaceward Foundation – organizers of the Space Elevator Games) for pointing out my error and also this website.

Now, if I could just make sense of that pesky Coriolis effect thingy…

2 thoughts on “Why the Space Elevator’s Center of Mass is not at GEO

  1. David Taylor, aka '3Davideo'

    Sure the center of mass is not at GEO, but isn’t the center of *gravity*? Since it’s long enough that gravity is not constant over its length, wouldn’t they be different?

  2. David Taylor, aka '3Davideo'

    I seriously don’t understand. Shouldn’t we determine the center of mass from the center of mass equation (average position weighted by mass)? What would result? Alternatively, we should determine the center of gravity, with the similar but in this case distinct center of gravity equation (average position weighted by *weight*).

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