## Space Elevators Do Too Stay Put

April 24th, 2007

In honor of Pixel-Stained Techno-Peasant Wretch Day, Karl Gallagher shows us some Engineering work he did for free, to end a flame war.

It’s a fine posting, calculations and all, there for anyone to verify…

Entry Filed under: Blogs / Discussion Groups

• 1. David L Beatty  |  June 8th, 2010 at 12:13 am

Has anyone addressed the problem of the change in angular momentum for objects going from the earths surface to Geosynchronous orbit. Conservation of angular momentum would require the angular momentum of what ever the ribbon is tethered to to decrease as that of the elevator increases it seems the whole idea of a space elevator is much the same as a perpetual motion machine . There is always a flaw

• 2. Ted Semon  |  June 9th, 2010 at 11:17 pm

This question is answered in the Space Elevator FAQ (http://www.spaceward.org/elevator-faq)

Won’t the ribbon “fall behind” every time you lift a payload?

Yes it will. But since the Space Elevator is stable around its vertical position, once it starts falling behind, it wants to return to the vertical. The invisible player that helps the Space Elevator straighten out is Earth. Every time a payload is lifted, the Earth’s rotation will slow down by an immeasurable amount!. This contribution is also the reason why a Space Elevator launch requires so little energy.

A rope cannot push anything sideways. How does the payload achieve its 8 km/sec orbital speed?

This question is related to the last one. As the payload ascend, for exactly the reason mentioned in the question, the payload begins to retard relative to the rotation of the system, and so it pulls the ribbon backwards (Westwards). Once this begins to happen, however, the ribbon has assumed a slight angle, and so is able exert a small component of force in the tangential direction - exactly what is needed to pull the payload in the right direction. Over the entire climb, this pull adds up and accelerates the payload, ever so gently, to orbital speed.

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