Author Topic: Velocity reference?  (Read 1065 times)

Offline mongo

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Velocity reference?
« on: 03/03/2011 01:06 PM »
I have some old Saturn V/IB documents that when it references velocity vs time, they have 2 charts; space based velocity and earth based velocity.  I assume earth based is the regular velocity that you normally hear about, but what is space based?

Online Jorge

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Re: Velocity reference?
« Reply #1 on: 03/03/2011 02:58 PM »
I have some old Saturn V/IB documents that when it references velocity vs time, they have 2 charts; space based velocity and earth based velocity.  I assume earth based is the regular velocity that you normally hear about, but what is space based?

They're both actually referenced to an Earth-centered frame, but for Earth-relative velocity, the frame rotates with the Earth. The frame for space-relative velocity remains fixed while the Earth rotates around it.
JRF

Offline Danny Dot

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Re: Velocity reference?
« Reply #2 on: 03/03/2011 03:26 PM »
Basically earth based velocity is more important when in the atmosphere and space based when out of the atmosphere.
Danny Deger

Online Jorge

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Re: Velocity reference?
« Reply #3 on: 03/03/2011 03:28 PM »
Basically earth based velocity is more important when in the atmosphere and space based when out of the atmosphere.

Right, drag is computed using Earth-based velocity but Newton's laws require space-based velocity.
JRF

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