# Orbital Speed?

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#### nopatience

##### Guest
I just wanted to clarify the orbital speed rule to make sure I understand.<br /><br />the lower the orbit of a planet the faster you have to travel to maintain an orbit.<br /><br />the further out your orbit the slower you have to go to maintain your orbit. <br /><br />Is this right?

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#### arobie

##### Guest
Shuttle_Guy, what is the altitude and speed of the ISS?

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#### jcdenton

##### Guest
Current altitude is 355km.<br /><br />Speed is 7.7 km/s in low orbit last I heard. <div class="Discussion_UserSignature"> </div>

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#### spacester

##### Guest
Correct. It seems weird, huh? You slow down to get higher, seemingly.<br /><br />The only way to make sense of it is to think about potential energy.<br /><br />When you raise an orbit, you have to invest twice as much of your rocket's deltaV into potential energy as the amount of kinetic energy you lose from going slower. This is shown in the vis-viva equation.<br /><br />So when you burn your engines to add energy to your orbit, you slow down by as much as you would think you would speed up if you could ignore potential energy.<br /> <div class="Discussion_UserSignature"> </div>

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#### nopatience

##### Guest
thanks alot for the info<br /><br />-Brad

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#### nopatience

##### Guest
Is that how they landed on the moon? they burned their rockets to speed up and lower their orbit until they were close enough to the planet to start slowing down again?

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#### nopatience

##### Guest
you slow down relative to space and you speed up relative to the planets surface?

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