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I can't find this information online and am wondering how fast each were going around the Moon when they reattached to one another after the moon landing.

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    $\begingroup$ In spaceflight "how fast?" always needs a "with respect to X" in order to be answerable. I assume you mean how fast is the pair traveling around the Moon so I've adjusted your wording. If you meant with respect to something else, or with respecte to each other then please feel free to edit further. Welcome to Space! $\endgroup$
    – uhoh
    Jul 30, 2019 at 1:00
  • $\begingroup$ Sounds like a question for Apollo by the Numbers! $\endgroup$
    – DrSheldon
    Jul 30, 2019 at 1:04

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The lunar orbit velocity for the Apollo missions was a little over 1600 meters per second (~5300 feet per second, ~3600 mph) according to Apollo By The Numbers (p.104). (h/t DrSheldon for the reference suggestion!)

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In low orbit, like the one Apollo used, the orbital speed around the moon is about 1.6 km/s. So that is the speed at which both the Command Module and Lander were going. Their speed relative to each other was 0 km/s when they connected ;-)

At uhoh's suggestion, here's how to calculate the speed of the spacecraft. Let G be the gravitational constant, M the mass of the body we're orbiting (the moon) and r the radius of the orbit. In that case, the speed v is $$v = \sqrt{G * M / r}$$ If we use $M=7.4*10^{22}kg$ (mass of the moon) and $r=1850 km$ (100 km above the surface) we get $$v=1.63 km/s$$

An online calculator can be found here.

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  • $\begingroup$ If their speed relative to each other was 0.0 m/s when they connected, they would never finish connection. A small minimum speed is required for a successful connection to close the interlocks. $\endgroup$
    – Uwe
    Dec 5, 2023 at 3:40
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    $\begingroup$ @Uwe I should have been more specific, and said "after" instead of "when". $\endgroup$
    – hdhondt
    Dec 5, 2023 at 21:51

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