# Orbital velocity of a craft at 4km above the Moon's surface

#### Fred Bobo

What would be the orbital velocity of craft at 4km above moon surface?
Assume a mass of 1,000,000 lb, US.

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#### Bandersnatch

For a circular orbit, it's $\sqrt{\frac{GM}{r}}$ where $G$ is the gravitational constant, $M$ is the mass of the body being orbited (here: Moon), and $r$ is the distance from the centre of the body. The mass of the craft doesn't matter.
Find the values on Wikipedia and plug them in. Or, you can make it even easier, and take the escape velocity listed on Wikipedia's page about the Moon, and divide it by $\sqrt{2}$. The result will be only marginally off.

Thank you.

#### Bandersnatch

You want the one in SI units. Use $6.674*10^{-11}$. You don't really need more significant numbers as it won't make much of a difference. Then use mass M in kilograms and distance r in metres - again, don't bother with too many significant numbers, unless you really feel like it matters to you if the result is very precise.

#### Fred Bobo

Thank you. All good now.

#### Nik_2213

Care: Due to the lunar mascons, low orbits are seriously non-circular, unto 'lumpy'...

"Orbital velocity of a craft at 4km above the Moon's surface"

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