# Earth, shuttle and the moon

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#### breezeit

##### Guest
Dear Members,

If the shuttle is to go from earth to moon, how can it be navigated when all the three bodies - earth, moon and the shuttle are moving at the same time. I am not sure if this is to do with the famous three body problem? I also want to understand how do the three bodies move relative to each other?

Many thanks...

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#### Shpaget

##### Guest
If by shuttle you mean Space Shuttle, it's not going to happen.

Modern inertial navigation system uses computer model of its surroundings and measures every movement any attitude change to calculate the change in position.

However, most of the space navigation is done while the aircraft is still on the ground and after the launch it is dead reckoning.

Back to Earth - Moon system. If you know the characteristics of the Moons orbit you can predict where will it be at any point in time, so you just calculate how long will it take you to get there and pint the nose of your rocket to the part of sky where at the time of launch is just empty space. By the time you get closed the Moon will have shifted and intercepted you.
If you want to make your approach more accurate you'll include the influences of gravity of both objects. That's it.

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#### satthralope

##### Guest
It is a little more complex than that. The spacecraft will follow a curving trajectory, called a ballistic trajectory. You need to make sure the curve of your trajectory meets the Moon's orbit and then launch at the right time for your spacecraft to reach the intersection at the same time as the Moon. If you point your rocket directly at the aim point, you will miss it.

If you wish to actually orbit the Moon, then you must also make sure that you arrive with the correct energy for the Moon to capture you. If you are traveling too quickly, you will fly right on past it. The Apollo spacecraft aimed for a point where they would pass from the Earth's gravitational influence to the Moon's gravitational influence. Once they were close enough, they fired engines to slow themselves down further and entered lunar orbit.

To maintain a proper heading, they had to perform several trajectory correction maneuvers, and this is not done by dead reckoning alone. Spacecraft are equipped with devices called star trackers to navigate by the stars, and sextants can be used to sight off of the Earth and Moon to deduce the actual position and attitude of the spacecraft. For an object as small as a spacecraft, dead reckoning is limited, because very small forces can affect their trajectories significantly.

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#### breezeit

##### Guest
Dear members,

thanks for the info...its very very helpful. thanks again.

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