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Name:  Cassim
Status: other
Grade: other
Country: Sri Lanka
Date: May 2, 2011
Question:
Is a stationary orbit over the Moon possible if the object were 'stationary' above the far side of the moon where gravitational effect of Earth is least?


Replies:
Cassim,

Lagrangian points are positions where, theoretically, a small massed object can remain stationary relative to two massive objects that are in circular orbits around a common center of mass. There are 5 Lagrangian points over any two massive bodies in which a smaller object can remain stationary relative to the two massive bodies. If the two massive bodies are the Earth and Moon, then the point you are looking for - where the satellite can maintain a fixed position over the moon - is directly in line with the Earth and Moon and behind the Moon (as observed from the Earth). This is commonly referred to as L2 (Lagrangian point 2). Here the combined gravitational pull of the Earth and Moon are canceled exactly by the centripetal force of the satellite's orbit.

Greg (Roberto Gregorius) Canisius College

I am no astrophysicist, but given that we have recently circumscribed the planet Mercury, I do not see anything that violates the Laws of Nature that a lunar navigator would not be possible.

Vince Calder

The short answer is yes (I think so). Note I am not certain, I am not an astrophysicist. My reasoning is this. Put the orbiting satellite on a trajectory that is pre-programmed to put it into a lunar-centric orbit. This satellite could be in contact with another satellite (call it 'B') that is not behind the Moon but can communicate with the stationary satellite, the Moon, and the Earth. So you have set up three communicating satellites -- the orbiting satellite, the Moon, and the Earth. So the signal can be sent from the target satellite that can see both it and the "off axis" satellite. It may even be possible that the Earth comes into play. All this requires some complicated orbital mechanics, but I don't see why it would be impossible.

Vince Calder


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