Geosynchronous orbit around the moon

[maliaki]

What altitude and speed would be a "geosynchronous orbit" around the moon?

 

[harmonicaman]

Here's a calculator.

 

[vogon13]

A seleno-synchronous orbit wouldn't be too practical. But the lunar Lagrange sites could be used for similar purposes.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[tony873004]

You can't do the equivalent of geosynchronous orbit around the Moon. If you compute the required distance, it lies beyond the Moon's Hill Sphere, and therefore it is not stable.<br /><br />L4 and L5 will only work with a little station keeping. They're not stable in the long term as there is too much eccentricity in the Moon's orbit and too strong of a solar tide through the Earth/Moon system. It's hard to keep exactly 60 degrees ahead of or 60 degrees behind something that keeps speeding up and slowing down. But a satellite carefully positioned can last several years without stationkeeping burns before it is expelled from its chaotic journey around the L4 or L5 point.<br /><br />But in L4 and L5, you would be the same distance from the Moon as you are when you are on Earth. And Earth is "sort of geostationary" to the Moon, hovering above its near side. A triangle of communication devices, one on Earth, one in L4 and one in L5 should allow you to cover almost all of the Lunar surface, but each station would be 1 Earth/Moon distance from the Moon.

 

[centsworth_II]

<font color="yellow">"A seleno-synchronous orbit wouldn't be too practical."</font><br /><br />What about for a lunar space elevator? To get all that He3 to Earth. <div class="Discussion_UserSignature"> </div>

 

[maliaki]

Thanks for all the replies so far!!! Sounds like it's questionable on if it can be done at all! If the Earth is in a geosynch orbit with the moon then it could be done I suppose.<br /><br />I see some are questioning why. Here's the real reason I ask.<br /><br />Could you build a tower tall enough to be at a geosynch point so that you could study microgravity from a moonbase?

 

[centsworth_II]

<font color="yellow">"Any orbit will do."</font><br /><br />And you don't need to go as far as the moon to study microgravity. That's ONE thing at least that the Internationl Space Station is good for. <div class="Discussion_UserSignature"> </div>

 

[nexium]

I think Tigerbiten is correct. The elevator end could reach within a few hundred miles of Earth (during the Moon's closest approach to Earth) but it would be quite fast with respect to Earth's atmosphere, making the cost of 230,000 miles of ribbon impractical. Neil

 

[nexium]

On 4 th thought the tip speed would be about 1000 miles per hour, so perhaps the tip could reach within 20 miles of Earth's surface when the moon was closest to Earth. At other times the tip would be almost 30,000 miles from Earth's surface and no longer a target for faster GEO and LEO sattelites.<br />Any one have an idea how to change the length of the ribbon by about 25,000 miles each month, without expending a huge amount of energy? The rail gun (top speed to date is about 300 miles per hour) might be less costly, but how would you keep the tanks of helium 3 from burning up in Earth's atmosphere? Neil