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 May 5th, 2017, 02:37 AM #1 Senior Member   Joined: Apr 2014 From: UK Posts: 780 Thanks: 292 Orbits I think it is possible to orbit the Earth such that the position is always directly between the Earth and Sol. Is this correct, and is it technically orbiting the Earth or the sun? How might I work out the distance from Earth of such an orbit (assuming it exists)? Thanks from Joppy
May 5th, 2017, 03:07 AM   #2
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 Originally Posted by weirddave I think it is possible to orbit the Earth such that the position is always directly between the Earth and Sol. Is this correct,
Yes. Such points are called Lagrange points.

Quote:
 and is it technically orbiting the Earth or the sun?
It orbits the Sun because the Earth orbits the Sun and the Lagrange point is always between the Earth and the Sun.

Quote:
 How might I work out the distance from Earth of such an orbit (assuming it exists)?
A simple calculation can be done based on equating the forces of gravitational attraction between a test mass and the two bodies; Sun and Earth and solving for the position of the test mass.

$\displaystyle F_{Earth} = G\frac{M_{test} M_{Earth}}{r^2}$

$\displaystyle F_{Sun} = G\frac{M_{test} M_{Sun}}{(d - r)^2}$

where G is the universal gravitational constant, r is the distance the test mass is from the Earth (in metres) and d is the Earth-Sun distance (in m)

A more difficult, detailed calculation can be done using Lagrangian mechanics and then you'll find many more Lagrange points
https://map.gsfc.nasa.gov/ContentMedia/lagrange.pdf

 May 5th, 2017, 03:42 AM #3 Senior Member   Joined: Apr 2014 From: UK Posts: 780 Thanks: 292 Interesting, I didn't understand a lot of it, but it seems L1, which is what I was aiming for, isn't stable, so it's either L4 or L5, I just need to work out how to get there
May 8th, 2017, 02:25 AM   #4
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 Originally Posted by weirddave Interesting, I didn't understand a lot of it, but it seems L1, which is what I was aiming for, isn't stable, so it's either L4 or L5, I just need to work out how to get there
Yes, L1 is a position of unstable equilibrium and any satellite placed there would need some sort of rocket to keep it there, adjusting its thrust in order to counteract any perturbations.

 May 8th, 2017, 08:29 AM #5 Senior Member   Joined: Apr 2014 From: UK Posts: 780 Thanks: 292 I doubt we could harvest enough power to keep ourselves stable at L1. Radiation is also a bit of an issue. Looks like I'll have to stay down here a bit longer
May 9th, 2017, 02:11 AM   #6
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 Originally Posted by weirddave I doubt we could harvest enough power to keep ourselves stable at L1. Radiation is also a bit of an issue. Looks like I'll have to stay down here a bit longer

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