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Added link to Lagrange point diagram
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PM 2Ring
PM 2Ring
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No, there are currently no plans to put a space telescope, or any other kind of satellite, at the Sun-Earth L3 Lagrange point.

The main problem is (as you mention) that it's impossible to communicate directly with a body that's always behind the Sun. So it's pointless putting anything at L3 if you don't have a relay station of some kind, probably at L4 or L5.

Such a relay needs to be fairly powerful. The side length of the L3, L4, L5 triangle is $\sqrt 3$ AU, and the distance from L4 or L5 to Earth is 1 AU, so the total distance from L3 to Earth via the relay is ~22.7 light-minutes. The line from L3 to L4/L5 passes within 0.5 AU of the Sun, where electromagnetic interference is more intense.

If you're going to L4/L5 you might as well put your 'scope there. It will be able to see most things behind the Sun that L3 can see. The L4 & L5 points are gravitationally stable, unlike L1 / L2 / L3, which are saddle points. However, that's not necessarily an advantage, because it means that there's a fair quantity of dust and a few asteroids in the vicinity.

By the way, it takes a fairly long time to get to L3 / L4 / L5 if you don't want to use a huge amount of fuel. The easy way to get a spacecraft to a point on (or near) the Earth's orbit is to put the ship on a heliocentric orbit with a semi-major axis that's slightly larger or smaller than 1 AU. Gradually, the ship will move behind or ahead of Earth. That's the strategy which was used for the STEREO mission. But this takes a while, due to the ship's synodic period relative to Earth.

If $T_1$ and $T_2$ are the orbital periods of two bodies (in concentric orbits), with $T_1<T_2$, their relative synodic period $S$ is given by $$1/S = 1/T_1 - 1/T_2$$

The synodic period is the time for the angle between the bodies (as measured at the primary) to go through a full cycle, eg the time between succesive conjunctions or oppositions. To send a ship to L3 we need to wait for half a synodic period.

Eg, if the ship's orbital period is 1.1 years, then its synodic period relative to Earth is 11 years, so it takes 5.5 years to reach L3 with that orbit.

I have an interactive 3D Lagrange point diagram on our sister site: https://space.stackexchange.com/a/57679/38535

No, there are currently no plans to put a space telescope, or any other kind of satellite, at the Sun-Earth L3 Lagrange point.

The main problem is (as you mention) that it's impossible to communicate directly with a body that's always behind the Sun. So it's pointless putting anything at L3 if you don't have a relay station of some kind, probably at L4 or L5.

Such a relay needs to be fairly powerful. The side length of the L3, L4, L5 triangle is $\sqrt 3$ AU, and the distance from L4 or L5 to Earth is 1 AU, so the total distance from L3 to Earth via the relay is ~22.7 light-minutes. The line from L3 to L4/L5 passes within 0.5 AU of the Sun, where electromagnetic interference is more intense.

If you're going to L4/L5 you might as well put your 'scope there. It will be able to see most things behind the Sun that L3 can see. The L4 & L5 points are gravitationally stable, unlike L1 / L2 / L3, which are saddle points. However, that's not necessarily an advantage, because it means that there's a fair quantity of dust and a few asteroids in the vicinity.

By the way, it takes a fairly long time to get to L3 / L4 / L5 if you don't want to use a huge amount of fuel. The easy way to get a spacecraft to a point on (or near) the Earth's orbit is to put the ship on a heliocentric orbit with a semi-major axis that's slightly larger or smaller than 1 AU. Gradually, the ship will move behind or ahead of Earth. That's the strategy which was used for the STEREO mission. But this takes a while, due to the ship's synodic period relative to Earth.

If $T_1$ and $T_2$ are the orbital periods of two bodies (in concentric orbits), with $T_1<T_2$, their relative synodic period $S$ is given by $$1/S = 1/T_1 - 1/T_2$$

The synodic period is the time for the angle between the bodies (as measured at the primary) to go through a full cycle, eg the time between succesive conjunctions or oppositions. To send a ship to L3 we need to wait for half a synodic period.

Eg, if the ship's orbital period is 1.1 years, then its synodic period relative to Earth is 11 years, so it takes 5.5 years to reach L3 with that orbit.

No, there are currently no plans to put a space telescope, or any other kind of satellite, at the Sun-Earth L3 Lagrange point.

The main problem is (as you mention) that it's impossible to communicate directly with a body that's always behind the Sun. So it's pointless putting anything at L3 if you don't have a relay station of some kind, probably at L4 or L5.

Such a relay needs to be fairly powerful. The side length of the L3, L4, L5 triangle is $\sqrt 3$ AU, and the distance from L4 or L5 to Earth is 1 AU, so the total distance from L3 to Earth via the relay is ~22.7 light-minutes. The line from L3 to L4/L5 passes within 0.5 AU of the Sun, where electromagnetic interference is more intense.

If you're going to L4/L5 you might as well put your 'scope there. It will be able to see most things behind the Sun that L3 can see. The L4 & L5 points are gravitationally stable, unlike L1 / L2 / L3, which are saddle points. However, that's not necessarily an advantage, because it means that there's a fair quantity of dust and a few asteroids in the vicinity.

By the way, it takes a fairly long time to get to L3 / L4 / L5 if you don't want to use a huge amount of fuel. The easy way to get a spacecraft to a point on (or near) the Earth's orbit is to put the ship on a heliocentric orbit with a semi-major axis that's slightly larger or smaller than 1 AU. Gradually, the ship will move behind or ahead of Earth. That's the strategy which was used for the STEREO mission. But this takes a while, due to the ship's synodic period relative to Earth.

If $T_1$ and $T_2$ are the orbital periods of two bodies (in concentric orbits), with $T_1<T_2$, their relative synodic period $S$ is given by $$1/S = 1/T_1 - 1/T_2$$

The synodic period is the time for the angle between the bodies (as measured at the primary) to go through a full cycle, eg the time between succesive conjunctions or oppositions. To send a ship to L3 we need to wait for half a synodic period.

Eg, if the ship's orbital period is 1.1 years, then its synodic period relative to Earth is 11 years, so it takes 5.5 years to reach L3 with that orbit.

I have an interactive 3D Lagrange point diagram on our sister site: https://space.stackexchange.com/a/57679/38535

Source Link
PM 2Ring
PM 2Ring
  • 15k
  • 2
  • 46
  • 61

No, there are currently no plans to put a space telescope, or any other kind of satellite, at the Sun-Earth L3 Lagrange point.

The main problem is (as you mention) that it's impossible to communicate directly with a body that's always behind the Sun. So it's pointless putting anything at L3 if you don't have a relay station of some kind, probably at L4 or L5.

Such a relay needs to be fairly powerful. The side length of the L3, L4, L5 triangle is $\sqrt 3$ AU, and the distance from L4 or L5 to Earth is 1 AU, so the total distance from L3 to Earth via the relay is ~22.7 light-minutes. The line from L3 to L4/L5 passes within 0.5 AU of the Sun, where electromagnetic interference is more intense.

If you're going to L4/L5 you might as well put your 'scope there. It will be able to see most things behind the Sun that L3 can see. The L4 & L5 points are gravitationally stable, unlike L1 / L2 / L3, which are saddle points. However, that's not necessarily an advantage, because it means that there's a fair quantity of dust and a few asteroids in the vicinity.

By the way, it takes a fairly long time to get to L3 / L4 / L5 if you don't want to use a huge amount of fuel. The easy way to get a spacecraft to a point on (or near) the Earth's orbit is to put the ship on a heliocentric orbit with a semi-major axis that's slightly larger or smaller than 1 AU. Gradually, the ship will move behind or ahead of Earth. That's the strategy which was used for the STEREO mission. But this takes a while, due to the ship's synodic period relative to Earth.

If $T_1$ and $T_2$ are the orbital periods of two bodies (in concentric orbits), with $T_1<T_2$, their relative synodic period $S$ is given by $$1/S = 1/T_1 - 1/T_2$$

The synodic period is the time for the angle between the bodies (as measured at the primary) to go through a full cycle, eg the time between succesive conjunctions or oppositions. To send a ship to L3 we need to wait for half a synodic period.

Eg, if the ship's orbital period is 1.1 years, then its synodic period relative to Earth is 11 years, so it takes 5.5 years to reach L3 with that orbit.