Why we cant “park” satellites and space station in Lagrange points, to avoid drag?
In: Physics
We can, we do. In fact, the European Space Agency, ESA, has a mission for a satellite called Legrange to go to L1.
We can and do. Lagrange point 1 is between the Earth and Sun and has the [Solar and Heliospheric Observatory](https://www.nasa.gov/mission_pages/soho/index.html) parked there. L2, on the opposite side of the Earth, has the [Gaia satellite](https://sci.esa.int/web/gaia) parked there. The other points are much further away and I’m not sure if we use them.
How would you get them there? Lagrange points are a long way out–the nearest one to Earth in the Earth-Moon system in the L1 point, which is 320,000km up, a *long* way higher than even geostationary orbit. And there’s the problem there that the L1 point isn’t actually stable–any spacecraft put there would still need station keeping thrusters of some kind to keep it there (even if you put it in a Lissajous orbit around the point, which is what usually happens). A stable Lagrange point would be even further out and require even more fuel to get there.
We can and we have done that.
Multiple satellites have been placed in the lagrange points around Earth. The James Webb Space Telescope will be placed at a lagrange point.
We don’t put space stations there because none of the benefits of doing so are really useful for a space station and it’s much more beneficial to have it be in low Earth orbit so it’s easier for resupply missions and such to reach it. The lagrange points aren’t close.
We can and do park man made objects at various Lagrange points. The reason for parking satellites there has little to do with drag however.
Drag from the thin atmosphere slows satellites and space craft in low earth orbit down a bit because they are so low to the ground.
Space “officially” begins by most definitions about a 100 km high up. that is about as far as you can reach in a car in an hour if it were vertical instead of horizontal.
The International Space Station is about 400 km high up. (A distance about equivalent to what a high speed train travel in a hour and a half or maybe a hour and a quatre) This is not very far either, enough of our atmosphere reaches that high that the ISS gets slowed down looses a bit of orbital height to drag and has to be boosted up again regularly.
The Lagrange point between the earth and the moon, is most of the way there. about 320000 km. ( This is a distance equivalent of about 10 days worth of travel at the speed of sound.)
My point here is that the Lagrange points even the closest ones are a whole lot father away than al the other stuff we normally put into orbit. The one between the earth and the moon is closer to the moon than to the earth (about 85% of the way to the moon).
At those distance from earth drag from the atmosphere no longer really matters.
This does not mean that stuff put there will not need to do station keeping at all.
3 of the 5 Lagrange points are inherently instable and the other two are still not perfect. For one thing other stuff may get trapped there like dust and even some captured rocks in some systems. For another thing the Lagrange points in the earth moon system get disrupted by the gravity of the sun quite a bit over time.
You will still need to spend some fuel if you want to stay in some of those places for a long time.
That being said, stuff put there tends to stay put much better than in most places. It also tends to stay put in relation to the other objects in the system in ways that no other place will easily allow.
The Lagrange points in the earth moon system will always be in the same place in relation to the earth and the moon and since the moon always shows more or less the same face to the earth, any object in an Earth moon Lagrange point will be stationary in the sky above the moon.
Similarly the Lagrange points in the sun-earth system are fixed between those two bodies, which comes in handy if you want to put a satellite somewhere where it can observe the sun without the earth getting in the way.
Additonal fun fact:
Some Lagrange points in our solar system have accumulated quite a number of natural objects over the ages. The L4 and L5 points of the Sun-Jupiter system are so full of asteroids that we have even developed a system for naming the biggest ones. The asteroids surrounding the points are named after heroes from Trojan war. With the ones at one point named after the defending Trojan heroes and the ones at the other named after invading Greeks.
Due to a minor mistake early on before the naming system was ironed out the asteroids named after Patroclus and Hector were named at the wrong Lagrange point and rather than renaming them, astronomers have simply decided that they must be ‘spies’ in the enemies camps to keep the logic of the naming system intact.
We can, it’s just too expensive for most purposes. A lot of satellites have to make a profit, others have to be serviced frequently (like the space station). Any scientific ‘set and forget’ satellite will be set to a Lagrange point
In addition to everyone else’s answers: we can and do … but bear in mind that the Lagrange points are POINTS, not parking garages. L4 & L5 are stable points, so there’s stable orbits around them possible (weird as that may sound), but not unboundedly many; sooner or later you’ll run out of room.
–Dave, and then you start welding all the stuff that’s there together, and you make a space station…
ps: there are actual small fleets of asteroids in the Lagrange points for Jupiter around the Sun, 1/6th of its orbit ahead of and behind it. They’re called the “Trojan asteroids”. I’m not actually sure if we’ve found anything sitting in the Earth-Sun L4 & L5 points.
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