According to this (https://en.m.wikipedia.org/wiki/List_of_objects_at_Lagrange_points) there are currently about 6 satellites at L1 and 5 more planned to be put there.
I don’t understand how they don’t collide with each other since the closer to the centre surely the less fuel needed to stay at L1.
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The L1 point is 1.5 million kilometers from the Earth. And satellites are small (~ 10 m).
They don’t have to be at the exact mathematical point given by theory (which anyway has its own uncertainty errors) to reap most of the benefits of being at a Lagrange point.
So the probability of hitting one another is very low: negligible.
All of the Lagrange points are, obviously, points in space, but you don’t have to be precisely on the point to get the lion’s share of the benefits of being close to the points.
Additionally; L1, L2, and L3 aren’t totally stable, so you’re going to need to expend fuel anyway to nudge yourself back to the point every now and again.
“At” is loosely defined. Look up “Halo orbit” and “Lissajous orbit”. A halo orbit might be 100,000 km across. There’s plenty of room, at least for now.
It might take less fuel to maintain position at or close to L1, but it also takes more fuel to get there than to insert into a loose halo. I reckon there’s a sweet spot somewhere, but I don’t know exactly where that might be. There are other reasons to prefer being somewhat offset from the Earth-Sun line, too. For instance, radio communications is harder when there’s a big bright radio noisemaker directly behind you.
You can actually orbit around many Lagrange Points, much like you can orbit around planets.
You don’t have to be right at the point. Space is gigantic. As long as you’re within a few hundred (or even thousand) miles of the mathematical “point” you still get the benefits of the point and need negligible fuel to stay there. Compared the size of satellites (a few meters), the available space is so huge that it’s not an issue.
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