So what exactly is the benefit of having Lagrangian spacecraft?

[Tex]

So I've been curious now for a long time. I understand what lagrange points are, and somewhat how they work due to gravity. The only thing that stumps me is what the benefit of having spacecraft in these points is. Just satisfying curiosity, here!

I assume they would be good for making observations of planets or the sun? Something regarding communication?

[billbobjebkirk]

For astronomical observations, it's good because you never lose the signal. For use as an exploration gateway, it's good because it takes very little Dv to get from L1 or L2 to the Moon or an escape trajectory.

[Tex]

Ahhhh, that makes complete sense.

[Kibble]

From Sun El Wun, one side of your spacecraft is permanently facing the Sun, and the other side is permanently facing the daylit side of Earth (or wherever). That's where we put all of our solar observation spacecraft and Al Gore's Triana, which was supposed to continuously broadcast a live feed of Earth, but evolved into another solar observatory, and got renamed DSCOVR. .02 astronomical units away, at Sun L2, one side will also permanently face the Sun, but the other side is facing out into the cosmos unobstructed by the face of our planet. That's where James Webb Space Telescope is going.

The Earth/Moon Lagrange points are also interesting - a little nudge from El Too or El Wun can do wonders! A path described by legendary rocket scientist Robert Farquhar (designer of ISEE-3) from EML2 takes .4 km/s to get to an atmosphere-grazing perigee. Aerobrake to low circular orbit, or enjoy a huge Oberth benefit to send something interplanetary. There are countless other promising paths and weak stability trajectories too.

[FishInferno]

For astronomical observations, it's good because you never lose the signal. For use as an exploration gateway, it's good because it takes very little Dv to get from L1 or L2 to the Moon or an escape trajectory.

But wouldnt it be easier to just ahve a station in Lunar orbit? How much Dv does it take to get to a L-point?

[billbobjebkirk]

If it was in lunar orbit, you would have to acieve lunar escape velocity and earth escape velocity, whereas with the lagrange point, you only have to use a little more time and Dv to go to the moon, and far less Dv for Earth Escape.

[B787_300]

plus there is very little need for station keeping at *some* of the L-points which is nice because you can stay there almost indefinitely. Plus if you put a fuel depot/ station there it is a good place for spacecraft to stop on missions

[billbobjebkirk]

plus there is very little need for station keeping at *some* of the L-points which is nice because you can stay there almost indefinitely. Plus if you put a fuel depot/ station there it is a good place for spacecraft to stop on missions

That's another reason that I forgot, in lunar orbit, masscons force you to perform frequent reboosts.

[moronwrocket]

Another reason for using L2 instead of LEO is that for a infrared telescope, Earth is actually "hot". Placing JWST at L2 means we can block the Sun and Earth heating with 1 heatshield.

http://www.nasa.gov/topics/universe/features/webb-l2.html

For a planet like Mercury, the surface is so hot that orbiters need to be careful about the reflected/re-radiated heat, and use elongated orbits to minimize time near periapsis.

http://messenger.jhuapl.edu/spacecraft/thermal.html

[RidiculousRichard]

Are Lagrange points usable in KSP?

I.e. is the physics model good enough to include them and can you practically find and utilise them with the stock instrumentation?

[maltesh]

Are Lagrange points usable in KSP?

I.e. is the physics model good enough to include them and can you practically find and utilise them with the stock instrumentation?

The two-body mechanics of Kerbal Space Program does not support Lagrange points, and the weird gravity gradient contours around them would not be accurately reproduced by phantom spheres of influence.

[Nibb31]

Are Lagrange points usable in KSP?

I.e. is the physics model good enough to include them and can you practically find and utilise them with the stock instrumentation?

No. Lagrange points require n-body gravity simulation, which is extremely complex to predict. KSP uses a simplified Newtonian model where you can only be under the influence of a single body at a time.

[TARDISES]

Are Lagrange points usable in KSP?

I.e. is the physics model good enough to include them and can you practically find and utilise them with the stock instrumentation?

No. Objects can only be under the gravitational influence of one object at a time, which object it is depending on the sphere of influence.

[RidiculousRichard]

Thank you for the replies. They saved me a great deal of time trying (and failing) to utilise them!

[YNM]

You can "use" (as it's not precisely the same) L3, L4, and L5 in game though - even to a far higher efficiency than in real world ! (real world Lagrangian points needs continuous stationkeeping from n-body perturbations, not to mention other problems regarding their nature as points, and not a volume. L3 is also slightly inwards compared to the second body orbit.)

[Yasmy]

I'm sure all of Earth's (and other planet's) Lagrange points will be used heavily some day, though it will probably be quite a while before we use Earth's L3.

Multiple spacecraft (ISEE-3, WIND, SOHO, ACE and others) have used L1 as a local space and solar observation point.

L1 is outside of Earth's magnetosphere and bow shock, so it is a good place to monitor the solar wind upstream of and unperturbed by Earth.

L1 has a continuous, unobstructed view of the sun.

If you are not familiar with any of these missions, check out SOHO. It has produced some of the most amazing movies of the active, dynamic solar surface, corona and even subsurface, featuring flares, sun spots, coronal mass ejections (eruptions which dump huge amounts of plasma into space), flux tubes (loops of magnetic fields jutting from the surface with high energy particles zipping along them), and even deep sun convection cells and whole-sun vibrations (helioseismology).