History
The key to the interplanetary transport network was investigating the exact nature of these winding paths near the Lagrange points. They were first investigated by Jules-Henri Poincaré in the 1890s. He noticed that the paths leading to and from any of these points would almost always settle, for a time, on the orbit around it. There are in fact an infinite number of paths taking one to the point and back away from it, and all of them require no energy to reach. When plotted, they form a tube with the orbit around the point at one end, a view which traces back to mathematicians Charles C. Conley and Richard P. McGehee in the 1960s. Theoretical work by Edward Belbruno in 1994 provided the first insight into the nature of the ITN between the Earth and the Moon that was used by Hiten, Japan's first lunar probe. Beginning in 1997 Martin Lo, Shane D. Ross, and others wrote a series of papers identifying the mathematical basis and applying the technique to the Genesis solar wind sample return, along with Lunar and Jovian missions. They referred to an Interplanetary Superhighway (IPS)
As it turns out, it is very easy to transit from a path leading to the point to one leading back out. This makes sense, since the orbit is unstable, which implies one will eventually end up on one of the outbound paths after spending no energy at all. However, with careful calculation, one can pick which outbound path one wants. This turned out to be exciting, because many of these paths lead right by some interesting points in space, like the Earth's Moon or the Galilean moons of Jupiter. That means that for the cost of getting to the Earth–Sun L2 point, which is rather low, one can travel to a huge number of very interesting points for a low additional fuel cost or even for free.
The transfers are so low-energy that they make travel to almost any point in the Solar System possible. On the downside, these transfers are very slow, and only useful for automated probes. Nevertheless, they have already been used to transfer spacecraft out to the Earth–Sun L1 point, a useful point for studying the Sun that was used in a number of recent missions, including the Genesis mission. The Solar and Heliospheric Observatory began operations at L1 in 1996. The network is also relevant to understanding Solar System dynamics; Comet Shoemaker–Levy 9 followed such a trajectory to collide with Jupiter.
Read more about this topic: Interplanetary Transport Network
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