Interplanetary Transport Network

The Interplanetary Transport Network (ITN)[1] is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow.

The key to discovering the Interplanetary Transport Network was the investigation of the nature of the winding paths near the Earth-Sun and Earth-Moon Lagrange points.

Beginning in 1997, Martin Lo, Shane D. Ross, and others wrote a series of papers identifying the mathematical basis that applied the technique to the Genesis solar wind sample return, and to lunar and Jovian missions.

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.

[9] The network is also relevant to understanding Solar System dynamics;[10][11] Comet Shoemaker–Levy 9 followed such a trajectory on its collision path with Jupiter.

In addition to orbits around Lagrange points, the rich dynamics that arise from the gravitational pull of more than one mass yield interesting trajectories, also known as low energy transfers.

[4] For example, the gravity environment of the Sun–Earth–Moon system allows spacecraft to travel great distances on very little fuel,[citation needed] albeit on an often circuitous route.

[citation needed] In a more recent example, the Chinese spacecraft Chang'e 2 used the ITN to travel from lunar orbit to the Earth-Sun L2 point, then on to fly by the asteroid 4179 Toutatis.

This stylized depiction of the ITN is designed to show its (often convoluted) path through the Solar System . The green ribbon represents one path from among the many that are mathematically possible along the surface of the darker green bounding tube. Locations where the ribbon changes direction abruptly represent trajectory changes at Lagrange points , while constricted areas represent locations where objects linger in temporary orbit around a point before continuing on.