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The Interplanetary Transport Network is a network of mathematically-defined paths through our solar system that would require little to no energy for a spacecraft to follow them, albeit at very low speeds. While these pathways would not be practical for manned spacecraft due to the low speeds they require, they have been proposed for use as transport pathways and trajectories for scientific missions.

I know that NASA has indeed used these pathways for a few of their missions, including the Genesis mission and the Solar and Heliospheric Observatory. The Chinese spacecraft Chang'e 2 also used this network on its voyage.

While there appear to be a relatively vast number of these pathways scattered throughout our solar system, not all of them are currently known. How many of these pathways have we documented so far? Are there any official (or unofficial) estimates out there for what proportion of these pathways have been discovered to date?

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  • $\begingroup$ A normal porkchop plot will show these paths. The problem is that you never know when a new one will show up if you resolve your plot at a higher resolution. $\endgroup$
    – Erik
    Dec 9, 2014 at 22:32

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The question is somewhat odd. The "Interplanetary Transport Network" may be a misleading term. When probes are sent into deep space, most of them make use of flybys or gravity assist manoeuvres. Virtually every celestial body can therefore be used for increasing the speed of a probe or decreasing it. The "network" refers to series of such manoeuvres. In the end, it is a pure mathematical question of how many interesting sequences one can find between planets, moons and the sun.

You might have a look at this:

The ITN
"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." Source: wiki/ITN

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    $\begingroup$ "probes are sent into deep space, most of them make use of flybys or gravity assist manoeuvres", but most of them are not sent using chaotic trajectories near Lagrange points, are they? The Low-energy transfer wiki article lists only three moon missions and Genesis, which orbited near L1 and L2 of the system Earth-Sun. $\endgroup$
    – osgx
    Mar 12, 2014 at 18:18
  • $\begingroup$ @osgx Your question is slightly confusing. Chaos Theory plays a roll in finding interesting as in fuel-saving trajectories although I would not refer to those trajectories as ultimately chaotic. In this context, Lagrange points are locations where trajectories can be redirected using very little energy. Besides, Lagrange points have lately received a lot more attention as points where space probes can be 'stably parked' which is a very often used feature. Can you elaborate on what you precisely want to know? $\endgroup$
    – s-m-e
    Mar 14, 2014 at 17:04
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    $\begingroup$ As I understand, ITN is about using only trajectories redirected using very little energy near Lagrange points. I think that classic flybys are not part if ITN. $\endgroup$
    – osgx
    Mar 14, 2014 at 17:36
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    $\begingroup$ I concur with osgx. Gravitational slingshots and unstable manifold transfers (the ITN) are related but distinct concepts. $\endgroup$
    – David Hammen
    Mar 14, 2014 at 18:40
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    $\begingroup$ @osgx I need to check the precise terminology. It was my understanding that the ITN includes all gravitational effects i.e. slingshots, too. I may be wrong here. Let me come back to you. $\endgroup$
    – s-m-e
    Mar 15, 2014 at 0:40

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