Lagrange point colonization

Lagrange point colonization is the colonization of the five equilibrium points in the orbit of a planet or its primary moon, called Lagrangian points. The most obvious such points for colonization are those in the Earth-Moon and in the Sun-Earth systems. Although it would generally take days or even weeks to reach these latter with current technology, it would be possible to generate energy from sunlight at them nearly continuously since they would, due to their considerable distance from Earth, be shaded from the Sun only seldom and then only shortly.

Earth-Moon

An L₁ station would have a number of important functions due to its stationary position between the Earth and Moon. It is in an excellent location to monitor and coordinate communications among various missions on the nearside of the Moon. A vessel launched from L1 could reach any place on the Moon within a few hours to a day. This would make it ideal for crisis management if an emergency occurred on the Moon. Furthermore, it could serve as a way station, especially once built up, and would probably be used to handle tourists and casual visitors to the Moon. A station like this could also serve as a repair center for ships moving throughout the Solar System.

The L₂ point, on the far side of the Moon, is completely shielded from the Earth by the Moon so radio telescopes placed there would receive much less interference than existing telescopes. Of course, since the Moon is tide locked, any colony on the far side of the Moon has this same benefit; a lunar facility, however, would suffer from "Moonquakes".

Both L₁ and L₂ require active stationkeeping since neither is fully stable. Colonies at the L₄ and L₅ positions would have the advantage of being stable without any need for stationkeeping, and could be used as a waypoint for travel to and from cislunar space.

In addition, they would significantly reduce the delta-V (velocity change) needed to move from one to another, or to enter or leave Earth orbit, an important drawback of any lunar surface station, which demands high energy expenditure to escape and a comparable or greater amount to soft-land.

Sun-Earth

Contour lines of the effective potential illustrate the five Lagrange points of the Sun-Earth system

The L₁ position is useful for solar observations since it is near the Earth but in constant sunlight. It could also be useful for collecting solar power. Conversely, the L₂ point is perpetually in the shadow of the Earth, and as such offers a prime location for observing the outer planets or deep space. L₄ and L₅ colonies could be used as waypoints in space travel, to expand the practical launch window for travel to and from the Earth and other planets. These positions are useful for colonies as they are stable without any need for stationkeeping.

Disadvantages

Schematic of Earth's magnetosphere. The solar wind flows from left to right.

The risk of proton exposure from the solar wind as well as the health threat from cosmic rays is significant. In the Earth-Moon system, the orbit of colonies at L₁ - L₅ will take them outside of the protection of the Earth's magnetosphere for approximately two-thirds of the time (as occurs with the Moon). Colonies at L₁ (located between the Earth and Moon) will experience this to a lesser degree while L₂ (located beyond the Moon) will experience this to a greater degree and all of them will be exposed to the little understood plasma sheet of the magnetotail.^[1]

In the Sun-Earth system, L₁ and L₃ - L₅ are all outside of the protection of the Earth's magnetosphere. L₂ periodically transfers from within the magnetotail, plasma sheet, and solar wind depending on the intensity and direction of the solar wind.

See also

• Lissajous orbit
• Interplanetary Transport Network

References

• Dictionary Definition
• European Space Agency
• Free Mars
• Orbital Vector
• NASA - The Moon and the Magnetotail