During the feasibility studies (1995-96), NASA and the STScI considered a wide variety of orbits for JWST. The most promising was the second Lagrange point (L2), approximately 1.5 million km from Earth, outside the orbit of the Moon. The region about L2 is a gravitational saddle point, where spacecraft may remain at roughly constant distance from the Earth throughout the year by small station-keeping maneuvers.
Animation showing JWST in orbit
JWST will be placed in a large halo orbit in a plane slightly out of the ecliptic plane. This orbit avoids Earth and Moon eclipses of the Sun. The halo orbit period is about 6 months. Nominal station keeping maneuvers will be performed every half orbit (3 months).
JWST, near the L2 point, is in a benign and essentially unchanging environment. There are no significant gravitational torques and thermal influence from the Earth and Moon are greatly reduced. The main operational influence to consider is the torque created by the Solar wind on the sunshield.
