The European Space Agency unmanned spacecraft, GAIA, has today reached its intended orbit around the L2 Sun-Earth Lagrange Point. The craft launched on December 19, 2013. Its mission is to make very accurate observations of one billion stars, charting their precise positions and motions, as well as their temperatures, luminosities and compositions. This enormous census will result in the most accurate 3D map yet of the Milky Way and allow astronomers to determine the origin and the evolution of our galaxy.
“Our Gaia discovery machine will keep us busy throughout the mission, with the final results coming only after the five years of data have been analysed. But it will be well worth the wait, ultimately giving us a new view of our cosmic neighbourhood and its history,”
–Timo Prusti, ESA’s GAIA project scientist.
GAIA’s orbit is a Lisajous orbit around L2. There are at least three well-established orbits that use L2 as a relative center–Halo orbits, Lyapunov orbits, and Lisajous orbits. A Lisajous orbit is non-periodic and is “tilted” compared to the Sun-Earth orbital plane. In contrast, Halo orbits are periodic tilted orbits and Lyapunov orbits are within the Sun-Earth orbital plane.
GAIA’s particular orbit around L2 is a stately 180-day per cycle path. The volume of space around which it traverses is 263,000 km × 707,000 km × 370,000 km. That’s a pretty big wobbly ellipse. So, while several missions have used Lissajous trajectories at L2 (e.g., WMAP, Herschel observatory, Planck observatory, and brief uses by THEMIS and Chang’e 2), there’s little risk of things getting crowded or hazardous to traffic anytime soon.
But L2 will eventually grow in importance. In fiction, it is an important location in my novel, Turnaround (not yet published), and played a key role in the SF novel Sunstorm by Clarke and Baxter.