Now that the Gaia Space Telescope is on it's way to the Sun-Earth L2 Lagrangian point (SEL2), I start wondering about the stability of Gaia's orbit there. The Planck Telescope is already there, as was Wilkinson Microwave Anisotropy Probe (WMAP) and other probes, and from Wikipedia I learned that:
In practice, any orbit around Lagrangian points L1, L2, or L3 is dynamically unstable, meaning small departures from equilibrium grow exponentially over time.
Gaia has some kind of Orbital Maneuvering System (to borrow a Space Shuttle term) and some propellant on board, so has Planck, however I wonder how deterministic these orbits are and if both Planck and Gaia have automatic corrections and collision detection in their flight computers; L2 is "only" 1.5 million km (or about 5 light-seconds) away so surely there's time for manual correction.
Does anyone know a source which tells how different Gaia's and Planck's orbits are, if there are intersections between their orbital planes or even how likely the need for an unplanned orbital correction is? I know Lissajou-shapes from maths classes and I know how much the projected trail can differ depending on the precision of data types used in calculations (e.g. float vs. double). How does ESA/NASA handle this, now that SEL2 seems it will become a crowded place?