Launch windows for libration point missions

Abstract

The four upcoming ESA missions to the collinear Lagrange points in the sun–Earth system, Herschel and Planck, GAIA, and LISA Pathfinder, will be launched from French Guiana by different Rockets, namely Ariane 5, Soyuz, and VEGA. Herschel and Planck will be launched together in 2008 on an Ariane 5. The launcher injects Herschel directly into the stable manifold of a large amplitude quasi-Halo orbit at L 2 . Departing from this launch orbit, Planck performs a three manoeuvre transfer to a Lissajous orbit, on which the sun–spacecraft–Earth angle remains below 15 ∘ . The daily and seasonal launch window for Herschel/Planck will be constrained by sun aspect angle conditions, by eclipse conditions, and by the propellant allocation on the Planck satellite. GAIA will be launched by Soyuz/Fregat end 2011. The target orbit at L 2 is similar to that of Planck, with a constrained sun–spacecraft–Earth angle. Initially, to reach a full year launch window, a launch scenario was preferred using a nearly circular parking orbit at 19 ∘ inclination, before igniting the Fregat upper stage to enter into the transfer. Recently alternative launch scenarios have been introduced, to guarantee a controlled re-entry of the Soyuz third stage, but leading to a reduction of the launch window. LISA Pathfinder will be delivered 2010 by the VEGA launcher to a low inclination elliptical orbit, with 1624 km apogee height. From there an apogee raising manoeuvre sequence, using a propulsion module connected to the spacecraft, reaches L 1 transfer conditions. Launch window calculations for these projects combine the choice of lift-off time and launch orbit conditions, with the selection of the target orbit at the Lagrange points and the minimisation of propellant to reach that orbit. For Herschel and LISA Pathfinder the target orbits have been chosen such that a transfer without deterministic manoeuvres is possible. Planck and GAIA both use a multiple manoeuvre fast transfer strategy reaching the Lissajous orbit at L 2 within 50 days.