Space weather events affect directly both manned and unmanned spaceflight missions. In order to determine the influence of such events, observations of the solar phenomena away from Earth and/or near Earth are mandatory. The Sun-Earth equilateral Lagrange point L5 (SEL5) is a perfect candidate for an observation post of the solar space weather mission due to the constant dynamical and environmental conditions a spacecraft would face in that position. For these reasons, SEL5 is selected for the ESA LAGRANGE Mission to be launched in 2023.

The Lagrange mission concept is overseen by the Space Situational Awareness Programme at ESA. On 2 February 2018, ESA signed technological contracts (Phase A) to be led by Airbus UK and OHB SE of Germany to design the spacecraft specifications and the instruments’ integration process. This mission concept proposes positioning two spacecraft in orbit at the L1 and L5 Lagrangian points, respectively, where gravitational forces interact to create a stable location to save propellant and from which to make observations. L1 is in the solar wind ‘upstream’ from Earth, so measurements at L1 provide information about the space weather coming toward Earth. In contrast, the L5 point provides a way to monitor coronal mass ejections (CMEs) from the ‘side’ in order to estimate their speed and direction.

The Lagrange mission to l5 considers four remote sensing optical instruments and several in-situ instruments to analyze the sun, the energetic particle streams, the magnetic field and solar wind conditions, in order to provide early warnings of increased solar activity.

Elecnor Deimos, with Deimos Space UK leading the project, is the responsible of the mission analysis of ESA LAGRANGE Mission in the OHB consortium, exploring interplanetary transfer to SEL5 as a phasing trajectory of 60 degrees in the Earth orbit around the Sun. Different set of trajectories can be investigated depending on the desired duration of the transfer: longer transfers require less propellant since longer time for the phasing is allowed. The number of possible solutions for the accounted set of operational orbits is extremely high since small variation of any orbital parameter would lead to orbits that, even if are not exactly at SEL5, they are still close enough to allow constant observations during a 10 years mission. Besides, the amount of ∆v is directly related to the final operational orbit considered, requiring to fully optimise both the operational orbit and the transfer trajectory together in order to find an optimal solution.

Image credits: ESA – A. Baker

Observation Geometry

Different transfer duration in rotating frame