Measuring the solar wind with Vigil: solar-terrestrial relations and space-weather forecasting

The Vigil mission is ESA's flagship operational space-weather mission, planned to be launched in 2027/28. It will combine remote-sensing and in-situ measurements to enable accurate space-weather predictions from its unique vantage point at the fifth Sun-Earth Lagrange point. This location will allow Vigil to observe remotely space-weather events that propagate along the Sun-Earth line. In addition, Vigil will observe the source regions of the solar wind and of other space-weather events about 4.5 days before these source regions will point at Earth. Likewise, in-situ measurements of the solar-wind plasma at the fifth Sun-Earth Lagrange point will sample solar-wind streams that point at Earth about 4.5 days later.

The Plasma Analyser (PLA) instrument onboard Vigil will measure the solar wind at the location of the spacecraft over a wide dynamic range of plasma parameters. The data from PLA will predict high-speed solar wind streams headed towards Earth. These high-speed streams can drive relativistic (>MeV) electron flux enhancements in the Earth's radiation belts. Although these events are less spectacular than coronal mass ejections and the associated geomagnetic storms, they are potentially more damaging to our infrastructure due to their longer duration. The associated flux enhancements especially pose a threat to spacecraft in Medium Earth Orbits and Geostationary Equatorial Orbits. PLA measurements will also support work to improve and validate models for solar-terrestrial relations in the inner heliosphere. These models can be used, for example, to provide better predictions of the background plasma conditions through which Earth-directed coronal mass ejections propagate.

PLA is currently designed and built at the University College London's Mullard Space Science Laboratory (UCL/MSSL). The instrument is an electrostatic plasma analyser that relies largely on the flight heritage of previous scientific instruments designed by UCL/MSSL. I will give a status update of the PLA development and an outlook into the space-weather prediction capabilities enabled by PLA and the other Vigil payload.