''ESA Vigil'', formerly known as ''Lagrange'', is a planned solar weather mission by the European Space Agency. It envisions two spacecraft to be positioned at Lagrangian points L₁ and L₅.Design call for 'solar sentinel' mission
Jonathan Amos, ''BBC News''. 2 February 2018.Monitoring space weather
European Space Agency (ESA). 4 December 2017.

coronal mass ejection A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accept ...

geomagnetic storm A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The disturbance that d ...

solar proton event In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in th ...

Overview

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 Airbus UK is a wholly owned subsidiary of Airbus which produces wings for Airbus aircraft. When Airbus was incorporated as a joint-stock company in 2001, BAE Systems transferred its UK Airbus facilities in return for a 20% share of the new comp ...

and OHB SE of Germany to design the spacecraft specifications and the instruments' integration process. UK's Rutherford Appleton Laboratory and Mullard Space Science Laboratory will assess the requirements of the science payload. This mission concept proposed positioning two spacecraft in orbit at the L1 and L5

Lagrangian points In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of t ...

, 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

s (CMEs) from the 'side' in order to estimate their speed and direction. The SOHO mission already collects data at L1, but it is not able to deliver a constant data stream of sensor data around the clock like weather satellites do, which is needed for space weather forecasts. SOHO also is expected to end its service around 2025 due to a lack of fuel. There is however the

Aditya-L1 Aditya L1 ( sa, आदित्य, lit: Sun, ) is a planned coronagraphy spacecraft to study solar atmosphere, currently being designed and developed by Indian Space Research Organisation (ISRO) and various other Indian research institutes. ...

mission of ISRO that fits the profile of the L1 mission very well and is scheduled to start in 2024. ESA has agreed to provide support by

ESTRACK The European Space Tracking (ESTRACK) network consists of a number of ground-based space-tracking stations belonging to the European Space Agency (ESA), and operated by the European Space Operations Centre (ESOC) in Darmstadt, Germany. The station ...

for this mission, and ISRO will exchange data with ESA to use it for space weather predictions.

Objectives

The preliminary mission objectives are: *the spacecraft at L1 is to provide observations of the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

speed, density, temperature and dynamic pressure,

charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary pa ...

environment and the direction and strength of the

interplanetary magnetic field The interplanetary magnetic field (IMF), now more commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar Sy ...

. *The spacecraft at L1 would also monitor the

solar disk A solar symbol is a symbol representing the Sun. Common solar symbols include circles (with or without rays), crosses, and spirals. In religious iconography, personifications of the Sun or solar attributes are often indicated by means of a hal ...

and

solar corona A corona ( coronas or coronae) is the outermost layer of a star's atmosphere. It consists of plasma. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. It is most easily seen during a total solar ...

and measure

solar energetic particles Solar energetic particles (SEP), formerly known as solar cosmic rays, are high-energy, charged particles originating in the solar atmosphere and solar wind. They consist of protons, electrons and heavy ions with energies ranging from a few ten ...

that may be associated with

solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sol ...

s and the onset of

s. *The spacecraft at L5 would complement measurements made from L1 by providing a side-view of the propagation of plasma clouds emitted by the Sun toward Earth. *The spacecraft at L5 would monitor of the solar disk and corona and carry out measurements of the

interplanetary medium The interplanetary medium (IPM) or interplanetary space consists of the mass and energy which fills the Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding ...

Payload

To achieve these objectives, the satellites at the L1 and L5 positions have to carry different types of remote-sensing and ''in-situ'' instruments. The suggested optical instruments take heritage from ESA and NASA science missions like

SOHO Soho is an area of the City of Westminster, part of the West End of London. Originally a fashionable district for the aristocracy, it has been one of the main entertainment districts in the capital since the 19th century. The area was develo ...

, STEREO and Solar Orbiter, but the instruments would be optimized for operational space weather monitoring. The notional science payload may require: ;Optical instruments *

Coronagraph A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view t ...

– for onset and characterisation of

s (CMEs). * Heliospheric imager (HI) – A wide-angle visible-light imaging system for the detection of coronal mass ejection events directed toward Earth. * Magnetograph - would scan a selected solar spectrum to generate 3D maps of the magnetic field. *EUV imager – Imaging of the complex

(the Sun's atmosphere) will support monitoring of the magnetic complexity and activity in the corona and location of the flaring active regions. *X-ray flux monitor – Detection of solar flares and quantification of the flare energy. ;''In situ'' instruments * Magnetometer – Measurement of the

. * Plasma analyser – To measure angular velocity components of the solar wind approaching the Earth and estimates of

strength. * Radiation monitor – Monitoring radiation storms (

Solar particle event In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in th ...

) is crucial, as these can disrupt and damage spacecraft, aircraft and ground systems. *Medium energy particle spectrometer – This can monitor clouds of medium-to-low energy

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s approaching the Earth.

References

{{ESA projects Proposed space probes 2020s in spaceflight Missions to the Sun European Space Agency space probes Solar space observatories Solar telescopes