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Spacecraft monitoring the Sun
Safety & Security

Lagrange mission

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ESA / Safety & Security

Providing timely and accurate space weather information, nowcasts and forecasts is possible only if sufficient observation data are continuously available.

Because Earth is well protected against space weather by its magnetic field and the atmosphere, only a limited amount of space weather observations are possible from Earth's surface. For example, our magnetic field deflects most of the solar wind charged particles away from Earth and the atmosphere filters out extreme ultraviolet and X-ray wavelengths from sunlight.

The baseline working approach for the SSA Space Weather Network is to collect as much of the required measurement data using ground-based instruments as possible, because ground-based instruments are usually less expensive and easier to maintain and upgrade than spaceborne instruments on board satellites.

However, to gain all the necessary, accurate, realtime data needed for future space-weather warning services, data from instruments in space are absolutely critical (see below).

Watching from down here

Kanzelhöhe Solar Observatory, Austria
Kanzelhöhe Solar Observatory, Austria

Examples of European and international observatories and instrument networks that could be utilised in ESA's Space Weather Network are shown, as examples, in the table below. More may be added in future.

Type of data  Source of data
Solar images in various wavelengths Use/reuse existing European solar telescopes such as the Kanzelhöhe Observatory for Solar and Environmental Research, Austria. Expand to global coverage through agreements with, for example, the Global High Resolution H-alpha Network 
Solar magnetogram images Use/reuse existing European solar telescopes such as the Instituto de Astrofísica de Canarias (IAC) contribution to the GONG network. Expand to global coverage through agreements with existing assets, e.g. GONG.
Solar indices (F10.7) Solar radiometer − data via Canada's Dominion Radio Astrophysical Observatory (DRAO
Solar radio bursts  Solar radio spectrograph network. Reuse existing assets such as the International Network of Solar Radio Spectrometers (eCALLISTO
Cosmic ray neutron flux (at Earth's surface) Existing neutron monitor network. Reuse existing assets such as the Neutron Monitor Database hosted by the Extraterrestrial Physics group at the Institute for Experimental and Applied Physics, Christian-Albrechts-Universität, Kiel, Germany
Vector magnetic field (Magnetograms at Earth's surface) Vector magnetometers, such as the International Real-time Magnetic Observatory Network (INTERMAGNET)
Total electron content (TEC) maps  GNSS receiver networks. Reuse of existing station networks such EUREF from the International Association of Geodesy (IGS)
Auroral visible imaging   Obtain from all-sky imagers. Reuse of imaging systems such as the Finnish Meteorological Institute (FMI) realtime auroral cameras
Ionosphere Sourced from ionospheric sounders such as the European Digital Upper Atmosphere Server (DIAS) network. Obtain complete global coverage through international cooperation agreements.
Ionospheric scintillation Dedicated GNSS receivers for scintillation monitoring. Detectors capable of sampling at the frequency required for scintillation measurement are less widely available and further deployment at high and low latitudes should be considered.
Ionospheric electric field Inchoherent/coherent radar network such as the Super Dual Auroral Radar Network (SuperDARN) and from the European Incoherent SCATter Scientific Association (EISCAT)
Ionospheric radio absorption From riometer networks. Reuse existing assets such as AAR/AIRS in Norway, IRIS in Finland and NORSTAR in Canada
Coronal mass ejection (CME) detections through cosmic ray anisotropy From muon telescope networks such as the Muon Spaceweather Telescope for Anisotropies at Greifswald (MuSTAnG) facility.

Watching from up there


The Earth is well protected against the effects of space weather by the magnetic field (magnetosphere) surrounding our planet and by our thick atmosphere.

The Earth’s magnetic field deflects the majority of the charged particles and solar wind emitted by the Sun, while the atmosphere filters out the dangerous wavelengths of the Sun’s electromagnetic radiation − such as Extreme Ultraviolet (EUV), X-rays and gamma rays.

For space weather monitoring and forecasting, however, we need observations from where these happen, i.e. from space, and this is why we need spaceborne observation systems to complement ground-based observations.

Flying instruments

ESA's Space Weather Network plans to obtain 'in-situ' measurements from space (but inside Earth’s magnetosphere) by using 'hosted payload' instruments − that is, instruments flown on spacecraft operated by ESA or by other organisations, which is a smart way to boost economic efficiency.

For a hosted payload instrument, measurements made from orbit will typically comprise monitoring of particles and fields within the magnetosphere (that is, inside Earth’s magnetic field) and Auroral images.

In addition, dedicated 'SmallSat' or cubesat missions may be needed to complement hosted payload instruments to cover all the needed measurements. The hosted payload instruments and potential SmallSat missions will form the SSA 'Distributed SWE Sensor System' (D3S). Observations gathered by D3S will particularly benefit satellite operations, spacecraft engineering, anomalous-event analysis and space-environment impact studies.

L1 lies between Earth and the Sun
L1 lies between Earth and the Sun

Remote sensing from Lagrange points

In contrast to in-situ measurements, forecasting space weather (predicting conditions in the future) and 'nowcasting' space weather impacts (detecting current conditions) at Earth requires remote sensing of the Sun, the solar corona and the free solar wind outside Earth’s magnetosphere.

To ensure a robust capability to monitor, nowcast and forecast potentially dangerous solar events, ESA has initiated the assessment of two possible future space weather missions. This assessment foresees positioning spacecraft in orbit at the L1 and L5 Lagrangian points - points in space where gravitational forces and the orbital motion of the spacecraft, the Sun and Earth interact to create a stable location from which to make observations. 

In particular, of the five Lagrangian points of the Earth-Sun system, L1 and L5 are very good locations from which spacecraft can monitor interplanetary space and solar activity.

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 (located 60 degrees behind Earth, close to its orbit) provides a way to monitor Earth-oriented coronal mass ejections (CMEs) from the 'side' so as to give more precise estimates of the speed and direction of the CME. These measurements can be used to provide space weather warnings, alerts and status information to customers on Earth.

Future mission study

The Lagrange points associated with the Sun–Earth system
The Lagrange points associated with the Sun–Earth system

The L1 and L5 mission objectives have been defined as:

  • The primary objective of the spacecraft at L1 is to provide in-situ observations of the interplanetary medium, including solar wind speed, density, temperature and dynamic pressure, as well as characteristics of the charged particle environment and the direction and strength of the Interplanetary Magnetic Field (IMF).
  • The L1 mission will also monitor the solar disc and solar corona and measure solar energetic particles that may be associated with solar flares and the onset of coronal mass ejections.
  • The L5 mission will complement measurements made from L1 by providing a view of the Sun away from the direct Sun-Earth line. This gives visibility of the propagation of plasma clouds emitted by the Sun toward Earth, as well as views of the solar disk before it rotates into view from Earth.
  • The L5 mission will carry out heliospheric imaging of the space between the Sun and Earth, monitoring of the solar disc and corona and carry out measurements of the interplanetary medium.

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 instruments on board the L1 and L5 missions will utilise technologies developed for, and tested on, earlier ESA and joint ESA/NASA solar science missions such as SOHO, STEREO and Solar Orbiter. For ESA's SSA missions, the instruments will be optimised for reliability and robustness to provide space weather monitoring data for operational applications, that is, for use in realtime systems that depend on a regular flow of data.

For the missions' preliminary design, the following instrument types are being assessed:

Optical instruments

  • Coronagraph – The onset and characteristics of a coronal mass ejection (CME) can be derived from coronagraph imagery and these data are a crucial input for predicting CME arrival times at the Earth and any potential effect on infrastructure.
  • Heliospheric imager (HI) – A wide-angle visible-light imaging system for the detection of coronal mass ejection events in interplanetary space and, in particular, of CME events directed toward Earth. HI data can be used to improve CME arrival time and effect predictions and monitor CME propagation as it travels toward Earth.
  • Magnetograph – This instrument will scan a selected spectral absorption line of the solar spectrum, and the data so generated will allow the current, three-dimensional magnetic field configuration of the Solar Disc to be established.
  • EUV imager – Imaging of the complex solar corona (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.
SOHO sees solar flares in 2017
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In-situ instruments

  • Magnetometer – Measurement of the interplanetary magnetic field will be essential for monitoring and modelling of its configuration and understanding how it is perturbed by CMEs prior to their arrival at Earth. These measurements are important for forecasting magnetic storms and disturbances caused by interaction of areas with different solar wind velocities. These observations assist space-weather forecasters in interpreting the evolution of the solar wind.
  • Plasma analyser – To measure angular velocity components of the solar wind, mostly protons and Helium atoms, in certain energy ranges. This will allow determination of solar wind properties, in particular density, velocity and temperature.
  • Medium energy particle spectrometer – This can monitor medium-to-low energy ions that can be the precursors of interplanetary shocks approaching Earth as well as proton effects on, for example, thin optical coatings (such as on spacecraft skins). This is required to provide warnings of up to 24 hours on shock arrival and estimates of expected geomagnetic storm strength. Monitoring particles can also provide an immediate indicator of possible CME occurrences.
  • Radiation monitor – Monitoring radiation storms (solar energetic particle events) is crucial, as these can disrupt and damage spacecraft systems. Higher energy particles can also affect aircraft and ground systems.

Data from all of ESA's space weather missions will be first processed and stored at the SWE Data Centre located at ESA Redu, Belgium. The calibrated and verified measurement data will then be disseminated in near-realtime to the teams in the Space Weather Service Network for further processing, validation and utilisation in in customer/end-user applications and services.

For the current space weather status and access to all of ESA's SWE services, access the Space Weather Service Portal via

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