This Sunday 8 September 2024, a first satellite of the Cluster mission (Salsa-C2) will reenter the Earth's atmosphere, ending a space adventure that has lasted more than 24 years. The Royal Belgian Institute for Space Aeronomy is proud to have played a part in it.
The Cluster mission
Launched in 2000, the European Space Agency's (ESA) Cluster mission aimed to study the interaction between the solar wind and the magnetic bubble surrounding the Earth, the magnetosphere. Composed of four identical satellites in an elliptical orbit around the Earth, Cluster collected unique data on the Earth's magnetosphere and the near-Earth solar wind using 11 scientific instruments over a period of more than 24 years. This unique configuration has enabled us to make precise measurements of magnetic field fluctuations, to analyze the electromagnetic waves and to detect the density, temperature and velocity variations of the ionized gas (a plasma consisting of ions and electrons) present in the different sub-regions of the magnetosphere. But every scientific mission comes to an end...
The beginning of the end
On 8 September this year, a first satellite of the mission (C2-Salsa) will re-enter the Earth's atmosphere, followed by the three others over the next few years (C1-Rumba in November 2025, C3-Samba and C4-Tango in August 2026). These 3 satellites will continue to carry out scientific measurements until the end of September 2024. Thereafter, the satellites will be put on standby and ESA operators will monitor them to minimize the risk of collision with other satellites and to avoid re-entry over inhabited areas of the Earth. The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) is proud to have played an important role in this mission.
BIRA-IASB's involvement in the Cluster mission
BIRA-IASB has been involved in the Cluster mission since its conception, in collaboration with ESA and other European and American scientific institutions. BIRA-IASB researchers contributed to the development of the instrument WHISPER (Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation), which was carried by each of the 4 Cluster satellites. This instrument not only measured the electromagnetic waves propagating in the magnetosphere, but also provided very precise values of electron density. BIRA-IASB has also been heavily involved in analyzing data from another wave measurement instrument, STAFF (Spatio-Temporal Analysis of Field Fluctuation).
The results and legacy of the Cluster mission
BIRA-IASB is proud to have participated in this mission and to be able to look back on the results that were achieved. As Cluster was the first multi-spacecraft mission, BIRA-IASB scientists have invented new techniques to interpret the measurements made simultaneously by the four closely spaced satellites. BIRA-IASB scientists have published numerous studies that exploit Cluster measurements, thereby contributing to improving our knowledge of our space environment, from the upper atmosphere where polar auroras form to the outer regions of the magnetosphere where it interacts with the solar wind. Examples include the edition of a book on the plasmasphere largely based on Cluster data, the creation of a video about the plasmasphere and the edition of a book on the magnetosphere. Over the last 2 years, BIRA-IASB has also been involved in the GRMB (Geospace Region and Magnetospheric Boundary) project, a global analysis of data from the entire Cluster mission.
The GRMB project: towards a more accurate classification of the magnetosphere
The correct classification of the regions and boundaries crossed by the satellites of any magnetospheric mission is very important to add value to the huge quantity of data acquired by the Cluster satellites over 24 years. This allows unambiguous statistical studies to be carried out regarding the fundamental plasma processes occurring in a particular region, such as plasmasphere refilling, reconnection at the magnetopause, turbulence or wave propagation in the magnetosphere.
Furthermore, the magnetosphere's environment is highly dynamic, and its regions are not accessible using orbital information alone. To remedy this, BIRA-IASB has been actively involved in an ESA project whose goal is to create a database providing the position of each Cluster satellite throughout its mission, not in the form of geographical coordinates, but by describing the regions, transition regions and boundaries crossed by the satellites. The result is a database called GRMB, which will be made available by the end of 2024 on the website archiving the Cluster scientific data.
Authors
Darrouzet Fabien, De Keyser Johan, Fratta Stéphanie, Maggiolo Romain
Internet links
- Salsa’s last dance targets reentry over South Pacific of the Cluster mission - ESA
- Cluster, science mission overview - ESA
- Cluster, measuring Earth's magnetic environment - ESA
- Cluster at BIRA-IASB
- Scientific data of the Cluster mission
- Book on the magnetosphere
- Book on the plasmasphere
