09/09/2024
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The primary satellite tv for pc in ESA’s Cluster quartet safely got here again all the way down to Earth final evening in a world-first ‘focused reentry’, marking a superb finish to this exceptional mission.
The spacecraft, dubbed ‘Salsa’ (Cluster 2), reentered Earth’s environment at 20:47 CEST on 8 September 2024 over the South Pacific Ocean. On this area, any threat of fragments reaching land are completely minimised.
Over the past twenty years Cluster has spent in area, it has offered invaluable information on how the Solar interacts with Earth’s magnetic discipline, serving to us higher perceive and forecast area climate. With this first-ever focused reentry, Cluster will go down in historical past for a second cause – serving to ESA turn out to be a world-leader in sustainable area exploration.
The reentry follows a tweaking of Salsa’s orbit again in January 2024 to focus on a area so far as doable from populated areas. This ensured that any spacecraft components that survive the reentry would fall over the open ocean.
Over the previous days, weeks and months, ESA’s spacecraft operators saved an in depth eye on Salsa because it got here nearer to Earth, barely adjusting the spacecraft’s trajectory simply as soon as to maintain it on monitor.
These days, satellite tv for pc missions are designed based on laws that require them to minimise the chance of inflicting injury on their return to Earth. Nonetheless, when Cluster was constructed again within the Nineteen Nineties no such laws had been in place. With out intervention, the 4 Cluster satellites would have reentered Earth’s environment naturally – however with much less management over when or the place this may occur.
ESA Director of Operations, Rolf Densing explains why ESA determined to finish the mission on this approach: “Salsa’s reentry was all the time going to be very low threat, however we wished to push the boundaries and cut back the menace even additional, demonstrating our dedication to ESA’s Zero Particles method.”
“By finding out how and when Salsa and the opposite three Cluster satellites deplete within the environment, we’re studying an excellent deal about reentry science, hopefully permitting us to use the identical method to different satellites after they come to the top of their lives.”
Cluster unveiled Earth’s invisible defend
Salsa’s reentry marks the top of a singular mission that can finally assist shield humanity from our tempestuous Solar.
Water? Heat? Minerals? All very important for all times, however not distinctive to planet Earth. Maybe the one key factor that makes Earth a exceptional liveable world the place life can thrive is its highly effective magnetosphere.
Just some hundred kilometres above our heads, a steady battle is being fought between the forces of nature. Like a ship in a endless storm, Earth is bombarded by swarms of particles ejected from the Solar at supersonic speeds.
Most of those photo voltaic wind particles are deflected by the magnetosphere, and sail harmlessly by. However Earth’s defend just isn’t bulletproof. Gusts of photo voltaic wind can squeeze it mercilessly, pushing energetic particles via weak spots, and doubtlessly damaging digital tools together with very important satellites orbiting in area.
It’d sound like science fiction, however scientists have been finding out this steady feud between the Solar and Earth for a few years, first from the bottom after which with assistance from single satellites. However the complexities of the Solar-Earth connection have all the time eluded them. Till Cluster got here alongside.
Director of Science Prof. Carole Mundell says: “Cluster is the primary mission to make detailed research, fashions and 3D maps of Earth’s magnetic discipline, in addition to associated processes inside and round it. We’re proud to say that via Cluster and different missions, ESA has superior humankind’s understanding of how the photo voltaic wind interacts with the magnetosphere, serving to us put together for the risks it could deliver.”
Magnetosphere monitoring: a nook piece within the area climate puzzle
Our understanding of area climate – the environmental circumstances in area attributable to the Solar’s exercise – is dependent upon understanding many various elements: the behaviour of the Solar, how the photo voltaic wind travels via area, and the way Earth’s magnetosphere responds.
With Cluster, ESA took on the problem of uncovering how Earth’s magnetosphere responds to the photo voltaic wind. Different ESA missions have studied completely different components of the method, with Photo voltaic Orbiter, SOHO, Proba-2 and Ulysses holding watching on the Solar itself, and Swarm and Double Star additionally finding out Earth’s magnetic surroundings. Double Star centered on the ‘magnetotail’ that stretches away from planet Earth, and Swarm continues to analyse Earth’s magnetic discipline itself.
Cluster’s scientific torch might be handed on to the ESA/Chinese language Academy of Sciences Photo voltaic wind Magnetosphere Ionosphere Hyperlink Explorer (Smile) mission, set to launch in late 2025.
A number of years later, ESA’s Vigil mission will head into area to place the completely different puzzle items collectively, aiming to offer steady, close to real-time information on doubtlessly hazardous photo voltaic exercise. In the end it will assist us guarantee secure satellite tv for pc communications and area and air journey.
What made Cluster so particular?
Whereas most missions exploring Earth’s magnetic phenomena concentrate on the equator, the Cluster quartet circled over the poles, the place there’s a variety of magnetic exercise. Photo voltaic wind on this space can dive deeper into Earth’s higher environment, giving rise to the spectacular auroras.
Cluster’s skill to look at greater latitudes than different missions meant that it revealed components of the magnetosphere that we’ve by no means been in a position to ‘see’ earlier than with a number of spacecraft on the similar time.
By its mapping of Earth’s magnetic discipline, and comparability of this to Mars’s lacklustre present-day magnetism, Cluster has reaffirmed the significance of our magnetosphere in shielding us from the photo voltaic wind.
The mission additionally helped us perceive weaknesses within the magnetosphere, together with how photo voltaic wind particles can break via the defend. It even found the origin of ‘killer electrons’, energetic particles within the outer belt of radiation surrounding Earth, that may trigger havoc for satellites.
By frequently monitoring and recording the dynamics and properties of Earth’s magnetosphere over twenty years, Cluster has amassed an unprecedented wealth of information, permitting scientists to make actually ground-breaking findings, together with on longer-term developments.
After an extremely profitable 24 years in area, ESA took the choice to deorbit the 4 Cluster satellites all through 2024–2026. Planning the reentries presently made it doable for the Cluster spacecraft to contribute to reentry science as a remaining farewell.
“Cluster’s multi-spacecraft design has all the time been key to its success,” explains Philippe Escoubet, Cluster Mission Supervisor.
“Through the use of 4 spacecraft as an alternative of 1, Cluster was in a position to uniquely measure a number of areas of area concurrently. When nearer collectively, the Cluster spacecraft might dig into the finer magnetic constructions in near-Earth area. When additional aside, they may receive a broader view of wider-scale exercise.”
And now ESA is utilizing the truth that there are 4 Cluster satellites to higher perceive how reentries work. By evaluating the reentries of 4 similar satellites underneath completely different area climate circumstances and with barely completely different trajectories, ESA’s area particles group is conducting a precious experiment on the break-up of satellites within the environment. In the end, it will make satellite tv for pc reentries even safer.
From zero to hero
Though Cluster has turn out to be an unlimited scientific success, its early days didn’t go off and not using a hitch.
The rocket used to launch the Rumba (Cluster 1) and Tango (Cluster 4) satellites in 2000 left them in an incorrect orbit, forcing them to depend on their very own propulsion, in addition to the higher stage of the rocket, to get to the appropriate place to hitch Salsa (Cluster 2) and Samba (Cluster 3).
The mishap adopted the failed launch of the unique Cluster quartet in 1996.
Since then, the mission has made great progress, far outlasting its authentic deliberate lifetime and contributing enormously to our understanding of the interplay between the Solar and Earth. And yesterday, Cluster turned a key piece in ESA’s efforts in the direction of extra sustainable area exploration.
For extra on Cluster’s scientific achievements, see our devoted article on how the mission spent twenty years finding out Earth’s magnetosphere.
For extra info, please contact ESA Media Relations:
media@esa.int
