Goodnight, Cluster: sensible finish to trailblazing mission

The reentry follows a tweaking of Salsa’s orbit again in January 2024 to focus on a area so far as potential 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 in response to rules that require them to minimise the chance of inflicting injury on their return to Earth. Nonetheless, when Cluster was constructed again within the Nineties no such rules have been in place. With out intervention, the 4 Cluster satellites would have reentered Earth’s ambiance naturally – however with much less management over when or the place this is able to occur.

ESA Director of Operations, Rolf Densing explains why ESA determined to finish the mission on this method: “Salsa’s reentry was at all times going to be very low threat, however we wished to push the boundaries and cut back the risk even additional, demonstrating our dedication to ESA’s Zero Particles strategy.”

“By learning how and when Salsa and the opposite three Cluster satellites dissipate within the ambiance, we’re studying an ideal deal about reentry science, hopefully permitting us to use the identical strategy to different satellites once they come to the tip of their lives.”

Cluster unveiled Earth’s invisible protect

Salsa’s reentry marks the tip of a novel mission that may in the end assist shield humanity from our tempestuous Solar.

Water? Heat? Minerals? All 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 these solar wind particles are deflected by the magnetosphere, and sail harmlessly by. But Earth’s shield is not bulletproof. Gusts of solar wind can squeeze it mercilessly, pushing energetic particles through weak spots, and potentially damaging electronic equipment including vital satellites orbiting in space.

It might sound like science fiction, but scientists have been studying this continuous feud between the Sun and Earth for many years, first from the ground and then with the aid of single satellites. But the complexities of the Sun-Earth connection have always eluded them. Until Cluster came along.

Director of Science Prof. Carole Mundell says: “Cluster is the first mission to make detailed studies, models and 3D maps of Earth’s magnetic field, as well as related processes within and around it. We’re proud to say that through Cluster and other missions, ESA has advanced humankind’s understanding of how the solar wind interacts with the magnetosphere, helping us prepare for the dangers it can bring.”

Magnetosphere monitoring: a corner piece in the space weather puzzle

Our understanding of space weather – the environmental conditions in space caused by the Sun’s activity – depends on understanding many different factors: the behaviour of the Sun, how the solar wind travels through space, and how Earth’s magnetosphere responds.

With Cluster, ESA took on the challenge of uncovering how Earth’s magnetosphere responds to the solar wind. Other ESA missions have studied different parts of the process, with Solar Orbiter, SOHO, Proba-2 and Ulysses keeping watching on the Sun itself, and Swarm and Double Star also studying Earth’s magnetic environment. Double Star focused on the ‘magnetotail’ that stretches away from planet Earth, and Swarm continues to analyse Earth’s magnetic field itself.

Cluster’s scientific torch will be passed on to the ESA/Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer (Smile) mission, set to launch in late 2025.

A few years later, ESA’s Vigil mission will head into space to put the different puzzle pieces together, aiming to provide continuous, near real-time data on potentially hazardous solar activity. Ultimately this will help us ensure safe satellite communications and space and air travel.

What made Cluster so special?

While most missions exploring Earth’s magnetic phenomena focus on the equator, the Cluster quartet circled over the poles, where there is a lot of magnetic activity. Solar wind in this area can dive deeper into Earth’s upper atmosphere, giving rise to the spectacular auroras.

Cluster’s ability to observe higher latitudes than other missions meant that it revealed parts of the magnetosphere that we’ve never been able to ‘see’ before with multiple spacecraft at the same time.

Through its mapping of Earth’s magnetic field, and comparison of this to Mars’s lacklustre present-day magnetism, Cluster has reaffirmed the importance of our magnetosphere in shielding us from the solar wind.

The mission also helped us understand weaknesses in the magnetosphere, including how solar wind particles can break through the shield. It even discovered 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 20 years, Cluster has amassed an unprecedented wealth of information, permitting scientists to make actually ground-breaking findings, together with on longer-term traits.

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 potential for the Cluster spacecraft to contribute to reentry science as a closing farewell.

“Cluster’s multi-spacecraft design has at all times been key to its success,” explains Philippe Escoubet, Cluster Mission Supervisor.

“By utilizing 4 spacecraft as a substitute 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 buildings 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 totally different area climate situations and with barely totally different trajectories, ESA’s area particles workforce is conducting a useful experiment on the break-up of satellites within the ambiance. Finally, this can make satellite tv for pc reentries even safer.

From zero to hero

Though Cluster has change into an unlimited scientific success, its early days didn’t go off with out 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 precise 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 super progress, far outlasting its authentic deliberate lifetime and contributing enormously to our understanding of the interplay between the Solar and Earth. And yesterday, Cluster grew to become 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 two decades studying Earth’s magnetosphere.

For more information, please contact ESA Media Relations:

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