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\t\t\t\t\t\t26\/08\/2024<\/span> On 8 September 2024, the first of four Cluster satellites will return home and burn up in Earth\u2019s atmosphere in an uncontrolled \u2018targeted reentry\u2019 over a remote area of the South Pacific Ocean.\u00a0<\/p>\n In the nearly 70 years of spaceflight about 10 000 intact satellites and rocket bodies have reentered the atmosphere. Yet we still lack a clear view on what actually happens during a reentry.\u00a0<\/p>\n An airborne observation experiment\u00a0will\u00a0now attempt to witness the \u2018Salsa\u2019 (Cluster 2) reentry. Scientists on board a small plane will\u00a0try to collect rare data on how and when a satellite breaks up, which can be used to make satellite reentries safer and more sustainable in the future.<\/p>\n<\/div>\n \u201cTo keep Earth\u2019s valuable orbits clean, it is important to remove a satellite quickly from orbits after their mission comes to an end, and thereby prevent more space debris,\u201d says Holger Krag, Head of Space Safety at ESA.<\/p>\n \u201cReentry science is an essential element of these efforts. Cluster\u2019s reentry can help us understand how to design and operate satellites so that they can be disposed of easily, safely and sustainably in the future.\u201d<\/p>\n Cluster offers a unique opportunity with its quartet of identical satellites. Starting with Salsa, each of them will reenter under slightly different circumstances and angles, offering up a scientist\u2019s dream: a repeatable experiment.<\/p>\n “Together with our partners at Astros Solutions we are sending a plane to observe Salsa\u2019s reentry live from the sky to observe a satellite class and reentry conditions which have never been accessible before,” says Stijn Lemmens, Space Debris Analyst in the ESA Space Debris Office.<\/p>\n \u201cThere\u2019s testing we can do on the ground, and we have virtual modelling, but we also need real-life observations right at the scene of a reentry to complete the picture. The observation experiment from a plane is an exciting new possibility for us to collect data and gain confidence in the modelling to support new missions.\u201d<\/p>\n<\/p><\/div>\n Already in January 2024, operators set up Salsa to\u00a0target a specific geographic location in one of the remotest regions on Earth on 8 September 2024.<\/p>\n It\u2019s not quite now or never, but it is now or in 24 years\u2019 time.<\/p>\n \u201cCluster\u2019s orbit takes it very close to Earth and then very far away again on a 12-year cycle,\u201d explains Cluster Operations Manager Bruno Sousa.<\/p>\n \u00a0\u201cSalsa naturally makes a close approach over the southern hemisphere this year, which we knew would lead to it being captured by the atmosphere. Its trajectory was slightly adjusted in January 2024, when we manoeuvred it to target a specific region of the South Pacific Ocean that is as far from populated regions as possible.\u201d<\/p>\n Whilst most of the spacecraft will disintegrate within less than a minute, a few parts are likely to survive. Targeting open waters upon reentry is hugely reducing the amount of land over which fragments could fall, making the reentry as safe as possible.<\/p>\n<\/p><\/div>\n The team needs a fixed time and a location to prepare the airborne observation experiment. A controlled reentry would make that a breeze, but Cluster was not designed with this capability.<\/p>\n The Cluster satellites\u2019 highly eccentric orbit does allow a \u2018targeted reentry\u2019. Its highly eccentric orbit means Salsa is experiencing a large loss of altitude at its closest point to Earth (perigee) from orbit to orbit due to the gravitational influence of the Sun and Moon. It is no coincidence this happens during Salsa\u2019s last orbits.<\/p>\n<\/p><\/div>\n Big drops of over 30 km in altitude between one orbit and the next means that the team can pinpoint the exact orbit when Salsa will go so low that it crosses the threshold where satellites start to burn up, at around 80 km altitude. That is how they know it will reenter and burn up on 8 September.<\/p>\n \u201cIt\u2019s because of this predictability in the reentry time and location that we can outfit a plane with scientific instruments and observe the reentry from as close as safely possible,\u201d says Stijn.<\/p>\n \u201cThere is however one unknown: the atmospheric density as we go lower and lower. Therefore, over the next weeks, ground stations will keep listening for Salsa hoping it can send telemetry right until the end. Telescopes are also tracking the spacecraft, because minor deviations from its predicted trajectory, if there would be any, could be important for the flight plan from Easter Island.\u201d<\/p>\n<\/p><\/div>\n It\u2019s not easy to conduct an airborne, experimental observation campaign at a location picked because of its remoteness.<\/p>\n \u201cThe airborne observation mission \u2018ROSIE-Salsa\u2018 is a joint effort of academic partners from\u00a0University of Stuttgart (IRS\/HEFDiG), Comenius University in Bratislava (CUB), University of Southern Queensland (UniSQ) and industrial partners from Hypersonic Technology G\u00f6ttingen (HTG) and Astros Solutions, in close cooperation with ESA,\u201d says Ji\u0159\u00ed Silha, CEO of Astros Solutions.<\/p>\n \u201cIt is a very challenging mission due to the unpredictable nature of reentry events, which makes the reentry break-up prediction as well as the planning of the aircraft positioning for the best observation very demanding. However, with experts in both science and technical preparation, our team consists of exceptionally capable people who will ensure that once the object is in sight, we will get all the relevant scientific data we need.\u201d<\/p>\n The plane will be mounted with the scientific instruments in Australia before making a test flight to check if everything is ready for the big event. Then the team moves to Easter Island to set up communications there and wait until it\u2019s time to fly out and meet up with Salsa.<\/p>\n Onboard the plane will be the science lead from IRS\/HEFDiG, the mission lead from UniSQ and mission participants from CUB and Astros Solutions, hoping to catch the reentry live. HTG supports the scientific analysis and modelling of the data as well as support the creation of the precise flight plan for the plane.<\/p>\n<\/p><\/div>\n Each window of the plane will have cameras and spectrographs peeking out of them. All in all, over 20 scientific instruments will be looking for the explosion, tracking the fragments and recording as much detail as possible.<\/p>\n Because the reentry takes place during the day, it will be harder to spot the reentry against the bright backdrop of the sky than it would be at night. It shortens the time that the scientists have to tune their instruments. It also makes it more complicated for some of the instruments that will have to quickly filter out the Sun\u2019s radiation from the signals they are trying to catch.<\/p>\n It will be a tense wait until there is confirmation if the observation was a success. It might take a few minutes, or even hours, because of the limited connectivity on the plane and its extremely isolated location.<\/p>\n<\/p><\/div>\n The exciting opportunity to send a plane to observe reentries live from the air is rare and promises a wealth of data on how and when exactly satellites break up.<\/p>\n Cluster\u2019s reentry follows those of ESA\u2019s Aeolus and ERS-2 Earth observation missions. ESA is setting a precedent for a responsible approach to reduce the every-increasing problem of space debris and uncontrolled reentries with its Zero Debris approach, committing to stop the creation of space debris by 2030.<\/p>\n Until the end of November 2024, ESA operators will manoeuvre the three remaining Cluster satellites to line them up for reentries in similarly remote locations over the South Pacific Ocean. \u2018Rumba\u2019 (Cluster 1) will come down in November 2025, and \u2018Samba\u2019 (Cluster 3) and \u2018Tango\u2019 (Cluster 4) in August 2026.<\/p>\n \u201cOn top of the four Cluster reentries, we are also looking ahead to ESA\u2019s exciting DRACO mission. With DRACO, we want to get the telemetry from a satellite recording what is happening from the inside during its own reentry,\u201d says Tim Flohrer, Head of the Space Debris Office at ESA.<\/p>\n \u201cDRACO will be an actively controlled reentry of a satellite that is fitted out with a \u2018black box\u2019 that will provide the telemetry for us to learn from. If all goes well, we\u2019re hopeful that we can have similar airborne observation campaigns of these reentries in the future.”<\/p>\n \u00a0<\/p>\n Stay tuned for updates on the reentry observation flight experiment on our Rocket Science Blog.<\/p>\n Learn more about the reentry in the Frequently Asked Questions.<\/p>\n<\/p><\/div>\n
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\n\t\t\t\t\t\t\t\t\t\t2<\/span> likes<\/small><\/span><\/p>\n<\/header>\nLearning from Salsa’s demise<\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nSalsa’s last dance targets the Pacific<\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nMeeting up with Salsa<\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nThe in-flight experiment<\/h2>\n
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nReentry science into the future<\/h2>\n
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