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\t\t\t\t\t\t27\/03\/2024<\/span> A small, shoebox-sized spacecraft delivered to ESA\u2019s Hera mission this week promises to make a giant leap forward in planetary science. Once deployed from the Hera spacecraft at the Didymos binary asteroid system, the Juventas CubeSat perform the first radar probe within an asteroid, peering deep into the heart of the Great-Pyramid-sized Dimorphos moonlet.<\/p>\n<\/div>\n \u201cToday\u2019s asteroids are collisional fragments of the original building blocks of our entire Solar System, so being able to see how the interior of an asteroid is structured will give us valuable insights into the evolution of the Solar System, as well as planetary defence,\u201d explains Michael Kueppers, ESA\u2019s Hera project scientist. \u201cIs this asteroid a solid monolith, or a rubble pile held together by its gravity? The answer has practical consequences for how incoming asteroids might be deflected away from Earth in the future.\u201d<\/p>\n Measuring just 37x23x10 cm in size, the Juventas CubeSat has been overseen for ESA by Luxembourg\u2019s\u00a0GomSpace\u00a0company with spacecraft integration taking place at GomSpace\u2019s head office in Denmark. The company specialises in CubeSats \u2013 small, low-budget satellites assembled from standardised 10 cm boxes \u2013 though usually these are destined for Earth orbit.<\/p>\n<\/p><\/div>\n Building for deep space<\/b><\/p>\n Jan Persson leads the Juventas project for GomSpace: \u201cThis is a very different mission compared to the usual CubeSats that we manufacture and fly. Going beyond Earth orbit and out into deep space is a rare opportunity, requiring extremely precise attention to detail. Juventas also needs a sufficiently agile navigation system to fly itself around an asteroid.\u201d<\/p>\n<\/p><\/div>\n ESA\u2019s Hera asteroid mission is Europe\u2019s contribution to an international planetary defence experiment. Following the\u00a0DART mission\u2019s impact with the Dimorphos asteroid,\u00a0a moon of the larger asteroid Didymos, in 2022 \u2013\u00a0modifying its orbit around Didymos and sending a plume of debris thousands of kilometres out into space\u00a0\u2013 Hera will return to Dimorphos to perform a close-up survey of the crater left by DART. The mission will also measure Dimorphos\u2019 mass and make-up, along with that of Didymos.<\/p>\n Hera is due for launch in October 2024, and aboard it will be two CubeSats for close-up observations of the asteroid pair: Juventas will be joined by the Milani hyperspectral mission. The trio will stay connected around the asteroids via an innovative inter-satellite link system.<\/p>\n<\/p><\/div>\n Smallest radar to be flown in space<\/b><\/p>\n Named for the Roman name for the daughter of Hera, Juventas might be small, but it has a wide technical footprint. Its low-frequency radar instrument \u2013 the smallest radar system flown in space \u2013 was designed by France\u2019s\u00a0Institut de Plan\u00e9tologie et d’Astrophysique de Grenoble\u00a0at the\u00a0Universit\u00e9 Grenoble Alpes\u00a0and\u00a0Technical University Dresden, with electronics coming from\u00a0EmTroniX\u00a0in Luxembourg. Its radar signals will be transmitted from a quartet of 1.5 m-long antennas, longer than the Juventas spacecraft itself, which have been contributed by\u00a0Astronika\u00a0in Poland.<\/p>\n \u201cThe Juventas Radar \u2013 or JuRa \u2013 instrument is unique, and will give the science community a rare insight into the making of an asteroid,\u201d explains Jan Persson. \u201cIt has been highly miniaturised to fit into the CubeSat envelope. The main challenge has been that the instrument generates a lot of heat inside the spacecraft, which our thermal design team at GomSpace has worked hard to take care of.\u201d<\/p>\n<\/p><\/div>\n Hera system engineer Franco Perez Lissi adds: \u201cTo fly itself, Juventas also embarks a visible light camera, lidar, startrackers for navigation and a cold gas propulsion system, plus the inter-satellite radio link to share its position and data back with Hera.\u201d<\/p>\n In order to perform its radar survey of the smaller asteroid, Juventas will go into a unique \u2018Self-stabilised Terminator Orbit\u2019 around Didymos. This involves orbiting in parallel with the asteroid\u2019s day-night terminator line, balancing the weak gravitational pull of the asteroid with the faint but steady push of sunlight itself \u2013 solar radiation pressure. In fact, Didymos\u2019s gravity is so low that Juventas will be orbiting at a rate of just centimetres per second, and JuRa will take advantage of that low speed to send the same coded signal down to the asteroid multiple times, boosting the instrument\u2019s overall signal to noise ratio. The reflected signals will be decoded and converted into a 3D picture back on Earth.<\/p>\n<\/p><\/div>\n \u00a0Coming in for landing<\/b><\/p>\n Once Juventas completes its radar survey, it will switch into orbit around Dimorphos to begin the next phase of its mission: landing on the smaller asteroid. Jan Persson notes: \u201cWe\u2019re still analysing the best way to do this, but our speed should be low enough \u2013 on the order of centimetres per second \u2013 that Juventas will come down without bouncing right the way up into space again. Onboard accelerometers and gyros will gather data from this moment to learn more about the surface properties. When Juventas finally comes to rest we want it to be in stable configuration to operate the spacecraft\u2019s second science payload, the GRASS gravimeter.\u201d<\/p>\n The first instrument to directly measure gravity on the surface of an asteroid, the Gravimeter for Small Solar System Objects, GRASS, has been developed by the Royal Observatory of Belgium (ROB) with Spain\u2019s EMXYS company. The plan is for it to record how the gravity levels on Dimorphos change over the course of its orbit around Didymos.<\/p>\n<\/p><\/div>\n Both the Juventas and Milani CubeSats have now joined their Hera mothership for testing at ESA\u2019s\u00a0ESTEC Test Centre\u00a0in the Netherlands, the largest spacecraft test facility in Europe. The trio will be placed in the Maxwell electromagnetic compatibility chamber to check their inter-satellite links work as planned.<\/p>\n<\/p><\/div>\n
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