In these cases, uncertainty begins high but narrows as the orbits of objects evolve. Credit: ESA/BepiColombo/MTM, CC BY-SA 3.0 IGOĮSA's Space Debris Office recently began risk assessments based on Solar Orbiter's trajectory and the expected position of cataloged objects in orbit around Earth, providing a collision probability for any specific close approaches. ESA’s Space Debris Office also performed a collision risk analysis for this flyby as the spacecraft passed through Geostationary orbit, although it flew well above the debris-filled low-Earth orbit. In April 2020, BepiColombo flew by Earth with a close approach of 12 500 kilometres. A flyby of Earth today, while still safe, is riskier than it used to be. Past Earth flybys, for example, when Cassini/Huygens flew by Earth in 1999, as Rosetta returned three times in 2005, 20, and Juno swung by in 2013, there were fewer satellites, fewer debris and no 'mega constellations' in orbit. While the risk to Solar Orbiter during its upcoming Earth flyby is small, it's still "non-zero." It didn't face this risk as it swung by Venus, nor did ESA's Space Debris Office have to perform collision risk analysis as BepiColombo recently zipped by Mercury, or when Cassini–Huygens flew by Jupiter. In that time, it has witnessed the skies fill with satellites and debris and felt the impact, as its own solar panels have been bombarded and degraded by small debris particles. Hubble, the NASA/ESA Space Telescope, has spent 31 years in Earth orbit at an altitude of around 547 kilometers. The Cupola window onboard the International Space Station developed a 7-mm chip, thought to be caused by a striking object no more than a few thousandths of a millimetre across. Hundreds of millions of debris particles this size are currently in orbit. Despite its size, its high relative speed meant it still damaged an area 40-cm across, leading to a small reduction in onboard power and slight changes to the orientation and orbit of the satellite. In 2016, a solar panel on ESA's Sentinel-1A spacecraft was struck by a particle thought to be less than five millimeters in size. However small the risk, collisions with debris at low-Earth altitudes do happen.
Earth observation missions spend their entire life in low-Earth orbit-the most debris-filled region of space, and while they perform 'collision avoidance maneuvers' a few times per year, Solar Orbiter will spend only a few minutes here as it heads towards closest approach and then leaves again, onward to Venus. These final gravity assists will hone and tilt Solar Orbiter's orbit, enabling the heat-protected probe to capture the first-ever direct images of our star's poles, and much more.īefore we worry too much, let's start by pointing out that the chance of Solar Orbiter being struck by debris is very, very, very small. This will line the spacecraft up for its next six flybys of Venus. On 27 November, after a year and eight months flying through the inner Solar System, Solar Orbiter will swing by home to 'drop off' some extra energy.
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