Inside GNSS Media & Research

JUL-AUG 2018

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38 Inside GNSS J U L Y / A U G U S T 2 0 1 8 www.insidegnss.com T he t hird launch of t he Ga li- leo constellation took place on August 22, 2014 by Soyuz ST- Fregat vehicle from Europe's Spaceport in French Guiana, carrying Europe's fih and sixth Galileo satellites. ese were the first series being built by OHB System AG, the company selected to complete the Galileo constellation. Due to a malfunction of Soyuz Fregat upper stage, the satellites were injected into a lower and elliptical orbit instead of the planned circular orbit and with only one out of the two solar array wings deployed on both spacecra. As a result, the sat- ellites were left in non-nominal orbit leading to exposure to the Van Allen radiation belts, non-nominal operation of the Earth Sensors and insufficient fuel to correct the orbits entirely. The prospects for the mission were gloom to say the least, however very quickly, experts across European institutions, space agencies and industrial partners joined forces to recover the satellites With plenty of promise, the third launch of Europe's Galileo constellation took place four years ago. What followed was not at all what was expected, as problems turned much of the promise into gloom. Unusually low power and instability in the radio signals received from the two satellites at the telemetry stations operated by the European Space Agency (ESA), the French National Space Agency (CNES) and the Swedish Space Corporation (SSC) showed that the satellites were not in their expected orbit. What followed, however, was a variety of procedures that led to the mission recovery and returned promise to the program. Here, the authors explain how Galileo satellites 5 and 6, which were almost considered lost, put under test the ingenuity of the many engineers involved in the recovery of this mission demonstrating the technical excellence and collaborations with experts from various institutions, space agencies and industrial partners. Galileo 5 and 6 Eccentric Satellites Mission Recovery and Exploitation | Part 1 Nityaporn Sirikan ESA - European Space Technology and Research Centre Hervé Côme ESA - European Space Operations Centre Igor Stojković ESA - ESTEC Javier Ventura-Traveset ESA - European Space Astronomy Centre Rafael Lucas ESA - ESTEC Marco Falcone ESA - ESTEC

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