During the Ariane 5 VA241 mission, carried out on January 25, 2018 from the Guiana Space Center in French Guiana (South America), telemetry from the launcher was lost 9 minutes and 26 seconds into the flight because of a deviation in the trajectory. Signals from the two satellites were acquired after the nominal mission duration, and the spacecraft were confirmed to be in good health, but in an orbit at an inclination of 20 degrees, rather than the targeted 3 degrees. The apogee and perigee attitudes, however, were very close to the targeted values (249 x 45,234 km.). The analysis of data received during the first minutes of the flight, and the reconstitution of the trajectory, confirmed that the launcher and the flight program operated perfectly. The two satellites are now in the process of reaching their final orbital positions, using their own propulsion systems.

Following the launch anomaly, Arianespace asked the European Space Agency (ESA) on January 26 to set up an Independent Enquiry Commission. Chaired by Toni Tolker-Nielsen, ESA Inspector General, this Commission submitted its conclusions on Thursday, February 22, 2018.

Investigations by the Independent Enquiry Commission showed that the trajectory anomaly resulted from an incorrect value in specifications for the implementation of the launcher’s two inertial reference systems. Given the special requirements of this mission, the azimuth required for the alignment of the inertial units was 70 degrees instead of 90 degrees, as is most often the case for missions to geostationary transfer orbit. This gap led to the 20-degree shift to the south in the launcher trajectory from the initial seconds of flight. The cause of the trajectory deviation, therefore, was due to a bad specification of one of the launcher mission parameters that was not detected during the standard quality checks carried out during the Ariane 5 launches’ preparation chain.

The Independent Enquiry Commission’s work has highlighted the need to increase the robustness of the control of certain data used in preparation of the mission. Its recommendations are intended to strengthen the process of developing and verifying the documents required for launcher preparation and to introduce additional consistency checks.

With the cause of the anomaly perfectly understood and corrective measures clearly identified, Arianespace and ArianeGroup immediately implemented the recommendations of the Independent Enquiry Commission. Applied to the current Ariane 5 launch campaign, they should enable the next flight of this heavy-lift launcher in March 2018, following a Soyuz mission.

Stéphane Israël, Chief Executive Officer of Arianespace, said: “I would like to thank ESA Inspector General Toni Tolker-Nielsen, who chaired the Independent Enquiry Commission, as well as all of its members. The Commission was able to quickly identify the cause of the anomaly and issue recommendations. Arianespace and ArianeGroup already are deploying the measures recommended by the Commission, paving the way for the next launch of Ariane 5, planned for March. Thanks to the establishment of these corrective measures, we will be able to further enhance the outstanding reliability of Ariane 5.”

Quelle: arianespace