Ariane 5 flight VA241 (2018)
The Ariane 5 launch of January 25, 2018 that placed SES-14 and Al Yah 3 in the wrong orbit because an inertial unit alignment parameter was off by twenty degrees.
A launch vehicle does not discover its trajectory in flight: it executes mission parameters prepared on the ground, including the reference value used to align its inertial units before liftoff. If that value is wrong, the vehicle flies perfectly, but toward another point, and no onboard sensor notices, since everything is consistent with the command it received. Flight VA241 illustrates exactly that: the inquiry board concluded that one parameter had been misspecified and that the quality checks in the launch preparation chain did not catch it. For insurance purposes, the event falls in the gray zone between success and failure: the satellites separated and were alive, but in an orbit that cost them propellant, and therefore service life. The question is then no longer a total loss but a partial loss, measured in years of service lost, and one satellite's electric propulsion weighed heavily in the recovery.
On January 25, 2018, Ariane 5 lifted off from Kourou carrying SES-14 and Al Yah 3; telemetry was lost about nine minutes into the flight. The independent inquiry board found that the azimuth used to align the inertial units had been set to 90 degrees instead of the 70 degrees this mission required, producing a twenty-degree deviation to the south from the first seconds of flight. Both satellites separated into the wrong orbit and had to burn propellant to reach geostationary orbit.
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