Ariane 5 Guidance Anomaly Sends SES-14 and Al Yah 3 Off Course (2018)
On January 25, 2018, an Ariane 5 ECA rocket lifted off from the Guiana Space Centre in Kourou, French Guiana, carrying two commercial telecommunications satellites and a NASA science instrument. A software error in the launcher's flight program sent the rocket onto an incorrect trajectory, ending Arianespace's celebrated streak of 82 consecutive successful launches and forcing both satellites to burn precious fuel correcting their paths.
A High-Value Dual Payload
The mission, designated VA241, launched at 19:20 UTC on January 25, 2018, atop a European Ariane 5 ECA rocket operated by Arianespace. The rocket carried two communications satellites into geostationary transfer orbit: SES-14, built by Airbus Defence and Space for Luxembourg-based operator SES, and Al Yah 3, built by Orbital ATK for Yahsat of the United Arab Emirates. SES-14 was designed to provide broadband and video services across the Americas and the Atlantic Ocean region, while Al Yah 3 was intended to expand broadband internet access across Africa, the Middle East, and Brazil. Notably, SES-14 also carried NASA's Global-scale Observations of the Limb and Disk (GOLD) instrument, a scientific payload designed to study the dynamics of Earth's thermosphere and ionosphere from geostationary orbit, marking one of the first times a NASA science instrument had hitched a ride on a purely commercial communications satellite. The dual mission represented a significant investment for all parties involved, with the successful delivery of both satellites critical to expanding telecommunications coverage and scientific observation capabilities for their respective operators.
Did You Know?
Despite being knocked off course by roughly 20 degrees of inclination, both SES-14 and Al Yah 3 survived the ordeal and reached their intended geostationary slots using their own thrusters—though the extra fuel expenditure likely shaved years off their expected operational lifespans.
A Guidance System Malfunction
Shortly after liftoff, ground controllers realized something had gone wrong. Telemetry from the rocket was lost for several minutes, causing tense uncertainty about the fate of the mission. Arianespace later determined that the upper stage's flight program contained an error in the azimuth, or directional heading, calculation. Instead of following its intended flight path, the Ariane 5 veered off course, resulting in the payloads being released into an orbit that was significantly different from planned, with an inclination of about 20 degrees off target relative to the equatorial plane needed for geostationary satellites. The rocket itself performed correctly mechanically, but the incorrect guidance data meant it flew a flawed trajectory from nearly the moment of liftoff. This was the first operational hiccup for the Ariane 5 since a partial failure in 2002, breaking a remarkable run of 82 consecutive fully successful launches dating back to April 2003. Arianespace and its manufacturing partners launched an investigation to pinpoint the root cause, which was ultimately traced to a mistake in setting up the initial azimuth parameters used to compute the rocket's steering commands during its ascent.
Recovery, Impact, and Legacy
Despite the anomaly, both SES-14 and Al Yah 3 were eventually recovered. Engineers at SES and Yahsat used the satellites' own onboard propulsion systems to gradually correct their orbits over the following weeks and months, successfully guiding both spacecraft to their intended geostationary positions. However, this recovery came at a cost: the extra maneuvering consumed fuel reserves originally intended for years of orbital station-keeping, likely shortening each satellite's operational lifespan. NASA's GOLD instrument aboard SES-14 also required an adjusted commissioning schedule but ultimately reached its designated position and began science operations later in 2018, studying space weather phenomena in Earth's upper atmosphere. The incident prompted Arianespace to implement corrective measures to its software verification processes before resuming Ariane 5 launches. The rocket returned to flight in June 2018 and went on to complete its service life without further major incidents, eventually being retired in 2023 after Europe's next-generation Ariane 6 began development, with Ariane 6 finally debuting in 2024. The January 2018 anomaly remains a notable case study in aerospace engineering, illustrating how a single software parameter error can jeopardize an otherwise reliable launch vehicle's flawless record.