News Item

Ariane launch navigation error

A 20º azimuth error fed to navigation computers aboard the Ariane 5 has led to 2 satellites requiring extensive re-positioning.

The problem was first discovered when the launch vehicle appeared to stop sending telemetry just over 9 minutes after liftoff from Europe’s Guiana Space Centre, Kourou, on 25 January. The incorrect track had taken the rocket outside the coverage of an early tracking station in Brazil.

The 2 comms satellites, SES-14 and Al Yah 3, were to be placed in geosynchronous (GEO) orbits, appearing to an Earth observer to be almost stationary over the equator. Such orbits are usually obtained by launching to the east from as low a latitude as possible - Kourou is ~5ºN - into a highly-eliptical orbit, typically of 250 x 45,000 km. The satellites use internal power to accelerate when close to apogee, gradually obtaining a 24-hr circular orbit at 42,164 km with an inclination to the equatorial within ~3º.

These satellites appear to have reached acceptably-sized initial orbits of ~235 x 43,150 km, but with inclinations of ~21º degrees, due to the initial azimuth error. This will necessitate extensive additional power and time to attain GEO.

Both satellite operators, SES and Yahsat, have confirmed that their respective spacecraft are healthy:
- Luxembourg-based SES explains that SES-14 will take an additional 4 weeks to reach its orbital position over the Americas.
- UAE-based Yahsat, adds that the hybrid chemical-electric propulsion Al Yah 3 satellite will use a 'revised flight plan' to reach an operational orbit and begin service later this year.

Arianespace announced that it has formed an independent commission in conjunction with ESA to investigate the anomaly, but upcoming launch campaigns already underway at the Kourou are 'proceeding as scheduled'.

Details from the links below . .

Image from Arianespace

  • 26 February 2018
  • RIN

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