|Zenit 3 SL|
|Launch vehicle||Zenit 3-SL/Block DM-SL|
|Launch site||International Waters, Pacific Ocean|
|Description||Upper stage partial failure|
|Payload||Telstar 18/Apstar V|
|Desired orbit||Geostationary transfer orbit|
Immediately following the mission, Sea Launch partner RSC Energia appointed a commission in Moscow to investigate a premature shutdown of the Block DM-SL upper stage. RSC Energia was able to recreate the anomaly on the ground in full scope, matching the flight telemetry data from the Telstar 18 mission.
The commission identified the most probable cause as a short in the onboard cable network. This short introduced electrical interference in the circuits that transmit liquid oxygen and fuel flow rate data to the main engine control system. The main engine control system performed nominally, given the distorted data it received from the flow rate sensors.
As a result of the main engine control system acting upon the distorted data, the Block DM-SL consumed more fuel than planned and prematurely shut down because of fuel depletion. The shutdown was performed nominally based on the ability of the Block DM-SL control system to handle contingency situations.
Corrective actions were developed and verified through test to prevent a similar anomaly from occurring in future flights. The IRB has confirmed the corrective actions are appropriate and will increase the overall Block DM-SL reliability through increased fault tolerance during flight and pre-launch screening for defects.
Despite the early shutdown of the upper stage engine, spacecraft manufacturer Space Systems/Loral raised the Telstar 18 satellite to its final orbital position, where it is now fully operational. Loral says it expects the spacecraft to meet or exceed its 13-year specified life.