Previous chapter: A complete flight history of the Zenit rocket
Above: Flight trajectory of the Zenit-3SL rocket with a single firing of the Block DM-SL upper stage. Credit: Sea Launch
Zenit fails in Sea Launch accident
Struggling on its way back into the commercial launch market, the Sea Launch venture failed to deliver a communications satellite into orbit from a floating platform in the Pacific Ocean.
Liftoff of a Zenit-3SL rocket carrying the 6,215-kilogram Intelsat-27 communications satellite took place as scheduled at 06:56 GMT (01:56 a.m. EST, 10:56 Moscow Time) on February 1, 2013, (22:56 Pacific Time on January 31) at the opening of the 58-minute launch window. However less than a minute into the flight, the RD-171 engine on the rocket's first stage was shut down by an emergency command and the vehicle crashed into the Pacific Ocean along with its payload around 50 seconds into the flight. According to preliminary data, the rocket continued powered flight for some 20-25 seconds. The Russian Interfax news agency reported that the rocket had deviated from its nominal ascent trajectory immediately after liftoff. According to industry sources, the launch vehicle headed west after liftoff, instead of its normal eastern direction. The command ship with all Sea Launch flight control personnel was stationed five kilometers northwest of the launch platform.
The official statement of the Russian space agency, Roskosmos, issued at the end of the day on February 1, confirmed earlier unofficial reports that the problem had developed at the initial phase of the flight after the liftoff. However the pre-programmed flight sequence would not allow to shut down the main engine until 20 seconds into the flight, Roskosmos said. (The 20-second delay was designed to enable the vehicle to clear the launch facility and spare it from damage in case of just such an accident.) This information suggested that the propulsion system of the rocket had functioned as planned and pointed to problems elsewhere, possibly in the flight control and guidance system of the rocket.
On February 2, Sea Launch published a press-release saying that the Zenit-3SL rocket had successfully completed all pre-launch processing activities, with all systems and environments within requirements up to the on time liftoff at 6:54:59 UTC. At approximately 11.4 seconds into flight, the Zenit flight control system detected an exceedance of a pre-programmed roll limit and responded appropriately with activation of the on-board thrust termination sequence, which is designed to ensure a safe outcome in the event of vehicle loss of control.
According to the company, based on preliminary information received from the launch vehicle designer, the investigation will focus on Zenit-3SL systems associated with thrust-vector control of the first stage engine. As per the Sea Launch Failure Review and Investigation Plan, each associate contractor will first perform an independent investigation of their respective systems, processes and procedures to identify any and all potential contributors to the failure.
Energia Logistics Ltd., ELUS, will form a Failure Review Oversight Board (FROB) to review the contractor findings and agree on root cause and appropriate corrective actions to prevent recurrence. The FROB will be led by ELUS Chief Operating Officer Kirk Pysher, along with co-chairman Dr. Valery Aliev, ELUS Executive Vice President and Mission Director, and Rick Pudil, ELUS Chief Systems Engineer. The first meeting of the FROB had been tentatively planned for late February to early March time frame, Sea Launch said.
On the morning of February 2, a reliable industry observer posted a message on the web forum of the Novosti Kosmonavtiki magazine pointing at the Ukrainian-built 11L729 hydraulic pump also known as BIM for "Bortovoi Istochnik Moshnosti - Onboard Power Source" as a likely culprit in the accident. The BIM pump provides hydraulic power to a steering mechanism that tilts combustion chambers of the main engine of the first stage from their vertical position up to six degrees in order to steer the rocket in flight.
Monitoring data available from the ill-fated launch indicated that despite its normal operation before liftoff, the pump's turbine had quickly slowed down its rotation and then completely stopped. As a result, the rocket likely lost its ability to follow its prescribed trajectory and the flight control system shut off the engine some 20 seconds after liftoff -- enough time for the vehicle to reach a safe distance from the launch platform.
The BIM unit is activated and driven by a high-pressure helium gas during its pre-launch checks and 10 seconds before liftoff, but switches to kerosene fuel as the main engine (also burning kerosene) reaches its operational thrust on the launch pad. The helium turbopump of the BIM unit can be tested during pre-launch processing of the rocket, however the kerosene turbopump can not be, because it is designed to function only alongside a firing main engine of the rocket.
On February 3, another poster further elaborated that according to the flight program, Zenit had to start its pitch maneuver 11.3 seconds after its vertical ascent following the liftoff. The vehicle was also programmed to start to roll around its main axis 14 seconds after liftoff. During the actual launch, the floating launch platform was aligned within two degrees from its prescribed east-west direction, therefore almost no roll was required from the rocket.
The BIM pump failed at 4.5 seconds after the engines were brought into launch-ready position known as OTP for Okonchanie tochnogo privedeniya, (or around half a second before liftoff, according to estimates), thus disabling the gimbal mechanism of the main engine and making it impossible to tilt its combustion chambers and steer the rocket in flight. As a result, the vehicle was not able to conduct its planned pitch maneuver and 16 seconds into the flight it exceeded allowable limit of 30 degrees for deviation in its rolling motion, triggering emergency actions by the flight control system. Although the rocket's pitch and course at that moment had not exceeded allowable 15 degrees, the flight control system issued a command to shut down the engine. However for another four seconds the rocket was continuing an uncontrolled powered flight, because according to a safety algorithm, the engine was programmed to fire for 20 seconds after liftoff. The uncontrolled vehicle was heading 270 degrees from its prescribed azimuth direction and after overlying its launch platform crashed 2.5 kilometers from it, 56 seconds after the liftoff.
Flight control was receiving telemetry from the rocket all the way until its crash into the ocean. Data confirmed that the propulsion system had been working perfectly, the flight control system had reacted to the situation correctly, however its commands to gimbal the combustion chambers had not been performed (obviously due to the failure of the BIM hydraulic pump.
The rocket's cargo -- Intelsat-27 -- was designed to operate in space for at least 15 years and was based on Boeing's mid-size 702MP platform. The spacecraft was intended to serve customers in North and South America, the Atlantic Ocean region and Europe, and to host a UHF communications payload for use by the military. The launch was to mark Intelsat’s completion of the world’s first global broadband mobility platform, which was designed to provide uninterrupted connectivity to customers at sea, on land and in the air.
Intelsat has remained the most loyal customer of Sea Launch as the international company struggled to emerge from bankruptcy and win back its share of the launch market. Launching and operating one of the largest commercial satellite fleets, Intelsat saw the survival of Sea Launch as critical for maintaining competition in the field of launches to the geostationary orbit currently dominated by the European Ariane-5 and Russian Proton rockets.
According to Sea Launch, from its launch platform stationed directly on the equator at 154 degrees West longitude, a Zenit-3SL launch vehicle was to lift Intelsat 27 into an optimized geosynchronous transfer orbit. The satellite would then use its own propulsion to enter its final geostationary orbit at 304.5 degrees East longitude.
After liftoff, the Zenit-3SL rocket was to begin its ascent phase of flight, achieving maximum acceleration at 116 seconds into the flight. The first stage of the vehicle was scheduled to separate 2:30 minutes (150 seconds) after liftoff, and the protective payload fairing was to be jettisoned 82 seconds later at 3:52 minutes. The second stage was to conduct a 6-minute burn, followed by its separation from the Block DM-SL upper stage. The Block DM-SL was scheduled to begin its first and only burn at 8:41 minutes (521 seconds) into the mission, for the duration of 699 seconds. The upper stage was then to shut down for an almost 10 minute coast period before spacecraft separation over equatorial South America.
Intelsat-27 mission timeline (according to Sea Launch):
Following the accident, Russian Prime-Minister Dmitry Medvedev appointed his deputy Dmitry Rogozin to investigate the causes and report on corrective actions, including administrative changes within a two-week period.
Next chapter: Zenit launch with AMOS-4 satellite
This page is maintained by Anatoly Zak; Last update: August 31, 2013
Page editor: Alain Chabot; Last edit: February 2, 2013
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Intelsat-27 satellite is being prepared for transportation. Credit: Boeing
Artist rendering of Intelsat-27 satellite in orbit. Credit: Boeing
Ill-fated launch of a Zenit rocket from the Sea Launch platform on Feb. 1, 2013. Credit: Sea Launch
By February 2, a 11L729 BIM turbopump assembly in the RD-171 engine was singled out as a likely culprit in the launch accident. Credit: Novosti Kosmonavtiki