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    The United Launch Alliance Atlas V rocket with Orbital ATK’s Cygnus spacecraft onboard is seen shortly after arriving at Space Launch Complex 41 on December 2, 2015

    Anomaly in Cygnus Spacecraft Launch Caused by Unexpected Fuel Changes

    © AFP 2019 / AUBREY GEMIGNANI
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    The anomaly that prompted the premature booster shutdown during the Cygnus spacecraft launch on March 22 was caused by unexpected changes in fuel pressure and flow, United Launch Alliance (ULA) announced in a release on Wednesday.

    WASHINGTON (Sputnik) — The ULA pointed out that the Cygnus spacecraft was successfully delivered to the International Space Station despite the early booster shutdown and degradation of the first stage performance.

    "An extensive review of all post-flight data observations determined that at approximately T+222 seconds, an unexpected shift in fuel pressure differential across the RD-180 Mixture Ratio Control Valve (MRCV)," the release stated.

    A second cause, ULA noted, was the reduction in fuel flow to the combustion chamber caused by a mixture of propellants and a reduction in first stage performance.

    "The imbalanced propellant consumption rate resulted in depletion of the first stage oxidizer with significant fuel remaining at booster engine shutdown," the release added.

    ULA also said in the release that the Russian RD-180 rocket engine manufacturer made necessary changes to prevent engine anomalies in the future.

    The Cygnus is an unmanned spacecraft that carries cargo to the International Space Station.

    The spacecraft was launched on Atlas V — a two-stage rocket that uses the Russian-made RD-180 rocket engine and a Centaur rocket as its second stage.

    The Atlas V launcher’s first stage RD-180 engine cut off 6 seconds earlier than planned, triggering a longer burn by the Centaur upper stage to compensate for the loss of thrust and velocity.

    The ULA is a joint venture owned by Lockheed Martin and the Boeing Company. It brings together two of the launch industry’s most experienced and successful teams — Atlas and Delta — to provide reliable, cost-efficient space launch services for the US government.

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    Cygnus, RD-180 rocket engine
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